Comparison of high-temperature tribological properties in different high-entropy sublattice ceramic coatings

Abstract

High-entropy sublattice ceramics are promising candidates for application as wear resistant thin films. Therefore, the tribological performance of three different sputtered high-entropy sublattice ceramic coatings, (Al,Cr,Nb,Ta,Ti)O2, (Al,Cr,Nb,Ta,Ti)N, and (Hf,Ta,V,W,Zr)B2, with excellent reported thermal stability up to 1200 °C, was analyzed and compared against TiN in dry pin-on-disk tests in ambient air at room temperature (RT), 400 °C and 700 °C, and in high-temperature (HT) scratch tests. In the dry pin-on-disk tests, all coatings show similar coefficients of friction (CoF) around 0.8-1.0 at RT. At elevated temperatures, the CoF of both nitrides decreases to ~0.4. The oxide coating suffers from poor adhesion, resulting in quick delamination during all tests. The boride coating increases its CoF at elevated temperatures to ~1.2 after a long run-in phase, signifying the formation of non-lubrication oxides, as confirmed by EDS and XPS analysis. The (Al,Cr,Nb,Ta,Ti)N and TiN perform similarly overall, where TiN shows better adhesion at high temperatures, as determined by the critical loads in the HT scratch test, but lower oxidation resistance. The (Hf,Ta,V,W,Zr)B2 shows the least abrasive wear, but suffers from poor adhesion and oxidation at elevated temperatures.