1. Microstructure evolution and phase transformations in Ti-22Al-25Nb alloys tailored by super-transus solution treatment.
- Author
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Huang, Yong, Liu, Yongchang, Li, Chong, Ma, Zongqing, Yu, Liming, and Li, Huijun
- Subjects
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TITANIUM alloys , *MICROSTRUCTURE , *PHASE transitions , *ELECTRON microscopy , *DIFFUSION - Abstract
Abstract The decomposition of metastable β phase and microstructural evolution of a forged Ti-22Al-25Nb orthorhombic alloys were investigated by the electron microscopes and phase identification. For the near-Ti 2 AlNb alloy, the processing temperatures were super-transus (over the transition temperature of the β phase). β phase was ordered before its decomposition and cooling rate could strongly influence the precipitation of the explored Ti-22Al-25Nb alloy. Water quenching could prevent the transformation related to diffusion and air cooling hindered the occurrence of fine lenticular O phase in the matrix. Comparison with previous researches and selected area diffraction patterns revealed that there did exist a displacive precursor that provided nucleation sites for the α 2 phase during B2 → α 2 transition. Due to the transient structure and diffusive gradient of Nb component during the transformation, a "cellular structure" was assembled and quantities of equiaxed α 2 precipitates were acquired. Simultaneously allotriomorph α 2 precipitates inclined to grow into coarse plates on the boundaries, which would have a detrimental effect on the mechanical properties of the alloy. Widmanstätten structure was formed during the (B2+α 2 +O) field and massive transformation of lenticular O phase occurred in the (B2+O) field. Highlights • Effect of cooling rates on the decomposition of B2 phase in the Ti 2 AlNb-based alloy is presented. • Precipitation and microstructural evolution during slow-cooling process are discussed in detail. • The mechanism of the formation of cellular structure was put forward and verified. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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