Strengthening mechanism of aluminum nitride ceramics from 293 to 77 K

In this study, the flexural strength of aluminum nitride (AlN) ceramics at cryogenic temperatures was reported for the first time. The flexural strength increased from 364.6±29.2 MPa to 415.3±21.7 MPa with temperature decreasing from 293 to 77 K. The strengthening mechanism was explored based on the Griffith equation for a brittle solid and was rationalized by the analysis of lattice constants of AlN and the Vickers indentation length at ambient and cryogenic temperatures. The increase of elastic modulus and fracture surface energy could contribute to the strengthening of AlN ceramics at cryogenic temperatures. The above results showed that AlN ceramics could be a promising candidate for cryogenic engineering.