Vibration and related noise have become an emergent environmental problem with the increased of power and speed of advanced machines. However, damping alloy as an integrated material with special structure and function, can remarkable inhibits the vibration and noise. In this dissertation, several damping alloys have been chosen to investigate the contribution of dislocation to the internal friction in different pure metals. In addition, the damping behaviors induced by dislocation under critical strain amplitude, the influences of different strengthening methods on the dislocation damping and the effects of different kind of interfaces on the internal friction have also been studied.
The contribution of edge perfect dislocations to the internal friction in six pure metals (Al, Cu, Ni, Nb, Mg, Ti) with different crystal structures has been analysis by employing Peierls-Nabarro model associated with experiments. It was found that the contribution of dislocation to the internal friction in pure metals was dependent on the Peierls force, which was overcame during dislocation moving. The higher Peierls force is, the little contribution of dislocation to the internal friction.
The damping behaviors of dislocation under critical strain amplitude have been studied in as-cast Mg-Zr alloy. It was found that new dislocations would be easily generated during dislocation oscillated motion, and a relevant IF peak P1 (93.5℃, 1Hz) was also presented in the internal friction spectrum. The P1 peak is strain amplitude and heating rate dependent. Corresponding to the appearance of P1 peak, the storage modulus shows an obvious “trough”. In addition, the existence of P2 (236.5℃, 1Hz) peak was a thermal relaxation peak and considered to be grain boundary relaxation peak of as-cast Mg-Zr alloy.
The effects of different strengthening methods on the dislocation induced internal friction have been investigated in as-cast AZ91 alloy by employing different heat treatments. It was shown that in solution treated AZ91 alloy proceeds the highest strain dependent internal friction as no precipitation will pinning the motion of dislocation. However, the alloy after precipitation strengthened had higher damping capacity at high temperature as α-Mg/β-Mg17Al12 interface relaxation and grain boundary relaxation were exited.
The influences of complex phase boundaries on the damping properties of alloy had been studied in Zn-Al eutectoid alloy after different heat treatment and minor addition of (Zr + Si) elements. The results indicated that the dendrites were coarsening during natural aging, and damping property is decreased. Damping capacity will decrease with the rise of aging temperature as the lamellar structure will coarsen and its volume is increased. In addition, the damping capacity of as-cast Zn-Al eutectoid alloy could be significantly improved by the addition of minor (Zr+Si) elements, which induced microstructure refinement and increase of interface volume. The dislocations induced by thermal mismatch between Si phase and matrix have little influence on the damping property of alloy, as the diffusion of atoms make dislocations decrease gradually.
A novel TiNi/AlSi composite with high compressive strength and high damping capacity was obtained by infiltrating Al-12%Si alloy into porous Ti-Ni alloy. It was found that the compressive strength of porous Ti-Ni alloy can be increased from 90MPa to 364MPa as the effective carrying area is increased. The high damping capacity of TiNi/AlSi composite is contributed by Ti-Ni carcass, Al-12%Si filling material and TiNi/AlSi physical interface. The results show that the damping capacity of TiNi/AlSi physical interface is proportionality to the friction coefficient of interface (μ), the porosity of porous Ti-Ni alloy (p), and also related to the degree of interface closing (k).
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