HIGH ANGLE BOUNDARY FORMATION IN DYNAMICALLY RECOVERED MATERIALS DURING SEVERE HOT FORGING

摘要

The evolution mechanisms of new high-angle boundaries as well as ultra-fine grains in large strain were studied using dynamically recovered materials, such as a ferritic steel, aluminum and magnesium alloys, by means of multidirectional forging (MDF). The compression tests were carried out using rectangular samples with consequent changing of loading direction in 90° through three of mutually perpendicular axes. The structural changes can be characterized by the evolution of deformation bands such as microshear and kink bands at moderate strains. MDF accelerates the evolution of many mutually crossing microshear and kink bands developed in various directions. The (sub)grains become more equiaxed and the misorientations between them gradually increase with increase in cumulative strain, finally leading to the development of a new fine-grained structure. It is concluded that the dynamic grain formation can result from a kind of continuous reactions involving grain fragmentation due to deformation bands, i.e. continuous or in-situ dynamic recrystallization.