Mechanical properties of AlN-polytypoids - 15R, 12H and 21R

Mechanical properties of three types of AlN-polytypoids with Ln(2)O(3)(Ln = Nd, Sm) and Ln(2)O(3):Al2O3 = 1:1, respectively, as sintering additives we re studied. The results showed that the hardness increased with the AlN-pol ytypoid compositions shifting towards AlN-rich side, that was 21R having th e highest hardness (12.7-14.4 GPa) and 15R the lowest values (11.5-12.8 GPa ). The fracture toughness and flexural strength had no such close relations hips to the type of AlN-polytypoids, which varied in a range of 3.8-4.8 MPa .m(1/2) and 313-366 MPa (at room temperature), respectively. However, for t he compositions with suitable amount of additives, the flexural strength gr eatly increased with increasing temperatures, especially for 15R and 12H. T his characteristic was discussed on the basis of the fracture morphology ob served by SEM. (C) 1999 Elsevier Science S.A. All rights reserved.