An Investigation of the Fibre/Matrix Interface Phenomena in a SiC Fibre Reinforced Ti Alloy Composite

  • Yingwei Fan

Student thesis: Phd

Abstract

In this thesis, the microstructure evolution and the debonding behaviour at the fibre/matrix interface in the SiC fibre reinforced Ti-17 composite are investigated. Further, the distribution of the residual stress thermally induced during cooling phase of the composite fabrication process and reaction zone growth at the interface are simulated. It is found that the fibre/matrix interface develops from a two-layered reaction zone (RZ) in the as-fabricated composite to a three-layered RZ in the composite after isothermal exposure. The RZ consists of TiC-type carbide in the as-fabricated composite and composites after isothermal exposure below 900℃ whereas the RZ is composed of a mixture of TiC-type and Ti3C2-type carbides after exposure at 900℃. The growth of the RZ is induced by the diffusion controlled chemical reactions between the carbon coating on the fibre surface and the matrix, which are governed by parabolic and logarithmic laws and Arrhenius relationship. Al, Mo and Cr in the matrix are found to be rejected in front of the RZ when carbon atoms in the carbon coating diffuses across the formerly formed RZ to interact with Ti, Zr and Sn transporting from the matrix at the RZ/matrix interface. The activation energies and rate constant factors are 49.93kJ/mol, 31.53 micro metre/h^(1/2) for reaction zone growth and 29.42kJ/mol, 1.13 micro metre/h^(1/2) for carbon coating consumption. The interface debonding strength increases from 108.2MPa in the as-fabricated composite to 140MPa in the composite after isothermal exposure at 450℃. The interface debonding occurs at interface between the RZ and the carbon coating on the fibre surface. The carbon coating/SiC fibre interface, the interface of the two sublayers within the reaction zone, and the reaction zone/matrix interface remain intact after the fibre is pushed out. The interface debonding initiates on the loading end and propagates along the carbon coating/RZ interface towards the supporting ends of the thin slice specimen employed for the single fibre push-out testing.The distribution of the thermally induced residual stress is simulated using two different models, one with the RZ and the other without the RZ. In the RZ-included model, the highest stresses are located in the RZ at the fibre/matrix interface area with the values of 2-3GPa (~800MPa for S_33) whereas the maximum stresses predicted using non-RZ model are approximate 1GPa present in the matrix adjacent to the fibre/matrix interface. On the other hand, each stress variable predicted by the two models has the minimum value on the same level in similar regions in the composite. The simulation of reaction zone growth shows that the RZ growth at 450℃ is not governed by the logarithmic model. However, the RZ growth at 650℃, 800℃ and 900℃ is perfectly simulated using the logarithmic model.
Date of Award1 Aug 2016
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorGeorge Thompson (Supervisor) & Xiaorong Zhou (Supervisor)

Keywords

  • Chemical reaction
  • Ti matrix composite
  • Continuous SiC fibre
  • Fibre/matrix interface
  • Debonding behaviour

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