Microstructural Characterization And Crack Propagation Behavior Of A Novel Beta-Solidifying Tial Alloy

Novel beta-solidifying TiAl alloys have great potential for engineering applications in the aerospace and automotive industries. The introduction of the beta(0) phase will inevitably affect crack propagation. However, the related mechanism is unclear. In this study, the crack propagation behavior of different beta(0)-containing microstructures was systematically investigated by three-point bending tests. The results show that the coarse gamma/alpha(2) lamellar microstructure exhibits better fracture toughness than the fine-grain microstructure because large numbers of gamma/alpha(2) lamellar boundaries can effectively hinder crack propagation. The propagation direction depends largely on the orientation of the gamma/alpha(2) lamellae. When the angle between the crack propagation direction and the gamma/alpha(2) lamellar boundary is small, the crack tends to propagate along gamma/alpha(2) lamellae. When the angle is close to 90 degrees, the crack generally propagates by the trans-lamellar mode. Moreover, the crack tends to traverse across the fine beta(0)/gamma duplex region due to the low resistance of fine grains in the crack propagation. The transgranular and intergranular modes are the main fracture mechanisms in the microstructure of the fine beta(0)/gamma grains. Some shear ligaments can also be identified in the lamellar microstructure and these can consume propagation energy. The enlarged image shows that the crack propagation direction can be changed by the beta(0) phase, owing to its high hardness. The crack tends to stop at the beta(0) phase region.