Microstructure And Mechanical Properties Of Powder Metallurgy Ti-Zr Alloys

Ti-Zr alloys are widely used in medical and engineering applications,due to their high strength,high plasticity,strong wear resistance,non-toxicity,non-sensitization,and good biocompatibility.TiZr alloys are usually prepared by casting method.Its microstructure can be further adjusted and the strength needs to be increased.According to recent studies,the addition of small amounts of oxygen to titanium alloys can significantly increase strength without causing brittleness.The preparation of Ti-Zr alloy by powder metallurgy method,which is easier to regulate the organization and introduce more uniform solid solution oxygen compared with the casting method,but there are fewer related studies.The causes of elemental segregation and tissue evolution patterns are not clear enough.In this study,Ti-Zr alloys with high oxygen contents(about 0.4～0.6 wt.%)are prepared by powder metallurgy,which has heterogeneous microstructures with the “Zr-rich/Zr-poor zone” organization.The microstructure and mechanical properties of the Ti-Zr alloys were analyzed.The mechanism of plastic deformation is clarified.In addition,the Ti-Zr alloys need surface modification in the biomedical field,so the surface biological properties of the alloy are modified by anodic oxidation.The main conclusions are as follows:(1)Ti-Zr alloys with high oxygen contents have good tensile strength and good wear resistance.The Ti-15 Zr alloy has 18.6% elongation even at a yield strength of 900 MPa.Solid solution strengthening of Zr and O atoms is an important strengthening mechanism.The interstitial soluted O atoms can change the slip pattern,and significantly improve the strength of the material by exciting the cross-slip migration of the spiral dislocations.(2)Heat deformation processing can change the “Zr-rich/Zr-poor zone” organization and improve the mechanical properties.Fine Zr-rich laths can be obtained after hot extrusion,while fibrous Zr-rich strips can be obtained after hot rolling.The Ti-15 Zr alloy in the rolled state has a yield strength of about 1000 MPa and plasticity of up to 20%,which is better than other Ti-Zr alloys reported.In addition,the Ti-15 Zr alloy has good fatigue properties,which is higher than the ISO 14801 international standard by 55%.The strengthening mechanism of the material includes the effect of Zr-rich striations forming incomplete hindrance to slip,fine grain strengthening,and dislocation strengthening by cross-slip migration.(3)The powder metallurgy Ti-Zr alloy has good dynamic mechanical properties,obvious strain rate strengthening effect,high flow stress,and excellent thermal softening resistance.The dynamic mechanical curves of Ti-Zr alloy can be described and fitted by using models,among which the J-C intrinsic model can fit well below 300 ℃,while the BP neural network model can better fit at 700 ℃.(4)Powder metallurgy Ti-15 Zr alloys were anodized and formed nanotube surfaces with micro/nano-scale structures.The formation of this micro/nanoscale structure is mainly due to the preferred orientation and heterogeneous microstructure of the matrix.When the as-cast Ti-15 Zr alloys were anodized,only nanotubes with nano-scale structures formed.The micro/nano-scale nanotube surfaces have higher roughness and hydrophilicity,which can promote protein adsorption and cell proliferation.Thus,this surface modification method improves the biocompatibility of Ti-Zr alloys.In this study,Ti-Zr alloys with a heterogeneous structure were prepared by powder metallurgy method.By adding oxygen and deformation,Ti-Zr alloys achieve excellent dynamic and static mechanical properties.The Ti-Zr alloys have good biocompatibility through surface modification.Therefore,powder metallurgy Ti-Zr alloys can be used for medical and engineering applications.