Brazing a Graphite Composite to Molybdenum Alloy TZM Using Active Copper-Based Filler Metals with Chromium Additive

Brazing a Graphite Composite to Molybdenum Alloy TZM Using Active Copper-Based Filler Metals with Chromium Additive The paper presents issues of brazing the graphite composite CFC 222 with the molybdenum alloy TZM. Both materials demonstrate significant differences in physicochemical and mechanical properties that significantly affect brazing conditions and properties of the brazed joints. The performed brazing operation was preceded by a wettability test that decided selection of the filler metal. From among various copper-based filler metals, the best appeared a copper brazing filler metal with some addition of active chromium. Presented is a model of the wedge test, helpful at optimising the brazing process of two materials with different properties. Width of the brazing gap was selected on the ground of metallurgical examinations after the wedge test and transferred to the joint with a parallel gap. Applied were various forms of copper-based filler metals in that chromium was present as an alloying component, a component of the brazing paste, powder between copper covers and as a galvanic coating of a pure-copper strip. Evaluation of brazed joints of the composite CFC 222 with the TZM alloy is presented on the grounds of metallographic examinations by means of light microscopy and microhardness measurements, electron microscopy, EDX analysis of elements and XRD analysis of phase composition of the reactive zone.