Effect Of Die Wall Lubrication And Pre-Diffusion On High Velocity Compaction Formed Fe-Based Powder Metallurgy Material

Research and development of Fe-based powder metallurgy materials with high-density and high-mechanical properties has become an important direction in the field of Fe-based powder metallurgy.The high velocity compaction technology is an important innovation for powder metallurgy materials to achieve the target of high density and high performance.However,the current high velocity compaction apparatus is expensive,which limits the development of high velocity compaction technology.In the high velocity compaction process,the impact force of the hammer on the mold is huge,accelerating the wear of the mold and reducing the life of the mold,which greatly restricts the application of the high velocity compaction technology in industrialization.Improving the powder properties can obtain better mechanical properties after high velocity compaction and sintering.The main contents of this study include:independently designed and manufactured a gravitational energy stored type-high velocity compaction device and carried out high velocity compaction experiments;The effect of die wall lubrication on high velocity compaction behavior and sintering properties of iron-based PM alloy was investigated.The effects of pre-diffusion and annealing on high velocity compaction behavior and sintering properties of iron-based PM alloy was investigated.The conclusions are as follows:Comprehensively analyzing the forming characteristics of the existing high velocity compaction device,independently designing and manufacturing a gravitational energy stored type-high velocity compaction device.After high velocity compaction experiment,the green density reaches 7.5 g/cm~3,the compact velocity,compact energy and other parameters reach the requirement of high velocity compaction.Compared with the traditional compaction,the green density obtained by high velocity compaction is obviously improved,the mechanical properties of the sintered sample are obviously improved,and a large amount of cold welding is formed during the high velocity compaction process,which promoting the diffusion of the alloy elements during the sintering process.The ejection force is significantly improved after high velocity compaction.Die wall lubrication can effectively increase the green density in the high velocity compaction process,green density of the die wall lubricated samples is 0.07-0.12 g/cm~3 higher than that of the non-die wall lubricated samples in the same impact velocity.Die wall lubrication can effectively reduce the internal lubricant content in the situation of high velocity compaction.The green density reaches a maximum value when the internal lubricant(zinc stearate)content is 0.1%.With the increase of green density,the amount of cold welding in the green compact is increased,which promoting the diffusion of alloying elements during sintering,the microstructure is more uniform.Die wall lubrication can effectively increase the maximal impact force in the situation of high velocity compaction,and significantly reduce the ejection force.Therefore,the percentage of pressure loss at the same velocity is reduced.The EDS shows that the Ni and Mo elements in the Fe powder after pre-diffusion treatment are more evenly distributed than annealing treatment.The microhardness of the powder decreases with the annealing temperature increases.When the annealing temperature is raised from 600°C to900°C,the microhardness of the powder decreases from 90 HV to 82 HV.After pre-diffusion treatment,the microhardness of the powder did not change much when the temperature was below800°C,and the microhardness increased significantly at 900°C.The green density after annealing treatment is higher than pre-diffusion treatment.The content of pearlite in pre-diffusion treated sintered sample is higher,and the grains are remarkably refined.Both annealing and pre-diffusion treatment can improve the mechanical properties of the sintered samples.When the temperatures below 800°C,the mechanical properties of the sintered samples after pre-diffusion treatment are better than those of the sintered samples after annealing treatment.When the pre-diffusion temperature is 800°C,the apparent hardness and bending strength increase to 72.3 HRB and 1326.6MPa,respectively.