A study was carried out on the influence of macroscopic defects on the damping behavior of commercially pure Al and Zn-27 pct Al alloy. The macroscopic defects, pores, and graphite particulates with a size of 0.001 Ϯ 0.0005 m and volume fractions ranging from 19 to 94 pct were introduced into the structures by infiltration technology. It has been shown that pores or graphite particulates can improve the damping capacity of commercially pure Al, due to the interaction between macro-and microdefects. Pores, however, show no detectable effects on the damping behavior of high damping Zn-27 pct Al alloy. Similarly, graphite particulates have little effect on the damping capacity of Zn-27 pct Al alloy at low temperatures and, on the contrary, make the transformation peak value of internal friction decrease. It is considered that graphite particulate may repress the eutectoid transformation process of Zn-27 pct Al alloy.
The effect of heat treatment and grain size on the damping capacity of an Fe-Cr-Al alloy with composition of (wt%) Fe-25Cr-5Al has been investigated. It has been shown that annealing temperature and grain size have a significant influence on the damping capacity and strain amplitude dependence of the alloy. Moderate annealing and grain size are necessary for a higher damping capacity, although if annealing does not yield relatively large grains, it has little effect on the damping capacity. The alloy has a rather low damping capacity after being water quenched or cold worked due to a high internal stress in the structure. It has been found that a relaxation maximum appears in the internal friction-temperature plot at about 550 C and its activation energy is 2.6 (AE0.3) eV. It is proposed that the peak originates from the Zener relaxation.
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