B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE 71–83 ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE NAPREDNI MATERIALI IN RAZISKAVE ZA ZELENO PRIHODNOST Bojan Podgornik Institute of Metals and Technology, Lepi pot 11, Ljubljana, Slovenia Prejem rokopisa – received: 2022-12-15; sprejem za objavo – accepted for publication: 2023-01-09 doi:10.17222/mit.2022.717 Environmental concerns, such as pollution, greenhouse-gas emissions, sustainability, global warming and climate change, are the biggest challenges of our times. In this respect, the more efficient use of energy and materials combined with technology op- timization and innovation are playing a key role in the quest to become a green society with green industry. Multiple environ- mental and economic benefits can mostly be achieved through novel, lightweight energy-efficient designs. In order to develop and properly use new materials and new designs, complete understanding and information on their properties must be obtained. It is also vital to know how these properties are affected by the conditions of a specific application. Furthermore, as the design of components is pushed towards the limits, unsuitable and outdated measuring methods, measuring uncertainty and deviations from the defined material properties can lead to unexpected premature failure of the component and environmental problems. For the green future, it is extremely important to develop new, advanced materials. However, it is often the changes of the pro- duction technology and to the surface of an already-existing material that can achieve great benefits to performance as well as the environment. It is all about modifying the material to perform better, last longer, be biocompatible and achieve different functionalities. Finally, besides high-tech equipment and research facilities, close cooperation between universities, research in- stitutes and industry is needed to develop technologies, functional materials and solutions that can effectively support the jour- ney of our society into a green future. Keywords: environment, pollution, advanced materials, surface engineering, research Okoljski problemi, kot so onesna`evanje, emisije toplogrednih plinov, trajnost, globalno segrevanje in podnebne spremembe, predstavljajo najve~je izzive na{ega ~asa. Klju~no vlogo pri prehodu v zeleno industrijo in dru`bo ima u~inkovitej{a raba energije in materialov,povezano s tehnolo{ko optimizacijo in inovacijami. [tevilne okoljske in gospodarske koristi je mo~ dose~i z uporabo novih lahkih in energetsko u~inkovitihkonstrukcij. Za razvoj in pravilno uporabo novih materialov in novih dizajnov je potrebno pridobiti popolno razumevanje in informacije o njihovih lastnostih. Pomembno je tudi, kako na te lastnosti vplivajo pogoji in parametri uporabe. Ker pa so zahtevane karakteristike in na~rtovanje komponent potisnjeno do samih zmo`nosti materialov, lahko `e neustrezne in zastarele merilne metode, prevelika merilna negotovost in odstopanja od specifikacij povzro~ijo nepri~akovano odpoved komponente in okoljske te`ave. Za zeleno prihodnost je izjemno pomemben razvoj novih naprednih materialov. Vendar pa so pogosto spremembe proizvodne tehnologije in povr{ine `e obstoje~ega materiala tiste, ki lahko zagotovijo izjemne okoljskekoristi in izbolj{anje funkcionalnosti. Vse se nana{a na spreminjanje materiala, da deluje bolje, traja dlje, je biokompatibilen in dosega najrazli~nej{e funkcionalnosti. Nenazadnje je poleg visokotehnolo{ke opreme in raziskovalnih zmogljivosti potrebno tudi tesno sodelovanje med univerzami, raziskovalnimi in{tituti in industrijo, kar omogo~a razvoj novih tehnologij, funkcionalnih materialov in re{itev, ki lahko u~inkovito podprejo prehod na{e dru`be v zeleno prihodnost. Klju~ne besede:okolje, onesna`evanje, napredni materiali, in`eniring povr{in, raziskave 1 ENVIRONMENTAL CONCERNS Environmental concerns, such as pollution, green- house-gas emissions, sustainability, global warming and climate change, which are some of the biggest chal- lenges of our times, have produced a variety of societal responses. 1 These include public policy measures such as the Geneva and Rio Conventions, the Paris Agreement, the U.S. Clean Air Act, the European Waste Electrical and Electronic Equipment Directive, the Japanese Home Electronics Recycling Law, and the latest European Green Deal, set to turn the EU into the first climate-neu- tral continent by 2050. 2 Actions are required across all sectors, including increased energy efficiency and renew- able energy, low-emission mobility and decarbonized transport, minimized material use, recyclability, no haz- ardousness and no-waste production. With transport contributing around5%toGDPand employing more than 10 million people in Europe alone, the transport system is critical to global businesses and supply chains, thus playing a vital role in society and the economy. At the same time, transport is not without costs to our society. It is a key source of environmental pressures, climate change, greenhouse gas (GHG) and pollutant emissions, noise, road crashes and congestion. It also takes up large strips of land and contributes to ur- ban sprawl, the fragmentation of habitats and the sealing of surfaces. Transport consumes one-third of all final en- ergy in the EU. The bulk of this energy still comes from oil. This means that transport is responsible for a large Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 71 UDK 658.5.018.2:502.3:504.7 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(1)71(2023) *Corresponding author's e-mail: bojan.podgornik@imt.si (Bojan Podgornik) share of the EU’s GHG emissions and a major contribu- tor to climate change. It is also a significant source of air pollution, especially in cities. While most other eco- nomic sectors, such as power production and industry, have reduced their emissions and pollution since 1990, those from transport have risen. Transportation accounts for more than one-quarter of the EU’s total GHG emissions and for 16 % ( 8 gigatons CO 2 e) of global GHG emissions. 3 The vast majority comes from road transport (75 %), i.e., cars and trucks, with most of the rest from aviation and ocean shipping (22.5 %). Only 1 % of the automobiles in oper- ation globally are currently electric, with the number growing rapidly, encouraged by favourable government policy and incentives. EU targets for reducing the CO 2 emissions of cars and vans are a 50–55 % reduction by 2030 and zero emissions from new cars by 2035. 3 A low-carbon, zero-emission mobility system will thus re- quire the near-complete replacement of the vehicle fleet. Passenger cars will likely be dominated by plug-in bat- tery electric vehicles. Heavier trucks will likely see greater deployment of green hydrogen and fuel cells. Harder-to-abate sectors such as aviation and shipping could rely on technological advancements in biofuels and green hydrogen. The transition to a low-carbon mo- bility system will likely entail shifting production to electric and green hydrogen powertrains, including re- tooling manufacturing facilities, expanding battery and fuel-cell production, working with the mining industry to find new materials and sources of critical minerals, in- crease efficiency and reduce energy consumption and power losses. However, in all sectors, fully-recyclable, lightweight and CO 2 -footprint materials will be required and will start to dominate. Reducing GHG emissions also requires higher shares of renewable energy and greater energy efficiency. The production and use of energy, including transportation account for more than 75 % of the EU’s GHG emissions. Thus, the binding target of renewable sources in the EU’s energy mix by 2030 is set to 40 % and overall reduction of energy consumption to 36–39 %. 3 Energy production itself, primarily electricity generation and heating, ac- counts for 31% ( 15 gigatons CO 2 e) of global GHG emissions. 4 Coal and natural gas are still the two largest sources of electricity generation, accounting for roughly 60 % of the total power produced. Nearly all the remain- der comes from low-carbon sources, a mix of renewables (wind, solar, and hydropower) and nuclear. However, wind and solar growth has outpaced other generation sources and are forecasted to become the largest sources of installed global electricity generation capacity by 2025. 4 The goal of a net-zero energy system will likely see nearly all electricity supplied by renewable energy, likely dominated by a mix of photovoltaic solar and onshore and offshore wind. A variety of other low-carbon power generation technologies potentially including bioenergy with carbon capture and sequestration, geothermal, mod- ular nuclear, and natural gas with carbon capture could all play roles as well. However, solutions of problems re- lated to energy transformation, storage, supply and effi- ciency, heat exchange, hydrogen storage, carbon capture and storage, etc., largely depends on materials and their properties. Last but not least, also industrial manufacturing and materials production require a large amount of energy and is in many countries responsible for a large portion of environmental impacts and pollution, producing ap- proximately 28 % ( 14 gigatons CO 2 e) of global GHG emissions. 4 And the emissions trend is upward over the last decade. The bulk are the result of energy consump- tion during production across industries, although direct emissions as a by-product of cement and chemicals man- ufacturing are significant contributors too. Materials pro- duction and manufacturing also produce large volumes of waste, both in production and at end-of-life disposal. The carbon-intensive nature of many processes has chal- lenged manufacturers seeking to transition towards lower-emission alternatives, increase efficiency, remove waste, and embrace circular approaches, especially in heavy industry. On the other hand, such hard-to-abate operations currently have few viable low-carbon alterna- tives and although environmental impacts and emissions of some pollutants may decrease over time due to in- creased efficiency in production and improved pollution controls, waste and GHG emissions typically go hand in hand with increasing materials production. However, the more efficient use of energy and mate- rials combined with technology optimization and innova- tion could play a key role in achieving multiple environ- mental and economic benefits. Although many opportunities exist, material efficiency is still not real- ized in practice to its full potential. In future steel, alu- minium, cement, and other hard-to-abate heavy indus- tries will see much wider use of green hydrogen and electrification, with on-site carbon-capture technology playing an important role. Furthermore, manufacturing should continue to obtain gains in efficiency, reducing emissions intensity, sensors deployment and analytics, digital transformation, etc. Additive manufacturing, lean production, circular design, and more robust material-re- cycling practices can reduce waste and emissions, at the same time providing low-weight, minimum-energy-de- manding designs. Increased recycling leads to reductions in waste volume and generally leads to reduced GHG emissions. 4 Nevertheless, some advanced materials have limited recycling potential, although they can still be used in downgraded end-of-life applications. Throughout their lifecycle, as materials are produced, converted to products, consumed, and discarded, the transformations use energy at every step. Industry is thus one of the largest energy-using sectors, emitting approxi- mately 36 % of global GHG emissions associated with energy and processes (Figure 1). The production of bulk B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE 72 Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 materials leads to approximately 25 % of all GHG emis- sions. This makes materials a key sector for climate, en- vironmental, and economic policy. Although there is still considerable potential for reductions in the energy and GHG intensity of material production, ultimately there are limits. 5 Materials also play a key role in the planned transformation to a low-GHG-energy system. Sustain- able energy technologies need novel materials as well as traditional materials such as steel, aluminium and cop- per, providing the highest level of re-use and recycling. 5,6 Hence, the transformation of the energy system is likely to lead to a changed and increased appetite for specific materials as a new energy infrastructure is built. Overall, the global consumption of materials such as aluminium and steel is likely to double if current developments con- tinue. Simultaneously, there is a trend towards substitu- tion with more energy-intensive and higher-CO 2 foot- print materials (e.g., replacing steel with aluminium, polymers, or carbon fibres), which may lead to the in- creased use of energy and CO 2 emission in production, although they are reduced during the operation of the product. If current trends in global demand for materials continue, the environmental impact (GHG emissions, water withdrawals, pollution) of materials production is likely to increase. For the bulk materials, future relative improvements in the intensity of production are con- strained given that the processes are already relatively energy efficient and are likely to be eclipsed by absolute growth in demand. For the critical materials, demand and performance needs may rise ahead of current trends driven by the development of new energy-supply and production technologies. 2 MATERIAL REQUIREMENTS As shown, materials are central to most of the envi- ronment-protecting strategies, faced with the following challenges to 2 : • reduce material intensity, • reduce energy intensity, • enhance material recyclability, • reduce dispersion of toxic substances, • maximize sustainable use of renewable resources, • extend product durability. To increase cost-effectiveness, efficiency, safety, per- formance, and to address environmental concerns there is an urgent need to develop advanced materials and manu- facturing technologies that allow novel, lightweight en- ergy-efficient designs. Lightweight designs mattes more now than ever before. The development and application of advanced lightweight materials, such as fibre-rein- forced plastic composites, ceramic fibre composites and light metals, contributes to a significant reduction in weight with a simultaneous increase in performance. Es- pecially in the automotive industry, aerospace, energy in- dustry and construction, the most important impulses in the field of lightweight construction have been and are still being achieved. Another important issue is energy efficiency, requiring materials (i.e., electrical steel sheets) with minimum power losses. Advanced materials generally mean materials that have novel or enhanced properties that improve performance over conventional products and processes. They can boost the transition to greener technologies, with improved characteristics and enhanced performance, contributing to a more sustain- able future. For each renewable technology to progress, the development and improvement of materials is needed to help us build a greener future. All renewable technolo- gies face material challenges. Materials must be lighter, stronger and able to resist corrosion from demanding at- mospheres and high temperatures. Advanced materials are defined as multifunctional materials categorized into 7 : • lightweight materials, • smart materials, • nanomaterials, • self-healing materials, • self-diagnostic materials, B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 73 Figure 1: Distribution of global CO 2 emissions among sectors and materials production 4 • photonic materials, • bio-inspired materials and designs. Some representatives of advanced materials are car- bon fibres, polymer composites, smart fibres, ceramics, intermetallic titanium aluminides, shape-memory alloys, carbon nanotubes, etc. A special group are bio-materials and bio-inspired design, known as bio-mimetics. Bio-mimetics has given rise to new technologies on the micro- and nano-scale, inspired by observing living or- ganisms that have evolved well-adapted structures and materials over time through natural selection. Nature has solved engineering problems, such as self-healing abili- ties, environmental exposure tolerance and resistance, hydrophobicity, self-assembly, and harnessing solar en- ergy. Some examples are shown in Figure 2. The specific properties of advanced materials give them a lot of advantages over traditional materials, but specifics related to resource availability, energy and CO 2 -footprint intensive production, degradability and recyclability, bio-compatibility, etc. may rise sustain- ability concerns and pose some serious environmental threats. With the environmental concerns now moved to the top of the engineering agenda, the development and selection of material is far from simple. Today, we see the huge proliferation of materials that were created over the last half-century. It is estimated that 32 % of the plas- tic produced annually goes into the oceans, while the production of carbon fibres is about 14 times as energy intensive as producing steel, and the creation process spews out a significant amount of GHGs (up to 20 times more than recycled steel 12 ). Furthermore, to become the strong, light composite material carbon fibres are com- bined with a plastic polymer resin, with the manufactur- ing process being wasteful. By the time carbon fibre sheets are trimmed to size, almost one-third ends up on factory floors and one-fifth goes straight into the waste, without ever making it into a product. Where the mate- rial does make it into products, most of it will ultimately end up in landfill due to the fact that the recycling of car- bon fibres is very limited 13 . Another problem with spe- cific modern materials is their availability. For example, indium-tin-oxide is currently used as a conductor in most of our touch screens, yet indium is one of the rarest ele- ments in the earth’s crust, meaning supply is very limited and expensive to mine. Metals on the other hand have excellent sustainable character. The growing importance of the consideration and use of sustainable materials depends on the relation- ship between the renewability of the natural resources and the material products that are generated from them. The risk of depleting a natural resource can make their use less desirable when other, more sustainable, alterna- tives exist. Metals such as iron (Fe) and aluminium (Al) are elements and therefore cannot be destroyed or de- pleted. The Earth’s overall resource deposits of metallic elements have not decreased but simply change locations and present themselves in different forms. Aluminium and steel have many product applications, and once these product applications cease to function the material can be recycled and reused in the creation of another prod- uct. This cycle allows the aluminium and steel to remain a permanently accessible material through recycling, re- taining the properties and thus making them one of the only truly cradle-to-cradle materials. 14 Metals may also possess exceptional properties if produced and processed properly. However, the applicability, capacity and poten- tial of metals is still not fully exploited and realized in practice. This requires an advanced materials-research approach combined with digitalization and the introduc- tion of green technologies. B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE 74 Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 Figure 2: Examples of nature engineering: a) shark skin with reduced drag, 8 b) self-cleaning lotus leaf, 9 c) super adhesion of gecko feet 10,11 The problem of many components, products and goods which society takes for granted, is they are quite difficult to recycle. Just a few decades ago, making dura- ble products resulted in special, hard-to-recycle materi- als, which were also so bound together that during the recycling process, it was really hard to separate them. And even when it is technically feasible to take apart a product and recycle its parts, it is often that new, ad- vanced materials are very technically challenging to re- cycle and not economically justified. To increase the po- tential and likelihood of products and materials being recycled, it is essential to consider recyclability during the design phase. Not only product design, but also the design of the material itself is crucial to increase recy- cling rate and sustainability. In parts design already a few simple steps can make a big difference, including the use of less impacting and easily recyclable materials, like metals, reduce the quantity and diversity of materials, not using materials which can reduce the quality of recy- cled ones, labelling parts that can be recycled, making them easy to dissemble and creating guides on how to take apart a product for recycling. 15 Although it is fore- seen that research and development will lead to less en- ergy required for both extracting and recycling materials, as well as an overall reduced carbon footprint, it is essen- tial that companies are forced into recycling by design and to fully recycle their products, i.e., high quality recy- cling and ultimate reuse. By exporting products to re- gions where a subsequent high-quality recycling is rather unlikely to happen, the material loop will not be closed, subsequently decreasing resource efficiency and limiting sustainability. Another issue is material production and recycling it- self. Processing of materials is one of the most signifi- cant sources of energy consumption and GHG emissions globally, forcing the need for “green materials” with re- duced direct emissions and energy needs. As part of this trend is increased interest in the recycling of materials and the development of materials being more recyclable by design. Historically, metals have higher rates of recy- cling, because scrap can more easily be collected and re- cycled. However, where there are challenges and physi- cal difficulties with the collecting, sorting and separating of waste materials or involves technically challenging and a more energy-intensive process, recycling rate may be very low or even non-existant. 16 The higher the value of the constituents and the lower the complexity of a spe- cific side stream or residue, the more of that material will be recirculated and recycled. There are several factors which make material less recyclable, including technical barriers and barriers linked to the traceability of materi- als due to their potential contamination. 17 However, when recycling is taking place in state-of-the-art pro- cesses, down cycling or materials quality issues can mostly be avoided. To make material more recyclable, it must maintain its mechanical and chemical properties af- ter recycling and be able to be sorted prior to recycling, so it needs to be transformable and sortable with an ac- ceptable cost-to-performance ratio and environment impact; recycling is not necessarily beneficial. 18 The main short-term efforts to increase recyclability of mate- rials are related to waste-material sorting and separation, medium-term to information tools supplying all the es- sential information regarding overall production chain through the so-called digitized circular economy 19 and the use of biodegradable and bio-sourced materials, while long-term to increased material recyclability by design, also requiring the development of new technolo- gies and research strategies. 18 Commonly downgrading of a certain material takes place by a common collection of different alloys. A separation afterwards is possible, but involving greater efforts. Even more critical is the mixing of residues from different processes. However, in some cases, the mixing of specific material streams can also lead to a higher recycling potential, if this improves the overall thermodynamic environment of the process. 18 Very complex are also recycling challenges related to critical metals, i.e., tantalum and indium, used in very low concentrations with respect to the overall composi- tion, which are lost almost completely at present. An ef- ficient and economical viable recovery and recycling of these metals is a major technological challenge, requir- ing multistage mechanical, thermal/metallurgical, and chemical treatment steps in multi-metal recovery processes 18 , taken into account already during the mate- rial design phase. The growing complexity of the prod- ucts also demands their full digitization. In terms of environment protection an important chal- lenge is how to reduce direct emissions during material production, i.e., the material CO 2 footprint. Currently the steel industry is among the three biggest producers of CO 2 , with emissions being mainly produced by a limited number of steel plants. In response, decarbonisation measures such as blast-furnace efficiency improvement, use of biomass reductants, carbon capture and usage, 20 and establishing or switching to hydrogen-based (H 2 ) steel production can be implemented either in future (greenfield) sites or existing (brownfield) facilities. 21 Blast-furnace efficiency programs do not eliminate CO 2 emissions completely, biomass reductants are only feasi- ble in certain regions, while carbon capture and usage is still in the early stages of development. Therefore, an ap- proach combining scrap, direct reduced iron, electric arc furnace (EAF) and use of green hydrogen is currently considered the most viable option and the long-term so- lution to achieve carbon-neutral steel production. 21 How- ever, the key challenge will be obtaining ssufficient amount of electricity from renewable energy to produce green hydrogen and run EAFs. Therefore, the optimal steps to steel-production decarbonisation will differ de- pending on the technical feasibility, the existing infra- structure, but mainly on the availability and price of re- newable electricity and scrap. B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 75 Also, in the case of aluminium production the use of renewable energy as the source of the green electricity is the best way to improve the carbon footprint of the pri- mary aluminium. 22 On average, 72 % of GHG emissions from the aluminium sector are from the primary produc- tion of aluminium. However, the electrolysis process still produces direct CO 2 emissions. Although they are on av- erage only about one-tenth of those from the energy source, they are still significant. Globally, they account for about 300 million tonnes of CO 2 . 23 These direct emis- sions could be reduced by using inert anodes and alu- minium chloride process. 24 Other alternatives are to use bio-carbon in the anodes or to employ carbon capture and use. In the case of copper production, GHG emis- sions are typically associated with the consumption of fuel in the mining and materials transport processes, as well as indirect emissions from electrical energy use in extractive and beneficiation processes. This is due to the high energy demand requirement to crush and grind ore. The average energy and GHG intensity is 4.5 t CO 2 -equivalent (CO 2 e) per tonne of copper produced. 25 With the increase in secondary smelting a decreasing de- mand for copper-mining activities are taking place. Also, energy demands for secondary smelting are on average lower than the one of primary, leading to about a fac- tor-of-2-lower specific CO 2 emissions. 26 However, the production of the electricity used in the copper-smelting process remains the major source of GHG emissions. Last but not least, we should also discuss batteries-re- lated GHG emissions. Lithium-ion batteries and electri- cal mobility play an important role in the world’s decar- bonisation and reduction of GHG. 27 However, climate impact, which derives from the mining and refining of battery materials, and manufacturing of cells, modules and pack must also be taken into account. The produc- tion of a battery cell requires sourcing of as much as 20 different materials from around the world, which will pass through several refining stages before entering an advanced and energy-intensive manufacturing process with very different climate impacts depending on which energy source is used. 27 In this respect climate impact re- lated to lithium-ion battery manufacturing (mainly asso- ciated with energy requirements) may range from about 40 kg to 200 kg CO 2 e/(kW·h), being equivalent to CO 2 emissions produced by a comparable diesel car in 1–7 years. 28 As much as 75 % of energy consumption comes from the cells production and 20 % of that for mining, conversion and refining of the active materials. However, the largest climate impact of the cell comes from the synthesis of the precursor and lithium compound into cathode powder, with the cathode production requiring 47 % of the cell energy demands. 27 For pack production the dominant energy consumption comes from the alu- minium used, resulting in about 140 kg CO 2 e/(kW·h). 29 As can be seen, the major environmental factor in many materials production, including batteries, is cumulative energy demand and its source. Using a less-carbon-inten- sive energy mix (mainly hydro and nuclear power in Sweden vs. coal and natural gas in Poland, Figure 3) will result in much lower CO 2 impact. To decrease the CO 2 impact, also recycling needs to be taken into ac- count, making already-extracted material available for the production of new batteries. By using direct recy- cling where the cathodes and anodes retain its composi- tion followed by different types of hydro metallurgic processing energy demand in material production can be reduced by as much as 48 %. 30 3 RESEARCH NEEDS Advanced metallic materials research should incor- porate: • materials testing and properties correlation, • measurement uncertainty and innovations, • modelling and simulation, • advanced heat-treatment strategies and surface engi- neering, • compatibility. B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE 76 Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 Figure 3: Average energy mix per region and country 27 In general, the properties of metals depend not only on the balanced chemical composition and the process- ing route, but also greatly on the final heat-treatment process, which defines the final microstructure. With the industry being confronted with ever-increasing demands on higher productivity, lower production costs, more complex products, lightweight design and environmental restrictions, requirements on a material’s properties are also becoming more demanding. Consequently, this means tougher property requirements for a large number of properties, which usually don’t go hand in hand. Im- provement in one property often results in another prop- erty’s deterioration. Furthermore, although different ma- terial properties (strength, hardness, toughness, wear resistance, machinability, etc.) can be determined using standard test methods, each one requires specific and of- ten unique test specimens, thus exposed to different con- ditions during manufacturing and heat treatment. This makes it practically impossible to evaluate and directly correlate multiple properties. On the other hand, a method based on circumferentially notched and fa- tigue-precracked tensile bar specimen – CNPTB 31 (Fig- ure 4) has been found as a very promising research test- ing method, with the cylindrical geometry providing uniform microstructure and the. possibility of preparing different test specimens. In this way many different prop- erties including fracture resistance, toughness, hardness, strength, fatigue and wear resistance, machinability etc. can be determined and mutually correlated, as shown in Figure 5. In order to properly use materials in design, a com- plete understanding and information on their mechanical properties must be obtained. It is also vital to know how these properties are affected by the conditions of a spe- cific application of the material. Factors such as the size of the part, surface condition, loading direction and load- ing rate may result in changes to these properties that must be considered in the design. 33 Furthermore, as the design of components, especially in automotive industry, is constantly pushed toward the limits of the material, unsuitable and outdated measuring methods as well as deviations from the defined material properties and ex- cessive measuring uncertainty can lead to unexpected premature failure of the component and environmental problems 34 . Therefore, a sophisticated and reliable deter- mination of material properties with low uncertainty is crucial in modern design aimed at a green future. Small deviations in testing specimen’s diameter or unsuitable surface preparation may result in a large increase in mea- surement uncertainty and failure probability 35 (Figure 6). With the modification of the composition and ele- ments, the effect of heat-treatment conditions on the metal’s microstructure evolution and properties, includ- B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 77 Figure 5: Examples of multiple tool-steel properties’ determination and correlation 32 Figure 4: Characterization versatility of CNPTB test specimen ing two the most important properties in material selec- tion in automotive industry, fracture toughness and hard- ness, will change, thus requiring tremendous experimental work. Although the influence of chemical composition on phase transformations, hardenability, and strength have been studied since late 1960s, with several models and equations being deduced by analysing avail- able data, they are too general and very seldom consider interactions of the alloying elements. Another technique of obtaining and optimizing material properties is based on processing and a trial-and-error approach. However, this requires an excessive use of resources. Therefore, there is a huge need for tools allowing the prediction of properties of metallic materials as a function of composi- tion and heat-treatment process variables. This can be done by the mathematical modelling process and the cal- culation of phase diagrams, but this is not an easy task, especially in the case of multiphase systems. First of all, heat flow and phase-transformation kinetics are coupled, with the results relying on the knowledge of thermody- namic processes and used database. Furthermore, also minor modifications in the geometry or properties can B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE 78 Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 Figure 6: Effect of specimen size mismatch and surface condition on measurement uncertainty in tensile and hardness testing of Al alloys, respectively 35,36 Figure 7: ANN based analysis of heat-treatment parameters and composition on steel properties 38 result in large variations in prediction, with any simplifi- cation of a complex system leading to greatly reduced accuracy of the model. On the other hand, soft comput- ing methods like genetic algorithms, fuzzy logic, artifi- cial neural networks (ANN) and artificial intelligence (AI) have been found to be able to perform highly com- plex mappings of nonlinearly related data by inferring subtle relationships between input and output parame- ters, thus providing good predictions in materials science regardless of any relational knowledge of the nature of the analysed system. 37 AI and ANN are particularly suited to problems that involve the manipulation of mul- tiple parameters and nonlinear interpolation, and as a consequence are therefore not easily amenable to con- ventional theoretical and mathematical approaches. With such an approach the multiphase analysis of different pa- rameters and elements can be carried out, as exemplified in Figure 7, providing valuable guidelines for focused experimental research and shortening development and time-to-market phase. Of course, modelling results strongly depend on the training dataset provided. The larger it is, the better are the results and predictions. Many materials have been developed to have specific properties, obtained through processing and heat treat- ments. However, although new processes, technologies and materials are developed constantly, their final treat- ments are not always up to date. The heat treatment of metals, for example, is an ancient art expanded down the ages from black art to science to improve mechanical properties. Furthermore, materials production is, in gen- eral, focused on bulk properties, without being particu- larly optimized for the surface properties. Recently, stud- ies of sub-zero cooling cycles have gained attention, showing a huge potential for improving the working per- formance of a wide range of materials (steels, cast iron, cemented carbide, aluminium alloys, copper alloys, super-alloys, ceramic materials, composites, polymers, wood, etc.) and in countless applications (metal-mechan- ics, automotive and transportation, aerospace, mining, timber industry, agriculture, electric/electronics, chemi- cal industry, medical, sports, music, etc.). One of the key factors contributing to the growth of advanced heat and thermo-chemical treatment strategies, involving sub-zero and deep cryogenic treatment, is the need to develop su- perior products with improved performance and proper- ties, especially in tooling, automotive, aerospace and en- ergy production industry. Through improved material properties (Figure 8), including wear resistance, tough- ness, corrosion and fatigue resistance, 39 cryogenic treat- ments are a very valuable tool for reducing the consump- tion of energy and strategic materials (steel, aluminium, light alloys, polymers) as well as their environmental footprint. Its use also enables shorter production times and savings, improved productivity and better quality. Furthermore, in contrast to conventional heat-treatment processes, which are specific for a particular material and mainly limited to ferrous metals, a deep cryogenic treatment is applicable to almost all engineering materi- als. Superior material properties are getting more and more important as the high-performance expectations, required levels of reliability and environment protection increase. The limits of materials are stretched primarily through alloy design and the utilization of composite technology. 40 However, the development of traditional metallic alloys using one or two principal alloying ele- ments has reached a saturation point. 41 Thus, multi- component alloy design and development is the way for- ward to realize a much wider spectrum of compositions with a superior combination of properties, as shown by high-entropy alloys (HEA). 42 These alloys contain multi- ple alloying elements (four or more) and are designed principally based on configurational entropy. Such alloys also have the potential to eliminate the need for heat treatment. Initially high-density elements such as Fe, Cu and Ni were used, targeting equi-atomic compositions and single-phase structures. Currently, multi-component high-entropy alloys with a different combination of ele- ments and different combination of properties are ex- plored. 43 These include low-density HEAs (i.e., Mg 43 (MnAlZnCu) 57 ) with density values lower than 3 g/cm 3 targeting weight-critical applications and high- density HEAs (i.e., V 20 Nb 20 Mo 20 Ta 20 W 20 ) for harsh envi- ronment applications providing excellent specific strength, superior mechanical performance at high tem- B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 79 Figure 8: Properties comparison between conventional vacuum heat treatment (VHT) and deep cryogenic treatment (DCT) of tool steels 39 peratures, exceptional ductility and fracture toughness at cryogenic temperatures, superparamagnetism and super- conductivity. 44 From the perspective of enhancing prop- erties, attention has to be placed on compositional con- trol to develop multi-component alloys where the secondary phases are developed inherently during a pro- cessing step to exhibit a superior combination of proper- ties without the need for heat treatment. However, there are still many fundamental issues related to the forma- tion of different phases, which need the development of new theories, models and mechanisms. Furthermore, al- though an almost unlimited number of compositions are possible (10 102 different alloy systems estimated that could potentially be useful to society) only a few may prove useful, requiring efficient high-throughput method for alloy screening. 45 Machine learning, showing fast and reasonably accurate property predictions combined with density function theory, is a promising approach to guide the new multicomponent alloy design. 46,47 In this way it can be determined whether a system is likely to be stable as well as to calculate many material properties. On the other hand, the inverse approach of choosing elements that can provide the needed specifications can be used when a specific combination of properties is needed for a given application. Surface engineering (Figure 9), on the other hand, can solve surface-related demands and properties, and offer materials savings and environmental benefits by: • implanting alloying atoms to different depths, thereby improving toughness and fatigue properties (surface modification), • depositing surface layers, thick or thin, including solid lubricants (surface coating), • redesigning the surface shape of the component to distribute stresses (surface texturing). Many modern surface engineering processes also have low environmental impact. For the green future, it is extremely important to de- velop new, advanced materials. However, it is often the changes to the surface of already-existing material that can achieve the greatest benefits to performance as well as environment. Surface engineering is about modifying the surface of what lies beneath, to make it perform better, last longer, or even achieve a different function entirely. So, surfaces can prevent or control the main “life-determining” characteristics of materials (such as wear, corrosion and fatigue). But they can also have a huge impact on sustainability, by ensuring optimized use of scarce materials, reducing energy losses due to fric- tion, increasing wettability, providing tissue-compatibil- ity, etc. 49 A very important issue in materials research is envi- ronment friendliness, biocompatibility, non-toxicity, degradability, recyclability, sustainability, etc. However, from the functionality and performance points of view, compatibility with other materials, compounds and sub- stances in the system is equally important. An example is the compatibility of coatings with lubricants. By improv- B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE 80 Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 Figure 10: Friction reduction through combined action of DLC coatings and additives, 50 and negative effect of oil penetration on strength of car- bon-fibre-reinforced composites 51 Figure 9: Examples of surface engineering by plasma nitriding, coating 48 and texturing ing tribological properties, i.e., reducing wear and coeffi- cient of friction of contact surfaces, hard coatings pro- vide great opportunity for further improving performance, durability and efficiency of tools and com- ponents, which can no longer be achieved by material se- lection, design or lubrication. At the same time, they even show the possibility of running components dry, thus potentially eliminating lubricants or at least replac- ing them with less hazardous ones. However, although certain coatings, especially carbon (DLC) and MoS 2 -based coatings show low friction and wear under dry-sliding conditions, the majority of components and tools will remain lubricated using the same oils origi- nally developed for uncoated metallic surfaces, at least for the near future. There are many reasons for this. Firstly, tribological properties of low friction coatings are sensitive to the surrounding and contact conditions, notably the relative humidity. Furthermore, the lubricant also serves other functions, such as cooling, insulation, wear-particles removal, etc. Therefore, the design of new materials and components for a green future needs to take into account also this aspect. As shown in Fig- ure 10, certain combinations may result in further tribological improvements and superior performance, while others can have detrimental or even disastrous ef- fect. 4 SLOVENIAN COOPERATIVE RESEARCH RESULTS Besides advanced research and high-tech research fa- cilities the close cooperation between universities, re- search institutions and industry is needed to develop ad- vanced functional materials and solutions that can effectively support journey of our society into green fu- ture. A great example of such collaboration is Slovenian research program MARTINA (Materials and Technol- ogies for New Applications), 52 involving 15 partners (2 universities, 6 research institutes and centres, 7 compa- nies), where through the joint research and development the following materials with superior properties were de- veloped and introduced (Figure 11): • Three ultra-high-strength steels for automotive and transportation industry, providing 10–20 % higher strength at up to 5-times better fatigue resistance, re- duced need for heat treatment and diminished heat affected zone influence. Two steels are aimed for forged load-bearing components and one for safety construction elements in light-weight designs. • Two tool steels with reduced non-metallic inclusions, better fatigue and heat checking resistance, improved machinability and 60 % higher thermal conductivity, thus focusing on reduced energy consumption and material use. • New high-strength Al alloy (registered as 6086 type) produced with a high share of scrap. This addresses requirements on light-weight design, reduced mate- rial CO 2 -footprint, reduced energy use and raw mate- rial input. • Completely new magnetic material and production process based on anisotropic magnetic particles in a thermoplastic matrix, allowing the production and magnetization in a single stage and magnets with up to 40 % better magnetic-field effectiveness. • Application of metallic nanoparticles in different polymeric materials, providing completely new struc- tural properties such as anti-bacteric and wear resis- tance, electrical conductivity, magnetic properties, etc. 5 SUMMARY For a green future, the development and progress of materials are extremely important. For each renewable technology to progress, the development and improve- ment of materials is needed. The development and appli- cation of advanced lightweight materials, regarded as materials with novel or enhanced properties that improve performance over conventional products and processes, contributes to a significant reduction in weight and in- crease in performance. The specific properties of ad- vanced materials give them a lot of advantages over tra- ditional materials, but specifics related to resources availability, energy and CO 2 -footprint intensive produc- tion, degradability and recyclability, bio-compatibility, etc. may raise sustainability concerns and pose some se- rious threats to the environment. Metals, on the other hand, have ann excellent sustainable character, without B. PODGORNIK: ADVANCED MATERIALS AND RESEARCH FOR THE GREEN FUTURE Materiali in tehnologije / Materials and technology 57 (2023) 1, 71–83 81 Figure 11: Forgings from ultra-high-strength steel, die from hot work tool steel with improved thermal conductivity and light-weight design with new Al 6086 alloy 52 their true properties and applicability potential being fully exploited. The limits of materials are stretched primarily through alloy design. However, the development of tradi- tional metallic alloys using one or two principal alloying elements has its limits. These can be overcome by multicomponent alloy design (i.e., high-entropy alloys), allowing a much wider spectrum of compositions with a superior combination of properties, such as low-density alloys with density values much lower than aluminium and high-density alloys providing excellent specific strength and performance at high temperatures, etc. However, although almost unlimited number of composi- tions are possible only a few may prove useful. Machine learning combined with computational modelling is a promising approach to guide the new multicomponent al- loy design. On the other hand, often already changes to the surface of the existing material can provide great benefits to performance and environment. Surface engi- neering is about modifying the surface through diffusion, coating or texturing processes to make material perform better, last longer, or even achieve a different function entirely. The problem of many products and goods that society takes for granted, is they are quite difficult to recycle. Even when it is technically feasible to take apart a prod- uct and recycle its parts, it is often that new, advanced materials are very technically challenging to recycle and not economically justified. To increase the potential and likelihood of products and materials being recycled, it is essential to consider recyclability during the design phase. Not only product design but also design of the material itself is crucial to increase the recycling rate and sustainability. Materials need to be more recyclable by design. The main short-term efforts to increase the recyclability of materials are related to waste-material sorting and separation, medium-term to information tools and use of biodegradable and bio-sourced materi- als, while long-term to new technologies and research strategies. In terms of environment protection an important chal- lenge is how to reduce direct emissions and CO 2 foot- print during material production. Steel, aluminium and copper production are the three biggest producers of CO 2 . An approach combining recycling, electrification and the use of green hydrogen is currently considered the most viable option and the long-term solution to achieve carbon-neutral production. However, the key challenge will be obtaining sufficient amounts of green electricity from renewable energy. The same is true when it comes to electrical mobility, regarded as a major step toward the world’s decarbonisation and reduction of GHG emis- sions. Climate impact which derives from manufacturing of cells, modules and pack, mining and refining of bat- tery materials, as well as origin of the electricity must all be taken into account. With the environmental concerns being at the top of the engineering agenda, the development and selection of materials is far from simple. 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