Fe-Al - based intermetallics materials obtained by modified method of pressing at elevated temperature
Tomasz Durejko, Zbigniew Bojar Wojskowa Akademia Techniczna, Instytut Materiałoznawstwa i Mechaniki Technicznej, ul. Kaliskiego 2, 00-908 Warszawa
Annals 2 No. 5, 2002 pages 323-327
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abstract Nowadays Fe-Al - based intermetallics are one of the most interesting new materials for high temperature application. Excellent oxidation and carburization resistance, very good corrosion and wear resistance and low cost of production are their most important advantages in comparison to another groups of intermetallics and other special alloys. The cost of manufacturing process is essential part of all cost, especially for new materials, so there are many trials to introduce unconventional solutions of processing or to modificate well known technologies, such powder metallurgy. Two stage manufacturing process of FeAl phase based intermetallic sinters was described in this work. The initial stage of manufacturing was mechanical forming of iron and aluminium elemental powders mixture (60/40 at. %) by pressing at pressure of 300 MPa, at the temperature of 620oC. Various value of cyclic pressure frequency was used - from static version up to 60 Hz. It was stated that application of cyclic loading during initial pressing at elevated temperature intensified of oxides film fragmentation and made easier the process of aluminium diffusion. The processes of mechanical fragmentation of grains at pre-sinter structure were also observed. The higher was a frequency of applied loading the smaller was grain average diameter in final sinter (up to 5 times smaller than average diameter of initial powders particle). The structure of pre-sintered sample, after finishing the first stage of manufacturing was consisted of Fe2Al5 intermetallic phase and remaining part of pure iron. On the basis of Fe-Al equilibrium system analysis the temperature of 1250oC was choose for second stage of manufacturing and chemically and structurally heterogeneous pre-sintered materials were changed into homogeneous Fe-Al - based intermetallics. Natural by - product of iron-aluminium powder mixture conversion into aluminium-rich sinter is rising (or rather remaining of previously existing) oxides particles, mainly Al2O3. Thanks to application of technological variant with cyclic loading, the films of oxides became fragmented and not play a role of diffusion barrier. Additionally, they distinctly influenced grain coarsening-average grain size of intermetallic matrix not exceed (10÷15 μm). The final structure of sinter, which may be treated as complex composite material is consisted of Al2O3 particles distributed in fine-grained FeAl intermetallic matrix.