Study On The Hardening And Thermal Shock Properties Of Tungsten Alloy Hardened By Electrospark

The electrospark hardening technology can obviously improve the material properties under the high energy pulse produced by the electrospark discharge,which makes the electrode and matrix re-alloy to form a hardened layer.The electrospark hardening has been widely used in the surface modification of nickel based alloys and steels,but research on the hardening of tungsten alloy has not been reported yet.In this paper,the fine grain W-Ni-Fe alloy material was prepared as electrode and matrix,a DJ-2000 electrospark surface hardening equipment was used to harden the matrix.By controlling the process parameters,such as hardened power,argon flow rate,hardening time,and adding different components,the morphology and properties of the hardened layer are compared and analyzed.The changes of the influence of the process parameters on the hardening layer are summarized,and the optimum process parameters are selected.The hardness,wear resistance and corrosion resistance of the hardened layer are studied.It is found that the mass transfer between the electrode and the matrix is nonlinear,and the surface of the electrode has happened "anodic adhesion" after long time hardening.The Single pulse hardened point is the smallest unit of the hardened layer,and the single pulse hardened point stacked repeatedly to form the hardened layer.Partial of the melting droplet on the electrode and the matrix surface had been splashed.The hardness of the outer surface of the hardened layer is higher than that of the inner side.The hardened layer has better corrosion resistance and lower corrosion rate than the matrix.In the aspect of technological parameters,the higher the hardened power of the electrospark is,the better the quality,hardness,wear resistance and corrosion resistance will be.However,when the hardened power is too large,the intense pulse discharge makes the hardened layer appear a large number of holes and cracks,which affect its performance.The hardness of the hardened layer under power of 1600 W is the best,which increases 35.3% than the matrix.The corrosion current density of the hardenedlayer under power of 2000 W is the smallest,which is about 0.17 A/cm²,decreases by almost two orders of magnitude than the matrix.The quality of the hardened layer is the best under the argon flow rate of 6L/min.If the argon flow is too small,it's not enough to protect the discharge area;while if the argon flow is too large,a turbulence area will be formed and the air will be involved,the quality and density of the hardened layer will be affected.The thickness and hardness of the hardened layer are best at the specific hardening time of 5min/cm².The hardened layer is thinner and the performance improves little if the specific hardening time is too short.When the specific hardening time is too long,the electrode clads and surfaces on the matrix,and the accumulation of thermal stress causes the hardened layer to break and fall,which affects its performance.The addition of Co element can enhance the grain bonding phase,and the hardened layer has better thickness and wear resistance.The addition of Al₂O₃ can improve the density and hardness of the strengthened layer.