Processing orientation - Fracture resistance relationships of V-5Cr-5Ti alloy

Vanadium alloys have been explored primarily for nuclear reactor applications. In the present study V-5Cr-5Ti was used as a candidate material to study the effect of rolling orientation on the fracture resistance of these alloys. Compact tension (1/2 T) specimens were prepared using Electrical Discharge Machining (EDM) from a vanadium block along the rolling A-direction and the perpendicular B-direction. The specimens were subjected to fatigue pre-cracking in order to introduce a sharp notch for the fracture resistance evaluation, according to ASTM standard E399. Three specimens were tested using an electromechanical materials testing system from each orientation. A value for the stress intensity factor KI was calculated based on the maximum load sustained by the specimens and found to be extremely consistent among the three tested specimens in each orientation. An average value of 65 MPa √m was obtained for the V-5Cr-5Ti along the rolling orientation. This value was only 56 MPa √m for the same material perpendicular to the rolling orientation. The rolling direction fracture displays ductile tearing features, plastic deformation, tearing ridges and pulled-up strips. On the other hand, the B-direction, displays cleavage facets, inter-granular secondary cracks and river patterns. These fracture surface morphologies correlate with the fracture resistance data.