Microstructure and phase transformation behaviour of Co–Ni–Al alloy by spark plasma sintering

Abstract

The CoNiAl alloys are prepared by using the spark plasma sintering (SPS) technique. The present study investigates the crystalline structure, Phase analyses, Physical and mechanical properties of the stoichiometric Co38 Ni35 Al27 alloys. The significant control over the magnetic and structural transformation temperature and high ductility of CoNiAl makes it a potential high-temperature Ferromagnetic shape memory alloy (FSMA). The test specimens were prepared at SPS temperature of 1000 °C at a sintering pressure of 50 MPa. The microstructural identification and the phase analyses of the mechanically alloyed powders and the SPS sintered specimens were investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. The room temperature XRD results revealed that the sintered samples have body centred cubic b phase. A comparison of the room temperature XRD results for alloy powders and that of the sintered alloys has been studied. From the SEM images, we observe that the sintered alloys have martensitic twin variants. Also in the optical microscope, we observe the martensitic variants in the b phase structure. From the thermal studies, we analysed the phase transformation behaviour of the sample from b’ martensite to b martensite at 120°.