Microstructure stability and mechanical properties of a new low cost hot-corrosion resistant Ni–Fe–Cr based superalloy during long-term thermal exposure. (15th March 2015)

• Record Type: Journal Article
• Authors: Sun, Wen; Qin, Xuezhi; Guo, Jianting; Lou, Langhong; Zhou, Lanzhang
• Is Part Of: Materials & design. Volume 69(2015:May)
• Page Start: 70
• Page End: 80
• Publication Date: 2015-03-15
• Subjects: Nickel superalloy -- Thermal exposure -- Microstructure stability -- Mechanical properties -- Cr addition; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2014.12.030
• Languages: English
• ISSNs: 0264-1275

Abstract

Highlights: A new hot-corrosion resistant Ni–Fe–Cr superalloy is designed and fabricated. γ′ precipitate coarsens greatly within 3000 h during thermal exposure at 850 °C. The γ′ coarsening degrades hardness and stress-rupture life significantly. Minor increase of Cr (from 20% to 21%) promotes large amount of σ precipitation. The σ phase enhances hardness but degrades the stress-rupture properties greatly. Abstract: A new low cost hot-corrosion resistant Ni–Fe–Cr based superalloy is designed and fabricated. The microstructure evolution, mechanical properties and effect of minor Cr variation on the microstructure stability during long-term thermal exposure have been investigated in details. Microstructure observations reveal that the new Ni–Fe–Cr based superalloy is constituted of γ matrix, γ′ precipitate, primary MC carbide and grain boundary (GB) M23 C6 carbide after standard heat treatment. During long-term thermal exposure at 850 °C, the γ′ precipitate coarsens greatly within 3000 h, which significantly degrades the room temperature hardness and stress-rupture life at 800 °C/294 MPa. The primary MC degenerates gradually by reactions of MC + γ → M23 C6 + γ′, MC + γ → M23 C6 + M6 C + γ′ and MC + γ → M23 C6 + M6 C + η, respectively. The growth of carbide and γ′ along GB changes it from thin discontinuous chain structure to coarse continuous chain structure, which might lead to the intergranular fracture during stress-rupture. In addition, small amount of grain interior (GI) M23 C6 carbide precipitates in the matrix, which has negligible influence on the stress-rupture property. Moreover, minor increase of Cr content (from 20% to 21%) extends the precipitating temperature range of σ phase and enhances its precipitating peak temperature, which results in a large amount of σ phase precipitates in the Ni–Fe–Cr based superalloy during long-term thermal exposure at 850 °C. The formation of σ phase increases the room temperature hardness but degrades the stress-rupture life and elongation of the Ni–Fe–Cr based superalloy greatly.