High-throughput Study On The Mechanical Properties Of BCC Ti-Nb-Zr-(Cr,Mo,Ta) Alloys And Its Applications

The demand for hard tissue implants is increasing in the clinical applications,which provides a huge market for the biomedical implant materials and puts forward higher requirements for the development of high-performance and non-toxic biomedical metallic materials.Compared with traditional biomedical metallic materials such as stainless steel,cobalt-based alloys and commercial pure Ti,Ti-Nb-Zr based Ti-alloys with the single BCC phase have received extensive attention due to their lower Young’s modulus,excellent corrosion resistance and biocompatibility.Apart from biocompatibility and corrosion resistance,the mechanical properties are also vital to the development of biomedical metallic materials.Up to now,the investigations on the mechanical properties of Ti-Nb-Zr based multicomponent Ti-alloys with the BCC phase is extremely limited.Therefore,this work used the combination of the diffusion couple,nanoindentation and electron probe microscopy(EPMA)techniques for the high-throughput determination of the mechanical properties such as Young’s modulus and hardness,and then the CALculation of PHAse Diagrams approach(CALPHAD)was used to construct the corresponding Young’s modulus databases.Finally,the multicomponent alloys with low Young’s modulus and high hardness were found according to the present mechanical properties database,and the key experimental verifications such as microstructure,mechanical properties,electrochemical corrosion and tribological properties were carried out.The mainly contents of this thesis are as follows:Firstly,31 groups of the single-BCC-phase diffusion couples in Ti-Nb-Zr-(Cr,Mo,Ta)systems were experimentally prepared.Secondly,the nanoindentation test was carried out near the interface of the diffusion couples.The hardness and Young’s moduli at each indentation positions were obtained by the Oliver-Pharr analysis method,and the elastic recovery of the alloy were calculated through the corresponding load-displacement curve.The relationship between “indentation position-Young’s modulus-hardness-elastic recovery” was obtained.And then,the composition gradients near the diffusion couple indentation were detected by the EPMA to obtain "indentation position-composition".Thus,the databases of "composition-Young’s modulus-hardnesselastic recovery" was established.Based on the measured Young’s moduli,the Young’s modulus databanks of BCC Ti-Nb-Zr-(Cr,Mo)systems were predicted by the CALPHAD method.Finally,the alloy composition suitable for clinical application was found from the predicted Young’s modulus databank,and the key experimental verification of microstructure,nanoindentation,compression,Vickers hardness,electrochemical corrosion and wear are characterized.In this thesis,the Young’s moduli and hardness of the BCC Ti-Nb-Zr-(Cr,Mo,Ta)systems within a wide composition range were determined by using the high-throughput method,and the relationship between mechanical and wear properties was obtained.The Young’s modulus databases of the BCC phase Ti-Nb-Zr-(Cr,Mo)systems were successfully established by the CALPHAD method.Moreover,a Ti-22.6 Nb-30Zr-3.8 Cr(at.%)(TNZC)alloy with a low Young’s modulus(57.42 GPa)was predicted from the Young’s modulus database.Its Young’s modulus and hardness measured from the nanoindentation test were 53.55±0.32 GPa and 3.37±0.04 GPa,respectively,which were consistent with the predicted results and can verify the reliability of the predicted Young’s modulus databank.Combined with the other key experiments,the results showed that the TNZC alloy has a high hardness and strength,low Young’s modulus,nice corrosion current density and wear rate in the simulated body fluids,which is expected to be a new generation of high-performance surgical implant materials.