Effects Of Diffusion Alloying And Compaction Process On Microstructure And Properties Of Fe-based Powder Metallurgy Materials

With the continuous increasing of the comprehensive performance requirements for the Fe-based PM materials in the automobile industry,it is very important and urgent to research and develop the high performance Fe-based PM materials.The main contents of this research include:(1)The effects of diffusion alloying treatment on microstructure and properties of TiCp/Fe-based PM materials were investigated.(2)The effects of zinc stearate,ethylene bis stearamide(EBS),composite lubricant and compaction temperature on warm compaction process of Fe-based PM materials were investigated.(3)By combining the high velocity compaction(HVC)and warm compaction technology,the microstructure,properties and densification mechanism of high velocity warm compaction Fe-based PM materials were investigated.The results show that spherical diffusion alloyed particles with rough surface are formed on the Fe-Ni-Mo-Ti mixed powder after diffusion alloyed at 800 ?.The porosity of the TiCp/Fe-based PM materials prepared by diffusion alloyed powders increases a little compared with that of the PM materials prepared by mixed powders.With increasing the diffusion time,the size of Ti-riched zone of the TiCp/Fe-based PM materials decreases,the microstructure is obviously refined,and the distribution of pearlite is more uniform.Meanwhile,a large number of TiC particles with size of 0.1~0.5?m are in-situ synthesized homogeneously.Both the hardness and the bending strength increase with increasing diffusion time,and the hardness and the bending strength of the Fe-based PM materials prepared by 60 min diffusion alloyed powders reach to 63.6 HRB and 613.7MPa,respectively,which are 11.8%,38.3% higher than that of the composites prepared by mixed powders.The fracture mode of samples prepared by diffusion alloyed powders is brittle fracture with some ductile fracture characteristics.The lubricant distribute uniformly in the surface of Fe particles for the Fe-based powders which is mixed with composite lubricant.The apparent density and flow rate of Fe-based powders decrease with increasing lubricant content when the lubricant content is higher than 0.4%,and the effect of EBS is the greatest.The density of Fe-based PM green compacts increases by the use of lubricants,and the particles combine more closely when zinc stearate and composite lubricant are used.The effect of lubricant on the green density,sintered density,and bending strength of Fe-based PM samples is composite lubricant > zinc stearate > EBS in order,the density and mechanical properties of Fe-based PM materials increase with increasing compaction temperature.When the lubricant content is 0.4%,the density of Fe-based PM samples by warm compaction at 120°C are improved by 0.14~0.21g/cm3 compared to that of the conventional compaction samples,the hardness and bending strength are increased by 40%~65%.Strong plastic deformation of metal powder particles occurred in the HVC Fe-based PM green compacts,metal particles are tightly engaged and there occurred micro welding phenomenon.The microstructure of HVC Fe-based PM samples prepared by diffusion alloyed powders was more uniform compared with that of the conventional compaction samples and HVC Fe-based PM samples prepared by mixed powders.The density,hardness and bending strength of HVC Fe-based PM materials were significantly higher than that of the conventional compaction Fe-based PM materials,the hardness and bending strength of HVC Fe-based PM materials which is prepared by diffusion alloyed powders reached to 75.77 HRB and 1157.82 MPa.The fracture mode of HVC Fe-based PM materials prepared by mixed powders is brittle fracture,the fracture morphology of HVC Fe-based PM materials prepared by diffusion alloyed powders shows typical ductile fracture characteristics,and a large number of TiC particles with size of 0.3~2?m were present at the bottom of the dimple.