Advantages of combined micro-XRF and micro-XRD for phase characterization of Ti-B-C ceramics compared with...

Design and processing of new materials with improved high-temperature properties is one of the most challenging tasks of modern engineering. Among such materials, nonoxidic ceramics hold an important place. When optimizing the synthesis conditions of these new materials in an largely empirical manner, the use of analytical methods that can fully document the resulting phase compositions is of great importance. In this paper, we demonstrate the advantages of using combined microbeam X-ray diffraction and X-ray fluorescence over conventional X-ray diffraction as the characterization method in the specific case of Ti-B-C ceramics. Ceramic samples were synthesized by the pulse plasma method starting from high-purity powders of titanium, boron, graphite, and nickel. Different mixtures were heated in a pulsed fashion and sintered by combustion synthesis at various temperatures and time durations, as is the case during empirical optimization of a synthesis procedure. Conventional X-ray diffraction showed the presence of two phases at the end of the sintering process, TiB(2) and TiC, irrespective of the conditions employed. Scanning micro-XRF/micro-XRD on the other hand allowed one to detect and visualize the distribution of additional phases present in the sintering products, during which a dependence on sintering conditions was apparent. The micro-XRD results showed that three phases (TiB(2), TiC, and TiB) instead of two were present in samples sintered during a short time interval. The addition of metallic Ni to the initial mixture as a sintering facilitator resulted in the formation of a Ni(3)B phase. All phases proved to have strongly heterogeneous distributions above the 15-microm level with the presence of TiB(2) anticorrelated to that of TiC and TiB, emphasizing the necessity of the use of laterally resolved methods of characterization.