Effect Of Si And GNP Addition And Sintering Process On Microstructure And Properties Of Ti-18Mo Alloy Prepared By High-Energy Ball Milling

The Ti-18Mo,Ti-18Mo-0.5Si,Ti-18Mo-1Si and Ti-18Mo-2Si alloys were prepared by vacuum and spark plasma sintering.Composite materials of Ti-18Mo-0.5Si-0.02GNP,Ti-18Mo-0.5Si-0.04GNP,Ti-18Mo-0.5Si-0.06GNP and Ti-18Mo-0.5Si-0.08GNP were prepared by spark plasma sintering.The sintering morphology and phase composition,porosity,hardness,high temperature oxidation resistance and corrosion resistance were analyzed.The research results are as follows:?1?The sintered phase composition of the material were analyzed.The phases of the two alloys prepared by two process are similar.Ti-18Mo alloy mainly has Ti and Ti_xMo_y and the Ti-18Mo-xSi alloy also has Mo₅Si₃,TiSi,Ti₅Si₄ and Ti₅Si₃ phases.In addition to the above phases,composite materials also has MoC,TiC and SiC phases.?2?The porosity and microhardness of the material were examined.Ti-18Mo-0.5Si has the highest density?VS:6.84%;SPS:3.44%?,which is 50%higher than Ti-18Mo.Compared with the four composite materials,the porosity of Ti-18Mo-0.5Si-0.04GNP?3.36%?,which is 2%lower than that of Ti-18Mo-0.5Si alloy.Among them,Ti-18Mo-2Si?VS:1098.3HV;SPS:1108.1HV?has the highest hardness among the four alloys.Among the four composite materials,Ti-18Mo-0.5Si-0.04GNP has the highest hardness?1389.1 HV?and nearly 34%higher than Ti-18Mo-0.5Si alloy?1032.4 HV?.?3?The oxidation performance of the alloys and composite materials at 700?,800?and 900?for 100 h was studied.The surface oxidation products of matrix and composite are mainly anatase or rutile TiO₂,SiO₂ and TiO phase.Among the alloys,the oxidation resistance of Ti-18Mo-0.5Si alloy is the best.The weight gain of Ti-18Mo-0.5Si by VS is 4.09 mg·cm^-2 and the K⁺of it is 0.37 mg^-2·h^-1.Ti-18Mo-0.5Si by SPS has the least weight gain with 3.52 mg·cm^-2 and 2.97 mg·cm^-2 and the smallest K⁺with 0.11 mg^-2·h^-1 and 0.14 mg^-2·h^-11 at 700?and 800?respectively,and the oxidation kinetics curves in accordance with the law of the cubic oxidation.Ti-18Mo-0.5Si-0.04GNP has the least oxidation weight gain at 800?and 900?(2.92mg·cm^-2 and 3.21 mg·cm^-2 respectively,which is about 25%lower than the matrix.Oxidation law of it conforms to cubic law,which has the best oxidation resistance.In addition,the oxidation performance of the SPS alloys at 700?is better than 800?,and that of the SPS composite at 800?is better than 900?.?4?The corrosion performance of the alloys and composites in HCl solution with the concentration of 1 mol/L for 100 h was investigated.Among the four alloys,Ti-18Mo-0.5Si has the best corrosion resistance,which has the complete corrosion layer with only 15?m and least weight loss of 7 mg·cm^-2.Ti-18Mo-0.5Si-0.04GNP has the flat corrosion surface and the least corrosion depth of only 5?m reduced by about 66.7%compared with the matrix.?5?The effects of two sintering processes on the matrix alloy were analyzed.The differences mainly included the phase composition,porosity and oxidation resistance of the sintered phase.After SPS sintering,the amount of more phases such as Mo₅Si₃and Ti₅Si₃ are more due to the diffusion between Ti,Mo and Si,which improves the density and hardness of the titanium alloy.So the oxygen can be better blocked in the high temperature oxidation test,which improves oxidation resistance.In general,the material properties prepared by the SPS sintering process are superior to that by vacuum sintering process.In summary,the addition of Si and GNP can improve the hardness,oxidation and corrosion resistance of the Ti-18Mo alloy.Among them,the Ti-18Mo-0.5Si and Ti-18Mo-0.5Si-0.04GNP have the best comprehensive performance,which provides the basis for the development of Ti-18Mo alloy.