US Patent 7600499 Titanium alloy valve lifter

A lightweight and high-strength valve lifter is excellent in wear resistance and sliding properties. The valve lifter is made of a titanium alloy having a hardened layer on the top surface thereof, on which a cam is caused to slide. The hardened layer is composed of an α-case and an oxygen diffusion layer under the α-case. The α-case 22 is formed in a thickness of not less than 3 μm and not more than 15 μm. The oxygen diffusion layer has a thickness of not less than 10 μm. The hardened layer on the top surface of the valve lifter is formed by oxidation treatment in a furnace at a temperature of not less than 600° C. An outermost oxide layer 21 formed on the α-case as a result of the oxidation treatment is removed.