Microstructure And Mechanical Properties Of Porous Titanium By Spark Plasma Sintering

As storage materials,pure titanium can be used to storage thermonuclear fusion reaction energy of tritium and deuterium.Generally,the helium generated by tritium decay will gather at the grain boundary,when its concentration exceeds the critical threshold will cause materials failures eventually.It is expected to improve the materials properties of storage tritium and helium by refining grains and introducing pores.At present,porous titanium alloy is mainly prepared by powder metallurgy.However,the porous titanium prepared by the traditional PM process usually have coarse grains,less grain boundary and poor mechanical properties.Titanium alloys prepared by Spark Plasma Sintering(SPS)often have fine grain size and excellent mechanical properties.In this study,four different particle size powder(45~180 ?m,75~110 ?m,110~150 ?m,150~180 ?m)were prepared by Plasma Rotating Electrode Method(PREP).The porosity of porous titanium samples ranged from 1.05% to 16.14% under different sintering pressure and sintering temperature.The relationship among microstructure,porosity,pore structure morphology,compression property and micro-hardness of samples were investigated.The main results are as follows:The microstructure of the samples was mainly composed of the equiaxial crystal and the lamellar and acicular ? tissue,but the pore size was large and the shape was irregular at 800 ?;The samples were dominated by lamellar,the sintering neck of the samples were good,the distribution of pores were uniform,and the shape of pores were mostly spherical and nearly spherical at 850 ?;The samples were mainly composed of dense ? lamella at 900 ?,and only little small pores in the samples,change thesintering pressure,the change of microstructure is not obvious.As the sintering pressure increases,the density of the sample increases and the size of grain becomes thinner.XRD analysis showed that the phase of samples were mainly hcp-? structure.The yield strength were distributed between 81.85 MPa to 122.36 MPa,the compressive strength of the porous titanium were distributed between 161.65 MPa to 498.86 MPa,the compression strain were distributed between 36.75% to 59.97%,and the elastic modulus were distributed between 2.79 GPa to 4.22 GPa,and the microhardness were distributed between 93.9 HV to 147.1 HV.There are more pores in the samples of75~110 ?m powder prepared by SPS,the pores are mostly spherical or nearly spherical and the distribution of pores is relatively uniform at 850 ? and 10 MPa.At the same time,the samples have higher strength and better plasticity of 75~110 ?m samples.Sintering occurs spontaneously due to the generation and growth of necks of powders system at high temperature.The growth of the necks and the densification of the samples are performed under the combined action of Vaporization-solidification,volume diffusion,surface diffusion and grain boundary diffusion.The HDH sample only contains little small pores and has a high density,but there are plenty cracks in the samples,the tissue is the isoaxial ? grain and thick ? layer,the size of equiaxial grain is small.The MSE sample contains little irregular coarse pores,and the microstructure tissue is the isoaxial ? grain and thick ? layer too,but the size of equiaxial grain is larger.The compression strength of HDH and MSE sample was526.85 MPa and 251.23 MPa respectively,while the compressive strain was 26.61%and 17.44%,and the microhardness was 203.4 HV and 293.1 HV,respectively.The compression strength of HDH sample and MSE sample are higher than PREP samples,but their plasticity are poor.