Freeze-form Extrusion Fabrication of Functionally Graded Material Composites Using Zirconium Carbide and Tungsten

摘要

Ultra-high-temperature ceramics are being investigated for future use in aerospace applications due to their superior thermo-mechanical properties, as well as their oxidation resistance, at temperatures above 2000°C. However, their brittleness makes them susceptible to thermal shock failure. As graded composites, components fabricated as functionally-graded materials (FGMs) can combine the superior properties of ceramics with the toughness of an underlying refractory metal. This paper discusses the grading of two materials through the use of a Freeze-form Extrusion Fabrication (FEF) system to build FGM parts consisting of zirconium carbide (ZrC) and tungsten (W). Aqueous-based colloidal suspensions of ZrC and W were developed and utilized in the FEF process to fabricate test bars graded from 100%ZrC to 50%W-50%ZrC (volume percent). After FEF processing,the test bars were co-sintered at 2300°C and characterized to determine their resulting density and microstructure. Four-point bending tests were performed to assess the flexural strength of the test bars made using the FEF process, compared to that prepared using conventional powder processing and isostatic pressing techniques, for five distinct ZrC-W compositions. Scanning electron microscopy (SEM) was used to examine the inner structure of composite parts built using the FEF process.