|Budget Amount *help
¥6,800,000 (Direct Cost : ¥6,800,000)
Fiscal Year 1997 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1996 : ¥5,600,000 (Direct Cost : ¥5,600,000)
Stress-strain behavior and microstructural developments in high temperature deformation of fcc metals (Al and Cu) were investigated. Emphasis was on the critical conditions for the occurrence of dynamic recovery and dynamic recrystallization as restoration processes.
In the compression tests of Al single crystals, at 400K - 500K with strain rates 10^<-2>s^<-1>-10^<-5>s^<-1>, intense fluctuation of flow stress was observed The critical strain, epsilon_c for the first stress maximum is largely depends on the crystallographic orientation of the specimen axis, in an increasing order of <111>, <110>, <100>.At a constant temperature, epsilon_c decreased to a minimum at a critical strain rate. The apparent activation energy for dynamic recrystallization in Al as estimated by using the first stress maximum is 65kJmol^<-1>, which is in good agreement with the reported activation energy for the motion of high angle grain boundaries in Al.
Stress-strain curves for Al single crystals, in tension at
773K-873K with strain rates 10^<-3>s^<-1>-10^<-5>s^<-1>, showed no work hardening, suggesting that dynamic recovery is taking place in the restoration process. Cu single crystals continue to work-harden when stressed in tension at 973K-1173K with strain rates -10^<-5>s^<-1>, until the flow stress suddenly drops at a critical point.
Microstructure analysis of the high temperature deformed Al and Cu single crystals, by X-ray Berg -Barrett topography, revealed subgrains bordered by polygonization walls and subboundaries, rather regularly distributed along the tensile axis of the crystals. No appreciable change in subgrain size was observed in the steady state for Al, but considerable decrease in size was observed in the work hardening stage for Cu. New recrystallized grains were clearly seen in the Cu crystal after the sudden stress-drop.
The present experimrntals results suggest that the size, shape, stress state of specimens, as well as stacking fault energy and purity of the crystals, are the important factors influencing the high temperature restoration mechanisms. Less