In this work, cristobalite crystallization and its effects on mechanical and chemical behaviour of injection moulded silica-based ceramic cores were investigated. In order to simulate casting process ...condition, the sintered samples at 1220°C were also heated up to 1430°C. Flexural strength test was carried out on both sintered and heat treated samples. Chemical resistance of the cores was evaluated by leaching the samples inside 43wt% KOH solution at its boiling point. Phase evolution and microstructure were investigated by thermal analyses (DTA and DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM). Results showed that cristobalite was crystallized on the surface of fused silica grains at about 1380°C. Flexural strength of the sintered cores was decreased after simulated casting heat treatment due to cristobalite phase transformation. The formed cristobalite on the surface of fused silica grains dramatically decreased the leachability of ceramic cores.
Display omitted
•Topology optimization of natural convection heat sinks.•Experimental validation of topology optimized heat sinks.•Investment casting of complex structures using stereolithography ...patterns.•Experimental cross-validation of topology optimized structures.
Topology optimization (TO) is an attractive numerical tool to obtain optimized engineering designs, which has been originally developed for mechanical optimization and extended to the area of conjugate heat transfer. With rapid developments in topology optimization models, promising designs have been proposed and presented recently for conjugate heat transfer problems. However, only a very small number of experimental validations of TO heat transfer devices have been reported. In this paper, investment casting (IC) using 3D stereolithography (SLA) printed patterns is proposed to fabricate 3D metal heat transfer devices designed by TO. Three heat sinks for natural convection are designed by a previously reported topology optimization model and five reference pin-fin heat sinks are devised for comparison. From those designs six heat sinks are cast in Britannia metal, fully reproducing the complex 3D optimized designs. It shows that SLA-assisted IC is a very promising technology with low cost and high accuracy for fabricating TO metal parts, which is not limited to heat transfer devices and can be extended to other areas such as structural optimization. A natural convection experimental setup is used to experimentally study the performance of the fabricated heat sinks. The results show that the tested TO heat sinks can always realize the best heat dissipation performance compared to pin-fin heat sinks, when operating under the conditions used for the optimization. Moreover, validation simulations have been conducted to investigate the temperature distribution, fluid flow pattern and local heat transfer coefficient for the TO and pin-fin designs, further evidencing that TO designs always perform better under the design conditions. In addition, the impact of heat sink orientation and radiation are presented.
Yttrium oxide (Y2O3) is widely used in titanium (Ti) alloy casting for its low activity, strength, and heat resistance. Wax mold and ceramic coating preparation in traditional investment casting is ...cumbersome; hence, this work proposes extrusion-based 3D printing of Y2O3-based ceramic shells. This study investigates how trace CaTiO3 affects sintering performance, showing that small amounts can reduce sintering temperature and significantly increase bending strength. Adding 2 mol% CaTiO3 increased the bending strength from 4.3 to 43.1 MPa after sintering at 1500 °C, while not wetting with the Ti–6Al–4V titanium alloy. This method offers a promising way to produce high-performance Y2O3-based ceramic shells with lower sintering temperatures.
This study fabricates a roughing electrode of electrical discharge machining (EDM) using a rapid prototyping (RP) system and investment casting technology, which reduces the overall time that is ...required for fabrication and the cost of the manufacturing process for a selected electrode. Pro/E (3D CAD) software is used to design the electrode prototype, which has a complex appearance, and to transform the CAD model into stereolithography (STL) format. An RP machine (Zcorp 402 3DP) is used to construct a gypsum-based powder model. After a sealing process using the permeation of resin, the water resistance and strength of the gypsum-based material are increased. The manufacturing process then involves creating a wax model with a gypsum electrode that is strengthened by resin permeation by casting a vulcanized silicone molding. The brass electrode is fabricated using investment casting technology. The results of an EDM test show that the brass electrodes with RP that are manufactured perform well and the total time that is required to machine the EDM electrode using RP is 15.8% less than the time that is required for a CNC machining process.
•The casting diameter has crucial impact on SDAS (secondary dendrite arm spacing).•Cooling rate in thin-walled castings can be calculated according to function model SDAS = 40.568•Vavg-0.478.•Mold ...temperature has more significant influence on SDAS than mold insulation in thin-walled castings (specimen diameter in the range of 1-3 mm).•The cooling rate affected macrostructure changes - significantly for cooling rate > 5 K/s.
The macro- and microstructure of nickel superalloys castings, especially thin-walled ones, have a large influence on their mechanical properties. Better understanding of the macro- and microstructure response to casting conditions will enable the optimization of technological and mechanical properties of the alloy. Presented research results refer to different diameter cylindrical specimens of Inconel 713C superalloy cast under various conditions to impose different cooling rates. The function model for correlation between secondary dendrite arm spacing (SDAS) and cooling rate was proposed. Statistical analysis of the influence of the main casting process parameters on the SDAS and cooling rate on grains morphology was performed. It was found that casting diameter had a biggest impact on the SDAS while mold temperature and thermal insulation had less influence on the alloy microstructure. Quantitative microstructural analysis results indicated also the effect of cooling rate on grain size.
Metal matrix composite: a methodological review Kumar, Sudhir; Singh, Rupinder; Hashmi, M. S. J.
Advances in materials and processing technologies (Abingdon, England),
01/2020, Letnik:
6, Številka:
1
Journal Article
Recenzirano
Metal matrix composites (MMC) find wide ranges of applications in manufacturing due to its lightweight, sound surface and mechanical characteristics. Its valuable applications in defence and space ...field make it worthy to be explored for possible low cost and ease to use solutions. In this paper, an effort has been made to make a comprehensive review on MMC preparation methods by different routes and materials employed for MMC preparation. Finally, a case study has been reported to suggest a novel way of preparing functionally graded MMC. Three-stage hybridisation is proposed using additive manufacturing-based master pattern, silicon moulding-based replica's prepared using master pattern and investment casted functionally graded MMC using replicas prepared by silicon moulding method.
AlSi7Mg0.6 alloy is widely used in the automotive and aeronautical industries, and metal additive manufacturing (AM) is a breakthrough technology that motivates foundry companies to explore its ...potential in these industries; however, there is no deep knowledge of the mechanical properties and their relationship to microstructure in parts obtained by selective laser melting (SLM), as there is for parts obtained by casting. In this work, a comparison of the microstructure and mechanical properties of AlSi7Mg0.6 alloy obtained by SLM and investment casting processes was made. The mechanical properties of tensile specimens processed by both technologies were evaluated by uniaxial tensile tests and microhardness measurements in as-built/as-cast and heat-treated conditions with different build orientations in the case of SLM. An advanced characterization of the microstructure by field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) analysis was also performed. After analyzing the microstructure and mechanical properties obtained with different heat treatments, the strengthening mechanisms of the two processes were identified. It is possible to obtain improved mechanical properties with SLM processing, exceeding the typical values required for aeronautical parts obtained in investment casting heat-treated (T6), and the ductility is satisfactory. Direct aging after SLM processing can effectively strengthen the AlSi7Mg0.6 alloy and is the more effective way to improve the as-built mechanical properties.
•AlSi7Mg0.6 alloy by additive manufacturing and investment casting processes were obtained.•Both processes generate quite different microstructures for the AlSi7Mg0.6 alloy.•Direct aging modify the silicon cells, making them smaller and better distributed.•High strength and improved ductility have been obtained with direct aging.•Natural aging, grain boundary and solid solution seem to be the main strengthening mechanisms.
Shell for investment casting is key in obtaining casting with high performances. In this study, carbon fibres were mixed with slurry, silica sol, and sanding materials to prepare fibre reinforced ...shell for investment casting. Suspension properties, slurry viscosity, and shell strength were all investigated. Failure surface of shell was observed by scanning electron microscopy (SEM). Results indicated that suspension percentage and viscosity of slurry containing fibre and silica sol were higher than those of fibre free slurry. The viscosity of slurry increased as carbon fibre length rose. Comparison of different mixing methods and fibre lengths revealed that addition of carbon fibre with 4 mm in length into silica sol under ultrasonic agitation yielded maximum bending strength of 3.97 MPa. SEM data illustrated that the longer fibres might increase bonding area, leading to increased shell strength.
This study presents experimental results on the mechanical behavior of aluminum alloy cellular structures filled with Polypropylene or ABS. Two types of base cell geometries were analyzed, having ...uniform cell structure and with a dual-size cell arrangement seeking optimized mechanical properties. The structures were manufactured by lost-wax casting using 3D printed components for internal structure definition. The polymer fill was introduced through a process of temperature assisted impregnation in a specially developed tool. Results for stiffness and energy absorption were obtained and compared on weight efficiency basis. The results are indicative of higher efficiency of the dual-size structures having PP/ABS filling that may be considered for energy absorption parts in compressive loading.
PDF
