Ni Matrix Research Articles

Effect of electrodeposition parameters on the evolution of crystallographic texture and internal stress of Ni/ZrC composite coatings

Crystallographic texture and internal stress are two important aspects of microstructures, responsible for various physical and chemical properties of electrodeposited composite coatings. This paper aims to understand how preparation parameters such as current density, size and concentration of second-phase particles, particularly deposition time, influence the crystallographic texture and internal stress of electrodeposited Ni matrix composites. The results show that the evolution of surface morphology, crystallographic texture and the internal stress of electrodeposited Ni/ZrC composites is strongly related to the content of incorporated ZrC in coatings, which increases after an increase in the amount of ZrC particles loaded in the electrolyte, from 0 g/L to 40 g/L, and from a decrease in applied current density, from 20 A/dm2 to 1.25 A/dm2. By increasing the ZrC content in coatings, the crystallographic texture of Ni/ZrC is depressed and internal stress is modified from 329.48 MPa to 56.71 MPa. During electrodeposition, the exhibited texture changes from <111> initial texture to <100> growth texture for pure Ni coatings, and to random orientation for Ni/ZrC coatings. The tensile internal stress of Ni/ZrC decreases, followed by a gradual increasing with an increase of thickness. ZrC nanoparticles incorporation results in Ni/ZrC coatings with a weaker texture and lower internal stress than Ni/ZrC coatings that incorporate ZrC micron particles.

Microstructure and mechanical properties of rhenium and GH3128 superalloy dissimilar welded joints by electron beam welding

This research aims to study the dissimilar welded joint of rhenium and GH3128 made by electron beam welding. The microstructure, solidification behavior, mechanical properties, and Re distribution behavior of the weld were systematically researched. The results showed that an excellently joint is obtained, and no defects such as cracks and pores were found in the weld. But thermal cracks occur on the Re base material under the influence of heat input. The fusion zone was mainly composed of columnar dendrites, while the plane grains grow near the Re-side fusion line (reaction layer), which was always enriched in the Re element. Re is evenly distributed in the Ni matrix as a solid solution element so that the hardness of the joint is always higher than that of the GH3128 base material. The tensile strength of the joint reached 498 Mpa and the elongation was about 3%. The tensile fracture occurred at the position of the reaction layer. The high hardness and brittleness of the reaction layer are attributed to the high content of Re and a lot of low-angle grain boundaries.

Surfactant-free commercial electroless bath with low concentration of SiC nanoparticles to prepare the NiP-SiC nanocomposite coatings

Fabrication of NiP-SiC nanocomposite coatings through the electroless deposition in a commercial electrolyte containing the low concentrations of SiC nanoparticles on carbon steel substrate was studied in this work. The confirmation of co-deposition of Ni matrix and SiC nanoparticles was investigated by evaluating the effect on morphology, crystal structure, and corrosion behavior of the heat-treated coatings which were investigated by scanning electron microscope, x-ray diffraction (XRD), and electrochemical measurements, respectively. The XRD results revealed that the heat-treated NiP and NiP-SiC coatings consisted of Ni and Ni3P phases, which the calculated faction of Ni3P phase for NiP and NiP-SiC samples is 58.2 and 62.2%, respectively. The corrosion resistance of nanocomposite samples is higher than that of pure NiP sample (9 to 76% corrosion inhibition efficiency. The tribological behavior of the coatings was characterized by microhardness measurement and ‘pin on disk’ wear test. By co-deposition of SiC nanoparticles, the hardness of heat-treated NiP is significantly increased (near 25%) and the wear loss is reduced (near 48%), especially at high sliding distance during wear test. The sample prepared through the surfactant-free electroless bath containing the 1 g l−1 SiC nanoparticle showed the best corrosion as well as wear resistance.

Scalable Synthesis of Hollow MoS2 Nanoparticles Modified on Porous Ni for Improved Hydrogen Evolution Reaction

Developing an inexpensive non-noble metal catalyst is essential in the electrochemical water reduction. However, to choose the support for hydrogen-producing catalyst is still a problem that needs to be solved. Herein, we report a novel route combining powder metallurgy and hydrothermal synthesis to fabricate Ni/MoS2 catalysts for boosting the hydrogen evolution reaction performance. Powder metallurgy produces the suborbicular pores on the surface and inside Ni once the sintering temperature reaches 1000 °C. The hollow MoS2 nanoparticles are successfully modified on the surface of porous Ni by hydrothermal synthesis. The hollow structure of MoS2 nanoparticles provides more active sites for electrochemical reaction and the porous Ni matrix with the porosity of 16.5% exhibits higher electronic conductivity, which endows the Ni/MoS2−1000 catalyst with an excellent hydrogen evolution reaction activity. The Ni/MoS2−1000 shows a low overpotential of 229 mV at the current densities of 10 mA·cm−2 with a small Tafel slope of 76 mV·dec−1. This study provides guidelines on the large-scale synthesis of nanostructured electrocatalysts with porous Ni as the support.

Pressureless sintering and tribological properties of in-situ TiC-Ni3(Al,Ti)/Ni(Al,Ti) composites

In this study, we report on the microstructure and tribological characterization of in-situ TiC and γ’-Ni3(Al,Ti) reinforced γ-Ni(Al,Ti) matrix composites, synthesized by in-situ reaction of Maxthal211 (Ti2AlC-Ti3AlC2, MAX phase) and Ni precursors. Three composites were elaborated from 10, 20 and 30 wt% of the MAX phase precursor which fully reacted with Ni-matrix at 1080 °C sintering temperature for 4 h; the MAX phase decomposed into TiC, and the released Al and Ti atoms diffused in Ni matrix forming γ-Ni(Al,Ti) solid solution and γ’-Ni3(Al,Ti) intermetallic. Scanning Electron Microscopy (SEM), X Rays Diffraction (XRD) and Raman spectroscopy were used to study the different microstructures and worn surface characteristics. Dry sliding properties of the composites under different normal loads were studied using a ball-on-disc tribometer. Addition of 10 wt% MAX phase procured the highest hardness (1.35 GPa) which is two times higher than that of pure Ni. Whereas all the reinforced composites exhibited better wear resistance. The formation of a lubricious layer during sliding and the good in-situ bonding between Ni/reinforcement phases, were the main cause to the enhanced wear resistance.

Dischargeable nickel matrix charges iron species for oxygen evolution electrocatalysis

Nickel-iron (oxy)hydroxide (NiFeOxHy) is a state-of-the-art non-precious electrocatalyst for oxygen evolution reaction (OER) in alkaline media. However, the origin of the synergy between Ni and Fe remains unclear. Here, operando X-ray absorption and ultraviolet photoelectron spectroscopy were used to prove the charging-discharging behavior of Ni and Fe when they are adjacent. Fe oxidation and Ni reduction were simultaneously observed during electrocatalytic OER in NiFeOxHy compared to unary metal (oxy)hydroxide. The higher Fermi level of FeOxHy compared to NiOxHy enables charge transfer from Fe to Ni domain near the boundaries. From the experimental results, the combination of Ni and Fe results in superior oxygen-evolving activity by exposing high valent Fe coupled with a dischargeable Ni matrix.

Tailoring effect of Cr and graphene particles on the microstructure and properties of Ni matrix nanocomposite coatings

Ni matrix nanocomposite coatings with a microstructure tailored by Cr and graphene particles were assembled at various current densities by electroplating. The tailoring effect of particles on the surface morphology, composition, microstructure, and properties of the nanocomposite coating was comprehensively explored. The results revealed that the contents of Cr and graphene particles in the nanocomposite coating were elevated by decreasing the current density, resulting in an increased amount of small dendrite-like surface structures. The embedded particles blocked the formation of [200] fiber texture and concurrently brought about crystallite refinement of the Ni deposits. A COMSOL simulation and BSE images revealed that the embedded particles tailored the microstructure of Ni deposits by heterogeneous nucleation, rearrangement, and local current density concentration. The current density concentration on the particles contributed to the selective growth of Ni deposits on the particles. The synergistic effect of the tailored microstructure and embedded particles substantially enhanced the corrosion resistance of the Ni–Cr–graphene nanocomposite coating. In 3.5 wt% NaCl media, the Icorr of the nanocomposite coating electroplated at 1 A/dm2 (0.1 μA/cm2) was an order of magnitude lower than that at 20 A/dm2 (2.63 μA/cm2) owing to the strengthened synergistic effect.

Electrodeposited nickel–graphene nanocomposite coating: influence of graphene nanoplatelet size on wear and corrosion resistance

In this paper, we broaden our previous work, which investigated the influence of graphene nanoplatelets (GNPs) size on microstructure and hardness of composite coatings, to determine the effect of GNP size on wear-resistance and anti-corrosion property of GNP-reinforced nickel coating (Ni/GNPs). The experimental results indicated that the small GNP material size could enhance the wear resistance for nickel composite coating with the wear rate of 13.2 × 10–4 mm3/Nm, the wear depth of 17.69 µm. Meanwhile, the anti-corrosion property is enhanced significantly, this is shown via the low corrosion current density (Icorr value of 1.16 × 10–7 A/cm2) and the high corrosion potential (Ecorr value of − 0.1661 V). In addition, the mass lost in salt fog testing is low with the weight of 12.3 mg, which decreased down to ~ 55.27% compared to pristine Ni coating. These results are attributed to the uniform distribution of the small GNP size inside Ni matrix as well as the grain refinement effect of composite coating when using the small GNP size.

The formation mechanism of TiC/Ni composites fabricated by pressureless reactive sintering

TiC/Ni composites were innovatively fabricated by pressureless reactive sintering method using Ni, Ti and graphite as raw materials. According to the sintering shrinkage curve, phase and microstructure evolution process of composites during reactive sintering, the formation mechanism of dense TiC/Ni composites could be divided in two stages. In the first stage, TiC layer is formed on Ti particles by the solid reaction between Ti and graphite, while Ni atom diffuses into Ti particles to generated NiTi, Ti2Ni and Ni3Ti. Besides, the solid-state sintering of Ni particles also occurs. At 1250 °C, the Ti is completely consumed, resulting in the TiC layer on Ni and continuous Ni skeleton in composites. In the second stage, the eutectic liquid phase of Ni-Ti-C is formed, and then shrinkage process begins through the dissolution-reprecipitation of TiC in Ni matrix. The relative density of TiC/Ni composites reaches 98.14% at 1360 °C.

Microstructure and wear behavior of laser-cladded Ni-based coatings decorated by graphite particles

Abstract In order to improve the anti-friction and wear-resistance properties of 42CrMo steel, Ni-coated graphite composite powder and Ni45 alloy powder were designed to fabricate Ni-based self-lubricating wear-resistant coating with simple process and low cost on 42CrMo steel substrate by laser cladding. The effect of scanning speed on pore defects, graphite particle distribution, microstructure and wear behavior of the coatings were investigated, respectively. Through the synergy between adjusting scanning speed and Ni-coated graphite composite powder, the contradiction among the coating density, the interface bonding strength between graphite and Ni matrix and the excessive loss of graphite caused by ablation and in-situ reaction during laser cladding were resolved. Results showed that Ni-coated layer could effectively prevent the graphite from ablation and delay the reaction between carbon and other components. Ni-based self-lubricating coating with low porosity, uniform microstructure, moderate hardness, low friction coefficient and low wear rate can be prepared at an appropriate scanning speed of 300 mm/s. Its average friction coefficient and wear volume were approximately 0.480 and 6.824 × 10−6 mm3/N·m, respectively. The main wear mechanism is slight abrasive wear and adhesive wear. These results obtained are not only applicable to Ni-based alloy coatings, but also to Ni-based composite coatings reinforced by ceramic particle, and even to other material systems. Particularly, when the reinforcing phase is carbide ceramics, the addition of graphite can also inhibit the dissolution of carbide during laser cladding.

In situ high-entropy solid solution and ceramic particles co-reinforced Ni-based composites with outstanding strength-ductility synergy and good pitting resistance

Abstract In present work, a novel Ni-based composite co-reinforced by in-situ solid solution and ceramic phase through a decomposition of metastable dual-phase (CoCrFeNiMn)90Al10 high-entropy alloy (HEA) was fabricated by spark plasma sintering (SPS). The SPS-ed composites with high relative density are composed of Al-rich oxide particles, γ* nanoprecipitates and Ni matrix, all of which reveal the face-centered cubic (FCC) structures with almost identical lattice constant. The maximum microhardness of composite is 321 HV, which is over 2 times larger than that of the SPS-ed pure Ni. It is worth noting that the composite with 20 vol.% HEA addition exhbits high ultimate tensile strength of 580 MPa, while maintaining excellent fracture strain of 32.2%. The notable improvement in mechanical properties is mainly attributed to the twin/stacking faults strengthening and precipitation strengthening, as well as grain-boundary strengthening. A coherent boundary between γ* phase and Ni matrix and a hierarchical precipitate spatial distribution of nano-γ* and micron-oxides in Ni matrix have been obtained. Combined with FCC characteristics of matrix and reinforcements, these scenarios effectively promote the coordinated deformation of composites during tensile testing, which are beneficial to the improvement of plasticity. In combined with the significantly broadened passive region and low passive current density, the SPS-ed composites present the good pitting resistance in seawater.

Electro-codeposition and properties of Cu–Ni-MWCNTs composite coatings

ABSTRACT In this work, multi-walled carbon nanotubes reinforced Cu–Ni matrix (Cu–Ni-MWCNTs) composite coatings were produced using the electro-codeposition method by adding different concentrations of MWCNTs (0.05, 0.1 and 0.15 g L−1) to the Cu–Ni plating bath. To achieve effective dispersion of the MWCNTs, the plating solution was stirred using an ultrasonicator (20 kHz and 500 W) for 120 min. Cu–Ni-MWCNTs composite coatings were characterised by scanning electron microscopy and X-ray diffraction to study the surface morphology and microstructure of the coatings. In addition, the effects of MWCNTs on the microhardness, wear resistance and electrical conductivity of the coating were investigated by microhardness tester, pin on disk wear tester and four-point probe system respectively. All Cu–Ni-MWCNTs composite coatings showed enhanced microhardness and wear performance as compared to the Cu–Ni coating. The Cu–Ni-MWCNT (0.15 g L−1) composite coating exhibited maximum microhardness of 438 HV and minimum wear loss of 0.9 mg among all the coatings, in the same pin-on-disk test conditions, which is attributed to the combined effect of microstructural refinement, higher content of MWCNTs and superior properties of MWCNTs. Electrical studies reveal that MWCNTs play a vital role in increasing electrical conductivity by 1.21 times of magnitude.

Precipitation behavior near shrinkage porosity in a large sand casting of Haynes 282 alloy

The precipitation behavior of L12 structure Ni3(Al,Ti)-type γ' precipitates near shrinkage porosity in a large sand casting of Haynes 282 alloy has been investigated by scanning/transmission electron microscopy in conjunction with energy dispersive x-ray spectroscopy. The experimental results revealed that in the carbonitride-rich region close to the shrinkage porosity, γ' precipitates could still form with comparable sizes though at lower volume density than those in the general cast Ni matrix. The resulting γ' precipitates had a very high Al/Ti ratio. Close to oxide-rich pore surfaces, an absence of γ' precipitates was observed due to Al and Ti depletion by forming Al oxides and Ti carbonitrides, respectively. This work suggests that Al rather than Ti plays a dominant role in the formation of γ' precipitates in porous regions in cast Haynes 282 alloys.

Tribological properties of Ni–W–TiO2–GO composites produced by ultrasonically–assisted pulse electro co–deposition

The Ni–W–TiO2–Graphene oxide co–deposition with excellent mechanical properties, high wear resistance was produced using ultrasonic–assisted pulse electrodeposition. In the present study, the effects of concentration of graphene oxide and TiO2 particle on the morphology, microstrain, crystallite size, hardness, elastic modulus, and tribological properties of the NiW co–deposition were studied. The morphology, microstructure, and phase analysis of the coatings were investigated using X–ray diffractometer (XRD) and Field Emission Scanning Electron Microscopy (FESEM). X–ray diffraction (XRD) analyses showed that the crystallite size of the Ni(W) matrix decreased with incorporated graphene oxide and TiO2 particles while increased microstrain. Raman analysis is used to confirm the existence of graphene oxide and ceramic particles in the Ni(W) matrix. FESEM results indicated that the Ni–W–TiO2–Graphene oxide co–deposition displayed a compact surface structure, while the crystallite size and microstrain of the composite coating were 7 nm and 3.5 × 10−3, respectively. Nano–mechanical test results showed a maximum of 8.1 GPa and ~209 GPa increases in hardness and elastic modulus with adding graphene oxide and TiO2, respectively. Incorporation of graphene oxide and TiO2 particles into the matrix, the wear rate of the resulting coating can be increased significantly. The tribological behavior of the Ni–W–GO composite coating deposited various graphene oxide concentrations and NiW, Ni–W–TiO2, the Ni–W–TiO2–Graphene oxide coating was compared, and their different wear mechanisms have been discussed. Detailed studies of the worn surface were performed with SEM, EDS, and Raman.

The defining role of phosphorous on microstructure, nanohardness and thermal stability of pulsed electrodeposited nanocrystalline nickel-phosphorous alloys

Free-standing nanocrystalline (NC) nickel-phosphorous (Ni–P) alloy foils with P content in the range of 0.2–5.0 wt percent are synthesized by pulsed electrodeposition technique. The aim of the present study is to evaluate the effect of P content on the hardness and microstructural evolution in Ni–P alloys during both electrodeposition and thermal treatment. The microstructure, hardness and thermal analysis of the alloys are investigated using electron microscopy, nanoindentation and differential scanning calorimetry (DSC), respectively. This study demonstrates that there is localized structural heterogeneity in conjunction with significant grain refinement in the alloys containing excessive P content beyond its solid solubility. Nanohardness measurements indicate that both the grain refinement and internal strain induced by codeposition of P solute atoms affect the strengthening of Ni matrix. The exothermic peaks observed in the DSC thermograms are found to be strongly dependent on P content in the alloy and these are associated with structural relaxation, formation of metastable and stable nickel phosphide phases along with concurrent grain growth and particle coarsening. The grain growth kinetics study showed that in Ni–P alloys Smith-Zener drag mechanism involving control of grain boundary mobility by Ni3P nanoparticles overtakes the solute drag effect of P with increasing temperature.

High temperature phase stability and wear behavior of laser clad Ta reinforced NiCrBSi coating

Ta is added to laser clad NiCrBSi coating to improve high-temperature wear resistance. The influence of heat treatment of 700 °C on Ta reinforced coating is studied. The microstructure is analyzed by XRD, SEM, EDS, TEM and XPS. The tribological performances were investigated on high temperature pin-on-disk tribometer at temperatures up to 700 °C. Ta reinforced coating mainly includes γ-Ni, TaC, Ni3Fe, CrB, M23C6 and Cr2.8Fe1.2B4. Under heat treatment, most of the phases remain stable except that M23C6 is dissolved and coarsened. CrB formed on TaC particle is evolved into Cr2.8Fe1.2B4. The heat treatment has little influence on the hardness of Ta reinforced coating. It is difficult to form an oxide layer on worn surface of NiCrBSi coating at any temperature. On the contrary, an oxide layer form on worn surface of Ta reinforced coating at 700 °C. Ta significantly improves the wear resistance of NiCrBSi coating at high temperatures, which is attributed to Ni matrix strengthened by Ta, TaC with high thermal stability, clean TaC/matrix interface, and compact oxide layer. The main wear mechanism below 600 °C is abrasion and adhesion, and oxidization, which transitions to delamination, abrasion, ploughing and oxidization at 700 °C.

Fabricating graphene nanoplatelets/nickel composites of balanced strength and ductility

In this work, a feasible strategy to fabricate graphene nanoplatelets (GNP) reinforced nickel (Ni) matrix composites is developed, in which the in-situ exfoliation and dispersion of GNP are synchronized. This strategy consists of preparing composite powders by three dimensional (3D) vibration milling Ni powders with graphite bulks and consolidation process by spark plasma sintering (SPS). Characterization results show that GNPs are stripped from the graphite bulk and homogeneously distributed on Ni powders surfaces. Compared with pure Ni, the 0.1 wt % GNP/Ni composites demonstrate a yield strength of 338 MPa and ultimate tensile strength of 593 MPa, achieving improvement by 29.5% and 24.8% respectively, and preserve good ductility simultaneously. Due to the grain refinement and efficient load transfer, the obtained GNP/Ni composites exhibit superior strengthening efficiency. This strategy can be disseminated to simple and economical preparation of other metal matrix composites reinforced with GNP.

Microstructure evolution and reaction behavior of Cu–Ni alloy and B4C powder system

Microstructure evolution and reaction behavior of Cu–Ni alloy and B4C power system was studied by in-situ and static experimental investigations along with theoretical calculations. The reaction process was as follows. Firstly, B4C decomposed into B and C atoms, and then B atoms diffused into Cu–Ni matrix, leading to the formation of Ni2B particles. Subsequently, Ni atoms diffused into B4C, forming a loose mixture of Ni2B and amorphous C at the initial powder boundary. Finally, with the completion of reaction, Ni2B particles at the powder boundary grew into a monolithic block, and then C substance was excluded out and accumulated at the edge of this monolithic Ni2B block. It is believed that the formation of Ni2B phase is caused by the most negative change of Gibbs free energy among all the potential reactions between Ni–B and Ni–B4C systems.

Atomistic simulation of energetic displacement cascades near an Ni–graphene interface

Ni–graphene nanocomposites have greatly promising applications in supercritical water-cooled reactors due to their outstanding performances. However, many fundamental mechanisms of irradiation behaviors in the composites are still unclear. Here we investigate the displacement cascades near an Ni–graphene interface using atomistic simulations. Different cascade energies and ambient temperatures were introduced to bring out the effect of irradiation. The increasing cascade energy in the interval 0.5–10 keV could significantly promote the formation of defects, while there is slight effect on the number of surviving defects in Ni matrix when adjusting the ambient temperature from 100 K to 900 K. The damaged graphene could be self-healing by the synergistic effects of irradiation annealing and ambient temperature annealing. The interface exhibits high sink efficiency for irradiation defects in all cases. This study provides an important insight into the understanding of the microscopic evolution of defects in cascades for the composites.

Microstructure and mechanical properties of Ni matrix B4C reinforced functionally graded composites

In this study, microstructure and mechanical properties of nickel matrix B4C reinforced functionally graded composites produced by powder metallurgy method were investigated. Samples with Ni+5% B4C, Ni +10% B4C, Ni+ 15% B4C and Ni+ 20% B4C compositions were sintered at 900 and 1050?C for 60 minutes. Microhardness and wear tests along with optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction (XRD) analyses were carried out to determine the mechanical properties, microstructure and phase composition of the samples. The results indicated that hardness and wear resistance increased with increases of B4C amount in nickel matrix.