Raman spectroscopy was utilized to investigate residual stresses found within a SiC/SiC ceramic matrix composite containing Hi-Nicalon ™ fibers, a slurry meltinfiltrated matrix of silicon carbide particles, and silicon matrix. Large gradients of electrically active boron are found throughout various regions within the crystalline lattice of the silicon matrix. The regions were identified by the varying degrees of asymmetry and peak width measured in the resonant Fano profile of the doped silicon. A methodology to determine the residual stress state of silicon exhibiting varying degrees of electrically active boron is presented by utilizing the changes in the Raman profile parameters. Previous works on similar SiC/SiC CMCs have attributed spatial gradients in the wavenumber to large fluctuations in stress. By applying the proposed methodology, we show that these observations are related to active boron that is segregated in various matrix areas. Utilizing this methodology, mean compressive stresses in various silicon regions were found to be approximately 300 MPa, with complementary tensile silicon carbide particle stresses of approximately 300 MPa.

The evolution of residual stresses found within a silicon carbide/silicon carbide (SiC/SiC) ceramic matrix composite through thermal treatments was investigated using Raman microspectroscopy. Constituent stress states were measured before, during, and after exposures ranging from 900 to 1300°C for varying times between 1 and 60 minutes. Silicon carbide particles in the as‐received condition exhibited average hydrostatic tensile stresses of approximately 300 MPa when measured at room temperature before and after heat treatment. The room temperature Raman profile of the silicon matrix was altered in both shape and location with heat treatment cycles due to increasing activation of boron within the silicon lattice as heat treatment temperatures increased. By accounting for boron activation in the silicon–boron system, little to no permanent change of any constituent stresses were observed, and the silicon matrix subsequently exhibited a complimentary average hydrostatic compressive stress of approximately 300 MPa at room temperature, measured before and after heat treatment. This result builds upon previous literature and offers increased insight into boron activation phenomena measured through Raman spectroscopy methods.

Multiple studies have investigated the residual stress state of melt-infiltrated SiC/SiC ceramic matrix composites (CMCs) through the utilization of Raman spectroscopy, 1-5 the common intersection point (CIP) method, 6-8 and surface X-ray diffraction (XRD) techniques. 9-11 Raman spectroscopy is predominately a surface technique, characterizing microstresses within tens of micrometers of the free surfaces, and thus Raman spectroscopy cannot capture volumetric stresses. The CIP method investigates large specimens and determines a single volume-averaged residual stress data point per specimen, consuming relatively