Preparation And Properties Of Fe-based Bulk Amorphous Alloys By Spark Plasma Sintering

Amorphous alloy is a kind of metal material with special atomic structure of long-range disorder and short-range order.It has no defects such as grain boundaries or dislocations that crystal materials have.Fe-based amorphous alloys have significant advantages due to their low cost,excellent mechanical and corrosion properties.However,due to their poor glass forming ability,most of them can only exist in the form of powders and ribbons,so their size and applications are limited.Preparing Fe-based amorphous alloy powder into bulk can effectively solve the above problems and continue the perfect performance advantages of amorphous alloys.Spark plasma sintering（SPS）technology has the advantages of low sintering temperature,short time,fast cooling rate,controllable microstructure and sintering atmosphere,energy conservation and environmental protection.Therefore,it is selected as the process method for preparing Fe-based bulk amorphous alloys.In this study,Fe-Cr-Mo-C-B bulk amorphous alloys were successfully prepared by SPS technology with different sintering process parameters（sintering temperature,sintering pressure,holding time）.The effects of process parameters on the thermal stability,phase composition,micromorphology,density,microhardness,compressive strength,and corrosion resistance of Fe-based bulk amorphous alloys were studied using synchronous thermal analyzer,X-ray diffraction,scanning electron microscopy,archimedes drainage method,microhardness tester,universal mechanical testing machine,and electrochemical workstation.What’s more,the samples with the optimal process parameters were subjected to heat treatment at different temperatures and holding times,and the changes in the microstructure and properties of Fe-based bulk amorphous alloys before and after treatment were compared.Furthermore,The effects of heat treatment temperature and time on the properties of sintered samples were also studied.The following conclusions are obtained:（1）Fe-based bulk amorphous alloy sintered samples 1～13#were successfully prepared using SPS technology.The Fe-based bulk amorphous alloy mainly consists of amorphous phases,including a small amount of hard phases such as B₆Fe₂₃and Fe C.With the increase of sintering temperature,pressure and holding time,the crystallization degree of Fe-based bulk amorphous alloys becomes more and more obvious.The crystallization degree of sintered sample 1#（500℃,550 MPa,1 min）has the lowest,and that of sintered sample 10#（540℃,550 MPa,2 min）has the highest.With the increase of sintering temperature and holding time,the compressive strength and microhardness of the sample first increase and then decrease.The compressive strength of sample 4#（560℃,550 MPa,1 min）reaches a maximum of678 MPa,and the microhardness also reaches a maximum of 1351.3 HV.The density of sample 13#（560℃,550 MPa,3 min）has a trend of increasing,with the highest density of 94.72%.With the increase of sintering pressure,the compressive strength,microhardness and density show an increasing trend.（2）Electrochemical tests were conducted on sintered samples 1～13#in 3.5wt%Na Cl solution,1 mol/L KOH solution,and 1 mol/L HCl solution.With the increase of sintering temperature and holding time,corrosion resistance increases first and then decreases.In the process of increasing sintering pressure,corrosion resistance shows a trend of continuous increase.Therefore,sintered sample 4#has high corrosion potential(E_corr)in all three corrosion solutions.The low corrosion current density(I_corr)and high charge transfer resistance（R₂）indicate that the sintered sample 4#has the best corrosion resistance.Among them,it is found that the sintered sample 4#has the best corrosion resistance in a neutral environment of 3.5 wt.%Na Cl solution,with the highest E_corrof-0.249 V,the lowest I_corrof 2.359×10^-8A/cm²,and a maximum R₂of129090Ω?cm²,followed by 1 mol/L HCl solution.The sintered sample 4#has the worst corrosion resistance in an alkaline environment of 1 mol/L KOH solution.（3）The sintered sample 4#with the best comprehensive performance was selected for heat treatment at different temperatures and times.After heat treatment,the compressive strength and density of the sample are effectively improved,while remaining its amorphous structure.With the increase of heat treatment temperature,the degree of crystallization increases,but the samples 4-1#（500℃,20 min）and 4-2#（550℃,20 min）still maintain the amorphous structure.The compressive strength and corrosion resistance of the samples first increase and then decrease with the increase of temperature,while the microhardness and density show an upward trend.Therefore,the performance is best when the heat treatment temperature is 550℃.With the increase of holding time,the diffraction peak narrows and there are weak crystalline precipitates.However,the diffraction peak remains amorphous at 550℃,and the compressive strength and corrosion resistance show a downward trend.Among them,the sample 4-2#has reached the highest compressive strength of 884 MPa and the best corrosion resistance.The E_corrreaches a maximum of-0.318 V,the I_corrreaches a minimum of 2.098×10^-7A/cm²and R₂reaches a maximum of 59379Ω?cm².The microhardness first increases and then decreases with time,while the density is always increasing and the maximum density of sample 4-4#（650℃,20 min）is97.23%.