| The good bioco MPatibility and corrosion resistance of pure Ti and β-Ti alloys have attracted much attention in the research and application of medical implantation.However,when pure Ti is implanted into the human body as a load-bearing component,it has the problem of low strength and large elastic modulus,which leads to the phenomenon of "stress shielding" and results in the final failure of implanted component The laminated composite of pure Ti andβ-Ti alloy can combine the good plasticity of pure Ti with the high strength and low modulus of β-Ti alloy to meet the mechanical properties of medical implant materials.Besides,in addition to the differences in composition,microstructure isomerism can also be introduced to further improve the mechanical properties of the composites.Based on this,in this paper,Ti-15 Mo and Ti-36Nb-2Ta-3Zr-0.35O(TNTZO for short),the two β-Ti alloys with significantly different phase transition temperatures were used as reinforcement layers,and two kinds of Ti/β-Ti alloy laminated composites were prepared preliminarily by spark plasma sintering: Ti/Ti-15 Mo laminated composite and Ti/TNTZO laminated composite.By taking Ti/Ti-15 Mo laminated composite as an example,the densification behavior and interfacial diffusion behavior of Ti/β-Ti alloy laminated composite during sintering were studied,and the corresponding densification mechanisms were revealed.Besides,the heterogeneity of microstructure in Ti layer and β-Ti alloy layer was realized by two different subsequent processes for the sintered Ti/β-Ti alloy laminated composites,and the microstructure evolution and mechanical behavior of the composites were systematically studied(1)By taking Ti/Ti-15 Mo laminated composite as an example,the densification mechanisms of Ti/β-Ti alloy laminated composite during sintering were revealed.When the sintering temperature is relatively low(600～700 ℃),both grain boundary sliding and dislocation climbing mechanisms are activated simultaneously to achieve the densification;the dislocation climbing mechanism is predominated at a medium sintering temperature(750～800℃);whereas the grain boundary sliding mechanism is more preferred at a high temperature above 850℃.Besides,the study of interfacial diffusion behavior shows that an obvious diffusion interfacial layer is formed between Ti layer and β-Ti alloy layer after spark plasma sintering,whose microstructure is mainly composed of α+β dual phase,and a small amount of transition phase,such as α’ phase and ω phase formed at higher sintering temperature.(2)For the β-Ti alloys with high phase transition temperature(such as Ti-15Mo),the preparation process of Ti/β-Ti alloy laminated composite by spark plasma sintering,hot rolling,and pre-deformation was obtained.After pre-deformation,the grain of Ti layer in Ti/Ti-15 Mo laminated composite is slightly elongated,and there are a certain number of deformation twins in Ti-15 Mo layer.These deformation twins induced by pre-deformation can improve strength and plasticity to a certain extent.The elastic modulus,elongation,yield strength and tensile strength of the composite after 5% pre-deformation are 73 GPa,23.6%,708 MPa and 810 MPa respectively.(3)For the β-Ti alloys with low phase transition temperature(such as TNTZO),the preparation process of Ti/β-Ti alloy laminated composite by spark plasma sintering,hot rolling with heat treatment,cold rolling and partial recrystallization annealing was obtained.After partial recrystallization annealing at 650℃,the Ti layer in Ti/TNTZO laminated composite presents equiaxed grains,while the TNTZO layer presents deformed structure.The composite exhibits an elastic modulus of about 82 GPa,an elongation of about 23.5%,a yield strength of549 MPa and a tensile strength of 705 MPa.(4)The effect of interfacial layer on the mechanical properties of Ti/β-Ti alloy laminated composites was revealed.Although the direct contribution of interface layer to the overall strength and plasticity of composites is limited.However,the restraint effect caused by the interface layer can lead to hetero-deformation induced strengthening and additional strain hardening.At the same time,the interface layer can also adjust the deformation and hinder the crack propagation,which improves the strength and plasticity of Ti/β-Ti alloy laminated composites. |
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