DEVELOPMENT OF FREE CUTTING DENTAL TITANIUM ALLOYS

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The purpose of this study was to evaluate the grindability of experimental titanium alloys with the hope of developing titanium alloys with better machinability than CP Ti for dental CAD/CAM applications. Experimental Ti-Ag alloys (5,10,20 mass% Ag), Ti-Cu alloys (2,5,10 mass%Cu) and Ti-Nb alloys (2,5,10,15,20,25,30 mass%Nb) were made by melting sponge titanium and pieces of silver, copper or niobium in an argon-arc melting furnace. The alloys were cast into a magnesia mold using a dental gas-pressure titanium casting machine. Cast alloy specimens (3.5 mm x 8.5 mm x 30.5 mm), from which the hardened surface layers (250 um) were removed, were ground using a SiC abrasive wheel on an electric handpiece at five circumferential speeds (500,750,1000,1250, or 1500 m/mm) with 100 gf. Grindability was evaluated by measuring the amount of metal volume removed after grinding during one minute.At the lowest grinding speed (500m/min), there was no statistical difference among the grindability of the Ti-Cu alloys, Ti-Ag alloys and CP Ti. The grindability of the alloys increased as the grinding speed increased. At 1000 and 1250 m/min, the grindability of the 20% Ag and 10% Cu alloys were higher than that of CP Ti. At the highest grinding speed (1500 m/min), the grindability of the 20%Ag, 5%Cu and 10%Cu alloys were higher than that of CP Ti. The grindability at 1500m/min for the 10%Cu was about 2.9 times as large as that for CPTi. In the case of Ti-Nb alloys, the grindability of Ti-30%Nb alloy was about 2 times as large as that of CP Ti at the lower grinding speed (500 and 750m/min).It was found that the grindability of the titanium was improved by alloying with silver, copper and niobium. The Ti-Cu alloys showed higher grindability at lower content of an alloying element than the Ti-Ag alloys.