Dissertation
Processing-structure-properties relations in titanium carbide-titanium boride composites fabricated by transient plastic phase processing
Doctor of Philosophy (Ph.D.), Drexel University
Jun 1996
DOI:
https://doi.org/10.17918/00000493
Abstract
A systematic study of processing-structure-properties relations was carried out for a class of titanium carbide-titanium boride composites produced by Transient Plastic Phase Processing (TPPP), novel processing technique capable of in situ net-shape manufacturing fully dense refractory ceramic composites at relatively low homologous temperatures. These fully dense TiCx-TiB₂-Ti3B4 composites were fabricated starting from Ti/B4C, TiC0.5/TiB₂, Ti/C/TiB₂ and TiC0.5/B4C mixtures of different molar ratios with the resulting different morphologies of the final phases. Plastic flow of TiC0.5 (the starting and/or intermediate phase) combined with particle rearrangement and comminution of porous reaction product are believed to be the operating mechanisms for the most part of densification process responsible for increase of relative density to ~95%. Reaction paths and microstructural evolution in the two starting compositions with 4:4:1 ratio of Ti:B:C, namely: 4:1 Ti/B4C and 1:1 TiC0.5/TiB₂, were examined in detail. In the former, the Ti3B4 phase nucleated and grew as platelets, whereas it exhibited roughly equiaxed morphology in the latter. The presence of TiB as an intermediate phase in "platelet" composition appeared to determine the morphology of the Ti3B4 phase. Based on XRD and SEM results from interrupted runs, a model is proposed according to which the faster diffusion of C, relative to B, is instrumental in the microstructural evolution of the "platelet" composite. The microstructural evolution of the "equiaxed" composite is less complicated in that there are no intermediate phases. The resultant microstructure is believed to develop by a displacive reaction that only involves the diffusion of B and C. The flexural strength in the temperature range 25[degrees]C-1400[degrees]C, plane strain fracture toughness in the temperature range 25[degrees]C-1000[degrees]C, room temperature hardness and microhardnesses of individual phases, thermal shock susceptibility, wear and oxidation resistance were measured for a variety of titanium carbide-titanium boride composites with different microstructures. The effects of various microstructural parameters such as the length scale of microstructure, the morphology of the Ti3B4 phase, and the volume fraction of borides on these properties were identified. The relatively high strength and thermal shock resistance of the TPPP composites, and their competitive wear behavior combined with economic processing requirements make this class of materials an excellent candidate for cutting tools.
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Details
- Title
- Processing-structure-properties relations in titanium carbide-titanium boride composites fabricated by transient plastic phase processing
- Creators
- Dmitri Brodkin
- Contributors
- Michel W. Barsoum (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xx, 242 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) (1970-2026); College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991014970340004721