Creep behavior in interlaminar shear of a Hi-NicalonTM/ SiC-B4C composite at 1200∘C in air and in steam

Marina Ruggles-Wrenn,Matthew Pope

doi:10.1051/matecconf/20152900006

Abstract

Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200 ∘ C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon TM fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16–22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Similar creep strains were accumulated in air and in steam. Furthermore, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. The tested specimens were also examined using electron probe microanalysis (EPMA) with wavelength dispersive spectroscopy (WDS). Analysis of the fracture surfaces revealed significant surface oxidation, but only trace amounts of boron and carbon. Cross sectional analysis showed increasing boron concentration in the specimen interior.

Highlights

Advanced aerospace applications such as turbine engine components, hypersonic missiles and flight vehicles, and spacecraft reentry thermal protection systems require structural materials that have superior long-term mechanical properties and retained properties under high temperature, high pressure, and varying environmental factors
This study investigates the creep behavior in interlaminar shear of a chemical vapor infiltration (CVI) ceramic composite comprised of Hi-NicalonTM fibers, pyrolytic carbon fiber coating with boron carbide overlay and a SiC-based multilayered matrix
While the shear stress distribution between the notches is not uniform, the average shear stresses provided by Eq (1) are useful when evaluating interlaminar shear strength values and comparing creep behavior of specimens subjected to identical mechanical tests in different environments

Summary

Introduction

Advanced aerospace applications such as turbine engine components, hypersonic missiles and flight vehicles, and spacecraft reentry thermal protection systems require structural materials that have superior long-term mechanical properties and retained properties under high temperature, high pressure, and varying environmental factors. Ceramic-matrix composites (CMCs) are prime candidates for such applications Because of their low density, high strength and fracture toughness at high temperatures SiC fiber-reinforced SiC matrix composites are currently being evaluated for aircraft engine hot-section components [1,2,3,4]. Since their constituents are intrinsically oxidation-prone, oxidation embrittlement is the most significant problem hindering SiC/SiC composites [5]. This study investigates the creep behavior in interlaminar shear of a CVI ceramic composite comprised of Hi-NicalonTM fibers, pyrolytic carbon fiber coating with boron carbide overlay and a SiC-based multilayered matrix. To better understand the post-test atomic composition of the composite material, electron probe microanalysis (EPMA) with wavelength dispersive spectroscopy (WDS) was performed

Material and experimental arrangements

Results and discussion

Concluding remarks