T. TAÑSKI et al.: SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM AND ALUMINIUM ALLOYS
699–706
SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM
AND ALUMINIUM ALLOYS
OBDELAVA POVR[INE TOPLOTNO OBDELANIH MAGNEZIJEVIH
IN ALUMINIJEVIH LIVNIH ZLITIN
Tomasz Tañski, Maciej Wiœniowski, Wiktor Matysiak, Marcin Staszuk, Rados³av Szklarek
Silesian University of Technology, Institute of Engineering Materials and Biomaterials, Konarskiego Str. 18A, 44-100 Gliwice, Poland
tomasz.tanski@polsl.pl
Prejem rokopisa – received: 2015-06-26; sprejem za objavo – accepted for publication: 2015-10-12
doi:10.17222/mit.2015.132
Modern coating systems deposited on surface layers of structural light materials are currently one of the most important issues
in up-to-date material engineering, where vacuum deposition techniques are often used to improve the mechanical and func-
tional properties of produced surface layers. Presented in this paper are gradient and monolithic coating types: Ti/Ti(C,N)/CrN,
Ti/Ti(C,N)/(Ti,Al)N, Ti/(Ti,Si)N/(Ti,Si)N, Cr/CrN/CrN, Cr/CrN/TiN and Ti/DLC/DLC deposited onto magnesium and
aluminium alloy substrates with the cathodic-arc-evaporation method (Arc PVD) and plasma-assisted process (PA CVD). Addi-
tionally, a thin metallic layer – in micrometers– (Cr and Ti) was deposited prior to the deposition of the final gradient coating to
improve its adhesion to the substrate. This work presents the investigation results concerning the obtained surface-layer micro-
structures and mechanical properties of the obtained bi-layer coatings (gradient/multicompound) deposited onto light-alloy
substrates using the chosen PVD and CVD methods, especially to meet the requirements needed for light-metal substrates – low
temperature and duration. The structure investigations of the deposited coating were performed using a scanning electron
microscopy (SEM) and glow discharge optical emission spectrometry (GDOES); the mechanical and functional properties were
examined using the ball-on-disk method for the wear-resistance determination, and microhardness tests were performed for the
functional usability of the coatings. The main finding is that the fracture morphology is characterized by a lack of columnar
structures in the obtained coatings. The metallographic examinations carried out proved that the coatings were deposited uni-
formly over the whole sample, onto the investigated substrate materials; the measured thickness is characteristic for the
produced coating type.It was also found that the particular layers adhere tightly to each other and to the light-metal substrate.
The investigation results of the up-to-date PVD methods, together with light alloys, led to obtaining new applications, especially
in the automobile and aviation industries.
Keywords: light alloys, PVD, CVD, structure, properties
Moderni sistemi nanosov na povr{inskih plasteh lahkih konstrukcijskih materialov so eden od najpomembnej{ih izzivov v
in`eniringu materialov, kjer se za izbolj{anje mehanskih in funkcionalnih lastnosti plasti na povr{ini pogosto uporabljajo tehnike
vakuumske depozicije. V ~lanku so predstavljeni gradientni in monolitni nanosi vrst: Ti/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti,Al)N,
Ti/(Ti,Si)N/(Ti,Si)N, Cr/CrN/CrN, Cr/CrN/TiN in Ti/DLC/DLC ki so bili nane{eni z metodo katodnega izparevanja v obloku
(Arc PVD) in s plazemskim postopkom (PA CVD). Dodatno je bila nane{ena tanka kovinska plast (Cr in Ti), debelina v mikro-
metrih, in sicer pred nanosom kon~nega gradientnega nanosa, da bi se izbolj{ala njegova oprijemljivost na podlago. ^lanek
predstavlja rezultate raziskave mikrostrukture povr{inskega nanosa in mehanske lastnosti dvoplastnega nanosa
(gradient/multicompound), nane{enega na podlago iz lahke zlitine, s pomo~jo izbranih metod PVD in CVD, da bi zagotovili
zahtevam podlage iz lahke kovine – nizka temperatura in kratko trajanje. Preiskave zgradbe nanosa so bile izvedene s pomo~jo
vrsti~ne elektronske mikroskopije (SEM) in z razelektritveno opti~no emisijsko spektrometrijo (GDOES), medtem ko so bile
mehanske in funkcionalne lastnosti, preiskane z uporabo metode kroglica na plo{~i za dolo~anje obrabne odpornosti ter
mikrotrdote za funkcionalno uporabnost nanosov. Glavna ugotovitev je, da v morfologiji preloma nanosov ni stebraste zgradbe.
Izvedene metalografske preiskave so pokazale, da so nanosi enakomerno nane{eni po vsej povr{ini preiskovane podlage,
izmerjene debeline so zna~ilne za to vrsto nanosov in ugotovljeno je tudi, da se posamezni nanosi med seboj tesno stikajo, tudi s
podlago iz lahke kovine. Rezultati raziskav ka`ejo, da uporaba sodobnih PVD metod, skupaj z lahkimi zlitinami, omogo~a nove
aplikacije, posebno v avtomobilski in letalski industriji.
Klju~ne besede: lahke zlitine, PVD, CVD, struktura, lastnosti
1 INTRODUCTION
Dynamic industry development introduces an escala-
tion of requirements concerning new needs and working
conditions, which facilitateand direct theprogress within
material engineering, especially in the case of fabrication
and examination of new materials.1–3 Properties of many
products and their elements depend not only on the pos-
sibility of transmitting mechanical loads through the
whole active intersection or the material’s physical and
chemical properties, but also on the structure and proper-
ties of the surface layer. The use of surface layers, fulfill-
ing thehigh requirements withsoft and cheap cores, is a
great way of reducing expenses. A wide range of avail-
able layers and ways of theirmodification facilitate the
design of thebest combination of core and layer proper-
ties possible. Modern surface-engineering techniques in-
cluding the use of a corrosion- and abrasive-resistant
hard material, despite the maintenance of accurate prop-
erties, should allow usto combine esthetic values and
ecological production.3
With many available techniques of improving engi-
neering materials, the physical vapordeposition (PVD),
Materiali in tehnologije / Materials and technology 50 (2016) 5, 699–706 699
UDK 621.7.015:621.78:669.721.5:669.715 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(5)699(2016)
chemical vapordeposition (CVD) and hybrid methods
(which enable a full control of thechemical composition,
structure and properties using characteristics of particu-
lar methods like CVD, PVD and conventional thermo-
chemical treatments – thermal spraying + heat treatment,
nitriding or cyaniding + pulsed-laser deposition (PLD),
autocatalytic layer deposition + plasma-assisted process-
ing) are essential.4–20 Anotherimportant surface engineer-
ing technology, applied inlight-alloy processing, is the
laser treatment including remelting and alloying.3 These
techniques allow us to make layers with special proper-
ties (high hardness and tribological resistance combined
with constant substrate properties) and the thickness in a
range from tenths of a millimeter to even a few millime-
ter scan be achieved. A layer obtained with the laser-al-
loying or remelting technique has a different structure
and properties than those of the base or the alloying ele-
ments.3 The morphology of a quasi-composite layer is
homogeneous and exhibits a proper dispersion of the al-
loying elements into the whole depth except for a very
thin diffusion-saturation layer.
The aim of this research was to obtain a hard coat for
a soft core – such a material can resist different amounts
of load (depending on many factors) because of the coat-
ing and thanks to the soft core, the internal forces are
transferred and reduced inside. In some cases, the corro-
sion resistance is also observed, which is very desirable.
An important part of the investigationdone on the mate-
rial was the examination of the structures and mechani-
cal properties of gradient/monolithic coatings deposited
with the PVD and CVD methods onto magnesium and
aluminum casting alloys after the heat treatment.5,9,16,18
2 EXPERIMENTAL PART
The materials used for the investigation includedcast
magnesium and aluminium alloys, whosechemical com-
positions are presented in Table 1. The deposition of
coatings Ti/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti,Al)N,
Ti/(Ti,Si)N/(Ti,Si)N, Cr/CrN/CrN, Cr/CrN/TiN and
Ti/DLC/DLC was made within a device based on the
CAE PVD method in anatmosphere of Ar, N2 and C2H2;
moreover, the DLC coating wasdeposited using acety-
lene (C2H2) as the precursor and was produced with the
PA CVD method. A gradient change in thechemical
composition ofthe PVD coatings’ cross-sections was
achieved by changing the proportion of the reactive-gas
dose or a variation in thearc-source current. The DLC
coating was characterized byavariation in the silicon
(Me) concentration, demonstrating that a gradient layer
wasobtained. Silicon was supplied to the furnace cham-
ber from the gas phase, Ti/a-C:H-Me/a-C:H. Cathodes
containing pure metals (Cr, Ti) and alloys of TiAl and
TiSi (50:50 % amount fractions) were used for the depo-
sition of the coatings. The diameter of the used cathodes
was 65 mm. The temperature was controlled with
T. TAÑSKI et al.: SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM AND ALUMINIUM ALLOYS
700 Materiali in tehnologije / Materials and technology 50 (2016) 5, 699–706
Table 1: Chemical compositions oftheinvestigated alloys
Tabela 1: Kemijska sestava preiskovanih zlitin
Type of material Mass concentration of the elements, in mass fractions (w/%)
Al Zn Mn Si Mg Fe Cu Rest
Magnesium alloy – AZ91 9.09 0.77 0.21 0.04 89.8 0.011 – 0.079
Magnesium alloy – AZ61 5.92 0.49 0.15 0.04 93.3 0.007 – 0.093
Aluminium alloy – AlSi9Cu4 85.4 0.05 0.01 9.27 0.28 0.34 4.64 0.01
Aluminium alloy – AlSi9Cu 88.86 0.16 0.37 9.1 0.27 0.18 1.05 0.01
Table 2: Deposition parameters of the investigated coatings
Tabela 2: Parametri nana{anja preiskovanih nanosov
Coating parameters
Type of the achieved coating and the applied coating technique
PVD CVD
Ti/Ti(C,N)-gra-
dient/CrN
Ti/Ti(C,N)-gra-
dient/(Ti,Al)N
Cr/CrN-gradi-
ent/CrN
Cr/CrN-gradi-
ent/TiN
Ti/(Ti,Si)N-grad
ient/(Ti,Si)N
Ti/DLC-gradi-
ent/DLC
Base pressure (Pa) 5×10–3 5×10–3 5×10–3 5×10–3 5×10–3 1×10–3
Working pressure (Pa) 0.9/1.1-1.9/2.2 0.9/1.1-1.9/2.8 1.0/1.4-2.3/2.2 1.0/1.4-2.3/2.2 0.89/1.5-2.9/2.9 2
Argon flow rate (sccm)
80* 80* 80* 80* 80* 80*
10** 10** 80** 80** 20** –
10*** 10*** 20*** 20*** 20*** –
Nitrogen flow rate (sccm) 225→0** 0→225** 0→250** 0→250** 0→300** –
250*** 350*** 250*** 250***
Acetylene flow rate (sccm) 0→170** 140→0** – – 230
Substrate bias voltage (V)
70* 70* 60* 60* 70* 500
70** 70** 60** 60** 100**
60*** 70*** 60*** 100*** 100***
Target current (A) 60 60 60 60 60 -
Process temperature (°C) <150 <150 <150 <150 <150 <180
*during the metallic-layer deposition, **during the gradient-layer deposition, *** during the ceramic-layer deposition
thermocouples. To improve the adhesion of the coatings,
a transition Cr, Ti interlayer was deposited. The working
pressure during the deposition process was 2–4 Pa, de-
pending on the coating type. The distance between the
cathodes and the deposited substrates was 120 mm. Just
before the coating-deposition process, the specimens
were prepared with the standard procedures of grinding,
polishing and chemical cleaning using multi-stage wash-
ing in an ultrasonic cleaner and a cascade washer, then
dried in hot air. The next step was ion etching in the
chamber to clean the surfaces atthe atomic scale and to
activate them. The parameters used were asubstrate-po-
larization voltage of 800/200 V and a period of 20 min.
The conditions of the coating deposition are presented in
Table 2.
The investigations of the microstructures, micro-area
qualitative and quantitative chemical compositionswere
performed using a scanning electron microscope (SEM)
ZEISS Supra 35. The cross-sectional atomic composition
of the samples (coating and substrate) was obtained by
using the glow discharge optical spectrometer GDOS-
750 QDP from Leco Instruments.
The microhardness tests of the coatings were made
with a SHIMADZU DUH 202 ultra-microhardness
tester. The measurements were made with a 10 mN load,
to eliminate the substrate influence on the coating hard-
ness. Wear-resistance investigations were performed us-
ing the ball-on-disk method. A tungsten carbide ball with
a diameter of 3 mm was used as the counter part. The
tests were performed at room temperature overa defined
time using the following test conditions: a load of Fn =
5N, a rotation of the disk of 200 min–1 20.94 r/s, a wear
radius of 2.5 mm and a sliding speed of 0.05 m/s.
3 RESULTS AND DISCUSSION
In order to determine the structures and relationships
between the type of substrate and the types of hybrid lay-
ers, the metallographic investigation was done under the
technological conditions (the soft substrate – the gradient
intermediate layer able to easily change the concentra-
tion of one or a few components between the base and
the surface – and the external layer) of the cathodic-arc
deposition, Arc-PVD, and plasma-assisted chemical va-
por deposition, PA-CVD processes.
The layers obtained with the CAE-PVD technique
are heterogeneous, as many drop-shaped micro-sized
molecules exist in their structures. This fact leads to
changes in the mechanical, physical and chemical prop-
erties of the examined layers (Figures 1 to 6). The big-
gest surface heterogeneity, in comparison to the other ex-
amined layer surfaces, is visible within the Ti/Ti(C,N)/
(Ti,Al)N and Ti/Ti(C,N)/CrN systems, in which a lot of
precipitation of the evaporated, metal, clotty drops were
identified (Figures 1 and 2). The occurrence of this mor-
phological defect is related with the Arc-PVD process
characteristics. Depending on the process parameters, in-
cluding the kinetic energy transferred to the drops that
are crashed due to the metallic base, and the type of the
metal-vapor source used, particles varyingin shape and
size are observed. It was confirmed that the clotty drops
are spheroidal or irregular or they form agglomerates
that often include a few equal drops (Figures 1 to 6).
Moreover, characteristic hollows that form because of
the clotty drops falling out, were observed after the PVD
process wasfinished. On the basis of the metallographic
observations it was confirmed that the hollows do not
reach the surface. On the DLC layer obtained within the
PACVD process fine drops, mostly spheroidal, were
identified as well (Figure 5). The surface morphology of
the DLC layer is different from that obtained with classi-
cal high-temperature CVD processes – no micro-gaps or
wavy and globular-like surfaces were observed. The
smallest amount of morphologic surface defects was
obtained with the Cr/CrN/TiN layer (Figure 4).
A fractographic examination of magnesium- and alu-
minum-alloy samples with the applied layers, done with
a scanning electron microscope, showed a sharp transi-
T. TAÑSKI et al.: SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM AND ALUMINIUM ALLOYS
Materiali in tehnologije / Materials and technology 50 (2016) 5, 699–706 701
Figure 2: Surface topography of Ti/Ti(C,N)/(Ti,Al)N layer obtained
on MCMgAl6Zn1 cast magnesium alloy
Slika 2: Topografija povr{ine nanosa Ti/Ti(C,N)/(Ti,Al)N na
MCMgAl6Zn1 livni magnezijevi zlitini
Figure 1: Surface topography of Ti/Ti(C,N)/CrN layer obtained on
AlSi9Cu4 cast aluminum alloy
Slika 1: Topografija povr{ine nanosa Ti/Ti(C,N)/CrN na AlSi9Cu4
aluminijevi livni zlitini
tion zone between the base and the layer. The layers are
compact in structure with no visible delamination or de-
fects. They are placed uniformly and they adhere to the
base hermetically (Figures 7 to 10). Observations of the
fractures confirm that layers like Ti/Ti(C,N)/(Ti,Al)N
and Ti/Ti(C,N)/CrN are laminar with a visible transition
zone between the gradient and the anti-wear layers ob-
tained with different metal-vapor sources (Figure 7). On
the cross-section of the Cr/CrN/CrN, Ti/(Ti,Si)N/
(Ti,Si)N layers, in which identical sets of chemical ele-
ments of gradient and anti-wear layers were used, no vis-
ible differences were observed (Figure 8). In addition,
multi-layer carbon coats like Ti/DLC/DLC obtained with
the CVD method, in which the gradient in the middle
coating allows a variable silicon concentration, do not
exhibit any visible transition zone between individual
layers. Moreover, in the range of the thin adhesive layer
(whose task is to improve the adhesion of the base and
DLC layers) is was possible to identify a bright, continu-
ous layer of titanium, which was also confirmed with
theEDS spectrometry analysis (Figure 9). It was con-
firmed that the titanium nitride layer obtained with the
Cr/CrN/TiN system has a close to columned rise charac-
ter of crystallite that is characteristic for titanium
T. TAÑSKI et al.: SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM AND ALUMINIUM ALLOYS
702 Materiali in tehnologije / Materials and technology 50 (2016) 5, 699–706
Figure 4: Surface topography of Cr/CrN/TiN layer obtained on
MCMgAl9Zn1 cast magnesium alloy
Slika 4: Topografija povr{ine nanosa Cr/CrN/TiN na MCMgAl9Zn1
livni magnezijevi zlitini
Figure 6: Surface topography of Ti/(Ti,Si)N/(Ti,Si)N layer obtained
on AlSi9Cu1 cast aluminum alloy
Slika 6: Topografija povr{ine nanosa Ti/(Ti,Si)N/(Ti,Si)N na AlSi9Cu1
livni aluminijevi zlitini
Figure 3: Surface topography of Cr/CrN/CrN layer obtained on
MCMgAl9Zn1 cast magnesium alloy
Slika 3: Topografija povr{ine nanosa Cr/CrN/CrN na MCMgAl9Zn1
livni magnezijevi zlitini
Figure 7: Fracture of Ti/Ti(C,N)/CrN layer obtained on AlSi9Cu4 cast
aluminum alloy
Slika 7: Prelom nanosa Ti/Ti(C,N)/CrN na AlSi9Cu4 livni aluminijevi
zlitini
Figure 5: Surface topography of Ti/DLC/DLC layer obtained on
AlSi9Cu1 cast aluminum alloy
Slika 5: Topografija povr{ine nanosa Ti/DLC/DLC na AlSi9Cu1 livni
aluminijevi zlitini
nitride-based layers achieved with the Arc-PVD (Figure
10).
The chemical-composition investigation carried out
with GDOES and SEM confirmed the existence of the
chemical elements of the obtained layers in a depth of
1.4–3.4 μm (Figures 11 and 12). The maximum thick-
ness of the layers was measured to beas follows:
Ti/Ti(C,N)/CrN ~3.3μm; Ti/Ti(C,N)/Ti(Al,N) ~3.4μm;
Cr/CrN/CrN ~1.8μm; Cr/CrN/TiN ~1.7μm; Ti/Ti(Si,N)/
Ti(Si,N) ~1.6μm; Ti/DLC/DLC ~2.5μm. The variation in
the bonding-zone character – an increase in the chemi-
cal-element concentration of the base and a decrease in
the chemical-element concentration of the layer – leads
to the conclusion about the existence of a transitory dif-
fusion zone between the base material and the layer,
which improves their adhesion. Moreover, with the
GDOES examination, the decrease zone of the linear
concentration of the chemical elements of the layer was
T. TAÑSKI et al.: SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM AND ALUMINIUM ALLOYS
Materiali in tehnologije / Materials and technology 50 (2016) 5, 699–706 703
Figure 11: Variation in the concentration of Ti/Ti(C,N)/CrN layer
chemical elementsobtained on AlSi9Cu1 magnesium alloy
Slika 11: Spreminjanje koncentracije elementov v Ti/Ti(C,N)/CrN
nanosu na AlSi9Cu1 magnezijevi zlitini
Figure 9: Fracture of Ti/DLC/DLC layer obtained on AlSi9Cu1 cast
aluminum alloy
Slika 9: Prelom nanosa Ti/DLC/DLC na AlSi9Cu1 livni aluminijevi
zlitini
Figure 12: Variation in the concentration of Ti/(Ti,Si)N/(Ti,Si)N layer
chemical elements obtained on MCMgAl6Zn1magnesium alloy
Slika 12: Spreminjanje koncentracije elementov v Ti/(Ti,Si)N/
(Ti,Si)N nanosu na MCMgAl6Zn1 magnezijevi zlitini
Figure 10: Fracture of Cr/CrN/TiN layer obtained on MCMgAl9Zn1
cast magnesium alloy
Slika 10: Prelom nanosa Cr/CrN/TiN na MCMgAl9Zn1 livni mag-
nezijevi zlitini
Figure 8: Fracture of Ti/(Ti,Si)N/(Ti,Si)Nlayer obtained on
MCMgAl6Zn1 cast magnesium alloy
Slika 8: Prelom nanosa Ti/(Ti,Si)N/(Ti,Si)N na MCMgAl6Zn1 livni
magnezijevi zlitini
confirmed – it proves that the layers are gradient (Fig-
ures 11 and 12).
The layers obtained with Arc-PVD and PA CVD on
the base of Mg and Al alloys significantly increased the
microhardness compared to the base material (Figure
13). This phenomenon is caused by the chemical- and
phase-concentration change, various conditions, the type
of the method (PVD or CVD) and the combination of the
layers.
The type of base material – Mg or Al alloys – has the
least influence on the microhardness (Figure 13). A sig-
nificant rise in the microhardness after the precipitation
hardening, exceeding 100 % compared to the base mate-
rial, took place due totheCr/CrN/CrN, Cr/CrN/TiN and
Ti/(Ti,Si)N/(Ti,Si)N layers obtained with the cathodic
PVD process and N2 as the protective gas. The layers’
hardness does not exceed 2000 HV according to the
microhardness test results, while the Ti/Ti(C,N)/CrN and
Ti/Ti(C,N)/(Ti,Al)N layers obtained within the mixture
of CH4 and N2 as the protective gas are even harder than
2000 HV.
In the case of the 5N load used in the examination,
the average friction factor for theDLC coatings (done on
Al and Mg) achieved with a 0.05 m/s slide velocity is in
a range of 0.06–0.16 (Figure 15). Thisis a decrease in
the whole order of magnitude in comparison to the other
layers. This state is characteristic for the DLC layers that
consist of graphite, which works like a lubricant during
the abrasion process. Moreover, a high traverse speed,
which causes heat accumulation, is responsible for an
easier self-lubrication of the layer, resulting in a reduc-
tion in the friction coefficient (Figures 14 and 15). The
sliding distance for the DLC coatings obtained on Mg is
even 70 times higher than those measured for Cr/CrN/
CrN or diamond-like layers (Figure 14). The sliding-dis-
tance values for all the examined layers were in a range
of 6–630 m (Figure 14). When examining all the
ball-on-disk test results, it was confirmed that the value
T. TAÑSKI et al.: SURFACE TREATMENT OF HEAT-TREATED CAST MAGNESIUM AND ALUMINIUM ALLOYS
704 Materiali in tehnologije / Materials and technology 50 (2016) 5, 699–706
Figure 15: Dependence of layer friction coefficient on the coun-
ter-samplesliding distance achieved withtheball-on-disc method on: a)
Ti/(Ti(C,N)/(Ti,Al)N, b) Ti/(Ti(C,N)/CrN, c) Cr/CrN/TiN, d)
Cr/CrN/CrN, e) Ti/(Ti,Si)N/(Ti,Si)N, f) Ti/DLC/DLC, obtained on
aluminum and magnesium cast alloys
Slika 15: Odvisnost koeficienta trenja od razdalje drsenja, dobljene
pri metodi kroglica na plo{~i pri: a) Ti/(Ti(C,N)/(Ti,Al)N, b) Ti/
(Ti(C,N)/CrN, c) Cr/CrN/TiN, d) Cr/CrN/CrN, e) Ti/(Ti,Si)N/(Ti,Si)N,
f) Ti/DLC/DLC na livnih aluminijevih in magnezijevih zlitinah
Figure14: Dependence of sliding distanceto the coating damage on
the minimum and maximum friction coefficients intheball-on-disc test
used on PVD and CVD layers obtained on aluminum and magnesium
cast alloys
Slika 14: Odvisnost razdalje drsenja do po{kodbe nanosa na mini-
malni in maksimalni koeficient trenja pri preizkusu kroglica na plo{~i,
uporabljenem na PVD in CVD nanosih, na livnih aluminijevih in
magnezijevih zlitinah
Figure13: Microhardness examination results forcast magnesium
Mg-Al-Zn and aluminum Al-Si-Cu alloys after ageing, PVD and CVD
processing
Slika 13: Rezultati meritev mikrotrdote na liti magnezijevi Mg-Al-Zn
in aluminijevi Al-Si-Cu zlitini, po staranju ter PVD in CVD obdelavi
of the sliding distance for magnesium coatings is larger
than the sliding distance obtained with the alumi-
num-layer dual system; moreover, the results for the
DLC coatings are even 30 % better (Figure 14).
For the tribological-resistance examination of the ob-
tained layers, the charts demonstrating the rotation quan-
tity or displacement of the countersample before the
coating damage, depending on the friction coefficient
and/or displacement of the countersample along the ver-
tical axis were created. For all the registered friction co-
efficients dependingon the rotation quantity or the slid-
ing distance, similar characteristic curves, which can be
divided into two parts, were determined (Figure 15). In
the first part, a significant increase in the friction coeffi-
cient with the sliding-distance increase was determined.
It was accepted that it is the transient friction state. The
second part of the chart is similar to the stationary state.
Large changes in the friction coefficient measured during
the examination were caused by a spallation of the sam-
ple and counter-sample surfaces.
4 CONCLUSION
Gradient and monolithic coatings including
Ti/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti,Al)N, Ti/(Ti,Si)N/
(Ti,Si)N, Cr/CrN/CrN, Cr/CrN/TiN and Ti/DLC/DLC
were successfully deposited onto magnesium- and alumi-
num-alloy substrates using the cathodic-arc-evaporation
method (Arc-PVD) and plasma-assisted process (PA
CVD). The layers obtained with Arc-PVD and PA CVD
on the base of Mg and Al alloys significantly increased
the microhardness compared to the base material. The
type of base material had the least influence on the
microhardness. The fracture morphology was character-
ized by a lack of columnar structures in the obtained
coatings. The metallographic examinations proved that
the coatings were deposited uniformly over the whole
sample onto the investigated substrate materials and that
the measured thickness was characteristic for this coat-
ing type. It was also found that individual layers adhered
tightly to each other and to the light metal substrate. The
average friction factor of the DLC coatings (on Al and
Mg) achieved at a 0.05 m/s slide velocity was in a range
of 0.06–0.16, which was a decrease in the whole order of
magnitude in comparison to the other layers. Examining
all the ball-on-disk test results, it was confirmed that the
value of the sliding distance for the magnesium coatings
was higher than the sliding distance obtained with the
aluminum-layer dual system; moreover, the results for
the DLC coatings were even 30 % better. The investiga-
tion results obtained for the PVD method make it possi-
ble to obtain interesting solutions, which are very prom-
ising for the use in the automobile and aviation
industries, for the production of the elements whose high
functional properties like hardness and wear resistance
are crucial for long-term service.
Acknowledgements
This publication was co-financed within the frame-
work of the statutory financial grant providedby the Fac-
ulty of Mechanical Engineering of the Silesian Univer-
sity of Technology in 2015.
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