| In this paper, 6061Al/SiCp and 6061Al/SiCp/Gr Metal Matrix Composite (MMC) was produced by spray codeposition, By means of changing the medium of quenching, influence of five types of heat treatment system(furnace cooling, air cooling, water quenching, dry ice quenching, liquid nitrogen quenching) on the microstructure, damping and modulus was studied systematically. Furthermore, relaxation damping peaks appearing in every heat treated sample were analyzed, the relevant activation energies were also calculated, and then the generation mechanism of these damping peaks were discussed.First of all, phase constitution and configuration of every heat treated sample were analyzed by using optical microscope (OM) and X radio diffraction(XRD). The results show that SiC particulate, with the shape of angle plank, distributes equably in the matrix, and that the interface between SiC particulate and matrix is distinct, it's acute edges and corners is clear seen. What's more, the microstructure of every heat treated sample has been observed and analyzed by using transmission electricity microscope (TEM), it is founded that the matrix mostly takes the shape of equiaxed crystal and there is large quantities of dislocation around the interface between SiC particulate and matrix, and the density of dislocation decrease with increasing the distance away from the interface. Meanwhile, a great deal of fine precipitation phase dispersed in the grain and then pinned the dislocation.Drawing on a multifunctional internal friction instrument, we tested the damping capacity of all the heat treated samples completely, and then got the damping-frequency spectrum, temperature spectrum and strain amplitude spectrum for the application of project. As the results manifest, damping capacity of different heat treated samples changes slightly at low temperature but remarkably at elevated temperature. Over a 100 to 270 ℃ temperature range, the damping capacities are ranked from great to small as follows: sample cooled infurnace, sample cooled in the air, sample quenched at -70 ℃, sample without heat treatment, sample quenched at -195 ℃ and sample quenched in water. In addition, the damping capacities of all the samples can amount tol X 10"2 when temperature is above 180℃, which exhibits excellent high temperature damping capacity; On the other hand, modulus does not change with frequency at low temperature, otherwise, it decreases linearly with increasing frequency above 160 ℃ temperature, meanwhile, the more frequency is low, the more modulus deterioration is serious. The decline of modulus is attributed to changes of organization on the peak temperature, namely, the relaxation mechanism of interface takes effect, and moreover, the appearing scope of the damping peak can be forecasted approximately; On current experiment, the strain amplitude, ranging from 5 to 40 (in units of 10"6), doesn't attain the critical value (above 10"3 in this material) corresponding to the break-away of pinned dislocation line, so there isn't distinct strain-amplitude dependency.It is considered that the damping of matrix, interface between reinforcement phase and matrix and the inherent damping of reinforcement phase constitute the three major micro-mechanism, the addition outcome of three factors determine the macro damping behaviors. The thermoelastic damping and grain boundary damping don't play a important role, but dislocation damping on low temperature and interface damping on elated temperature perform an dominant function in the resultant damping of the MMC. Dislocation damping may be interpreted with Granato-Lucke theory, which assumes that dislocation moves with vibration, then breaks away in the snowslide-like mode from weak pinning points (such as some solute atoms, vacancies, etc.), and then forms the dislocation loop around hard pinning points (such as network node of dislocation, the second phase, etc.), consequently causes relaxation of the applied stress and dissipation of the mechanical vibration energy. In addition, interface dampi... |
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