High-temperature tribological behavior of high-entropy sublattice oxide, nitride, and diboride coatings

The tribological performance of sputtered (Al,Cr,Nb,Ta,Ti)N, (Hf, Ta, V, W, Zr)B 2 , and (Al, Cr, Nb, Ta, Ti)O coatings on steel substrates was compared against TiN in dry ball-on-disk and scratch tests in ambient air at 20 degrees C, 400 degrees C and 700 degrees C. The (Al,Cr,Nb,Ta,Ti)N and TiN perform similar in all tests, with (Al,Cr,Nb,Ta,Ti)N showing higher oxidation and abrasion resistance. The adhesion of (Al,Cr,Nb,Ta,Ti)N is superior to TiN at 20 degrees but worse at elevated temperature due to an earlier onset of recovery processes that increase the mismatch in coefficient of thermal expansion with the substrate. The (Hf, Ta, V, W, Zr)B 2 is the most abrasion resistant coating at room temperature owing to its high hardness, but suffers from oxidation in hot air. Scratch tests yield a similar adhesion strength to TiN at 20 degrees C, but the anisotropic lattice expansion and shrinkage of the hexagonal structure at elevated temperatures lead to early delamination in the scratch test. The (Al, Cr, Nb, Ta, Ti)O 2 also adheres poorly on the steel, resulting in quick delamination during all tests.