Ni Si Alloy Research Articles

Experimental study and thermodynamic modelling of the ternary system Fe–Ni–Si with re-modelling of the constituent binary systems

The present paper reports on the thermodynamic modelling of the complete ternary Fe–Ni–Si system based on key experimental results and information reported in literature. The key experiments were performed to verify phases and phase fractions in selected ternary Fe–Ni–Si alloys using samples in the as-cast state as well as annealed samples. Chemical compositions of the samples were analysed by Energy Dispersive X-Ray Spectroscopy. Microstructure characterization was performed by Scanning Electron Microscopy and Electron Backscatter Diffraction techniques. Phase transformation temperatures were determined by Differential Scanning Calorimetry operated in the Differential Thermal Analysis mode. Calculations performed using proposed thermodynamic description reproduce experimental data well, including data from available literature. In particular, the Fe-rich corner of the Fe–Ni–Si system has been modelled in detail, with emphasis on the A2 and B2 phase fields. The developed ternary database was used to compute phase diagrams and thermodynamic properties of the constituent binary systems as well as selected isothermal and isopleth sections. Due comparison with commercially available and previously modelled thermodynamic descriptions is presented and discussed.

Effects of Co/Si Atomic Ratio on Hardness and Electrical Conductivity of Cu–Co–Si Alloys

Cu–Co–Si alloys are being intensively studied as alternative candidates for Cu–Ni–Si alloys for integrated circuit lead frames. However, the effects of different precipitate types on the comprehensive properties of Cu–Co–Si alloys are not clear. Herein, several Cu–Co–Si alloys with various precipitates (CoSi, Co2Si, and Co) are designed based on phase diagrams calculation. The designed alloys are melted, cold‐rolled, and aged to test the corresponding hardness and electrical conductivity (EC). X‐ray diffraction and transmission electron microscopy are utilized to analyze the precipitates generated in those alloys. In the alloys with Co/Si ≤ 1, the excess Si atoms are not easy to precipitate from the copper lattice after CoSi precipitation, which seriously damages the EC. Co‐precipitation in alloys with Co/Si > 2 is beneficial to improve EC without sacrificing hardness. According to thermodynamic calculation, precipitates in Cu‐1.62Co‐0.35Si (wt%) alloy with total elements between 1.5 and 2.0 wt% are all Co2Si and have the highest mass fraction in the equilibrium state. The different precipitates are highly dependent on the Co/Si atomic ratio and essential to Cu–Co–Si alloys’ mechanical and electrical performances.

Characterization of Precipitated Phase in Cu–Ni–Si Alloy by Small-Angle X-ray Scattering, Small Angle Neutron Scattering and Atom Probe Tomography

Characterization of Precipitated Phase in Cu–Ni–Si Alloy by Small-Angle X-ray Scattering, Small Angle Neutron Scattering and Atom Probe Tomography

Enhancing the comprehensive properties of as-cast Cu–Ni–Si alloys by continuous extrusion combined with subsequent thermomechanical treatment

Producing high-strength and high electrical conductivity Cu–Ni–Si alloys from as-cast state to thin strips is a challenging issue in the industry, as high-temperature homogenization, multi-step rolling, and aging processes are frequently employed and, any mistakes in each step can affect the quality of the product. In the present study, the comprehensive properties of an as-cast Cu–Ni–Si alloy were improved by a short process, i.e., continuous extrusion combined with rolling and aging processes, without homogenization treatment. The results indicated that both the mechanical and electrical properties of the alloy at the optimized route were dramatically enhanced. A final microstructure containing fine grain sizes, massive precipitates, and dislocations was obtained, thus contributing to high tensile strength (763 MPa), high electrical conductivity (49.6% IACS), and good ductility (5.8% fracture elongation). The strengthening mechanisms were then quantitively calculated. The results showed that the dislocation strengthening, grain boundary strengthening, and precipitation strengthening take 25.2%, 16%, and 51.2% of the total yield strength, respectively. It has also been found that there are two sizes of precipitates and both were identified to be δ1-Ni2Si. Although the volume fraction of the fine Ni2Si is small, it contributes to a large portion of the yield strength. Hence, there is great potential to control the precipitate size to enhance the strength of the Cu–Ni–Si alloy further for this combined technique.

Effect of the energy density deposited by a 3.66-MeV Nickel ion beam on the sputtering yield of a hypereutectic alloy

Dilute alloys of Ni–Si binary system have been used as base material to study microstructural changes caused by irradiation in complex alloys. However, non-dilute Ni–Si alloys, which are themselves also important for high-temperature applications, have been little studied under irradiation. In this paper, the behavior of a hypereutectic alloy, Ni22at.%Si, under severe irradiation conditions is evaluated, to determine changes induced on the surface and elucidate the possible mechanisms that promote them. As a result of irradiating this alloy with Ni ions of 3.66 MeV at 650°C and an incidence perpendicular to the surface, the presence of nanohills is detected, as well as groove patterns and craters, which formation is attributed to different sputtering mechanisms. To characterize these changes, optical, scanning electron and atomic force microscopies were used. Comparing the experimental findings with some of the most important physical models of sputtering, it was concluded that such changes to the surface microstructure strongly depend on the amount of energy deposited during irradiation and on how it is distributed in the microstructural features developed in the alloy during its manufacture. Moreover, when the radiation dose was changed to evaluate the sputtering yield as a dose function, it was detected as geometric sputtering mechanism.

Non-Arrhenius behaviour of nickel self-diffusion in liquid Ni77Si23

Nickel self-diffusion was measured for a Ni77Si23 alloy in the liquid state over a temperature range of about 400 K through quasielastic neutron scattering. At the two lowest temperature points the derived diffusion coefficients deviate from a high-temperature Arrhenius-type behaviour and indicate a change in dynamics above the liquidus temperature. A fit with a power-law temperature dependence as predicted by the mode coupling theory for the liquid to glass transition can describe the diffusion coefficients quite well over the whole measured temperature range. The obtained results agree with predictions from a classical molecular dynamics (MD)-simulation, which evidenced an increasing glass forming ability with increasing silicon content. A crossover to a super-Arrhenius behaviour was reported for metallic glass formers above the liquidus temperature and the here investigated NiSi alloy demonstrates the same signature.

Low-thermal-budget n-type ohmic contacts for ultrathin Si/Ge superlattice materials

Thermal budget is a vital element of Si-based superlattice material processing. In this work, a novel n-type ohmic contact scheme with a low thermal budget process is developed by combining high-dose ion implantation and low-temperature alloying techniques. The optimized specific contact resistivity (ρ c) is reduced to 6.18 × 10−3 Ω cm2 at a low thermal budget of 400 °C, and this is a result of the efficient low-temperature electrical activation of amorphous substances. It is indicated that both the high doping concentration and the formation of a NiSi(Ge) alloy phase contribute to the linear ohmic contact behavior. The ohmic contact resistance dependence on processing temperature is further revealed by a detailed Ni/Si(Ge)alloying model. A minimum ρ c of 2.51 × 10−4 Ω cm2 is achieved at a thermal budget of 450 °C, which is related to the high bonding intensity at the metal–semiconductor interface. Note that this technique is compatible with standard Si-based CMOS process flows and can be applied in high-performance insulated-gate field-effect transistor (IGFET) fabrication. Furthermore, it is verified that the Si/Ge superlattice structures in our IGFETs can serve as an efficient potential barrier to constrain electrons.

Resistivity of solid and liquid Fe–Ni–Si with applications to the cores of Earth, Mercury and Venus

Electrical resistivity measurements of Fe–10wt%Ni–10wt%Si have been performed in a multi-anvil press from 3 to 20 GPa up to 2200 K. The temperature and pressure dependences of electrical resistivity are analyzed in term of changes in the electron mean free path. Similarities in the thermal properties of Fe–Si and Fe–Ni–Si alloys suggest the effect of Ni is negligible. Electrical resistivity is used to calculate thermal conductivity via the Wiedemann–Franz law, which is then used to estimate the adiabatic heat flow. The adiabatic heat flow at the top of Earth’s core is estimated to be 14 TW from the pressure and temperature dependences of thermal conductivity in the liquid state from this study, suggesting thermal convection may still be an active source to power the dynamo depending on the estimated value taken for the heat flow through the core mantle boundary. The calculated adiabatic heat flux density of 22.7–32.1 mW/m2 at the top of Mercury’s core suggests a chemically driven magnetic field from 0.02 to 0.21 Gyr after formation. A thermal conductivity of 140–148 Wm−1 K−1 is estimated at the center of a Fe–10wt%Ni–10wt%Si Venusian core, suggesting the presence of a solid inner core and an outer core that is at least partially liquid.

High strength and high electrical conductivity C70250 copper alloy with fibrous structure reinforced by high density, multi-scale nano-precipitates and dislocation

Cu–Ni–Si alloy has a difficult combination of high strength and high electrical conductivity, which limits its further application in electronics industry. In this work, the effects of large deformation double cold rolling-aging processes on the microstructure, mechanical properties and electrical conductivity of the columnar grain alloy were studied, and its mechanism was revealed. The results show that the C70250 copper alloy strip prepared by hot mold continuous casting technology can be directly subjected to large deformation double cold rolling-aging treatments without solid solution process. The excellent balance of tensile strength and electrical conductivity, as high as 884 MPa and 45.7% IACS, respectively, can be obtained for the alloy after primary 95% cold rolling and aging at 450 °C for 45 min followed by secondary 60% cold rolling and aging at 400 °C for 10 min. The strength and electrical conductivity is better than the similar products reported. The realization of high strength and high electrical conductivity is attributed to the interaction between strain hardening and precipitation behavior of columnar alloy during double deformation and aging treatment. The repeated introduction of large deformation cold rolling provides a new short diffusion driving force for the precipitation of solute atoms by GPA and APT results, the precipitation rate is increased in the second stage of aging. At the same time, the nanometer-sized strengthening phase formed by primary aging can effectively nail the dislocations formed in the secondary cold rolling process, and finally form a fibrous structure with uniform mixing of multi-scale nano cluster and Ni2Si phase. The strength of the alloy is significantly improved by dislocation strengthening and multi-scale precipitation strengthening. C70250 copper alloy precipitate as many solute atoms as possible, and retains fibrous structure, the dispersing of electrons by solute particles and grain boundary limits is fundamentally diminished, and the electrical conductivity is improved.

Splitting of γ′ Precipitates in the Context of Phase Equilibrium

The splitting of γ′ (Ni3Al and Ni3Si) precipitates in five binary Ni-Al alloys and one Ni-Si alloy is reviewed in the context of phase equilibrium. Two mechanisms are considered: Purely Elastic (PE) splitting, driven solely by competition between elastic and interfacial free energies; Thermodynamically Driven (TD) splitting, involving precipitation of the Ni-Al or Ni-Si solid solution γ phases within supersaturated γ′ particles. The main assertion is that TD splitting is responsible for all the observations, with the possible exception of dendritic growth of Ni3Si precipitates; dendritic morphologies can mimic split configurations. In three of the six investigations splitting was reported for alloy compositions lying within the single-phase γ regions of the binary Ni-Al and Ni-Si phase diagrams wherein the γ′ phases are unstable. For the three others the aging temperatures were at or barely below the solvus temperatures, suggesting that five of the alloys were compositionally heterogeneous, “solution treatment” having failed to dissolve pre-existing γ′ particles. TD splitting was thus a byproduct of slow cooling to the aging temperatures, as in the formation of hierarchical microstructures. The nature of secondary γ′ precipitation in some of the alloys indicates that their compositions exceeded the authors’ quoted values, the enrichment enabling precipitation of γ′ during solution treatment followed by TD splitting on slow cooling. PE splitting is the only possible mechanism in solution-treated specimens that are quenched and subsequently isothermally aged. Splitting under such conditions has never been reported, lending further support to the viability of the TD mechanism.

Effect of high contents of nickel and silicon on the microstructure and properties of Cu–Ni–Si alloys

Cu-Ni-Si alloys have been widely used in electronics and electrical industries.The preparation method of alloy was not limited to smelting, powder metallurgy method has also attracted the attention of many researchers. In this study, Cu-Ni-Si alloys were prepared using hot-pressed sintering and elemental copper powders, in which nickel and silicon powders were used as raw materials. The results show that, when the Cu-Ni-Si alloys were prepared using hot-pressed sintering, there were no Ni-Si intermetallic compounds except the δ-Ni2Si phase in the microstructure of alloys. After the ageing treatment, when the mass ratios of Ni/Si were 2:1 and 3:1, the precipitation of δ-Ni2Si phase was significantly less. However, when the mass ratios of Ni/Si were 4:1 and 5:1, the precipitation of δ-Ni2Si phase particles increased significantly. The results from electrical conductivity and Vickers hardness show that, after the ageing treatment, both the electrical conductivity and Vickers hardness of the alloys greatly improved.

Simultaneous enhancement of mechanical and electrical properties of Cu–Ni–Si alloys via thermo-mechanical process

Developing high-performance copper alloys while simultaneously improving ultimate tensile strength (UTS) and electrical conductivity (EC) has been a key challenge and direction. Two thermo-mechanical processes were employed in this study to achieve simultaneous enhancement of UTS and EC of the Cu-3.08Ni-0.61Si-0.17Zn-0.17Cr-0.04P alloy. After the two-stage cold-rolling and aging process (85% cold-rolling + 450 °C@60 min aging + 95% cold-rolling + 450 °C@30 min aging, referred to as Process A), the alloy's UTS and EC of the alloy are 856 ± 26 MPa and 52.4 ± 0.8% international annealed copper standard (IACS). The mechanical and electrical properties of the alloy with process A are much better than those of the alloy with single stage cold-rolling and aging treatment process (85% cold-rolling + 450@60 min aging, 786 ± 12 MPa, 47.5 ± 0.9% IACS). The UTS of the alloy reaches 905 ± 11 MPa with pre-aging + two-stage cold-rolling-aging (450 °C@90 min pre-aging + process A, referred to as process B), and the EC reaches 52.5 ± 0.2% IACS, indicating that process B enhanced the strength over process A. A large number of nano-scale δ-Ni2Si precipitates are observed in the samples after primary aging of process A and pre-aging of process B, leading to a more diffuse dislocation distribution during subsequent cold-rolling and then promoting further precipitation of the solute atoms during subsequent aging processes. In the samples treated by both process A and B, there are two sizes of δ-Ni2Si phase precipitates, simultaneously enhancing UTS and EC of the Cu–Ni–Si alloy.

In situ observation of solidification and subsequent evolution of Ni-Si eutectics

Eutectic growth of Ni-Si alloy with a composition of Ni44Si56 was observed in situ during directional solidification. Lamellar structure was evident behind the solidifying interface, which indicates that the two intermetallic phases, NiSi and NiSi2, generated a regular eutectic. The lamellae spacing was approximately 9.8 μm at a growth rate of 149.6 μm s−1. The phase boundaries migrated rapidly during the cooling stage and the lamellae enlarged significantly, which suggests that the lamellae spacing measured after the solidification may not be accurate for obtaining the relationship between the growth rate and the lamellae spacing. The in situ observation provides a promising way to obtain the exact eutectic spacing of Ni-Si eutectics.

Heterogeneous–Nano Structure and Mechanical Properties of Co–added Cu–Ni–Si Alloy

Heterogeneous–Nano Structure and Mechanical Properties of Co–added Cu–Ni–Si Alloy

Influence of Substitution of Co for Ni in Cu–Ni–Si Alloy on Work and Precipitation Hardening

Influence of Substitution of Co for Ni in Cu–Ni–Si Alloy on Work and Precipitation Hardening

Effect of multiple forging on the microstructure and properties of an as-cast Cu–Ni–Si alloy with high Ni and Si contents

A Cu–Ni–Si alloy with high Ni and Si contents was prepared by the traditional melting and casting method, and then multiple forging and ageing were conducted to investigate their effect on the microstructure and properties. The results show that reticular Ni31Si12 phases are located on the grain boundaries of the dendritic α-Cu(Ni, Si) solution matrix in the as-cast Cu–Ni–Si alloy because of the high Ni and Si contents, and some rice-like Ni2Si phases precipitate in the interior of α-Cu(Ni, Si) grains during cooling. With increasing number of forging passes, the morphology of the α-Cu(Ni, Si) matrix changes from dendrites to elongated dendrites and then equiaxed grains, the Ni31Si12 phase changes from reticular to irregular and then particle-like, while the Ni2Si phase gradually disappears. As a result, the hardness increases continuously up to 18 forging passes, while the electrical conductivity first increases and then decreases significantly. The hardness and electrical conductivity achieve the highest values with 18 forging passes and a subsequent ageing treatment at 450 °C for 4 h, and the corresponding microstructure comprises an equiaxed α-Cu(Ni, Si) matrix with microscale Ni31Si12 particles and sub-microscale Ni2Si precipitates.

Recycling of the Diamond-wire Saw Powder by Ni-catalyzed Nitridation to Prepare Si3N4

In this paper, the acceleration effect of nickel (Ni) on the direct nitridation process of the diamond-wire saw powder (DWSP) was investigated. The DWSP doped with Ni additives were nitrided at different temperatures. To study the mechanism of accelerated nitridation, the thermodynamics of Si-O-N-Ni and nitridation processes were analyzed by FactSage 7.2 and single-crystal silicon blocks were also nitrided instead of the DWSP. The results revealed that Ni decreased the nitridation temperature at which the DWSP began to gain significant weight and exhibited an excellent accelerating effect on the nitridation of the DWSP. At 1300°C the DWSP containing 2.0 wt% Ni additives had been completely nitrided within 2 h, whereas the DWSP without Ni additives had not been nitrided yet. Based on the equivalent substitution experiment, it could be concluded that the presence of Ni additives accelerated the nitridation and promoted the formation of the α-Si3N4 nanorods through facilitating the generation of the SiO(g) and destructing the silica film on the surface of silicon at lower temperature. Meanwhile, Ni additives also played an important part in the growth of α-Si3N4 nanorods by forming liquid Ni-Si alloy in the product.

Role of solidification texture on hot deformation behavior of a Cu–Ni–Si alloy with columnar grains

Hot deformation behavior of an as-cast Cu–Ni–Si alloy with columnar grains in terms of flow stress, constitutive equation, processing map, microstructure evolution, and dynamic precipitation was investigated at deformation temperatures of 500 °C~800 °C and strain rates of 0.01 s−1~1 s−1. The results revealed that the true stress-strain curves of the as-cast Cu–Ni–Si rods exhibit continuously increased flow stresses. The relationships between the material parameters and strains were then modified by fourth power polynomial functions. Good fitness between the material parameters and strains was obtained. The constitutive equation derived using these relations predicts quite accurate values. Microstructure observed by confocal laser scanning microscopy, electron back-scattered diffraction, and transmission electron microscopy indicated that the main hardening mechanisms of the continuously increased flow stress are attributed to the progressively occurred dynamic recrystallization and dynamic precipitation. The dynamic precipitates, unlike in the aged alloys, are very fine and have multiple orientation relationships with the Cu matrix, which is likely linked with the change of edge-on habit planes due to the plastic deformation and temperature imposed. It has also been found that the processing map developed is also dependent on the strain selected. The processing maps developed at low strains contain larger instability regions than those developed at high strains, which agree with the results of microstructure observations.

Electropulsing Aging Treatment of Cu–Ni–Si Sheet for Microforming

Electropulsing aging treatment (EAT) can achieve a significant increase in the strength and conductivity of a Cu–Ni–Si alloy in a short time while maintaining a lower temperature. Compared with aging treatment in a conventional heating furnace at 450 °C for 120 min, EAT can reach or even exceed the same strength and conductivity in only 5 min. The mechanical and electrical properties of samples treated with 630 and 680 A mm−2 current density are prominently improved. After 45 min of treatment with 680 A mm−2 current density, the tensile strength exceeds 600 MPa, and the conductivity reaches 33.45% International Annealed Copper Standard. The main precipitates of the EAT sample is the δ‐Ni2Si nanoscale strengthening phase, and there is also the β‐Ni3Si phase in the copper matrix. The strengthening mechanism is the localized Joule heating generated by the electropulsing and the kinetic energy conversion caused by drift electrons, which increases the migration rate of solute atoms Si and Ni and reduces the energy barrier required in the precipitation process, thereby accelerating the formation of precipitates. EAT has the potential to become a new process for the preparation of high‐strength and high‐conductivity copper alloys.

High‐Pressure Deformation of Iron–Nickel–Silicon Alloys and Implications for Earth’s Inner Core

AbstractEarth’s inner core exhibits strong seismic anisotropy, often attributed to the alignment of hexagonal close‐packed iron (hcp‐Fe) alloy crystallites with the Earth’s poles. How this alignment developed depends on material properties of the alloy and is important to our understanding of the core’s crystallization history and active geodynamical forcing. Previous studies suggested that hcp‐Fe is weak under deep Earth conditions but did not investigate the effects of the lighter elements known to be part of the inner core alloy. Here, we present results from radial X‐ray diffraction experiments in a diamond anvil cell that constrain the strength and deformation properties of iron‐nickel‐silicon (Fe–Ni–Si) alloys up to 60 GPa. We also show the results of laser heating to 1650 K to evaluate the effect of temperature. Observed alloy textures suggest different relative activities of the various hcp deformation mechanisms compared to pure Fe, but these textures could still account for the theorized polar alignment. Fe–Ni–Si alloys are mechanically stronger than Fe and Fe–Ni; extrapolated to inner core conditions, Si‐bearing alloys may be more than an order of magnitude stronger. This enhanced strength proportionally reduces the effectivity of dislocation creep as a deformation mechanism, which may suggest that texture developed during crystallization rather than as the result of postsolidification plastic flow.