Effect Of High Pressure Torsion On Microstructure And Properties Of Zirconium

Material plays a decisive role both in human life and in human development, Zr has very important applications prospect in many areas as structural materials and functional materials because of its superior performance. Zr and Zr alloys have traditionally found applications as fuel rod materials in nuclear power plants. In those cases, coarse grained structures are preferred since they are more resistant to irradiation creep. In addition,pure Zr has outstanding in plasticity and elongation,the tensile strength of the pure Zr is240 MPa,Zr and Zr alloys have great potential in improving their strength and toughness.Thus, Some research regard as fine grain behavior of Zr have become the hot topic of common concern to scientists.Pure Zr(99.99%) with 10 mm diameter was used in this study. High pressure torsion(HPT) was conducted at room temperature,the disc samples were processed to N=0,1,5revolutions under a pressure of 4 and 6Gpa.Two kinds of mould(an unconstrained and a constrained high pressure torsion die)were used in this experiment. After the pressure torsion, some properties of Zr has been tested such as the micro-hardness, tensile strength.We use X-ray Diffraction(XRD), Electron Back-Scattered Diffraction(EBSD),Transmission Electron Microscope(TEM),Scanning Electron Microscope(SEM),and other experimental methods to study the organization structure and mechanical properties change, and analyze the effect of high pressure torsion of pure Zr.The results show that α phase to ω phase transformation takes place at 6Gpa 5 turns in the unconstrained HPT setup, but nothings happens in other conditions.The results of the micro-hardness shows that the hardness value in center is low, but the hardness of the samples located away from the center position increased obviously for the high pressure torsion. The hardness reaches a saturation level with increasing pressure when P=6Gpa N=5 turns. The results of the tensile test reveal that the tensile strength increased significantly with the increasing of the pressure. The tensile strength of the original samples is 465 MPa, and the tensile strength of the samples when P=6GPa N=5 turns is1040 Mpa. TEM and EBSD analyses show that grain refinement and dislocationmultiplication is the root cause excellent mechanical properties. SEM analysis shows that the fracture mechanism of material is micropore aggregation fracture, and there are many micropore in fracture.