Caractérisation de microstructures de joints brasés avec les alliages BCu-1, BAg-13a, BAu-4, BAu-6, BNi-1a, BNi-2, BNi-3 et Palnicro 36M ayant pour métal de base un superalliage base nickel

Abstract

The main goal of this study was the characterization of microstructures of brazed joints using Inconel 625 as base metal. The braze alloys of the study are used in production at Pratt & Whitney Canada and are: BCu-1, BAg-13a, BAu-4, BAu-6, Palnicro 36M, BNi-1a, BNi-2 and BNi-3. One of the requirements of the study was to stay close to what happens in production to have a better understanding of the mechanical and microstructural behavior of pieces on duty. First, some tests were running about wetting in order to observe the behavior of the studied braze alloys, because some were totally unknown. The wetting angles and the diameter of the spreading of a braze alloy droplet were noted for different associations of brazing furnace parameters. This was made for all the braze alloys. The study went on with tests for the watching and the understanding of brazed microstructures. In order to study the evolution of microstructures and the impact of brazing parameters for a wide range of industrial cases, the gap of the joints had different values between 0 and 175 μm and the assemblies were brazed 15 or 150 minutes in furnaces. To characterize these microstructures, the phases of brazed joints needed to be identified, listed, quantified and finally named. All these analysis used sophisticated devices such as scanning electron microscope or electron probe microanalyzer because of the presence of boron, chemical element, in some braze alloys. The wetting tests showed that all the braze alloys have an excellent wetting with a good flow for furnace brazing under partial pressure of inert atmosphere. Some values of furnace parameters were determined to optimize the wetting. The characterization of microstructures put in highlight that the joint had a repartition in different zones, often in common for the different braze alloys. The braze alloys of a same family have a very similar microstructure morphology but specificities are visible for each alloy and could make the difference for the mechanical behavior. Nickel braze alloys are very complex and comprise binary or ternary eutectic phases which go with other boride, silicide and precipitated phases. Gold base braze alloys show eutectic microstructures with very tiny needles of solid solutions of gold and nickel but with particular repartition. The Bag-13a alloy is mostly characterized by eutectic structure in lacelike whereas BCu-1 is made of a solid solution of copper with few scattered phases rich in chromium in the central line of the joint.

Date	23 Aug 2011
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Philippe Bocher (Supervisor)