A Comparison of Weldability, Structure, and Mechanical Properties of CM64 and Tribaloy T-800 Welds for Hard-Facing of Turbine Blades

Abstract

Weldability, microstructure and tensile properties of CM64 and Tribaloy T-800 (T800) cobalt-based hard-facing materials were studied. Successful CM64 hard-facing could be achieved at ambient temperature using manual gas tungsten arc welding (GTAW-MA). It was shown that T800 welded at ambient temperature was prone to cold cracking due to a combination of low ductility with high welding stresses that limited accommodation of residual stresses by a plastic deformation within the weld beads, which was not the case for CM64 welds. Sound T800 welds of various geometries and sizes were produced on cobalt- and nickel-based superalloys using GTAW-MA when preheating above 900°C was applied prior to welding. T800 welds possessed lower ultimate tensile strengths and elongations from room temperature up to 1093 ºC when compared to CM64 alloy.

Enabling Multi-Material Structures of Co-Based Superalloy Using Laser Directed Energy Deposition Additive Manufacturing

“…However, controlling the cooling rate in a laser DED process is challenging. Base plate heating and/or heating the region of interest was previously found to control the cooling rate so that cracking does not occur [40,41]. Conventionally, thermal residual stresses are eliminated via post heat treatment.…”

“…The T800 alloy can be deposited up to a 5 mm thickness with the laser DED system by preheating the base plate to 500 • C [40]. Keshavarz et al used the preheating method for welding a T800 alloy and to mitigate the heat-affected-zone liquation cracking by heating over 900 • C [41]. This approach may be suitable for small components where preheating the substrate alleviates rapid cooling through conductive heat transfer but would not work for larger components where the conductive heat transfer is diminished with increasing the thickness of the component.…”