The Opportunity of Modern High-Toughness Technical Ceramics for Undersea Systems

Abstract

AbstractA confluence of recent developments in the formulation and processing of technical ceramics enables an important opportunity for submersible designers, namely, the reliable use of ceramics having density of near 3 g/cm3, compression strength of >4 GPa, tensile strength of >690 MPa, and fracture toughness (KIc) of 8‐10 MPa-m1/2. Concurrent developments in high-strength brazing of ferrous and nickel-based metals to these tough ceramics enables the integration of pressure envelopes with removable endcaps or ports, as well as optimum stiffener configurations and other internal or external design features. The specific opportunity presented by this confluence of tough ceramics and brazed metallic fittings is the possibility of full-ocean-depth (>6,000 m) dry submersible structures with weight/displacement (W/D) ratio < 0.7, as compared to W/D > 1.0 for metallic structures. Self-buoyant dry hull structures at these depths will greatly expand submersible design options, minimizing the need for full-ocean-depth syntactic foams to float key functionalities. The processing of these ceramics requires a cold isostatic press (CIP) or slip cast “green forming” step, plus sintering to near full density, followed by hot isostatic press (HIP) to final density. Present HIP facilities can support processing of 81-cm diameter × 190-cm-long ceramic vessels and brazing of ceramic/metal assemblies to ~163-cm diameter × 254-cm-long in the United States. If larger ceramic pressure hull components are desired, a “tiled” ceramic structure can be assembled and brazed or bonded together with thin metallic skins in a sandwich structure.