Fabrication of Ni-Al Intermetallic Compounds on the Al Casting alloy by SHS Process

摘要

Combustion synthesis with the advantages of time and energy savings has been recognized as an attractive alternative to the conventional methods. In order to improve the surface properties of Al casting components, Ni-AI intermetallic compounds are fabricated by the SHS(Self-propagating High temperature Synthesis) process using the reaction heat of the elemental powders. Three kinds of nickel aluminides, Ni_3Al, NiAl and NiAl_3 were produced by the emission heat from the Al molten metal and a coating layer of intermetallic phase was simultaneously formed on Al casting alloy surface. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM), energy dispersive x-ray spectrometer (EDS), Electron Probe Micro Analyzer (EPMA) and X-ray diffractometer(XRD). The microstructures of nickel aluminides were varied by casting temperature, mixing condition and mixing ratio of elemental powders. The reaction layer formed between Al alloy and the powder mixtures of nickel aluminide was observed to be different depending on process conditions such as green density of elemental powders, molten metal temperature and chemical composition. The differences of junction behavior with pouring casting alloys were compared and the schematic model of bonding reaction was defined.