Nucleation and Growth of α-Ti on TiB Precipitates in Ti–15Mo–2.6Nb–3Al–0.2Si–0.12B

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The microstructure was investigated of a β-stabilized Ti–15Mo–2.6Nb–3Al–0.2Si–0.12B alloy at two different aging temperatures, 540°C/8 h and 660°C/8 h. In particular, the heterogeneous nucleation of α-Ti from TiB particles was studied at these aging temperatures. At the lower aging temperature, α-Ti precipitated as needle-like shapes on the TiB phase. In contrast, the higher aged sample exhibited globular α-Ti morphology around the TiB phase. This difference was rationalized in terms of the coarsening behavior of α-Ti around the TiB phase. Various orientation relationships were observed between these two samples. This difference is because of the precipitation of α-Ti on two different TiB planes. In addition, atom probe analysis confirmed the segregation of alpha and beta stabilizing elements to the respective phases. At the lower aging temperature, it was noted that silicon enriched the α-Ti/β-Ti interface when the α-Ti/β-Ti/TiB were all in contact. Upon α-Ti coarsening, silicon enrichment was observed at the α-Ti/TiB interface at the higher aging temperature.



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