Near net shape production of monolithic and composite high temperature ceramics by hot isostatic pressing (HIP)

Improved properties of high temperature ceramics in general are achieved by compositional and processing research and development-compatible with sintering and forming needs. Pressure can be used to increase the driving force for densification and with hot isostatic pressing (HIP) the form can be closely controlled, even of complex shaped parts, like turbine wheels. Recent development within the EUREKA-AGATA hybrid electric car gas turbine project shows that improved high temperature material properties can be achieved, while at the same time fabricating components like combustion parts and turbine wheels, to near-net-shape. For such components a highly uniform green powder body is desired. Combined with a type of encapsulation during HIP, which does not create shear stresses at the surface of the green body during the shrinkage/sintering to full density, but at the same time prevents penetration into the body, optimal near-net-shape results can be achieved. Recent studies, e.g. by TEM, have confirmed that some encapsulation glass constituents can form new compounds with silicon nitride, at the very surface, which appear to help develop these desired characteristics. Non-homogeneous and nonisotropic ceramics, like fiber reinforced composites, may be fabricated using rigid, shape controlling tools on one or several sides. Particularly for large (and curved) panels such use of a hot isostatic press can be an advantage. (C) 1999 Elsevier Science Ltd. All rights reserved.