Tech Briefs

Determining the potential of ceramic-based materials for reducing weight, saving fuel, and improving performance in aerospace gas turbine engines.

The purpose of this endeavor was to investigate the effect of 3-D weave architecture on PIP-processed ceramic-matrix composites (CMC). Microstructural studies were performed to document the resulting microstructure and mechanical testing was performed to determine the high-temperature durability of the five different variants of SiC/SiNC CMC investigated.

Simple schematic of the PIP manufacturing process used to manufacture CMC panels used in this study.

Ceramic-based material systems have the potential for significant weight reduction, greater fuel savings, and performance improvements in aerospace gas turbine engine (GTE) applications over their conventional metallic counterparts due to their higher specific strength properties and temperature capabilities. Of current interest to the United States Air Force (USAF) is the use of CMC materials such as SiC/SiNC laminates for aerospace turbine engine exhaust nozzle applications.

For these types of applications, there is concern over inadequate interlaminar shear strength. In an attempt to reduce delamination problems that sometimes occur in two-dimensional (2-D) laminates, three-dimensional (3-D) architectures were examined. It is thought that a 3-D fiber preform should increase shear strength of the resulting laminate. Improvements in shear properties through 3-D architectures will result in changes to the in-plane strength and durability properties. Thus, the influence of the 3-D architecture on mechanical properties needed to be thoroughly evaluated.

In this effort, two lay-up constructions (i.e., 2-D and 3-D weave) were examined, along with two different precursor resin systems. Properties examined include tensile, creep, fatigue, and interlaminar shear, all at 1000°C. In addition to the varying weave construction and matrix resin systems, two laminate thicknesses (i.e., varying number of plies) were evaluated. Details of the materials, procedures, and resulting mechanical properties are described in the following sections.

The overall objective of this research project was to evaluate the effect of a 3-D weave on the mechanical behavior and durability of SiC/SiNC by using the 2-D CMC as the baseline. The 3-D specimen would evaluate the standard-matrix precursor (S200) and one made by a Starfire ®. Applying coatings to the fibers in a 3-D preform is challenging, so preforms with thicknesses of 2.03 mm (0.080 inches or 80 mil) and 3.68 mm (0.145 inches or 145 mil) were investigated. In much of the report, the preforms are referred to as either 80 mil or 145 mil preforms. In addition, these thicknesses are representative of exhaust nozzle components.

The following CMCs were manufactured: 1) 2-D material with the S200 matrix pre-curser and 6 plies to produce a 2.03 mm (80 mil) thickness; 2) 3-D material with S200 prepreg followed by infiltration with S200 matrix precursor and 2.03 mm (80 mil) thickness; 3) 3-D material with S200 prepreg followed by infiltration with S200 matrix precursor and 3.68 mm (145 mil) thickness, 4) 3-D material with S200 prepreg followed by infiltration of Starfire matrix precursor and 2.03 mm (80 mil) thickness; and 5) 3-D material with S200 prepreg followed by infiltration of Starfire matrix precursor and 3.68 mm (145 mil) thickness.

The following mechanical behavior tests were utilized to evaluate the strength and durability of the five CMC systems: tensile, creep, fatigue, interlaminar tension, and interlaminar shear. In addition, extensive characterization was performed. This included optical and scanning electron microscopy (SEM) of the microstructure, porosity measurements, and studies of fracture surfaces of the failed specimens from the mechanical behavior testing.

This work was done by Larry Zawada of Universal Technology Corporation, and Lawrence E. Carson and Craig Przybyla for the Air Force Research Laboratory. For more information, download the Technical Support Package (free white paper) here under the Materials category . AFRL-0267