Effect of post-treatment on the microstructure and properties of Ti-27 Nb-5Zr-2Cr alloy prepared by laser powder deposition

Abstract

A metastable titanium alloy of Ti-27 Nb-5Zr-2Cr (wt%) was fabricated by laser powder deposition (LPD), and the bulk samples were then treated with hot forging (HF) and hot forging + surface shot blasting (HF + SB). The microstructures and mechanical properties of the laser-deposited Ti-27 Nb-5Zr-2Cr alloy in LPD, LPD + HF, and LPD + HF + SB were investigated. The obtained results showed that the microstructure of the LPD specimen was composed of β phase and isothermal ω phase. Due to the exist of the isothermal ω phase, the alloy was significantly strengthened and the deformation twinning was suppressed completely. As a result, the LPD specimen exhibited high strength (yield strength 728 ± 72 MPa) but low plasticity (6 ± 1%); after hot forging, the isothermal ω phase transformed to β phase and the deformation twinning occurred during tensile deformation. The yield strength and tensile strength of LPD-HF specimen decreased by 45% and 29%, respectively, but the plasticity increased by 483% to 35 ± 2%. Shot blasting was used to introduce gradient nanostructures on the surface of LPD-HF-SB specimens, which suppressed surface wrinkling caused by deformation twinning while improving strength and plasticity. Compared with the LPD-HF specimen, the yield strength, tensile strength, and plasticity of the LPD-HF-SB specimen were increased by 18%, 8%, and 6%, respectively.