Study On The Phase Equilibria Of Fe-Pt-M(M=Au,Cu) Ternary Systems

There are a lot of potential binary and ternary magnetic functional materials and catalytic functional materials in Fe-Pt-M(M=Au,Cu)ternary systems.In this study,the phase equilibria of Fe-Pt-Au and Fe-Pt-Cu ternary systems were studied by alloy method and diffusion couple method to establish the complete isothermal sections of Fe-Pt-Au ternary system at 650? and 950? and the isothermal sections of Fe-Pt-Cu ternary system at 600?,750? and 1000?,in order to provide theoretical guidance for the composition design of Fe-Pt-M(M=Au,Cu)ternary alloys.For Fe-Pt-Au ternary system,6 kinds of ternary alloys with different compositions were designed to achieve phase equilibrium at 650? and 950?;for Fe-Pt-Cu ternary system,a ternary diffusion couple was designed annealing at 600?,750? and 1000?.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffraction(XRD)and electron probe microanalysis(EPMA)were used to analyze the microstructure,phase structure and compositions of alloy samples and diffusion couple samples.The research results are as follows.(1)The isothermal sections of Fe-Pt-Au ternary alloy at 650? and 950? were established.The results show that the Fe-Pt-Au ternary system is mainly composed of a series of orderdisorder transitions between the ordered fcc phases in the Fe-Pt binary system and the disordered Au-rich fcc phase,and the misbility gaps between the disordered fcc phases in the Fe-Pt system and the disordered Au-rich fcc phase.Specifically,on the Fe-Au side is the miscibility gap between ?Au and yFe.With the increase of Pt content,the order-disorder transitions of L12_Fe3Pt,L10_FePt and L12_FePt3 and followed by is the miscibility gap between aAu and ?Pt.Comparing the isothermal sections at 650? and 950?,it can be found that Fe3Pt exists at 650? and disappears at 950?,FePt and FePt3 can still exist at 950?,and because FePt and FePt3 have high thermodynamic stability,the solid solubility of Fe and Pt in ternary phase aAu is very low;The three binary ordered intermetallic compounds Fe3Pt,FePt and FePt3 can dissolve a certain amount of Au,and their solid solubility of Au at 650?is 10 at%,12 at%and 9 at%,respectively.(2)The isothermal sections of Fe-Pt-Cu ternary system at 600?,750? and 1000? were established.Compared with Fe-Pt-Au,in addition to Fe-Pt ordered intermetallics,L12_Cu3Pt and L11_CuPt ordered phases also exist in the system.The results show that Cu has great solubility in ordered Fe3Pt,FePt and FePt3,especially in FePt,the maximum solid solubility of Cu reaches 40 at%and 38 at%at 600? and 750?,and in these ordered phases,the substitution between Fe and Cu atoms is obvious.On the contrary,the solid solubility of Fe in the ordered Cu3Pt and CuPt is limited,which is 5 at.%and 3 at.%;In addition,there is always a miscibility gap between yFe and yCu in the Fe-Cu side at the three studied temperatures.When the content of Pt exceeds 18 at.%at 1000?,the miscibility gap disappears,forming a continuous ternary ? phase region.(3)For Fe-Pt binary phase diagram,the phase equilibria at low temperatures have been determined for the first time in this study.The results show that the composition range of?Fe+?Fe should shift to the Pt rich side comparing with the theoretical predicted value.According to the phase boundary of ?Fe measured at 750? and 600?,it can be inferred that the eutectoid temperature of ?Fe??Fe+Fe3Pt should be about 580?,and the eutectoid composition about 19 at.%Pt.In addition,the composition ranges of FePt and FePt3 at low temperatures are much narrower,and the trend of convergence to the ideal composition at low temperature is more reasonable.For the Cu-Pt binary phase diagram,the phase equilibrium on the Cu rich side predicted by the calculation is verified by experiments.On the rich Pt side,the equilibrium compositions of the CuPt obtained in this study are shifted to the Cu rich direction.