Influence of heat treatment on microstructure and tensile property of a new high strength beta alloy Ti-2Al-9.2Mo-2Fe

An investigation is given on the influence of heat treatment by the microstructural characteristics and tensile properties of a new high strength alloy Ti-2Al-9.2Mo-2Fe. Both of the alpha/beta and p solution treatment (alpha/beta-ST and beta-ST), then aged at temperatures ranging from 400 degrees C to 600 degrees C, were prepared. The primary a phases having 2-5 mu m are formed during the alpha/beta-ST and restrain the size of beta grains below 10 mu m. As a result of the fine beta grains, the alpha/beta-ST contributes a higher strength than the beta-St The coexistence of alpha and athermal omega phase is found in the beta-ST and water quenched samples. However, these have little influence on the alloy hardening. After aging, the alloys in the alpha/beta-ST and beta-ST condition reveal the phase transformation of beta to isothermal omega, and beta to a depending on the aging temperature. Although the primary alpha phase formed during the alpha/beta-ST increases the stability in the beta matrix, and the isothermal omega phase also appears to occur during aging at 400 C and 450 degrees C for 2 h. These phenomena are less common in beta titanium alloys, when treated in the alpha/beta-ST and aged at lower temperatures. The isothermal omega phase formed in both conditions results in high strength levels (1600 MPa of ultimate strength) with much ductility loss (2.5-4.5% of elongation) as a result of the superior hardening effect and brittleness of omega phase. However, the secondary a phase with the size of 1-3 mu m leads to attractive combinations of strength and ductility (1200-1400 MPa of ultimate strength with 7.5-12.5% of elongation). The reason for that is too fine a phase below 1 mu m tends to result in ultra-high strength with much ductility loss. As a whole, the alloy can be heat treated to obtain excellent balances of strength and ductility, and provided abundant stress levels with optional ductility as a usable material. (C) 2013 Elsevier B.V. All rights reserved.