Fabrication And Properties Of Nanodiamonds Reinforced Titanium Metal Matrix Composites

Nano-diamonds?ND_s?have outstanding advantages,such as high strength,high hardness,good abrasion resistance,and non-toxicity.They are used in composite coatings,abrasives,and medical drug carriers,but the research which is used as reinforcing particles to strengthen metal are still in its infancy,and research on ND_s reinforced titanium-based composites is rare at home and abroad.However,the excellent performance of ND_s bonded titanium metal has potential application values and broad application prospects in biomedical and other fields.Therefore,in this paper,the preparation process,microstructure and properties of ND_s reinforced titanium matrix composites and their porous materials were studied in detail.Depending on solid solubility theory and reinforcement theory,the research ideas of this article were designed.Firstly ND_s contents?0,0.1wt%,0.25wt%,0.35wt%,0.5wt%?and sizes?5nm,100nm,200 Nm,3?m?were set,and then prepared the T_i MMCs via plasma sintering?SPS?process.The 5nm diamond was used as the research object and its content was set as a variable.The results showed when the sintering temperature is 1173 K,the heat preservation time is 10 min,and the sintering pressure is 60 MPa,a trace amount of T_iC phase is generated in the composites and the density can reach to 99.3%.The micro-hardness and Young's modulus of composites increased with the increase of ND_s content,and the yield strength showed a trend of increasing first and then decreasing.0.35wt.%ND_s/T_i composites had the best comprehensive mechanical properties:Compared with pure titanium,the hardness?52.3%?and the yield strength?23.7%?increased significantly,the Young's modulus?129 GPa?was acceptable,and the ductility?49%?slightly decreased.The wear resistance of 0.35 wt.%ND_s/T_i composites was the best?71.5%lower than that of pure titanium at 200 N load?.The corresponding wear mechanism changed from lapping wear to abrasive wear.The thermal conductivity decreased with the increase of ND_s content,but the overall reduction range was around 2 W/?m·k?.When 0.25 wt.%and 0.35 wt.%ND_s were added,because the sample was dense and ND_s/T_iC was difficult to corrode,the composite material had better corrosion resistance in saline and SBF solution at 25?.In addition,the results of cytotoxicity experiments showed that the cell viability of the ND_s/T_i composites was 6.7%higher than that of the blank control group,indicating that the composites have no cytotoxicity.The main reinforcement mechanism of ND_s/T_i composites is dispersion strengthening.Uniform dispersion of ND_s nanoclusters and a small amount of in situ generated T_iC phase can effectively hinder the movement of dislocations and strengthen the matrix.Based on the results of the ND_s content research,the second step was to set the diamond content to 0.35 wt%and set the size as a variable,the T_i MMCs were prepared under the same sintering parameters and had a density of 99.2%.As the diamond size increased,the density gradually decreased.The effect of 5 nm and 3?m diamonds on the composites were better.The hardness of the 5 nm ND_s/T_i composites was 27.4%higher than that of pure titanium.The yield strengths of the two samples were higher,and?_0.2.2 values were 1024 MPa and 1039 MPa respectively.When the diamond size showed nano-scale growth,that is,from 5 nm to 100 nm and200 nm,the dispersion strengthening effect weakened,and the mechanical properties of the composites became worse.As the diamond size increased,the ultimate compressive strain decreased from 51%?5 nm?to 39%?3?m?.The 5 nm ND_s/T_i composites had the best comprehensive mechanical properties:the hardness and yield strength increased significantly,and the ductility was better.The 3?m diamond composites had high strength and hardness,but at the same time,the ductility of the materials was sacrificed.Micro/nano-diamonds particles made the wear resistance of ND_s/T_i composites significantly improved.Among them,the composites with 5nm diamonds exhibited the best wear resistance?74.2%lower than that of pure titanium at 200 N load?.The thermal conductivity of the composite increased when the size of the diamond increased,but the overall rise range is small,about 1 W/?m·k?.The corrosion resistance of composites with 5nm ND_s was better in saline and SBF solutions at 25?.This showed that the 0.35wt.%ND_s/T_i composite with a size of 5 nm had the best overall performancetI which is caused by nanometer size effect.On the basis of the study of dense T_iMMCs,using SPS sintering and dissolving process,with the sintering temperature of 993K and 1123K which were preserved at 10 min and sintering temperature of 40MPa,NaCl and NaF pores with 5 nm ND_s/T_i porous composites were prepared respectively.The X-CT results showed when the porosity factor was 60%,the pores are uniformly distributed in the samples,and the particle diameters are respectively concentrated between 280-320?m and 36-106?m.As the porosity increased to 70%,the wall of the pores became thinner,and pore collapse and large area connectivity occurs.Among the porous materials with 60%porosity,the yield strengths of 0.35 wt.%ND_s/T_i composite reached the highest,respectively 62.54 MPa and136.48 MPa,which were 65.27%and 18.27%higher than that of pure titanium with the same porosity.As the porosity increased from 55%to 70%,the yield strength of the porous material continued to decrease.The SEM morphology analysis showed that the strengthening phases were mainly ND_s.Based on the comprehensive analysis,the macro-porous T_i MMCs composites are expected to be applied in the biomedical field,and the composite materials with small pores are expected to be used in the filtration separation field in corrosive environments.