Alloying Effect on Mechanical Properties and Oxidation Resistance of Cold-Rolled Ni 3 (Si,Ti) Foils
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1128-U05-31
Alloying Effect on Mechanical Properties and Oxidation Resistance of Cold-Rolled Ni3(Si,Ti) Foils Yasunori Fujimoto, Yasuyuki Kaneno and Takayuki Takasugi Department of Materials Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
ABSTRACT Four kinds of L12 -type Ni3 (Si,Ti) intermetallics alloyed with a quaternary element X (X: Al, Cr, Co and Mo) were warm rolled accompanied by intermediate annealing and then cold rolled to thin foils. The effects of the alloying elements on microstructure, tensile properties and oxidation resistance of the cold-rolled Ni3 (Si,Ti) foils were investigated. The Al-alloyed Ni3 (Si,Ti) showed an L12 single-phase microstructure, while the Cr-, Co- and Mo-alloyed Ni3 (Si,Ti) exhibited a two-phase microstructure consisting of L12 and fcc Ni solid solution. Room-temperature strength of the Ni3 (Si,Ti) foils was slightly enhanced by the addition of the quaternary elements, whereas high-temperature strength was significantly enhanced especially by the addition of Mo and Co. High-temperature tensile elongation was remarkably improved by the additions of all the elements investigated. On the other hand, the oxidation resistance was improved by the addition of Al and Cr.
INTRODUCTION Many ordered intermetallic alloys and compounds show a poor ductility due to their complex crystal structures and lack of sufficient slip systems. However, some ordered alloys with L12 structure such as Ni3 Al micro-alloyed with boron [1], Ni3 Si alloyed with Ti (i.e., Ni3 (Si,Ti)) [2] and Co3 Ti [3] show a fairly good ductility even at low temperature, and thereby heavy cold working is applicable to these intermetallic alloys. It has been reported that Ni3 Al foils were fabricated by heavy cold rolling of directionally solidified single crystals [4] and also by heavy cold rolling at liquid nitrogen temperature and subsequent annealing of coarse grained cast materials [5]. Recently, the present authors have found that Ni3 (Si,Ti) foils as well as Co3 Ti and Ni3 Al foils could be fabricated from arc-melted polycrystalline materials by thermomechanical processing and subsequent heavy cold rolling [6]. The obtained Ni3 (Si,Ti) foils were found to exhibit good mechanical properties: low- and intermediate-temperature tensile strength is extremely superior to that of conventional alloys such as nickel-based alloys and stainless steels. However, further improvement is desired for the high-temperature tensile properties and the oxidation resistance because these properties are important for hightemperature structural materials. Earlier studies have shown that some interstitial and substitutional elements were useful for the improvement of the mechanical properties of the warm-rolled Ni3 (Si,Ti) sheets [7-9]. However, the effect of alloying elements on the mechanical and chemical properties of the cold-rolled Ni3 (Si,Ti,) foils has been little studied [10]. In this study, microstructures, tensile properties and oxidization resistance of the cold-rolled Ni3 (Si,Ti) foils
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