Effect of Si Addition on Microstructure and Mechanical Properties of Dual Two-Phase Intermetallic Alloys Based on the Ni
- PDF / 7,638,926 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 80 Downloads / 247 Views
Effect of Si Addition on Microstructure and Mechanical Properties of Dual Two-Phase Intermetallic Alloys Based on the Ni3Al-Ni3V Pseudo-Binary Alloy System Yuki Hamada, Yasuyuki Kaneno, Hiroshi Numakura and Takayuki Takasugi Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan. ABSTRACT The effect of Si addition on microstructure and mechanical properties of dual two-phase intermetallic alloys was investigated. Si was added to the base alloy composition Ni75Al9V13Nb3 + 50 wt. ppm B by three substitution ways in which Si was substituted either for Ni, for Al and for V, respectively. The alloys added with 1 at.% Si showed a dual two-phase microstructure composed of Ni3Al (L12) and Ni3V (D022) phases, while the alloys added with over 2 at.% Si exhibited the same dual two-phase microstructure but contained third phases. The third phases were G phase (Ni16Si7Nb6) and A2 phase (the bcc solid solution consisting of Nb and V). Yield and tensile strength of the 1 at.% Si-added alloys were high in the alloy in which Si was substituted for Al but low in the alloys in which Si was substituted for Ni or for V, in comparison with those of the base alloy. Tensile elongation was lower than that of the base alloy irrespective of substitution ways. The density of the Si added alloys was close to or slightly lower than that of the base alloy. Oxidation resistance of the Si added alloy was increased. Si addition to the dual two-phase intermetallic alloys is beneficial for reducing the density and enhancing the oxidation resistance without a harmful reduction of strength properties. INTRODUCTION Geometrically close packed (GCP) Ni3X intermetallic phases generally exhibit high phase and microstructural stabilities up to their melting point because of low atomic diffusivity originating from their close packed structures [1-4]. Thereby some of these intermetallic phases are used as strengthener for conventional Ni base superalloys. Although Ni base superalloys exhibit excellent mechanical strength at high temperatures, further improvement of hightemperature strength is required in terms of energy conversion efficiency, which increases with increasing combustion temperature. However, further enhancement of strength of the Ni base superalloy is not so easy because the Ni solid solution phase becomes soft at high temperature. In order to overcome this drawback for the Ni base superalloys, the present authors have developed a Ni-based two-phase intermetallic alloy [5-7]. This intermetallic alloy is composed of two ordered intermetallics of Ni3Al (L12) and Ni3V (D022): it shows an upper two-phase microstructure consisting of primary Ni3Al precipitates and the channel composed of Ni solid solution at high temperature. The Ni solid solution in the channel region decomposes into Ni3Al (L12) and Ni3V (D022) by a eutectoid reaction at low temperature (i.e., lower two-phase microstructure). This alloy has a highly crystallographic coherency among the constituent phases, and a high microst
Data Loading...
