Ti{sub}2AlNb-BASED TITANIUM INTERMETALLIC ALLOYS FOR HIGH TEMPERATURE APPLICATIONS

摘要

The effects of microstructural and compositional modifications on the mechanical properties of an orthorhombic Ti2AlNb-based intermetallic alloy were investigated. In addition, Ti-22Al-27Nb alloy-based particulate composites reinforced with 6.5%TiB were produced and evaluated. A Ti-22Al-27Nb alloy with a prior B2 grain size ranging from 10μm to 200μm was successfully obtained by using spherical α2 particles as obstacles against grain growth. An alloy with a B2 grain size of 50μm and a lamellar microstructure within the grains exhibited higher tensile strength (1371MPa) and elongation (7%) at room temperature. The substitution of 2%W for 7%Nb in a Ti-22Al-27Nb was quite effective in increasing tensile strength at temperatures above 923K. This substitution was also effective in reducing the steady state creep rate and primary creep strain. 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.