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DISPERSION STRENGTHENED MOLYBDENUM AND MOLYBDENUM-BASE ALLOYS
Technical documentary rept.
AEROSPACE CORP EL SEGUNDO CA LAB OPERATIONS
Pagination or Media Count:
Study was begun on the possibility of introducing a dispersoid capable of increasing the strength and recrystallization temperature and decreasing the grain growth characteristics of molybdenum. Candidate dispersoids were screened on the basis of physical properties, chemical inertness, and availability. The most promising candidate was found to be thoria. Additions of ThO2 were made by adding an aqueous or alcohol solution of ThNO34 to the powders, then decomposing the compound by heating in dry hydrogen. Billets were hot-pressed in graphite dies lined with molybdenum foil. The as-pressed densities were in the order of 98 of theoretical. The hot- pressed billets were extruded and swaged to bar stock. The bar stock was evaluated in terms of recrystallization behavior, grain growth characteristics, and elevated temperature strength properties. The uniformity of the matrix and the composition of dispersed phase were followed by electron probe analysis at various stages of the fabrication schedule. Thoria was found to be quite effective in stabilizing the microstructure and increasing the strength of molybdenum. The TZM alloy with ThO2 was found to have better workability than molybdenum with ThO2. Due to an interaction between Ti, Zr, and ThO2, the distribution of ThO2 became quite coarse and no strength improvement was experienced. Out of several alloying elements only Hf showed promise for combined alloy and dispersion strengthening because of its compatibility with ThO2.
APPROVED FOR PUBLIC RELEASE