Nix Alloys Research Articles

Microstructure and mechanical property of Al56-xCo24Cr20Nix eutectic high-entropy alloys with an ordered FCC/BCT phase structure

A Fe-free Al56-xCo24Cr20Nix (x = 34, 36, 38, 40, and42, denoted as Nix alloys hereafter) eutectic high-entropy alloys were designed and prepared to investigate the effect of Al and Ni content on the microstructure and mechanical property. It was found that all five alloys exhibited a typical eutectic microstructure and an ordered FCC/BCT phase structure, and the volume fraction of BCT phase reduced with an increase in Ni content. The FCC and BCT phases were enriched in Cr-Co and Al-Ni elements respectively, and the nano-scale precipitates forming in BCT phase also exhibited a BCT phase structure but enriched in Cr element. The Ni38 alloy displayed an entire eutectic microstructure with two types of eutectic lamellas, the long and straight one, and the short and curve one. The irregular lamellas resulted in an unsatisfactory tensile property in Ni38 alloy with a yield strength of 543 MPa and a fracture strain of 8.1 %. To optimize the strength-plasticity configuration, the Ni content was further fine-turned. The Ni38.5 alloy, exhibiting a regularly and fine lamellar hypereutectic microstructure with bits of primary FCC phase, was found presenting an improved fracture strain of 14.5 % and without any reduction in yield strength compared with Ni38 alloy.

Strain-modulated initial oxidation of Al(1-x)Nix alloy surface

Despite of extensive studies about surface oxidation of metals and alloys, the impact of external loadings on nanoscale initial oxidation remains relatively unclear. Here, we demonstrate that surface prestrains and dynamic loadings can effectively modulate the initial oxidation of Al(1-x)Nix alloys. We find that prestrains can not only suppress or promote outward and inward ionic diffusions, but change the oxygen Ehrlich-Schwöbel (ES) barrier across oxide islands. The former affects the oxidation kinetics while the latter leads to a oxide growth mode transtion, which comprehensively determines the evolution of oxide nanostructure. In addition, we propose a theoretical chemo-mechanical coupling model to predict the internal stress evolution and the stress relaxation in Al0.7Ni0.3 oxidation. Finally, the study of Al and Al0.7Ni0.3 oxidations under dynamic strains shows that alloying nickel in aluminum effectively enhances the oxidation resistance under cyclic loadings by intensifying the chemo-mechanical coupling effect. Findings in this work may shed the light on the modulation of surface oxidation through applying mechanical loadings, and is helpful to the materials design and protection.

Factors affecting the depth of the Earth’s surface on the heterogeneous dynamics of Cu1−x Nix alloy, x = 0.1, 0.3, 0.5, 0.7, 0.9 by molecular dynamics simulation method

This paper studies the influence factors of the Earth's surface such as: Impurity concentration of Ni in Cu, alloy, x = 0.1 (10%), 0.3 (30%), 0.5 (50%), 0.7 (70%), 0.9 (90%); Temperature (T), T = 300 K, 500 K, 600 K, 700 K, 900 K at pressure (P), P = 0 GPa; pressure P = 50 GPa, 100 GPa, 150 GPa, 200 GPa, 250 GPa, 300 GPa, 350 GPa, 400 GPa at T = (300 K, 550 K, 900 K); annealing time (t), t = 200 ps at the depth of the Earth’s surface (h), h = 273 km (300 K, 14.05 GPa), 546 km (550 K, 28.104 GPa), 820 km (900 K, 42.16 GPa) on the heterogeneous dynamics of Cu1−xNix alloy by Molecular Dynamics (MD) simulation method with Sutton-Chen (SC) potential embedded and free boundary conditions. The results show, that for Cu1−xNix alloy, there always exist links Cu-Cu, Cu-Ni, Ni-Ni, and 04 types of structural units: FCC (Face-Centered Cubic), HCP (Hexagonal Close-Packed), BCC (Body-Centered Cubic), Amor (Amorphous). When the impurities concentration of Ni in Cu1−xNix alloy increases, structural units’ number of FCC, HCP, BCC, Amor change, and the largest crystallization process appears at the impurity concentration of Ni with x = 90%. When the temperature is increased, the structure of Cu1−xNix alloy changes from the crystallization state to a liquid state, the crystallization temperature (Tg) identified as Tg = 550 K. When increase pressure (P), the annealing time (t), then crystallization process occurs at T = 550 K faster than at T = 300 K and doesn’t occur at T = 900 K. Whereas increasing h leads to increasing Etot, structural units’ number of FCC, HCP and Amor decreases, which lead to the decreasing crystallize process of the Cu10Ni90 alloys. The results obtained could be used as the basis for experimental research in the future.

Change of electronic properties on transition from high-entropy to Ni-rich (TiZrNbCu)[formula omitted]Nix alloys

We present results of comprehensive study of electronic properties of (TiZrNbCu)1−xNix metallic glasses performed in broad composition range x encompassing both, high entropy (HE) range, and conventional Ni-base alloy concentration range, x ≥ 0.35. The electronic structure studied by photoemission spectroscopy and low temperature specific heat (LTSH) reveal a split-band structure of density of states inside valence band with d-electrons of Ti, Zr, Nb and also Ni present at Fermi level N(EF), whereas LTSH and magnetoresistivity results show that variation of N(EF) with x changes in Ni-base regime. The variation of superconducting transition temperatures with x closely follows that of N(EF). The electrical resistivities of all alloys are high and decrease with increasing temperature over most of explored temperature range, and their temperature dependence seems dominated by weak localization effects over a broad temperature range (10–300 K). The preliminary study of Hall effect shows positive Hall coefficient that decreases rapidly in Ni-base alloys.

Application of Box Behnken Design to Model Crater Size Generated during Micro-EDM of NI-X Alloy

Application of Box Behnken Design to Model Crater Size Generated during Micro-EDM of NI-X Alloy

On microstructure and mechanical performance of AlCoCrFeMo0.5Nix high-entropy alloys

A high-entropy alloy system, AlCoCrFeMo0.5Nix, was designed based on the AlCoCrCuFeNi alloy, by replacing Cu with Mo in order to improve strength and thermal stability. Ni content was monitored to see its effect on microstructure and properties. The microstructure of AlCoCrFeMo0.5Nix alloys consists of B2, FCC, and σ phase which are all multi-element solid solutions. As nickel content increases, the constituent phases change from B2 + σ phases at x = 0 to B2 + FCC + σ phases at x = 2.0, reflecting Ni is an FCC stabilizer. The room temperature hardness of the present alloy system decreases from Hv 904 at x = 0 to Hv 404 at x = 2.0. AlCoCrFeMo0.5Nix alloys with x = 0, 0.5, 1.0, and 1.5 exhibit higher hot hardness level than that of Ni-based superalloys, In 718 and In 718 H, up to 1273 K. Furthermore, they possess the less negative value of softening coefficient (BII) at high-temperature regime as compared with those of In 718, In 718 H, and T-800. This superiority can be explained with the slow diffusion rate of vacancies in the multi-element matrix. The present alloy system has great potential in high-temperature applications.

Effects of alloying elements and temperature on the elastic properties of dilute Ni-base superalloys from first-principles calculations

The variation of elastic properties, e.g., elastic constants, bulk modulus, and shear modulus of dilute Ni-base superalloys due to alloying elements (X's) and temperature, has been studied via first-principles calculations. Here, 26 alloying elements are considered: Al, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Sc, Si, Ta, Tc, Ti, V, W, Y, Zn, and Zr. It is found that (i) both the bulk and shear moduli of Ni-X decrease approximately linearly with increasing equilibrium volume, especially within each group of 3d, 4d, or 5d transition-metal alloying elements; (ii) all alloying elements considered herein increase the ratio of bulk to shear modulus (i.e., the ductility) and the elastic anisotropy of the Ni-X alloys; and (iii) the largest decrease of elastic properties of Ni is caused by alloying element Y. It is observed that the change of elastic properties of Ni due to various alloying elements is traceable from the distribution of (magnetization) charge density, for instance the spherical distribution of charge density facilitates shear deformation, resulting in a lower shear-related property. Using a proposed quasistatic approach based on the predicted elasticity-volume-temperature relationship, the isothermal and the isentropic elastic properties are predicted for the dilute Ni-X alloys at finite temperatures, displaying a decreasing trend with respect to temperature for each Ni-X system. Computed elastic properties are in favorable accord with available experimental data.

Gibbs energy calculation of liquid Zr–Al–Ni and Zr–Al–Cu–Ni alloys with clusters

The Gibbs energies of liquid Zr-Al-Ni and Zr-Al-Ni-Cu alloys with multi-clusters are calculated based on the statistical mechanism in this paper. The results show that the quantity of clusters depends mainly on the temperature and the concentration of the melt. It increases gradually with the decrease of temperature or with the increase of x(Ni) in liquid (Zr80Al20)(1-x)Ni-x alloys; the quantity of Zr2Ni clusters reaches its maximum of 0.061 mole at. x(Ni) = 0.336. In (Zr80Al20)(1-x)Ni-x liquid alloy the existence of clusters causes the falling of the Gibbs energy. The Gibbs energy drops about 4000 J/mol at x(Ni) = 0.35 if the effect of cluster of Zr2Ni is considered or about 8000 J/mol at x(Ni) = 0.40 if both of clusters of Zr2Ni and ZrNi are taken into account.

New Precipitate Phase in Pd and Ni Rich Ti-Pd-Ni Shape Memory Alloys

The decomposition behavior and morphology of new precipitate in Pd and Ni rich Ti-Pd-Ni high temperature shape memory alloys have been studied by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The precipitate is formed in Ti 48 Pd 52-X NiX alloys with X = 11 to 36 at%Ni. The precipitate appears with exothermic peak about 650 to 700 K and resolves with endothermic peak with about 740 to 780 K in DSC heating curve for the quenched alloys. The both peak temperatures increase with increasing Ni concentration. The shape of precipitate changes from cuboid to oval sphere shapes with increasing Ni concentration. The electron diffraction patterns of the precipitate are characterized by 1/4{111} superlattice reflections in B2 reciprocal space. The Ti 48 Pd 31 Ni 2 alloy aged under constrained condition at 673 K for 36 ks shows reversible shape memory effect during thermal cycling between room temperature and 523 K.

Fractal morphologies from decomposition of Fe−Ni−Invar alloys

Small angle neutron scattering investigations performed on Fe1−x–Nix alloys with 0.26 ≤ x ≤ 0.45 revealed a thermodynamically driven decomposition below 800 °C. The miscibility gap extends at least from 30 at.% Ni to 45 at.% Ni. The diffusioncontrolled decomposition produces fractal morphologies during the early stages of the process. During annealing the structure of the precipitated phase densifies continuously from mass fractals with small dimensionality (1 ≤ dm ≤ 3) to surface fractals with 2 ≤ ds ≤ 3. The results are compared with recent simulations of aggregation and growth as well as with a new analysis of spinodal decomposition, both predicting fractal morphologies.