Based on the fatigue crack propagation experiments did by A.-L. Gloanec et al., the fatigue crack propagation rates of TiAl alloy of two processing routes, namely casting and PM, and stress ratios had been tested, in order to find out the effects of microstructure and stress ratio. An improved fatigue crack propagation formula for region Ⅱ (the expansion region) was derived according to Paris formula. The specific values of the constants in the formula were calculated. Fatigue crack propagation resistance of nearly fully lamellar microstructure is superior to that of equiaxed γ grain. The experimental results present that both microstructure and stress ratio has a significant influence on fatigue crack growth rate.
The Cu50Zr42Al8dumbbell-shaped alloy with original scale distance of 25 mm and diameters of 4.5 mm was prepared by the suspend melting-copper mould suction casting. The structure tensile performance testing and the fracture morphology observation of Cu50Zr42Al8BMG as-quenched and 400k/1h isothermal annealing were investigated, respectively. The deformation and fracture behavior of samples had been studied. The results showed that the structure of all samples were composed of amorphous phase and possess good glass formation abilitysample as-quenched is always in the elastic deformation stage during elongation and the tensile strength is 629MPa; however ,for specimen after 400k/1h isothermal annealing ,the yield phenomenon occurs before breaking and the maximum tensile strength is 755Mpa, and the same time, the maximum failure extensibility increases from 0.56% for sample as-quenched to 0.80% for 400k/1h isothermal annealing. The fracture pattern of test sample at annealing assumes venation pattern, which is similar to fractography of Cu50Zr42Al8BMG as-quenched, in addition, which appeared apparent viscous flow behavior and melting characteristics.
The alloy rods with diameters of 3.0 mm of Cu50-xZr42Al8Agx(x=0,2,3,4)were prepared by means suspend melting-copper mold suction casting. The structure and thermal stability of the alloys were analyzed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Subsequently, compression performance and fracture morphology of these bulk metallic glasses were investigated .we focus on analysis that influence of Ag micro-addition on the deformation and fracture of speciments. The results showed that the addition of Ag can enhance the forming ability and thermal stability of amorphous alloys. At the same time, with the increase of Ag content, the breaking strength of samples was improved from 1747Mpa to 2038Mpa. Without obvious plastic elongation percentage in bulk metallic owing to non-homogeneous modes of texturing at room-temperature. The compression failure behavior of test samples belong to elastic failure and the maximum failure extensibility is 3.7%.The fracture pattern of test samples all assume venation pattern.
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