Effect of grain size, notch width, and testing temperature on the fracture toughness of Ti_3Si(Al)C_2 and Ti_3AlC_2 using the chevron-notched beam (CNB) method

摘要

In this work, the effects of grain size, notch width, and testing temperature on the fracture toughness of two typical MAX phases, Ti_3Si(Al)C_2 and Ti_3 AlC_2, were investigated using the chevron-notched beam (CNB) method. The high-fracture toughness in the range of 6.43-10.19 MPa m~(1/2) was determined. The critical notch width is about 250 mu m for the valid fracture toughness measurements of Ti_3Si(Al)C_2 and Ti_3AlC_2. For a fixed notch width and testing temperature, the fracture toughness of coarse-grained (CG) samples is higher than that of fine-grained (FG) samples, and the toughness of Ti_3AlC_2 is higher than that of Ti_3Si(Al)C_2. Furthermore, the high-temperature fracture toughness of Ti_3Si(Al)C_2 and Ti_3AlC_2 samples show a similar trend that the measured toughness is nearly a constant when the testing temperature is before the ductile-brittle transition temperature (DBTT) and then it declines fast over DBTT. The mechanism for the high-fracture toughness of Ti_3Si(Al)C_2 and Ti_3AlC_2 is also discussed.