Research On The Constitutive Model Of Ti-6Al-4V Powder Compaction

Titanium and its alloys have a wide range of applications in aerospace,aviation,automobile,marine,ocean engineering,armor and biomedical fields because of their low density,good welding performance,high specific strength and rigidity,nonmagnetic properties,good corrosion resistance and excellent biocompatibility.The usage amount of Ti-6Al-4V alloy account for about 80% of the total titanium and its alloys,and it is the ace alloy in the titanium alloys.The research on the forming process of Ti-6Al-4V alloy is very important for the use and development of all the titanium alloys.The powder metallurgy technology of Ti-6Al-4V powder avoids various defects and deficiencies in the forging and casting process of titanium alloys,and it inherits and combines the advantages of both process crafts,has a good development prospect.With the development of the research on the powder metallurgy technology of Ti-6Al-4V powder,people begin to numerically simulate the compaction process in powder metallurgy of Ti-6Al-4V powder,and the constitutive model determines the accuracy of numerical simulation of Ti-6Al-4V powder compaction.Due to the complexity of its compaction process of Ti-6Al-4V powders,currently,there is no widely accepted constitutive model can be used to describe the compaction process.In view of this situation,the modified Drucker-Prager Cap model of Ti-6Al-4V powder compaction was established by experiments,and the established model was verified by the ABAQUS,then,analyzed the influences of friction coefficient,compression pattern and height-diameter ratio on the average density and density distribution of compacts.Firstly,the modified Drucker-Prager Cap constitutive model for cold compression of Ti-6Al-4V powder was established by uniaxial compression experiments,Brazilian disk experiments and molding experiments at room temperature,and the relationship between the friction coefficient and the top punch pressure was also obtained.When the upper punch’s pressure is less than a certain value(50 MPa),the friction coefficient decreases with the increase of punch’s pressure,and when the upper punch’s pressure is greater than this value(50 MPa),the friction coefficient remains basically unchanged with the increase of punch’s pressure.Then,the modified Drucker-Prager Cap constitutive model of Ti-6Al-4V powder cold compaction was verified by ABAQUS.The simulation demonstrates show that it has a good agreement with the results of compaction experiments,which shows that the established constitutive model can effectively analyze cold compaction of Ti-6Al-4V powder.And the model was used to analyze the influence of friction coefficient,compression pattern and height-diameter ratio on the density and density distribution of compacts by ABAQUS.The simulation results show that,the smaller the friction coefficient is,the higher the average relative density of compacts are,and the smaller the density distribution range will be.When pressure is applied to the two cylindrical surfaces of the compact,the density distribution is more uniform.When the heightdiameter ratio is bigger,the delamination of compacts are more severe,and the density distribution range will be larger.Finally,the hot-compaction experiments were carried out at 80°C,140°C,200°C,and 260°C,respectively,and the green compacts obtained under various temperatures were used to conduct the corresponding uniaxial compression test and Brazilian disc experiment.The relationship between the parameters of the linear shear failure surface and the temperature was summarized through the experimental data analysis,then the modified Drucker-Prager Cap model of Ti-6Al-4V powder with the change of compaction temperature was established and verified by the ABAQUS.