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In this work, the effects of grain size, notch width, and testing temperature on the fracture toughness of two typical MAX phases, Ti3Si(Al)C-2 and Ti3AlC2, 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 Ti3Si(Al)C-2 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)C-2. Furthermore, the high-temperature fracture toughness of Ti3Si(Al)C-2 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)C-2 and Ti3AlC2 is also discussed. (c) 2007 Published by Elsevier Ltd.