Study On The Microstructure And Mechanical Properties Of Ti-6Al-4V Doped With Rare Earth Admixtures

Ti-6Al-4V titanium alloy has been widely used in aerospace and biomedical fields due to its stable structure,excellent corrosion resistance and good biocompatibility.However,Ti-6Al-4V titanium alloy has poor plasticity,wear resistance and severe work hardening at room temperature,which limits its application range.In order to solve this problem,this research uses spark plasma sintering(SPS)process optimization and the addition of rare earth compounds(Y₂O₃,YH₂ and YbB₆)were used to improve the mechanical properties of Ti-6Al-4V titanium alloy.The experimental results show that the best parameters of SPS are as follows:sintering pressure 30 MPa,sintering temperature 1100°C,heating rate 100°C/min,and holding time 5min.The results of research on rare earth admixtures have found that the type and amount of rare earth compounds have significant effects on the microstructure and mechanical properties of titanium alloys.When Y₂O₃ is added to the titanium alloy,the microstructure of the Ti-6Al-4V+x Y₂O₃ composite prepared by SPS sintering changes from Widmanstatten structure to bi-modal structure,and the grains were significantly refined.When the amount of Y₂O₃ added was0.7wt%,the density and Vickers hardness of the prepared composite material were 99.35%and392HV,respectively;the tensile yield strength,maximum tensile strength and elongation also increased to 913MPa,1088MPa and 7.9%.SEM analysis found that the fracture mode of the composite prepared after adding Y₂O₃ was ductile fracture.When YH₂ is added to the titanium alloy,the microstructure of the prepared Ti-6Al-4V+x YH₂ composite material changes from lamellar?and intergranular?,the?phase becomes coarse and tends to be lamellar,and the structure is mainly composed of?phase and transform?phase.And after YH₂ is added,Y₂O₃ is generated in the composite material through in-situ reaction.The Y₂O₃ generated in-situ is mainly distributed in the crystal,and a small part is distributed at the grain boundary,which has an inhibitory effect on the growth of crystal grains.When 0.5wt%YH₂ is added,the density and Vickers hardness of the prepared composite material are 99.50%and 565HV,respectively;the compressive yield strength and maximum compressive strength are increased to 1740MPa and 2199MPa,respectively.The research results of YbB₆ show that Ti B and Yb₂O₃ generated by in-situ reaction will appear in the sintered Ti-6Al-4V+x YbB₆ composite material.The generated Ti B has high elastic modulus and hardness and good chemical compatibility with Ti matrix.When the amount of YbB₆ added is 0.6wt%,the density and Vickers hardness of the prepared composite material are 99.43%and 403HV,respectively;the tensile yield strength,maximum tensile strength and elongation are increased to 903MPa,1148MPa and respectively 4.3%.The fracture form of the composite material prepared after adding YbB₆ is a mixed fracture of toughness and brittleness.The comprehensive research results found that the addition of Y₂O₃significantly improves the toughness of the titanium alloy composite material,and the mechanical properties are also superior due to the effect of fine-grain strengthening;the addition of YH₂ greatly increases the hardness of the titanium alloy composite material,so the wear resistance is improved,the compressive strength is also greatly improved,because the in-situ reaction greatly improves the deoxygenation effect of the composite material,but the material is too brittle;after adding YbB₆,an in-situ reaction will occur to produce Ti B whiskers and Yb compound particles,resulting in Ti B in the form of long blocks and whiskers exists inside the crystal grains and has a hexagonal cross section,which is conducive to the improvement of the strength of the titanium alloy composite material.