Processing, microstructure, and mechanical properties of (Nb)/Nb 5 Si 3 two-phase alloys
- PDF / 1,069,354 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 246 Views
I. INTRODUCTION
IN order to drastically improve the fuel efficiency and at the same time to effectively reduce CO2 emission in gas turbine engines, development of ultra-high-temperature structural materials has been attempted by many investigators to provide elevated temperature mechanical properties that are “beyond the nickel-base superalloys.” For such alloy design, it is natural to select a refractory metal element as a base, and previous research can be classified into the following: (1) heavily solid solution-hardened Nb, Mo, and W-base alloys;[1,2] (2) Nb or Mo alloys in which bcc solid solution matrix is strengthened by silicides or aluminides of a base metal;[3–11] and (3) precious metal alloys with L12 precipitates as strengtheners of fcc solid solution matrix, being analogous to the nickel-base superalloys.[12,13] The present authors have investigated the binary Nb-Si and the ternary Nb-Si-Ti systems within the scheme of the second type of the preceding classification. The binary Nb-Si phase diagram is shown in Figure 1.[14] The microstructure consisting of Nb solid solution, hereafter (Nb), and an intermetallic compound Nb5Si3 in a wide range of composition through various heat-treatment paths can be seen. The Ti additions to the binary system have been shown to stabilize the Nb3Si phase toward lower temperatures, because the Nb3Si YOSHISATO KIMURA and YOSHINAO MISHIMA are with the Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan. Contact e-mail: [email protected] HIROAKI YAMAOKA, formerly Graduate Student, Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, is with the Petroleum Association of Japan, Chiyoda-ku, Tokyo, 100-0004 Japan. NOBUAKI SEKIDO, formerly Graduate Student, Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, is with the Department of Materials Science and Engineering, University of Wisconsin–Madison, Madison, WI 53706. 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
phase forms a continuous solid solution with Ti3Si, the melting point of which is much lower than that of Nb3Si. The main feature of the as-cast microstructure of this class of alloys is the lamellar consisting of (Nb) and Nb5Si3 resulting from the eutectoid decomposition of a high-temperature phase, Nb3Si, and the additional feature is the primary solidification phase of either (Nb) or Nb5Si3. As the alloy composition is chosen t
Data Loading...
