Mechanical strength properties of Cu/AlN composites subjected to cyclic thermal loadings

Abstract

We investigate the mechanical strength of ceramic/metal composites subjected to cyclic thermal loading. First, test samples of Cu/AlN systems are prepared via brazing. Next, short-term thermal cycle tests (25, 50, and 100cycles) are conducted at temperatures ranging from -40 to 125°C. Four-point bending tests are conducted to evaluate the residual strength. Further, thermal stress analysis is performed using the finite element method in order to examine the thermal stress behaviors during cyclic heating. The results reveal that the residual strength increases during 0∼20cycles because of residual thermal stress relaxation. This relaxation is generated by the cyclic softening of the metals owing to combined hardening. In contrast, relatively long-term thermal cycling (20∼100cycles) reduces the residual strength owing to damage growth to AlN. The AlN plates exhibit variability in residual strength, and the distribution of the residual strength for each cycle number conforms to the two-parameter Weibull curve. The variability in residual strength increases with the cycle number, and it is attributed to variabilities in the pre-existing crack size and damage accumulation. We conclude that the residual strength of the Cu/AlN composites depends on the thermal stress behavior and damage growth to the AlN plates. © 2012 The Society of Materials Science, Japan.