UNIQUE FINE MICROSTRUCTURES OF IRON CAUSED BY INTENSE SHEARING UNDER SHOCK COMPRESSION

Sample assemblies consisting of an iron rod and a concentric 2024-aluminum alloy cylinder were shock-treated by impaction of an iron flyer plate. Since the shock wave velocity of the rod is slower than that of the cylinder, oblique shock waves from the cylinder interact with the plane shock waves in the iron rod and form a conical region of plane loading in the front one-third of the rod. An ellipsoidal region, due to Mach eff ect, might even be formed in the next one-third. Outside of the conical region, intense shearing is anticipated. Microstructures of a longitudinal cross section of the recovered rod and Vickers hardness were axis-symmetric. The ellipsoidal region could not be seen in the cross section. However, outside of the region, fine microstructures were observed. These fine structures might be formed during the intense shearing in the high-pressure epsilon phase of iron and subsequent reverse transition to the normal alpha phase.