Ni Alloy Research Articles

Outstanding shape memory effect and thermal stability of Cu–Al–Ni-based high temperature shape memory alloys achieved by Gd and Mn doping

In this paper, the effects of Mn element and rare earth element Gd on the microstructure, thermal stability, mechanical properties and shape memory effect of polycrystalline Cu-12.0Al-4.0Ni and Cu-12.0Al-4.0Ni-1.5Mn-xGd high-temperature shape memory alloy were investigated. The results show that the Cu-12.0Al-4.0Ni alloy exhibits millimeter-sized grain, dual-phase structure with coexistence of 18R and 2H martensite and poor thermal stability. When the Mn and Gd element was added to Cu-12.0Al-4.0Ni alloys, the grain size can be refined by an order of magnitude, and the 2H martensite disappeared completely, accompanied by the formation of the AlCu4Gd phase, meanwhile, thermal stability is significantly improved. The grain refinement improves the mechanical properties and shape memory effect of Cu-12.0Al-4.0Ni-1.5Mn-xGd alloys. When x = 0.3, the compressive fracture stress, compressive fracture strain and recoverable strain can reach 969 MPa, 15 % and 8 %, respectively.

A2B7-type La–Mg–Ni alloys prepared by Mg thermal diffusion for improved hydrogen storage performance

A2B7-type La–Mg–Ni alloys prepared by Mg thermal diffusion for improved hydrogen storage performance

Cooling Curves of Concentrated Alloys, Steelmaking Slag, and Lithium Iron Phosphate

AbstractOver the past few years, a variety of melting casting projects have been performed, in collaboration with industries and universities. Concentrated alloys and nonmetallic compounds were studied including high-Si cast iron, high-Mn steel, Al-added stainless steel, high-entropy alloy, Permalloy 80 Ni alloy, Stellite Co alloy, steelmaking slag, and lithium iron phosphate (LFP). A melt synthesis of LFP was developed. Cooling curves were measured using the thermal analysis cup method and differential thermal analysis. In addition, the phase diagrams of alloys were calculated using Thermo-Calc. This paper draws on some examples of the measured cooling curves to illustrate the thermal behaviors of melts, along with a quick review of each project.

Microstructure, mechanical and electrical properties of a novel low-cost high-strength Pt-xAu-5Ni alloy

The present study designed and prepared a novel platinum alloy system Pt-xAu-5Ni (x = 0, 2, 5, wt.%) with high strength and good electrical resistivity. The mechanical, electrical properties and related microstructure during the cold deformation and subsequent aging process were investigated. The cold-deformed Pt–5Ni alloy obtained the yield strength of 581 MPa, the ultimate tensile strength of 828 MPa, the hardness of 283 HV, and the electrical resistivity of 23.9 μΩ⋅cm. The subsequent aging process and the Au addition into Pt–5Ni alloy were found to both enhance the mechanical properties. Therefore, with the dual strengthening effect of the subsequent aging and the Au addition, Pt–5Au–5Ni alloy achieved the high yield strength of 889 MPa, the high ultimate tensile strength of 1117 MPa, the high hardness of 361 HV with the electrical resistivity of 26.7 μΩ⋅cm. The precipitation of L12-type Pt3Ni nanoparticles and L11-type CSRO dominated the age-strengthening behavior of Pt–2Au–5Ni and Pt–5Au–5Ni alloys after cold deformation. The Au addition refined the grains via the experimental observations, and predictably favored the L12-type Pt3Ni nanoprecipitation based on the thermodynamical calculations, thus the Au addition effectively strengthened Pt–5Ni alloy. This study provides a novel platinum alloy system with excellent mechanical and electrical properties, which has potential application in the electrical contact field.

Impact of intermetallic phases on the localised pitting corrosion and high-temperature tensile strength of Al–Si[sbnd]Mg[sbnd]Cu[sbnd]Ni alloys

The influence of Ni-rich intermetallic particles (IMPs) on the microstructure, high-temperature mechanical properties, and corrosion behaviour of Al–Si–Mg–Cu–Ni alloys was investigated. The presence of coarse block-like γ-Al7Cu4Ni and thin needle-like δ-Al3NiCu IMPs contributed to low-temperature alloy strengthening during tensile tests. However, void nucleation and coalescence within the IMPs facilitated ductile fracture and alloy rupture, resulting in a lower tensile strength at high temperatures. Although both IMP phases had a cathodic electrochemical nature, resulting in strong galvanic corrosion, the γ-Al7Cu4Ni phase acted as the primary cathode, amplifying localised pitting while reducing the overall alloy corrosion resistance.

Corrosion behavior of two Cu‐based shape memory alloys in NaCl solution: An electrochemical study

AbstractThe corrosion behavior of two different Cu–Al–Mn–Ni alloys, pseudoelastic and pseudoplastic, was studied in a 0.6 M sodium chloride aqueous solution by monitoring the open circuit potential for 100 h and characterizing the resulting corrosion products. Electrochemical impedance spectroscopy analysis detected three processes related to the electrochemical double layer, a passive film and a diffusive contribution associated with the dissolution/precipitation of corrosion products. Potentiodynamic scans revealed a cathodically controlled corrosion mechanism and the presence of active–passive behavior at anodic potentials for both alloys studied. Polarization of the samples at selected potentials in the anodic branch allowed the investigation of the reactions involved, highlighting an improved corrosion resistance of the pseudoelastic alloy. The corrosion rates of the pseudoelastic and pseudoplastic alloys, after 100 h of immersion, were determined to be 0.007 and 0.011 mmpy, respectively. The post‐experiment characterization was carried out by means of scanning electron microscopy, micro‐Raman spectroscopy and X‐ray diffraction, supporting the electrochemical results.

Artificial Slags with Modulated Properties for Controlled Nickel Dissolution in Smelting Process

In pyrometallurgy process involving drying, calcination and reductive smelting steps, Saprolite ore is subjected in an electric arc furnace to produce Fe–Ni alloy and Ni matte. To optimize the nickel smelting step, the slag consisted of MgO–SiO2–FeO and having a lower viscosity and high fluidity is required. In this study, a number of new slag samples with varied degree of compositions are manufactured and used to examine the effect of their viscosity on nickel dissolution. Further correlation between the slag basicity and FeO addition on the smelting was also tested and simulated using Fe–Ni alloy from saprolite ore. As per the observations, the nickel dissolution increases with the increased content of FeO at a certain degree of activity which in turn can cause oxidation of nickel during the process. The slags with the ratio of MgO/SiO2 = 0.4–0.6, 30% fraction of FeO, and a viscosity of 1.8–1.06 poise in the olivine zone are found effective for the lowest dissolution rate of nickel with 0.021, 0.022, and 0.018 wt.%. The lowest dissolution rate is recorded for the slag with MgO/SiO2 ratio about 0.6. These slags with controlled amount of constituents could be used to recover precious metal from nickel smelter at a lower dissolution rate and thereby allowing to reduce the waste of the metal during smelting process.

Laser additive manufacturing of TiB2-modified Cu15Ni8Sn/GH3230 heterogeneous materials: Processability, interfacial microstructure and mechanical performance

Cu/Ni heterogeneous materials integrate excellent thermal conductivity and high-temperature mechanical properties, enabling them to be widely used in the aerospace domain. Differences in the thermal and physical properties of the Cu and Ni materials, however, make them difficult to be processed using the laser powder bed fusion (LPBF) additive manufacturing process. This study systematically examines the effects of various LPBF process parameters on microstructure, element diffusion, bonding strength and microhardness at the Cu/Ni interface, as well as investigating the mechanisms of defect formation within Cu/Ni heterogeneous materials. The results indicate that a reasonable control of laser energy input (<100 J/mm3) facilitates the Cu/Ni components through strong interfacial metallurgical bonding without pore defect formation. Compared to single-material Cu alloy, the ultimate tensile strength (UTS) of the horizontally bonded Cu/Ni specimen increased by 55.25 %, without significant reductions in elongation. The vertically bonded Cu/Ni tensile specimen fractured in the middle of the Cu region rather than the interfacial region, indicating superb interfacial bonding strength. Another advantage lies in the enhancement of thermophysical properties, with a 109.5 % increase in thermal conductivity achieved in the LPBF-fabricated Cu/Ni heterogeneous materials compared to the single-material Ni alloy. Quasi-static compression experiments indicated that the Cu/Ni lattice structure could absorb more energy when compressed parallel to the build direction (BD), compared to being perpendicular to the BD. This study provides guidance for the design and manufacture of high-performance Cu/Ni heterogeneous components via LPBF.

Electrodeposition of nanocrystalline Ni and NiCr alloy coatings: Effects of Cr content on microhardness and wear resistance improvement

The safety and reliability of high-speed trains depend on the brake disc. In order to improve the lifetime of brake disc and reduce the waste of resources, a coating with higher microhardness and well wear resistance is urgently needed. The effect of chromium content on the microstructure, microhardness and wear resistance of NiCr coating has been studied. Nano-crystalline Ni and NiCr coatings with superior mechanical properties were successfully prepared on the 30CrNiMo steel substrate by pulse current electrodeposition method. The inclusion of formic acid and sodium citrate was found to significantly expedite the co-deposition of Ni and Cr. The NiCr coatings with various Cr contents were prepared at current densities ranging from 200 to 300 mA/cm2. These coatings significantly enhance microhardness and wear resistance of the substrate. The microhardness of the NiCr coating increased to 603 HV, outperforming pure Ni coating by 119 HV. Additionally, the wear rate of the NiCr coating decreased by 50% at a load of 10 N in comparison to the Ni coating. The high microhardness is attributed to grain refinement and solution strengthening. This study successfully addresses the challenges associated with electrodepositing Ni-based coatings on 30CrNiMo steel substrate and lays a theoretical foundation for the utilization of Ni-based coatings to enhance the tribological properties of materials used in high-speed train brake disc.

Effect of the third element on the wetting of alumina by TiAl-X (X = Fe, Ni) alloys at 1500 °C

In this work we show how the addition of a third element, namely Fe or Ni, influences the interfacial behaviour of liquid TiAl alloys on polycrystalline alumina. Wetting of these alloys was studied by the sessile drop method at 1500 °C and the interfacial microstructures were characterised to determine the relation between the contact angle and the interfacial reaction with the aid of the relevant phase diagrams. The equiatomic TiAl intermetallic wetted the alumina substrate forming a contact angle of 60°. On the other hand, increasing concentrations of Fe and Ni were found to improve the wetting behaviour of ternary TiAl-X alloys: for third-element atomic concentrations of 5 at. %, contact angles decreased to 32° and 29° by adding Fe and Ni, respectively. Neither reactive-formed interlayers nor newly formed phases were observed for any binary or ternary composition as confirmed by thermodynamic calculations. A slight dissolution of the ceramic occurred during liquid/solid contact and became more evident with the increase of concentration of the third element. The introduction of oxygen into the melt provided by the dissolution of alumina improved the wetting behaviour.

Enhancing electrochemical corrosion resistance in Al–6Ni alloys through trace Sc additions

Al–Ni-Sc alloys exhibit superior mechanical properties at both room and elevated temperatures, owing to the high thermal and chemical stability of Al3Ni microfibers, and Al3Sc nanoprecipitates. This study explores the impact of scandium additions (0.2 and 0.4 wt%) in eutectic Al–6Ni casting alloys and the influence of aging treatment on electrochemical corrosion behavior in a 0.05 M NaCl solution. Scandium addition did not alter the polarization curve direction but reduced the anodic current density, slowing corrosion. Scandium strengthened the passive film, evident in Electrochemical Impedance Spectroscopy (EIS) with higher Rp values. Sc addition influences the susceptibility to localized corrosion in Al–Ni alloys by promoting the coherence of passive films through the formation of Al3Sc nanoprecipitates and affecting the distribution of Al3Ni. XPS results show that as-aged Sc-containing increases the density of coherent Al3Sc nanoprecipitates, which could result in the formation of Sc2O3 film along with films like Ni2O3 and Al2O3. These synergistic effects contribute to improving the overall corrosion resistance with Sc additions subjected to aging treatment. The microgalvanic effects between the matrix and reinforcement phases, as a result of the formation of nobler Al3Ni and Al3Sc that serve as cathodes within anode Al matrix, cause severe pitting. Nevertheless, after aged treatment, the corrosion resistance dramatically drops for alloys with 0.2 wt% Sc and remains unchanged for 0.4 wt% Sc, due to higher density of nobler Al3Sc nanoprecipitates phase that can counteract the microgalvanic effects and lead to less extensive pitting than as-aged Al–6Ni-0.2Sc.

Effect of Fe doped Co–Ni protective coatings on the oxidation behavior and electrical properties of SOFC alloy interconnect materials

In order to enhance the oxidation resistance and electrical properties of interconnects for solid oxide fuel cells (SOFCs), three Co–Ni alloy coatings with varying contents of Fe doping were prepared onto SUS 430 substrate using electroplating method and oxidized in air at 800 °C for 1000 h. The experimental results demonstrated that the alloy coating significantly enhanced both the oxidation resistance and electrical properties of the interconnect substrate. The multi-layer oxidation structure blocked Cr from diffusing outward. Notably, the (Co,Fe)3O4/(Ni,Co)O in the oxidized layer of 5% Fe doped Co–Ni coated steel completely transformed into (Fe,Co,Ni)3O4 spinel layer after long term oxidation, which had the lowest activation energy and the strongest ability of restricting oxygen diffusion inward. Thus, the 5% Fe doped Co–Ni coated steel showed superior oxidation resistance (kp = 8.76 × 10−14 g2 cm−4 s−1) and excellent electrical properties (ASR = 13.19 mΩ cm2) following oxidation for 1000 h.

Full-composition-gradient in-situ alloying of Cu–Ni through laser powder bed fusion

Multi-material laser powder bed fusion has long been a challenge in additive manufacturing, especially in terms of controlling spatial variations and joining multiple materials. The challenge is even greater when multi-material components have different physical properties (e.g., different thermal expansions, thermal conductivities and laser reflectivities). The aforementioned scenario is applicable to copper–nickel (Cu–Ni) alloy. The simultaneous printing and controllable mixing of pure Cu and pure Ni within a single print have not been accomplished due to the substantial disparity in the physical properties of pure Cu and pure Ni. In this work, a full composition with different mixing proportions (100 % Cu to 100 % Ni) was fabricated in a single printing process through in-situ alloying based on our process of micro laser powder bed fusion. A transition from a columnar grain to a quasi-equiaxed grain morphology with texture variation from <110> to <111> was found in the full–composition–gradient of the Cu–Ni alloy. Microstructural variations, such as fine grain strengthening and grain boundary strengthening, greatly affected the mechanical properties of the alloys: the ultimate tensile strength ranged from 303 to 488 MPa and the yield strength ranged from 231 to 445 MPa. Moreover, the electrical conductivity of the alloys with a compositional gradient ranged from 3.6 % IACS to 96 % IACS due to the electron scattering induced by lattice distortion. In summary, a full-composition Cu–Ni gradient alloy was fabricated through in-situ alloying adopting micro laser powder bed fusion for the first time, enabling the investigation of the evolution of the microstructure and properties of the alloy as the alloy composition varies.

Structure, Martensitic Transformations, and Mechanical Properties of Aging Nanocrystalline Ti–50.9 at % Ni Alloy

Structure, Martensitic Transformations, and Mechanical Properties of Aging Nanocrystalline Ti–50.9 at % Ni Alloy

Investigation of the thermodynamic, structural, electronic, mechanical and phonon properties of D0c Ru-based intermetallic alloys: an ab-initio study

Abstract We present the structural, elastic, electronic, magnetic, and phonon properties of D0c X3Ru (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) alloys in their respective ground-states at zero pressure using first-principles density functional theory (DFT). The calculated heat of formation for Sc3Ru, Ti3Ru, V3Ru, Mn3Ru, and Zn3Ru are negative, signifying their thermodynamic stability. Meanwhile, we find that Sc3Ru, V3Ru, Mn3Ru, Co3Ru, Ni3Ru, Cu3Ru and Zn3Ru alloys are mechanically stable. The electronic properties indicate a metallic nature in all the X3Ru alloys due to valence-conduction band overlap at the Fermi energy. Additionally, the phonon dispersion curves suggest that Cr3Ru, Fe3Ru, Ni3Ru, Cu3Ru, and Zn3Ru are dynamically stable. These results provide a comprehensive overview of the stability, electronic, and mechanical properties of D0c Zn3Ru structures, suggesting their suitability for engineering novel alloys in high-temperature structural applications.

Deformation behavior and magnetic properties of equiatomic FeNi single crystals

An equiatomic Fe–Ni alloy in its disordered A1 structure is a soft magnetic alloy. On ordering to the L10 ordered phase, it shows significant magneto-crystalline anisotropy and a strong permanent magnet behavior and is of interest as a rare earth-free permanent magnet. However, synthesis of an L10 phase in a bulk form remains a challenge due to its low critical ordering temperature Tc and consequent extremely slow ordering kinetics. This phase is present in asteroids, and how it was formed remains unclear. The likely mechanism is enhanced diffusion kinetics due to extreme dislocation densities and vacancy concentrations produced by deformation during asteroid collisions and the presence of S. Prior to examining extreme deformation in an FeNi alloy comparable to that in asteroid collisions, low strain rate deformation behavior, magnetic properties, and the structure of undoped and S-doped [100]-oriented FeNi single crystals were carried out. Controlled deformation at a strain rate of 1 × 10−5/s showed the yield point to be 89 MPa, and the critical resolved shear stress was 25.7 MPa. The dislocation densities obtained were ∼1017/m2. The saturation magnetization value was ∼147–151 emu/g both before and after deformation, comparable to NdFeB magnets. Coercivity increased slightly from ∼0.04–0.4 to ∼5 Oe after deformation due to an increase in dislocation density. The x-ray diffraction scan of S-doped and deformed single crystals after annealing at 300 °C, just below Tc, showed no evidence of L10 order. These data serve as a baseline for extreme strain rate deformation where much higher dislocation densities and vacancy concentrations can be obtained to facilitate L10 order.

Improved contact performance and thermal stability of Co–Ni alloy barrier layer for bismuth telluride-based thermoelectric devices

Improved contact performance and thermal stability of Co–Ni alloy barrier layer for bismuth telluride-based thermoelectric devices

Electrochemical Corrosion Resistance Evaluation of Zn–Ni Alloy Electroplating Process in Zincate Bath

Electrochemical Corrosion Resistance Evaluation of Zn–Ni Alloy Electroplating Process in Zincate Bath

Ultrathin Ni–N–C layer modified Pt–Ni alloy nanoparticle catalysts for enhanced oxygen reduction

Accelerating the commercialization of fuel cells requires the development of Pt-based alloy cathode catalysts with high ORR operation, low price, and excellent reliability. However, it is a challenging task to fabricate uniformly dispersed, low-loaded, and small-sized Pt-based alloy catalysts to resolve the contradiction between activity and stability. Here, sub-3 nm N-doped PtNi nanoparticles (NPs) are synthesized as high-performance PEMFC cathode catalysts. PtNi/Ni-NC exhibits excellent electrocatalytic activity (0.51 A mgPt−1@0.8 V and peak power density of 328 mW cm−2) as well as stability (only 15 mV loss in E1/2 after 5000 cycles of ADT tests) in oxygen reduction reaction (ORR). The experimental results show that N doping modulates the electronic structure around Pt and optimizes the lattice compressive strain, thus attenuating the adsorption of oxygen intermediates on the surface Pt and enhancing the ORR activity. Meanwhile, the encapsulation of PtNi NPs by the constructed ultrathin Ni–N–C layer accounts for the improved stability. This work offers a novel perspective f for raising the stability and catalytic performance of Pt-based catalysts.

Investigating the ductile to brittle transition phenomenon in binary Fe-Ni systems using molecular dynamics simulation

Ductile to brittle transition (DBT) phenomenon is commonly observed in BCC Fe-based systems, which significantly deteriorates their low temperature fracture toughness. Ni is known to be an effective alloying element to improve the low temperature toughness by reducing the ductile to brittle transition temperature (DBTT). The present article investigates the role of Ni in tailoring the DBT curve of BCC Fe by employing molecular dynamics (MD) simulation. Here, we performed mode-I loading of different pre-cracked systems (pure Fe, Fe-2 wt% Ni and Fe-4 wt% Ni alloys) over a temperature range of 1–800 K to construct their DBT curves. The DBT curves are subsequently correlated with the temperature sensitivity of fracture stress, which is estimated using the concept of critical strain energy release rate (GIC). The role of Ni in reducing the fracture stress sensitivity is responsible for decreasing the DBTT as well as the slope of the DBT region. The underlying mechanism is discussed in terms of the crack blunting effect of Ni which effectively increases the GIC and hence the fracture stress, particularly at the low temperature regimes. Besides, the significantly large strain rate imposed in MD simulation is mainly responsible for the higher DBTT values when compared with the experimental results. The present paper tackles this strain rate issue by using an appropriate strain rate sensitivity factor to rescale the simulated DBTT values down to the experimental ones, resulting in a good match between the simulated and experimental DBTT.