Mechanical and structural characterization of uniaxially cold-pressed Fe 2 Mo powders
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V. Agarwala Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Roorkee, 247667, Uttaranchal, India (Received 29 January 2002; accepted 6 May 2002)
In this work, Fe2Mo intermetallic powder, produced by H2 gas reduction of Fe2MoO4 was characterized by techniques like x-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM studies confirmed the presence of nano- and microcrystalline grains of Fe2Mo. The above powders when compressed uniaxially showed a logarithmic relation with “relative density”, ␦r, of the compacts. The multiple compaction mechanisms were analyzed by Kawakita’s and Balshin’s models. Vickers hardness number, VHN, was found to increase linearly with ␦r of the compacts. The hardness of Fe2Mo intermetallic when ␦r ⳱ 1 was estimated as 343 VHN. Using Tabor’s analysis, the yield strength of Fe2Mo was found to be about 1100 MPa. This value was further confirmed from the details of relative broadening (112) Bragg peak of Fe2Mo obtained from XRD analyses of Fe2Mo at different compaction pressures.
I. INTRODUCTION
Intermetallics form an exclusive class of materials with the advantages inherent of both ceramic and metallic materials. The materials exhibit properties being distinctive of ceramics like high-temperature stability (approximately 0.5 Tm, where Tm is the melting temperature), wear, oxidation, and corrosion resistance as well as high Young’s modulus, in addition to those characteristic of metallic materials, viz., toughness and thermal shock resistance and other physical properties. Molybdenum has several properties that make it attractive for application as an alloying/reinforcement agent as, for example, contribution to hardness and toughness of steels and high corrosion resistance. Its outstanding refractory properties maintain functional reliability under ever increasing temperatures meeting requirements for electronic and aerospace industry. While structural intermetallics are most suited for high-temperature applications due to their unique mechanical properties, the main obstacle to overcome is their brittleness. The causes of brittleness in intermetallics are mainly due to either insufficient number of slip systems or grain boundary weakness.1 One technique to improve ductility in intermetallics is by microstructural control, which calls for grain refinement and grain boundary cohesion. On the other hand, the grain size required to produce ductility may be very small (submicron order) and difficult to achieve.2 Schulson and 1954
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J. Mater. Res., Vol. 17, No. 8, Aug 2002
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Barker3 suggest a critical grain size in the intermetallic NiAl below which polycrystalline aggregates are ductile in tension. According to these authors, the finer the grain size below the critical values, the greater is the ductility. Inoue, Tomioka, and Masumoto4 employed rapid solidification by a melt-spinning method to obtain very fine grain size in Ni–Al–X composites (X ⳱ Fe, Mn, Cr, Si, and Co). These auth
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