Strengthening And Microstructure Evolution Of Zr-Ti Binary Alloy

Zirconium is abundant in the earth. And the cost of sponge Zr is close to sponge Ti. Pure Zr and Zr alloys with small neutron absorption cross section, irradiation resistance and corrosion resistance, are widely used in the nuclear industry. Except the usage of Zr alloys in the nuclear industry, no other wide application of Zr alloys has been reported because no efficient way of strengthening and toughening is found.In the past, moving components in spacecrafts are mainly made by various steels. But steels have some disadvantages like high denstiy(difficulty in lightweight), large expansion coefficient(affection in precision of space mechanisms) and short life in spcae enviroment. Considering that Zr alloys are successfully used in nuclear industry, they should have the potential to resist the space irradiation and the corrosion of atomic oxygen. As Zr alloys also have low density and small expansion coefficient, they are important to lightweight and operation precision of spacecraft moving mechanisms. Therefore, Zr alloys are considered in this work to have great potential to be used in space environment.Traditional Zr alloys, which have been used in nuclear industry are normally with low strength and toughness, and do not meet the requirements as space componet materials. New Zr-based alloys with excellent mechanical properties are needed. This paper aims to develop a new type of Zr alloys for spacecraft component. Detailed studies are carried on about the relationship among composition, mechanical properties, phase transformation and microstructure evolution and strengthening mechanism of Zr-Ti binary alloy. An optimization composition of Zr-Ti binary alloy with good mechanical properties is discovered. Also, the preparation techniques for Zr-Ti binary alloys are investigated.Zr and Ti can form a continuous solid solution, so the alloy compostions can be adjusted in a large range. A series of different compositions of Zr-Ti binary alloys are prepared and the effects of composition on microstructure and mechanical properties are investigated on Zr-Ti binary alloys with different conditions. The results show the strength of Zr-Ti binary alloys are increased with Ti content. Zr50Ti50 alloy has the maximum strength at 1170 MPa. The main strengthening mechanisms of Zr-Ti binary alloys are solution strengthening and grain refinement.The optimum composition is found to be Zr50Ti50 through the hot-rolled process. The tensile strength is 1063 MPa with elongation of 7%. A large amount of nano twins are found in hot-rolled Zr50Ti50 alloy which improve the plastic deformation ability of Zr-Ti alloy. According the results, a new strengthening and toughening mechanism by nano twins is found. This may provide a new method for strengthening and toughening of Zr alloys.Thermal deformation simulation tests are conducted by Gleeble-3500 with different conditions. The true stess-strain curves are obtained. The thermal deformation activation energy is calculated(Q = 103274.9J/mol). The main thermal deformation mechanism is found to be dynamic recovery through the analysis of the thermal deformation activation energy and microstructure. Also the constitutive equation is created. The processing map for hot working shows the optimum hot working condition(T = 830~850°C, rate = 0.56~1s-1) and instability region.Widmanstatten microstructure is showed to suffer the plasticity of forged Zr50Ti50 alloy. An efficient way to eliminate widmanstatten microstructure is by solid solution treatment. With such a treatment, the elongation of Zr50Ti50 alloy reaches 8%.