Aluminothermic preparation of Hf-Ta and Nb-10Hf-1Ti alloys and their characterization

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Aluminothermic preparation of Hf-Ta and Nb-10Hf-1Ti alloys and their characterization

Sharma, I.G. / Majumdar, S. / Chakraborty, S.P. / Suri, A.K.

The high temperature materials capable of withstanding high stress levels at elevated temperature together with excellent oxidation resistance have received considerable attention since the emergence of aerospace industries. Alloys such as Nb-10Hf-1Ti and Hf-20 to 30 wt.% Ta are being considered seriously for development to meet the growing demand for aerospace and other high temperature requirements. Currently the alloys are prepared by conventional melting route either by arc or induction melting techniques. However, use of high vacuum and high temperature expensive furnaces, high cost of the alloying constituents, probability of segregation of alloying components during melting are some of the major deterring factors in the production of these alloys through melting route. In the present investigation, the above problems have been eliminated to a great extent by adopting aluminothermic (thermit) smelting technique for the preparation of Nb-10Hf-1Ti and Hf-Ta alloys by direct co-reduction of the oxides of individual components. In the adopted process the heat generated from the chemical reactions, serves the function of melting and alloying. By maintaining 10% excess aluminium in the charge, specific heat in the range of 600-700 kcal kg^-1 and varying CaO and CaF₂ from 10 to 15% of overall charge has enabled to achieve a yield figure of 95% for both the alloys with excellent quality of the alloy product. The alloys are further remelted and characterized with respect to composition, microstructure, thermal analysis, hardness and rolling.