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Our research this past year focused on a thorough characterization of the effects of hydrogen exposure temperature on the mechanical properties of a series of palladium-silver (Pd/Ag) alloys. In particular, we investigated Pd/Ag alloys that were 5 weight % silver, 15 weight % silver, and 25 weight % silver. For each alloy studied, hydrogen exposure occurred over an extended temperature range. The characteristics measured were yield strength, ultimate strength, elongation at failure, and microhardness. The goal of the project is to see if the detrimental effects of hydrogen embrittlement can be mitigated in these alloys.

The initial phase of the work was a characterization of each alloy in a well-annealed state prior to any hydrogen exposure. The results of these investigations were as expected. The presence of silver in the alloy resulted in solid-solution strengthening as shown in the following table: 

The effects of hydrogen exposure on these properties were found to be quite dependent on the silver content of the alloy.  Of significant note was the finding that the properties of the Pd/Ag (25 weight %) alloy did not change as a result of exposure to hydrogen at any temperature studied. This alloy appears to be completely resistant to hydrogen embrittlement over the entire temperature range studied.

Both the Pd/Ag (5 weight %) and Pd/Ag (15 weight %) did show changes in the above properties over a portion of the temperature ranges studied. The Pd/Ag (5 weight %) alloy showed significant strengthening and embrittlement up to a hydrogen exposure temperature of 525 K, with the amount of strengthening and embrittlement being temperature dependent. At low hydrogen exposure temperatures, the decrease in total elongation (compared to the annealed alloy) was ~ 75 %, indicating very pronounced embrittlement. Interestingly, for hydrogen exposure temperatures above 525 K, the properties of the Pd/Ag (5 weight %) alloy were unchanged from those of the annealed alloy. Thus this alloy appears to be resistant to hydrogen embrittlement above 525 K.

The Pd/Ag (15 weight %) alloy showed significant strengthening and embrittlement up to a hydrogen exposure temperature of 425 K, with the amount of strengthening and embrittlement being temperature dependent. At low hydrogen exposure temperatures, the decrease in total elongation (compared to the annealed alloy) was ~ 60 %, indicating very pronounced embrittlement. For hydrogen exposure temperatures above 425 K, the properties of the Pd/Ag (15 weight %) alloy were unchanged from those of the annealed alloy. Thus this alloy appears to be resistant to hydrogen embrittlement above 425 K.

There appears to be a trend in susceptibility to hydrogen embrittlement that is dependent on the silver content of the Pd/Ag alloy. That trend is that as the silver content of a palladium-silver alloy increases, the larger is the temperature range over which the alloy is resistant to hydrogen embrittlement.