Fabrication And Performance Of Spherical Alloy Powder Via De-wetting Of Liquid-solid Interface

With the development of metal three dimensional printing (3DP), ball grid array (BGA), and metal injection molding (MIM), shpercial metal powders with good spherical morphology and high coordination number have been used as high-performance powder metallurgy materials. Presently, the synthesis of a spherical metal powder mainly depends on general surface tension principles for the metal droplet in a gas medium (i.e., the liquid/gas interface), or in liquid medium (i.e., the liquid/liquid interface). Now, we will develop the third manufacturing mechanism, namely in solid medium (i.e., the liquid/solid interface) to expand the traditional powder technology. The main research contents and results are as follows:In order to achieve the diverifivcation regulation, we have studied the element volatile of liquid alloy with different pressures and successfully prepared high-performance spherical CuZn aolly powder. As reported, the Zn atoms were quite active and easily evaporated in the liquid state due to its high saturated vapor pressure of up to 0.101 MPa (normal atmospheric pressure) at 1178 K. The fast evaporation of surface Zn seriously influences the surface properties of non-equilibrium alloy droplet. Here, we develop an effective liquid-solid interfacial method to fabricate mono-disperse spherical Cu-Zn alloy powders. The structural analysis of these spherical alloy powders synthesized from the limited solid-solution of Zn in the Cu-38Zn alloy indicate that higher gas pressures can decrease Zn volatility without affecting the overall spherical morphology. These test also indicated that the Zn volatility was controllable by adjusting the atmosphere, and that the prepared particles were perfectly spherical even with a negative 0.04 MPa pressure. Furthermore, the large Zn solubility for the Cu-50Zn alloy with a smaller surface tension mean that the spherical powder fabricated under a 0.22 MPa argon atmosphere can confirme shape stability.To expand the traditional powder technology, we designed the in-situ de-wetting assisted fabrication of spherical Cu-Sn alloy powder via the reduction of mixture metallic oxides. As a traditional powder metallurgy technology, hydrogen reduction of metal oxides has some problems such as liquid sintering, agglomeration, non-sufficent reduction, etc. Here, we take advantage of liquid-solid interface dewetting to avoid the liquid phase sintering and annexation growth. After hydrogen reduction, the SEM micrographs of Cu-10wt.% Sn alloy powders fabricated at different temperature exhibit the spherical process. The perfect sphericity confirms that the liquid Cu-10wt% Sn alloy de-wets from the graphite surface. The cross-sectional micrographics of the spherical particles indicate that the particles are fully dense without pores and bulk inclusions, and the element mapping shows an evenly distribution of the Cu and Sn. Neither metal oxides nor pure metal was observed, the XRD of the spherical powder revealed that the intermetallic compounds are formed by the reaction between the reduced Cu and Sn. The particle size distribution is 10-30 μm. The narrow size distribution of spherical powder confirms the feasibility of the strategy using graphite as solid dispersant to suffer from agglomeration.To investigate the wetting or dewetting of the reaction system for liquid metal on graphite or alumina, we designed an experiment that Fe-based alloy powder was dispersed and spherized in a graphite or alumina medium. A carbide reactant at the interface or from carburization in the liquid metal makes the droplet less spherical. The splidfication process will also impact on the structure, reactants and morphology. However, low level surface impurities residue on the surface of spherical Fe-based alloy particle to suppress the wetting of the alloy on graphite. The cross-sectional micrographics of the spherical particles indicate that the particles are fully dense without pores and bulk inclusions. In addition, the differences of spherical morphological indicate that the FeSiB-AQ sample exhibit smooth surface, whereas the FeSiB-WQ sample contract and crinkle. The amorphous degree of spherical FeSiB-WQ powder directly exposed to water has been improved than that of raw materials. Magnetic characteristics of spherical powder quenched directly in water exhibit an excellent soft magnetic property (Ms=145 emu/g, Hc=2.8 Oe).