Environmental degradation of SiC/SiC

Lead Research Organisation: Swansea University
Department Name: College of Engineering


Key Objectives and Aims
Current variants of SiCf/SiC ceramic matrix composites produced by Rolls-Royce High Temperature Composites (RRHTC) contain matrix additions that control oxidation degradation via the formation of a low viscosity high oxygen permeability borosilicate glass. This low viscosity glass provides a "self-healing" mechanism for matrix cracks but also results in an oxidation and environmental resistance behaviour that is path dependent due to the variable chemistry of the oxidation product. This program will investigate the stability of these oxidation products in humid and/or marine environments and how this impacts subsequent mechanical performance. Specific objectives include:
1. Quantify/qualify how environmental exposure affects the monotonic constitutive performance.
2. Establish whether the evolution of strain (damage) is affected by environmental exposure.
3. Monitor damage progression under the impact of oxidation/environmental exposure throughout fatigue loading regimes.
4. Characterise fracture morphology due to environmental exposures and correlate to ultimate mechanical performance.
Novel Methodologies
Rolls-Royce and Swansea University will collaborate together to generate a suitably scaled test matrix that would examine the impact of environmental exposure on life. Determination of the impact on environmental exposures will require comparison of baseline test data and the examination of the specimens tested by the student. Previous test data and specimens will be provided by Rolls-Royce to the student when it is applicable to supplement the new specimens evaluated by the student.
Deformation and ultimate failure in fibre reinforced CMC systems is highly complex and attracts highly sophisticated and novel characterisation techniques to describe mechanical behaviour. This project will extend our laboratory expertise in the use of acoustic emission (AE), digital image correlation (DIC) and electrical resistance monitoring when applied to macro-scale axial test coupons. However, the recent procurement of an in-situ SEM loading stage will allow novel experiments on the micro-scale, incorporating DIC of SEM imaging to record surface matrix cracking, sub-surface fibre-matrix de-cohesion and fibre rupture. High magnification SEM and chemical mapping will be employed to identify environmentally induced glassy phases.
Due to the relatively brittle response of this class of material, improvements to traditional mechanical test controls will be required to accurately reproduce low magnitude strain controlled fatigue conditions.
CMCs are focussed towards future applications in the high temperature stages of aero and land based gas turbines. The information and methods developed in this research will inform future CMC material developments. Understanding the deformation mechanisms that occur under simulated, high temperature, oxidising, service environments will improve the design of new CMC variants and inform engineers of future structural integrity assessments.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R512102/1 01/10/2017 30/09/2022
1939588 Studentship EP/R512102/1 01/07/2017 30/06/2020 Steven Jordan
Description Novel damage monitoring techniques related to Ceramic Matrix Composites. Several new test methods have been researched to help understand the damage mechanisms involved with fatigue and damage of CMC systems.
Strain controlled Low Cycle Fatigue , Thermo-mechanical fatigue and in-situ tensile testing using a Scanning Electron Microscope have been developed and used succesfully.
Exploitation Route All 3 new test types have been developed to help Rolls Royce understand the damage mechanisms associated with their CMC products. Further use of the techniques can be used to increase this knowledge and help advance maturity of the product. Data obtained from in situ testing has been used to help validate data produced by computational modelling.
Sectors Aerospace, Defence and Marine

URL http://httpism.com
Description Key findings from this research have been used buy Rolls Royce to fully understand their product and how it can be improved. This improvement will lead to a new product being used on jet engines reducing fuel usage and climate impact in the future.
First Year Of Impact 2019
Sector Aerospace, Defence and Marine
Impact Types Economic