α-Phase Precipitation Behavior in β-Type Ti–15V–3Cr–3Sn–3Al Alloys Aged by Different Aging Processes, Investigated Using Transmission Electron Microscopy

Abstract

Two-step aging method using high temperature to low temperature sequence has been developed to improve the mechanical properties of Ti–15V–3Cr–3Sn–3Al alloys. α-precipitation behavior due to the 1st-step and the 2nd-step aging on this alloy has been investigated using electron microscopy. Due to the 1st-step aging, grain-boundary α-precipitates and extreme fine α-precipitates were observed. Due to the 2nd-step aging, needle-shaped α-precipitates in high density were observed. To clarify roles of the 1st-step aging process, precipitation behavior of a simple-aged specimen at the same condition as the 2nd-step aging was investigated. It is concluded that the principal factor to grow needle-shaped α-precipitates in high density was considered as extreme fine α-phase precipitates due to the 1st-step aging.

Dark field image of a 2nd-step aged specimen, showing needle-shaped α-precipitates and ω′-precipitates.