Damping capacity and its mechanisms of ultrafine-grained structural materials produced by ARB process.

点击翻译按钮获取中文摘要

This research was made in 2003 to 2005 to investigate the damping properties of structural metals with ultrafine grains fabricated by Accumulative Roll-Bonding (ARB) process and to clarify their damping mechanisms. The materials of pure aluminum (1100 Al), Ni, low carbon IF steel with Ti element and Fe-Cr-Al alloys were severely deformed by up to an equivalent strain (e) of 4.8 by the ARB process to have the ultrafine grain structures to about 0.1um in diameter. The severely deformed materials were annealed at various temperatures for 30min to change the structures of metals. They were observed by transmission electron microscopy, magnetic measurement, tensile test, microVickers measurement and internal friction measurement.Internal friction (Q^1) of Al and Ni increased with increasing amount of deformation. The deformed materials of e=3.2 had the quite high Q^1 of 6.6×10^<-3> and it kept about constant against the deformation. These internal frictions were explained as follows. The di … More stance of the dislocation motion under vibration stress seemed to be small due to the smallness of the grain size. The change in the Q^1 with number of the ARB cycles was attributed to the changes in the dislocation density and the distance of dislocation motion under vibrating stress which is controlled by the pinning points and the grain boundaries. As for the internal friction of IF steel, the Q^1 was 1.4×10^<-3> for IF steel with grains of 22um in diameter, 1.6×10^<-3> for that of 0.4um and 1.8×10^<-3> for that of 0.2um ; that is, the internal friction increased with decreasing diameter of grains. On the other hand, the strengths were 270MPa for the IF steel with grains of 22um in diameter and 900MPa for 0.2um ; that is, the strength increased by 3 times with decreasing diameter of grains. The internal friction were decreased to 1.57×10^<-3> by the annealing at 873K, but it recovered to be 1.72×10^<-3> by the annealing at 973K. Thus, the strength of IF steel with ultrafine grains becomes by three times higher than that of the ordinary IF steel and its damping property is improved to increase by 30% when compared with the ordinary IF steel. Because this damping for the IF steel occurs due to the dislocation damping mechanism, the control in the amounts of dislocation density, mobility and wipe area can increase the strength and damping ability of IF steel. As for the Fe-Cr-Al alloys, the strength of Fe-Cr-Al alloys increased to twice of the strength of the ordinary Fe-Cr-Al alloy due to the ultrafine grains structure of about 0.11um in diameter, while its internal friction was lowered to half. However, after the annealing near 773K, the internal friction increased largely although the strength retains constant or little decreased. This reason is that the strength is lowered little due to small change in grain size, and the internal friction is increased by the increment in the magnetic wall shift. Thus, it was found from this research project, grant- in-aid for scientific research that the high performance damping materials can be produced by the combination of severe plastic deformation and annealing. Less