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Microstructure And Properties Of Fe-Al-Ta Eutectic Alloy Prepared By Directional Solidification

Posted on:2017-01-25Degree:MasterType:Thesis
Country:ChinaCandidate:M YangFull Text:PDF
GTID:2271330503470363Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
Intermetallic compounds have been paid more attention in the area of high temperature structural materials in these years,because they have many characteristics, e.g. high strength, superior oxidation and corrosion resistance,thoughness between high temperature ceramic and Ni based alloy and good wear and impact resistance.Therefore intermetallic compound are expected to replace stainless steel,titanium alloys and Ni based alloys. Fe-Al alloy plays an important role in these intermetallic compounds due to its low price and light density. However the applications of Fe-Al alloy in engineering have been limited by their poor ductility, low strength and creep resistance above 600℃.In this paper, Ta was added in Fe-Al alloy and the Bridgman directional solidification technique was adopted to produce Fe-Al-Ta eutectic in situ composites at different solidification rate. The optical microscope, scanning electronic microscope, transmission electron microscope, X-ray diffraction, microhardness tester and tensile tester were used to analysis the microstructure morphology, phase composition and the effects of solidification parameters on the microstructure and properties of the Fe-Al-Ta eutectic alloy.This eutectic alloy is metal matrix composite, its microstructure is regular eutectic structure at the solidification rate=6-80μm/s, because of high temperature gradient and the single direction of heat flow. Reinforced phase Laves Fe2Ta(Al) evenly arranged in the matrix phase Fe(Al Ta) in the form of lamellar or rod. At the low solidification rate R=6μm/s, the Laves phase in form of lamellar and matrix are coordinated growth. With the increase of solidification rate the morphology of Laves Phase transform from lamellar to fiber gradually, and the solidified microstructure can be refined. Due to the high constitutional undercooling, the lamellar or rod spacing will be decreased too with the increase of solidification rate, the relation between the spacing and the solidification rate meets the Jackson-hunt criterion λ2R=K well. The morphology of the solid/liquid interface evolves from planar to cellar, then to planar interface again. The relationship of the Fe-Al-Ta eutectic was(221)Fe(AlTa)//(101 1)Fe2Ta(Al)且[002]Fe(AlTa)//[02 20]Fe2Ta(Al) and the phase interface was a semi-coherent boundary.The microhardness of Fe-Al-Ta eutectic alloys at different solidification rates are lower than that of Fe3 Al. Meanwhile, the microhardness is decreased with the increase of solidification rate. Tensile test was carried out for four samples of different solidification rate. The result shows that the maximum tensile strength can reach 343.64 Mpa at room temperature. The tensile strength will be stronger with the increase of solidification rate.
Keywords/Search Tags:intermetallic compound, directional solidification, eutectic in situ composite, microstructure, solidification rate, mechanical property
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