Abstract
This paper deals with the investigation of complex-alloyed nickel aluminides obtained from oxide compounds by aluminothermic reduction. The aim of the work was to study and develop the physicochemical basis for obtaining complex-alloyed nickel aluminides and their application for enhancing the properties of coatings made by electrospark deposition (ESD) on steel castings, as well as their use as grain refiners for tin bronze. The peculiarities of microstructure formation of master alloys based on the Al–TM (transition metal) system were studied using optical, electronic scanning microscopy and X-ray spectral microanalysis. There were regularities found in the formation of structural components of aluminum alloys (Ni–Al, Ni-Al-Cr, Ni-Al-Mo, Ni-Al-W, Ni-Al-Ti, Ni-Cr-Mo-W, Ni-Al-Cr-Mo-W-Ti, Ni-Al-Cr-V, Ni-Al-Cr-V-Mo) and changes in their microhardness, depending on the composition of the charge, which consisted of oxide compounds, and on the amount of reducing agent (aluminum powder). It is shown that all the alloys obtained are formed on the basis of the β phase (solid solution of alloying elements in nickel aluminide) and quasi-eutectic, consisting of the β′ phase and intermetallics of the alloying elements. The most effective alloys, in terms of increasing microhardness, were Al-Ni-Cr-Mo-W (7007 MPa) and Al-Ni-Cr-V-Mo (7914 MPa). The perspective is shown for applying the synthesized intermetallic master alloys as anode materials for producing coatings by electrospark deposition on steel of C1030 grade. The obtained coatings increase the heat resistance of steel samples by 7.5 times, while the coating from NiAl-Cr-Mo-W alloy remains practically nonoxidized under the selected test conditions. The use of NiAl intermetallics as a modifying additive (0.15 wt. %) in tin bronze allows increasing the microhardness of the α-solid solution by 1.9 times and the microhardness of the eutectic (α + β phase) by 2.7 times.
Highlights
Alloys with refractory metals, such as W, Mo, Cr, V, Zr, etc., play an essential role in forming physical and mechanical properties of high-quality Al–Ni-based alloys
The most effective way to control the structure of aluminum alloys is to introduce small amounts of transition metals (TM) as additions to binary [5,6,7,8,9,10] and multicomponent [11,12,13,14,15,16,17,18,19] master alloys: Al–TM (Ti, Zr, Sc, Hf, etc.) and Al-Sc-Zr; Al-Zr-Ti; Al-Sc-Ti; etc
The process of obtaining alloys is represented by a series of partial reactions of aluminothermic reduction and is described generally by the chemical reaction equation: Mn Om + pAl = nM + Alp Om, where Mn Om is a reducible metal oxide, Al—a reducer, nM—a reduced metal, Alp Om —a compound formed in the reaction; n, m, p—stoichiometric coefficients
Summary
Alloys with refractory metals, such as W, Mo, Cr, V, Zr, etc., play an essential role in forming physical and mechanical properties of high-quality Al–Ni-based alloys. NiAl—are formed, which are in an equilibrium state with metals of group VIB: W (f14d4s2), Cr and. Mo (d5s1), having occupied the intermediate position between electropositive (Al) and electronegative (Ni) metals in the ternary systems Al-Ni-X (transition metals). Their initial melting point is higher than that of Ni-Al alloys [4]. The most effective way to control the structure of aluminum (nickel) alloys is to introduce small amounts of transition metals (TM) as additions to binary [5,6,7,8,9,10] and multicomponent [11,12,13,14,15,16,17,18,19] master alloys: Al–TM (Ti, Zr, Sc, Hf, etc.) and Al-Sc-Zr; Al-Zr-Ti; Al-Sc-Ti; etc.
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