Microstructure and elevated-temperature behavior of molybdenum silicide/silicon carbide and iron-aluminum intermetallics synthesized by powder metallurgy techniques

MoSi{dollar}sb2{dollar}-based composites are promising for elevated-temperature structural applications, as a result of their unique combination of elevated-temperature strength and excellent oxidation resistance. Plasma spray offers advantages over conventional materials processing techniques, such as refined microstructure, accelerated chemical reaction kinetics and near-net shape manufacturing. In this work SiC-reinforced MoSi{dollar}sb2{dollar} was fabricated by a low-pressure plasma deposition technique. A significant improvement in room-temperature fracture toughness compared to monolithic MoSi{dollar}sb2{dollar} was obtained, as a result of SiC toughening and highly-refined microstructure. However, poor creep strength was also found, due to the formation of amorphous silica phase and the highly-refined microstructure. It is believed that the dominant mechanism for creep deformation in the plasma-sprayed MoSi{dollar}sb2{dollar}/SiC is grain boundary sliding.; Aluminides are potential elevated-temperature materials as replacements for Ni-base superalloys. Among various aluminides, Al-rich iron aluminides are of particular interest, due to their high-temperature strength and excellent resistance to oxidizing/sulfudizing environments, and low material costs. In this work, dual-phase Al-rich, Fe-Al intermetallic powders (i.e., FeAl{dollar}sb2{dollar}-Fe{dollar}sb2{dollar}Al{dollar}sb5{dollar} and FeAl{dollar}sb3{dollar}-Fe{dollar}sb2{dollar}Al{dollar}sb5{dollar}) were first produced by inert-gas atomization. The monolithic Fe-Al alloy and composite (containing Al{dollar}sb4{dollar}C{dollar}sb3{dollar}, Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, Y{dollar}sb2{dollar}O{dollar}sb3{dollar}, Ni or Cr) powders were subsequently consolidated using hot pressing and hot extrusion. The microstructure, room-temperature fracture toughness, oxidation resistance and creep behavior of consolidated materials were studied. Dense, equiaxed structures were obtained. Very low fracture toughness values were observed ({dollar}<{dollar} 2 MPam{dollar}sp{lcub}1/2{rcub}{dollar}), indicating the brittle nature of these materials. Only the Cr-reinforced FeAl{dollar}sb3{dollar}-Fe{dollar}sb2{dollar}Al{dollar}sb5{dollar} exhibited a K{dollar}sb{lcub}rm IC{rcub}{dollar} value greater than 2 MPam{dollar}sp{lcub}1/2{rcub}{dollar}. Excellent oxidation resistance and creep strength were obtained. The creep strength of monolithic FeAl{dollar}sb3{dollar}-Fe{dollar}sb2{dollar}Al{dollar}sb5{dollar} was found to be better than most aluminides compared, with the exception of TiAl. If oxidation resistance and material costs are considered, the FeAl{dollar}sb3{dollar}-Fe{dollar}sb2{dollar}Al{dollar}sb5{dollar} alloy may be more desirable than Ti and Ni aluminides for elevated-temperature applications.