Papers by Author: Nutthita Chuankrerkkul

Abstract: This research investigated metal injection moulding of dental pins for orthodontics application. 316L stainless steel powder was selected as an alternative low-cost material in comparison to the more expensive titanium alloy counterpart. The feedstock was prepared at 60% solid loading using an environmentally friendly multi-component binder. Injection moulding was operated using a four-cavity mould. The effects of moulding temperature of 250-280 °C measured at the barrel on mouldability, and specimen properties were studied. After debinding, specimens were sintered at 1250 °C for 2 hours in a hydrogen atmosphere. Experimental results indicated that injection at moulding lower temperature of 250-260 °C gave better mouldability, providing less specimen distortion and demoulding difficulty. The green density was 5.49 g/cm³, giving 93.41% theoretical density. Injection at lower temperature of 250-260 °C also provided higher sintered density and slightly lower volume shrinkage. Sintered microstructure experienced densification with small degree of isolated porosity in specimen center, however with interconnected porosity along specimen edges, responsible for 6.87 g/cm³ sintered density (86.01% theoretical density).

Abstract: Metal matrix composite has been increasingly appreciated by many engineering applications due it its tailored properties for specific uses. Powder injection moulding is one of the most effective composite processing essentially for small and complex parts. Moulding of feedstock is the key step determining green and sintered properties. This research investigated effects of moulding parameters which are % solid loading and moulding speed on microstructure and properties of aluminium composite. Commercial aluminium alloy powder and SiC particulate at 15 vol.% addition were formulated at 55 % and 60 % solid loading. Injection moulding were operated using a horizontal screw driven typed machine at 1600-1800 rpm speed and 280 - 300 °C moulding temperature. After sintering at 655 °C, property assessment via microstructure, density, % shrinkage, distortion and hardness were carried out. It was found that feedstock of 55 % solid loading occasionally led to flash problem while that of higher solid loading experienced higher viscosity to fulfill four-cavity mould. Moulding speed investigated did not significantly affect mould filling and overall properties. Sintered microstructures generally showed well-distributed SiC particulate in the aluminium matrix. The optimum injection moulding condition was the feedstock prepared at 60% solid loading, moulding at 1800 rpm speed, which offered theoretical density of greater than 98.5 % and micro Vickers hardness of 125.2 H_v.

Abstract: 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.

Abstract: This research investigated mechanical degradation of powder injection moulded SiC_p-reinforced aluminium composite subjected to moderate temperature exposures. Aluminium composite of 20 vol.% SiC_p reinforcement was produced by powder injection moulding and sintering at 680°C, followed by 500°C solution treatment plus 150°C for 6 hours artificial aging, and subsequent exposures at 100, 200 and 300°C for 10 and 100 hours. It was found that short-term exposure for 10 hours provided increasing hardness with increasing exposure temperature, while long-term exposure for 100 hours led to an opposite result. The maximum micro Vickers hardness was obtained at 182.2 H_v for Al-SiC_p composite exposed at 300°C for 10 hours. Tensile strength was however found deleterious with increasing both exposure temperature and time. The maximum tensile strength was achieved at 191.2 MPa for Al-SiC_p composite exposed at 100°C for 100 hours. The formations of AlN, Mg₂Si and Al₂Cu were observed in both age-hardened and as-exposed conditions. Furthermore, the highest temperature exposure at 300°C and extended exposure time at 100 hours resulted in the lowest hardness and tensile properties due possibly to the loss of coherency of precipitates. SiC_p clusters were the main cause of the tensile failure.

Abstract: 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.

Abstract: 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.

Abstract: The aim of this work is to propose the application of statistical methods (linear regression and statistical hypothesis test) to analyze the effect of parameters used in powder injection molding including sintering temperature and the feedstock composition on the flexural strength, the porosity and the density of the sintered specimens of mullite prepared by powder injection molding (PIM) and using the composite binder consisting of 80 wt% polyethylene glycol (PEG) and 20 wt% polyvinyl butyral (PVB) for molding. The lab-scale plunger type PIM machine was used to prepare the specimens. The feedstock compositions were 50 to 54 vol% mullite, and the sintering temperatures were 1300 and 1400 °C. At level of significance 0.05 for statistical analysis, feedstock composition did not affect flexural strength, porosity, and density of the sintered specimens. For sintering temperature, the specimens sintered at 1400 °C have the greater density and the lower porosity. However, the flexural strength of the specimens sintered at 1300 °C and 1400 °C are statistically similar.

Abstract: The purpose of this work is to use the statistical methods including linear regression and statistical hypothesis test to study the dissolution behavior of polyethylene glycol (PEG), a water-soluble binder, during debinding step of the green specimens of mullite formed by powder injection molding (PIM). Two systems of composite binders were investigated including (A) 80 wt% polyethylene glycol (PEG) and 20 wt% polyvinyl butyral (PVB) and (B) 78 wt% PEG, 20 wt% PVB, and 2 wt% steric acid (SA)The lab-scale plunger type PIM machine was used to prepare the green specimens consisting of mullite powder and the composite binder. The possible solid loadings of the green specimens that could be prepared by this machine were 50, 52, and 54 vol% mullite (50, 48, and 46 vol% binder). The debinding was done by soaking the green specimens in the warm water at 40 or 60 oC to remove PEG. At level of significance 0.05 for statistical analysis, the dissolution behavior of PEG can be fitted with Avarami equation. In addition, from the Avarami equation obtained from each experimental condition, the dissolution rate of PEG was independent of the parameters used in this study including solid loading in the green specimens, water temperatures for debinding, and composite binder systems.

Abstract: Zirconia toughened alumina (ZTA) ceramic has been fabricated by the powder injection moulding process. The ZTA ceramic, composed of 80 wt% alumina and 20 wt% zirconia, was mixed with a water-soluble, multi-component binder system. The binder ingredients were polyethylene glycol (PEG), polyvinyl butyral (PVB) and stearic acid (SA). Powder injection moulding was performed with powder loadings in the range of 48-52 vol%, using a laboratory-scale injection moulding machine. Water leaching was used for partial binder removal prior to thermal debinding and then sintering at 1650 °C for 2 hours. Microstructural examination of the ZTA ceramic revealed that zirconia inhibited alumina grain growth and, therefore, improved the mechanical and physical properties of the specimens. It was found that powder loading had an influence on density, hardness and strength of the specimens. A flexural strength of 334 MPa and hardness value of 2093 kg/mm² was obtained from specimens injection moulded with 52 vol% powder loading feedstock. The highest sintered density achieved was 97% of the theoretical value.

Abstract: This work focuses on the debinding conditions of the ceramic materials fabricated by powder injection moulding. Ceramic powder materials, including alumina and alumina-based composites were prepared as feedstocks and mixed with water-soluble polyethylene glycol (PEG) and polyvinyl butyral (PVB). The PEG/PVB binder mixture, with PEG to PVB ratio of 85:15 by weight and powder loading of 44 vol%, were thoroughly mixed and injected into the mould at the temperature of 190 °C to obtain rod-like specimens. Prior to sintering, the as-injected specimen was then leached in water, the temperature of which was varying from 30 (ambient temperature), 45 to 60 °C, in order to get rid of PEG and leave the specimens in shape by PVB. The rate of PEG removal according to different water temperatures was investigated. The experimental results suggested that PEG could completely be eliminated by 45 and 60 °C water without any dimensional disintegration in 5 hours whereas those leached in 30 °C water showed only 70% PEG removal. Higher water temperatures led to fast PEG removal rate at the beginning and then gradually decreased with elapsed times.