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Directionally Solidified in situ Metal Matrix Composites. Part 1

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Final rept. 1 Nov 1974-1 Jan 1976,

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The aim of the present alloy screening program was to identify new eutectic superalloys suitable for the manufacture of directionally solidified turbine blades operating at up to 1150 C. In the course of this program, five eutectics not previously investigated have been found to meet the corresponding objectives of a melting point above 1200 C, a specific gravity below 9 gcc and a reasonably low oxidation rate. The properties are comparable to those of the presently most advanced eutectic superalloys, such as Ni-2.5A1-19.7Nb-6Cr or Co20TaC-15Cr-8.5Ni-6W. Their oxidation rates, already comparable to that of Co- TaC, measured in the present study, could be further improved by compositional adjustments. These results were obtained on the basis of a screening of available phase diagrams for 107 alloy systems based on Ni, Co and Fe, from which 52 alloy systems were retained for further study. Twenty-eight simple ternary systems, either not previously evaluated or not described in sufficient detail, were examined experimentally by preparing several samples of compositions close to that determined by a semi-empirical graphical method as closest to the expected eutectic. As a result, 22 eutectics were identified and characterized in terms of melting temperature, microstructure and estimated density. Of these, 10 eutectics were found to meet the objectives of a melting point above 1200 C, a regular microstructure presumably amenable to directional solidification and a density below 9 gcc. They were therefore subjected to a systematic investigation of their oxidation resistance, leading to the identification of the 5 promising eutectics previously mentioned.

Subject Categories:

  • Properties of Metals and Alloys

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