Phase (matter)

Metallurgy

Materials science

Intermetallic

Nickel aluminide

Melting point

Organic chemistry

Alloy

Microstructure

Superalloy

Composite material

Chemistry

Nial

Nickel

Journal of Alloys and Compounds

The formation mechanism of the Ru-rich β-NiAl phase in a nickel-based single crystal superalloy and its evolution course during the long-term aging were investigated. The β-NiAl phase confirmed via the XRD and TEM analysis was observed in the solidification process for casting alloy. The intensive study on the formation mechanism of the β-NiAl phase was conducted based on the analyses of the phase diagram, the incipient melting experiment, and the segregation behavior. In addition, a new phase identified as the δ phase was also observed in the β-NiAl phase, which was enriched in Re, Co, W, and Ni. The solidification path was determined as L → β, L → β + δ, L + β → γ′, L → γ′, L → (γ + γ′), which took into consideration the influence of the β-NiAl phase and the δ phase. Besides, the high melting point of the β-NiAl phase induced impediment in homogenizing heat treatment, long-term aging at 1100 °C from 100 h to 1000 h was carried out to eliminate the β-NiAl phase. Hence, the γ’/β-NiAl and γ/β-NiAl diffusion couples were put forward to interpret the evolution of the β-NiAl phase during the long-term aging. The TCP phase which was determined as μ phase via the selected diffraction spot was examined in the full heat-treated and long-term aging specimens. The morphology of the TCP phase could be divided into three types: needle-like, rod-like, and bulk-like. The influence of the β-NiAl phase on the formation of the TCP phase was researched in detail.

The formation and evolution of NiAl phase in a fourth generation nickel-based single crystal superalloy