On the development and investigation of quaternary Pt-based superalloys with Ni additions
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I. INTRODUCTION
CURRENTLY, precipitation-hardened Ni-based superalloys dominate high-performance applications, where they are exposed to temperatures up to 90 pct of their incipient melting points.[1] Their extremely good creep resistance is caused by a two-phase microstructure consisting of L12-ordered precipitates with cube shape, which are coherently embedded in a face-centered cubic (fcc) Ni-rich matrix. However, a further increase of operation temperature is limited in view of the incipient melting temperatures of Nibased superalloys. In this context, high melting platinum group metals Ir, Rh, and Pt are of rising interest for very high-temperature applications.[1–20] A small number of research groups worldwide try to copy the highly successful strengthening mechanism of Ni-based superalloys in new high-temperature materials based on platinum group metals. Drs. Harada and Yamabe-Mitarai, National Institute for Materials Science (NIMS, Tsukuba, Japan)[2–10] have been developing Ir- and Rh-based superalloys, so-called “refractory superalloys,” since 1995. However, a major drawback of Ir-based alloys is still their limited low-temperature ductility. The element Pt shows a better ductility than Ir and Rh at room temperature. Although pure Pt melts already at 1772 °C, excellent high-temperature corrosion and oxidation resistance make it a promising candidate to serve as a base for a new family of superalloys. Research groups in South Africa[11–19] and Germany[1,11,20] are M. WENDEROTH, Doctoral Student, U. GLATZEL, Professor, and R. VÖLKL, Senior Researcher, are with the Metallic Materials Department, University Bayreuth, D-95440 Bayreuth, Germany. Contact e-mail: [email protected] L.A. CORNISH, Head, and R. SÜSS, Senior Engineer, are with the Advanced Materials Group, Physical Metallurgy Division, MINTEK, 2125 Randburg, South Africa. S. VORBERG, Doctoral Student, and B. FISCHER, Professor, are with the University of Applied Sciences Jena, D-07745 Jena, Germany. 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
investigating refractory superalloys based on the system Pt-Al. On the Pt-rich side of the Pt-Al system, the intermetallic phase Pt3Al called is in equilibrium with a fcc Pt-rich solid solution called (Figure 1(a)). The Pt-rich side of the Pt-Al phase diagram is very similar to the Ni-rich side of the Ni-Al system (Figure 1(b)), which is the base for precipitation hardening in Ni-based superalloys. L12-Pt3Al does not show a flow stress anomaly like L12Ni3Al; i.e., the mechanical strength of L12-Pt3Al does not pass through a maximum with increasing temperature.[23] Nevertheless, L12-Pt3Al is stronger than Ni3
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