Effect Of Different Deformation On Microstructure And Mechanical Properties Of Zr702

Zirconium and its alloys are widely used in nuclear power plants and chemicalindustries for their excellent corrosion resistance, mechanical strength, ductility and lowcapture cross-section for thermal neutrons. To date, the deformation mechanism of pure Zrhas been studied in detail. The resulting microstructure and mechanical properties after thedeformation process has captured the most attention of researchers. But the evolution ofmicrostructure and mechanical properties during the deformation process was ignored, andthis play an important role in the comprehensive understanding of materials.In this paper, the deformation behavior of commercial Zr702(pure zirconium) wassystematic studied through cold-rolling, tensile test, compression test and high speedpounding at room temperature. The evolution of microstructure during deformation wasinvestigated by optical microscopy (OM), transmission electron microscopy (TEM) andscanning electron microscopy (SEM).Through the investigation of the mechanical properties and microstructure evolutionof cold-rolled Zr702, it can be found that with increasing the extent of deformation from0to90%, the yield strength increased from248to637MPa and the tensile strengthincreased from341to723MPa, while the elongation decreased from23.5%to10.8%.After analysised the TEM we can see that the microstructure experienced dislocationtangles, dislocations arrangement, dislocation cells, nanocrystalline. The high densitydislocations and grain refinement caused the increased strength and decreased ductility.Annealing test of cold-rolled Zr702with a deformation of90%showed that both thestrength and the elongation increased after annealed at500-600℃.Investigation on the mechanical properties of annealed and cold-rolled Zr702showeda strain softening behaviour (SSB) during tension and compression deformation. And SSBappeared more easily on high strain rate deformation.Via TEM analysis, the dynamicrecovery was ascertained to be the origin that resulted in SSB. That was because dynamicrecovery is very easy to occur in pure Zr which has a high stacking fault energy of240mJ/cm2. Surface deformation of Zr702was studied by using high speed pounding (HSP). Theresults showed that a hardened layer of~10mm thick with hardness gradually decreasedfrom surface to matrix was achieved HSP treatment. TEM showed that surface grainrefinement can be abtained through HSP.