Materials Chemistry and Physics, Vol.193, 244-252, 2017
Effect of low and high heating rates on reaction path of Ni(V)/Al multilayer
The effect of heating rates of Ni(V)/Al NanoFoile (R) was investigated with transmission electron microscopy (TEM). The Ni(V)/Al were subjected to heating by using differential scanning calorimetry (DSC), in situ TEM or electric pulse. Local chemical analysis was carried out using energy dispersive X-ray spectroscopy (EDS). Phase analysis was done with X-ray diffractions (XRD) and selected area electron diffractions (SAED). The experiments showed that slow heating in DSC results in development of separate exothermic effects at similar to 230 degrees C, similar to 280 degrees C and similar to 390 degrees C, corresponding to precipitation of Al3Ni, Al3Ni2 and NiAl phases, respectively, i.e. like in vanadium free Ni/Al multilayers. Further heating to 700 degrees C allowed to obtain a single phase NiAI foil. The average grain size (g.s.) of NiAl phase produced in the DSC heat treated foil was comparable with the Ni(V)/Al multilayer period (similar to 50 nm), whereas in the case of reaction initiated with electric pulse the g.s. was in the micrometer range. Upon slow heating vanadium tends to segregate to zones parallel to the original multilayer internal interfaces, while in SHS process vanadium rich phases precipitates at grain boundaries of the NiAl phase. (C) 2017 Elsevier B.V. All rights reserved.