The Ni3Al-Ni3Cr-Ni3Mo section of the Ni-Cr-Al-Mo system

An investigation is reported of the constitution of the 75 at % nickel section of the Ni-Cr-Al-Mo system in the temperature range 1523 to 1073 K. Alloys in the region 10 to 20 at % Al were annealed at 1523, 1273, and 1073 K, respectively, and subjected to electron microprobe analysis, X-ray diffraction, and microscopical and hardness examination. Constitutional data are presented as partial isothermal sections and as vertical sections. At 1523 K the section consists only of fields containing ,+ and , the last mentioned phase being predominant. With decreasing temperature the and + fields increase in extent. Also, the NiMo and Ni₃Mo phases were encountered in the ternary Ni-Al-Mo alloy studied. The quaternary + alloys showed small lattice mismatch values, i.e. up to 0.25%. Raft like morphologies of were found in the quaternary alloys, resulting from directional coarsening. Observations of as-cast structures are also reported.     

Constitution of the Ni3Cr-Ni3Al-Ni3W system

Isothermal sections of the Ni-Cr-Al-W system have been investigated at 75 at % Ni and temperatures of 1523 and 1273 K, by means of phase compositional analysis, X-ray diffraction and microscopical examination. The alloys studied lay in the range 2.5 to 10 at % Cr, 12.5 to 20 at% Al, 2.5 to 6.25 at % W, The phases formed were, and the bcc solid solution based on tungsten (designated ₂). The maximum extent of the region was found to be 3 at % each of chromium and tungsten. Preferential partitioning of tungsten to occurred. Study of an Ni-10Cr-12.5Al-2.5W alloy aged at 1273 and 1073 K, after quenching from 1573 K, showed that changes in and compositions and lattice parameters occur as a function of ageing time.     

Investigation on Ni3Al-Ni7Hf2 unidirectionally solidified eutectic composite

The formation of a Ni₃Al()+Ni₇Hf₂ unidirectionally solidified lamellar eutectic composite has been investigated in this paper. The results show that Ni-5.8Al-32Hf alloy, which has the Ni₃Al+Ni₇Hf₂ eutectic structure, is a suitable composition of D.S eutectic material. The melting range of this composition is 41 °C as determined by DTA. The critical ratio of G/R for Ni₃Al+Ni₇Hf₂ eutectic is found to be 5× 10⁵ °C · s · cm^–2, and the lamellar Ni₃Al+Ni₇Hf₂ eutectic aligned parallel to the direction of solidification was made with R = 5 m/s and G = 250 °C/cm. The investigation shows that the lamellar eutectic has a preferred crystallographic orientation between the Ni₃ Al and Ni₇Hf₂ lamellae, i.e., (111)_NiAl//(100)_NiHf and [110]_NiAl//[010]_NiHf. The lamellar Ni₇Hf₂ did not degrade or coarsen obviously, and no harmful phase formed in the interface of Ni₃Al/Ni₇Hf₂ after long time soaking of 1100 °C/110 h. This demonstrates that the Ni₃Al+Ni₇Hf₂ lamellar eutectic has high interface thermal stability.     

High-temperature strength and ductility of L12-type Ni3Al-Ni3Mn intermetallic compound

The mechanical properties of L1₂-type pseudobinary intermetallic compound Ni₃Al-Ni₃Mn were investigated in relation to testing temperature and alloy composition. A positive temperature dependence of yield stress was found in manganese compositions lower than 15 at %, suggestive of the Kear-Wilsdorf mechanism, while a negative dependence was found in the high manganese alloys. The composition dependence of yield stress at room temperature in the low manganese alloys was attributed to the solid solution hardening while that in the high manganese alloys was attributed to imperfect ordering. The elongation exhibited a maximum around 700 K irrespective of compositions, while the maximum and minimum were observed approximately in 9 and 12 at % manganese alloys, respectively. The high values of elongation obtained in 20 and 25 at % manganese alloys were probably due to imperfect ordering. Both the temperature and composition dependences of UTS were quite similar to those of elongation. The fractographic observation showed that the more ductile specimen tended to fracture more transgranularly.     

Microstructure, mechanical property and chemical property in Ni3Al-Ni3Ti-Ni3Nb-based multi-intermetallic alloys

Microstructure, high-temperature compressive and tensile deformation, and corrosion property of multi-phase alloys based on Ni₃Al-Ni₃Ti-Ni₃Nb pseudo-ternary alloy system were investigated. The microstructures of these alloys were largely dependent on alloy composition but independent of annealing temperature. Alloys composed of multi-phase microstructures of L1₂, D0₂₄ and D0_a showed substantially enhanced compressive yield stress as well as a certain amount of compressive plasticity at whole temperature, while they did not show reasonable tensile elongation at whole temperature. Also, alloys composed of lamellar-like multi-phase microstructures are effective in enhancing compressive yield stress particularly at high temperature. Multi-phase alloys with low Nb contents have good corrosion resistance, especially in high concentration of sulfuric acid.     

Barothermal analysis and structure of the eutectic Al-Ni (2.7 at % Ni) alloy

Phase transformations of the 2.7Ni + 97.3Al eutectic alloy have been characterized by differential barothermal analysis (DBA) at temperatures of up to 750°C and pressures of up to ∼100 MPa. The results demonstrate that the Al matrix of the as-prepared alloy was saturated with micropores. After melting and crystallization in compressed argon, the micropore density increased. As a result of melting and solidification, the fine-grained structure of the as-prepared alloy transformed to a macrocrystalline, dendritic structure. Electron microscopy was used to determine the volume fraction of the intermetallic phase NiAl₃ in the Al matrix. Supersaturated solid solutions of nickel in aluminum decompose at 626°C to give a mixture of Al〈Ni〉 and NiAl₃. At 100 MPa, the nickel-aluminum solid-solution range extends to 2.7–2.8 at % Ni, and the nickel content at the eutectic point may reach 3.1–3.3 at %. The Al and NiAl₃ in the alloy solidified at 100 MPa had reduced lattice parameters. We determined the microhardness of the Al matrix after DBA.     

Ordering and recovery processes in the Ni/Fe system near Ni3Fe

The ordering and recovery processes in 72/28 and 80/20 at.% Ni/Fe alloys have been investigated. A parameter related to the thermal scattering contribution of the electrical resistivity was used to follow the establishment of atomic order. It was found that the initial condition of the alloys — quenched or cold-worked — has little influence on the ordering kinetics at high temperatures. However, it greatly influences the recovery behaviour, as indicated by the residual resistivity measurements. Strain-ageing effects reported earlier are interpreted in the light of the present findings. Results are also discussed on the basis of existing theories for atomic ordering.     

Formation and growth of Ni3Sn4 intermediate phase in the Ni - Sn system

Dipping experiments of Ni foils in molten tin were made in the temperature range, 280–310°C. In addition, experiments were conducted while passing a constant current through the system, the foils being used as electrodes. In SEM - EDS observations and analysis the Ni₃Sn₄ equilibrium intermediate phase was found to grow both as a layer at the solid/liquid interface and as platelets in the melt. Growth kinetics were found to be influenced by the dissolution of Ni in the melt. The voltage between the electrodes vs. time (V(t) curve), measured in-situ, was found to conform to SEM observations. The V(t) curves permit a qualitative evaluation of the layer growth process.     

Discontinuous precipitation of β-Ru phase in Ni–18Ru alloys

The precipitation of β-Ru phase upon aging of a solutionized Ni–18 at.% Ru alloy was studied by X-ray diffraction and electron microscopy. It was shown that: the β phase forms by discontinuous lamellar decomposition from nucleation sites on α grain boundaries; the phases exhibit well-defined orientation relationships; and the hardness of the alloy correlates strongly with the extent of decomposition. The implications for the use of heat treatment to control the microstructure and mechanical properties of the alloy are discussed.     

The thermal stability of pre-strained Al-Al3Ni eutectic

A detailed study has been made of the thermal stability of aligned Al-Al₃Ni eutectic after prior compressive deformation at room temperature. Compressive strains of between 6% and 50% were imposed perpendicular to the axis of alignment of the eutectic. Annealing of deformed and undeformed material at 883 K led to spheroidization of the Al₃Ni rods at a rate which increased rapidly with increasing prestraining. Thus, for eutectic previously strained by 50%, almost complete spheroidization was observed after only 10 h at 883 K. The present behaviour was explained partly in terms of enhanced diffusion along matrix dislocations introduced during deformation.     

Fe-Co-Nb三元系相图的1173 K等温截面

根据扩散偶局部平衡原理,用电子探针微区成分分析,测定了Fe-Co-Nb三元系1173 K的等温截面相图.结果表明,Fe-Co-Nb三元扩散偶在1173 K时生成Fe7Nb6,Fe2Nb和Co7Nb6,Co3Nb、Co2Nb五种中间化合物.Fe7Nb6与Co7Nb6形成连续固溶体(Fe,Co)7Nb6.Fe-Co-Nb三元系的1173 K等温截面由αFe αCo Co3Nb,αFe Co3Nb Co2Nb,αPe Fe2Nb Co2Nb,Fe2Nb Co2Nb (Fe,Co)7Nb6四个三相区组成,没有发现三元化合物.     

A New Type of Li‐Rich Rock‐Salt Oxide Li2Ni1/3Ru2/3O3 with Reversible Anionic Redox Chemistry

Li‐rich oxide cathodes are of prime importance for the development of high‐energy lithium‐ion batteries (LIBs). Li‐rich layered oxides, however, always undergo irreversible structural evolution, leading to inevitable capacity and voltage decay during cycling. Meanwhile, Li‐rich cation‐disordered rock‐salt oxides usually exhibit sluggish kinetics and inferior cycling stability, despite their firm structure and stable voltage output. Herein, a new Li‐rich rock‐salt oxide Li₂Ni_1/3Ru_2/3O₃ with Fd‐3m space group, where partial cation‐ordering arrangement exists in cationic sites, is reported. Results demonstrate that a cathode fabricated from Li₂Ni_1/3Ru_2/3O₃ delivers a large capacity, outstanding rate capability as well as good cycling performance with negligible voltage decay, in contrast to the common cations disordered oxides with space group Fm‐3m. First principle calculations also indicate that rock‐salt oxide with space group Fd‐3m possesses oxygen activity potential at the state of delithiation, and good kinetics with more 0‐TM (TM = transition metals) percolation networks. In situ Raman results confirm the reversible anionic redox chemistry, confirming O^2?/O^? evolution during cycles in Li‐rich rock‐salt cathode for the first time. These findings open up the opportunity to design high‐performance oxide cathodes and promote the development of high‐energy LIBs.     

The structure identification of epitaxial Ru2Si3 on (111) Si

Epitaxial Ru₂Si₃ has been successfully grown on (111) Si for the first time by using the new method of chemical electroless plating of Ru thin film on silicon with subsequent annealing schemes. The crystal structure of Ru₂Si₃ reported in the literature, which was identified by X-ray diffraction, was ambiguous to be tetragonal or orthorhombic. The study of stereomicroscopy and Kikuchi lines of the Ru₂Si₃ by scanning transmission electron microscopy shows that the structure of Ru₂Si₃ is orthorhombic with four-fold like symmetry rather than tetragonal.