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Chromium (Cr) metal has attracted a great amount of attention as a possible base for alloy systems since the late 1950s due to its higher melting point (1863 °C), lower density, and higher thermal conductivity than Ni-base superalloys.[1–5] In general, however, the implementation of Cr-base alloys as a viable substitute for Ni-base alloys has been impeded by its high ductile-to-brittle transition temperature (DBTT), which for unalloyed re-crystallized Cr with commercial purity is approximately 150 °C in tension. Below the DBTT, Cr has almost a complete lack of ductility.[6,7,8] Some research indicates that the presence of the DBTT in Cr is associated with impurities, particularly nitrogen content, because the DBTT decreases as purity increases.[9,10] Therefore, an obvious way to effectively improve the ductility at low temperature is either to stabilize or to remove the interstitial impurities by adding a scavenging element. The work described in this article is a part of a board investigation to survey some of the binary Cr-rich alloys in order to discover the most promising base for further alloying to produce improved ductility at ambient temperature and enough strength at high temperature. In this article, we first report that silver (Ag) is an effective alloying element to improve the tensile ductility of Cr at room temperature. Starting materials were Cr (99.87 at. pct) and Ag (99.98 at. pct). Five compositions (up to 3 at. pct Ag) were chosen for this study. For each composition, the raw materials were mixed and prepared as a 50-g button ingot by arc melting under argon in a vacuum furnace. Homogeneity of the ingots was ensured by re-melting the ingots at least 5 times. The nominal and analysis compositions for the Cr and the Cr-2 at. pct Ag alloy are shown in Table I. We are surprised that only about 5 pct added Ag was really alloyed with Cr in the Cr-2 at. pct Ag alloy (about 0.24 mass pct Ag) and the other was lost during the melting process. To obtain information about the melting temperatures of the tested alloys as well as other solid-state phase transformations that may occur during heating and cooling, hightemperature differential thermal analysis (DTA) was performed,

Y.F. GU and Y. RO, Senior Researchers, and H. HARADA, Project Leader and Senior Researcher, are with the High Temperature Materials 21 Project, National Institute for Materials Science, Ibaraki 305-0047, Japan. Contact email: [email protected] Manuscript submitted April 15, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A

using a high-temperature instrument, on as-cast samples (approximately 3 mm in diameter and 5 mm in height). The plate-shaped tensile specimens with a gage length approximately 2.2
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0.5 mm were machined from the ingots by using an electron-discharge machine. The surfaces of the specimens were carefully machined and finally polished by 1000-grit SiC grinding paper and cleaned in acetone before testing. The average grain size for all as-cast specimens was about 250 m. The tensile tests were conducted using a te