Preparation Of Porous Titanium Matrix Composites By High Pressure Torsion

Ultra-fine-grained materials(UFG)have many advantages,such as high strength,good plasticity,excellent mechanical properties and processability,which have attracted wide attention of many scholars.Ultra-fine grained materials can be prepared by Severe plastic deformation(SPD)method.At present,three SPD methods are widely used,namely equal channel angular pressing(ECAP),cumulative rolling and high-pressure twisting.High-pressure twisting(HPT)is widely used because of its simple operation and principle.The degree of deformation is very important to the properties of materials,and the friction coefficient,torsion angle and pressure in high-pressure torsion will all affect the degree of deformation.Due to the time-consuming and labor-intensive experimental research,and with the development of computer,we can carry out finite element simulation research to partially replace experimental analysis,find out the optimized process and reduce the number of experiments.Titanium and titanium alloys have been widely used by people because of their many advantages.In order to study the strain law of titanium-magnesium alloy after large plastic deformation and its application after deformation,this paper sets different values according to the three influencing parameters of high-pressure torsion,and carries out finite element simulation through deform to analyze the distribution law of equivalent strain,the thickness of billet and the diameter of billet.It is found that after high-pressure torsion,the strain changes in the surface layer and the center layer of Ti-Mg alloy basically show an English letter "M" trend,but the "M" in the surface layer is in a sharp angle distribution,and the middle layer is relatively soft,which also shows that the same strain on the surface layer is distributed on a circle away from the center of the circle,while the middle layer is concentrated on an annular belt away from the center of the circle.It also shows that the deformation transfer effect of the surface layer and the middle layer is uneven.With the increasing values of the three parameters,the strain of billet is also increasing,the thickness is decreasing and the diameter is expanding.In order to improve the deformation uniformity and transfer effect of the surface layer and the middle layer,this paper developed three different HPT processes based on the traditional HPT process: repeated HPT(repeated twisting of the lower die),co-directional asynchronous HPT(twisting of the upper and lower dies in the same direction with different angular velocities)and counter-directional synchronous HPT(twisting of the upper and lower dies in different directions).The control variable method is adopted to ensure that the absolute angle of pressure and torsion is the same,and the analysis results and rules are summarized.The basic rules of strain produced by three HPT processes are the same as those of unidirectional HPT,and they are distributed in the shape of letter "M".The strain produced by repeated HPT and unidirectional HPT is smaller than that produced by unidirectional HPT,while the strain produced by asynchronous HPT is higher than that of unidirectional HPT,and the transmission effect is good.In order to verify the accuracy of the simulation,under the existing conditions,an experimental study on unidirectional high-pressure torsion was carried out,and the thickness,diameter and hardness of the deformed billet were analyzed to verify the laws obtained from the simulation.After high-pressure torsion,the grain size and microstructure of the sample will change obviously.On this basis,the material after high-pressure torsion will be corroded by chemical reagents.In recent years,with the rise of porous titanium,titanium-based composites have made new development in many fields.The titanium-based composites described in this paper,because of the magnesium element in the titanium-based composites,will undergo acid corrosion on the titanium-based composites after high-pressure torsion,and the magnesium in them will react with hydrochloric acid,and the magnesium in the materials will be corroded away,so that the titanium-based composites will become porous titanium-based composites.Porous titanium matrix composites are widely used in various fields,and its role in the medical field can be studied by analyzing the porosity.The porous structure is also conducive to promoting the absorption of nutrients by human bones.