Thermal stresses in a macroscopic graphite particulates reinforced CuAlMn shape memory alloy studied by internal friction

In the present study, a novel metal matrix composite (MMC) has been fabricated with a Cu-11.9Al-2.5Mn (wt%) shape memory alloy (SMA) and macroscopic graphite particulates with the objective of damping enhancement. The functional properties of such MMC are directly related to the constraining behavior that the composite reinforcement has on the SMA. Following temperature changes large internal stress can be induced due to the difference in coefficient of thermal expansion (CTE) between reinforcement and matrix, resulting in the change of the configuration of martensite variants or the microplastic deformation of the matrix, leading to the appearance of high dislocation density. The damping behavior of the novel MMC has been measured using a multifunction internal friction apparatus (MFIFA) through the method of forced vibration at low frequencies of 0.5, 0.8 and 1.0 Hz. In addition to the remarkable elevation of the internal friction background an internal friction peak appears at around 240 °C, while it is absent for the corresponding block CuAlMn alloy. The internal friction peak has been attributed to the interaction between the dislocations and the cyclic stress applied during internal friction measurement.