Enhanced mechanical properties of orthorhombic Ti₂AlNb-based intermetallic alloy

Abstract

Attempts were made to improve the mechanical properties of an orthorhombic Ti₂AlNb-based Ti−22Al−27Nb intermetallic alloy through microstructural and compositional modifications, and the dispersion of fine TiB particulates. A Ti−22Al−27Nb alloy with a prior B2 grain size ranging from 8 μm to 49 μm was successfully obtained using spherical α₂ particles as obstacles to grain growth. The finest grained material showed an excellent combination of room temperature tensile strength (around 1,000 MPa) and tensile ductility (more than 15%). Transition metal elements such as Mo, V and W for a portion of the Nb in the Ti−22Al−27Nb were substituted. The guideline for this compositional modification required that the beta phase stability in the modified alloy be equal to that of the Ti−22Al−27Nb. It was found that the substitution of 2% W for 7% Nb was quite effective in increasing tensile strength at temperatures above 923 K and reducing the steady state creep rate and primary creep strain. The Ti−22Al−27Nb alloy-based particulate composites reinforced with 6.5% TiB were successfully produced with the gas atomization P/M method. The dispersion of extremely small TiB was very uniform. Most of the mechanical properties of the composites, including the yield stress, tensile strength, Young's modulus, resistance to creep, and high cycle fatigue strength were greatly superior to those of the matrix alloy.