Ni Powders Research Articles

Explosion hazard and prevention of Al–Ni mechanical alloy powders

Al–Ni mechanical alloys containing nickel are synthesized to explore the explosion hazard of fuel additives in energetic formulations in this study. Explosion severity and ignition sensitivity of Al and Al–Ni powders are measured. The results show that as the nickel content increases, the synthesizing heat of Ni-aluminide will firstly increase, and then decrease, which may also make the explosion severity of aluminum powder increase firstly and then decrease accordingly. The powder's sensitivity to electrostatic ignition will grow as the nickel content increases. As the nickel content increases from 0 to 17%, the average activation energy of Al–Ni powder decreases by 77.5%. The increase of ignition energy mainly affects the flame propagation, but with few effects on the process of Al–Ni combustion. Therefore, as the ignition energy increases, the explosion severity of the Al and Al–Ni powders decreases slightly. For safety's sake, the production and storage devices must be inert, and the concentration of oxygen should be less than 5%.

SHS compaction of TiC cermets using mechanically activated mixtures

This paper focuses on obtaining cermet composite materials by SHS compaction. The study covers the effect of mechanical activation of metal components contained in reaction mixtures based on the Ti + C + Cr + Ni system when treated with grinding media in a ball mill. Two mechanical activation methods were used for Ti, Cr and Ni metal powders. In the first method, Cr and Ni powders were activated with grinding media separately from other reaction mixture components, and then mixed with titanium and carbon black powders. It is shown that the preliminary mechanical activation of inert components reduces the temperature and rate of combustion and increases the average size of carbide grains. In the second method, Ti + + Cr, Ti + Ni, and Ti + Cr + Ni powder mixtures were jointly processed in a ball mill, and then mixed with carbon black. This method provided mechanical activation of titanium particles with a minimum effect of grinding media on Cr and Ni powders. This led to an increase in the combustion rate and temperature, a decrease in the average size of carbide grains, and an increase in the composite structure homogeneity. A mechanism is proposed for the interaction of reagents (Ti + C) with the participation of activated Cr and Ni particles in combustion and structure formation zones, according to which the mechanical activation of inert components leads to their direct participation in the reaction interaction of titanium with carbon, which determines a decrease in the combustion rate and temperature and affects the fineness and structural homogeneity of compact composites. The results obtained were used to increase the structural homogeneity and fineness of the STIM-3B composite (Grade 3B synthetic hard tool material).

Microstructure and mechanical properties of novel tungsten heavy alloys prepared using FeNiCoCrCu HEA as binder

In the present work, novel tungsten heavy alloys (WHAs) have been developed using FeNiCoCrCu high entropy alloy (HEA) as binder through conventional sintering process. The composition of the alloy is 90 wt% W-10 wt% HEA. FeNiCoCrCu HEA was prepared by mechanical milling of elemental Fe, Ni, Co, Cr, and Cu powders in an equiatomic ratio for 60 h. XRD analyses revealed that HEA contains predominant FCC phase along with BCC minor phase. In order to evaluate the effectiveness of FeNiCoCrCu HEA as a binder of WHA, in this study, W and HEA were mixed in the ratio of 9:1, pressed and sintered at temperatures of 1470 and 1500 °C for dwell time of 1 h 30 min under hydrogen atmosphere. These sintered samples are mentioned as WHEAs (W-High Entropy Alloys). The evolution of phases, microstructures, and mechanical properties was investigated as a function of sintering temperature vis-á-vis those prepared by mixing of W and Fe, Ni, Co, Cr, Cu in the same proportion as in HEA (W-EleMental: WEM). The effect of hydrogen treatment (HyT) prior to the sintering of WHEAs on above mentioned characteristics was studied. Structural investigation of WEMs and WHEAs showed high intense W-peaks. Micrographs of these sintered samples showed typical liquid phase sintered microstructures having three distinct phases: bright W-phase, gray matrix phase, and black Cr-oxide phase. With the increase of sintering temperature and introduction of HyT step, the volume fraction of solid W-grain has been increased and W-content in the matrix of WHEAs is reduced. Upon sintering, WHEAs yield better densification, higher compressive strength, and higher bulk hardness. This increase of strength from WEMs to WHEAs was attributed to better densification of WHEAs compared to the former. The maximum values of compressive strength (1912 ± 14 MPa) and bulk hardness (479 ± 16 VHN) were achieved in the case of hydrogen treated W-HEA powder sintered at 1500 °C.

Improved cohesion strength of plasma-sprayed TiCN coating by adding Ni and post annealing

In this work, the TiCN(15Ni) coatings were plasma-sprayed using the mixed Ti-graphite aggregates and Ni powders, and their microstructure evolution and cohesion strength after annealing at 200 °C, 400 °C and 600 °C were studied. The TiCN coating was plasma-sprayed with a lamellar structure and its phase compositions were TiC0.7N0.3, TiC0.3N0.7, Ti2O, and residual graphite. For the TiCN–15Ni coating, besides the above phase compositions, metallic Ni phase was also detected. The addition of Ni could promote the reactions of Ti-graphite-N2 system and make the microstructure compact. After annealing, the microstructure became more compact by crack-healing, internal stress decrease, and elemental diffusion. The cohesion strength of the TiCN coating was enhanced after adding Ni and post annealing at 400 °C and 600 °C, which was mainly because of the compact microstructure, toughening effect of the metal Ni, crack-healing and the decreased internal stress.

Study on the Microstructure, Electrical and Mechanical Properties of Hot Pressing Cr-50 Mass% Ni Alloys Fabricated by Addition of Various Ratios of Nanosized Ni Powders

Study on the Microstructure, Electrical and Mechanical Properties of Hot Pressing Cr-50 Mass% Ni Alloys Fabricated by Addition of Various Ratios of Nanosized Ni Powders

In situ alloying of NiTi: Influence of laser powder bed fusion (LBPF) scanning strategy on chemical composition

NiTi alloys are widely used in different industrial and medical applications. Due to the inherent difficulty in the machining of these alloys, the use of Additive Manufacturing (AM) methods has become a popular method for their production. When working with NiTi alloys, there is a requirement on the precise control of their chemical composition, as this determines the phase transition temperatures which are responsible for their shape memory or superelastic behaviour. The high energies used in AM to melt the NiTi alloy leads to nickel evaporation, resulting in a chemical change between the batch powder and the additively manufactured part. Therefore, in AM techniques applied to different NiTi alloys, understanding the relationship between the melting strategy and nickel evaporation is crucial during the developing the desired chemical composition of the final-fabricated material. In this study, three NiTi alloys were fabricated using laser powder bed fusion (LPBF) starting from elementally blended Ni and Ti powders. Different melting strategies, including single and multiple melting, were studied in this work. Remelting improved the density and reduced cracking of the AM part. Microscopic observations, using a Scanning Electron Microscope (SEM) with a Backscattered Electron (BSE) detector, showed that the chemical homogeneity of the materials was enhanced by multiple remelting. Pure Ni and Ti were not found in any of the samples, proving that the applied melting strategies ensured good alloying of both powders. Regardless of the number of melting runs, X-ray diffraction (XRD) analysis showed the presence of NiTi (B2) and (B19′) phases, as well as NiTi2, Ni4Ti3 and Ni3Ti precipitates in all samples. The research demonstrated that, during the AM process, and depending on the melting strategy, 1.6–3.0 wt% of nickel evaporates from the material. It was demonstrated that the amount of evaporated nickel increased with the increasing number of melt cycles.

Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO3-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H3BO3. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H2O2 in the electrolytic bath is also proposed.

Study on the effect of different additives on improving the thermal conductivity of organic PCM

ABSTRACT Graphite (Grp) powder, nano-silicon (Si) powder, nano-copper (Cu) powder, nano-tungsten (Wu) powder, and nickel (Ni) powder were selected as the additives in this study. Meanwhile, stearic acid (SA), paraffin wax (P), and a P-SA mixture were added in 5%, 15%, 30%, and 50% proportions, to prepare 63 combinations of composite Phase Change Materials (PCM). The variation of thermal conductivity of the 63 sorts of composite PCM were studied experimentally. The aim of study was to understand the impact of the five additives on the thermal conductivity of the PCM. The results show that each of the additives can facilitate in the thermal conductivity of the PCM, and through 500 heating and cooling cycles, the fluctuation range is still less than 10%. Among the additives tested, graphite powder displayed the best performance. The addition of tungsten powder to the PCM resulted in poor fusibility, and the lowest increase in thermal conductivity.

Surface Alloying of Internal Surfaces of Low‐Carbon Steel Castings through Incorporation of Nickel, Nickel and Chromium, and 316L Stainless Steel Powders to Mold and Core Surfaces

A surface alloying technique is developed to enrich the internal surfaces of low‐carbon steel casting with nickel or nickel and chromium. This unique technique involves the incorporation of nickel (Ni), nickel and chromium (Ni + Cr), or stainless steel (SS) powders into a slurry, and then applying the slurry onto the surface of cores used in sand molds which comes in contact with molten metal during casting. Various properties, including coating thickness, composition, microstructural phases, surface hardness, and corrosion resistance of the surface‐alloyed layer, are studied. The internal surface of the substrate metal is enriched with nickel and chromium, up to 16.32 wt% Ni or 7.79 wt% Ni and 15.85 wt% Cr. Optical microscopy shows that the surface‐enriched layer is continuous over the entire surface of the casting and ranges in thickness from 229 to 1342 μm. When alloyed with Ni and SS powders, the surface‐alloyed layers demonstrate a dendritic solidification microstructure, suggesting complete dissolution of powders in steel followed by solidification. While the substrate primarily displays pearlitic and ferritic structures, simulation and X‐ray diffraction confirm the presence of austenite and ferrite in the surface‐alloyed layer when Ni + Cr is used. Microhardness testing and corrosion studies show significant improvement after surface alloying.

High temperature and room temperature tribological behaviors of in-situ carbides reinforced Ni-based composites by reactive sintering Ni and Ti2AlC precursor

The in-situ carbides reinforced Ni-based composites were fabricated by reactive hot-pressing sintering Ni and Ti2AlC powders. Tribological performance and mechanisms at room temperature and 800 °C were studied. Sintered composites contain Ni-based solid solution, Ni2TiAl, Ni3Al, TiCx, Ti3NiAl2C and Al2O3. At room temperature, the elastic modulus, hardness and H/E of composites enhanced due to the increase of carbides, resulting in wear rate declined with the rise of Ti2AlC. At 800 °C, because of the formation of reducing-friction and anti-wear oxide layers consisting of TiO2, NiO, Al2O3, NiTiO3, and NiAl2O4, wear rate was further decreased to 4.2 × 10−6 mm3/Nm. Composition differences on the surface between worn and static oxidized at 800 °C show that tribo-chemical reaction promotes the generation of NiO and NiTiO3.

Novel synthesis and magnetic properties of Ni@NiO nanoporous nanowires

We present a novel route to fabricate Ni@NiO nanoporous nanowires (NPNWs) through simple chemical dealloying of rapidly solidified Al–Al3Ni fibrous eutectic precursor in an alkaline solution. The dealloying inheritance effect and spontaneous oxidation of nanostructured Ni play vital roles in the formation of Ni@NiO core-shell (NiO shell on the Ni core) NPNWs. The length scale (nanowire diameter) of the Ni@NiO NPNWs could be regulated by facilely changing the rotating speed (cooling rate) during fabrication of the Al–Ni precursor. The Ni@NiO NPNWs exhibit unique magnetic properties, including lower saturation magnetization and enhanced coercivity relative to bulk Ni, commercial Ni powders (∼75 μm) and Ni nanoparticles (∼50 nm). Such exceptional magnetic properties could be rationalized in terms of the surface effect (the NiO shell), the core-shell structure and the shape anisotropy of nanowires. Moreover, this strategy can be generalized to fabricate other nanoporous nanowire materials as the introduction of traditional metallurgical solidification technique into the synthesis of advanced nanomaterials.

Synthesis and Characterization of FeNi-based Composite Powder from the Mixture of Fe-based Amorphous Powders and Crystalline Ni powders

Fe–Ni alloys have attracted interest as important magnetic alloys without rare-earth (RE) elements, which exhibit a wide variety of magnetic properties depending on the atomic ratios of Fe and Ni. Here, we attempted to synthesize Fe-Ni magnetic materials using a Fe based amorphous alloy precursor that is thermodynamically metastable and has more open atomic packing structure than crystalline alloys. High energy ball milling was applied to promote the formation of various Fe-Ni phases using mixtures of the amorphous precursor powder and 10-50% crystalline Ni powder. The as-milled composite powders as well as the composite powders annealed at 673 K were analyzed by X-ray diffractometer, differential scanning calorimeter, scanning electron microscope, and vibrating sample magnetometer to investigate their magnetic properties in terms of phase transformation behavior of the composite powders.

Effect of Ni Addition on the Corrosion Resistance of NiTi Alloy Coatings on AISI 316L Substrate Prepared by Laser Cladding

In this paper, an equiatomic NiTi (55NiTi) alloy powder was mixed with pure Ni powder to prepare laser cladding coatings on a 316L stainless steel substrate to study the effect of Ni addition on the microstructure and corrosion resistance of the coatings. The microstructure and phase composition of the coatings were analyzed using a scanning electron microscope (SEM) with configured energy-dispersive spectrometer (EDS) and X-ray diffractometer (XRD). OCP (open-circuit potential), PD (potentiodynamic polarization) and EIS (electrochemical impedance spectroscopy) experiments were conducted by a Gamry electrochemical workstation, and corresponding eroded morphologies were observed to evaluate the coating’s anti-corrosion performance. The addition of Ni led to fine and uniform dendrites and dense microstructure under the metallurgical microscope, which were beneficial for the formation of the passive film mainly consisting of titanium dioxide (TiO2). The results show that the pitting potential of the 55NiTi + 5Ni coating was 0.11 V nobler than that of the 55NiTi coating, and the corrosion current density was less than half that of the 55NiTi coating. The corrosion initiated preferentially at the interfaces of dendrites and inter-dendritic areas, then spread first to dendrites rather than in the inter-dendritic areas.

Porous Ni-Cr-Mo-Cu alloys fabricated by elemental powder reactive synthesis

Fabrication of porous Ni-Cr-Mo-Cu alloys is available through Ni, Cr, Mo and Cu elemental powder reactive synthesis at the sintering temperature of 1150 °C. The pore structures, including swelling behavior, open porosity, pore size and viscous permeability of the porous Ni-Cr-Mo-Cu alloys are systematically investigated. The results revealed that the parameters of pore structure firstly increased, and then decreased with the increase of the sintering temperature. When the sintering temperature rose to 1000 °C, the volume expansion, open porosity and viscous permeability of porous Ni-Cr-Mo-Cu alloys reached the peak value of 8.0%, 41.6% and 17.2 μm2, respectively. In addition, it was confirmed that the pore structure evolution was based on three stages, that is, in the low temperature section before stearic acid decomposition, the formation of pores was initiated by the volatilization of pore-forming agent and the interstitial pores of green compact; when the temperature was lower than 1083 °C, the increase of open porosity was mainly due to the Kirkendall effect caused by solid partial diffusion; while, when the temperature is within the range of 1083 ∼ 1150 °C, the shrinkage behavior at high temperature and a small amount of metal solution formed by the unreacted Cu led to decrease in pore structure parameters.

Features of the Sintering of Fe–Cu–Sn–Ni and Cu–Ti–Sn–Ni Powders during Hot Pressing

Features of the Sintering of Fe–Cu–Sn–Ni and Cu–Ti–Sn–Ni Powders during Hot Pressing

High-temperature stability of Ni-Sn intermetallic joints for power device packaging

In this study, the feasibility and high-temperature stability of Ni-Sn bonded joints fabricated by transient liquid phase sintering (TLPS) were investigated for high-temperature power electronics applications. A 30Ni-70Sn (wt%) TLPS paste was fabricated with micro-sized pure Ni and Sn powders, and chip bonding was performed on a direct bonded copper (DBC) substrate. During TLPS bonding, Sn particles melted and reacted with Ni particles, which resulting in the formation of stable Ni-Sn TLPS intermetallic joints. During aging treatments at 150 and 200 °C, the formed Ni3Sn4 phases were transformed into the Ni3Sn2. With increasing aging treatments, the reactions between Ni3Sn4 intermetallics and remaining Ni particles increased, which resulted in the formation of the Ni-rich Ni-Sn intermetallics. Even after 1000 h at an aging temperature of 200 °C, there is no significant difference in the stable and dense microstructure of Ni-Sn TLPS joints. In addition, their mechanical strengths did not vary significantly even after long-term treatment for 1000 h at 150 and 200 °C. This means that the Ni-Sn TLPS joints have a good long-term microstructural stability and mechanical reliability at high temperatures up to 200 °C. Therefore, we conclude that the Ni-Sn paste is a promising candidate as a die-attach material for high-temperature electronic assemblies.

Investigation of characteristics and properties of spark plasma sintered ultrafine WC-6.4Fe3.6Ni alloy as potential alternative WC-Co hard metals

The present study proposed the fabrication of a WC-6.4Fe-3.6Ni hard metal alloy using spark plasma sintering (SPS) as a potential alternative to the WC-Co hard metal. Fe-36%Ni powder (mean particle size 26.9 μm) was produced from Fe and Ni commercial powders via high energy milling and the effect was analyzed. WC-6.4Fe-3.6Ni (alternative grade) and WC-Co (reference grade) were obtained from ultrafine WC powder (particle size 0.45) with 10%wt binder. SPS sintering of WC-6.4Fe3.6Ni was performed at 1100, 1200 and 1300 °C with a holding time of 5 min achieving 99.8% higher densification at 1300 °C and WC-Co was sintered at 1200 °C. The results show that increasing the sintering temperature enhanced the microstructure and hardness with a decrease in fracture toughness. The wettability of milled Fe-Ni binder during heating in the SPS process contributes to enhance densification and properties. The decrease in fracture toughness is attributed to a decrease in the binder mean free path. The XRD analysis showed that η phase was not detected for either composite grades. Studies of sintering kinetics were applied to determine the sintering mechanisms involved in the final stage of sintering, which can be elucidated by calculating the slope exponent (n) from the relationship between the shrinkage rate and sintering time. Slope exponent consistent with WC diffusion in the liquid phase was found for WC-6.4Fe-3.6Ni sintered at 1300 °C. Good properties was found for WC-6.4Fe-3.6Ni sintered at 1300 °C, showing higher hardness ~1633 HV30 and fracture toughness ~11 MPa m0.5. WC-6.4Fe-3.6Ni sintered at 1200 °C has superior hardness (1786 HV30) than WC-Co (1689 HV30). A comparison of these properties with results from similar grades in the literature shows that the WC-6.4Fe-3.6Ni alternative grade has optimal properties and can be adopted as an alternative to WC-Co grades.

A study on the possibility to process dense 60NiTi from elementally blended Ni and Ti powders

This research aimed to process 60NiTi with a dense and homogeneous microstructure from a Ni–Ti powder mixture. It was noted that the optimum route, amongst the ones studied in this research, for obtaining parts having a homogeneous microstructure and the highest amount of relative density is as follows: The powder mixture being initially CIPed was sintered at 750 °C for a holding time of 8 h. To homogenize the microstructure and to obtain the required phases, a secondary sintering treatment was applied on samples cut from elementary sintered parts. After conducting this treatment at 1050 °C for 4 h, the formation of a homogeneous microstructure containing mainly NiTi, Ni3Ti and Ni3Ti2 phases was observed in the samples. However, the microstructures of these treated samples consisted of ∼34% porosity. Applying HIP treatments, under 180 MPa and for a holding time of 1 h, at different temperatures above the melting start temperature of the samples, treated by the secondary sintering procedure, successfully increased the density of parts. 1181 °C was the maximum temperature at which the parts could be treated without losing their dimensional integrity and parts with the highest relative density of ∼92% were obtained.

The Effect of Powder Composition on the Microstructure and Corrosion Resistance of Laser Cladding 60NiTi Alloy Coatings on SS 316L

Two kinds of 60NiTi powders were prepared by pure Ni mixed with Ti powders, and 55NiTi alloy powder with pure Ni powder and both the powders were fully mixed by alcohol ball milling. Two kinds of coatings (denoted as 60Ni-40Ti and 55NiTi-5Ni) were prepared on a 316L stainless steel substrate by laser cladding. The microstructure, microhardness and electrochemical behavior of the prepared coatings were investigated extensively. The results show that 55NiTi-5Ni has a typical dendritic eutectic structure, but 60Ni-40Ti tends to form a eutectic network structure. The main phases in both coatings are (Ni, Fe)Ti and (Ni, Fe)3Ti; however, the (Ni, Fe)Ti phase is dominant in 55NiTi-5Ni, but the (Ni, Fe)3Ti phase is more prevalent in 60Ni-40Ti. The microhardness was significantly improved with the 316L stainless steel substrate, and the microhardness of 55NiTi-5Ni is slightly higher than 60Ni-40Ti. The corrosion resistance of the two coatings in 3.5 wt% NaCl solution also leads to significant improvements compared with the substrate, and the corrosion resistance of 55NiTi-5Ni was also increased. These different behaviors and characteristics might be related to the different microstructures. Uniform and fine eutectic structure in 55NiTi-5Ni coating lead to better performance, which is also conducive to the formation of the dense oxide film to improve corrosion resistance.

Mechanically Alloyed CoCrFeNiMo0.85 High-Entropy Alloy for Corrosion Resistance Coatings.

High-entropy alloys could provide a solution for corrosion resistance due to their impressive properties. Solid-state processing of high purity Co, Cr, Fe, Ni and Mo metallic powders and consolidation resulted in a bulk material that was further machined into electro spark deposition electrodes. After the stainless steel substrate surface preparation, thin successive layers of the high-entropy alloy were deposited and Pull-Off testing was performed on the newly obtained coating, for a better understanding of the adhesion efficiency of this technique. Good adhesion of the coating to the substrate was proved by the test and no cracks or exfoliations were present. Corrosion resistance testing was performed in a liquid solution of 3.5 wt.% NaCl for 6 h at room temperature and the results obtained validated our hypothesis that CoCrFeNiMo0.85 high-entropy alloys could provide corrosion resistance when coating a stainless steel substrate.