Propriétés et applications des alliages intermétalliques B2-FeAl

Abstract

Ordered FeAl intermetallic alloys are attractive materials for medium and high temperature industrial applications but their use has been restricted until now by their room temperature brittleness and their poor creep resistance. Powder metallurgy (P/M) techniques such as gas atomization and mechanical milling have been used to develop FeAl alloys with enhanced ductility and strength at both low and high temperatures. The improvement method combines ductilization by grain boundary strengthening, grain size reduction and oxide dispersion strengthening. These materials named FeA140 Grade 3 have been characterized and tested in the form of extruded bars. Microstructure and texture of as-extruded and heat treated samples have been studied by TEM and X-ray diffraction. Grains are 0,5 μm in size, resistant to recrystallization up to 1100°C and exhibit a strong wire texture parallel to the extrusion axis. The Y 2 O 3 dispersoids (20-30 nm in size) are cylindrical in shape and partially coherent with the matrix. The yield strength and the elongation of such alloys can reach 900 Mpa and 6,4% in air. Physical and mechanical properties of these materials are compared to some conventional engineering alloys in order to discuss the conceivable applications in aeronautical and automotive industries. Due to the high specific stiffness and strength of FeA140 Grade 3 alloys, promising applications are the substitutions of steels and superalloys for the fabrication of moving parts in thermal and aeronautical engines, and especially parts submitted to critical vibrating modes.