1. Manipulating the strength and tensile ductility of a PM near α titanium alloy by adjusting the morphologies and volume fractions of α and βt domains.
- Author
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Wu, Xiaogang, Zhang, Bowen, Zhang, Yanhu, Niu, Hongzhi, and Zhang, Deliang
- Subjects
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TITANIUM alloys , *TENSILE strength , *HEAT treatment , *POWDER metallurgy , *DUCTILITY , *STRAIN hardening - Abstract
Powder metallurgy (PM) near α Ti−6Al−2Sn−4Zr−2Mo−0.1Si−0.5Y (wt.%) alloy with a low oxygen content and fabricated by thermomechanical powder consolidation of an elemental powder blend with a trace amount of Y addition was subjected to two heat treatments to obtain different microstructures which were free of grain boundary α (α GB) layers. One heat treatment (960°C/1h/AC, AC = air cooling) led to the formation of an α/β t microstructure consisting of 75.3 vol% primary α (α p) domains with globular and platelike morphologies, 21.5 vol% β transformed structure (β t) domains comprising ultrafine secondary α (α s) lamellae in a β matrix and 3.2 vol% thin β strips. The other heat treatment (960°C/1h/WQ+580°C/6h/AC, WQ = water quenching) led to the formation of a microstructure consisting of 38.2 vol% isolated α p plates, slabs, and globules dispersed in a β t matrix comprising nanometer-sized α s lamellae and residual β strips. The first microstructure rendered the alloy with high tensile strength of 1128 MPa and excellent tensile ductility of 15.6%, thanks to the activation of abundant and
slips in all α grains and tensile twinning in the "hard" <0001> micro-textured α grains with the c-axis parallel to the tensile force direction which mitigated the strain localization and enhanced strain hardening. On the other hand, the harder nanostructure of the β t matrix in the second microstructure resulted in a significantly increased tensile strength of 1351 MPa while maintaining an excellent tensile ductility of 10.5%. This can be attributed to the activation of abundant and slips in thin α plates and a limited degree of tensile twinning in the "hard" α domains, as well as a large number of statistically stored dislocations (SSDs) within the micron-scaled α slabs/globules. Both microstructures rendered the alloy with favorable ductile fracture. [ABSTRACT FROM AUTHOR] - Published
- 2022
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