A novel ternary eutectic in the Nb-Al-Ni system

This study investigated the Al-Nb-Ni system to address the demand for advanced materials with superior high-temperature strength, fracture toughness, and oxidation resistance for aerospace and energy applications, particularly focusing on intermetallic-based composites suitable for use above 1500^C. The primary objective was to explore the impact of nickel addition on the Al₃Nb-Nb₂Al eutectic, identify a novel ternary eutectic transformation, and characterize the resulting phases, as a comprehensive literature review revealeda lack of data on this specific ternary system. The methodology involved preparing alloys through arc melting, followed by thermal analysis using Differential Thermal Analysis (DTA) to ascertain transformation temperatures. Phase identification and compositional analysis were performed on as-cast and directionally solidified samples utilizing Wavelength-Dispersive Spectroscopy (WDS) and X-ray Diffraction (XRD). The research successfullyidentified a novel ternary eutectic reaction, L Nb₂Al+Al₃Nb+AlNbNi, occurring at 1553. 6^C with a composition of Al-40. 4Nb-2. 42Ni. The third phase was confirmed as an Al-rich AlNbNi phase. The ternary eutectic exhibited a regular, predominantly fibrous microstructure, despite being composed of intermetallic phases. Observations also showed that increasing the growth rate reduced interphase spacing and the volume fraction of the AlNbNi phase, slightly increasing the Al₃Nb phase, and ultimately led to a degeneration of the eutectic microstructure marked by the formation and ramification of eutectic cells. Furthermore, the study concluded that the previously suggested Al₅Nb₂Ni phase does not exist in the Al-rich corner.