Papers by Keyword: Cryogenic Deformation

Abstract: Influence of a nearly room and cryogenic severe deformation of a Cu-Zn powder mixture on a structural and phase transitions and kinetics of mechanical alloying was investigated. A sufficient retardation of structural and phase transformations and low homogeneity of solid solution made at 80K were established in comparison to processing at 273K. A lowering of solution formation kinetics rate is supposed to be due to lock of plastic deformation mechanisms, activated by thermal impact.

Abstract: The grain structure and texture evolution during annealing an Al-0.13%Mg submicron grained alloy, deformed by plane strain compression (PSC) at cryogenic temperatures, has been investigated. On annealing the grain structure coarsened and transformed from lamellar to equiaxed. But, remarkably, the fraction of low angle boundaries (LABs) increased, from less than ~ 25% to ~50% above 300 °C, leading to instability and discontinuous coarsening at higher temperatures. The surprisingly large increase in LAB fraction on annealing is shown to be related to orientation impingement originating from the strong texture present after PSC in liquid nitrogen.

Abstract: In the paper the concept of structure refinement due to mechanical twinning is discussed. It is postulated that the process of structure refinement may occur when dominant crystal shear proceeds across twin-matrix interface (Mode 2). Contrary, if the crystal shear proceeds parallel to the interface (Mode 1) no condition for structure refinement is satisfied. The conditions of the structure refinement and no structure refinement are shown taking example of tensile Cu-8%at. Al single crystals of two orientations [1 4 5] and [1 1 2] tested in liquid nitrogen. The tensile characteristics are therefore divided into stages associated with the Mode 1 and Mode 2, which correspond to the fact whether refinement of single crystal structure is present or not, as it is proved by the EBSD analysis. The performed analysis showed that structure refinement consists of formation of regions of new orientations, where the most common feature is the II order twinning (the case [1 4 5]) supported by other regions of specific orientations necessary to accommodate mainly the transfer of crystal twin shear across the twin-matrix interface. Moreover, if the II order twinning plays the dominating function (the case [1 1 2]) higher order twins are to bring into operation to assure further ductility of a deformed sample.

Abstract: The effects of severe plastic deformation (SPD) by isothermal rolling at the temperature of liquid nitrogen combined with prior- and post-SPD heat treatment, on microstructure and hardness of Al-4.4%Cu-1.4%Mg-0.7%Mn (D16) alloy were investigated. It was found no nanostructuring even after straining to 75%. Сryodeformation leads to microshear banding and processing the high-density dislocation substructures with a cell size of ~ 100-200 nm. Such a structure remains almost stable under 1 hr annealing up to 200oC and with further temperature increase initially transforms to bimodal with a small fraction of nanograins and then to uniform coarse grained one. It is found the change in the alloy post–SPD aging response leading to more active decomposition of the preliminary supersaturated aluminum solid solution, and to the alloy extra hardening under aging with shorter times and at lower temperatures compared to T6 temper.

Abstract: Recent advances in the severe plastic deformation technique have shown that effective refinement of the microstructure can be achieved in pure metals as well as in alloys. Among the various methods of severe plastic deformation, equal channel angular pressing has been the subject of numerous research works. Since the grain refining effect of this technique appears to reach a peak at a level of approximately 200 nm further microstructural changes are sought—deformation at a cryogenic temperature being one of the candidate routes. In the present study, we opted to combine equal channel angular pressing and low temperature plastic deformation to refine the microstructure of commercially pure V. The starting microstructure consisted of equiaxed grains with an average size of 100 micrometers. This microstructure was refined to a 200 nm thick lamellar microstructure by 8 passes of equal channel angular pressing at 350°C. The lamellar thickness was further reduced to 140 nm upon subsequent cryogenic rolling, which resulted in room temperature yield strength of 768 MPa. In the specimens, recrystallization annealed at 850°C, the grain size reached 1000 nm or larger, and the yield strength obeyed the Hall-Petch relationship with that grain size. The tensile elongation value, which was low and insensitive to the grain size in the as-deformed state, increased significantly up to 43% with the recrystallization annealing.