Character and chemical-wear response of high alloy austenitic stainless steel (Ortron 90) surface engineered with magnetron sputtered Cr-B-N ternary alloy coatings

Many transition metal borides, in particular CrB2, show high inherent hardness, corrosion resistance and chemical stability. Appropriate additions of nitrogen to the Cr-B material system could in principle allow the synthesis of multi-phase materials containing hard, corrosion resistant (Cr-B, Cr-N) and lubricious (h-BN) phases providing a combination of good corrosion-wear resistance and in-situ lubrication. This factor has stimulated interest in the development of Cr-B-(N) magnetron sputtered thin tribological coatings. In the present reported work, several Cr-B-(N) coatings were produced by reactively sputtering a CrB2 target in an argon atmosphere containing increasing amounts of nitrogen. They were mostly applied to Ortron 90 (Fe-20Cr-10Ni-2Mo-0.4N) austenitic stainless steel substrates. The coating structure changed from crystalline to largely amorphous with increasing nitrogen content, this was accompanied by a fall in nano-indentation hardness from 40 GPa at 0 at.% to 18 GPa at 21 at.%. N. The corrosion-wear performance of Cr-B-(N) coated Ortron 90 stainless steel when sliding against aluminium oxide in 0.9% saline solution, was worse than uncoated Ortron 90, due to their propensity to undergo chemical (dissolution) based wear. In these tests, no friction reduction was noted for the Cr-B-N coated materials. However, the CrB1.87 coated Ortron 90 displayed superior corrosion-wear resistance and a slightly lower friction coefficient. (C) 2013 Elsevier B.V. All rights reserved.