On the Mechanism of Oxidation Resistance of W-Cr-Pd Alloys

Abstract:

While studying activation sintering of tungsten, Evans [5] and Ito and Furusawa [6] revealed that W-Cr-Pd alloys exhibit unexpected oxidation resistance at elevated temperatures. The role of palladium in stimulating oxidation resistance in W-Cr alloys is the main aim of the present contribution. As previously observed, at 800 °C these alloys form a relatively dense protective scale that consists of an inner layer of Cr₂O₃, an intermediate layer of Cr₂WO₆ and an external layer of WO₃. At 1200 °C only Cr₂WO₆ layer is found, since the Cr₂O₃ and WO₃ evaporate. To determine the role of paladium, W and W-Pd alloys were coated with Cr layers and undergone diffusion experiments. An extraordinary affinity between the Cr and Pd was revealed, manifested by extremely fast inward diffusion of Cr along grain boundaries. In a second experiment the dissolution of Cr into W grains at 1300°C was followed and found to take place preferentially along grain boundaries. These observations assess that the Pd segregated at grain boundaries provides fast diffusion channels for Cr to the free surface and it imparts the significant improvement of the oxidation resistance of W alloys, as suggested by Lee and Simkovitz [10-12].

• Periodical: Defect and Diffusion Forum (Volume 383)
• Pages: 133-141
• DOI: https://doi.org/10.4028/www.scientific.net/DDF.383.133
• Online since: February 2018
• Authors: Alon Kafri, Alexandra Makonovitsky, Roni Z. Shneck*
• Keywords: Fast Diffusion, Oxidation, Refractory Metals

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