Effects of Ti on the Microstructural Evolution and Mechanical Property of the SiBCN-Ti Composite Ceramics

In this study, amorphous + nanocrystalline Ti-BN mixed powders were obtained through first-step mechanical alloying; subsequently, almost completely amorphous SiBCN-Ti mixed powders were achieved in the second-step milling. The SiBCN-Ti bulk ceramics were consolidated through hot pressing sintering at 1900 °C/60 MPa/30 min, and the microstructural evolution and mechanical properties of the as-sintered composite ceramics were investigated using SEM, XRD, and TEM techniques. The as-sintered SiBCN-Ti bulk ceramics consisted of substantial nanosized BN(C), SiC, and Ti(C, N) with a small amount of Si₂N₂O and TiB₂. The crystallized BN(C) enwrapped both SiC and Ti(C, N), thus effectively inhibiting the rapid growth of SiC and Ti(C, N). The sizes of SiC were ~70 nm, while the sizes of Ti(C, N) were below 30 nm, and the sizes of Si₂N₂O were over 100 nm. The SiBCN-20 wt.% Ti bulk ceramics obtained the highest flexural strength of 394.0 ± 19.0 MPa; however, the SiBCN-30 wt.% Ti bulk ceramics exhibited the optimized fracture toughness of 3.95 ± 0.21 GPa·cm^1/2, Vickers hardness of 4.7 ± 0.27 GPa, Young's modulus of 184.2 ± 8.2 GPa, and a bulk density of 2.85 g/cm³. The addition of metal Ti into a SiBCN ceramic matrix seems to be an effective strategy for microstructure optimization and the tuning of mechanical properties, thus providing design ideas for further research regarding this family of ceramic materials.

Highly oriented platinum/iridium thin films for high-temperature thermocouples with superior precision

The long-term precise high-temperature measurement of thin-film thermocouples (TFTCs) has attracted attention due to the capability of instantaneous temperature detection. However, related technologies have seen slow development, and there is no one standard TFTC yet. Here, we focus on a new strategy of reducing alloys for the easy preparation and performance enhancement of TFTCs via nanostructure and interface design. To this end, we fabricated a platinum/iridium (Pt/Ir) pure-element TFTC with a well matched interface and few defects, which demonstrated excellent long-term service stability over a high-temperature range. The corresponding polynomial fitting coefficients were ≥0.99999, indicating the accurate acquisition of temperature data. A reduced deviation (<0.21%) between three calibration cycles was obtained over a wide temperature range of 300 °C to 1000 °C, which is better than the maximum precision of a standard wire thermocouple. Superior properties are achieved because of the resulting fewer defects in the Pt and Ir thin films with highly preferential orientation along the (111) plane. The results indicate that our Pt/Ir TFTCs have significant potential for application in many domains such as thermal detection, microelectronics and aero-engines.

Structure evolution, amorphization and nucleation studies of carbon-lean to -rich SiBCN powder blends prepared by mechanical alloying

Carbon strongly impacts microstructure evolution, amorphization and nucleation of SiBCN ceramics revealing an intense relationship between chemistry and final structure.