Microstructural characterization of ceramic–intermetallic composites using TEM related techniques

TiCxNy/Ti–Ni and TiCxNy/Ti–Co composites formed by ceramic and intermetallic binder phases were produced by pressureless sintering at 1400 °C from powders synthesized by a mechanically induced self-sustaining reaction (MSR) process. Four different composites were characterized using high-resolution electron microscopic techniques, in both scanning (SEM, HRSEM) and transmission (TEM, HRTEM, ED, EDS and EELS) modes and using an energy filtered technique (EFTEM) associated with electron energy loss spectroscopy (EELS). The microcharacterization showed that the ceramic phase with an fcc-cubic structure displayed a short-range order in many crystals detected by diffuse scattering in the ED patterns. This was possibly due to a sequence of C, N, and vacancies of both atoms along certain directions in the structure. On the other hand, even though the binder phase was introduced as metal in the reaction process, it was formed by Ni–Ti or Co–Ti known intermetallic compounds (NiTi2, Ni3Ti, and Co3Ti). An unknown Ni–Ti intermetallic structure with a Ni:Ti ratio close to 2:1 was only found in one of the synthesized composites and displayed a cubic structure with a lattice parameter, a, of about 8.7 Å.