Material Design And Performance Prediction Of Tungsten Based Pin Tool Based On First-Principles

As a widely used solid phase connection method,friction stir welding technology is restricted by pin tool materials in commercialization and engineering development in the welding field of high melting point materials.Tungsten rhenium alloys are currently recognized as good wear-resistance pin tool materials.However,the high price of rhenium has become the main factor that limits large-scale use of tungsten rhenium alloy.From the angle of atomic structure,this paper used the first-principles method to design cheap tungsten based pin tool materials with high strength and toughness properties.Then,tungsten based materials were prepared by powder metallurgy.The results of the first-principles calculation showed that the covalency of the tungsten was weakened by adding rhenium which increases the plasticity of the tungsten matrix.It was the reason why tungsten rhenium alloy own good strength and toughness properties.Meanwhile,the addition of rhenium changed the electronic cloud chart of the tungsten matrix.In addition,rhenium could also increase the bonding strength of tungsten grain boundaries which leaded to increase the strength and toughness of tungsten.However,the calculation results showed that the angle of preparating tungsten based alloys from the doping elements did not find the cheap elements to replace rhenium.Duo to TiC and ZrC based cermet own excellent strength and toughness as well as wear-resistance properties,the Castep module in Materials Studio software had been used to study the electronic structure of cermet interface to explore the feasibility of TiC/W and ZrC/W used as pin tool materials,which could provide guidance for preparing corresponding materials.The calculation results showed that the density of state of TiC and ZrC at Fermi level was not equal to zero indicating they own metallicity.Through calculating the changes of surface structure layer spacing and the surface energy with the changes of thickness of the layer,it could be seen that the surface structure of TiC,ZrC and W with 9 layer thickness could possess the bulk-like characteristic interiors.The internal relaxation of layer spacing was close to 0with the thickness changes of the layer and the surface energy of TiC,ZrC and W converged to 1.62J/m~2,1.56J/m~2 and 4.00J/m~2,respectively.The results of charge density diagram showed that the interface of TiC/W and ZrC/W had become bonding.It showed that hard phase in the composite materials was not easy to fall off,which could enhance the wear-resistance property of the composite materials.Meanwhile,a good interface bonding could also improve the strength and toughness of the composite materials.The result of the difference of the charge density contours showed that C atoms often got electrons and W and Zr atoms lost electrons.The projected density of states of TiC/W and ZrC/W interface showed that there was no electronic structure distortion on both sides.Meanwhile,smooth and distortionless interface electronic structure was the prerequisite for forming good interface.The density of state of C atom at the interface was more localized than that in the bulk phase,indicating that the bonding of C atom at the interface is enhanced.Finally,TiC/W,ZrC/W and(TiC+ZrC)/W composite materials were prepared by powder metallurgy.The dispersive distribution of hard phase in the matrix was observed by Zeiss microscope and some agglomeration phenomena were also observed in the hard phase.SEM energy spectrum analysis showed that three kinds of cermet contained almost no impurities,only including titanium,zirconium,tungsten and carbon.The hardness test results showed that the hardness values of TiC/W,ZrC/W and(TiC+ZrC)/W composite materials were 932HV,1290HV and 1002HV,respectively.The wear tests of the three composite materials were carried out at 600?in one hour and the weight loss of the three materials is not large.The high temperature wear-resistance properties of the ZrC/W composite was the best and the mass wear rate was 0.046g/h.The three materials were all oxidation wear and abrasive wear.