Showing papers by "Amol A. Gokhale published in 2017"

Niobium and Other High Temperature Refractory Metals for Aerospace Applications

Abstract: Refractory metal alloys based on Nb, Mo, Ta, W, and Re find applications in the aerospace industries because of their high melting points and high temperature strengths. They are generally produced by powder metallurgy technique due to their very high melting points. However, when refining is desired, melting under high vacuum becomes necessary, for which nuggets or powder based electrodes are employed. Niobium is the lightest refractory metal with density close to that of nickel, and exhibits good thermal conductivity. Niobium can be alloyed to improve high temperature strength and oxidation resistance. Applications in nuclear, aerospace, and defence sectors have been reported. The goal of current research in Nb alloys is to simultaneously achieve high strength and workability, and provide protection from oxidation for long-term operation. There is strong research interest in intermetallics also. This chapter will discuss the salient features of refractory metals and alloys in general, and Nb-based alloys in particular.

Aluminium–Lithium Alloys

Abstract: This chapter summarises the development and limitations of the first and second generation Al–Li alloys, and then discusses the recent developments leading to the third generation alloys. Emphasis is placed on the physical metallurgy of Al–Li alloys, progressive development of the three generations of these alloys, and finally the strategies for obtaining improved property combinations via various microstructural modifications closely linked to multistage processing. The way forward for Indian development of Al–Li alloys is also briefly discussed.

Effect of TiB2 and ZrB2 additions on structure and properties of Fe-7Al based light weight steel

Abstract: Microstructural modifications and their effect on tensile properties in an Fe-7 wt.% Al alloy by additions of 0.5% TiB2, 0.5% ZrB2 or both has been studied. Alloys are examined in the as-cast as well as in the hot-rolled and annealed conditions. Solidification structure of the Vacuum Arc Remelted pancake ingots was columnar dendritic. Further, boride modified alloys are found to have finer grains in as-cast as well as in hot-rolled and annealed conditions. In the annealed condition, boride containing alloys were found to have superior tensile yield strength, ductility and strain hardening behaviour. These property improvements are attributed to boride aided grain refinement during casting as well as during thermo-mechanical processing of the steels.

Prediction of Bubble Size Distribution in Aluminium Foam as a Function of %Titanium Hydride Addition

Abstract: Foaming of liquid aluminium by addition of foaming agent (TiH2 particles) is numerically simulated using population balance equations. Phenomena such as hydrogen release by the TiH2 particles, heterogeneous nucleation of bubbles in oxide surface cavities, and diffusion based bubble growth are modelled. A simple mass transfer coefficient, which varies inversely with the bubble size is used to estimate the bubble growth rate. Simulation is performed to study the effect of TiH2 content on the final bubble size distribution, total number of bubbles and average bubble size. In general, the average properties of the predicted distributions are close to the experimental values, whereas the spread in the bubble size is observed to be considerably narrower for the predicted values. The deviation in the spread of the distributions is attributed to the inverse bubble size dependent growth rate and non-inclusion of bubble coalescence in the model.

Melting, Processing and Characterization of Nb-10W-2.5Zr (Cb-752) Alloy

Abstract: Niobium based alloys are most promising materials for high temperature aerospace and defence applications at temperature above the use of nickel base superalloys (1100 °C). Cb-752 (Nb-10W-2.5Zr) alloy pancakes were prepared by non-consumable arc melting process under argon atmosphere using thoriated tungsten electrode. In view of the very high melting point of tungsten as compared to niobium, it was found necessary to melt the pancake multiple times to ensure complete dissolution of tungsten in the alloy. The temperature of hot forging as well as method for oxidation protection during hot forging was optimised. It was observed that the alloy could be hot forged at 1300 °C. It was further found that the silicide and aluminide coatings, and evacuated stainless steel jacket protected the alloy from oxidation during hot forging. The forged pancakes were cold rolled to 1.5 mm thick sheets. The room temperature mechanical properties of Cb-752 alloy sheet produced from the pancakes were comparable to the data reported in literature.