Abstract
Ti3AlC2-Ti5Al2C3 materials were neutron irradiated to 2 x 1025 n/m2 (E > 0.1 MeV), a displacement dose of ~ 2 dpa. Irradiation temperatures were ~400, 630 and 700°C. XRD showed MAX phases respond similiarly to HCP ceramics: anisotropic lattice swelling occurs at ~400°C and is thermally mitigated after ~630-700°C. X-ray diffraction did not detect any satisfactory TiC1-x solution after irradiation, but an increase in density is observed at ~400°C and decreases to as-received values after irradiation at ~700°C. Strength and modulus are unchanged at ~630-700 °C. While unstable kink-bands are present, delamination is limited to 5-20 μm, resulting in diffuse microcracking in the post-irradiation morphology. Fracture surfaces suggest delamination occurred during irradiation and provide crack branching. TEM indicates absence of voids at all temperatures. Lamellar of TiC6 and Al layers are preserved but show disturbance on the (0004) planes via diffraction. Image analysis indicated a number density of dislocation loops is in the order of 1023 m-3 of size 5-10 nm after irradiation at ~630°C, and STEM HAADF suggests the presence of Ti antisite loops of size 3-20 nm. The location of the displaced Al atoms could not be determined. Therefore ~630°C would be close to the minimum use temperature for MAX phases based the supposition that the majority of A-layer recovery returns mechanical strength, but antisite defects and/or interstitial loops appear to be maintained.
