Structure And Thermodynamic Parameters Of Fe Based Amorphous Alloy

Fe-based amorphous alloys are one of the most widely used amorphous alloys as their excellent performance.Although the Fe-based bulk amorphous alloys have been only found several years ago,but the research methods and theoretical system of amorphous alloys have got great breakthrough and lots of Fe-based bulk amorphous samples have been prepared.But so far, none of the theoretical or a parameter could fully evaluate the glass forming ability of amorphous alloy.Therefore,it is necessary for a thorough study of amorphous alloys.This paper mainly studied the effects of adding elements and different treatments(relaxation treatment,pre-annealing cycle processing,low-temperature liquid nitrogen cycle treatment) on thermodynamic parameters,thermal stability and internal structure of Fe-based amorphous alloy.Based on the early studied work,we analyzed the relations between glass transition temperature Tg,crystallization temperature Tx,glass-forming ability parameters Trgl,γand mixing enthalpyâ–³H of FeNiAlGaPBSiC and FeYB series amorphous alloys.The results showed that the thermodynamic parameters Tg,Tx and Glass-forming ability parameterγwere all increased with the increased of mixing enthalpyâ–³H in a certain region.We found that Tg and Tx had an increasing trend with the enhancement of annealing temperature of Fe₆₈Ni₁Al₅Ga₂P_9.65B_4.6Si₃C_6.75 amorphous alloy after pre-annealing relaxation one hour at 573K and 673K,but Tp1 and Tp2 had little changed.Simultaneously,the enthalpy relaxation peak near glass transition temperature after annealing.And the enthalpy relaxation peak was more clear at 673K.The results also showed that the Fe₆₃Ni₁Al₅Ga₂P_9.65B_4.6Si₃C_6.75Co₅ amorphous alloy still remains amorphous state after cycle treatment.But the XRD curves showed that the amorphous peaks' intensity were all decreased after processing,and the glass transition temperature,crystallization temperature and crystallization peak temperature were all changed with a different degree,which showed that some micro-structures of samples had been changed.We calculated the glass transition temperature alloy activation energy Eg,the beginning of crystallization activation energy Ex temperature and peak temperature of crystallization activation energy Ep by Kissinger equation.The results indicate that adding micro amount of Sn(0.5%at) would lead to the thermal stability of Fe₆₈Ni₁Al₅Ga₂P_9.65B_4.6Si₃C_6.75 amorphous alloy fall,and adding proper amount of B would increase the thermal stability of Fe₆₅Ni₁Al₅Ga₂P_9.65B_8.6Si₃C_5.75 amorphous alloy.The glass transition activation energy,crystallization activation energy and peak crystallization activation energy of Fe₆₃Ni₁Al₅Ga₂P_9.65B_4.6Si₃C_6.75Co₅ amorphous alloy after(low-temperature liquid nitrogen +473K annealing relaxation) cycle treatment were all larger than as-quenched,which indicate that the alloy has better thermal stability after processing.We also studied the microstructure of amorphous alloys after treatments by TEM.The results showed that there were nano-crystal precipitation on amorphous matrix after low-temperature liquid nitrogen cycle treatment,low-temperature liquid nitrogen treatment+473K annealing relaxation cycle treatment and 473K annealing relaxation cycle treatment.There were some random distribution grains and with the average size of about 30nm after low-temperature liquid nitrogen cycle treatment.And it has little amount of grain precipitation after 473K annealing relaxation cycle treatment with the average size of about 25nm.The size of grain becomes small and the distribution of it is more uniform after(low-temperature liquid nitrogen+473K annealing relaxation) cycle treatment,and with the average size of about 15～20 nm.