Microstructure And Mechanical Properties Of Ultrafine Structured Titanium Prepared By Powder Metallurgy And TiH₂ Powder

Pure titanium is a metal material with small specific gravity,high melting point,strong resistance of corrosion and good biocompatibility.It is an ideal structural material due to the excellent performance.However,the application of titanium at this stage is mainly focused on these areas with low cost sensitivity.The further application of titanium products was restricted by the high cost of titanium products.If pure titanium are used as engineering materials,their mechanical properties are lower than some titanium alloys,which can not meet the requirements of high strength fields.On the one hand,the preparation of high strength pure titanium can expand the application field of pure titanium,which meets the requirements of different strength.On the other hand,improving the performance of titanium by means of alloying will increase the cost of titanium products,which is not conducive to the expansion of the application field.This shows that the preparation of high strength pure titanium has the great meaning both in application and reality.Titanium hydride powder is low in price,which was used as raw material.At first,titanium hydride powder with ultra-fine grain was prepared by high energy ball milling.Then ultrafine grained titanium hydride powder was compacted and consolidated rapidly in the self-made consolidation system.Finally,the pure titanium rods with ultrafine structure were obtained by extrusion.Titanium rods were obtained by the way of extrusion after consolidated at 1050℃,1150℃,1250℃ with a holding time of 10 minutes,which was prepared by the titanium hydride with the ball milling time of 1 hour.The samples extruded at 1050℃ has the finest and most uniform microstructure,transverse section was composed of fine acicular structure and ultrafine grained structure,a part of acicular structure formed lamella clonies like Widmanstatten structure.The microstructure of longitudinal section was composed of coarse acicular structure,equiaxed crystal structure and ultrafine grained structure,which distributed along the extrusion direction.The mechanical properties of the sample extruded at 1050℃ has the better mechanical properties,the tensile strength and yield strength of which were 859.23 MPa and 732.76 MPa,respectively,and the elongation was 2.8%.The microhardness was 293 HV,but the relative density was only 97.89%.With the prolongation of holding time at 1050℃,the metallographic structure of the sample grew up gradually,and the axial diameter ratio of fine acicular structure decreased.The sample with a holding time of 15 minutes has the highest proportion of ultrafine grained structure.It was found that the field of ultrafine grained structure is mainly composed of α-Ti and TiH phase,and the fine acicular grained structure was α-Ti.The mechanical properties of the sample extruded at the 1050℃ with a holding time of 15 minutes has the best comprehensive mechanical properties,the tensile strength and yield strength of which is 903.12 MPa and 731.11 MPa,respectively,and the elongation was 8.8%.The microhardness is 296 HV.It was found that the microstructure changed into equiaxed crystals for the sample consolidated at 1050℃ with the holding time of 15 minutes after 700℃/6h annealing treatment.Meanwhile,the hydrogen content of the sample decreased to 0.001%and the relative density reached 99.93%,which was close to the state of full density.The mechanical properties of the sample after heat treatment was increased significantly,which has the yield strength,tensile strength and elongation of 794.37 MPa,932 MPa and 26.23%,respectively.It is determined that 1050℃/15 minutes is the best consolidation process.The grain sizes of the powders with ball milling time of 1,3,6 and 9 hours were 101 nm,84 nm,90.25 nm and 96.5 nm,respectively.With the decrease of the grain size of titanium hydride powder,lamella clonies like Widmanstatten structure increased,the hydrogen content decreased and relative density increased.The pure titanium prepared by 6 hours powder has the highest strenth,the yield strength and tensile strength of which were 1046.96 MPa and 1118.91 MPa,respectively,but the elongation is only 2.9%.The microhardness increased to 529 HV.