レーザ加熱による表面溶体化処理を応用したβ型チタン合金の表面時効硬化処理とその摩耗特性

摘要

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 titanium alloy specimens by using different age-hardening speeds caused by different conditions of solution treatment. The solution treatment involved furnace and laser heating. After the solution treatment, we performed an accelerated aging treatment at 300℃ for aging times in the range 86.4-432.0 ks. Changes in the titanium alloy specimens after the aging treatment were examined by hardness and wear tests and microstructure observations.rnThe results revealed that the laser-heated part hardened at an early stage during aging. Because of the difference in the hardening speed, a hardened layer was formed. Except for the case of furnace heating at 700℃, the grain diameter of the laser-heated specimens barely changed after furnace heating. The wear amount of the titanium alloy specimens decreased with hardness; this decrease was remarkable especially at 450 HV and higher. For the specimens that were both furnace- and laser-heated and had the same hardness, the wear amounts were the same. The specimen that was laser-heated for 259.2 ks after furnace heating at 800℃ had an effective hardened layer with hardness in the range 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.%チタン合金は硬さが低く凝着しやすい欠点を有するため，しゅう動材料に用いられることが少ない．このため，耐摩耗性の改善を目的とした表面処理法の研究が盛んに進められている.現在，利用されている表面処理法による硬化層の多くは，高硬度で優れたしゅう動特性を有しているが，厚さは数～数十μmと薄い．