Publications

Multi-principle element alloy FeCoNiCu with varying Sn addition was undercooled using the meltfluxing technique to illustrate the dependence of growth kinetics on Sn addition. The alloy FeCoNiCuSn0.5 shows morphological variation in the microstructure from dendritic to equiaxed grain morphology with the increase in undercooling. The alloy FeCoNiCuSn5 shows dendrite morphology with undercooling. The dendritic growth velocity was sluggish with solute addition,i.e., at an undercooling of 200 K, the growth velocity decreased from ~25 m/s to 6 m/s while varying Sn concentration from 0.5 to 5 at % suggesting solute drag effect. The microhardness improvement could be correlated to the microstructure refinement achieved during undercooling.

A nanosecond laser ablation combined with LIBS is demonstrated for a micro-scribing of copper film on dielectric material. NaCl solution was used as a laser-activated etchant in the final scan for minimizing the thermal damage.

The influence of a subnanosecond pulsed laser-based scribing of copper (Cu) and aluminum (Al) in salt solutions (NaCl and KCl) on the formation of microchannels is reported. This technique allows laser scribing along with selective etching of Cu and Al thin films. The focused laser beam can elevate the surface temperature on the sample and hence the chemical reaction rate, resulting in combined ablation with selective-area etching. The depth of microchannels in Cu and Al films is increased by 3–5 μm using the proposed hybrid technique. The average surface roughness values in the microchannel are decreased compared to that of scribing in water and air. The hybrid approach of laser-based scribing combined with electrochemical etching in neutral salt solutions allows uniform channel with almost no redeposit layer and debris on the channel edges. Further, an approach wherein, an application of direct current (DC) voltage (1.2 V) between the tool and the workpiece while laser scribing of Cu and Al in salt solution was demonstrated to improve the channel depth by few micrometers. This hybrid machining technique has also resulted in a reduction in the surface oxidation near the laser-ablated zone compared to that observed in air and water-based experiments.

Ti activated 72Ag-28Cu filler alloy was reinforced with micro/nano-Al2O3 ceramic particles for active brazing of synthetic diamond grits with 1045 steel. Microstructural changes due to reinforcement and corresponding influence on abrasion resistance characteristics of the modified filler alloy were observed. Different weight percentages (wt%), each of micro and nano-Al2O3 reinforcements, were tried. Micro-Al2O3 ceramic reinforcements were found to be uniformly distributed in the microstructure of the modified filler material. Alumina particles reacted with titanium to form hard Cu3Ti3O and TiO reaction compounds. Nano-Al2O3 reinforcements showed a tendency to get clustered, impairing the improvement in abrasion resistance property of the primary filler alloy. 1 wt% micro-Al2O3 added filler alloy underwent 58% less volumetric wear than the primary Ag-Cu-Ti alloy during the pin-on-disc test. This micro- reinforced filler also could effectively braze diamond grits with the steel without any significant deterioration in its wetting ability on diamond surface and joint strength, compared to its counterpart having the primary formulation.

This paper covers the efforts of developing a compact dressing attachment on a cylindrical grinding machine for on-line laser dressing of wheels used in internal grinding of SAE-52100 bearing steel parts. With this attachment, alumina wheel was dressed with different conditions of dressing and its suitability for grinding was evaluated by analysing the topography on laser dressed wheel surface with scanning electron microscope and confocal laser scanning microscope. Out of these images, confocal microscopic images were found to present 3d images of dressed wheel surface. Evaluation of these images, in terms of Spk, Sk and Svk parameters obtained from bearing area curves, and their comparison with those parameters obtained from the images over diamond dressed surface, indicated the suitability of dressing leads of 0.016 mm/rev and 0.032 mm/rev for dressing of wheels with pulsed laser radiation. Effectiveness of these conditions was further established by evaluating the performance of laser dressed wheels in terms of G-ratio values, form error and finish observed on ground parts. Further, this work suggests the application of on-line imaging and analysis of laser dressed surface for quickly identifying suitable conditions of dressing of internal grinding wheels with on-line laser dressing attachment so as to make laser dressing as an economically viable process for certain critical applications.