Microstructural evolution and mechanical properties of Cr-Ru alloys
- PDF / 1,573,625 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 65 Downloads / 222 Views
I. INTRODUCTION
IN the search for new materials to be used as components in gas turbine engines, considerable interest has been shown in chromium (Cr) and Cr-rich alloys since the late 1950s because Cr has a high melting point (1863 °C) and good oxidation resistance. Its low density (20 pct less than that of most Ni-base alloys) and high thermal conductivity (2 to 4 times higher than that of most Ni-base superalloys) are also attractive since they may result in increased efficiency.[1–6] However, the implementation of Cr-rich alloys as a viable substitute for Ni-base alloys has been impeded by their poor ductility at ambient temperature, or high ductile-to-brittle transition temperature (DBTT), which for unalloyed recrystallized Cr with commercial purity is approximately 150 °C in tension.[7,8,9] Below the DBTT, Cr has virtually no ductility. There have been numerous studies concerned with decreasing the DBTT or improving the poor ductility of Cr and Cr-base alloys at ambient temperature. Some results indicate that the presence of the high DBTT is associated with impurities, particularly nitrogen content, because the DBTT is lowered as purity increases.[10,11] Therefore, purification is an obvious way to decrease the DBTT and thus increase the ductility at ambient temperature for Cr and Cr-base alloys. According to theoretical and experimental observations, the reduction of nitrogen (and possibly other similar elements) to extremely low levels such as 0.0001 pct (compositions will be stated in atomic percent unless otherwise noted) should result in adequate ductility for all conditions.[1] Such purification is possible in principle, but it is doubtful whether it can be achieved and maintained in practice. Another obvious way to improve the ductility at ambient temperature is either to stabilize or to remove the interstiY.F. GU, Y. RO, and T. KOBAYASHI, Senior Researchers, and H. HARADA, Senior Researcher and Project Leader, are with the National Institute for Materials Science (NIMS), Tsukuba-Shi, Ibaraki 305-0047, Japan. Contact e-mail: [email protected] This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A
tial impurities by adding a scavenging element. Geach and Hughes first observed in 1955 that alloying of tungsten and molybdenum with a relatively high concentration of rhenium (Re), at least 20 pct, can considerably improve their fabricability and low-temperature ductility as compared to the corresponding unalloyed metals.[12] This Re-ductilizing effect was later shown by Klopp et al.[13] to apply to Cr as well. Several non-Re systems, such as Cr-Fe, Cr-Co, Cr-Ir, and Cr-Mn appear to show an analogous effect in that they exh
Data Loading...
