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УДК 539.5
Влияние содержания алюминия на ударную усталость покрытий системы CrAlN, нанесенных на инструментальную сталь методом сильноточного импульсного магнетронного
распыления
K. Bobzin, C. Kalscheuer, M. Carlet, M. Tayyab
Рейнско-Вестфальский технический университет Ахена, Ахен, 52072, Германия
Напыление покрытий в вакууме (physical vapor deposition, PVD) используется для увеличения срока службы деталей и инструментов, эксплуатируемых в зависимости от области применения при различных видах нагружения. Например, при холодной штамповке инструменты испытывают преимущественно циклические ударные нагрузки. Ранее было исследовано усталостное поведение PVD-покрытий на основе Ti и покрытий CrN при циклических ударных нагрузках и выявлена его взаимосвязь с упругопластической деформацией подложки. Однако влияние химического состава покрытия на ударную усталость, особенно для покрытий CrAlN, практически не изучено. В настоящей работе исследовано влияние содержания Al на ударную усталость покрытий CrAlN, полученных методом сильноточного импульсного магнетронного распыления. Покрытия CrAlN с низким, средним и высоким содержанием Al наносили на подложки из стали марки HS6-5-2C. Химический и фазовый состав определяли с помощью электронно-зондового микроанализа и рентгеноструктурного анализа соответственно. Упругопластические свойства покрытий определяли методом наноиндентирования. Испытание твердости по Роквеллу проводили для анализа адгезии между покрытием и стальной подложкой. Во время ударных испытаний образцы с покрытием подвергали циклической ударной нагрузке F = 1000 Н с частотой f= 50 Гц и числом циклов N = 0.1 х 106, 0.5 х 106, 0.75 х 106, 106. Методами сканирующей электронной и конфокальной лазерной сканирующей микроскопии изучены усталостное растрескивание и пластическая деформация стальных подложек с покрытием CrAlN в области отпечатка с учетом ударной усталости стальной подложки без покрытия. Установлено, что сталь с покрытием CrAlN имеет более высокое сопротивление ударно-усталостному разрушению по сравнению с подложками без покрытия. Увеличение содержания Al также повышает сопротивление ударной усталости стали с покрытием.
Ключевые слова: PVD, HPPMS, CrAlN, усталостный режим, ударный, усталость, циклическая нагрузка
DOI 10.24412/1683-805X-2021-5-138-146
Influence of aluminum content on the impact fatigue of HPPMS CrAlN coatings on tool steel
K. Bobzin, C. Kalscheuer, M. Carlet, and M. Tayyab
Surface Engineering Institute, RWTH Aachen University, Aachen, 52072, Germany
Physical vapor deposition (PVD) coatings are utilized to improve the service life of tools and components. Depending on the application, these tools and components undergo various stress types. For instance, in cold forging applications the tools predominantly endure cyclic impact loads. Previous studies on fatigue response of PVD coatings under cyclic impact loads focus on Ti-based or CrN coatings and attribute the coating fatigue behavior to the elastic-plastic deformation of the substrate. However, the influence of the coating chemical composition on the impact fatigue behavior, particularly for CrAlN coatings, is rather missing in the literature. The current work aims to investigate the influence of Al content on the impact fatigue response of CrAlN high-power pulsed magnetron sputtering (HPPMS) coatings. CrAlN coatings with low, medium and high Al content were deposited on HS6-5-2C steel substrates. The chemical and phase compositions were determined by electron probe microanalysis and X-ray diffraction analysis, respectively. The elastic-plastic properties of the coatings were determined by nanoindentation test. Rockwell C indentation test was used to analyze the adhesion between coating and steel substrate. The coated samples were subjected to a cyclic impact load of F = 1000 N and frequency of f= 50 Hz during the impact tests with N = 0.1 х 106, 0.5 х 106, 0.75 х 106, and 106 impacts. Finally, the fatigue behavior of the CrAlN coated steel substrates was analyzed inside the impact imprint area for fatigue cracks and plastic deformation using scanning electron microscopy and confocal laser scanning microscopy, respectively. Additionally, the impact fatigue response of the uncoated steel substrate was also taken into consideration. CrAlN/steel compounds showed better impact fatigue response as compared to the uncoated steel substrates. Moreover, the increase in Al content resulted in an improved impact fatigue behavior for the CrAlN/steel compounds.
Keywords: PVD, HPPMS, CrAlN, fatigue behavior, impact, fatigue, cyclic load
© Bobzin K., Kalscheuer C., Carlet M., Tayyab M., 2021
1. Introduction
Physical vapor deposition (PVD) coatings are frequently used to address the wear reduction requirements of modern tribological systems in various industrial applications. Among these coatings, nitride hard coatings with a thickness of few micrometers are particularly in demand due to higher wear resistance [1]. However, the tools and components with such coatings are subjected to changing thermal and mechanical stresses depending on the area of application [2]. These mechanical stresses can be further classified into different categories such as rolling contact stress, torsional stress, impact stress or bending stress [3]. The tools and components often experience a combination of these stress types. For instance, cyclic impact stress with the superimposed bending stress are among the predominant stress types for tools in cold forging processes, e.g. full-forward or cup-back extrusion. The investigation of the fatigue behavior of PVD coatings under such cyclic stresses is imperative for their service life improvement.
The tribological impact test is commonly used to investigate the fatigue behavior of PVD coatings under cyclic impact load [4]. During the test, a spherical ball of a predetermined material and diameter periodically exerts an impact force on the coating surface with a certain frequency. The impact force and number of impacts can be varied according to the requirements of the investigation. Finally, the impact imprint area is investigated for cracks, damage and deformation to study the fatigue behavior of the coatings.
Previous investigations on impact fatigue of nitride hard coatings are mostly focused on Ti-based or CrN coatings [4, 5]. Bouzakis et al. [6] investigated the impact fatigue behavior of (Ti, Al)N and CrN on 100Cr6 steel substrates using cemented carbide ball for impact tests. The coatings went through an elastic deformation whereas the substrates revealed an elastic-plastic deformation at higher impact loads. This elastic-plastic deformation of the substrate eventually introduced the fatigue failure resulting in the coating cracks and delamination. Similar results were reported for TiN/CrN multilayer coatings on HS6-5-2C steel substrates [5]. However, any such investigation focusing on the effect of the coating composition on the impact fatigue behavior, particularly for CrAlN coatings, could not be found in the literature. CrAlN coatings are of special interest due to their higher oxidation resistance [7] and better impact wear response [8] as compared to CrN and TiAlN coatings.
Moreover, CrAlN coatings exhibit higher hardness along with an increased resistance to plastic deformation and crack propagation as compared to binary CrN coatings [9]. Furthermore, in order to establish the beneficial role of PVD coatings in improvement of impact fatigue behavior of the coated substrate, the impact fatigue response of the corresponding un-coated substrate is also missing from the literature. In the current work, the impact fatigue behavior of CrAlN steel compounds with low, medium and high Al content CrAlN coatings along with the uncoated steel substrate are investigated.
2. Experimental details
2.1. Materials and coating deposition
The CrAlN coatings were deposited on the HS6-5-2C high-speed tool steel substrates using a hybrid direct current magnetron sputtering (dcMS) and high power pulsed magnetron sputtering (HPPMS) coating process. The samples went through tempering and quenching process to achieve the final hardness of H = 61 ± 1 HRC. The substrate surfaces were prepared to the average line roughness of Ra = 0.005 ^m using grinding, lapping and polishing processes, respectively. The steel substrates were coated using an industrial coating unit CC800/9 Custom from Ceme-Con AG, Wuerselen, Germany. The coating unit consists of four dcMS and two HPPMS cathodes. For current investigation, three different CrAlN coatings with low, medium and high Al content were developed. The process to deposit the coating with low Al content denoted as CrAlN-1 was carried out using CrAl20 targets at all six cathodes. The cathodes for CrAlN-2 process to deposit the coating with medium Al content were loaded with three CrAl20 and three AlCr30 targets. Finally, the CrAlN-3 process to deposit the coating with high Al content was carried out using two CrAl20 targets, three AlCr30 targets and one AlCr20 target. Each target had a length of L = 500 mm and width of W= 88 mm. The CrAl20 target consisted of a Cr base with 20 Al plugs, whereas the AlCr30 and AlCr20 targets had Al base with 30 and 20 Cr plugs of diameter d = 15 mm, respectively. A schematic of the coating chamber along with the target configurations of the three CrAlN coating processes is shown in Fig. 1.
The substrate samples were placed parallel to the targets by using a sample holder mounted on a substrate table with a rotation speed of ntable = 1 min-1. During the coating process, the substrate samples were subjected to a three-fold rotation. The planetary
Fig. 1. Schematic of the coating chamber and the target configurations for CrAlN coatings
gear box drive between the substrate table and substrate holder accounted for a double rotation in addition to the individual rotation of the sample skewers inside the sample holders. Table 1 shows the process parameters used for the deposition of the three CrAlN coatings. The coating time for each process was adjusted to achieve the coatings with almost similar thickness in the range of As = ±0.1 ^m. To improve the coating adhesion to the substrate, the substrates were coated with a chromium rich inter-layer of thickness s ~ 250 nm using the CrAl20 target before proceeding with the main coating layer. All three CrAlN coatings were deposited using the same process parameters except the target configuration and the deposition time.
Table 1. Process parameters for the deposition of the CrAlN coatings
Parameter Value
Pressure p, mPa 620
Argon flow j(Ar), sccm 200
Nitrogen flow j(N2), sccm Pressure controlled
Heating power PH, kW 4
Substrate bias UB, V -100
Average power of HPPMS cathodes Phppms, kW 5
Pulse frequency f, Hz 1000
Pulse duration ton, |is 40
Power of dcMS cathodes PdcMS, kW 3
2.2. Coating characterization
The coating morphology in the cross-section along with the coating thickness were measured using scanning electron microscopy (SEM), ZEISS DSM 982 Gemini, Carl Zeiss AG, Oberkochen, Germany. The chemical composition of the coatings was determined through electron probe microanalysis (EPMA) through a Schottky emitter electron microprobe, JEOL JXA8530F, Tokyo, Japan. Both, the cross-section morphology and the chemical composition, were analyzed at Central Facility for Electron Microscopy (GFE) of RWTH Aachen University. The presence of different phases in the coating was analyzed by X-ray diffraction (XRD) with a grazing incidence diffraction (GID), XRD 3003, GE Energy Germany GmbH, Ratingen, Germany. The analysis was carried out using Cu-Ka radiation with wavelength X=0.1540598 nm, U = 40 kV, I=40 mA, diffraction angle 20 = 20°-80°, incidence angle © = 2°, step width ds = 0.01° and step time t = 10 s. The average line roughness Ra and mean line roughness depth Rz for the coatings were determined according to ISO 4287 using confocal laser scanning microscopy (CLSM), Keyence VK-X210, Tokyo, Japan. To determine the adhesive strength category (HF) of the coating according to DIN 4856, Rockwell C indentation tests were carried out using a HP100 Rockwell tester, KNUTH Machine Tools GmbH, Wasbek, Germany. During the Rockwell tests, a Rockwell indenter with a cone angle of 0 = 120° and a tip radius of R = 200 ^m penetrated the coating surface perpendicularly with a force of F = 1471 N. The Rockwell C indentation
imprints were analyzed for edge cracks and spalling using CLSM. The coatings were categorized from HF1 to HF6 where HF1 represents excellent adhesion between the coating and the substrate.
2.3. Determination of coating properties by nanoindentation
The elastic-plastic properties of the coatings were determined by nanoindentation test according to ISO 14577 using a calibrated TI 950 Tribolndenter, Bruker Corporation, Billerica, Massachusetts, USA. The tests were performed using a Berkovich indenter with a nominal tip radius of R = 20 nm. To minimize the influence of the substrate on the results, maximum indentation depth was kept below 10% of the coating thickness [9]. Consequentially, the maximum test force was limited to Fmax = 8 mN. A constant Poisson's ratio of v = 0.25 for the coatings was assumed as common for ceramic coatings. A total of 50 indentations were carried out for each coating. The indentation hardness HIT and indentation modulus EIT were determined based on the Oliver and Pharr method as in [9]. Furthermore, the maximum indentation depth hmax of the indenter inside the coating and the permanent indentation depth hp after removal of the test force were recorded. The area under the loading section of the force-displacement curve, representing the total mechanical work of indentation, was calculated through integration. Similarly, the area under the unloading section of the force-displacement curve, representing the elastic reverse deformation work of indentation, was also calculated through integration. Finally, the elastic work ratio nrr for each coating was determined by dividing the area under the unloading section with the area under the loading section.
2.4. Impact tests
The impact fatigue behavior of the coated and un-coated samples was investigated through room temperature impact tests using Apollo NXG impact tester, Impact-BZ, London, UK. A cemented carbide ball with a diameter of d = 5 mm was used to exert a cyclic impact load of F = 1000 N on the surface of the samples with a frequency of f = 50 Hz. The impact tests were carried out with N = 0.1 * 106, 0.5 * 106, 0.75 * 106 and 106 impacts to observe the fatigue behavior of the samples with the increase in number of impacts. Each test was repeated twice to confirm the reproducibility of the results. The impact imprint area was analyzed for coating cracks and
spalling using SEM. The substrate exposure, representing the complete removal of coating if any, was confirmed by carrying out energy dispersive X-ray spectroscopy (EDX) analysis at several points inside the impact imprint area. Furthermore, the deformation in the samples was characterized by evaluating the maximum remaining imprint depth (RID) inside the impact imprint area using CLSM.
3. Results and discussion
3.1. Coating composition and characterization
The coating thickness, deposition rate, the line roughness and chemical composition of the coatings are shown in Table 2. With the increase of Al content, a slight increase in the line roughness is observed. The coating morphology changes from fine crystalline to fine columnar with increasing Al content as shown in Fig. 2. This could be attributed to microstructural changes and variation of grain size at higher Al content [10]. The corresponding increase in the line roughness is also visible from the surfaces of the cross-sections in the images.
The presence of cubic CrN and AlN is confirmed from the XRD analysis as shown in Fig. 3. All coatings show a similar phase composition with (111), (200) and (220) as main diffraction peaks. The highest peak occurs at 29 ~ 38° with the preferred orientation of (111) for all three coatings. The slight deviation of (200) and (220) diffraction peaks from x(Al) = 10% to x(Al) = 34% could be attributed to increased formation of AlN phase resulting from replacement of Cr atoms with Al atoms. Furthermore, the addition of Al in CrN crystal lattice forms solid solution due to the occupation of Al atoms at interstitial lattice sites [10].
Table 2. Coating thickness s, deposition rate s, line roughness Ra and Rz, chemical composition and percentage of Al content x(Al) of CrAlN coatings
Coating process CrAlN-1 CrAlN-2 CrAlN-3
s, ^m 1.6 1.7 1.7
s, ^m/h 1.7 1.5 1.3
Ra, ^m 0.01 0.01 0.02
Rz, ^m 0.11 0.13 0.13
Cr, at % 43 35 31
Al, at % 5 12 16
N, at % 52 53 53
x(Al) = Al/(Al + Cr), % 10 26 34
Fig. 2. Cross-section morphology of the coatings with different Al content: x(Al) = 10% (a), 26% (b), 34% (c)
The force-displacement curves from the nanoin-dentation tests of the coatings are shown in Fig. 4. The force-displacement curves are averaged from the 50 indents. The indentation hardness HIT, indentation modulus EIT, maximum indentation depth hmax, permanent indentation depth hp and elastic work ratio nIT calculated from the force-displacement curves are shown in Table 3. A gradual increase in the indentation hardness HIT and indentation modulus EIT is observed with the increasing Al content of the coatings. Furthermore, the maximum indentation depth hmax and permanent indentation depth hp decrease along with an increase in elastic work ratio nIT from x(Al) = 10% to x(Al) = 34%. All force-displacement curves from the indents were also examined separately. They showed no distinct drop-in which would have indicated the formation of cracks in the coating underneath the indenter. As suggested in [1], an increase in elastic work ratio can therefore be attributed to a higher resistance against plastic deformation. Hence, an increase in Al content increases the resistance against plastic deformation for the investigated CrAlN coatings. As atomic radius of Al atom is smaller than Cr atom, higher Al content led to an in-
crease in lattice distortion and corresponding compressive residual stresses in CrAlN coatings. Furthermore, the solid solution strengthening also increased with addition of Al content. Therefore, higher compressive residual stresses and solid solution strengthening might result in the increased indentation hardness HIT, indentation modulus EIT and resistance to plastic deformation at higher Al contents.
The CLSM images of the Rockwell C indentation imprints are shown in Fig. 5. The coatings with low and medium Al content exhibit good adhesion with no spalling and are classified as HF1. However, the coating with x(Al) = 34% exhibit significant cracks and spalling around the edges to be classified as HF3. A compound with higher elastic modulus difference between the coating and substrate is expected to have a reduced adhesion between the coating and substrate [1]. The higher elastic deformation of the substrate tends to put the coating under tension which leads to an early coating failure. As the coating with x(Al) = 34% exhibit a higher indentation modulus EIT as compared to the coatings with x(Al) = 26% and x(Al) = 10%, a low adhesion strength is observed as expected.
Fig. 3. XRD analysis of CrAlN coatings, x(Al) = 10% (1), 26% (2), 34% (3)
Fig. 4. Averaged force-displacement curves of nanoin-dentation tests for CrAlN coatings, x(Al) = 10% (1), 26% (2), 34% (3)
Table 3. Elastic-plastic properties of the CrAlN coatings determined by nanoindentation test
Al content, % HIT, GPa EIT, GPa hmax, nm hp, nm nIT, %
x(Al) = 10 20.9 ± 2.4 293.4 ± 26.3 143.8 ± 7.4 72.9 ± 7.6 54.2 ± 2.4
x(Al) = 26 22.5 ± 2.5 300.1 ± 28.9 140.0 ± 6.6 67.7 ± 7.3 57.2 ± 1.8
x(Al) = 34 26.7 ± 3.1 347.9 ± 36.5 129.7 ± 6.3 58.9 ± 6.4 59.8 ± 2.5
Fig. 5. Rockwell C indentation imprints of CrAlN coatings: HF1 (a, b), HF3 (c); x(Al) = 10% (a), 26% (b), 34% (c)
Fig. 6. SEM images of impact imprint with enlarged crack region for CrAlN/steel compounds with x(Al) = 10% at N = 0.5 * 106 (a, b), 0.75 * 106 (c, d), 106 impacts (e, f)
Fig. 7. SEM images of impact imprint with enlarged crack (a, b) and 106 impacts (c, d)
for CrAlN/steel compounds with x(Al) = 26% at N = 0.75 x 106
3.2. Impact fatigue behavior
The CrAlN/steel compounds reveal circumferential cracks with no spalling or substrate exposure at differing number of impacts under the impact force of F = 1000 N. The maximum remaining indentation depth inside the impact imprint area increased from RID = 5.1 ± 0.2 ^m at N = 0.1 x 106 impacts to RID = 5.7 ± 0.2 ^m at N = 1 x 106 impacts for all three coat-
ings. Therefore, no significant influence of the Al content on the remaining indentation depth of the CrAlN/ steel compounds is found. Circumferential cracks occur at N = 0.5 x 106 impacts for the CrAlN coated steel substrates with x(Al) = 10%, as shown in Fig. 6. The number and length of cracks increase at N = 0.75 x 106 and 1 x 106 impacts. The adhesion of WC particles from the cemented carbide ball to the
Fig. 8. SEM images of impact imprint with enlarged crack region for CrAlN/steel compounds with x(Al) = 34% at N = 106 impacts
Fig. 9. SEM images of impact imprint with enlarged surface chipping region for uncoated samples at N = 0.5 * 106 (a, b), 0.75 * 106 (c, d) and 106 impacts (e, f)
impact imprint area, visible as white adhesions in the SEM images, is confirmed from the EDX analysis. However, no adhesive failure or substrate exposure is identified even at N = 106 impacts for the coating. For the CrAlN coated steel substrates with x(Al) = 26%, no circumferential cracks appear at N = 0.5 * 106 impacts. However, the circumferential cracks occur at N = 0.75 * 106 impacts as shown in Fig. 7. Again, no adhesive failure or substrate exposure other than the random adhesion of WC particles from the cemented carbide ball is identified even at N = 106 impacts. For the CrAlN coated steel substrates with x(Al) = 34%, circumferential cracks appear only at N = 106 impacts without any coating spalling or substrate exposure as shown in Fig. 8. The results indicate an increased resistance to fatigue cracks under cyclic impact load for CrAlN/steel compounds with the higher Al content CrAlN coating.
The results from the impact tests of the uncoated steel substrates are shown in Fig. 9. As opposed to coated samples, surface chipping occurs on the un-coated steel substrates. Furthermore, increase in surface chipping and radial cracks is visible from N =
0.5 * 106 to 106 impacts. These results evidence a significant improvement in the fatigue behavior of the CrAlN coated steel substrates compared to the un-coated steel substrates.
4. Conclusions
Within the scope of this paper, the influence of Al content on fatigue behavior of CrAlN/steel compounds under cyclic impact load was investigated. Three CrAlN coatings with low, medium and high Al content were deposited on HS6-5-2C steel substrates using a hybrid dcMS/HPPMS coating process. The increase in Al content of the CrAlN coatings resulted in an increased resistance to the plastic deformation along with higher indentation hardness and indentation modulus. Furthermore, the impact fatigue behavior of the CrAlN/steel compound improved with the increasing Al content of the coating as fatigue cracks appeared at higher number of impacts. A higher resistance to plastic deformation of the CrAlN coating seems to result in an increased resistance to the impact fatigue cracks for the CrAlN/steel compounds.
Moreover, the CrAlN/steel compounds showed better impact fatigue response as compared to the uncoated steel substrates. The results demonstrate the positive influence of Al content on CrAlN HPPMS coatings for applications involving cyclic impact loads.
Funding
The authors gratefully acknowledge the financial support from the German Research Foundation (DFG) within the project BO 1979/71-1.
References
1. Bobzin K., Brogelmann T., Kruppe N., Arghavani M. Investigations on mechanical and tribological behavior of dcMS/HPPMS CrN and (Cr, Al)N hard coatings using nanoscratch technique // Adv. Eng. Mater. -2017. - V. 19. - No. 6. - P. 1600632. - https://doi.org/ 10.1002/adem.201600632
2. Bouzakis K.-D., Maliaris G., Makrimallakis S. Strain rate effect on the fatigue failure of thin PVD coatings: An investigation by a novel impact tester with adjustable repetitive force // Int. J. Fatigue. - 2012. -V. 44. - P. 89-97. - https://doi.org/10.1016/j.ijfatigue. 2012.05.010
3. Gonzalez-Velazquez J.L. A Practical Approach to Fracture Mechanics. - Elsevier, 2020. - https://doi. org/10.1016/B978-0-12-823020-6.00001-3
4. Bouzakis K.-D., Batsiolas M., Skordaris G., Stergiou-di F., Michailidis N. Repetitive impact test near un-coated and coated cutting edges for assessing their fatigue behavior // CIRP J. Manuf. Sci. Technol. -
2015. - V. 8. - P. 63-69. - https://doi.org/10.1016/j. cirpj.2014.09.001
5. Mendibide C., Steyer P., Fontaine J., Goudeau P. Improvement of the tribological behaviour of PVD nano-stratified TiN/CrN coatings—An explanation // Surf. Coat. Technol. - 2006. - V. 201. - No. 7. - P. 41194124. - https://doi.org/10.1016/j.surfcoat.2006.08.013
6. Bouzakis K.-D., Siganos A., Leyendecker T., Erkens G. Thin hard coatings fracture propagation during the impact test // Thin Solid Films. - 2004. - V. 460. -No. 1-2. - P. 181-189. - https://doi.org/10.1016/j .tsf. 2004.02.009
7. Chim Y., Ding X., Zeng X., Zhang S. Oxidation resistance of TiN, CrN, TiAlN and CrAlN coatings deposited by lateral rotating cathode arc // Thin Solid Films. - 2009. - V. 517. - No. 17. - P. 4845-4849. -https://doi.org/10.1016Zj.tsf2009.03.038
8. Mo J., Zhu M., Leyland A., Matthews A. Impact wear and abrasion resistance of CrN, AlCrN and AlTiN PVD coatings // Surf. Coat. Technol. - 2013. -V. 215. - P. 170-177. - https://doi.org/10.1016/j. surfcoat.2012.08.077
9. Brogelmann T., Bobzin K., Kruppe N., Arghavani M. Understanding the deformation and cracking behavior of Cr-based coatings deposited by hybrid direct current and high power pulse magnetron sputtering: From nitrides to oxynitrides // Thin Solid Films. - 2019. -V. 688. - P. 137354. - https://doi.org/10.1016/j .tsf. 2019.06.004
10. Fu Y., Li H., Ji L., Liu X., Liu L., Zhou H., Chen J. Insight into Al existing form and its role on microstructure and properties of Cr1-xAlxN films // Surf. Interface Analysis. - 2016. - V. 48. - No. 1. - P. 26-33. -https://doi.org/10.1002/sia.5882
Received 14.05.2021, revised 26.07.2021, accepted 26.07.2021
Сведения об авторах
Kristen Bobzin, Prof., RWTH Aachen University, Germany, [email protected] Christian Kalscheuer, Chief Engineer, RWTH Aachen University, Germany, [email protected] Marco Carlet, Research Associate, RWTH Aachen University, Germany, [email protected] Muhammad Tayyab, Associate Researcher, RWTH Aachen University, Germany, [email protected]
