Mechanical properties and structure of age-hardened Ti-Cu alloys

The room temperature tensile properties of age-hardened Ti-Cu alloys, 0.9 and 4 at. pct Cu, were investigated. The results were correlated to the microstructure and to the observed interaction mechanism between moving dislocations and precipitated particles. Two types of precipitates were observed upon aging between 400° and 500°C. One type was identified as a metastable, ordered precipitate coherent with the matrix. The other type was the stable Ti₃Cu phase which was partially coherent with the matrix. Both types of particles were precipitated from a martensitic microstructure which resulted from the β → α transformation. Although the martensitic microstructure contributed to the high flow stress, the elongation to fracture was principally determined by the dislocation-particle interaction mechanism. The maximum elongation to fracture was obtained by inducing a dislocation by-pass mechanism in a structure containing homogeneously distributed, partially coherent Ti₃Cu particles. The tendency of the Ti₃Cu particles to precipitate preferentially on boundaries was minimized by low temperature aging. Formerly Assistant Professor Materials Research Laboratory, Rutgers University, New Brunswick, N.J.