Research On Preparation, Microstructure And Mechanical Properties Of Ultrafine Grained Ti-3Zr-2Sn-3Mo-25Nb Alloy

In recent year, more and more attention has been focused on ultrafine grained (UFG)metal material cause it has a lot of advantages of high strength, high hardness, superplastic, elastic modulus, abrasion resistance and high fatigue strength and so on. Using severe plastic deformation (SPD) to prepare UFG metal material has some advantages such as strong grain refining ability, not introducing pores and impurity and it can prepare bulk UFG metal material, so it has a broad application prospect. Several methods have been extensively studied, such as Equal Channel Angular Pressing (ECAP), Accumulative roll-bonding(ARB), High Pressure and Torsion(HPT), Multiple Forging(MF), Cyclical Extrusion-Compression(CEC), Repetitive Corrugation and Straightening(RCS) and so on.Ti-3Zr-2Sn-3Mo-25Nb (TLM for short) alloy developed by Northwestern institute for nonferrous metal research independently is a metastable β-type biomedical alloy with excellent synthesis mechanical properties and without toxic element. It is low density, high yield strength, low elastic modulus, anti-corrosive, easily processed and low cost therefore, as dentalimplant, bone joint’s substitution material and stent, it has broad application prospect in biological and medical. To further improve its mechanical properties, extend the limits of application, this paper use one of a SPD method, an improved ARB, to prepare UFG TLM sheets.OM, SEM, TEM, XRD was used to observe the microstructure evolution in the sheets. Instron universal testing machine was used to test the strength, plasticity and elastic modulus of the sheets. Then analyze the relationship between microstructure and mechanical properties. From this experiment, some conclusions are as follows:Using this improved ARB technique and common rolling mill, we can prepare UFG TLM alloy sheets. Clear confine in the middle of the2layer sheets was observed by OM.4layers,8layers,16layers sheets have good composite. There is no significant confine, and bonding strength approach matrix strength. The interface of sheets was observed by SEM, and through analysis, mechanism of interface composite is crack-combine mechanism.Observed by TEM, grain size of UFG2layers sheets is about150-200nm. In the sheets, substructure and high density dislocation can be observed in grain. And grain is surrouded by low angle boundaries; grain size of UFG4layers sheets is about150nm. The proportion of the uniform UFG organization has increased. Grain boundaries are still low angle boundaries. Grain size of UFG8layer sheets was80-90nm. Dislocation walls are refined to sub-boundary. Uniform UFG organization surrounded by high angle boundaries is found in material. Grain size of UFG16layers sheets is further refined, and high angle boundaries surround the UFG organization.The mechanical properties of UFG TLM alloy sheet are as follows:(a) Strength:With layers and strain increasing, the yield strength and tensile strength of UFG sheets increases, tensile strength of8layers is1200MPa, which is49%higher than as-received material,(b) Elongation:With layers and strain increasing, elongation increases. Elongation of UFG8layers sheets achieves5%, which is4.3times of as-received material. Elongation of16layers sheets decreases.The modified accumulative roll-bonding technique make mechanical properties of sheets improved. Strength and elongation increase. UFG8layers sheets has the best mechanical property:Yield strength and tensile strength is955MPa and1200MPa respectively. Elongation is5%and microhardness is391MPa. To compare with as-received material, UFG8layers foil is2.14times,1.49times,4.3times and1.45times of as-received material respectively.