Comparative Analysis Of Isothermal And Cellular Coupled Growth Between Directionally Solidified Fe-Ni And Cu-Ge Peritectic Alloys

Regularly arranged two-phase (quasi) coupled growth microstructure, prepared by directional solidification technology, is a kind of important in-situ composite. Currently, this technology is widely applied in eutectic alloys, however, it has obtained little mature developments in peritectic alloys because the formation of solute diffusion couple between two phases in peritectic alloys is more difficult than that in eutectic alloys. Accordingly, systemic studies on peritectic (quasi) coupled growth mechanism possess significant values in both theory and application. In this dissertation, Fe-Ni and Cu-Ge peritectic alloys, whose physical parameters contradict each other drastically, are selected for directional solidificaton respectively, exploring the forming condition, morphology evolution and growth stability of peritectic (quasi) coupled growth microstructure. Additionally, the influence of physical parameter differences on peritectic (quasi) coupled growth is also deep discussed via comparing coupled growth behaviors of each alloy.For Fe-Ni peritectic alloys, this paper chose Fe-4.1at.%Ni hypo-peritectic alloys and Fe-4.4at.%Ni hyper-peritectic alloys for directional solidification at the temperature gradient of 22K/mm. Steadily long-range fiber isothermal coupled growth(PCG) microstructure is obtained in Fe-Ni hypo-peritectic alloy at relatively high G/V and steadily long-range fiber cellular coupled growth(CPCG) microstructure is obtained in Fe-Ni hypo-peritectic at relatively low G/V, indicating that isothermal and cellular coupled growth microstructures can be successfully prepared and put into industrial application in Fe-Ni hypo-peritectic. While in Fe-Ni hyper-peritectic alloys at relatively high G/V, unsteadily short-range lamella PCG microstructure is gained and then disappeared immediately, replaced by single peritectic phase; in Fe-Ni hyper-peritectic at relatively low G/V, we got cellular peritectic phase microstructure instead of CPCG microstructure, illustrating that in-situ composite cannot be prepared in Fe-Ni hyper-peritectic alloys. Furthermore, this paper compared the morphology characteristics, originating position and existing distance of the coupled growth microstructure obtained in diverse C0 and G/V, and proposed that the increasingly remained liquid concentration is the critical factor to limit the existing distance of PCG microstructure. In addition, this paper pointed out that fiber PCG microstructure originated from the direct nucleation of peritectic phase on the plane interface of primary phase; lamella PCG microstructure originated from the bifurcate cross growth of primary phase on the island banding structure of peritectic phase; firber CPCG microstructure originated from the celluar growth of primary phase generated by the constitutionalsupercooling. For Cu-Ge peritectic alloys, this paper selected Cu-12.8at.%Ge peritectic point alloys and Cu-13.9at.%Ge hyper-peritectic alloys for directional solidification at the temperature gradient of 25K/mm. Fiber CPCG microstructure is obtained in the both constituent alloys, nonetheless, its morphology regularity increases with the increasement of C0 and as well as G/V. Yet, no PCG microstructure was gained in Cu-Ge alloys.Finally, comparison of PCG and CPCG microstructrue was conduted between Fe-Ni and Cu-Ge peritectic alloys to analyze the influence of physical parameters, namely crystallized temperature range, peritectic platform temperature, the peritectic platform composition range and the ratio of solute and solvant, on PCG and CPCG behaviors of the two alloys. It was found in this paper that the bigger the crystallized temperature range is, the weaker the interface stability is, the longer the paste area is and the more difficult the PCG and CPCG microstructures can be formed; the higer the peritectic platform temperature is, the more obvious the radial gradient is and the more deflected the growth direction will be; the wider the peritectic platform constituent range is, the more difficult the solute couple can be formed and the more difficult the PCG microstructure will be formed; the smaller the ratio of solute and solvent is, the easier the interface is to be bent at the verge of the sample. Ultimately, Hillert peritectic reaction model is modified and the shape of three-phase region is re-discussed considering the additory surface tention generated by curvature.