Effect Of Continuous Rapid Annealing On Microstructure And Properties Of Fe-Based Amorphous Alloys

Fe-based amorphous alloy is a new type of soft magnetic material with excellent properties such as high magnetic permeability,low coercivity and low loss.Currently,it is mainly used in power equipment fields such as transformers,motors and sensors.Since its saturation magnetization is lower than that of Si-Fe alloys,appropriate heat treatment is usually used to improve its soft magnetic properties.However,the furnace annealing method commonly used in the industry makes the amorphous ribbons seriously brittle after annealing,and is prone to breakage during subsequent storage,handling and transformer assembly,which is one of the problems that limit its wide application.In recent years,studies have found that rapid heat treatment can suppress the annealing-induced brittleness of alloys,while achieving matrix crystallization and soft magnetic properties enhancement.However,most of the current rapid annealing processes are difficult to implement and do not have continuity,so it is difficult to meet the requirements of industrialized and efficient production.In view of this situation,a new rapid annealing technology was developed in this study,which can obtain continuous ribbons with both good toughness and excellent soft magnetic properties after heat treatment.This work provides a new idea for developing and optimizing the rapid heat treatment process of amorphous alloys.In this paper,the Fe₇₃Si_16.2B_6.8Nb₃Cu₁ amorphous alloy commonly used in industry and the new Fe₈₅P₁₁C₂B₂ amorphous alloy are used as the research objects.First,the thermal properties,soft magnetic properties,electrical properties and mechanical properties of the two alloys are compared and studied.Then,the self-developed continuous rapid annealing equipment was used for contact heat treatment,and the treatment effect of the conventional annealing process was compared,and the effect of rapid/conventional annealing on the structure and properties of the two alloys and its mechanism were deeply studied.The details are as follows:1.The basic working principle of the continuous rapid annealing equipment is:preheat the heating roller made of gray cast iron to the pre-set annealing temperature,and drive the amorphous ribbons to contact the heating roller under the protection of Ar atmosphere through the variable speed motor.The annealing time is controlled by the linear speed of the thin ribbons passing through the heating roller,and the annealing temperature is measured by a K-type thermocouple.2.Fe₇₃Si_16.2B_6.8Nb₃Cu₁ and Fe₈₅P₁₁C₂B₂ amorphous alloys have good bending toughness,but there are also obvious performance differences.Among them,Fe₇₃Si_16.2B_6.8Nb₃Cu₁ alloy has higher thermal stability,tensile fracture strength and hardness,its T_x1 is about 800 K,crystallization activation energy is about 280 k J/mol,the tensile fracture strength and hardness are as high as 1697.7 MPa and 915.6 Hv,respectively;The Fe₈₅P₁₁C₂B₂ alloy has higher saturation magnetization and resistivity,and its B_s andρvalues are as high as 1.56 T and 185.9μΩ·cm,respectively.3.Compared with conventional annealing,the continuous rapid annealing process can also effectively improve the soft magnetic properties of Fe-based amorphous alloys.The H_c of Fe₇₃Si_16.2B_6.8Nb₃Cu₁ alloy decreased from 2.5 A/m to 1.2 A/m after rapid annealing at 803 K for 3 s;The B_s increased from 1.2 T to 1.43 T,and the H_c decreased to 2.2 A/m.The Fe₈₅P₁₁C₂B₂ alloy obtained excellent soft magnetic properties after annealing at 773 K for 0.3 s and 0.75 s,respectively,with B_s and H_c values of 1.66 T,7.6 A/m and 1.63 T,5.1 A/m,respectively.4.In the process of rapid/conventional annealing,with the increase of annealing temperature and the prolongation of annealing time,the alloy will gradually form a highly fine nanocrystalline structure,and the internal atomic arrangement will gradually change from amorphous disordered state to crystalline ordered state,the scattering effect on electrons is weakened,thereby reducing the resistivity of the alloy.Among them,the resistivity of Fe₇₃Si_16.2B_6.8Nb₃Cu₁ alloy decreased from 137.6μΩ·cm to 98.0μΩ·cm after rapid annealing at 873 K for 10 s,and decreased to 91.8μΩ·cm after conventional annealing at 923 K for 10 min;The resistivity of Fe₈₅P₁₁C₂B₂ alloy decreased from 185.9μΩ·cm to 146.4μΩ·cm after rapid annealing at 773 K for 1.2 s,and decreased to 143.9μΩ·cm after conventional annealing at 723 K for 10 min.5.The degree of ductile-brittle transition of the alloy after annealing is mainly affected by the composition of the alloy system and the parameters of the annealing process.Among them,compared with conventional annealing,rapid annealing has the effect of inhibiting the annealing-induced brittleness of the alloy;compared with Fe₇₃Si_16.2B_6.8Nb₃Cu₁ alloy,Fe₈₅P₁₁C₂B₂ alloy has good relaxation brittleness resistance.Fe₇₃Si_16.2B_6.8Nb₃Cu₁ alloy hasε<1 after annealing at 773 K,and microcracks appear near the hardness indentation,that is,ductile-brittle transition has occurred,but compared with the alloy samples after rapid annealing,the bending rate of the alloy after conventional annealing is significantly lower and the brittleness is more serious;Fe₈₅P₁₁C₂B₂ alloy retains good toughness after rapid annealing at 773 K for 0.3 s.