Grain Refinement And Thermal Stability Of Materials With Different Stacking Fault Energy Subjected To Constrained Groove Pressing

Constrained groove pressing (CGP) is a severe plastic deformation technique. The ultra-fine grain of the plate-shaped metallic materials can be obtained through repeated shear deformation by constrained groove pressing. Q235 steel, pure copper and H62 brass, which have different stacking fault energy (SFE) were deformed by using constrained groove pressing. The effects of SFE on the microstructures、 thermal stability and mechanical properties were systematically investigated by optical microscopy, transmission electron microscopy, micro-hardness tests and tensile tests. The relationship between grain refinement and stacking fault energy has been discussed and the grain refinement mechanism of CGP has been studied.The influence of stacking fault energy on the microstructure of Q235 steel、 pure copper and H62 brass were investigated. Microstructural observations indicated that the grain size of Q235 steel、 pure copper and H62 brass reduced with increasing the CGP passes number. Compared with the parallel CGP, there is a larger speed of grain refinement and more homogeneous microstructures of the specimen subjected to cross CGP. The Influence of CGP manner is more apparent on H62 brass, which has low stacking fault energies. A low stacking fault energy is especially favorable for the introduction of an exceptionally small grain size using the CGP procedure. The grain refinement mechanisms of a high SFE (e.g. in Q235, Cu) is dislocation cell subdivision, however dislocation and twin fragmentation play an important role of the grain refinement in H62 brass.The influence of stacking fault energy on the mechanical properties of Q235 steel、 pure copper and H62 brass were studied. The tensile strength and hardness of Q235 steel、 pure copper and H62 brass alloys were simultaneously enhanced owing to the significant grain size refinement, strengthening and enhanced strain hardening capability. The hardness of samples deformed by cross CGP is higher than the parallel CGP. After four passes the strengths of Q235 steel、 pure copper appear to approach a saturated condition; while H62 brass still had a significant increasing trend; Tensile strength of three materials reached peak value after eight passes by cross groove pressing. Compared with the original, the tensile strength of Q235 steel、 pure copper and H62 brass are increased 45.8%、33.2% and 52.2% respectively.The influence of stacking fault energy on the thermal stability of Q235 steel、 pure copper and H62 brass after CGP were studied. The results show that the size of grain grown and hardness decreased with the increasing of annealing temperature. The hardness of H62 brass decreased rapidly and has a worse thermal stability.