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

本研究于2003-2005年间进行，旨在研究累积滚压成形(ARB)工艺制备的超细晶结构金属的减振性能，并阐明其减振机理。采用ARB工艺对纯铝(1100Al)、镍、含钛低碳IF钢和Fe-Cr-Al合金进行了剧烈变形，当量应变(E)达到4.8，获得了直径约为0.1um的超细晶组织。将严重变形的材料在不同温度下进行30min的退火热处理，以改变金属的结构。用透射电子显微镜、磁测量、拉伸试验、显微维氏测量和内耗测量等手段对其进行了观察。Al和Ni的内耗(Q^1)随变形量的增加而增大。E=3.2的形变材料具有较高的Q^1，达到6.6×10~(-3)&gT；这些内部摩擦的解释如下。The di…由于晶粒度较小，振动应力下位错运动的更大姿态似乎较小。Q^1随ARB循环次数的变化归因于位错密度和位错在振动应力作用下运动距离的变化，而位错运动受钉扎点和晶界的控制。IF钢的内耗Q^1对于直径为22um的IF钢为1.4×10^&lt；-3&gt；，对于0.4um的为1.6×10^&lt；-3&gt；对于0.2um的为1.8×10^&lt；-3&gt；即内耗随晶粒度的减小而增大。而晶粒直径为22um和0.2um的IF钢的强度分别为270和900 Mpa，即随着晶粒直径的减小，强度提高3倍。在873K时，内耗降至1.57×10^&lt；-3&gt；，而在973K时，内耗恢复到1.72×10；-3&gt；这样，超细晶IF钢的强度比普通IF钢提高了3倍，其减振性能比普通IF钢提高了30%。由于IF钢的这种减振是由于位错的减振机制造成的，控制位错密度、迁移率和擦除面积可以提高IF钢的强度和减振能力。对于Fe-Cr-Al合金，由于其直径约为0.11um的超细晶结构，使其强度提高到普通Fe-Cr-Al合金的两倍，而内耗降低了一半。然而，在773K附近退火后，尽管强度保持不变或略有下降，但内耗却大幅增加。这是因为晶粒度变化不大，强度降低不大，而内耗随着磁壁位移的增大而增大。因此，从这项科研资助的研究项目中可以发现，通过大塑性变形和退火相结合的方法可以生产出高性能的减振材料。较少

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