Fe–Al–Si alloys have been previously reported as an interesting alternative to common high-temperature materials. This work aimed to improve the properties of FeAl20Si20 alloy (in wt.%) by the application of powder metallurgy process consisting of ultrahigh-energy mechanical alloying and spark plasma sintering. The material consisted of Fe3Si, FeSi, and Fe3Al2Si3 phases. It was found that the alloy exhibits an anomalous behaviour of yield strength and ultimate compressive strength around 500 °C, reaching approximately 1100 and 1500 MPa, respectively. The results also demonstrated exceptional wear resistance, oxidation resistance, and corrosion resistance in water-based electrolytes. The tested manufacturing process enabled the fracture toughness to be increased ca. 10 times compared to the cast alloy of the same composition. Due to its unique properties, the material could be applicable in the automotive industry for the manufacture of exhaust valves, for wear parts, and probably as a material for selected aggressive chemical environments.
Fe-Al-Si alloys have been recently developed in order to obtain excellent high-temperature mechanical properties and oxidation resistance. However, their production by conventional metallurgical processes is problematic. In this work, an innovative processing method, based on ultra-high energy mechanical alloying, has been tested for the preparation of these alloys. It has been found that the powders of low-silicon alloys (up to 10 wt. %) consist of FeAl phase supersaturated by Si after mechanical alloying. Fe2Al5 phase forms as a transient phase at the initial stage of mechanical alloying. The alloy containing 20 wt. % of Si and 20 wt. % of Al is composed mostly of iron silicides (Fe3Si and FeSi) and FeAl ordered phase. Thermal stability of the mechanically alloyed powders was studied in order to predict the sintering behavior during possible compaction via spark plasma sintering or other methods. The formation of Fe2Al5 phase and Fe3Si or Fe2Al3Si3 phases was detected after annealing depending on the alloy composition. It implies that the powders after mechanical alloying are in a metastable state; therefore, chemical reactions can be expected in the powders during sintering.
Iron aluminides are still deeply investigated materials for their use in power plants, automotive and chemical industry, and other sectors. This paper shows that it is possible to strongly improve their oxidation behavior by the addition of silicon. The description of the synergic effect of aluminum and silicon on the oxidation behavior of Fe–Al–Si alloys at 800 °C in air is presented. The oxidation rate, microstructure, phase, and chemical composition of these ternary alloys are compared with the binary Fe–Al and Fe–Si alloys. Results showed that the oxidation of Fe–Al–Si ternary alloys provides an oxide layer based on aluminum oxide with a low concentration of iron and silicon. Below this oxide layer, there is a layer of silicides formed as a result of depletion by aluminum, which forms a secondary oxidation protection.
Mechanical alloying is an interesting method of direct synthesis of various kinds of compounds and preparation of solid solutions using pure elemental powders by high-energy milling. In this paper, the modified process of mechanical alloying, which was developed at UCT Prague, is applied for the synthesis of intermetallics. This process-ultra-high energy mechanical alloying-uses extremely high ball-to-powder ratio (50-70:1), thus enabling very high degree of deformation of the powders, as well as the friction. Due to these effects, the temperatures up to 700 • C can be probably achieved locally for a short period. It enables to initiate the same chemical reactions between metallic powders as in self-propagating high-temperature synthesis. This study compares the ultra-high energy mechanical alloying with self-propagating high-temperature synthesis in selected alloy systems (Fe-Al, Ni-Ti, Fe-Al-Si) in order to explain the formation of intermetallics in this innovative process.
Magnesium alloy WE43 is well known for its low density and good mechanical properties. It has also fair corrosion resistance and relative usability up to 300 °C. All those properties are connected with the content of rare earth elements and determine this alloy not only for automotive and aviation industry, but also for applications as biodegradable materials. In this work, WE43 alloy prepared by powder metallurgy methods is characterized. Final products are prepared by cold uniaxial pressing with subsequent extrusion or spark plasma sintering (SPS). Present paper deals with the characterization of processing methods used for the WE43 alloy preparation and also the characterization of prepared WE43 products as themselves.
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