Time evolution of precipitates related to age-hardening in Ti–2.3 wt pct Cu alloys was investigated by electron microscopy. In isothermal aging at 723 K, the hardness increases continuously owing to precipitation strengthening, whereas in two-step aging where the aging temperature is switched from 673 K to 873 K after 100 hours, the hardness is found to drastically drop after the aging temperature switches. In isothermal aging, metastable and stable precipitates are independently nucleated, whereas characteristic V-shaped clusters of precipitates are observed during the two-step aging. It is revealed by atomic-scale observations that the V-shaped clusters are composed of metastable and stable precipitates and each type of precipitate has a different orientation relationship with the α phase: (10 3 ¯) //(0001)α and [0 1 ¯ 0] //[11 2 ¯ 0] α for the metastable, and (201)//(1 1 ¯ 03) α and [0 1 ¯ 0] //[11 2 ¯ 0] α for the stable precipitates, respectively. The drop in hardness during two-step aging can be explained by a synergistic effect of decreased precipitation strengthening and solid solution strengthening.
|ジャーナル||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|出版ステータス||出版済み - 7 2021|
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