HIGH TEMPERATURE TENSILE PROPERTIES AND FRACTURE MECHANISM OF ULTRA-FINE GRAIN Cu-Cr-Zr ALLOY

Cu-Cr-Zr alloy usually applys to the complex environment at high temperature. The mechanical behaviors of alloy are different from the condition of normal temperature. At high temperature, grains and precipitates of ultra-fine grain Cu-Cr-Zr alloy become coarse and it would affect the hot deformation behavior of alloy. To solve the thermal stability of the ultra-fine grain materials, the grain growth mechanism and the driving force of ultra-fine grain materials must be studied, as well as trace elements on the thermal stability mechanism. Tensile properties, microstructure of fracture and fracture mechanism of ultra-fine grain (UFG) Cu-Cr-Zr alloy made by two different treatment methods were studied at the temperature range of room temperature to 600 degrees C. The results show that the ultimate tensile strength (UTS) of alloys decreases with increasing temperature. The UTS and elongation of No.1 alloys are about 577.17 MPa and 14.6% at room temperature, respectively. And No.1 alloy start to occur dynamic recrystallization and UTS decreases fast at 300 degrees C. The UTS of No.1 alloy are only 59.12 MPa at 600 degrees C. The UTS and elongation of No.2 alloy are about 636.71 MPa and 12.1% at room temperature, respectively. The pinning effect by precipitation on grain boundary in the No.2 alloy begins to weaken at 400 degrees C. The UTS of No.2 alloy decreases fast and are only 65.20 MPa at 600 degrees C. Compared to No.1 alloy, No.2 alloy have better room temperature property and thermal stability. The elongation of all alloys increases with increasing temperature and show superplasticity on elevated temperature. The high temperature tensile fracture morphologies are an intense and deep dimple pattern. The high temperature fracture mechanism is ductile fracture by gathered microporous.