Experimental And First-princinples Study On The Strenth And Ductility Of O/Si Solid Solution Strenthened Ti Alloys

Due to its high specific strength and stiffness,good corrosion resistance and creep resistance,Ti alloys have broad application prospects in aerospace,petroleum equipment,biomedicine and other fields.Nevertheless,most of the Ti alloys are consisting of expensive chemicals,such as Ta and Nb,V,Co,Cr,Ni,and Mo.These expensive elements,which not only increase the cost of Ti alloys,but also has certain toxicity,limiting their application in the biological field.If non-toxic and inexpensive metal or non-metallic elements,as well as traditional impurity elements such as O and N,can be used as alloying elements to prepare Ti alloys,while coordinating their strength and plasticity,it can further promote the application of Ti materials in production with low cost advantages,which has important engineering value and academic significance.In this paper,α-Ti alloys strengthened by the replacement type(Si)and interstitial type(O)atomic solid solution were prepared by powder metallurgy method,the effect of the type and content of solid solution atoms on the lattice parameters and mechanical properties of Ti alloys was investigated by OM,SEM,XRD analysis,hardness test,tensile test at room temperature.Based on the square,electronic density of state and differential charge density,the effect of O and Si atom solid solution on the strength and plasticity of Ti alloys is proposed.The criterion of plastic damage of Ti alloys and the mechanism of strong plasticity are revealed from the electronic scale.The results have important guiding significance for the preparation of strong plastic compatible Ti alloys that meet industrial needs.The main conclusions of this paper were as follows:1.With the increase of O content,c/a gradually increased from 1.5905 to 1.5935,with a growth rate of 0.0057/1 wt.%O.With the increase of Si content,c/a gradually decreased from 1.5905 to 1.5860,with a decrease rate of 0.0050/1 wt.%Si.The microstructure of Ti-O alloy and Ti-Si alloy prepared by powder metallurgy mainly consisted of equiaxed precipitated at one time α-Ti and needle-like secondary precipitation α-Ti composition.2.Both O and Si can improve the hardness and strength of Ti alloy,and the strengthening effect of O in interstitial solution is better than that in replacement solution.while O decreases the elongation of Ti alloy,and Si increases first and then decreases the elongation of Ti alloy.Both Ti-O and Ti-Si alloys exhibit a complex quasi cleavage fracture with morphology including dimples,tear edges,cleavage steps,and microcracks.3.The simulation results showed that with the increase of O content,c/a value of Ti gradually increased from 1.5940 to 1.6170,with a growth rate of 0.0467/1wt.%O.With the Si content increased,c/a gradually decreased from 1.5940 to 1.5860,with a decrease rate of 0.025/1wt.%Si.The simulation results agreed with the experimental results,This indicated that simulation can provide scientific guidance for experiments.4.With the content of O and Si increased,the strong hybridization between the p-electron orbitals of Ti atoms and the p-electron orbitals of O and Si atoms gradually increased,indicating that the covalent bond like properties of the alloy gradually increased.The bonding strength between Ti-O and Ti-Si gradually increased,thereby improving the strength of Ti alloys.The solid solution of O and Si atoms will cause the rearrangement of electrons,with the content of O increased,the charge density between other Ti atomic layers decreased,resulting in a decrease in the bonding strength between other Ti atomic layers,which was the reason why O solid solution reduces the elongation of Ti alloys.However,with the addition of Si atoms,the charge density between different Ti atomic layers increased simultaneously,indicating that within a certain range,Si can increase the elongation of Ti alloys.5.Based on the tensile strength and added element content,the strengthening efficiency criterion was given,and the strengthening effect of O and Si was better than that of Si.Combining elongation and c/a value,the elongation criterion was given:the range of c/a value with good elongation in the experiment was 1.5876-1.5910;The range of c/a values corresponding to good simulated elongation is 1.5905-1.6040.According to the simulation results,Ti-SiO2 alloys were prepared to verify the strong plasticity criterion.With the increase of SiO2 content,the tensile strength increased continuously,and the c/a value increased from 1.5879 to 1.5919,while the elongation decreased from 33.5%to 4.0%.When the SiO2 content was 1.0wt.%,the c/a value was 1.5915,and the elongation began to drop abruptly,verifying that the elongation criterion was reliable.