Improving phase stability, hardness, and oxidation resistance of reactively magnetron sputtered (Al,Cr,Nb,Ta,Ti)N thin films by Si-alloying

SURFACE & COATINGS TECHNOLOGY

卷:416

Article

Kretschmer, Andreas¹  Kirnbauer, Alexander¹  Moraes, Vincent¹  Primetzhofer, Daniel²  Yalamanchili, Kumar³  Rudigier, Helmut^3,4  Mayrhofer, Paul Heinz¹ 

[1] TU Wien, Inst Mat Sci & Technol, Getreidemarkt 9, A-1060 Vienna, Austria

[2] Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden

[3] Oerlikon Surface Solut AG, Oerlikon Balzers, Iramalli 18, FL-9496 Balzers, Liechtenstein

[4] OC Oerlikon Management AG, CH-8808 Pfaffikon, SZ, Switzerland

关键词: High-entropy metal-sublattice nitrides (HESN);    High-entropy alloys (HEA);    Oxidation;    Thermal stability;    Magnetron sputtering;    PVD;   

DOI  :  10.1016/j.surfcoat.2021.127162

来源: Elsevier

【 摘 要 】

Reactively magnetron sputtered high-entropy metal-sublattice (Al,Cr,Nb,Ta,Ti)N coatings have been alloyed with Si concentrations between x(si) = 6.4 and 15.0 at.%. All coatings are single-phase fcc structured and their hardness initially increases from similar to 32 to 35 GPa with Si-alloying up to x(si) = 9.8 at.%, and then decreases to similar to 24 GPa for higher Si contents. Contrary, the indentation modulus E continuously decreases from similar to 470 to 350 GPa by Si-alloying. Also, the decomposition of the fcc structure during vacuum annealing is shifted from 1000 to 1200 degrees C with the addition of Si. The hardness initially increases during vacuum annealing and reaches a maximum of 37 GPa with T-a = 1000 degrees C at x(si) = 12.0 at.%. During oxidation experiments in ambient air at 850 degrees C for up to 100 h, a 2700 nm single-phase rutile-structured oxide scale forms at the Si-free (Al,Cr,Nb,Ta,TON with a parabolic growth rate. The rate changes to a logarithmic-like behavior with the addition of Si, resulting in only similar to 280 nm oxide scale after 100 h. Also, for the Si-containing coatings, the oxide scale shows only one crystalline rutile structure. The pore size in the oxide scale of the Si-free coating is considerably reduced by Si-addition. The oxides growing at the Si-containing coatings show an opposing Si- and Cr-gradient - with much smaller pores in the Si-rich inner region - which shows a gradual transition to the remaining nitride. Ab initio based calculations confirm that the formation of a single-phase rutile-structured solid solution oxide, (Al,Cr,Nb,Ta,Ti)O-2, is energetically preferred over separate phases above 509 K, due to the higher configurational entropy. Below this temperature the decomposition towards (Al,Ta,Ti)O-2 + (Cr,Nb)O-2 would be favored (when considering just chemical contributions), but kinetically restricted.

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