The structure and microhardness evolution in submicrocrystalline molybdenum processed by severe plastic deformation followed by annealing

A possibility to form submicrocrystalline structure in molybdenum using severe plastic deformation treatment by torsion under high pressure (HPT) at elevated temperatures has been studied. Quantitative parameters of grain-subgrain structure have been obtained by optical microscopy and transmission electron microscopy methods. Thermal stability of microstructure and mechanical properties have been studied. It is established that HPT results in the formation of a submicrocrystalline structure in Mo and in disappearance of residual porosity. The average grain size of HPT-Mo is 0.2 mum. The formation of submicrocrystalline structure enhances significantly (by 2.4 times) the microhardness of Mo relative to that in the as-received (before HPT treatment) state. It is found that grain growth begins at 1173 K and develops intensively at T greater than or equal to 1273 K. (C) 2003 Elsevier Science Ltd. All rights reserved.