Studies on Combustion Synthesis of a Ti-B4C System with Addition of Different Elements
| Autor: | Wei-zuo Lin, 林韋佐 |
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| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 This study presents an investigation on the addition of Ⅵ and ⅦB metals (Cr, Mo, W, and Mn) and Ⅲ and ⅣA elements (Si and Al) into a Ti-B4C system proceeding under a self-propagating high-temperature synthesis (SHS) process. The main objective was to realize the formation of either borides or carbides of the added elements. Moreover, effects of the element addition on the flame-front velocity, combustion temperature, and product microstructure were studied. Experimental results indicated that self-sustaining combustion was readily attained upon ignition, except for the Ti-B4C-W powder compact which required a Ti-C pellet serving as an ignition enhancer. The flame velocity and combustion temperature decreased with increasing contents of Cr, Mo, W and Mn in the Ti-B4C combustion system. Similar results were observed for the Ti-B4C system with the addition of Si and Al. Based upon the XRD analysis, the reaction of Ti with B4C yielded a TiB2-TiC composite. When Cr was incorporated into the Ti-B4C system, the formation of Cr7C3 along with TiB2 and TiC was found. In contrast to the production of a carbide phase, the inclusion of Mo, W, and Mn into the Ti-B4C system resulted in the formation of their corresponding borides, MoB, WB, and MnB. On the other hand, when Si and Al were adopted as the additional elements, the Ti-B4C-Si and Ti-B4C-Al systems produced the composites composed of TiB2-TiC-SiC and TiB2-TiC-Al4C3, respectively. Formation of either borides or carbides associated with the added elements was attributed to the difference in the Gibbs free energy of the compound. For example, Cr7C3 features a larger negative Gibbs free energy than CrB2, which means that the yield of Cr7C3 is more favorable than CrB2. However, the Gibbs free energy of formation of WB is negatively larger than that of WC, which responsible for the production of WB rather than WC from the Ti-B4C-W system. Based upon the Gibbs free energy of the compound, the production composition was verified. The synthesized products of this study are in situ composites composed of binary borides and carbides of the transition metals. According to the SEM observation, the products showed a granular microstructure typical of the binary borides and carbides. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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