Non-equilibrium Preparation And Thermodynamic Stability Mechanism Investigation Of Ternary Single Phase Supersaturated Solid Solution

In this paper,two non-equilibrium processing ways of alloys--rapid solididication and high-energy ball milling were applied respectively to prepare supersatureted NiFe-Pb undercooled alloy and Fe-Cr-C nanocrystalline powders.The micro structure and structure evolution of the alloys were investigated systematically by SEM,XRD and HRTEM methods.Moreover,the growth of alloy grains and atoms segregation were analyzed combining a series of thermodynamic models of alloys.The main conclusions are as follows:(1)In the rapid solididication Ni-Fe-Pb alloys,two grains refinement happen.The first refinement occurs because of the dendrite break-up or ripening induced by remelting.While,the second refinement is caused by the stress accumulation originating from the rapid solidification with recrystallization which can be proved by HRTEM and SAED.By using the method of heat treatment,it can be founded that the average size of grains grow with the increase of annealing temperature,and with the increase of annealing time,the average size of grains grow twice.The first growth is resulted from the segregation of Fe and Pb atoms which leads to the decrease of grain boundary energy.While,the second growth comes from the Fe Pb3 second phase particle precipitate which results in the increase of grain boundary energy.(2)By improving the ball milling time and dispersants,the best process of preparing single phase supersaturated solid nanocrystalline Fe-Cr-C alloy powders was obtained.Combining the methods of XRD,SEM and HRTEM,it can be founded that the nanocrystallines sizes grow with the increase of annealing temperature and the function relationship between them also was obtainted.The thermal stability of nanocrystalline is induced by the segregation of Cr and C.(3)A ternary non-equilibrium alloy thermodynamic stability model was established.Stable grain thermodynamic parameters can be obtained with the fitted calculation of the experiment data of ternary alloys Ni-Fe-Pb,Fe-Cr-C,Fe-Cr-Zr and Fe-Ni-Zr.It can be founded that multicomponent co-segregation prompt the stagnation of grain growth and stability of grain size.