Showing papers by "Amol A. Gokhale published in 2018"

Additive laser deposition of YSZ on Ni base superalloy for thermal barrier application

Abstract: In the present work, the feasibility of additive laser deposition (ALD) of YSZ on IN625 substrate was studied using two different bond coats (BC) viz. NiCr and NiCrAlY and two different deposition schemes, consisting of direct deposition of YSZ (DI) and compositionally graded (CG) deposition of bond coat-YSZ. These deposits were examined for microstructural features, and their ability to provide thermal barrier to heat flow and to withstand thermal cycling were evaluated. It has been observed that DI and CG NiCr-YSZ coatings survive 240 cycles whereas CG NiCrAlY-YSZ samples survive

Role of Temperature and SiC P Parameters in Stability and Quality of Al-Si-Mg/SiC Foams

Abstract: Composites of Al-Si-Mg (A356) alloy with silicon carbide particles were synthesized in-house and foamed by melt processing using titanium hydride as foaming agent. The effects of the SiCP size and content, and foaming temperature on the stability and quality of the foam were explored. It was observed that the foam stability depended on the foaming temperature alone but not on the particle size or volume percent within the studied ranges. Specifically, foam stability was poor at 670°C. Among the stable foams obtained at 640°C, cell soundness (absence of/low defects, and collapse) was seen to vary depending on the particle size and content; For example, for finer size, lower particle contents were sufficient to obtain sound cell structure. It is possible to determine a foaming process window based on material and process parameters for good expansion, foam stability, and cell structure.

Effect of tungsten and zirconium on structure and properties of niobium

Abstract: Abstract The individual and combined effects of W and Zr additions on macrostructure, microstructure and mechanical properties of Nb have been investigated. Nb, Nb-10 wt% W, Nb-2.5 wt% Zr and Nb-10 wt% W-2.5 wt% Zr alloy ingots were prepared by electron beam drip melting using high purity Nb, W and Zr rods. Additions of W and Zr resulted in significant improvement in hardness and room temperature tensile strength. It is seen that the effect of 10 wt% W addition is more than that of 2.5 wt% Zr addition in improving room temperature strength of Nb, although on ‘per wt% addition’ basis, Zr is a more effective strengthener than W. It is also observed that the cumulative effects of 10 wt% W and 2.5 wt% Zr on grain refinement and strengthening are more than their respective individual effects.

Foaming and Compressive Properties of A359/SiCP Metal Matrix Composites

Abstract: In this work, a commercial MMC (A359-20% SiCP) was remelted, diluted to different particle contents (5 to 20 vol. %), and foamed at a fixed temperature using titanium hydride. In general, excellent foamability could be obtained for all SiC contents. Foam stability (retention of expansion), on the other hand, depended on SiC content. Remelting and diluting procedures also influenced the foam stability on account of varied oxide contents generated upon impeller stirring. The foam quality, in terms of cell wall integrity, improved with increasing SiC content. Despite the defect levels, good compression properties were obtained in these foams, which are close to model predictions. Overall, this system is very promising for producing good quality foams by melt processing technique.

Effect of Foaming Temperature on Bubble Size Distribution of Liquid Aluminium Foam: Modeling and Experimental Studies

Abstract: The present study examines the effect of foaming temperature on the final foam expansion and the bubble size distribution of liquid aluminium foam through mathematical modeling and validation experiments. The model calculates the rate of hydrogen release from the foaming agent (TiH2) particles, super saturation of the melt, nucleation and growth of bubbles and finally, evaluates the evolving bubble size distribution using a population balance approach. The model does not consider bubble coalescence and breakage and uses only solute diffusion for bubble growth. The simulation is performed for two conditions; firstly, for pure temperature effects and secondly, for temperature and TiH2 quantity combined effects. Upon comparison of simulation results with the experiments, following important observations are made; firstly, the predicted total number of bubbles is found to be one order of magnitude higher than the experiments while the predicted average size is one order of magnitude lower. Secondly, the spread of the predicted distributions is observed to be much narrower. These discrepancies are considered to be due to bubble coalescence and coarsening which are not modeled and shown to be strongly influenced by the foaming temperature.