Fracture toughness of V-5Cr-5Ti alloy at room temperature and 100{degrees}C

The critical mixed-mode I/III fracture toughness, J-integrals (J{sub MC}), at room temperature (RT) and 100{degrees}C were examined for a V-5Cr-5Ti alloy. Fracture toughness at 100{degrees}C was evaluated with a J-integral test and at RT with a K (the stress intensity factor) test. The determination of J{sub MC} was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 45 from the load line. Crack angles used in this study were 0, 15, and 45 degrees. A specimen with 0 degree crack angle is the same as a standard mode I compact tension specimen. In this limit, J{sub MC} becomes J{sub IC}. Specimens were annealed at 1125{degrees}C for 1 hour in a vacuum of 10{sup {minus}7} torr. J{sub MC} and mixed-mode tearing moduli (T{sub M}) were determined at 100{degrees}C with the single specimen technique. Crack lengths were calculated with partial unloading compliances. The J{sub MC} values at RT were calculated from critical stress intensity factors (K{sub C}). The results showed that at RT the V-5Cr-5Ti alloy was brittle and experienced unstable crack growth with a mixture of intergranular, cleavage and some microvoid coalescence (MVC) fracture while atmore » 100{degrees}C it exhibited high fracture toughness and fractured with a mixture of MVC and intergranular failure. SEM investigation showed that some cleavage facets initiated at grain boundaries. The results suggest a low intergranular fracture strength and tendency towards cleavage fracture at room temperature. Preliminary data from Auger electron microscopy showed significant sulfur segregation on grain boundaries. The possible mechanism which might reduce intergranular fracture strength is discussed.« less