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Microstructure evolution and phase transformations in Ti-22Al-25Nb alloys tailored by super-transus solution treatment

Journal Article


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-Ti2AlNb 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 α2 phase during B2 → α2 transition. Due to the transient structure and diffusive gradient of Nb component during the transformation, a “cellular structure” was assembled and quantities of equiaxed α2 precipitates were acquired. Simultaneously allotriomorph α2 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+α2+O) field and massive transformation of lenticular O phase occurred in the (B2+O) field.

Publication Date


  • 2019

Published In


Citation


  • Huang, Y., Liu, Y., Li, C., Ma, Z., Yu, L., & Li, H. (2019). Microstructure evolution and phase transformations in Ti-22Al-25Nb alloys tailored by super-transus solution treatment. Vacuum, 161, 209-219. doi:10.1016/j.vacuum.2018.12.044

Scopus Eid


  • 2-s2.0-85059162432

Web Of Science Accession Number


Start Page


  • 209

End Page


  • 219

Volume


  • 161

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-Ti2AlNb 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 α2 phase during B2 → α2 transition. Due to the transient structure and diffusive gradient of Nb component during the transformation, a “cellular structure” was assembled and quantities of equiaxed α2 precipitates were acquired. Simultaneously allotriomorph α2 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+α2+O) field and massive transformation of lenticular O phase occurred in the (B2+O) field.

Publication Date


  • 2019

Published In


Citation


  • Huang, Y., Liu, Y., Li, C., Ma, Z., Yu, L., & Li, H. (2019). Microstructure evolution and phase transformations in Ti-22Al-25Nb alloys tailored by super-transus solution treatment. Vacuum, 161, 209-219. doi:10.1016/j.vacuum.2018.12.044

Scopus Eid


  • 2-s2.0-85059162432

Web Of Science Accession Number


Start Page


  • 209

End Page


  • 219

Volume


  • 161