Effects of Mo and Cr contents on microstructures and mechanical properties of near β-Ti alloy

Three alloys with the same molybdenum equivalent (Mo-[eq], Mo-[eq]approximate to 9) were prepared by adjusting the Mo and Cr contents in novel Ti-3Al-1.2V-1Zr-2Nb-1Sn-xMo-yCr (x = 6,4,1; y = 2.7,4,5.7, wt.%) alloys. Differences of microstructures, mechanical properties and deformation mechanisms in the three alloys under the same solution and aging treatment conditions were investigated. Effect of Mo on grain refinement during quenching is more notable than Cr in multi-element alloys. The change of elements ratio has little effect on the strengths of these alloys, but a significantly impact on their ductilities. After solution treated at 780 degrees C and aged at 530 degrees C, three alloys show similar strength (UTS similar to 1400 MPa) but the difference of their ductilities is more than 5%. The alloy with the same Mo and Cr contents exhibits the best elongation (El similar to 14.0%). Moreover, detailed analyses of transmission electron microscopy (TEM) results indicate that the dislocation slipping is the main deformation mechanism in beta matrix, and the slipping hindered by various boundaries (grain boundaries and alpha(GB), alpha(s)/beta and alpha(p)/beta interface) is the main strengthening mechanism. The ductility difference in the three alloys is mainly caused by the deformation ability of alpha phase. Formation of alpha-twin, alpha sub-boundary and other deformation products could accommodate local deformation and relieve stress concentration. This study provides a good guidance for high strength and toughness titanium alloy design.

Automated summary

The study investigated the effects of molybdenum and chromium content on the microstructure, mechanical properties, and deformation mechanisms of novel titanium alloys. Molybdenum notably influenced grain refinement during quenching, while the ductility of the alloys was mainly affected by the deformation ability of the alpha phase.