Turbine blades have complex geometries with free form surface. Blades have different thickness at the trailing and leading edges as well as sharp bends at the chord-tip shroud junction and sharp fins at the tip shroud. In investment casting of blades, shrinkage at the tip-shroud and cord junction is a common casting problem. Because of high temperature applications, grain structure is also critical in these castings in order to avoid creep. The aim of this work is to evaluate the effect of different process parameters, such as, shell thickness, insulation and casting temperature on shrinkage porosity and grain size. The test geometry used in this study was a thin-walled air-foil structure which is representative of a typical hot-gas-path rotating turbine component. It was observed that, in thin sections, increased shell thickness helps to increase the feeding distance and thus avoid interdendritic shrinkage. It was also observed that grain size is not significantly affected by shell thickness in thin sections. Slower cooling rate due to the added insulation and steeper thermal gradient at metal mold interface induced by the thicker shell not only helps to avoid shrinkage porosity but also increases fill-ability in thinner sections.

Characterization of amorphous SiO2 surfaces after biasing pretreatments, which induce nucleation of diamond, has been carried out using x-ray photoelectron spectroscopy and Raman spectroscopy. A mixture of silicon carbide, silicon oxycarbide, and diamond are formed upon exposure of biased SiO2 surfaces to a CH4+H2 plasma used for diamond deposition. It is concluded that nucleation of diamond on amorphous SiO2 surfaces is promoted by formation of a SiC surface layer. Textured diamond films have been fabricated on bulk SiO2 substrates using biasing pretreatments to induce diamond nucleation.

Simulation tools have improved significantly and are now capable of accurately predicting mould filling behavior. The quality of prediction is highly dependent on material properties and set-up of boundary conditions for the simulation. In this work material properties were measured and casting conditions were analyzed to accurately replicate the casting process in simulation. The sensitivity of the predictions to minor process variations commonly found in foundries was evaluated by comparing simulation and cast samples. The observed discrepancies between simulation and cast samples were evaluated and discussed in terms of their dependency on process variations. It was concluded that the simulation set-up was capable of reasonable predictions and could replicate the asymmetry of the filling however did not accurately predict the absolute value of the unfilled area. It was discovered that asymmetric flow due to variations in the orientation of the casting mould during filling could have greater influence on the predictions than the actual variation in fill time. The quality of simulation is dependent on equipment and techniques used in the foundry as well as the metallurgical model to simulate the process.

Global requirements of lower fuel consumption and fewer emissions are increasing the demand for decreasing the weight of cast components. Reducing the wall thickness of cast components is one way of achieving this. The aim of this work was to investigate castability of 17-4PH stainless steel in thin-walled test geometries (≤2 mm). The casting trials were performed to investigate fluidity as a function of casting temperature, mold preheat temperature, and filling systems in thin-walled sections. It was observed that fluidity in a top-gated configuration is strongly affected by casting temperatures; however, the effect of mold preheat temperature on fluidity was not significant. On the other hand, castings made in bottom-gated configuration were more stable, and fluidity was not significantly affected by variation in casting temperature and mold preheat temperature. Fewer porosity and flow-related defects were observed in the bottom-gated system as compared to the top-gated one. Keywords: investment casting, fl uidity, thin sections, porosity, 17-4PH Streszczenie Światowe wymagania niższego zużycia paliw i mniejszej emisji gazów powodują wzrost zapotrzebowowania na wyroby odlewane o mniejszej wadze. Zmniejszenie grubości ścianki odlewów jest jedną z metod spełnienia tego założenia. Celem niniejszej pracy jest badanie lejności stali nierdzewnej 17-4PH w próbach o cienkościennej geometrii (≤2 mm). Badania odlewania zostały przeprowadzone w celu przeanalizowania lejności w funkcji temperatury zalewania, temperatury nagrzania formy oraz cienkościennych przekrojów elementów układu wlewowego. Zaobserwowano, że w przypadku górnego układu wlewowego temperartura zalewania ma duży wpływ na lejność, jednakże wpływ temperatury nagrzania formy na lejność był nieznaczny. Z kolei odlewy 86otrzymane w konfiguracji z dolnym układem zalewania były bardziej stabilne, a różne temperatury zalewania oraz temperatury nagrzania formy nieznacznie wpłynęły na lejność. Zaobserwowano mniejszą porowatość oraz mniejszą ilość wad przy zastosowaniu dolnego układu wlewowego w porównaniu z górnym układem wlewowym. Słowa kluczowe: odlewanie precyzyjne w formach ceramicznych, lejność, odlewy cienkościen-ne, porowatość, 17-4PH

Defects in cast metals remain a common problem in many areas of the foundry industry, particularly in the investment casting of large area, thin-walled components for aerospace applications. During previous research, the thermophysical properties, density and porosity of a fibre reinforced ceramic investment casting mould were determined using several experimental techniques. Without verification, these experimental results remain nothing more than educated guesswork. The purpose of this study is to verify previous results and to more fully characterise the ceramic mould material with complementary measurements. A commercially available computational fluid dynamic (CFD) simulation package, Flow-3D®, was used in conjunction with a full-scale Ni-superalloy (IN718) casting to assess the accuracy of these results. By placing thermocouples strategically across the mould thickness, temperature profiles were determined and compared directly to predicted profiles extracted from the simulation by a custom-written Python script.