Build direction dependence of microstructure and high-temperature tensile property of Co–Cr–Mo alloy fabricated by electron beam melting

• Published in: Acta materialia Vol. 64; pp. 154 - 168
• Main Authors: Sun, Shi-Hai, Koizumi, Yuichiro, Kurosu, Shingo, Li, Yun-Ping, Matsumoto, Hiroaki, Chiba, Akihiko
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.02.2014; Elsevier
• Subjects: Applied sciences; Cobalt chromium alloys; Exact sciences and technology; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Phase transformation; Powder processing; Tensile behavior; Texture; Phase transformation; Powder processing; Tensile behavior; Cobalt chromium alloys; Texture; Temperature; Melting; Electron beam; Mechanical properties; Tensile property; High temperature; Chromium; Microstructure
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2013.10.017

The microstructures and high-temperature tensile properties of a Co–28Cr–6Mo–0.23C–0.17N alloy fabricated by electron beam melting (EBM) with cylindrical axes deviating from the build direction by 0°, 45°, 55° and 90° were investigated. The preferred crystal orientations of the γ phase in the as-EBM-built samples with angles of 0°, 45°, 55° and 90° were near [001], [110], [111] and [100], respectively. M23C6 precipitates (M=Cr, Mo or Si) were observed to align along the build direction with intervals of around 3μm. The phase was completely transformed into a single ε-hexagonal close-packed (hcp) phase after aging treatment at 800°C for 24h, when lamellar colonies of M2N precipitates and the ε-hcp phase appeared in the matrix. Among the samples, the one built with 55° deviation had the highest ultimate tensile strength of 806MPa at 700°C. The relationship between the microstructure and the build direction dependence of mechanical properties suggested that the conditions of heat treatment to homogenize the microstructure throughout the height of the EBM-built object should be determined by taking into account the thermal history during the post-melt period of the EBM process, especially when the solid–solid transformation is sluggish.