The effect of low-pressure oxygen exposure on the high-temperature tensile impact ductility of a thorium-doped iridium alloy
- Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.
In an alloy of Ir-0.3 wt% W, the high temperature tensile impact ductility has been shown to be improved significantly by the addition of trace levels (30--100 wt ppm) of thorium. The beneficial effect of thorium stems from two factors: Thorium segregates strongly to the grain boundaries, resulting in increased cohesive strength of the boundaries and a change in fracture mode from intergranular in the undoped alloy to ductile transgranular fracture in the thorium-doped alloy. In addition to segregating to grain boundaries, thorium in excess of the solubility limit forms a second phase with a composition of Ir{sub 5}Th, which pins the grain boundaries and results in grain size refinement and improved ductility. Anomalous growth of near-surface grains has also been shown to occur as a result of exposure at high temperatures (1,280--1,330 C) to a low partial pressure of oxygen (1.3 mPa) for extended periods of time. Although uniform grain growth is known to be deleterious to the high-temperature tensile impact ductility of iridium-based alloys, it is not clear how anomalous growth in oxygen affects impact ductility. Therefore, as a further extension of the grain-growth studies, this report presents data on the high-temperature tensile impact ductility of an Ir-0.3wt%W + Th alloy which was exposed to a low partial pressure of oxygen (1.3 mPa) at 1,330 C and compares the data to results taken from specimens annealed in vacuum.
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 276164
- Journal Information:
- Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 2 Vol. 35; ISSN 1359-6462; ISSN XZ503X
- Country of Publication:
- United States
- Language:
- English
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