Study On Microstructure Regulation And Mechanical Properties Of Biomedical TiZrNbB Alloy

As a new type ofβmedical titanium alloy,Ti₄₅Zr₄₅Nb₁₀（TZN）alloy has many excellent properties,such as elastic modulus,high biocompatibility,good corrosion resistance,non-toxicity and good processability,so it has a broad application prospect in the field of biomedical implant materials.However,the low strength of TZN alloy limits its application in the field of orthopedic implants.In this study,trace boron was added to TZN alloy by composition design.After recrystallization heat treatment and aging heat treatment,the microstructure and mechanical properties of as-cast,recrystallization heat treatment and aged Ti Zr Nb B（TZNB）alloys were analyzed by means of XRD,SEM,EBSD and universal testing machine,and a new type of medical TZNB alloy with high strength,high plasticity and low elastic modulus was obtained.Firstly,(Ti₅₀Zr₅₀)_90-xNb₁₀B_x（x=0、0.1、0.3、0.5、1.0、4.0 at%）alloy ingots were prepared by vacuum arc melting furnace.After adding boron element,the as-cast TZNB alloy is composed ofβphase and Ti B phase.With the increase of B content,theβgrain of the alloy is obviously refined,and the number of Ti B compounds is also increased,which gradually changes from dispersion distribution in the matrix structure to a large amount of precipitation at the grain boundary and dendritic arm.The yield strength and tensile strength of TZN alloy are 635 MPa and 642 MPa,respectively,and the elongation is 22.1%.With the increase of boron content,the strength and hardness of TZNB alloy increase and the elongation decreases.When boron content is 0.5%,the yield strength and tensile strength of the alloy are the highest,732 MPa and 758 MPa,respectively,and elongation is 12.9%.When the boron content is 1%,the microstructure of alloy changes from equiaxedβstructure to dendritic structure.Moreover,the strength and elongation of TZNB1.0 alloy decrease greatly,and its yield strength and tensile strength are only 640 MPa and 665 MPa.Secondly,TZNBx（x=0、0.1、0.3、0.5 at%）alloy ingots were rolled and recrystallized at 550℃,600℃and 650℃.After recrystallization heat treatment at 550℃,only partial recrystallization occurs in the alloy,and the TZN alloy without boron element is a singleβphase.After a small amount of B element is added,α"phase is formed in theβphase matrix of TZNB alloys.With the increase of boron content,the strength,elastic modulus and hardness of the alloys increase,but the elongation decrease.The yield strength,tensile strength and elastic modulus of TZNB0.5 alloy are the highest,about 821 MPa,860 MPa and75 GPa,respectively,while the elongation is only 6.1%.After recrystallization heat treatment at 600℃,the recrystallization process of the alloy was basically completed,andα’phase was precipitated in the TZN alloy without boron.During the tensile process,the alloy appeared the"double yield phenomenon",resulting in the tensile strength and elongation of TZN alloy reaching 796 MPa and 18.4%,respectively.However,with the addition of boron,the double yield phenomenon disappears,the their mechanical properties of the alloys are consistent with those of the recrystallization heat treatment samples at 550℃.TZNB0.3 shows good comprehensive mechanical properties,with the highest yield strength and tensile strength of752 MPa and 804 MPa,elongation 13.3%,elastic modulus 65 GPa.When the recrystallization heat treatment temperature is increased to 650℃,the grain size of TZN alloy without boron is about 29.9μm.Compared with the sample recrystallization heat treatment at 600℃,the grain size grows up about 2.4 times.The tensile strength and elongation are greatly reduced,which are only 540 MPa and 11.5%,respectively.However,Ti B pahse has an obvious inhibitory effect on grain growth in TZNB alloy containing boron.The grain sizes of TZNB0.1,TZNB0.3 and TZNB0.5 alloys grow only slightly,which are 10.4μm,8.3μm and7.8μm,respectively.With the increase of boron content,the strength of TZNB alloy first increases and then decreases,while the plasticity gradually decreases.The yield strength and tensile strength of TZNB0.3 alloy are the highest,about 748 MPa and 786 MPa,respectively.Finally,the aging treatment of recrystallization heat treatment TZNB0.3 alloy at 600℃shows that the hardness and elastic modulus increase,while the plasticity decreases after low temperature aging（300℃and 350℃）.With the increase of aging temperature to 400℃and450℃,the content and size ofαphase increase,and the strength,hardness and elastic modulus of the alloy also increase.After aging at 450℃,the yield strength and tensile strength of the alloy are 807 MPa and 849 MPa,respectively.After aging at 500℃,the microstructure of the alloy is agingβphase,and the elastic modulus,hardness,tensile strength and elongation of the alloy decrease.After short aging at 450℃for 1 h and 2 h,the strength,hardness and elastic modulus of TZNB0.3 alloy increase with the increase ofαphase content.After aging for 4 h,the strength,hardness and elastic modulus of alloy decrease due toαphase coarsening.After aging for 6 h,a large amount ofαphase precipitates in the alloy,which leads to the increase of strength,hardness and elastic modulus and the decrease of elongation.TZNB0.3 alloy has a good combination of mechanical properties after aging at450℃for 2 h,its yield strength,tensile strength,is,elongation and elastic modulus are 838MPa,889 MPa,13.1%,and 65 GPa,respectively.Compared with as-cast TZN alloy,the yield strength and tensile strength respectively increase by 203 MPa and 247 MPa.