Processes involved during the production of Fe–W–Mo alloys by powder metallurgy

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Sintering of Fe–W–Mo systems under a dynamic atmosphere of argon has been studied by different experimental techniques, including dilatometric trials, X-ray diffraction, optical microscopy and electron probe microanalysis. It has been found that sintering at 1300°C for only 10 min allows compacts to be obtained with a relative density close to 80%. The results also show an improvement in the final density by molybdenum addition. On the other hand, the structure of the sintered samples was, mainly, constituted of a soft matrix of (Fe–M)α solid solutions (∼300 Hv) in which hard intermetallic compounds (∼1200 Hv) are dispersed. Furthermore, perturbing expansions have been observed during the sintering cycle. The first expansion occurred at about 620°C as a consequence of a Kirkendall effect. The second one arose at about 890°C in relation to Fe7M6 (where M is tungsten or molybdenum) formation. The latter expansion occurred at about 1200°C as a consequence of an increase in tungsten diffusion from indiffused areas to (Fe–M)a solid solutions and intermetallic compounds.

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