Study On Compression Damage And Fracture Behavior Of TiAl Based Alloys

Deformation, damage and fracture behavior of TiAl based alloys were studied under compression condition in this paper. Combined with the practice application the connection experiment and FEM calculation have also been done. The damage parameter, fracture mechanism of fully lamellar and duplex microstructure and the loading speed effect on mechanical property and fracture behavior were attained. It is shown that: (1) the compression property of TiAl based alloy is excellent to tensile property. No appreciable effects of the preloading-unloading-reloading processes on global compression deformation behavior are produced, until compression preloading stress surpasses the maximum compression stress. Because of the accumulation of damage effect, the big main crack was formed, and then the ture loading cross-section was descended, so the fracture stress was reduced when the specimen was reloaded again; (2) in compression tests, surface microcracks parallel to compression axis are produced on the specimen surface at about 800MPa of the applied compression stress. Four types of microcracks were initiated and propagated on the surface of the specimens with increasing applied compression stress: (a) longitudinal interlamellar cracks parallel to the compression axis; (b) interlamellar cracks inclined to the compression axis with a small angle; (c) longitudinal translamellar cracks inclined to the compression axis with a small angle; (d) longitudinal trans-granular (y grain) crack. With increasing the applied compression stress the densities of surface cracks increase remarkably, yet the lengths of the cracks are limited at the range of the grain sizes; (3) in compression test, the fracture starts from the inclined shear cracking at the top or/and the bottom surfaces. For FL specimen the shear cracking propagates through whole specimen and dominates the fracture. While for DP specimen the inclined shear cracking transform to longitudinal normal cracking which dominates the fracture; (4) the mechanical property was affected by loading speed, as well as the micro-fracture behavior; (5) the joint strength of turbine machine is effected by the following aspects, such as the material and thickness of high temperature alloy sleeve, the diameter and length of shaft, fitting parameter and the stability of machine processes quality, assemble temperature and environment and so on; (6) value and distribution of internal stress, which was produced by the interference fitting, were calculated by FEM software-ABAQUS. The results showed that the internal stress is related to the geometry size and structure. The whole joint sample is located at the range of elastic deformation, but the stress concentration and stress fluctuation were appeared in the tip of joint sample. The stress concentration and stress fluctuation were reduced when the joint sample was added a groove which act as a release character.