Ni-coated Powders Research Articles

Enhanced densification of copper during laser powder bed fusion through powder surface alloying

In this study, a novel approach of powder surface alloying is proposed to address the issue of insufficient densification of printed copper (Cu) from high laser-absorbing Ni coated Cu powder through laser powder bed fusion. Three types of powder consisting of original Ni-coated powder (surface adhesion), partially Ni-diffused powder (partial surface alloying) and surface Ni-alloyed powder (complete surface alloying) were adopted to validate the effectiveness of the approach. All these powders significantly decreased the high laser reflectivity of Cu powder. The surface Ni-alloyed powder successfully melted the Cu powder to eliminate the lack-of-fusion pores in the printed Cu samples such that best dimensional accuracy and highest relative density of up to 99.6% was obtained. The interface condition between outer Ni coating and Cu powder played an important role in the densification process. The solid solution Ni in the surface Ni-alloyed powder maximized the contact area, reduced the thermal resistance and enhanced heat transfer efficiency, which eventually promoted the melting of Cu powder and eliminated the lack-of-fusion pores. Ni content is also revealed as an important factor in balancing electrical conductivity and mechanical properties. The optimal Ni content has been determined as 0.4 wt% for powder with surface Ni-alloyed.

Ni-loss compensation and thermomechanical property recovery of 3D printed NiTi alloys by pre-coating Ni on NiTi powder

The approach of pre-coating Ni on NiTi powder was adopted as an effective route to address the thermomechanical property degradation of NiTi alloy caused by Ni-loss during the printing process of laser powder bed fusion. The electroless plating process of Ni on NiTi powder was initiated with the removal of the outermost TiO 2 layer by alkaline solution and the exposure of Ni catalytic nucleation site. The newly exposed Ni was an active catalyst for coating Ni and eventually triggered the deposition of Ni on NiTi powder via self-catalytic reaction. The intrinsic homogeneity of Ni, as a major alloying element in NiTi powder, ensured high uniformity of Ni-coating on the surface of the powder and good sphericity, necessary for good printability. Furthermore, Ni-coating increased laser absorbability, and a higher content of Ni compared to the theoretical value was thereby required to compensate for the Ni-loss. Simultaneously, densification was enhanced even at lower laser energy density on using Ni-coated powder. During the printing process, ultrafine Ni-coating was rapidly homogenized such that the thermomechanical property was completely recovered. As a consequence, it is underscored that Ni-loss can be addressed by compensating Ni on the original powder prior to the printing process, providing a new pathway toward printing of high-performance shape memory alloys.

High temperature oxidation behavior of micro/nanostructured WC-Co coatings deposited from Ni-coated powders using high velocity oxygen fuel spraying

Abstract High temperature oxidation of WC-based cermet coatings deposited from electroless Ni-coated micro- and nanostructured WC-Co powders (Ni/mc-WC and Ni/nc-WC) was studied. High velocity oxygen fuel (HVOF) spraying was employed for coating deposition, and thermo-gravimetry analysis (TGA) was carried out to examine the oxidation kinetics at 600–800 °C. For comparison, the same experiments were performed on conventional micro/nanostructured WC-Co coatings (mc-WC and nc-WC). Oxidation resistance of Ni/mc-WC and Ni/nc-WC coatings at 800 °C was improved by 88.5% and 89.3% compared to mc-WC and nc-WC coatings, respectively. Linear kinetics with activation energies of 90.4 and 78.9 kJ/mol were obtained for mc-WC and nc-WC, respectively, while oxidation kinetics of Ni/mc-WC and Ni/nc-WC coatings obeyed the parabolic law with greater activation energies of 212 and 197.5 kJ/mol.

Synthesis and characterization of Ni–P coated hexagonal boron nitride by electroless nickel deposition

Electroless plating has been receiving a steady progress over the last decade on the modification of the surface properties of ceramic materials in order to produce composite coatings with unique characteristics for critical tribological systems. In this work, an electroless nickel deposition process was used to deposit nickel-phosphorous (Ni–P) coating on hexagonal boron nitride (h-BN) particles via hypophosphitereduced acid bath solution. The substrate particles were initially subjected to series of pre-treatment operation in order to ensure that the particles are cleaned and catalytically active prior to electroless plating. The characterization of the as-received and Ni-coated powder was studied through scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and field emission scanning electron microscopy (FESEM). The result reveals that the pretreatment of h-BN powder provides substrate particle surfaces with coarse and roughened structures which are normally considered suitable for Ni–P deposition. Moreover, the result of the EDX analysis confirms the existence of nucleating agents and Ni–P coating on the surface of the treated h-BN powder. The cross-sectional microstructure of the coated powder shows that the h-BN particles were embedded in a continuous matrix layer of Ni–P deposit. The EDX mapping profiles further indicate that the deposited Ni–P alloy mass was uniformly distributed on the surface of the Ni–P codeposited h-BN particles (Ni–P–h-BN). The successful development of Ni coated h-BN powder will raise the potential of h-BN as a high-performance coating material.

Preparation of nickel-coated titanium carbide particulates and their use in the production of reinforced iron matrix composites

Ni-coated titanium carbide (TiC) composite powders were prepared by electroless plating (EP). Further, using hot isostatic pressing (HIP), iron matrix composites reinforced with 4wt% Ni-coated TiC particulates with relative density close to 100% were prepared. The microstructure and phase composition of the Ni-coated powders and the composites were analyzed using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The results showed that the TiC particles were distributed uniformly in the matrix and were free of segregation or coarsening. Compared to the TiC particles without Ni coating, the reinforced iron-based composites containing the Ni-coated particles showed higher relative densities and better mechanical properties. The density, hardness, tensile strength, and elongation were enhanced to 99.98%, 243HV, 565MPa, and 11.7%, respectively in composites containing Ni-coated TiC particles from 99.70%, 210HV, 514MPa, and 10.3%, respectively in composites that were prepared using particles without Ni coating. In addition, the mass losses in the composites containing the Ni-coated particles were reduced by 32–75% in the abrasive wear test with various vertical loads. We propose that the nickel coatings on the particulates had a beneficial effect on the microstructure and properties of the reinforced iron-based composites is due to promotion of neck formation and growth between TiC and iron powders during sintering, which enhanced the density of the sintered compact and the bonding strength between the TiC particles and the iron matrix.

B4C/Ni Composite Coatings Prepared by Cold Spray of Blended or CVD-Coated Powders

In this work, the microstructures of B4C/Ni coatings by cold spray with blends or chemical vapor deposited (CVD) Ni-coated powders were investigated and compared. Powder blends with Ni powder and fine or coarse B4C powders were prepared for various B4C content ranging from 54 to 87 vol.% (equal to 25-65 wt.%). Three CVD Ni-coated B4C powder batches were also synthesized with various B4C content using the fine B4C as core particles. Ni-coated powders and both types of cold sprayed coating microstructures with blends or coated powders were investigated by optical and scanning electron microscopy. Further quantitative image analysis was carried out on scanning electron microscopy (SEM) images to measure the B4C content within the coating regarding the influence of the nominal content in the feedstock for each coating type. Both types exhibited fine fragments and unfragmented B4C, but coatings with CVD-coated powders had many more unfragmented particles. Moreover, the higher levels for both B4C (44.0 ± 4.1 vol.%) and coating microhardness (429 ± 41 HV0.5) were obtained in case of the CVD-coated powders. However, it was assessed that the highest microhardness was not obtained for the highest B4C content. This questionable result is discussed with regard to the fully original composite microstructure obtained from CVD Ni-coated B4C powder.

Surface modification of spherical NdFeB magnetic powders by a fluid-bed nickel electrodeposition

The spherical NdFeB magnetic powders were coated with Ni using a fluid-bed electrodeposition device. The oxidations of rich Nd phase or Fe phase were restrained after Ni coating. After annealing at 300 °C for 30 min, the magnetic properties of both coated and uncoated magnets were decreased. However, the Ni-coated powders showed better magnetic properties than the uncoated powders after the annealing. The compressive strength of bonded magnets improved after annealing due to enhancement of the adhesion between the adhesive and the surface of the magnetic powders.

Preparation and microwave absorption properties of nanosized Ni/SrFe12O19 magnetic powder

A new type of Ni-coated strontium ferrite powder was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The morphology, crystal structure and microwave absorption properties of the Ni-coated powder were investigated with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), EDS and vector network analyzer. The results show that the powder possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −41.3 dB. The bandwidth with the loss above −10 dB reaches 8 GHz.

Preparation of nickel-coated powders as precursors to reinforce MMCs

The preparation of nickel-coated ceramic particles as precursors for MMC fabrication was studied. Al2O3 and SiC powders of three different particle sizes were successfully coated with Ni using an electroless metal plating technique. Uniform and continuous nickel films were deposited on both, alumina and silicon carbide powders, with a final composition ranging from 1.6 to 1.9wt% phosphorus, 18–21wt% of metallic nickel and the balance is ceramic. XRD showed that the Ni-P deposit was predominantly amorphous. However, after heat treatment, the metallic deposits crystallize into Ni and Ni3P phases, as confirmed by DSC analyses. Preliminary results showed that the use of Ni-coated powders enhances the wettability between the matrix and ceramic phase when processing particulate MMCs by infiltration techniques. The coating promoted easy metal flow through the preform, compared to the non-infiltration behavior of the uncoated counterpart samples.