Effect of temperature on tensile behavior of Ni-Cr-W based superalloy

The temperature dependence of tensile behavior of Ni-Cr-W based superalloy has been studied by tensile tests in the temperature range of 25-900°C. The results indicated that the yield strength was anomaly with increasing temperature. Below 600°C, both the tensile and yield strength decreased slightly with increasing temperature; above 600°C, the tensile strength decreased rapidly while the yield strength almost kept invariable; the elongation had its minimum value at 600°C. Microstructure analysis showed that M₂₃C₆ carbides including of lamellar carbides (600°C) and discrete carbides (above 600°C) precipitated at the grain boundaries. The lamellar M₂₃C₆ carbides with the width of 1-3μm weakened the strength of grain boundary, and thus led to the premature failure of the alloy. But the grain boundary sliding was effectively restricted by discrete M₂₃C₆ carbides. TEM analysis showed that the high dislocation density and cross-slip also contributed to the yield strength anomalous.