Papers by Keyword: Liquid Phase Separation

Abstract: Liquid phase separation is a common phenomenon observed in various types of condensed matter, including metals. The microstructure of Co-Cr-Mn-Fe-Ni-Cu and Co-Cr-Fe-Mn-Ni-Ag high entropy alloys (HEAs) with liquid phase separation was investigated. Dual fcc phases were observed in CoCrFeMnNiAg, CoCrFeMnNiCu, and CoCrFeMnNiCu₂ HEAs. A macroscopically phase separated structure formed via liquid phase separation was observed in CoCrFeMnNiAg HEA, and conventional dendritic structures were observed in CoCrFeMnNiCu and CoCrFeMnNiCu₂ HEAs.

Abstract: In this paper, the liquid phase separation and solidification process of the Al₇₅Bi₉Sn₁₆ immiscible alloy were studied with calorimetric and resistivity methods to make the melt superheated treatment process. The impact of melt overheating treatment (MOT) on the phase constitution and solidification microstructures were investigated using X-Ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to determine the structural sensitivity to the melt superheated degree, and find a new strategy for improving the forming ability of the core-shell structure of the Al₇₅Bi₉Sn₁₆ alloy. The results show that: the liquid phase separation and precipitation of primary (Sn) phase occur in 1039K-880K and 460K-403K; the core-shell structure with Sn-Bi-rich core and Al-rich shell can be formed under conventional casting conditions; the melt overheating treatment (MOT) can promote the formation of core-shell structure by increasing solidification time t₀ and decreasing the average solidification rate v.

Abstract: In order to solve a problem of the low mechanical properties of Manual SHS Welding joint, a new iron-base manual SHS welding material was developed by CuO+Al and Fe₂O₃+Al being the thermit and adding iron alloy materials. The structure and properties of the welded joint were studied. The results indicated that: Cu-Fe alloy in the molten pool experiences liquid phase separation during rapid solidification, and the weld metal is macroscopically separated into one Fe-rich part and one Cu-rich part. Fe-rich phase is filled in the welding line. The higher Fe supersaturation is in the Cu-Fe weld metal, the more notablely and quickly liquid phase separates. At the same time, tensile strength of the welded joint was close to 520 MPa, and impact toughness was close to 32.1J/cm², and surface hardness was also close to HB360. It also indicated this technology can meet the need of repair of metal parts in field.

Abstract: The microstructure of Cu₇₅Cr₂₅ alloys was investigated by using vacuum non-consumable arc melting, electromagnetic levitation and splat quenching. The microstructure and solidification behavior of the Cr-rich were investigated by scanning electron microscopy (SEM). The results showed that inhomogeneous Cr-rich dendrite distributes on Cu-rich matrix for arc melted alloys. The microstructure consisting of a fine dispersion of Cr-rich dendrite in a Cu-rich matrix for electromagnetic levitated alloys. However, the morphology and size of the Cr-rich phase vary greatly with the cooling rate for splat quenched alloys. The Cr-rich phase show both dendrites and spheroids, this means liquid phase separation occurred during rapid solidification.

Abstract: Phase selection of undercooled Cu₈₅Cr₁₅ composites was analyzed by using different solidification conditions. The results revealed that the arc melted composites generally have non-uniform Cr-rich dendrites distributes on Cu-rich matrix. Due to strong electromagnetic stirring, uniform Cr-rich dendrites distributes on Cu-rich matrix for electromagnetic levitation melted composites. Both fine Cr-rich dendrites and Cr-rich particles coexisted in Cu-rich matrix for splat quenched composites, which means liquid phase separation occurred for the high cooling rate.

Abstract: Behavior of Cr-rich phase in rapid solidification Cu71Cr29 alloys was investigated by using melt spinning and splat quenching. The microstructure and solidification behavior of the Cr-rich were investigated by scanning electron microscopy (SEM). The results showed that the alloys generally have a microstructure consisting of a fine dispersion of a Cr-rich phase in a Cu-rich matrix. However, the morphology and size of the Cr-rich phase vary greatly with the cooling rate. On the one hand, the average size of the Cr-rich phase is reduced with increasing cooling rate. On the other hand, the Cr-rich phase show both dendrites and spheroids for lower cooling rate but only spheroids for the higher cooling rate. This means liquid phase separation occurred during rapid solidification. The results were discussed with respect to the formation of the Cr-rich spheroids during rapid solidification.

Abstract: The paper presents a Fe-base manual SHS Welding material with CuO+Al and Fe2O3+Al being the thermit and adding ferroalloy materials for solving the problem of low mechanical properties of the manual SHS Welding joint. The structure and properties of the welded joint were studied. The results indicated that: the welding was fusion welding, and weld appearance is good. Cu-Fe alloy in the molten pool experiences liquid phase separation during rapid solidification, and the weld metal is macroscopically separated into one Fe-rich part and one Cu-rich part. Fe-rich phase is filled in the welding line. At the same time, tensile strength of the welded joint was close to 500 MPa, and impact toughness was close to 40J/cm2, and surface hardness was also close to HB350. It also indicated this technology can meet the need of repair of metal parts in field.

Abstract: Rapid solidification of CuFe10 alloys was carried out by melt spinning at three wheel speeds 4, 12 and 36 m/s. The microstructure and solidification behavior of the ribbons was investigated by scanning electron microscopy (SEM). The results showed that the ribbons generally have a microstructure consisting of a fine dispersion of a Fe-rich phase in a Cu-rich matrix, and that the morphology and size of the Fe-rich phase vary with the wheel speed. For lower wheel speeds, the Fe-rich phase shows dual morphologies, dendrites and spheroids. The Fe-rich spheroids show a wide distribution of size, and have a larger mean size on the free surface than on the wheel surface. Some Fe-rich dendrites are distributed around the Fe-rich spheroids, this means liquid phase separation occurred during rapid solidification. The Fe-rich phase shows one morphology-spheroids and the size of Fe-rich spheroids decreasing as the wheel speed increasing. The results were discussed with respect to the formation of the Fe-rich spheroids during rapid solidification. The microhardness of the ribbons increasing with the increasing of the wheel speed for the grain refining and the increasing of supersaturated solid solution.

Abstract: A Fep/Cu composite coating was developed based on laser cladding process in immiscible liquid system. The microstructure of the coatings is characterized by a homogeneous distribution of Fe-rich spherical particles dispersed in the Cu-rich matrix. The size of the Fe-rich spheres decreases and their number density increases with the decrease of the heating input. The micro-hardness and wear resistance results show that the micro-hardness of the composite coating (spherical particle (380 ~ 450 HV0.2) and the Cu-rich matrix about 200 HV0.2) is far better than that of the copper (70 HV0.2), the wear resistance of the composite coating is almost twice of the copper. Such Fep/Cu structure composite coating have a good combination of high strength and corrosion resistance (Fe-rich phase) and high electric and thermal conductivities (Cu-rich phase) with many potential advanced applications in electronic devices.

Abstract: A possibility of a modification of the Jackson-Hunt theory of an oriented structure formation is analysed. A new model for the formation of a concentration field ahead of growing regular lamellae with respect to the solid / liquid interface shape is presented. A coordinate system applied in the model is attached to the solid / liquid interface to be advancing in the z - direction, identically with interface moving at a constant velocity, v . The solution to a diffusion equation is given for the improved formulation of the boundary conditions. The boundary conditions are related to the interplay between the diffusion required for phase separation and the formation of the interphase between both lamellae. The boundary conditions are formulated to establish the stability of lamellar structure formation under steady-state conditions. It is assumed that stable growth of the lamellae is ensured by the separation of concentration fields within a boundary layer ahead of the solid / liquid interfaces of both the α and β " phases. Coupled lamellar growth with the presence of a leading phase protrusion is defined. The general mass balance is analysed for a solute concentration in the liquid, taking into account a planar solid / liquid interface. A local mass balance is also ensured but it requires envisaging a protrusion of the minor eutectic phase. The existence of a lead distance is confirmed experimentally for the (Pb)-(Cd) eutectic system. The difference in undercooling is also considered as a phenomenon associated with the separation of concentration fields and the existence of a protrusion to relax the assumption of an isothermal interface (ideally coupled growth) given by the Hunt and Jackson theory.