Preparation And Mechanism Of Ultrafine Fe-Ni-Cu Prealloyed Powder

With the development of the times and the progress of science and technology,the demand for ultrafine metal powder is becoming higher and higher.In order to obtain high performance materials,people begin to control the physical and chemical properties of metal powder,the metal powder with high purity,fine grain,even component distribution and higher dispersity was developed.The traditional methods of preparing pre-alloyed powder include mechanical alloy method,plasma atomization method,inert gas condensation method,ultrasonic chemical synthesis method and so on.In this thesis,ultrafine Fe-Ni-Cu pre-alloyed powder was prepared by mechanical-chemical method,which is different from the traditional Powder metallurgy method.This subject experiment is based on the thermodynamic analysis of hydrogen reduction composite metal powder;orthogonal test;preparation of pre-alloy powder;The effects of four factors,i.e.milling time,flow rate of hydrogen,reduction temperature and reduction time,on the prealloyed powder were studied.Firstly,the reduction temperatures of Fe₂O₃,CuO and NiO are calculated.Then the orthogonal experimental design method with four factors and three levels was used to optimize the technological conditions according to L₉3⁴orthogonal table,and the optimum technological conditions were obtained.The ultrafine Fe-Ni-Cu pre-alloyed powder was prepared under the optimum process conditions,and the Scanning electron microscope was analyzed by laser particle size analyzer,X-ray diffraction analyzer and X-ray diffraction analyzer,energy Spectrum Analyzer and a series of detection methods for analysis and detection.The results show that the optimum technological conditions of ultrafine metal powder are ball milling time 90 min,flow rate of hydrogen 40 L/h,reduction temperature 700℃and reduction time 40 min under the condition of ball to powder ratio 10:1.The pre-alloyed powder was prepared by the reduction of precursor powder prepared by ball milling.The surface of the pre-alloyed powder was smoother and more spherical with lower porosity.The average particle size decreased from 57.66μm to 30.69μm,the specific surface area increased from 3.57 cm²/g to 11.69 cm²/g,the particle size decreased,the specific surface area increased and the activity increased.The composite metal oxides were reduced to Fe₁₉Ni,Cu_0.81Ni_0.19and Cu₃Fe₁₇intermetallic compounds.The results show that when the ball milling time increases,the particle size of the pre-alloyed powder will decrease after the impact,extrusion and crushing of the stainless steel ball,and when the ball milling time is too long,the particle size of the pre-alloyed powder will decrease,will increase the probability of collision between particles,adhesion,welding,particle size will increase.As the flow rate of hydrogen increases,the reaction becomes more complete and the particle size becomes smaller and smaller.In this experiment,the chemical reaction is an endothermic reaction,the higher the temperature is,the more complete the reaction is.With the increase of reduction time,the water generated inside will drain out through the pores,the inside will collapse and shrink when the furnace cools,and the particle size will become smaller.When the particles are reduced in high temperature for a long time,the particles tend to agglomerate and grow up,the granularity will increase again.