Satnam Singh

Effect of quenching rate on the properties of melt-spun FeNbCuSIB ribbons

Abstract Amorphous ribbons of composition Fe 73.5 Nb 3 Cu 1 Si 13.5 B 9 and Fe 72 Nb 4.5 Cu 1 Si 13.5 B 9 were prepared by rapid solidification technique. A convergent nozzle of suitable dimensions was chosen so as to minimise the turbulent flow of the fluid. The separation between the nozzle and the quenching wheel surface was kept constant at 0.5xa0mm. The quenching rate was directly proportional to the wheel velocity as the dimension of the crucible and the position of crucible with respect to wheel surface were kept fixed in all the trials. The thickness of ribbon was found to decrease while the ductility increased with the increase of wheel surface velocity, i.e. with the increase of quenching rate. The amorphous to nanocrystalline transformation temperature was found to remain constant when the wheel surface velocity was more than 32xa0m/s and also the soft magnetic properties were found to be superior.

Phase-transformations in Mn-Al permanent-magnet alloys

Phase transformation studies have been made of the Mn-Al alloys with compositions near the equiatomic range with or without small amounts of carbon, copper and nickel, using differential thermal analysis, X-ray diffraction and optical and electron microscopy. The high temperature hexagonalɛ phase obtained by quenching, transforms to the ferromagneticτ phase between 500 and 550° C and on further heating transforms back to the hexagonal phase between 750 and 950° C. Also, on controlled cooling of theɛ phase from about 900° C, the ferromagneticτ phase is formed between 800 and 670° C. TEM studies have shown the presence of the B19 ordered phase, ferromagneticτ phase and Mn5Al8 precipitates even in quenched alloys.

Functional gradation through preferential crystallisation and interfacial activity in rapidly quenched Fe/Co-based bilayered ribbons for bend sensors

Rapidly quenched bilayered ribbons comprising one layer as Fe73.5Nb3Cu1Si13.5B9 (FM) and the other layer either as Fe74.5Nb3Si13.5B9 (FNb) or Co72.5Si12.5B15 (CSB) alloy designated as BLFM/FNb and BLFM/CSB, respectively, have been addressed. Phase transformation, thermomagnetic transitions, saturation magnetization, and soft magnetic properties of individual layers were revealed in the functional properties of bilayered ribbons. Properties of bilayer could be endorsed with respect to the single layered Fe73.5Nb3Cu1Si13.5B9, Fe74.5Nb3Si13.5B9, and Co72.5Si12.5B15 alloy ribbons. Selective devitrification of the layers in the bilayers could be induced through optimum heat treatment. Enhanced bend sensitivity was revealed in BLFM/CSB through generation of desirable phases in the bilayers of the bilayered ribbon. Synergistic diffusivity of Fe and Co with its consequent effect on interfacial zone of BLFM/CSB bilayer was observed.

Effect of magnetizing field on the martensitic transformations in a melt spun NiMnGa alloy

The investigation addresses the effect of magnetizing field on the magnetic properties of melt spun Ni52.84Mn19.6Ga27.56 (at%) alloy ribbons. Magnetization behaviour at different fields was observed using a superconducting quantum interference device magnetometer for heating and cooling cycles. The plots showed distinct changes in magnetization around the characteristic temperatures at austenitic start and finish (AS, AF), martensitic start and finish (MS, MF). With increasing field AS, MF were unaffected. In the range of martensitic start and its finish temperature, the zero field cooled and field cooled measurements indicated magnetization drops indicating antiferromagnetic interactions, which is characteristic of the martensitic phase formation. It was shown from x-ray diffraction analysis that the low martensitic fraction in the majority austenite phase induced the splitting in the L21 austenitic ordering. This was further corroborated by the evidence of a few martensitic plates around grain boundaries at room temperature which is close to martensitic start temperature.