Effect of grain size, notch width, and testing temperature on the fracture toughness of Ti3Si(Al)C2 and Ti3AlC2 using the chevron-notched beam (CNB) method

In this work, the effects of grain size, notch width, and testing temperature on the fracture toughness of two typical MAX phases, Ti3Si(Al)C2 and Ti3AlC2, were investigated using the chevron-notched beam (CNB) method. The high-fracture toughness in the range of 6.43–10.19 MPa m1/2 was determined. The critical notch width is about 250 μm for the valid fracture toughness measurements of Ti3Si(Al)C2 and Ti3AlC2. 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 Ti3AlC2 is higher than that of Ti3Si(Al)C2. Furthermore, the high-temperature fracture toughness of Ti3Si(Al)C2 and Ti3AlC2 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 Ti3Si(Al)C2 and Ti3AlC2 is also discussed.