Nutthita Chuankrerkkul

Application of PEG/PMMA Binder for Powder Injection Moulding of Hardmetals

Powder injection moulding (PIM) is a cost effective powder metallurgical process for the fabrication of small, complex-shaped components for high performance applications. A binder system, which comprises a major fraction of polyethylene glycol (PEG) and a minor fraction of a very finely dispersed polymethyl methacrylate (PMMA), has been applied for tungsten carbide (WC) – cobalt (Co) hardmetal powders. PEG can be removed rapidly by water leaching and PMMA is removed by subsequent pyrolysis when the components are ramped up to the sintering temperature. In this work, the development of feedstock formulations and of the processing parameters for a successful injection moulding and to achieve high density has been investigated. The present study has demonstrated that the binder can be employed for the production of WC-Co hardmetal components by PIM process. The maximum density achieved thus far is 97% of the theoretical value.

Characterisation of NiO-YSZ Porous Anode-Support for Solid Oxide Fuel Cells Fabricated by Ceramic Injection Moulding

Ceramic injection moulding (CIM) has advantages for a cost effective fabrication of large-scale, near-net-shape products. In this work, CIM is carried out to prepare porous anode-support for solid oxide fuel cells (SOFC) applications. The CIM process started with a preparation of feedstocks by mixing powder with binder. The feedstock is then injected into the mould of desired shapes. The mouldings were subsequently undergo the removal of the binder (debinding) and, finally, sintering. It is shown that porous nickel oxide-yttria stabilized zirconia (NiO-YSZ) anode-support for SOFC were successfully prepared by CIM technique. In addition, a water-soluble based binder system, consisted mainly of polyethylene glycol (PEG), has been used in this work. This is to avoid the use of organic solvents when wax-based binder was used. Therefore, it can promote more environmentally friendly process. The removal of binder was carried out using water debinding technique. The porous anode for SOFC was subjected to systematic characterisation. The effect of processing parameters, such as powder characteristics and powder/binder ratio has been investigated. Rate of binder removal was also studied. The porous anode specimens were characterised for their properties and microstructure. It was also found that the porosity of the specimens can be controlled by adjusting the sintering temperatures and holding times.

Powder Injection Moulding of Alumina Using PEG/PVB Binder Systems

Powder injection moulding (PIM) is a process that is suitable for a fabrication of small and complex shape components. It consists of 4 main steps: feedstock preparation by mixing powder and binder, injection moulding of the prepared feedstock into the desired mould, removal of the binder and finally sintering to obtain materials with specific properties. In this study, powder injection moulding of alumina (Al2O3), using polyethylene glycol (PEG) based binder systems, was investigated. PEG is soluble in water; therefore, the use of organic solvents required for debinding of wax-based binder system can be avoided. PEG with a molecular weight of either 1500 or 4000 was used as a major constituent together with polyvinyl butyral (PVB) as a minor component. Stearic acid was also added during feedstock preparation to act as a lubricant. After mixing the powder with the binder, a variety of Al2O3 feedstocks were injected into the moulds. The mouldings were prepared by a laboratory-scaled plunger-typed machine. Debinding was carried out using a combination of solvent extraction and thermal debinding. Water leaching tests were performed at 30 and 50 °C to study PEGs removal rate. The pyrolysis of PVB was completed during ramping up of the mouldings to the sintering temperature. The mouldings were subjected to sintering at 1500 °C in air. It was found from the study that PEG/PVB binder systems can be used for the preparation of alumina powder injection moulding feedstocks. Specimens retained their shapes during and after leaching of the PEGs.

Effect of Co Addition to Heat- Treated P/M 316L Stainless Steel on α′-Martensite Formation and Mechanical Properties

Abstract The effect of various Co additions to P/M 316L stainless steel on α ’-martensite formation and mechanical properties (bending strength and hardness) were investigated. Powder mixtures were compacted using a single action press at 498 MPa and sintered at 1,300°C for 30 min under hydrogen atmosphere, followed by heat-treating in air at 800°C and 900°C for 25 h, 50 h, 75 h, and 100 h, respectively. It is found that oxide formation in closed pores at high temperatures can induce the α ’-martensite formation and reduce the area fraction of porosities, resulting in higher hardness of the heat-treated specimens than that of the sintered specimens. The Co additions can also reduce the amount of α ’-martensite. Long-term heating results in a slight decrease of bending strength due to high connected oxide formation in the internal pores.

Fabrication of Injection Moulded 304L Stainless Steels Reinforced with Tungsten Carbide Particles

Powder injection moulding of 304L stainless steel - tungsten carbide (WC) composites were carried out in the present work. Two different WC particle i.e. WC having average size of 4.8 µm and 1.6 µm were used. Feedstock of powder loading up to 55 vol% were successfully prepared using binder composed mainly of polyethylene glycol (PEG) and a minor constituent of polymethylmethacrylate (PMMA). The mouldings were leached in water at temperatures of 40 °C and 60 °C from 30 minutes to 24 hours in order to study the effect of leaching conditions on the removal of the PEG. The remaining binder, PMMA, provided strength to the mouldings after leaching of the PEG and it could be removed by pyrolysis during ramping up to the sintering temperature. Specimens were sintered under hydrogen atmosphere at 1250 °C for 1 hour. Sintered components were subjected to testing and characterisation. Scanning electron microscope was used to observe microstructure of specimens after moulding, leaching and sintering. It was found that the hardness of the sintered specimens increased with either increasing the amount of the powder loading in the feedstock or reducing the average size of WC in the powder mixture. In addition, the water leaching of the PEG linearly correlates with the natural log of time and the equation predicts that PEG will be removed completely in 11.24 ± 1.31 hours which corresponds with the experiment result that PEG completely removed in 12 hours.

Process Optimization and Characterization of YSZ Thin Film Electrolyte on Anode Substrate Prepared by Electrophoretic Deposition Technique

Thin film electrolyte made of 8-mol% yttria stabilized zirconia (8YSZ) was fabricated on porous NiO-8YSZ anode substrates using electrophoretic deposition (EPD). The porous NiO-8YSZ anode substrates were prepared by powder injection molding technique. The electrolyte suspensions containing 8YSZ nanoparticles and polyethylene glycol (PEG) as a dispersant (1-19 wt%) were formed in ethanol. The maximum zeta potential value was obtained from the 8YSZ suspension with 5 wt% PEG considered as an optimal content of PEG dispersant. The electrophoretic deposition of 8YSZ film was performed on the porous anode substrate using a constant voltage of 30 V for 150 sec prior to co-sintering at different temperatures in order to obtain dense 8YSZ electrolyte film on the porous anode substrate. Co-sintering at 1250°C for 1 h resulted in a formation of a dense 8YSZ thin-film electrolyte with a thickness of 6.35 mm. An open circuit voltage at 800°C of a single cell having 8YSZ thin-film electrolyte on porous NiO-8YSZ anode substrate was 1.09 V, indicating a gas-tightness of 8YSZ thin-film electrolyte fabricated by using EPD.

Effects of Ni and Ni + Co Additions in P/M Stainless Steel 316L on Sigma Phase and Oxide Formations after Long Term Heating

The effects of various Nickel and Nickel with Cobalt additions in P/M 316L stainless steel on sigma phase and oxide formations were investigated. Various powder mixtures of P/M316L with Ni and both Ni + Co powders as 1, 2, 3 and 4% by wt.%, were compacted using single action press under 498 MPa and sintered at 1300 °C for 30 minutes in hydrogen atmosphere. Then specimens were exposed at temperature of 800 °C and 900 °C for 25, 50, 75 and 100 hours in order to investigate the microstructural stability. It was found that specimens with both Co and Ni additions could reduce amount of sigma phase formation especially at heating of 900 °C. After all heat treatments, oxide scales had grown in closed pores during heating, therefore, the amount and size of internal porosity were decreased. It was also observed that the amount and size of porosity of heated specimens still have the same tendency as sintered specimens. The oxide scale in the matrix is mainly composed of Fe3O4 and Cr2O3 in the closed pores.

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.

Characterization of Feedstocks for Injection Molded SiCp-Reinforced Al-4.5 wt.%Cu Composite

Characterization of feedstocks for powder injection molding of SiCp-reinforced aluminium composite, as potential use for automotive and light-weight applications, has been studied in this research. Al-4.5 wt.% Cu powder, SiCp and polymeric binder were pre-mixed and compounded using a twin screw extruder at 170oC prior to powder injection molding at 170 oC. Effects of varied solid loadings at 52, 55 and 58% on green properties of the feedstocks have been investigated. Experimental results showed that compounding followed by powder injection molding allowed uniform distribution of SiCp surrounding the aluminium powder. It was found that higher solid loading improved bulk density while hardness values were observed to be similar. Molded specimens of 55% solid loading provided the optimum bend strength and strain at failure. Moreover, it was observed that the opposing abrasive property with angular shape of SiCp resulted in SiCp scratching effect, leading to irregular surface of aluminium powder after injection molding. This consequence and molding porosity were expected to be responsible for relatively low density of the molded specimens, giving the difficulty in molding at higher solid loading.

Feasibility Study of Using Basalt Fibers as the Reinforcement Phase in Fiber-Cement Products

The aim of this work was to study the feasibility of using basalt fibers as the reinforcement phase in fiber-cement products which was the fiber-reinforced construction materials used for roof, wall, ceiling, and floor applications. The feasibility study included (1) the alkaline resistant test of the basalt fibers by soaking the basalt fibers in 1 N Ca(OH)2 up to 28 days, and (2) the mechanical test based on ASTM C1185 standard on the fiber-cement board that used basalt fibers as a reinforcement phase. Scanning electron microscope (SEM) and x-ray diffractometer (XRD) were used to characterize the basalt fibers after alkaline resistant test. The basalt-fiber reinforced cement board was produced on the industrial level by using Hatschek process.From the alkaline resistant test, basalt fibers had well alkaline resistant. From the mechanical test, the modulus of rupture (MOR) of basalt-fiber reinforced cement boards passed the requirement of TIS 1427-2540 and ASTM C1186 standard. Therefore, basalt fibers could be considered as a good candidate for using as a reinforcement phase in the fiber-cement products.