Path to single-crystalline repair and manufacture of Ni-based superalloy using directional annealing

• Published in: Surface & coatings technology Vol. 405; p. 126494
• Main Authors: Kalfhaus, T., Schaar, H., Thaler, F., Ruttert, B., Sebold, D., Frenzel, J., Steinbach, I., Theisen, W., Guillon, O., Clyne, T.W., Vassen, R.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15-01-2021; Elsevier BV
• Subjects: Annealing; Bridgman method; Bridgman technique; Crystal growth; Crystal structure; Crystallinity; Gas turbines; Grain growth; Nickel alloys; Nickel base alloys; Numerical models; Repair; Single crystals; Substrates; Superalloy; Superalloys; Temperature; Temperature gradients; Thermal spray; Turbine blades; Superalloy; Annealing; Bridgman technique; Nickel alloys; Thermal spray
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126494

Advanced methods for the repair of single-crystalline (SX) Ni-based superalloys are of special interest for the gas turbine industry. Polycrystalline repair approaches show promising results, while the repair of SX materials is still challenging. Directional annealing experiments resulted in large columnar grains by imposing thermal gradients at the abnormal grain growth temperature of a specific Ni-based superalloy. A numerical model of the Bridgman process is applied to provide an insight into the temperature evolution during zone annealing of the Vacuum-Plasma-Spray (VPS) repair coatings with the aim of promoting grain growth from the SX substrate. The results presented here suggest that this is a promising approach to repair or manufacture SX turbine blades.
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•Abnormal grain growth behavior of vacuum plasma sprayed superalloy coatings.•Directional annealing of fine-grained repair coating results in columnar grains.•FEM simulation of a Bridgeman furnace for directional annealing•Single crystalline repair by simulating grain growth from single crystal substrate