The Investigation Of On The Phase Composition,Microstructure And The Magnetic Properties Of Non Rare Earth Co-Zr-Mo Based Permanent Magnetic Alloys

In recent years,due to the scarcity of rare earth resources in the study of permanent magnet materials,the research on non-rare earth permanent magnet materials has been increasing rapidly.Co-Zr-based non-rare earth permanent magnet alloys exhibit good permanent magnet performance as the most promising candidate materials,it has attracted extensive research attention.In this paper,Co-Zr-Mo based non-rare earth permanent magnet alloys are studied as the research object.Through the method of element doping,the quenching process and heat treatment methods are used to study the use of a small amount of magnetic elements Fe and Ni instead of Co element in the Co-Zr-Mo alloys.The influence of its phase composition,microstructure,and magnetic properties.The main results and conclusions of this paper are as follows:Firstly,according to the design concept of multi-element alloys and elemental doping methods,it is found that the small substitution of Fe for Co in the Co72Zr15Mo3 melt-spun ribbons are resulted in a significant improvement of magnetic properties.The Co72-x Zr15Mo3Fex(x = 0、1、3、5)series melt-spun ribbons were successfully prepared using a single-roller fast quenching process at a wheel speed of Vs =40m/s.X-ray diffraction(XRD)analyzed that substitution of Fe atoms for Co atoms resulted in a significant change in phase composition.The ribbons are initially mainly composed of metastable Co11Zr2 phase and Co5 Zr phase and as the Fe content increases,a small amount of soft magnetic phase fcc-Co is generated;when the Fe content reaches a certain level,It was found that the α-Fe phase appeared in the ribbons,which revealed that when the doped iron element reaches a certain amount,it is difficult to enter into the lattice of the alloy,so that the α-Fe phase precipitates.Through the thermomagnetic analysis(TMA),there are two magnetic transition points in the thermomagnetic curve of the sample ribbon,which represent the two main phases in the ribbons: Co5 Zr phase,Co11Zr2 phase,and their corresponding Curie temperatures are 450°C,500°C respectively.With the continuous incorporation of Fe atoms have entered into the alloy ribbons resulting in the increase of their Curie temperature.The investigation of Vibrating Sample Magnetometer(VSM)indicated that with the increase of Fe content,the coercivity of the ribbons first increases and then decreases,and its saturation magnetization shows an increasing trend.The optimal magnetic properties of coercivity i Hc = 4.1k Oe,and maximum energy product(BH)max =1.68 MGOe were obtained in the Co71Zr15Mo3 Fe ribbons.The cross section of the sample was analyzed by scanning electron microscopy.It was found that the grain size of Co72-x Zr15Mo3Fex(x=0、1、3、5)alloy ribbons was significantly reduced after adding appropriate amount of Fe atom,which indicates that Fe atoms can be plays a role in the appropriate refinement of grain.Secondly,we carried out a vacuum rapid annealing process on the Co71Zr15Mo3Fe1 melt-spun ribbons.It was found that the heat treatment of the alloy ribbons caused a significant change in its magnetic properties and phase composition.The rapid quenching ribbons are annealed 2 min at the temperature range of 500℃-700 ℃ spaced 50 ℃ apart,respectively.When the ribbons were annealed at 600°C,which achieved the best magnetic properties with coercivity i Hc =4.6 k Oe,and the maximum energy product(BH)max =1.89 MGOe.After the ribbons were annealed for different times at 600°C,we found that the coercivity of the Co71Zr15Mo3 Fe ribbons decreased with increasing the annealing time,which indicates that the alloy strips were annealed at a suitable temperature for a suitable time.In order to make the grain size closer to Lex,the best permanent magnet performance is achieved.Finally,Using a partial substitution of Ni for Co,the Co72-x Zr15Mo3Nix(x=1、2、3、4、5)melt-spun ribbons were prepared by a single-roller rapid quenching process.The high-performance of coercivity i Hc=4.3k Oe,and maximum energy product(BH)max =2.53 MGOe were obtained in the Co71Zr15Mo3 Ni ribbons produced at a wheel speed of Vs =40m/s.Through XRD and thermo-magnetic analysis of the phase composition of the alloy ribbons,it was found that all samples consisted of a single hard magnetic phase Co11Zr2.It is further obtained from the thermomagnetic curve,as the Ni content increases,the Curie temperature gradually decreases.This shows that the Ni atoms radius is smaller than the Co atoms,when the Ni atoms enter into the lattice of Co11Zr2,due to Co-Ni exchange function is weaker than the exchange between Co and Co,resulting in the decrease of their Curie temperature.The scanning electron microscopy(SEM)results suggest that the grain size of the Co72Zr15Mo3 alloy ribbons gradually increased after adding Ni atoms,indicating that the Ni atoms effectively promoted the grain growth.The coercivity mechanism of Co-Zr-Mo-Ni ribbons was found to be the mechanism of Anti-magnetized nucleation.Subsequently,through the study of magnetic properties of Co71Zr15Mo3 Ni melt-spun ribbons,the coercivity of the ribbons gradually increases with the increase of the wheel speed Vs,but the saturation magnetization increases first and then decreases.For the analysis of the annealing treatment problem,the hard magnetic properties of the Co-Zr-Mo-Ni alloy ribbons were all increased after heat treatment in a vacuum atmosphere.After the annealing of Co67Zr15Mo3Ni5 melt-spun ribbons at the temperature of 600°C,the hard magnetic properties are coercivity i Hc=5.1k Oe,(BH)max=3.06 MGOe.In summary,the appropriate amount of Ni atoms instead of Co atoms can promote the phase composition,microstructure,and magnetic properties of the Co72Zr15Mo3 melt-spun alloy ribbons.