The effect of matrix strength on the fracture resistance of an alpha-Beta titanium alloy,corona-5

This paper presents the results of a study of the effect of matrix yield strength, at constant Widmanstätten α microstructure, on the fracture resistance of an α-β Ti alloy, CORONA-5. Fracture initiation resistance,J _q, and the stable crack growth resistance,T, were evaluated by the single specimen, unloading compliance method for four different microstructures and three yield strengths. The microstructures involved coarse or fine Widmanstätten α particles in a heat treated β-matrix; the yield strength ranged from 765 to 1018 MPa. It was found thatJ _q/σ_Y, where σ_Y is the effective yield strength, decreased with increasingσ _Y.T/σ _Y also decreased with increasing σ_Y for fine structures. For the coarse α structures, however, T/σ_Y revealed intermediate maxima. Coarser structures, in general, revealed higher values ofJ _q/σ_Y andT/σ _Y. The cause was found primarily to be due to the effect of increased α particle thickness. The effect of grain size was secondary. J_q/σ_Y increased with increasing tensile strain hardening rate, obtained at the onset of void nucleation. T/σ_Y was found to decrease with increasing tensile void growth rate. In general, J_q/σ_Y and T/σ_Y revealed different relationships with microstructure. Fatigue precrack front- and the stable crack length-tortuosities did not yield any general relationship to fracture resistance at different yield strengths.