A scalable near-net-shape process for producing ultra-high-temperature carbide/refractory metal composite plates with tailorable channel patterns for compact heat exchangers for efficient electricity production

Concerns over increasing greenhouse gas emissions have led to growing interest in heat and electricity generation from non-fossil-fuel-based sources, including from advanced nuclear reactors. Among Generation IV nuclear reactor systems, very high temperature reactors (VHTRs) are particularly attractive for producing high-temperature (>950 degrees C) heat for efficient electricity and hydrogen generation, and for a range of industrial processes. The efficiency (and cost effectiveness) of electricity production by a VHTR, operating with an indirect Brayton power cycle, can be enhanced by raising the temperature of heat transferred through an intermediate heat exchanger (HEX) to a turbine. While compact, printed-circuit-type HEXs are well-suited for such heat transfer, operation at >950 degrees C will require VHTR HEXs comprised of new materials with enhanced high-temperature creep resistance and thermal conductivity relative to conventional stainless steels. Ultra-high-temperature, co-continuous zirconium carbide/tungsten (ZrC/W) composites possess an attractive combination of mechanical and thermal properties for high-temperature HEXs. The purpose of this paper is to introduce and demonstrate a scalable, cost-effective, near-net-shape/size process for fabricating thin, dense, co-continuous ZrC/W-based plates with tailorable channel patterns for high-temperature HEXs. Porous rigid WC preform plates with patterned channels were first produced by low-cost pressing/stamping of WC/binder mixtures, followed by binder evaporation and light sintering. The green body binder content, powder bed aspect ratio, and compaction pressure were tailored to produce rigid, porous WC preform plates with desired relative porosity and minimal shrinkage after firing. A continuous thermal treatment was then used to generate a Zr-Cu alloy liquid and for reactive infiltration of this liquid into stationary porous WC preform plates. Such reactive melt infiltration yielded dense, channeled ZrC/W-based composite HEX plates that retained the shapes and dimensions (within a few percent) of the preform plates. By avoiding the need for high pressures and temperatures, for extensive machining/grinding, and for complicated fixturing for melt infiltration, this near net-shape process is a cost-effective, scalable means of producing ZrC/W-based plates with tailorable channel patterns for high-temperature heat exchangers for efficient electricity or hydrogen production by VHTRs or other systems.