Nuchthana Poolthong

Primary particle movement and change of property of cast iron by centrifugal effect in semi-solid processing

Abstract The particle distribution in semi-solid slurry under centrifugal field was simulated and the main factors such as fraction of solid, rotation speed, and holding time effecting the particle distributions are discussed. The simulation results showed that primary particles rich zone is produced in radially outer area and these results are in good agreement with the experiment. The centrifugal effect produces the primary particles distribution along the radial direction. Denser particles are concentrated in outside than inner side. For high fraction of solid samples, ‘wall’ appear in the middle of samples because of high viscosity region making particle difficult to move. Longer holding time gives denser primary particles concentrated more in outside than inner side. Higher rotation speed gives increased gradient of hardness in the radial direction. It is due to that number of primary austenite at inner side at higher rotation speed is less than that at lower rotation one. At higher rotation speed, ledeburite forms more at inner side of specimen than at the other one. It is also shown that semi-solid processing at lower fraction of solid gives higher hardness because smaller number of primary austenite, namely more ledeburite forms in microstructure. The present study gives useful information on producing material with locally changing property by semi-solid processing.

Effect of heat treatment on microstructure, wear properties and corrosion characteristics of semi-solid processed high chromium cast iron

Semi-solid processed high chromium cast irons were produced using a copper cooling plate and metal mould. A series of experiments were carried out to clarify the effect of heat treatment on microstructure, hardness, wear properties and corrosion characteristics. The results show that semi-solid processing by heat treatment improves wear resistance and corrosion resistance of high chromium cast iron. IJCMR/480

Effect of Reaction between Fe and Carbide Particles on Mechanical Properties of Fe-Base Composite

Sintered Fe-5 wt. % carbide (SiC or TiC) composites have been prepared via a powder metallurgy (P/M) route. Two carbide particle sizes, < 20 µm and 20-32 µm, were mixed with Fe powder. The powder mixtures were compacted and sintered at 3 different temperatures, 1100, 1150 and 1200 °C. Microstructures of sintered Fe-5 wt. % SiC composites showed evidence of SiC decomposition. The decomposed Si and C atoms diffused into Fe particles resulting in formation of solid solution of Si and C in Fe during sintering. During cooling, the solid solution of C in Fe decomposed to pearlite structure (ferrite and cementite (Fe3C) lamellar structure). Microstructures of sintered Fe-5 wt. % TiC composites showed no evidence of TiC decomposition at the investigated sintering temperatures. Because of the reaction between SiC and Fe, tensile strength and hardness of the sintered Fe-SiC composites were higher than those of the sintered Fe. Experimental results showed that strength and hardness of the sintered Fe-SiC composites increased with increasing sintering temperature and with decreasing SiC particle size. In contrast, mechanical properties of the sintered Fe-TiC composites were inferior to those of the sintered Fe. The reason of poor mechanical properties may be attributed to poor bonding between Fe and TiC particles.

Effect of alloying elements on structure and mechanical properties of semi-solid processed cast iron

Semi-solid metal processing of alloys is one of the key technologies for producing advanced materials. Through semi-solid processing, it is possible to produce high quality cast components from grey cast iron. A series of experiments were carried out to clarify the effect of the alloying elements copper, chromium, molybdenum, and nickel on the properties of cast iron. A comparison was made of the microstructure and mechanical properties in semi-solid processed cast iron and ordinary cast iron. This showed that an increase in the level of alloying elements in cast iron gave a higher level of hardness. However, the tensile strength of alloyed semi-solid cast iron did not exceed that of grey iron, for every composition, as a result of the characteristic microstructure produced by semi-solid processing. Thus, the alloying elements had little effect on the tensile strength of semi-solid cast iron, but did have an effect on elongation. The tensile strength of semi-solid cast iron, however, still depends on the cooling rate.

Sintered Titanium-Hydroxyapatite Composites as Artificial Bones

The design of engineered bone substitutes takes biocompatibility and mechanical compatibility into account as prerequisite requirements. Titanium (Ti) and hydroxyapatite (HA) with chemical formula of Ca10(PO4)6(OH)2, show good biocompatibility and are known as biomaterials. To combine metal powder (Ti) and ceramic powder (HA) as a composite material with mechanical properties comparable to those of natural bones needs strategy. In this work, powder metallurgy process was employed to produce Ti-HA composites, with nominal HA powder contents in the range of 0-100 vol.%. Mixtures of Ti and HA powders were pressed in a rigid die. Sintering was performed in vacuum atmosphere. The as-sintered specimens were tested on biocompatibility in a human-osteoblast cells. It was found that processing and materials parameters, including compaction pressure, control the composite microstructures and mechanical properties. Laboratory bone tissue culturing showed that a bone tissue could grow on the artificial bones (sintered Ti-HA composites).

Corrosion Behavior of Al-Zn-In Sacrificial Anode Alloys Produced by Conventional Casting and Semi-Solid Metal Casting Processes

A challenge in producing a sacrificial anode through conventional casting method is that the alloying elements in casting segregate during solidification, which further causes non-uniform anode corrosion reducing anode performance. In this paper, we investigated the performance of Al-5Zn-0.02In anode produced by conventional casting compared with by semi-solid casting technique. The performance of produced anodes were measured in terms of anode potential, current capacity, consumption rate and anode efficiency in 3.5% NaCl solution for 14 days. We found that the microstructure of the conventional cast anode had dendrites and coarse grains and the corrosion caused pitting corrosion. In contrast, the semi-solid cast anode had fine grains without any dendrites. The corrosion attacked mainly the grain boundaries and less on the matrix. Surprisingly, the conventional cast anode has about 10% higher efficiency than that of semi-solid cast anode.

Design of Runner and Gating Systems for the Investment Casting of 431 Stainless Steel Netting Hook through Numerical Simulation

In the production of netting hook, which requires wear resistance and long service life enabling the fishing net production with high efficiency, there has been some studies to achieve its forming method for high durability and designated smooth surface. The process of investment casting or known as “lost wax casting” is one of casting methods to fabricate metal part with a complex shape. Flow behavior of stainless steel grade 431 at the temperature higher than 1600°C is a critical factor in casting mold design of the lost wax process. In the study, CAST-DESINERTM simulating software was used to analyze flow of liquid metal to clarify the solidification of SS431 which caused defects in the product. Non-preferred heat transfer phenomena and using of the unsuitable mold design normally lead to defects in casting such as misruns, cold shuts, shrinkage, pin holes and porosity. Parameters in casting such as pouring temperature, preheating temperature, preheat time, pouring rate and cooling rate were given by the current production condition. The experimental design technique for simulation analysis of casting and gating system has been designed to be consistent and appropriate to the casting part. The cross-sectional design of the runner was two types of hexagonal and circular cross-section runner. The angle of gating system was kept constant at 90 degrees to the runner. As a results of the simulations, shrinkage porosity, filling time as well as solidification time were used to evaluate the cross-sectional design of runners. It was found that a circular cross-section runner led to the shorter filling time than a hexagonal one. Furthermore, there was no remarkable difference of shrinkage porosity in all simulated conditions. However, in terms of filling time, the results depended on the combination of runner design and gating system.

Synthesis and Characterization of Artificial Bone Material Using Calcium from a Natural Source

Hydroxyapatite (HAp), with chemical formula of Ca10(PO4)6(OH)2,is one of the most popular biomaterials applied as a scaffold or a scaffold component in bone tissue engineering. Synthesis of this material using calcium from a natural sourcewill be a good strategy for cost reduction. Waste cockle shells containing abundance of nearly pure calcium carbonate (CaCO3) are ideal sources of calcium. In this study, the waste cockle shells were turned to CaO nanoparticles using a simple chemical route. The CaO nanoparticle was used as a starting material to react with hydrous and anhydrous calcium hydrogen phosphate (CaHPO4) with calcium-to-phosphate (Ca/P) ratios in the range of1.5-1.67 under a mechanochemical process. The synthesized products were characterized by X-ray diffraction technique and scanning electron microscope.The experimental results revealed that under the same reaction timethe reaction using the dehydrated CaHPO4yielded a mixture ofHApand residual CaHPO4whereas the reaction using hydratedCaHPO4(CaHPO4.2H2O) yieldeda mixture of HApand beta tricalcium phosphate (β-TCP). The HAp yields of the reactions using dehydrated and hydratedCaHPO4were 71% and 51 %, respectively.

Enhancing wettability of SiC in semisolid A356 aluminium matrix composites

Abstract Stir casting plus cooling plate technique has been used for the fabrication of Al matrix composites based on alloy 356. Improvement of the wettability of SiC particles was carried out, employing the oxidisation of SiC particles, the use of wetting agents by adding magnesium into the matrix and the coating of SiC particles using a sol–gel technique. The introduction of SiC particles into partially solidified alloy with high viscosity prevents the particles from floating and agglomerating. Unoxidised SiC particles are mostly detached from the Al matrix during the grinding suggesting poor adhesion and poor wettability between the matrix and the particles. Oxidised SiC particles and sol–gel silica coated SiC particles indicate good binding between composite and matrix. The use of magnesium promoted wettability of SiC with A356 alloy. The eutectic silicon phase formed on the surface of SiC particles during solidification may be due to nucleation effects provided by the particles.

Effect of WC Addition on Phase Formation and Microstructure of TiC-Ni Composites

In this research, titanium carbide-nickel (TiC-Ni) composites, with tungsten carbide addition, were fabricated by using a powder metallurgy technique. The TiC-Ni mixtures containing between 0-15 wt. % tungsten carbide (WC), were compacted and then sintered at 1300°C and 1400°C, respectively. The phase formation and microstructure of the WC-added TiC-Ni composites have been investigated by X-ray diffraction and scanning electron microscopy techniques. Mechanical properties of these composites were assessed by an indentation technique. The X-ray diffraction patterns showed no evidence of tungsten rich phases in the sintered WC-added cermets. This indicates that during the sintering process, tungsten carbide particles were dissolved in metallic binder phase (Ni phase) via dissolution/re-precipitation process during liquid phase sintering. The liquid phase formed during sintering process could improve sinterability of TiC-based cermets i.e., it could lower sintering temperatures. The TiC-Ni composites typically exhibited a core-rim structure. The cores consisted of undissolved TiC particles enveloped by rims of (Ti, W)C solid solution phase. Hardness of TiC-Ni composites increased with WC content. Sintering temperature also had a slight effect on hardness values.