Reliable ceramics for advanced heat engines

A silicon nitride processing method has been developed as part of a four-year DOE-funded program in processing for reliability. The program focused on attainment of high strength and reliability through identification and subsequent control of strength-degrading flaw populations. The material produced is designated NCX-5102 and consists of a silicon nitride-4% yttria composition that is densified by glass encapsulation HIPing. The effort concentrated on the near-net-shape fabrication of large aspect ratio, axisymmetric buttonhead tensile bars. This geometry served as a challenging forming requirement, sufficient for development of a general shape-forming capability. It also provided a direct means to assess tensile strength levels attributive to the process. The program was conducted in three stages: baseline process definition, process optimization and large-scale production demonstration.