Effect of surface reaction layer on grindability of cast titanium alloys

Objective The purpose of this study was to investigate the effect of the cast surface reaction layer on the grindability of titanium alloys, including free-machining titanium alloy (DT2F), and to compare the results with the grindability of two dental casting alloys (gold and Co–Cr). Methods All titanium specimens (pure Ti, Ti–6Al–4V and DT2F) were cast using a centrifugal casting machine in magnesia-based investment molds. Two specimen sizes were used to cast the titanium metals so that the larger castings would be the same size as the smaller gold and Co–Cr alloy specimens after removal of the surface reaction layer (α-case). Grindability was measured as volume loss ground from a specimen for 1 min using a handpiece engine with a SiC abrasive wheel at 0.1 kgf and four circumferential wheel speeds. Results For the titanium and gold alloys, grindability increased as the rotational speed increased. There was no statistical difference (p>0.05) in grindability for all titanium specimens either with or without the α-case. Of the titanium metals tested, Ti–6Al–4V had the greatest grindability at higher speeds, followed by DT2F and CP Ti. The grindability of the gold alloy was similar to that of Ti–6Al–4V, whereas the Co–Cr alloy had the lowest grindability. Significance The results of this study indicated that the α-case did not significantly affect the grindability of the titanium alloys. The free-machining titanium alloy had improved grindability compared to CP Ti.