Evaluation of precipitation hardening in TiC-reinforced Ti₂AlNb-based alloys

Abstract

Ti₂AlNb-based alloys with 0.0wt%, 0.6wt%, and 2.0wt% carbon nanotube (CNT) addition were fabricated from spherical Ti–22Al–25Nb powder by sintering in the B₂ single-phase region. Phase identification and microstructural examination were performed to evaluate the effect of carbon addition on the hardness of the alloys. Carbon was either in a soluble state or in carbide form depending on its concentration. The acicular carbides formed around 1050°C were identified as TiC and facilitated the transformation of α₂ + B2 → O. The TiC was located within the acicular O phase. The surrounding O phase was distributed in certain orientations with angles of 65° or 90° O phase particles. The obtained alloy was composed of acicular O, Widmanstatten B2 + O, and acicular TiC. As a result of the precipitation of carbides as well as the O phase, the hardness of the alloy with 2.0wt% CNT addition increased to HV 429 ± 9.

Keywords

Ti₂AlNb alloy / carbides / microstructure / precipitation hardening / hardness

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