Ductility and impact resistance of powder-metallurgical molybdenum-rhenium alloys
- PDF / 273,028 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 343 Views
I. INTRODUCTION
II.
GEACH and Hughes, in 1955, were the first to demonstrate the remarkable effect of rhenium on improving the room-temperature ductility of molybdenum. The ‘‘Re effect’’ was substantiated soon afterward by Jaffee et al.[2] More recently, Agnew and Leonhardt[3] reviewed the literature for Mo-Re and carried out experiments illustrating the important role of twinning for the high ductility of Mo-47.5 wt pct Re at temperatures as low as 180 °C. An important factor limiting the application of Mo-Re alloys is the scarcity and high price of rhenium. If the rhenium concentration could be significantly reduced below the typical 40 to 50 wt pct, more applications would likely emerge. Interestingly, according to Lundberg et al.,[4,5] the room-temperature tensile elongation of Mo-Re appears to have a pronounced maximum, approximately 50 pct, for rhenium concentrations between 10 and 15 wt pct. This might suggest Mo-13 wt pct Re alloys as a suitable substitute for the more expensive Mo-47.5 wt pct Re. The main motivation for the present work is to reappraise Lundberg et al.’s ductility maximum for Mo-13 wt pct Re by examining Mo-Re alloys with concentrations ranging from 5 to 47.5 wt pct Re. In addition, low-temperature and high strain rate (impact) tests were carried out. A further motivation to revisit the Re effect in molybdenum stems from the renewed interest in refractory metal silicide alloys for structural applications at ultra-high temperatures in air.[6] The successful application of these alloys requires a judicious balance between oxidation resistance at high temperatures and toughness at ambient temperatures. While rhenium will not have a beneficial influence on the former property, there is a possibility that it improves the latter by ductilizing the Mo-Si solid solution phase in Mo-Si-B alloys. [1]
GERHARD LEICHTFRIED, Manager IPR, is with Plansee SE, Technologiezentrum, A-6600 Reutte, Austria. JOACHIM H. SCHNEIBEL, Research Staff Member, is with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Contact e-mail: [email protected] MARTIN HEILMAIER, Professor, is with the Institute of Materials and Joining Technology, Otto-von-Guericke University Magdeburg, D-39016 Magdeburg, Germany. Manuscript submitted February 6, 2006. METALLURGICAL AND MATERIALS TRANSACTIONS A
EXPERIMENTAL PROCEDURE
A nominally pure molybdenum rod was fabricated by cold isostatic pressing of molybdenum powder with a metallic purity of 99.9 wt pct (carbon concentration typically , 10 mg/g) followed by sintering in hydrogen (dew point , 10 °C). The sintered Mo was processed by hot radial forging with an area reduction of 73 pct using WC hard metal tooling in air. The final diameter of the forged rod was 12 mm. Mo-Re alloys containing between 5 and 47.5 wt pct Re (Table I) were processed in the same way, except that the starting material was a proprietary Mo-Re composite powder (Plansee AG, Reutte, Austria) ensuring a highly homogeneous rhenium distribution. Any contamination due to
Data Loading...
