Research Onmicrostructure And Performance Of NiAl SHS With Induction Heating

The unique properties of intermentallic NiAl,including its high melting point,low density and good thermal conductivity,have attracted wide attention and extensive industrial studies.Owing to its high oxidation resistance properties it has been used as a coating material and sintered components for elevated temperature applications.This project applied high frequency induction heat assisted self-propagating high-temperature synthesis(SHS)to synthesis NiAl intermetallic compound.Analysis in induction heating parameters and particle size effects on microstructure and mechanical properties was conducted.Three different particle sizes of Al powders were mixed with 9 ?m Ni powders into slabs in Moore ratio 1:1.A high frequency induction heating process was used to ignite SHS reaction of the powder compact and NiAl intermetallic samples were successfully synthesized.To monitor the heating and reaction process,infrared thermometers were installed and focused on samples' surface.Characterization of phase composition and morphology included XRD,SEM,EDS and EBSD.For assessment of synthesis products' mechanical properties performance,Vickers hardness test and Nano-indentation test was conducted.Experimental results showed that in the case of Al powder particle size 0.05 ?m with 200 A induction heating current,compact was heated to about 350 degrees and no longer rising.No reaction had been found,echoed with the XRD results.When the induction heating current increased to 300 A,combustion synthesis occurred.With the same induction heating parameters,1 ?m and 10 ?m Al compacts were triggered SHS reactions,remained products contained NiAl phase.Presumably under these experimental conditions,when Al particle size at 0.05 ?m,compact particles lack to continuous contact between each other,preventing heat conduction.Also,as the coil current set at lower value the heating generation was slow,rendering it unable to quickly accumulate enough heat to ignite combustion reaction.The synthesized NiAl compounds of different process parameters showed uniform grain size in 40~90 ?m and Vickers hardness between 250~370HV.Large induction current promoted nucleation of liquid NiAl processes in the system,but prolong the induction heating time inhibited the grain grew up,led to grain shape change.Thus,larger particle size of Al powder,the smaller load current and longer continuous heat would generate finer grain and better mechanical properties.After corrosion,it's found that there were some multilayer polygon crystal structure distributed along crystal territories,particles of size in 10~40 ?m.The Nanoindentation showed the central regional of crystals exhibited higher value than outside side regional,at a scale of 8%~15%.The participation of electric magnetic field during the synthesis process showed effects on products crystal orientation.By EBSD analysis revealed that with the electromagnetic fields after combustion,samples' grain orientation distribution is more homogeneous.There was no discernible texture observed.In the absence of electromagnetic field after ignition,crystal orientation in the(111)plane showed preference as textures.In this end,this article attempted to analyze the synthesis mechanism and the effects on the crystal orientation as well.