2016 年 57 巻 9 号 p. 1440-1446
In the present work, Ti-25Nb-11Sn (mass%) alloys were successfully prepared by an advanced powder metallurgy method. The alloys were synthesized by mechanical milling of powder mixture, consisting of titanium hydride (TiH2), elemental niobium (Nb) and elemental tin (Sn) powders, followed by their consolidation via Spark Plasma Sintering (SPS) method. The use of brittle TiH2 powder, instead of ductile elemental Ti powder, resulted in ~100% powder yield of mechanically milled (MMed) powder even after long time mechanical milling. The resulting MMed powders consisted of homogeneously distributed nano-sized titanium/niobium hydride powder particles together with a few micron-sized pure Nb particles. The mechanical milling also led to the lowering of dehydrogenation temperature of the hydride particles. Sintering of short time mechanically milled powder (72 ks) resulted in the fine-grained heterogeneous microstructure consisting of β phase and orthorhombic martensitic α'' phase. On the other hand, sintering of long time mechanically milled powder (180 ks) resulted in the evolution of β-phase and α-phase. The specimen containing α+β phase exhibited higher average hardness as compared to the average hardness of specimen containing α''+β phase.
