Study On The Dynamic Evolution Of Pores In Porous Stainless Steel Prepared By Microwave Sintering

Porous stainless steel can be used in injection molds due to the through pores which solve the product defects caused by air trapping during injection molding.In this paper,porous stainless steel is prepared by gel-casting molding and microwave sintering.By establishing a mathematical model of the growth of powder sintering neck,the dynamic growth mechanism of sintering neck during the microwave sintering process and its influencing factors were researched.Furthermore,the dynamic evolution mechanism of pores and its influencing factors were studied.Combined with the experiments,the growth of the sintering neck and the pores were investigated.(1)Firstly,the mathematical model of the double-ball sintered neck with catenary was built.Secondly,Comsol with Matlab co-simulation was used to explore the dynamic growth mechanism of the sintered neck during the microwave sintering process.During the simulation,the neck growing equation is used to set the boundary condition of the neck growth.Then,the electromagnetic power loss with the increase of sintering time under different sintering temperatures were studied.The direction of the magnetic field and particle size impact on the growth of sintering neck were investigated.The result shows that the electromagnetic power loss gradually increases When the sintering temperature is lower than 1250℃.When the sintering temperature is 1250℃,the electromagnetic power loss decreases after 25 min sintering.With the angle between the direction of the magnetic field and the sintering neck increases,the increase of intersection angle between the magnetic field and the sintering neck,the electromagnetic power loss gradually increases,and there is a threshold.When it is below this the threshold,the electromagnetic power loss gradually decreases as the sintering progresses,the neck is difficult to grow;in addition,the threshold gradually increases as the sintering temperature and particle size increase.(2)The evolution of different pore structures at different sintering temperatures was studied.The results show that the electromagnetic power loss of the three-particle and four-particle pore structure decreases with the increase of sintering time.When the sintering temperature is higher than 1100℃,the electromagnetic power loss of two types of pores decreases after 20 minutes sintering.During this period,the pores shrink slowly.Compared with the three-grain pore structure,the electromagnetic power loss of the four-grain pore structure decreases more slowly and the sintering efficiency is higher.With the increase of sintering temperature,the electromagnetic power loss increases faster and reaches the peak point is earlier.In addition,with the increase of particle size,the electromagnetic power loss of the pores and the sintering efficiency begins to decrease earlier.(3)Experimental of the microwave sintering process parameters(sintering temperature,sintering time)effect on the sintering neck size and pore diameter was carried out.The results show that with the increase of sintering temperature and sintering time,the size of the sintering neck gradually increases and the pore diameter gradually decreases.After 20 minutes of sintering,the change of the sintering neck size and pore diameter gradually slows down,meanwhile the higher the sintering temperature,the shorter the sintering time required.When the sintering temperature is higher than 1100°C,the pore diameter of the three-particle and four-particle pores changes less after sintering for 20 minutes,which is consistent with the simulation results.