Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... 307–316 EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT MULTI-CRITERIA DECISION-MAKING METHODS OCENA OBRABE NITRIDNEGA PVD NANOSA Z UPORABO RAZLI^NIH METOD VE^KRITERIJSKIH POSTOPKOV ODLO^ANJA Yýlmaz Küçük1, Ahmet Öztel2, Mehmet Yavuz Balalý3, Mecit Öge1, Mustafa Sabri Gök1 1Bartin University, Faculty of Engineering, Department of Mechanical Engineering, 74100 Bartin, Turkey 2Bartýn University, Faculty of Economics and Administrative Sciences, Department of Management, 74100 Bartýn, Turkey 3Turkish Military Academy, 06654 Ankara,Turkey mecitoge@bartin.edu.tr, mecitoge@yahoo.com Prejem rokopisa – received: 2016-03-02; sprejem za objavo – accepted for publication: 2016-05-05 doi:10.17222/mit.2016.041 In this study, AISI 7131 (16MnCr5) case-hardened steel specimens were prepared in two groups, carbonitrided and without heat treatment, and the specimen surfaces were coated with three different coating materials (CrN, TiAlN and TiN) as a single layer using the physical vapor deposition (PVD) cathodic arc method. The wear behaviors of the coated specimens were tested with the micro-abrasion method. The test results of the micro-abrasion wear tests were analyzed with Multi-Criteria Decision Making (MCDM) techniques to determine the combination of coating and heat treatment that yields the lowest wear rate. According to the analyses conducted with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), Multiple Attribute Utility Theory (MAUT) and Compromise Programming (CP) MDCM techniques, the TiAlN coating exhibited the best wear performance. The MAUT and CP methods produced an identical ranking of the alternatives, whereas a slight deviation was found in the ranking with the TOPSIS method. Uncoated and CrN-coated specimens exhibited the worst wear performance of all the MCDM methods. Keywords: wear, micro-abrasion, multi-criteria decision making, PVD coating V {tudiji sta bili pripravljeni dve skupini jekla za cementacijo AISI 7131 (16MnCr5), karbonitrirana jekla in jekla brez toplotne obdelave, katerih povr{ina vzorcev je bila prekrita s tremi razli~nimi nanosi (CrN, TiAlN in TiN) v enem sloju, s pomo~jo fizikalne depozicije preko plinske faze (angl. PVD) z metodo obloka. Obna{anje vzorcev z nanosom pri obrabi je bilo preizku{eno z mikroabrazijsko metodo. Rezultati preizkusov mikroabrazijske obrabe so bili analizirani z uporabo ve~kriterijske tehnike odlo~anja (angl. MCDM), za dolo~itev kombinacije nanos – toplotna obdelava, ki ka`e najmanj{o hitrost obrabe. Glede na analize, ki so bile izvedene s pomo~jo tehnike, ki je najbli`ja idealni re{itvi (angl. TOPSIS), s teorijo ve~kratne prednosti (angl. MAUT) in s programsko tehniko (angl. CP) MDCM-kompromisov, je najbolj{o odpornost na obrabo pokazal TiAlN. MAUT- in CP-metodi dajeta enakovredne alternative, medtem ko je bilo manj{e odstopanje ugotovljeno pri TOPSIS-metodi. Vzorci brez nanosa in s CrN nanosom so pokazali najslab{o odpornost na obrabo od vseh MCDM-metod. Klju~ne besede: obraba, mikroabrazija, ve~kriterijsko odlo~anje, PVD-nanos 1 INTRODUCTION Many of the machine parts used in automotive, air- craft and machine tools are exposed to mechanical loads under certain conditions in which they are in contact with their counterparts. Hence, many researches are con- ducted to understand the tribological properties of such parts to improve their service life and reduce the main- tenance costs. One of the methods used to solve this problem is the thin-film coating application. In the thin- film coating process, the adhesive characteristics and hardness of the coatings are improved through optimi- zation of the coating parameters using various deposition techniques. In this work, the coatings (TiN, CrN and TiAlN) widely employed in actual industrial applications were selected and deposited by the cathodic arc-evaporation PVD technique in order to make a comparative analysis of their tribological performances. In general, TiN and CrN coatings are known to be the most commonly employed thin hard coatings,1,2 whereas TiAlN is gener- ally used for the coating of cutting tools in special ma- chining operations.3 TiN, CrN and TiAlN thin hard coatings exhibit diffe- rent wear behaviors due to their differing characteristic properties, such as friction coefficient, hardness, abrasive wear and corrosion resistance under various service con- ditions.3,4 Abrasive wear is one of the most commonly known wear mechanisms and it is of great importance in terms of the evaluation of the wear performance of coatings and the selection of abrasive wear-resistant coatings suitable for specific applications.5 The micro-abrasion wear-testing method is widely used to determine the abrasive wear resistance of thin Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 307 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS UDK 620.193.95:621.793.8:669.058 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)307(2017) hard coatings.6–11 In the micro-abrasion wear test, the most effective test parameters that affect the test results can be classified as the rotational speed of the ball,12,13 the normal load,12 the ball sliding distance,13–14 the ball surface condition15, the size6,16–19 and the type of abrasive particle in the slurry.20 The coating materials may exhibit different wear per- formances depending on various test conditions. There- fore, it is necessary to determine the optimum test para- meters that simulate the best service conditions. To select the most suitable material for a specific application, the criteria affecting the material selection should be properly identified.21,22 The selection of suitable thin hard coatings having the best wear performance among seve- ral choices for a specific application can be considered as a MCDM problem.23–24 The selection of the best method for a given problem is yet another important issue with no definite answer.25 A. Abrishamchi et al.26 state that the selection of an appropriate MCDM from a long list of available MCDM methods is a multi-criteria problem itself. There is no single MCDM technique that can be deemed superior for all decision-making problems.27 TOPSIS, EXPROM2 (Preference Ranking Organization Method for Enrichment Evaluation), VIKOR (Vi{ekri- terijumsko Kompromisno Rangiranje – Multicriteria Optimization and Compromise Solution), ELECTRE (Elimination and Choice Expressing the Reality), Linear Assignment Method, and COPRAS (Complex Propor- tional Assessment)24 are among the MCDM methods used by researchers for optimum selection among a variety of options in industrial problems. A determination of the effects of the coating material and the nitriding processes on the wear behaviour of coating is a complex, multi-factorial problem and a limited number of studies are available in the literature on the use of MCDM techniques in the selection of coating materials. The TOPSIS method was used by A. Chauhan and R. Vaish27 for the selection of the best alternative among hard coatings based on their hardness, Young’s modulus, thermal expansion coefficient, H/E and H3/E2 ratios. H. Çalýþkan et al.24 used EXPROM2, TOPSIS and VIKOR methods to select the best coating material among a variety of multicomponent nano- structured boron-based hard coatings deposited using magnetron-sputtering and ion-implementation-assisted magnetron-sputtering methods in consideration of their hardness, Young’s modulus, elastic recovery, friction coefficient, and critical load. Again, the EXPROM II, TOPSIS and VIKOR methods were used by H. Çalýþkan et al.24 to determine the best selection among a variety of materials for tool holders used in hard milling. TOPSIS was developed by Hwang and Yoon (1981)28 as a value-based compensatory method in conception and application,29 which attempts to choose alternatives that are both closest to the positive-ideal solution and farthest from the negative-ideal solution.30 The benefit criteria are maximized and the cost criteria are mini- mized by a positive-ideal solution, and the opposite applies for the negative-ideal solution.31 TOPSIS pro- vides a cardinal ranking of alternatives through the full use of the attribute information without a requirement for independent attribute preferences.32,33 The main strengths of the TOPSIS method can be listed as its understandable principle and easy implementation, its applicability, which requires a collection of precise and overall infor- mation,34 a consideration of both positive and negative ideal solutions, the provision of a well-structured ana- lytical framework for ranking of alternatives, and the use of fuzzy number to deal with alternatives.35 The require- ment of vector normalization for multidimensional problems can be regarded as a weakness of the method. MAUT is a systematic method for the analysis and identification of multiple variables for obtaining a decision on a common basis.36 In this method, a multi-attribute utility function is derived, which requires single utility functions and related weighting factors.37,38 For an evaluation of the performance criteria individually in the same units, single utility functions are used as a means to render their aggregation possible in the multi- attribute utility function. In this procedure an objective is set and attributes are established for the goal; a range of attributes are set; single utility functions are derived for each attribute; weighting factors are estimated for each attribute; and a multi-attribute utility function is de- rived.39 The MAUT strategy allows the decision maker to make more objective decisions based on their experience and the result of the analysis. The CP method was first developed by M. Zeleny40 and later extended by A. Bárdossy, I. Bogárdi, L. Duck- stein41 as composite programming for dealing with problems of a hierarchical nature. CP is within the class of distance-based, multi-criteria analytical methods, designed to identify non-dominated solutions, closest to an ideal solution by some distance measure.42 Its simple structure is one of the main advantages of this method. This is a simple and easily understandable method that provides good performance when compared with complicated and time-consuming methods.43 In this study the micro-abrasion wear behaviour of single-layer CrN, TiN and TiAlN coatings was inves- tigated using the fixed-ball micro-scale abrasion test. Afterwards, some of MCDM techniques such as TOPSIS, MAUT and CP, were implemented to compare their outputs as a means to determine the thin hard coating having the highest wear resistance. As indicated, there are studies23–24,28 available in the literature on the use of the TOPSIS method for the selection of the best alternative among a variety of coating applications. In this study the MAUT and CP methods are used to make a comparative analysis between TOPSIS and these me- thods. Also, among the other MCDM methods, the TOPSIS, MAUT and CP methods were chosen for their widespread usage,44 easy computation and for being Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... 308 Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS within the same class of unique synthesis criterion approaches in which different points of view are merged into a unique functional structure for further optimiza- tion, which in turn facilitates the solution of material selection problems.45 2 MATERIALS AND METHODS 2.1 Substrate and coating Test samples made of AISI 7131 (16MnCr5) steel with a diameter of 40 mm and a thickness of 10 mm were used as a substrate for the deposition of TiN, TiAlN and CrN thin hard coatings. After the sample polishing process, all the test samples were subjected to a car- burizing process performed in accordance with the heat treatment procedure given in Figure 1. The substrate surface is hardened through a duplex surface treatment, a combination of nitriding and carbu- rizing, since most of the applied forces must be supported by the substrate due to the thin structure of the PVD coatings.46–48 The nitriding process can provide a significantly high wear and adhesion resistance for TiAlN coatings.49 Therefore, in this study, in addition to carburizing, a nitriding process was also applied to some samples to determine its synergistic effect on the abrasive wear behaviour of thin hard coatings. The nitriding process parameters are given in Table 1. The list of prepared samples is given in Table 2. After the carburizing and/or nitriding surface-hardening processes, polishing was performed as the last operation before the deposition process to remove the white layer (oxide or nitride layer) emerging during the heat treatment and having an adverse effect on the coating’s adhesion.50 The average surface roughness of the polished samples was measured as Ra = 0.02 μm after measurements conducted with a Mitutoyo SJ 201 profilometer. Before the coating pro- cess, the sample surfaces were washed 2 times with an alkaline detergent using an ultrasonic washing device. Then, the samples were washed 3 times with distilled water, each time for a period of 30 s, and then dried with hot air. Table 1: Nitriding parameters Tabela 1: Parametri nitriranja Process type Plasma nitriding Temperature 480 °C Duration 10 h Gas mixture/ratio Nitrogen-Hydrogen / 3:1 Pressure 2.5 mbar (in vacuum) Table 2: Test sample classification Tabela 2: Razvrstitev preizkusnih vzorcev Coating material Carburizing Nitriding Notation CrN + - CrN CrN + + CrN+N TiN + - TiN TiN + + TiN+N TiAlN + - TiAlN TiAlN + + TiAlN+N Table 3: PVD deposition parameters Tabela 3: Parametri PVD-depozicije Parameter Coating material TiN CrN TiAlN Cathode current 70 A 70 A 60 A Bias voltage (DC) 50–60 V 50–60 V 50–60 V Number of cathode 6 6 8 Duration 1 h 1 h 30 min 1 h 10 min Following the ion bombardment on the coated sample surface, thin hard coatings were deposited on the sample surfaces using the parameters given in Table 3 by the cathodic arc PVD technique. 2.2 Micro-abrasion test The micro-abrasion wear test is a widely used method in the determination of the abrasive wear perfor- mance of thin hard coatings. In this study, micro-abra- sion wear tests were carried out using a fixed-ball-crater- ing device shown in Figure 2. In micro-abrasion tests, an Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 309 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 1: Process diagram of carburizing Slika 1: Diagram poteka naoglji~enja Figure 2: Scheme of the fixed-ball micro-abrasion test set up Slika 2: Shema postavitve mikro-abrazijskega preizkusa s fiksno kroglo abrasive slurry composed of 25 g of SiC in 75 mL distilled water for each abrasive mesh size (800, 1000 and 1200) mesh, was applied as 3 drops per minute, onto an AISI 52100 steel polished ball with a diameter of 25.4 mm. 2.3 Multi-criteria decision making method 2.3.1 Definition of the problem and setting up Coating materials may yield differing wear results under different test conditions. In such situations a determination of the best choice for a coating material may be addressed as a multi-criteria decision making (MCDM) problem.23,24 In this study, implementation of MCDM methods is based on the assumption that each wear value obtained under different conditions is a criterion. The alternatives for the coating material are shown in Table 4. Table 4: Alternatives for coating material Tabela 4: Izbire materiala za nana{anje Alternative Material A1 CrN A2 N+CrN A3 N+TiAlN A4 N+TiN A5 TiAlN A6 TiN A7 Uncoated Table 5: Wear test factors Tabela 5: Faktorji preizkusa obrabe Abrasive (mesh) Load (N) Speed (r/min) 800 0,5 45 1000 1 90 1200 1,5 140 The factors for the wear test and their levels are shown in Table 5. 27 tests were conducted with these coating materials for three different factors. On the assumption that the wear rate found in each test is a criterion for a decision, our criteria can be organized as C(Abrasive, Load, Speed). Our criteria and the test parameters are shown in Table 6. 2.3.2 Entropy method for criteria weighting In MCDM problems, the significance level of each criteria cannot be the same. A weighting value must be specified for each criterion to evaluate this significance level. Several objective weighting methods are proposed by researchers. One of the most prominent of them is the entropy method. This method is based on the concept of Entropy, which is defined as a measure of uncertainty by Shannon.51 In the information theory, entropy is a criterion for the level of uncertainty given by discrete probability distribution, such that, the ones with signifi- cantly high values exhibit higher levels of uncertainty.52 If the decision matrix with sufficient information for the alternatives is available, then the entropy method can be used as a tool to determine the significance rankings, i.e., the weighting values of the criteria.28,53–55 The method can be summarized as follows:56–57 Let the decision matrix for a multi-criteria decision making problem with m alternatives and n criteria be Equation (1): X X X Xj n1 2   D A A A A x x x x x x x x x x i m j n j n i = 1 2 11 12 1 1 21 21 2 2 1             i ij in m m mj mn x x x x x x 2 1 2           ⎡ ⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎤ ⎦ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ (1) Here, xij: is the success value of i-th alternative according to j-th criterion. i = 1,2,...,m and j = 1,2,...,n. Here, A and X stand for the alternative and the criterion, respectively. Step 1: With the following Equation (2): r x x ij ij pj p m= = ∑ 1 i = 1,2,...,m and j = 1,2,...,n (2) [ ]R rij m n= × normalized decision matrix is obtained. Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... 310 Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Table 6: Criteria parameters Tabela 6: Merila parametrov Criterion Abrasive(mesh) Load (N) Speed (r/min) Criterion Abrasive (mesh) Load (N) Speed (r/min) Criterion Abrasive (mesh) Load (N) Speed (r/min) C1 800 0.5 45 C10 1000 0.5 45 C19 1200 0.5 45 C2 800 0.5 90 C11 1000 0.5 90 C20 1200 0.5 90 C3 800 0.5 140 C12 1000 0.5 140 C21 1200 0.5 140 C4 800 1 45 C13 1000 1 45 C22 1200 1 45 C5 800 1 90 C14 1000 1 90 C23 1200 1 90 C6 800 1 140 C15 1000 1 140 C24 1200 1 140 C7 800 1.5 45 C16 1000 1.5 45 C25 1200 1.5 45 C8 800 1.5 90 C17 1000 1.5 90 C26 1200 1.5 90 C9 800 1.5 140 C18 1000 1.5 140 C27 1200 1.5 140 Step 2: With the following Equation (3): e m r rj ij i m ij= − = ∑1 1ln ln j = 1,2,...,n (3) entropy value of each criterion is found. Here, ej is the entropy value of the j the criterion. Step 3: The weighting values of the criteria are assigned with Equation (4): W e e j j p p n= − − = ∑ 1 1 1 ( ) j = 1,2,...,n (4) It is apparent that Wj j n = ∑ = 1 1 3 RESULTS AND DISCUSSION In this study, TOPSIS, MAUT and CP methods among the MDCM methods are used with the wear results obtained from the conducted micro-abrasion tests for the selection of the most suitable coating material, and afterwards the solutions proposed by each method are compared. First, the criteria were weighted through the imple- mentation of the Entropy method on the decision matrix (Table 7) consisting of the test results obtained from the micro-abrasion tests conducted in accordance with the test parameters given in Table 3, and then the analyses were carried out for each of the TOPSIS, MAUT and CP methods, as a means for the selection of the most suitable coating material. The resulting solutions were listed in descending order (from the most to the least suitable) by a comparative evaluation. The criterion weights obtained with the Entropy method are given in Table 8. The criteria weights were objectively determined with the Entropy method. The criteria weights calculated using the Entropy method are given in Table 8. According to these results, the criterion weights of the 26th, 22nd, 25th and 19th criteria were found to be higher than the other criteria. This arises from the fact that the 7th alternative Uncoated sample and 1st alternative CrN coating result in relatively higher wear rates, whereas N+CrN,TiAlN and TiN coatings result in lower wear rates. Consequently, the coatings providing lower wear rates under these criteria are favored over the other coat- ings. Other criterion weights generally had approximate values. 3.1 Analysis using TOPSIS method The Technique for order preference by similarity to ideal solution (TOPSIS) method developed by C. - L. Hwang and K. Yoon28 is based on the basic concept of Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 311 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Table 7: The decision matrix for coating-material selection Tabela 7: Matrica odlo~itev pri izbiri materiala nanosa Material C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 CrN 0.0097 0.0134 0.0135 0.0149 0.0195 0.0221 0.0169 0.0226 0.0267 0.0071 0.0047 0.0044 0.0050 N+CrN 0.0047 0.0061 0.0066 0.0073 0.0099 0.0106 0.0104 0.0096 0.0094 0.0016 0.0013 0.0055 0.0078 N+TiAlN 0.0060 0.0071 0.0074 0.0055 0.0067 0.0077 0.0043 0.0067 0.0123 0.0031 0.0079 0.0020 0.0054 N+TiN 0.0042 0.0060 0.0093 0.0085 0.0129 0.0161 0.0088 0.0185 0.0189 0.0015 0.0037 0.0059 0.0026 TiAlN 0.0030 0.0050 0.0073 0.0059 0.0119 0.0111 0.0073 0.0130 0.0190 0.0013 0.0024 0.0075 0.0019 TiN 0.0041 0.0059 0.0083 0.0070 0.0093 0.0130 0.0074 0.0156 0.0108 0.0042 0.0061 0.0065 0.0039 Uncoated 0.0094 0.0147 0.0147 0.0220 0.0214 0.0228 0.0196 0.0220 0.0267 0.0081 0.0102 0.0122 0.0117 Material C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 CrN 0.0055 0.0072 0.0100 0.0064 0.0118 0.0021 0.0024 0.0013 0.0020 0.0021 0.0022 0.0024 0.0021 0.0029 N+CrN 0.0058 0.0093 0.0051 0.0036 0.0094 0.0005 0.0006 0.0009 0.0008 0.0006 0.0006 0.0005 0.0003 0.0004 N+TiAlN 0.0092 0.0026 0.0054 0.0068 0.0050 0.0003 0.0008 0.0005 0.0004 0.0015 0.0007 0.0009 0.0010 0.0005 N+TiN 0.0018 0.0117 0.0065 0.0016 0.0064 0.0009 0.0011 0.0015 0.0011 0.0014 0.0009 0.0012 0.0017 0.0012 TiAlN 0.0056 0.0054 0.0012 0.0028 0.0034 0.0015 0.0006 0.0006 0.0004 0.0004 0.0007 0.0004 0.0004 0.0007 TiN 0.0045 0.0011 0.0072 0.0092 0.0090 0.0004 0.0009 0.0012 0.0005 0.0007 0.0006 0.0006 0.0007 0.0008 Uncoated 0.0139 0.0246 0.0164 0.0166 0.0255 0.0048 0.0049 0.0024 0.0053 0.0030 0.0040 0.0055 0.0067 0.0027 Table 8: The criterion weights obtained using the entropy method Tabela 8: Kriterijske ute`i, dobljene z metodo entropije Criterion C1 C2 C3 C4 C5 C6 C7 C8 C9 Weight 0.0158 0.0163 0.0082 0.0245 0.0131 0.0120 0.0203 0.0126 0.0131 Criterion C10 C11 C12 C13 C14 C15 C16 C17 C18 Weight 0.0403 0.0297 0.0196 0.0279 0.0259 0.0571 0.0321 0.0414 0.0357 Criterion C19 C20 C21 C22 C23 C24 C25 C26 C27 Weight 0.0758 0.0616 0.0219 0.0866 0.0353 0.0540 0.0790 0.0922 0.0482 the selection of the alternative closest to ideal solution and the farthest to anti-ideal solution. The consecutive stages of this method are as follows:28,56 Step 1: Constructing the normalized decision matrix: with the following Equation (5): r x x ij ij pj p m = = ∑ ( ) 1 2 i = 1,2,...,m and j = 1,2,...,n (5) Normalized decision matrix [ ]R rij= is obtained. Step 2: Constructing the weighted normalized deci- sion matrix, with the following Equation (6): v w rij j ij= i = 1,2,...,m and j = 1,2,...,n (6) Normalized decision matrix [ ]V v ij m n= × is obtained. Here, wj : j-th criterion’s weight value obtained with the entropy method. Step 3: Determination of ideal and negative-ideal solutions: If the two artificial solutions A* (ideal solution) and A– (negative-ideal solution) are defined as follows: { }A v j J v j J i m v v i ij i ij * (max ), (min ' ) , , ..., , , .* * = ∈ ∈ = = 1 2 1 2{ }.., , ... ,* *v vj n (7) { }A v j J v j J i m v v i ij i ij – – – (min ), (max ' ) , , ..., , , . = ∈ ∈ = = 1 2 1 2{ }.., , ... ,– –v vj n (8) here, { }J j n= =1 2, , ..., in case of benefit criterion { }J j n' , , ...,= =1 2 in case of cost criterion Step 4: Calculation of the separation measure: Each alternative’s measure of separation from the ideal solution S i* and from the negative-ideal solution S i – , is given as follows: S v v i m i ij j j n * ( ) , , , ..., *= − = = ∑ 2 1 1 2 (9) S v v i m i ij j j n – ( ) , , , ..., –= − = = ∑ 2 1 1 2 (10) Step 5: Calculation of the relative proximity to the ideal solution: The relative proximity to the i-th alternative to the ideal solution (A*) is defined as follows: C S S S C i m i i i i i* – * – * ( ), , , ...,= − < < =0 1 1 2, (11) Step 6: Performing the decision ranking: The deci- sion ranking of the alternatives is performed in accord- ance with the descending order of C i* values. The weighted and normalized decision matrix, related to the analysis conducted in accordance with the steps defined in the TOPSIS method, is given in Table 9. Ideal and anti-ideal solutions obtained using Equations (7) and (8), are given in Table 10. As indicated in the table, the highest C i* valued alternative stands for the best selection in the TOPSIS method. Positive and negative separation measures given in Table 11 and relative proximities to the ideal solution are calculated respectively with Equations (9), (10) and (11). Also, the ranking of the coating materials based on the relative proximities to ideal solution are given in Table 11. According to this ranking, TiAlN is qualified as the best coating material owing to its excellent performance, which is followed by N+CrN, TiN and N+TiAlN with similar performance values. N+TiN and CrN resulted in low performance values, whereas the uncoated material resulted in the worst performance value. Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... 312 Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Table 9: Weighted normalized decision matrix Tabela 9: Pretehtana normalizirana matrica odlo~itev Material C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 CrN 0.0091 0.0091 0.0042 0.0118 0.0069 0.0063 0.0109 0.0066 0.0070 0.0235 0.0089 0.0047 0.0083 N+CrN 0.0044 0.0041 0.0020 0.0058 0.0035 0.0030 0.0067 0.0028 0.0024 0.0053 0.0024 0.0059 0.0130 N+TiAlN 0.0056 0.0048 0.0023 0.0044 0.0024 0.0022 0.0028 0.0020 0.0032 0.0102 0.0150 0.0021 0.0091 N+TiN 0.0039 0.0041 0.0029 0.0068 0.0045 0.0046 0.0057 0.0054 0.0049 0.0048 0.0069 0.0063 0.0044 TiAlN 0.0028 0.0034 0.0023 0.0047 0.0042 0.0032 0.0047 0.0038 0.0050 0.0042 0.0045 0.0080 0.0032 TiN 0.0038 0.0040 0.0026 0.0056 0.0033 0.0037 0.0048 0.0045 0.0028 0.0137 0.0116 0.0070 0.0065 Uncoated 0.0088 0.0100 0.0046 0.0175 0.0075 0.0066 0.0127 0.0064 0.0070 0.0267 0.0192 0.0131 0.0196 Material C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 CrN 0.0072 0.0135 0.0141 0.0121 0.0132 0.0289 0.0257 0.0080 0.0292 0.0171 0.0244 0.0304 0.0259 0.0325 N+CrN 0.0076 0.0175 0.0072 0.0069 0.0105 0.0065 0.0062 0.0053 0.0115 0.0046 0.0069 0.0058 0.0037 0.0044 N+TiAlN 0.0119 0.0048 0.0075 0.0130 0.0055 0.0038 0.0082 0.0032 0.0055 0.0127 0.0073 0.0111 0.0122 0.0051 N+TiN 0.0023 0.0220 0.0092 0.0030 0.0070 0.0128 0.0112 0.0093 0.0159 0.0114 0.0104 0.0155 0.0209 0.0133 TiAlN 0.0073 0.0101 0.0017 0.0053 0.0037 0.0206 0.0062 0.0036 0.0055 0.0030 0.0082 0.0051 0.0044 0.0073 TiN 0.0058 0.0020 0.0102 0.0176 0.0100 0.0048 0.0096 0.0073 0.0069 0.0059 0.0066 0.0070 0.0088 0.0089 Uncoated 0.0181 0.0464 0.0231 0.0316 0.0283 0.0651 0.0526 0.0149 0.0784 0.0243 0.0447 0.0696 0.0845 0.0302 Table 11: Positive and negative separation measures, relative proxi- mities to the ideal solution and the ranking Tabela 11: Pozitivni in negativni ukrepi lo~evanja, relativni pribli`ki idealni re{itvi in razvrstitev Material S+ S- C+ Sýra CrN 0.0724 0.1104 0.6039 6 N+CrN 0.0234 0.1632 0.8747 2 N+TiAlN 0.0262 0.1610 0.8602 4 N+TiN 0.0371 0.1433 0.7946 5 TiAlN 0.0212 0.1648 0.8861 1 TiN 0.0255 0.1620 0.8640 3 Uncoated 0.1742 0.0023 0.0132 7 3.2 Analysis using MAUT method According to the basic principle of MAUT (Multiple Attribute Utility Theory) method, there is an U utility function with a real value, defined over the set of suitable alternatives, and the decision maker maximizes this.58 The procedure followed in the MAUT method is defined in 4 steps:59–60 Step 1: Utility values are determined according to the benefit criteria and the normalized values rij are calcu- lated using these values: r x l u lij ij l j l = − −+ – – , u xj i ij + = max , l xj i ij – min= (12) Similarly, the utility values are also determined based on the cost criterion, and normalized values rij are calcu- lated accordingly: r u x u lij l ij j l = − − + + – , u xj i ij + = max , l xj i ij – min= (13) Step 2: Weighted sum of rij values gives the total uti- lity value. U w ri j j n ij= = ∑ 1 (14) Step 3: Decision ranking is performed. The alterna- tive with the highest total utility value is deemed the best alternative. The single-attribute utility function values of the alternatives calculated with MAUT method based on the criteria, are given in Table 12. MAUT multi-attribute utility function values and their ranking are given in Table 13. As shown in Table Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 313 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Table 10: Ideal and anti-ideal solutions Tabela 10: Idealne in neidealne re{itve Criterion C1 C2 C3 C4 C5 C6 C7 C8 C9 A* 0.0028 0.0034 0.0020 0.0044 0.0024 0.0022 0.0028 0.0020 0.0024 A– 0.0091 0.0100 0.0046 0.0175 0.0075 0.0066 0.0127 0.0066 0.0070 Criterion C10 C11 C12 C13 C14 C15 C16 C17 C18 A* 0.0042 0.0024 0.0021 0.0032 0.0023 0.0020 0.0017 0.0030 0.0037 A– 0.0267 0.0192 0.0131 0.0196 0.0181 0.0464 0.0231 0.0316 0.0283 Criterion C19 C20 C21 C22 C23 C24 C25 C26 C27 A* 0.0038 0.0062 0.0032 0.0055 0.0030 0.0066 0.0051 0.0037 0.0044 A– 0.0651 0.0526 0.0149 0.0784 0.0243 0.0447 0.0696 0.0845 0.0325 Table 12: MAUT single-attribute utility function values Tabela 12: Posamezni MAUT-atributi vrednosti funkcije koristnosti Material C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 CrN 0.0000 0.1299 0.1556 0.4352 0.1283 0.0498 0.1777 0.0000 0.0000 0.1428 0.6139 0.7683 0.6856 N+CrN 0.7483 0.8835 1.0000 0.8920 0.7841 0.8094 0.6014 0.8183 1.0000 0.9493 1.0000 0.6587 0.3997 N+TiAlN 0.5519 0.7813 0.8990 1.0000 1.0000 1.0000 1.0000 1.0000 0.8310 0.7342 0.2495 1.0000 0.6384 N+TiN 0.8212 0.8924 0.6653 0.8215 0.5769 0.4445 0.7070 0.2588 0.4521 0.9742 0.7299 0.6205 0.9282 TiAlN 1.0000 1.0000 0.9083 0.9812 0.6450 0.7784 0.8047 0.6033 0.4462 1.0000 0.8771 0.4622 1.0000 TiN 0.8332 0.9034 0.7956 0.9099 0.8235 0.6514 0.7982 0.4395 0.9160 0.5800 0.4557 0.5562 0.7969 Uncoated 0.0450 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0399 0.0000 0.0000 0.0000 0.0000 0.0000 Material C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 CrN 0.6906 0.7401 0.4203 0.6811 0.6160 0.5904 0.5791 0.5917 0.6755 0.3393 0.5349 0.6074 0.7250 0.0000 N+CrN 0.6669 0.6501 0.7451 0.8653 0.7248 0.9560 0.9991 0.8200 0.9174 0.9229 0.9944 0.9889 1.0000 1.0000 N+TiAlN 0.3921 0.9361 0.7284 0.6518 0.9275 1.0000 0.9580 1.0000 1.0000 0.5444 0.9827 0.9071 0.8948 0.9741 N+TiN 1.0000 0.5491 0.6526 1.0000 0.8645 0.8520 0.8925 0.4780 0.8575 0.6050 0.9001 0.8378 0.7873 0.6851 TiAlN 0.6856 0.8163 1.0000 0.9198 1.0000 0.7259 1.0000 0.9622 1.0000 1.0000 0.9589 1.0000 0.9915 0.8953 TiN 0.7755 1.0000 0.6055 0.4903 0.7436 0.9834 0.9266 0.6537 0.9804 0.8625 1.0000 0.9698 0.9372 0.8410 Uncoated 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0822 13, TiAlN takes the first place with its superior perfor- mance, followed by N+CrN, N+TiAlN and TiN with similar performance values. N+TiN, CrN and especially uncoated material exhibited significantly low perfor- mances, as the highest total utility valued alternative stands for the best selection. Table 13: MAUT Multi-utility function and the ranking Tabela 13: MAUT Ve~vrednostna funkcija in razvrstitev Material Multi utility values Ranking CrN 0.509431 6 N+CrN 0.879946 2 N+TiAlN 0.860277 3 N+TiN 0.784909 5 TiAlN 0.909513 1 TiN 0.841247 4 Uncoated 0.005178 7 3.3. Analysis using CP method CP (Compromise Programming) is a MCDM method developed in the 1970s by M. Zelen61 and P. – L. Yu.62 This method is based on minimization of the distance to the ideal point f*. The Lp metric is used for the calcul- ation of distance. The method can be summarized as follows:63–66 Step 1: Ideal point f* and anti-ideal point f* are estab- lished. f f f fn * * * *, , ...,≡ 1 2 , f f f fn* * * *, , ...,≡ 1 2 (15) here, f j j i m i * , ,... , , max min= = = 1 2 1 2 {x }ij . criterion utility ,... , m j{x }ij . criterion cost ⎧ ⎨ ⎩ (16) f j j i m i * , ,... , , min max= = = 1 2 1 2 {x }ij . criterion utility ,... , m j{x }ij . criterion cost ⎧ ⎨ ⎩ (17) here, xij: is the success value of the i-th alternative according to the j-th criterion. i = 1,2,...,m, j = 1,2,...,n. Step 2: The distance to the ideal point is minimized: min ( )* * * L W f f x f fp jj n j j i j j p /p = − − ⎛ ⎝ ⎜⎜ ⎞ ⎠ ⎟⎟ ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ = ∑ 1 1 , i = 1,2,...,m (18) Step 3: The alternative giving the minimal value is the best alternative. L1, L2 and L are, respectively, named as the Man- hattan, Euclidean and Tchebycheff metrics. The optimal values obtained using the CP method and the ranking are shown in Table 14. Given that in the CP method the alternative giving the lowest optimal value is the best alternative; TiAlN may be considered to have shown the best performance by far, as the highest total utility valued alternative stands for the best selec- tion. N+CrN, N+TiAlN and TiN materials underper- formed compared to the performance values of TiAlN. The performance values of N+TiN, CrN and the un- coated materials lined up at the bottom of the performance list. Table 14: CP optimal values and the ranking Tabela 14: CP optimalne vrednosti in razvrstitev Material Optimal value Rank CrN 0.269379 6 N+CrN 0.070013 2 N+TiAlN 0.080999 3 N+TiN 0.120416 5 TiAlN 0.055632 1 TiN 0.089914 4 Uncoated 0.543521 7 The rankings obtained using the TOPSIS, MAUT and CP methods are shown in Figure 3. As seen in the figure, the MAUT and CP methods produced the identical ranking of the alternatives, whereas there is a slight deviation in the ranking obtained with the TOPSIS method. However, all the methods indicate that TiAlN is the best material, followed by N+CrN. CrN and the uncoated materials displayed the best performances, according to all the MCDM methods implemented in the study. 4 CONCLUSIONS In this study, abrasive wear tests were conducted using the micro-abrasion wear technique on TiN, CrN and AlTiN coatings, which were deposited on nitrided and non-nitrided substrates with the PVD technique, then the measured wear values were used so as to determine the best coating selection through analyses with each of the TOPSIS, MAUT and CP methods among the MCDM techniques. The most suitable coating types, according to each method, were determined and comparatively eva- luated. The obtained results are summarized as follows: • According to the TOPSIS method TiAlN was deter- mined to be the coating with the best performance; which was followed by N+CrN, TiN and N+TiAlN, respectively. The N+TiN and CrN coatings under- Y. KÜÇÜK et al.: EVALUATION OF THE WEAR BEHAVIOR OF NITRIDE-BASED PVD COATINGS USING DIFFERENT ... 314 Materiali in tehnologije / Materials and technology 51 (2017) 2, 307–316 MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS Figure 3: Ranking of the alternatives obtained with MCDM methods Slika 3: Razvrstitev alternativnih variant, dobljenih z MCDM meto- dami performed compared to other coatings; however, the uncoated material displayed the worst performance, with a dramatic decline compared to all the coated materials. • According to the MAUT method, TiAlN exhibited the best performance. Other coatings were ranked as N+CrN, N+TiAlN and TiN, respecively. N+TiN, CrN and especially the uncoated material displayed re- markable underperformances. • The CP and MAUT methods produced the same ranking of alternatives. In the TOPSIS method only N+TiAlN and TiN shifted places in the ranking differently from the CP and MAUT methods. 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