An experimental characterization of thermophysical properties of a porous ceramic shell used in the investment casting process

This study presents the results of an investigation that characterises the thermophysical properties of an investment casting mould, comprising of a Zirconium dioxide/Cobalt aluminate prime slurry and a fused Silica/fibre reinforced backup slurry. Growing prevalence of successful computer simulations within the foundry industry enables defects that emerge during the casting process to become increasingly predictable, providing cost-effective alternatives to trial castings. The viability of these simulations as predictors is heavily dependent upon the facilitation of accurate material property data, as attained through this investigation. Differential scanning calorimetry (DSC) and laser flash analysis (LFA) were utilized to determine the specific heat capacity and thermal diffusivity, respectively. These values, in combination with the material density and linear coefficient of thermal expansion, have been used to determine the thermal conductivity of the mould. With the aim of verifying these parameters, initial studies in Flow-3D® simulation software have been performed to determine the constraints needed to reduce variability in simulation parameters. Due to the diversity of casting moulds used throughout the industry, ensuring the material database is kept as comprehensively populated as possible is a crucial undertaking

A new semi-solid casting technique for fabricating SiC-reinforced Mg alloys matrix composites

The capability of the newly developed rheocasting (RC) technique in combination with the RheoMetal process for producing SiC particulate-reinforced AM50 and AZ91D matrix composites (Mg-based MMCs) was investigated. The quality of the MMCs was studied by analyzing the fraction of casting pores, number density of SiC clusters and the uniformity of SiC particles. Solid fraction, particle size and oxidation of SiC particles had strong impacts on the overall quality of the MMCs. The MMCs produced by 40% solid fraction and oxidized micron-sized SiC particles exhibited an excellent casting quality. A low-quality MMC was obtained when non-oxidized sub-micron sized SiC particles were employed. The results showed the formation of various types intermetallic particles and carbides such as MgO, Mg2Si, Al2MgC2, Mg2C3, Al4C3 as the interfacial reaction products of SiC/Mg alloy's melts. Mg hydride (alpha-MgH2) was also identified in inter-dendritic regions of the MMCs for the first time

A mathematical examination of the impact of mould transparency to infrared radiation on solidification during the investment casting process

Investment casting is a highly dynamic process during which multiple competing physical phenomena are at work. Those seeking to understand and simulate such processes computationally are confronted with a considerable task, balancing accuracy with efficiency. Approximations and models based on well-understood and documented fundamental physics are powerful tools in a modeller's arsenal. Driven by observed discrepancies between experimental thermocouple measurements and simulation predictions of casting temperatures, this work explores the additional alloy cooling mechanism of mould transparency to infrared radiation, targeting a new mathematical approximation applicable in such situations. Direct attenuation, scattering from coarse sand, sand distribution in the mould and material temperatures play a role in the extent of radiation transparency that must be considered. From this model, estimation of the additional cooling rate resulting from expected mould transparency can be determined and applied as a corrective measure to computation fluid dynamics (CFD) simulation results that do not capture this phenomenon

STR/03/001/FT Development of Nanocrystalline Ti-Si and Ni-Ti Alloys for Biomedical Application

Abstract – Mechanical alloying of Ti-Si and Ni-Ti was performed by high-energy ball milling at ambient temperature. The structural and compositional evolutions during mechanical alloying were investigated. Results showed that the crystallite size of mechanically alloyed Ti-Si and Ni-Ti powders decreased with increasing milling time and the steady-state crystallite size was approximately 10 nm. The mechanically alloyed Ti-Si and Ni-Ti powders were predominantly nanocrystalline with traces of the remnant amorphous phase. It was found that a significant increase in solid solubility of Si (or Ni) in Ti was achieved by mechanical alloying. The optimum milling time for the synthesis of nanocrystalline/amorphous Ti-Si and Ni-Ti with least impurities was 75 h. Keywords: Ni-Ti, Ti-Si, Mechanical alloying

Thermal conductivity of liquid cast and rheocast telecom component using Al-6Si-2Cu-Zn (Stenal Rheo 1) in as-cast and heat treated condition

The thermal conductivity of a rheocast telecom component produced using Al-6Si-2Cu-Zn alloy (Stenal Rheo 1) was investigated in the as-cast, T5 and T6 conditions. Conventionally liquid cast samples were produced in a permanent mold and used as a reference material. In the rheocast component in as-cast condition, a thermal conductivity of 153 W/mK at room temperature were measured. A T5 treatment at 250 or 300°C increased thermal conductivity to 174 W/mK. A T6 treatment resulted in further increase in thermal conductivity to 182 W/mK. The liquid cast alloy exhibited a lower thermal conductivity and a higher hardness for all conditions compared to the as-rheocast component.The microstructure of rheocast component showed material consisted of relatively large α1-Al particles formed during the slurry fabrication process and fine α2-Al particles formed in the die cavity. The macrosegregation in the form of the different ration of the primary α1-Al particles to secondary α2-Al particles in different positions of the rheocast component was observed. The relation between microstructural characteristics and thermal diffusivity was investigated by determining the local thermal conductivity in the rheocast component and ration of α1-Al particles to α2-Al particles. The results revealed that samples from the regions of the component with a high amount of α1-Al particles had a higher thermal conductivity. WDS measurement results pointed to that Si and Cu concentration in the α1-Al particles contained lower concentrations value compare to the α2-Al particles and therefore α1-Al particles has higher value for thermal conductivity.Silicon precipitation was confirmed using calorimetry and dilatometry to take place between 200 and 250°C. A linear relation between the fraction of Si precipitates formed and the increase in thermal diffusivity was obtained. Silicon in solid solution is shown to have a strong influence (negative) on thermal conductivity. When the silicon is precipitated by heat treatment the thermal conductivity increases. For an optimal combination of thermal and mechanical properties it is therefore important to use an ageing temperature above the temperature for Si precipitation