純チタンの高硬度化におよぼすメカニカルミリング処理条件の影響

概要

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Effect of mechanical milling conditions on hardness and constituent phase of pure titanium was investigated. The mechanical milling atmosphere and amounts of stearic acid, added as a process control agent (PCA), were varied. The hardness of mechanically milled (MMed) pure titanium powders in the air atmosphere was approximately 15 % higher than that in the argon atmosphere. The mean particle size of the MMed powders in the air atmosphere was smaller compared to that in the argon atmosphere. The MMed pure titanium powders produced by two different atmospheres had almost the same constituent phase. The MMed powders were consolidated into bulk materials by spark plasma sintering (SPS). The hardness of the SPS materials produced from the MMed powder in the air atmosphere was 13 % higher than that in the argon atmosphere. The oxygen content in the SPS materials significantly increased by the MM processing in the air atmosphere. Formation of β-Ti or ω-Ti was observed in the all SPSed materials. The products formed by phase transformation were not influenced by the heating rate and the hold time in SPS process. Vickers hardness of 881 HV was obtained for the SPSed material fabricated from 4 h of MM with 0.50 g of PCA in Ar atmosphere at 1073 K for 180 s with the heating rate of 2.33 K/s.