Study On Fatigue Damage And Fracture Behavior Of γ-TiAl Based Alloys

Tensile tests, compression tests, in-situ tensile tests, bending tests, fatigue tensile tests and fatigue bending tests were carried out for a TiAl alloy. Based on the global experimental results and microscopic observations of fracture surfaces and crack initiation and propagation on metallurgical surfaces of unloading specimens, the fracture mechanisms of the fully lamellar (FL) TiAl alloys at various loading modes are summarized as: (1) Cracks initiate at grain boundaries and/or interfaces between lamellae, and lamellar interface is the most weakest part. Fracture surface is composed of the trans-lamellar fracture and inter-lamellar fracture, and trans-lamellar fracture is dominant. (2) when a crack extends to a length, which acts as a Griffiths crack and matches the loading stress the crack propagates catastrophically through entire specimen, (3) The crack acting as a Griffiths crack can be produced promptly by the applied load in the tensile and bending test or be produced step by step by a much lower load in the fatigue tensile test. (4) In compressive tests cracks initiate and propagate in directions parallel or inclined to the compressive load after an appreciable plastic strain. The fracture mechanisms in compressive tests are controlled by shear stress and tensile stress, and the specimen is fractured by the propagation of cracks in both directions. (5) In the notched bending tests, the fracture mechanisms are also brittle cleavage fracture, once cracks are produced in the notch root, accumulated enough energy makes the material fracture. (6) For fatigue bending tests, the fatigue crack initiated and extended directly from the notch root, then extends step by step by the fatigue bending loads. The fatigue crack maybe extends through entire specimen at a lower fatigue load or triggers the cleavage at a higher load through the whole specimen.