Microstructural characterization of multicomponent Nb-Ti-Si-Cr-Al-X alloys
- PDF / 1,071,211 Bytes
- 14 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 145 Views
INTRODUCTION
IN search of newer materials that can perform at elevated temperatures (;800 °C to 1200 °C), several intermetallics and materials based on refractory metals have been explored.[1] Intermetallics such as Ni3Al and g-TiAl have been found to possess attractive properties with their own shortcomings, whereas in comparison with these alloys, refractory metals based silicides (Nb-Si, MoSi2) exhibited better high-temperature strength and superior high-temperature creep properties, but very poor toughness and comparable oxidation resistance in some cases.[1–4] In order to improve the intrinsic toughness of the silicide-based materials, a multiphase design approach of developing a composite comprising the hard silicide phase distributed uniformly in a softer, solid solution b phase has been adopted.[1,3,4] In this context, Nb-Si in-situ composites consisting of b-Nb and Nb silicides have shown an attractive balance between high- and low-temperature mechanical properties.[3–8] However, the binary alloys exhibited poor oxidation resistance, and, in general, any alloying addition to improve the hightemperature oxidation leads to deterioration of the hightemperature mechanical properties of these materials.[7] It has thus become clear that a multicomponent approach is necessary to counterbalance the negative effects of one alloying element by the other.[3,7] In the binary Nb-Si system, the b-Nb 1 Nb5Si3 twophase field extends over a wide composition range from RAGHVENDRA TEWARI, Scientist, is with the Materials Science Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India. HYO-JIN SONG, Graduate Research Assistant, and VIJAY K. VASUDEVAN, Professor, are with the Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0012. Contact e-mail: [email protected] AMIT CHATTERJEE, Consultant, is with Materials and Processes, Rolls Royce Corporation, Indianapolis, IN 46206. Manuscript submitted December 10, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
0.6 to 37.5 pct Si, providing large flexibility for tailoring the microstructure. However, as the Si content is increased from 10 to ;16 at. pct, the mode of failure changes from mixed to brittle.[1] Therefore, in the current study, Si content has been kept below 10 at. pct in the basic composition of the alloy. The results of previous studies[3] have indicated that partial substitution of Nb by Ti leads to appreciable improvement in the oxidation resistance of these alloys. The Ti also improves the intrinsic ductility and hence the toughness of the material, but, on the other hand, reduces the melting point and the high-temperature strength of the alloys. Therefore, to counteract the latter effect of Ti, elements such as Zr and Hf were added, as these provide strong solid solution strengthening of the Nb-based solid solution phase.[3,8] Both Al and Cr have also been reported to improve the high-temperature oxidation properties of the Nb alloys. Tungsten was added to improve strength by solid solution strengthen
Data Loading...
