Effect of composition on the fatigue failure behavior of vanadium alloys

In this work, the effect of composition on the fracture surface morphology and fatigue failure behavior of two vanadium alloys (V-4Ti-4Cr and V-5Ti-5C r) under cyclic tensile loading was investigated. In the beginning of the s table crack growth stage, the crack speed for both vanadium alloys is very close; however, in the remainder of the stable crack growth stage, and the unstable crack stage, the crack speed for V-5Ti-5Cr is higher than that for V-4Ti-4Cr. The fracture surface features in the stable crack propagation r egion of the V-4Ti-4Cr show fatigue striations, drawn-out material, micro-c racks and micro-voids, indicating the various damage species associated wit h stable fatigue crack growth. The V-5Ti-5Cr, on the other hand, displayed twinning, cleavage tongues and tearing steps, in addition to slip in the st able crack propagation region of its fracture surface. Plastic deformation and ductile fracture mechanisms characterized by tearing and void coalescen ce can also be observed on the fracture surface in the fast crack region of the V-4Ti-4Cr. Nevertheless, the V-5Ti-5Cr shows more inter-granular fract ure and quasi-cleavage features in the fast crack propagation region. It wa s also found that the specific energy of damage (gamma'), a material parame ter characteristic of the alloys' fatigue fracture resistance, is compositi on dependent. A 1% increase of both the Ti and Cr content resulted in about a 30% reduction in the value of gamma'. This has also resulted in a signif icant change in the fracture surface morphology and the fatigue fracture me chanisms. (C) 2000 Elsevier Science B.V. All rights reserved.