Reassessment of the Matrix Composition of Co-Re-Cr-Based Alloys for Particle Strengthening in High-Temperature Applications and Investigation of Suitable MC-Carbides

• Published in: Materials Vol. 16; no. 12; p. 4443
• Main Authors: Seif, Eugen, Rösler, Joachim
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 17-06-2023; MDPI
• Subjects: Alloys; Chromium base alloys; Co-Re alloys; Composition; Crack propagation; Hafnium carbide; HfC; High temperature; high-temperature alloys; Hydrofluorocarbons; Investigations; Particle precipitation; Particle size; Precipitation hardening; Precipitation heat treatment; Ratios; Solid solutions; Solubility; Specialty metals industry; Strengthening; TaC; Temperature; TiC; Titanium carbide; Germany; Co-Re alloys; HfC; high-temperature alloys; TaC; TiC
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16124443

This study reassesses the optimum matrix composition of Co-Re-Cr-based alloys for strengthening by MC-type carbides. It is found that the composition of Co-15Re-5Cr is ideally suited for this purpose as it allows the solution of the carbide-forming elements such as Ta, Ti, Hf, and C within a matrix consisting entirely of fcc-phase (typically at 1450 °C), having a high solubility for these elements, while precipitation heat treatment (typically at 900-1100 °C) occurs in a hcp-Co matrix, displaying a much lower solubility. In the case of the monocarbides TiC and HfC, this was investigated and achieved for the first time in Co-Re-based alloys. TaC and TiC emerged as suitable particles in Co-Re-Cr alloys for creep applications due to a large population of nano-sized particle precipitation, which is not the case for the mainly coarse HfC. Both Co-15Re-5Cr-xTa-xC and Co-15Re-5Cr-xTi-xC exhibit a formerly unknown maximum solubility close to x = 1.8 at.%. Therefore, further research on the particle-strengthening effect and the governing creep mechanisms of carbide-strengthened Co-Re-Cr alloys should focus on alloys with the following compositions: Co-15Re-5Cr-1.8Ta-1.8C and Co-15Re-5Cr-1.8Ti-1.8C.