Internal friction of Ni-Al intermetallic compound formation in sintering process

Abstract

The Ni-Al intermetallic compounds, as important high-temperature structural materials, have clear target requirements in a number of fields. Powder metallurgy is an important candidate for preparing the Ni-Al intermetallic compounds. Clarifying the formation and transformation process of Ni-Al intermetallic compounds in sintering process and determining the solid diffusion reaction temperature and types of intermetallic compounds are greatly important for tailoring sintering process and optimizing product quality. In this paper, the internal friction behaviors of Ni-Al powder mixture compacts in the sintering process are systematically investigated by the internal friction technique. A typical internal friction peak is observed in the internal friction-temperature spectrum. The peak height decreases with the measuring frequency increasing, but the peak temperature is independent of frequency. Moreover, the internal friction peak shifts toward higher temperature and the peak height increases as the heating rate increases. It is reasonable that the internal friction peak belongs to the typical phase transformation internal friction peak which is associated with the formation of intermetallic compounds NiAl<sub>3</sub> and Ni<sub>2</sub>Al<sub>3</sub> in the heating process. Furthermore, the microstructure of the Ni-Al powder mixture can be tailored by mechanical ball-milling. The internal friction peak shifts toward lower temperature and the peak height decreases with the ball-milling time increasing, which indicates that the solid diffusion reaction can be activated at lower temperature with a slower reaction rate. This decrease is related to the refinement of powder particles, the lamellar formation of powder mixture, the enhancement of solid solution degree and surface energy, and the shortened atomic diffusion distance due to the mechanical ball-milling. It is also indicated that the mechanical ball-milling can effectively reduce the initial temperature of solid diffusion reaction, thus lowering sintering temperature.