Structure, hardness and mechanical properties of magnetron-sputtered titanium-aluminium boride films

TiAlB films nominally 2 mu m thick were produced by simultaneous sputtering from TiAl and TiB2 targets onto Si-(110) and AISI316 stainless steel subst rate materials at a temperature of 170 degrees C. The influence of differen t B/Al ratios on the structure, hardness and mechanical properties of coati ngs containing 32 at.% Ti was investigated. over a range of chosen composit ions between B/Al=1 and B/Al=10. All coatings showed a very dense microstru cture, and evidence of Al, Al3Ti, Ti and TiB2 phase-bonding was observed in X-ray diffraction and X-ray photoelectron spectroscopy analyses of selecte d coatings. Correlation of compositional and mechanical data showed that fi lm hardness approximately trebled (from 12 to 35 GPa) and elastic modulus a pproximately doubled (from 185 to 340 GPa) with increasing B/Al ratio over the selected range. Reciprocating-sliding wear tests with both SAE52100 and WC-6% Co counterface materials indicated that the lowest coating wear occu rred at B/Al ratios greater than 2, although the wear rate increased slight ly at B/Al ratios greater than 4, indicating a gradual reduction in coating toughness as the boron content exceeded 50%. All coatings with B/Al greate r than or equal to 2 exhibited lower wear than untreated AISI316 substrates and, particularly in the case of the WC-6% Co counterface material (for wh ich the contact forces were higher), they were significantly better than co mmercial TiN of a similar thickness. These results demonstrate the advantag es which relatively low modulus hard coatings can provide - particularly on softer substrate materials which provide limited load support. (C) 1999 El sevier Science S.A. All rights reserved.