Microstructures And Mechanical Properties Of Pure Zr And Ti-Zr-based Alloy Subjected To Thermomechanical Processing

Pure Zr and Ti-Zr-based alloys characterized by high specific strength, excellentcorrosion resistance and fatigue properties, are specially applied as structural componentsin aerospace area, shipping industry and nuclear industry. However, their strength,ductility and fracture toughness are usually exclusive; as a result, low ductility andtoughness greatly limit the applications of hcp materials of high strength. Therefore, it issignificant to achieve the optimum combination of high strength and good ductility andfracture toughness of Pure Zr and its alloys. In this paper, the subjects about themicrostructures and mechanical properties of pure Zr and TiZr51alloy are studied byemploying tensile testing, small puch test and Ansys finite element analysis, X-raydiffraction (XRD) and optical (OM) and transmission electron microscopy (TEM)techniques as following:Small puch test is now adopted to evaluate the fracture toughness of samples with smallsizes. Through studying and evaluating several common alloys, it is confirmed to befeasible to use the combination of small puch test and conventional compact tension withthe local strain energy density as the medium for evaluating the fracture toughness ofmaterials with small sample sizes. It is also proved to be reliable to evaluate the fracturetoughness of disc-like small samples with0.3mm-thickness and10mm-diameter using thesmall puch test.By employing the combination of severe cold rolling and heat treatment, wesuccessfully prepare a tri-modal microstructure consisting of primary αplarge grainscombined with coarse α plates and acicular α″precipitates in TiZr51alloy. The effect ofthe aging parameters on the microstructures and mechanical properties of TiZr51is alsostudied. By properly tailoring processing variables, a good balance of high strength andreasonable ductility and fracture toughness can be achieved in TiZr51alloy.By employing a combination of cryorolling and thermal annealing treatment, we havesuccessfully produced multi-modal Zr of different-volume-fraction coarse-grains (CG).The strength of the multi-modal Zr follows approximately the rule-of-mixtures with CG volume fraction, while the ductility in the rolling direction deviates positively from therule-of-mixtures, which may result from the existence of strong (002) texture. Anappropriate grain size distribution favors an optimum combination of high strength andhigh ductility and fracture toughness.