INNOVATIVE CERAMIC MATERIALS AND PROCESSES FOR AERONAUTIC APPLICATIONS

Abstract

In the field of aerospace, aircrafts are the most dominant element with other spacecrafts and research satellites finding a limited usage. All the space vehicles are run by the highly efficient engines to make them escape the gravity in case of spacecraft or enable them to carry heavy loads and move quickly to the long destination as achieved by the civil and military planes. To achieve the excellence in transportation in the space, air vehicles are fitted with the engines (rocket or jet engines), these are termed as the power houses and are operated at extremely high temperature and pressure. Such a high temperature achievement and sustainment over the passage of time has put the challenges to the manufacturers and material producers. Spacecrafts and other research crafts which are specifically designed to achieve supersonic flights use special type of non-air breathing engines (rocket engine or scramjet/ramjet) and materials and comprise only up to 10% of the aeronautical industry. All other planes used by the airliners or being used as military planes rely on the air-breathing engines (jet engines). Depending upon the function and role of a plane these jet engines have different modifications but the operating unit and principle of all these engines remain same and is a variant of gas generator. Common goal of achieving the maximum fuel efficiency (thermal efficiency) in all the planes still remain same. Achievement of high thermal efficiency led to the development of materials and new methods to extract the maximum possible effectiveness of the materials. Simultaneously, new techniques also emerged to boost the overall operation. One such milestone was the development of superalloys and evolve of the process to fabricate superalloyed blades from equiaxed to single crystal. And introduction of cooling channels and thermal barrier coatings has carried this to limits of the current systems. With the metals and existing technology reaching the limit, focus is placed on the development of ceramic materials. Most of the technical (high temperature) ceramics are brittle and difficult to fabricate, Si3N4 one among this class is overlapping with metals in terms of toughness but production of this material into useful components is challenging. There are some derivatives of Si3N4 which are easy to produce (develop) into components but their development is limited to few special ceramic processing techniques. These derivatives are α-Sialon and β-Sialon later is easy to fabricate and develop into the components but is very soft, the former is hard and strong and impossible to be synthesized without the use of hot isostatic pressing (HIP), hot pressing and spark plasma sintering (SPS). All of these methods limit the size and geometry of the object to be produced. Machining of these hard materials at cost of diamond to make useful shapes is another restriction; additionally highly machined components may get notches and other fabrication defects which limit the mechanical properties. Production of Si3N4 based materials, Sialons, using the colloidal processing and pressure less consolidation (sintering) technique has been the challenge. Composition of the pure α-Sialon material was modified with another material, aluminosilicate (β-Sialon former) and this system could be sintered without applying pressure. Modification of this system (material-method) as influenced by the other useful additives like MgO, Spinel and Ce2O3 was also observed. Hence a new material system capable to be processed by shaping and forming methods linked to colloidal processing was designed