Research Of Intermetallic Compound Ni-Al By SHS Using Nanopowder

Self-propagating High-temperature Synthesis (SHS) is a relativelynovel and simple method for making certain advanced ceramic,composite and intermetallic compounds. This method has obtained aconsiderable attention as an alternative to conventional furnacetechnology. In recent years, much attention has been given to nanometerpowders. Extensive fundamental and applied investigations of powdershave been performed worldwide. Physical and chemical propertydependence on particle size, which might be different from that of bulkmaterials , has been a most interesting subject on improving theproperties of some materials and obtaining the powders for newapplication as technological advancement demands. Fabrication byusing nano-powders prepared by wire electrical explosion successfullyby means of self-propagating high-temperature synthesis (SHS) is apiece of meaning work.Ni-Al of intermetallic compounds was made from SHS, whichreact in vacuum. Nano-Al powder made by electric exploded canreduce Tig evidently. We think there are several reasons. Lager numberof surface atoms, nano-Al surface atom is more active. Its surface atomhas more energy than inside atom. Electric exploded nano-Al powderhas more surface energy and deposited energy. So the atoms ofnano-Al surface can easily escape from inside atom magnetism. Afterit is pressed into cylinder, the up-down surfaces have much higherinterface energy. Higher interface energy becomes the drive power ofatom move. Along with the increasing of temperature the atom ofNano-Al crystal face diffuse at a high speed on to Ni crystal face.Before the surface of cylinder was ignited, the system has reacted. Thisis solid state reaction. But nano-Al content is high to 28.6%. Itsproduct is monophased Ni3Al. Obviously Binary phase diagram ofNi-Al system is not fit for nano-Al powder. It is expected to build newBinary phase diagram of Ni-Al system. Because nano-Al crystal grainsare small, and then the size of product becomes smaller. Small crystalgrains have some influence on physical mechanics property forexample hardness. We analysis separation product made by reaction invacuum. Toward Ni-Al reaction system, heat the cylinder and there isliquid phase on the nano-Al crystal surface when it reaches Al meltingpoint. Under gravity, liquid-state Al flows along unreacted nano-Aland Ni grain boundary. At this time Al liquid can dissolve solid-stateNi and form Ni-Al solid solution. Then along with the increasing oftemperature, there is more liquid phase. At this time, Ni-Al solidsolution flows and spreads all around in the form of volumetrical flow.When solid solution flows onto the outside surface of cylinder, it canform round sphere adhered to the cylinder. Experiments prove that itgenerated more round sphere on the outside surface of cylinder whennano-Al powder is deviation stoichiometric ratio.Above all, SHS by nano-powders by electrical explosion invacuum has much value. Work such like this is fully promising.