Precipitation and phase transformation mechanism of additive manufactured Ni-Co base superalloy

• Published in: Materials characterization Vol. 151; pp. 252 - 259
• Main Authors: Tang, Ling, Liang, Jingjing, Cui, Chuanyong, Li, Jinguo, Zhou, Yizhou, Sun, Xiaofeng, Ding, Yutian
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.05.2019
• Subjects: Additive manufacturing; Element loss; Ni-Co base superalloy; η phase; Element loss; Additive manufacturing; Ni-Co base superalloy; η phase
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2019.03.015

Microstructures of a newly developed Ni-Co base superalloy with different contents of Co manufactured by additive manufacturing (AM) have been investigated using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results show that, the Ni-Co base superalloy made by AM presents a columnar microstructure. This columnar microstructure is achieved through epitaxial growth of fine parallel dendrites from a substrate. η phase and γ′ phase precipitate during the deposition process. After heat treatments, there are primary γ′, secondary γ′ and tertiary γ′ precipitated. The heat treatments also promote the precipitation of η phase. The inductively coupled plasma atomic emission spectroscopy (ICP-AES) investigation shows that the loss and segregation of elements can account for the formation of η phase. The results also indicate that the addition of Co promotes the precipitation of γ′ and impedes the precipitation of η phase. Electron probe microanalyser (EPMA) results show that increasing of Co content decreases the segregation of Ti in the heat-treated state and is beneficial for decreasing the precipitation of η phase. TEM analysis confirms that the phase transformation mechanism is mainly the reordering of atoms and the formation of stacking faults. •The Ni-Co base superalloy made by AM shows a columnar microstructure;•There are η precipitates in the deposited samples and the heat treatments promote the precipitation of η phase;•Severe losses of Al and Ti during deposition and the element segregation can account for the precipitation of η;•Addition of Co can inhibit η phase precipitation and lower the element segregation.