2011 Volume 52 Issue 4 Pages 714-718
This paper describes the creation of a surface-hardened layer with a minimum thickness of 1.0 mm on a titanium alloy. Two layers, a soft layer and a thick surface-hardened layer, were created on the titanium alloy specimens by using different age hardening speeds caused by different conditions of solution treatment. The solution treatment used furnace heating and laser heating as heating methods. Our accelerated aging treatment was conducted at temperature 300°C for aging times 86.4–432.0 ks after the solution treatment. Changes in the titanium alloy specimens after the aging treatment were examined by hardness and wear tests and microstructure observation.
The results revealed that the laser-heated part hardened at an early stage in aging time. Because of the difference in hardening speed, a hardened layer was formed. Except for the case of furnace heating at 700°C, the grain diameter of the laser-heated parts barely changed after furnace heating. The wear amount of the titanium alloy decreased with hardness; this decrease was remarkable especially at 450 HV and higher. For the specimens of both furnace- and laser-heated parts having the same hardness, the wear amounts were the same. The specimen that was laser heated for 259.2 ks after furnace heating at 800°C had an effective hardened layer with hardness 490–500 HV, ranging from the surface to a thickness of about 1.0 mm. The hardness of the internal unhardened layer for this specimen was 260 HV.
