Mechanical properties of alloys of IrNb and other high-temperature intermetallic compounds
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I.
INTRODUCTION
INTERMETALLIC compounds that are structurally useful at high temperature are being tested for potential aerospace and engine applications. The recent renewed interest in these compounds I1'2'3] is based on the prospects of high specific strength and specific modulus at elevated temperatures and the fact that there are hundreds of mechanically untested binary compounds. [4] In particular, diverse binary high-temperature materials have received intensive attention in a recent survey.t5] The stiffnesses of intermetallics are often greater than those of the metals from which they are formed t61 and they frequently maintain their strength better with increasing temperature than do disordered alloys, t7,81 The low specific gravities of many of them produce high specific stiffness and specific strength, two quantities that are critical to most uses in aircraft and rotating parts. This paper reports results of alloy variations on a few of the ordered intermetallics that were screened tSj as part of a search for future high-temperature materials. II.
SELECTION OF ALLOYS
The primary focus in this work is on alloys of the Llo compound IrNb, which was shown to be strong to high temperature and tough at room temperature, tSj The iridium makes this alloy dense and expensive. The challenge in alloying is to replace as much Ir as possible while retaining the desirable properties of IrNb. In this paper, lesser attention is given to alloys of four other binary compounds: A13Nb, A18Vs, Si2V, and Si3Ys. All four have specific gravities between 4 and 5 but suffer from low toughness at room temperature. However, A13Nb is less fragile than most intermetallics and has a finite brittle-to-ductile temperature, Tbu (900 ~ so that changes in Tou might be observed after alloying. A18V5 (Figure 2) has a still lower Toa ( - 5 0 ~ and very low specific gravity. Si2V also has finite Tbd (--900 ~ is strong at 1000 ~ and has very high elastic constants. Si3Y5 has some chisel toughness prior to annealing and is strong at 1000 ~ Each of the compounds has virtues
R.L. FLEISCHER, Physicist, K.K. DENIKE, Metallurgical Technician, and R.J. ZABALA, Metallurgical Specialist, are with General Electric Corporate Research and Development, Schenectady, NY 12301. R.D. FIELD, Metallurgist, is with GE Aircraft Engines, Evendale, OH 45215. Manuscript submitted February 1, 1990. METALLURGICAL TRANSACTIONS A
and defects; the hope is that the undesirable features can be improved by alloying. The compositions selected and obtained are given in Tables I and II, along with other data to be described shortly. The Tm's for the base binary compounds are > 1650 ~ so that likely operating temperatures as singlephase materials are expected to exceed 900 ~ (1650 F). t91
III.
PROCEDURE
A. Preparation of Samples Samples were arc melted into disk-shaped ingots using as high-purity components as were reasonably available. Although occasionally portions of the arc-melted ingots contained porosity that was visible on polished sections, the least porous fracti
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