Metal Science and Heat Treatment最新文献

We study Inconel 718 refractory alloy produced by using different modes of electron beam melting. The phase composition and specific features of the microstructure of alloy are analyzed both in the initial state and after hardening heat treatment. The fracture surfaces of the samples of alloy are analyzed after uniaxial tensile tests. It is shown that the fracture of the material occurs according to the ductile mechanism. However, fracture surfaces contain significant amounts of defects in the form of unmolten areas and porosity, which is typical of the products obtained by using additive technologies from powder materials. It is shown that the fracture of the analyzed alloy is provoked by the presence of unmolten areas and intermetallic particles of the δ-phase in the structure.

Use of scandium as an alloying element in aluminum alloys is considered. The choice of component systems (alloys) that it is expedient to alloy with scandium to improve the properties of semi-finished products is substantiated. It is shown that alloying aluminum alloys with scandium to improve their mechanical properties may be effective if certain rules for choosing the chemical composition and temperature-time production parameters are observed during preparation of deformed semi-finished products.

On the example of linear substructures of Mn modifications, we show two types of spirals formed by tetrablocks assembled along their sides, namely, seven-vertex unions of four tetrahedra. Experimental data that confirm the existence of spiral packings of this kind in the structures of metallic nanowires are discussed. The noncrystallographic symmetry of the spiral packing of tetrablocks enables us to adequately describe the crystalline and noncrystalline tetrahedral structures that are also present in densely packed metals.

We study the phenomenon of strain hardening of 1565ch and AMg6 aluminum alloys of the Al – Mg system with high magnesium contents and 01570 and 1580 alloys with additions of scandium in the process of cold rolling of plates. We plot hardening curves approximated by the well-known empirical expressions in the form of power functions constructed with an accuracy sufficient for the engineering calculations of the characteristics of strength within the range of total relative compressions 0 – 35%. It was shown that, in the alloys alloyed with scandium, the phenomenon of hardening observed in the course of cold rolling is weaker than in alloys without scandium.

Scientific foundations for creating aluminum alloys sparingly alloyed with scandium are considered. A partial replacement of costly scandium in the Al₃Sc strengthening phase with another metal is proposed. This results in the formation of an Al₃(Sc_1–xMe_x)-type strengthening phase, which preserves the L1₂ crystal lattice of the Al₃Sc phase and all its beneficial properties. When creating such materials, complex alloying with transition and rare earth metals is advisable. Such an approach leads to the appearance of Al₃(Sc_{1–x–y–z}, Me_1x, Me_2y, Me_3z) phases with an L1₂ lattice, contributing to the formation of a complex supersaturated solid solution. Metals substituting scandium should meet the following two requirements: exhibit sufficient solubility in the Al₃Sc phase and, at least, some solubility in aluminum.

The effect of niobium modification on refinement of primary austenite, shrinkage characteristic, and solidification behavior of medium-carbon cast steel melted in a medium-frequency induction furnace is studied. It is established that the modification with 0.1 wt.% niobium increases the fluidity of the steel liquid, enhances the feeding capacity of the cast steel, turns the dispersed shrinkage porosity into concentrated shrinkage cavity, changes the coarse dendrites to fine ones, even in equiaxed grain structures, and dwindles the primary austenite grain size greatly. Using electron microscopy and energy-dispersive analysis, it is discovered that niobium combines with carbon to form solid phase particles of NbC. These particles are chemically stable at high melting temperatures and facilitate the primary austenite nucleation effectively by non-spontaneous nucleating. A model of matching between the crystal lattices γ-Fe and NbC is suggested. The mechanism of NbC heterogeneous nucleation consists in that the primary austenite grows on {111}_γ-Fe along to the closest-packed plane {111}_NbC in crystal orientation ({langle 011rangle }_{gamma -mathrm{Fe}}Vert {langle 112rangle }_{mathrm{NbC}}), and the mismatch ({updelta }_{{langle 111rangle }_{mathrm{NbC}}}^{{langle 111rangle }_{gamma -mathrm{Fe}}}) of the crystal planes is only 9.79%.

The effect of microstructure on fatigue properties and fracture mechanisms in drill pipes made of aluminum alloys 1953 and 2024 (D16) has been studied experimentally. It is shown that the more hardened α-solid solution and the presence of reinforcing intermetallics MgZn₂ and Al₂CuMg in the structure of alloy 1953 provide more effective resistance to fatigue crack nucleation as compared to alloy 2024 with Al₂CuMg and Al₂Cu intermetallics and a less hardened matrix α-solid solution. Accordingly, the fatigue limit of the pipe made of alloy 1953 is 192 MPa, and that of alloy 2024 is 179 MPa. However, the ratio of the fatigue limit to the yield strength of the aluminum alloy 2024 is 40%, while for the 1953 alloy it is 32%. This is explained by a higher fracture toughness of alloy 2024 as compared to 1953, a greater degree of deformation and uniformity of the structure of alloy 2024.

The effect of cold drawing on the evolution of microstructure and texture of near eutectoid steel wire is studied to understand the deformation micromechanism of the wire drawing process. The texture evolution during wire drawing is simulated using a viscoplastic self-consistent (VPSC) model and successfully validated by experimental results. The favorable pearlitic colonies having lamellas aligned along the wire axis are found to undergo thinning and form a fibrous structure. On the other hand, the lamellas oriented perpendicularly to the wire axis are found to undergo bending and kinking in the process of aligning themselves with the wire axis. A (langle 011rangle ) crystallographic texture develops after the wire drawing from the (langle 111rangle ) and (langle 110rangle ) texture of the as-received steel. The VPSC simulation illustrates the relative significance of the {112}(langle 111rangle ) slip in comparison to that of the traditionally used {110} (langle 111rangle ) slip. The VPSC simulation also illustrates presence of about 5 – 6 active slip systems (AVACS) that make it possible to maintain strain compatibility in polycrystalline materials.

The effect of austempering temperatures varied from 300 to 400°C to form bainite in the structure on the corrosion resistance and mechanical properties of two newly developed FeNi steels containing 1 and 2 wt.% Al is investigated. Corrosion tests of the steels are carried out in a 3.5 wt.% NaCl solution. It is found that an increase in the Al content and in the austempering temperature promotes formation of a bainite lath structure in the steels; however, this has an insignificant effect on the hardness. The results of an electrochemical test show that the corrosion resistance of the steel in marine-like atmosphere increases upon increasing the Al content from 1 to 2 wt.%. The increase of the austempering temperature tends to improve the corrosion resistance of both steels, except for the steel with 1 wt.% Al processed at the highest temperature. It is shown that the corrosion resistance of the steels is more affected by the hardness than by the volume fraction of bainite laths in the structure.

Electrode-induction gas atomization (EIGA) is a promising and cost-effective method for producing spherical intermetallic titanium powders used in additive manufacturing. The present study investigates the morphology, microstructure, chemical and phase compositions, nanoindentation properties of a commercial pre-alloyed TiAl-based EIGA alloy powder. The Ti – 48Al – 2Cr – 2Nb powder is characterized by a spherical shape and dendritic structure with the dendrites enriched with Nb and the interdendritic areas enriched with aluminum and chromium. The temperature ranges of the phase transformations in the powder with precipitation/dissolution of phases α₂ , α, γ, B2, (TiNb)Cr₂ are determined using thermal analysis during heating and cooling in an inert atmosphere of argon at a rate of 50 K/min. Development of an oxidation process at the temperatures above 500°C and significant increase in its rate at the temperatures above 900°C is detected.