Cryogenic Mechanical Behaviors Of Zr702Zirconium And ZrTiAlV Alloy

In this paper, the tensile behaviors of Zr702at temperatures from room temperatureto-196℃, the compressive behaviors of a ZrTiAlV alloy at temperatures from roomtemperature to-150℃and the cryogenic wear-friction behaviors of Zr702and ZrTiAlValloy have been investigated by using electrical universal material testing machine andfriction-wear testing facility as well as OM, XRD, SEM and TEM techniques. Based onthe above investigations, the cryogenic mechanical features of pure zirconium and anew zirconium alloy were characterized.The results show that the as-rolled Zr702, consisting of single α phase, exhibitstypical plastic deformation features at temperatures from room temperature to-196℃.With decreasing temperature, the ultimate tensile strength of Zr702increases, whilethe elongation of Zr702decreases down to-150℃and increases at-196℃.The tensilefractured surface of Zr702samples tested at various temperatures displays typicaldimple fracture features, indicating that dislocation slip still dominates plasticdeformation process at cryogenic temperature. Meanwhile, with decreasing tensiontemperature, more twins were found in the fractured samples, it is implied that twinningbecome active during cryogenic plastic deformation of Zr702.The as-forged ZrTiAlV alloy consists of α+β two phase structure which ischaracterized by interlaced lamellar α phase in original β phase matrix. After a treatmentof heated at575℃for30minutes followed by water quenching, the volume fraction ofretained β phase increases, and the ultimate tensile strength of the ZrTiAlV decreasesfrom1690MPa to1502MPa, and the elongation increases from1.1%to1.5%. Theas-foraged and heat-treated ZrTiAlV samples exhibit favorable compressive propertiesat temperatures from room temperature to-150℃. With decreasing temperature, thecompressive strength increases, and the compressive fracture strain increases at-50℃and then decreases. At the same temperature, the heat-treated sample gives a lowercompressive strength and a higher compressive fracture strain than the as-forgedsample.It is indicated by the friction-wear test results that the friction coefficient of bothZr702and ZrTiAlV alloy is smaller in vacuum at cryogenic temperature than that in airat room temperature, and the mass loss of Zr702and ZrTiAlV alloy is also muchsmaller, respectively, in vacuum at cryogenic temperature than that in air at roomtemperature. Under the sample testing condition, the heat-treated ZrTiAlV sample givesa higher friction coefficient and mass loss than the as-forged sample. The wearmechanism of Zr702and the ZrTiAlV alloy in air at room temperature is abrasive wear,while the mechanism in vacuum at cryogenic temperature is adhesive wear. It was foundthat irradiation of low-energy proton has a little effect on friction-wear behaviors of Zr702and ZrTiAlV alloy either in vacuum at cryogenic temperature or in air at roomtemperature.