Evaluation On Gas Atomization Processing And Properties Of Fe-based Amorphous Alloy Powders

Fe-based amorphous alloys have much attracted attention due to their excellent comprehensive properties,such as high wear resistance and corrosion resistance,especially in the fields of thermal spraying and laser cladding coatings with alloy powders as raw materials.The quality of powder material is crucial to the preparation of high quality Fe-based amorphous coating.Gas atomization is widely used in various types of metal powder preparation as an efficient powder preparation method,however,the powder prepared by this method in the actual production process has the problems that the fine powder yield is low,the particle size distribution range is not concentrated,the amorphous content is low,the hollow powder phenomenon is serious,cannot meet the requirements for high performance coating preparation.Regarding the key issues above,Fe-based amorphous alloy powders were prepared by gas atomization based on FeCrMoMnWBCSi alloy with high amorphous forming ability.By means of optical microscope(OM),scanning electron microscopy(SEM),differential scanning calorimetry(DSC),X ray diffraction(XRD)measurements,the synergetic relationship between gas atomization processing parameters and Fe-based amorphous alloy powders was systematically studied.Based on the theoretical analysis of melt breaking and experimental verification,the main controlling factors affecting the properties of Fe-based amorphous alloy powders were revealed,the crystallization way and crystallization dynamics of Fe-based amorphous powders were clarified.The main conclusions are as follows:(1)The fine powder yield of Fe-based amorphous alloy powders had positive relationship with atomization pressure,melt superheat degree and gas-liquid mass flow ratio,but inverse relationship of median particle size(d₅₀).The results of research showed that:When the atomization pressure increased from 4.5MPa to 5.0MPa,the superheat increased from 300? to 350? and the draft tube diameter reduced from 5.0mm to 4.5mm,the median particle size of powders decreased from 62.51?m to 48.12?m,and the fine powder yield(18?45?m)increased from 28.6%to 43.1%.(2)The transition size of the Fe-based amorphous alloy powders was determined to be 18?m.When the powder particle size was larger than 18?m,the powder was partially crystallized,followed by ?-Fe,Fe₂C,M₂₃C₆ and the unknown oxide.The results of DSC fitting showed that critical cooling rate of Fe-based amorphous alloy powders was 110K/s,the crystallization activation energy of glass transition temperature,crystallization start temperature and peak temperature were calculated by Kissinger method with 279.75KJ/mol?191.31KJ/mol?243.04KJ/mol?297.75KJ/mol?255.24 KJ/mol respectively.Avrami exponent calculated under nonisothermal condition showed that the growth mechanism of crystal phase was cubic nucleation,two or three dimensional growth mechanism.(3)Hollow powder rate was calculated by image analysis.The results of research showed that hollow powder rate increased with the increase of particle size of powders.Among them,the powder cavity of the single powder was about 30%to 50%,but almost no hollow powder in the fine powders of 18?m.