Investigation On Microstructure Evolution And Liquid Phase Separation Behavior Of Cu-Fe-P Monotectic Alloys

Monotectic alloy have been considered to be one of the advanced industrial materials with potential development due to its excellent performances,such as electrical conductivity,soft magnetism and strong bearing capacity.However,the development and application of monotectic alloys in industry was limited by the liquid-phase separation and component segregation during conventional solidification.The investigations of the solidification process of monotectic alloys played an important role in the regulation of microstructure and the improvement of properties.Hydrogen energy was an environmentally friendly,low-carbon and widely used secondary energy source,accelerated the development of hydrogen energy industry was a key way to realize the"two-carbon"strategy.As a new catalyst for hydrogen production,transition metal phosphide has the properties and stability of noble metal in acidic and alkaline media.To account for this,the method of combination of simulation and experiment was used to further study the relationship between the characteristic structure,separation phase precipitation,structural evolution and material properties of Cu–Fe–P monotectic alloys containing in-situ generated TMPs,and develop functional TMPs@Cu matrix composites.The main conclusions were as follows:（1）The liquid structure of Cu–Fe–P monotectic alloy was studied by ab initio molecular dynamics simulation.According to the partial correlation function（PCFS）curves,it was found that P atoms tend to bond with Fe in the first coordination layer shell.Based on the values of N_PCu,N_PFe and N_PP at 1773K,1523K and 1273K,it could be inferred that（5Cu+5Fe）P,（6Cu+4Fe）P and（5Cu+5Fe）P phosphorous clusters might be exist in the melt.In addition,further observation of 3D simulation configuration analysis showed that the Fe and Cu atoms in the phosphorus rich atomic clusters were localized distribution,and the Fe and Cu atoms were distributed on both sides of the P atom.The existence of such clusters provides genetic factors for the subsequent solidification process of Cu–Fe–P alloy,and had certain guidance for the solidification structure state.（2）The effect of thermal treatment on microstructure control and phase separation behavior of Cu₆₀Fe₃₂P₈ monotectic alloy was investigated.Based on XRD analysis,it was found that the phase composition of the monotectic alloy had no significant affected by the thermal treatment,which was composed of Cu,Fe₂P and Fe₃P phases before and after the thermal treatment.The statistical analysis of the particle size of second phase was shown that there were few coarse particles with a particle size of more than 150μm in the central part of the original sample,and the size of the other particles was relatively small,about 31.2%of the particle size was less than 10μm.After four temperature-cooling cycles,the uniform melt state and temperature distribution made the probability of condensation in each region similar,and the second phase condensation was relatively equal,the particle size distribution range decreased,and the maximum particle size decreased to 90μm.（3）The effect of cooling rate on microstructure evolution and liquid phase separation behavior of Cu₇₄Fe₁₇P₉ monotectic alloys was investigated.When the cooling rate was 1580K/s,the Fe–P second phase was ellipsoidal in the Cu-rich matrix with a narrow size range of 1-80μm.When the cooling rate was 300K/s,the spheroids of the second phase decrease,and the size distribution ranges from 1 to 200μm,in which the proportion of particles between 1 and 20μm was about 38%.In comparison with that,the cooling rate was decrease to 30K/s,the relatively sufficient liquid phase separation time caused the second phase particles to seriously aggregate in the central region of the Cu matrix,formed an evolving core-shell structure.In the horizontal direction,the droplet movement was dominated by Marangoni convection.In the vertical direction,due to the difference in the density of the two phases,the second phase particles were driven by Stokes motion and formed a mushroom structures in the process of rising.Based on the microstructure evolution of the alloy,it was found that the Marangoni convection and Stokes motion could be inhibited by the faster cooling rate,and the distribution of the second phase was relatively uniform.The second phase droplets fully coagulated and grew up,eventually formed a typical core-shell structure when the cooling rate was slowly.（4）The effect of Co addition on the microstructure evolution and catalytic hydrogen evolution of Cu₆₀Fe₃₂P₈ monotectic alloys was investigated.Through first-principles molecular dynamics simulation,it was found that P in the monotectic alloy tends to bond to Fe and Co atoms in the first coordination layer,which promoted the in-situ autogenesis of TMPs.Based on the analysis of SEM results,it was observed that the microstructure of Fe–P@Cu monotectic alloy was obviously refined by the addition of Co,which might be due to the effect of Co on the interfacial energy in melt,and weakened Marangoni convection and Stokes motion.The overpotential of(Fe_xCo_1-x)n P@Cu samples with 8%and 16%Co in acidic electrolyte was only 160m V and 155m V when the current density was 10 m A cm^-2,indicated that electron transfer induced by Co doping can improve the hydrogen evolution performance of Fe–P@Cu alloy.