| Titanium and titanium alloys show good development prospects in aerospace,deep sea exploration,biological medicine and other fields because of their many excellent properties.In this paper,nano-diamond(ND)with higher strength and hardness is selected as the reinforcing phase,which is uniformly distributed on the surface of TC4 powder through mechanical ball milling,and then ND /TC4 composite material is prepared quickly and efficiently through spark plasma sintering technology.A new idea of heterogeneous structure is introduced into the material,which is a great innovation in the field of titanium matrix composites.It is expected that with the addition of ND and the design of heterogeneous structure,the overall properties of the composites can be significantly improved.The main research contents and results are as follows:(1)The effects of the shape and chemical composition of TC4 powder on the microstructure and properties of TC4 powder were studied.TC4 powders come in two forms-spherical and irregular.The sintered ND /TC4 composites were tested.The results show that the ND /TC4 composite sintered with irregular TC4 has many holes,and the density is less than 98%,which is obviously lower than that of the composite sintered with spherical TC4.Although the strength of the material is improved,the tensile plasticity is very poor,and its compression plasticity is far less than that of the spherical TC4 powder sintered with the same proportion of ND composite material.Then the influence of the preparation method of the composite material was explored.The sample was prepared by thermal diffusion method.The presence of ND and titanium carbide was not found by scanning electron microscopy and line scanning analysis.From XRD,it was found that titanium carbide was produced on the surface of the sample.In general,spherical TC4 powders show better properties,and SPS sintering is a better preparation method.(2)The effect of ND content on the microstructure and properties of ND /TC4 composites was studied.Spherical TC4 powder has fine powder size of 10-50 ?m,coarse powder size of 50-105 ?m,and average ND powder size is 5 nm.With the addition of ND,the microhardness of the composites is greatly improved,up to368.8.The microhardness of pure TC4 is 330,which is increased by about 11.76%.The maximum yield strength of compression test is 1177 MPa,and the yield strength of pure TC4 is 1013 MPa.The best comprehensive performance is 0.5% ND /TC4 composite,whose elongation is 34.7% and yield strength is 1156 MPa,which is14.12% higher than pure TC4.(3)The effect of the coarse and fine crystal ratio of TC4 matrix on the microstructure and properties of the composite was studied.With the decrease of the ratio of coarse and fine grains and the addition of nano-diamond(ND accounts for 5% of the total mass of ND and fine powder),the strength and hardness of the composites are improved,and the micro-hardness is up to 382.Compared with pure TC4,the hardness increased about 15.76%.The yield strength and elongation of the compressive properties are 1225 MPa and 32.2% respectively.The highest tensile strength reaches 1017 MPa and 1045 MPa respectively,and the lowest elongation is 17.8%.The high ductility is retained while the strength is increased.In terms of the strengthening and toughening mechanism,the reinforcing phase ND and titanium carbide are distributed around the TC4 matrix,forming a network boundary,which constrains and restricts the deformation of the matrix,and thus producing a synergistic strengthening effect.The reinforcing phase is distributed around the matrix discontinuously and the coordinated deformation can still occur between adjacent grains.In addition,the effect of the coarse and fine grains of the heterogeneous structure can increase the strength of the material,while the plasticity is still retained to a certain extent. |
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