Yuttanant Boonyongmaneerat

Co-electrodeposition of hard Ni-W/diamond nanocomposite coatings.

Electroplated hard chrome coating is widely used as a wear resistant coating to prolong the life of mechanical components. However, the electroplating process generates hexavalent chromium ion which is known carcinogen. Hence, there is a major effort throughout the electroplating industry to replace hard chrome coating. Composite coating has been identified as suitable materials for replacement of hard chrome coating, while deposition coating prepared using traditional co-deposition techniques have relatively low particles content, but the content of particles incorporated into a coating may fundamentally affect its properties. In the present work, Ni-W/diamond composite coatings were prepared by sediment co-electrodeposition from Ni-W plating bath, containing suspended diamond particles. This study indicates that higher diamond contents could be successfully co-deposited and uniformly distributed in the Ni-W alloy matrix. The maximum hardness of Ni-W/diamond composite coatings is found to be 2249 ± 23 Hv due to the highest diamond content of 64 wt.%. The hardness could be further enhanced up to 2647 ± 25 Hv with heat treatment at 873 K for 1 h in Ar gas, which is comparable to hard chrome coatings. Moreover, the addition of diamond particles could significantly enhance the wear resistance of the coatings.

Microstructural examination and mechanical properties of replicated aluminium composite foams

Open-cell aluminium foams can be produced with the structural replication of dimensional accuracy from polymeric foam patterns through a pressure infiltration casting process. The strength of open-cell foam is much less than that of the closed-cell counterpart, and thereby subjects to mainly functional applications. An improvement in mechanical properties of the foams can be implemented with the addition of ceramic particles. In the present study, the composite foams were produced using AC3A alloy added with varying contents of SiC particles. The resultant foams have ceramic particles embedded in the alloy matrix and on the strut surface. Higher volume fraction of ceramic particles resulted in an increase in the compressive strength, energy absorption and microhardness of the foams. The improvement of these properties is due to the modification of the microstructure of the foams and the increased strength in the node and struts at which the ceramic particles reside.

Effect of NiCl2-Based Fluxes on Interfacial Layer Formation of Hot Dip Galvanized Steels

While the thick growth of intermediate phase layers generally benefits the corrosion resistance of galvanized steels, it is unfavorable from the standpoints of mechanical integrity and economics. Thus, the influence of nickel chloride-based fluxes and the typical zinc-ammonium chloride flux on galvanized coating thickness as well as coating morphology and composition is examined. The investigation of pretreated hot dip galvanized steel specimens for various durations has verified that nickel chloride fluxes influence the growth rate of the zeta interlayer. This results in the overall reduction of the coating thickness by as much as two times compared to those prepared with the conventional flux. Nickel from the fluxes gradually diffuses away from the substrate s surface, and hence the initial concentration of the nickel salts along with the hot dip duration needs to be controlled appropriately for effective use of nickel chloride-based fluxes in the galvanizing process.

Recent Developments in Ni-Mn-Ga Foam Research

Grain boundaries hinder twin boundary motion in magnetic shape-memory alloys and suppress magnetic-field-induced deformation in randomly textured polycrystalline material. The quest for high-quality single crystals and the associated costs are a major barrier for the commercialization of magnetic shape-memory alloys. Adding porosity to polycrystalline magnetic-shape memory alloys presents solutions for (i) the elimination of grain boundaries via the separation of neighboring grains by pores, and (ii) the reduction of production cost via replacing the directional solidification crystal growth process by conventional casting. Ni-Mn-Ga foams were produced with varying pore architecture and pore fractions. Thermo-magnetic training procedures were applied to improve magnetic-field-induced strain. The cyclic strain was measured in-situ while the sample was heated and cooled through the martensitic transformation. The magnetic field-induced strain amounts to several percent in the martensite phase, decreases continuously during the transformation upon heating, and vanishes in the austenite phase. Upon cooling, cyclic strain appears below the martensite start temperature and reaches a value larger than the initial strain in the martensite phase, thereby confirming a training effect. For Ni-Mn-Ga single crystals, external constraints imposed by gripping the crystal limit lifetime and/or magnetic-field-induced deformation. These constraints are relaxed for foams.

Corrosion Behavior of Reverse-Pulse Electrodeposited Zn-Ni Alloys in Saline Environment

The study investigates the relationship of the reverse-pulse electrodeposited zinc-nickel alloy coatings’ characteristics and their corrosion behaviors in a saline environment, using both anodic polarization and electrochemical impedance analysis. The introduction of anodic pulsation gives deposits of more refined grain sizes and increased nickel contents, resulting in improvement of the corrosion resistance. High anodic current densities employed in the reverse-pulse electrodeposition, however, modulate crystallographic orientations of the grains, introduce porosity to the structure, and hence adversely affect the corrosion resistance of the coating deposits.

TiO2 sol-embedded in electroless Ni–P coating: a novel approach for an ultra-sensitive sorbitol sensor

A Ni–P–TiO2 coating was readily prepared by direct incorporation of nano-TiO2 sol into a Ni–P solution followed by electroless deposition. This coating was applied as a working electrode in an electrochemical sensor for the first time. The morphologies of the TiO2 sol and the coated surface were well characterized by TEM, SEM and AFM. The high hydrophilicity of this surface was verified by contact angles of 40.7/41.8. Here, the appropriate amount of TiO2 within the nanocomposite was optimized (2 g L−1) prior to applying as an electrode. Interestingly, the electrocatalytic activity of the coating towards the oxidation of alcoholic compounds was investigated by linear sweep voltammetry. Apparently, incorporation of TiO2 into the composites substantially improved the electrocatalytic activity of Ni–P and 2 layers of Ni–P/Ni–P–TiO2 coating provided the highest sensitivity for all analytes, especially for sorbitol. A low LOD value of 1.0 nM and a wide linear range of 2.0 nM to 0.2 mM were achieved for sorbitol. Furthermore, a high stability and high reproducibility (2.96% RSD) for this system were obtained. Owing to ultra-high sensitivity, wide linearity, high stability, easy preparation and low cost, it might be a promising tool for early diagnosis of diabetes via sorbitol detection.

Injection Moulding of Tungsten Carbide-Nickel Powders Prepared by Electroless Deposition

Tungsten carbide with nickel (WC-Ni) is generally used in applications in which high wear and corrosion resistance are required. In most cases, WC is mixed with Ni powder through a powder-processing route. In the present study, an electroless deposition technique was employed in order to prepare Ni coated WC particles prior to forming specimens by powder injection moulding method. The starting WC powders were subjected to surface activation followed by electroless Ni coating. The effects of a variety of processing parameters, including coating time and powder to electrolyte content ratio, were examined. The characteristics of the prepared powders were assessed by scanning electron microscopy and laser particle size analysis. It has been found that the fabrication of WC powder coated with Ni can be achieved through the electroless deposition technique. The amount of Ni introduced to the WC particles can be controlled by the powder to electrolyte content ratio and the deposition duration. The use of small particle loadings can ensure relatively large deposition and uniformity of the coatings. It is widely known that powder injection moulding (PIM) is an effective process for fabrication of small and complex shaped components of high performance materials. The PIM process includes 4 main steps: feedstock preparation, injection moulding, debinding and sintering. In this work, the WC-Ni powders were mixed with polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) binder to form feedstock for injection moulding. The injection moulding process was carried out by a laboratory scaled, plunger-type machine. The mouldings were subjected to debinding and sintering. It was found that the PEG could be removed by water leaching. Specimens retained their shapes during and after leaching of the PEG. The remaining binder could be removed through pyrolysis. The mouldings were sintered under vacuum at 1400 °C for 1 hour. The sintered density achieved was at 88% of the theoretical value due to the low powder loading employed in the study.

Effects of Heat Treatment on the Interfacial Structure of Nickel-Aluminum Coating Composites

Nickel(Ni) layer was applied to the surface of pure aluminum(Al) by electrodeposition for 15 minutes using a direct current (DC) condition at 0.13 Acm-2. Heat treatment was employed subsequently for 1, 2.25 and 4 hours at the temperatures of 600 and 650oC, which are below and above the eutectic temperature of Al-NiAl3, respectively. All samples were characterized by OM, SEM, EDS and GIXD. DTA was also performed to study heat release in the reactions. After heat treatment at 600oC, the specimens exhibit the non-uniform formation of Ni2Al3 and NiAl3, even after 4 hours of heat treatment where local melting possibly occurs due to the exothermic heat of formation. In contrast, owing to fast interdiffusion of Al and Ni as assisted by a liquid phase formation, multi-layer of Ni2Al3 and NiAl3 was uniformly formed along the interface of the specimens heat treated at 650oC.

Effects of Current Pulsation on Magnetic Properties and Giant Magnetoimpedance of Electrodeposited NiFe Coatings on Cu Wires

This work presents a systematic study of the effects of current pulsation on soft magnetic properties and giant magnetoimpedance (GMI) of nickel-iron (NiFe) coatings electrodeposited on copper wires. The specimens were prepared by the electrodeposition technique with controlled bath compositions and varied applied current waveforms. The microstructural and chemical investigations indicate that current pulsation with 50% duty cycle and 50 Hz frequency provides significantly smoother coating surface of uniform nodules, with comparable Fe content but different phase composition, as compared to the direct current condition. The vibrating sample magnetometer evidently shows that the deposits prepared with a pulsed current exhibit relatively small coercivity, below 4 Oe. Using the four-point probe technique, the MI ratio of the pulse deposits is found to reach a significantly high value above 2,000% with decent sensitivity. The benefits of current pulsation in improving the characteristics of NiFe deposits, and correspondingly the alloys’ soft magnetic properties and MI effects are demonstrated.

Factors Affecting on the Corrosion Resistance of Electroless Ni-Zn-P Coated Steel

Electroless Ni-Zn-P coating with the optimal content of Ni and Zn in the alloy provides high corrosion resistance for steel. Ni-rich phase of this high hardness Ni-Zn-P alloy offers barrier protection property and sacrificial protection property is obtained from the alloy with proper content of Zn. In this work, the Ni-Zn-P coatings were prepared on steel substrates by using alkaline electroless deposition. The parameters of deposition process including complexing agent concentration, bath pH, zinc ion and nickel ion concentration were systematically studied. The microstructural morphology and elemental composition of the coatings were characterized by scanning electron microscopy. It was found that complexing agent, zinc ion and nickel ion concentrations play important role on Zn content of Ni-Zn-P alloy whereas alkalinity of the solution bath directly affects the deposition rate. The results of corrosion resistance investigated by linear polarization illustrate that the corrosion potential (Ecorr) of Ni-Zn-P coatings is negatively shifted by an increase of Zn content in the alloys. From this work, Ecorr of 83%Ni-11%Zn-6%P coating prepared in this system is slightly lower than steel. To achieve a higher effect of sacrificial protection for corrosion protection of steel, Ni-Zn-P with higher content of Zn should be further studied.