The Effect of Cu-Macroalloying Additions to Rapidly Solidified NiAl Intermetallic Compound
- PDF / 196,732 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 109 Downloads / 199 Views
The Effect of Cu-Macroalloying Additions to Rapidly Solidified NiAl Intermetallic Compound J. Colin, B. Campillo, C. Gonzalez, O. Alvarez-Fregoso and J. A. Juarez-Islas Instituto de Investigaciones en Materiales-UNAM Circuito Exterior S/N, Cd. Universitaria Mexico, D. F., 04510, MÉXICO. ABSTRACT The effects of two variables on the NiAl intermetallic compound were studied: 1) copper macroalloying additions and 2) rapid solidification processing. For that purpose, several NiCuAl alloys were vacuum induction melted and rapidly solidified by using a copper wheel, rotating at 15 m/s, under an argon atmosphere. Chemical analysis of as-rapidly solidified ribbons indicated, that four alloy compositions lie in the β-(Ni, Cu)Al field, one alloy composition lie in the boundary of the β-(Ni, Cu)Al/(Ni, Cu)2Al3 fields, one alloy composition lies in the boundary of the β-(Ni, Cu)Al/β-(Ni, Cu)Al + (Ni, Cu)3Al fields and two alloy compositions lie in the β-(Ni, Cu)Al + (Ni, Cu)3Al field. Transmission electron microscopic observations carried out in asrapidly solidified ribbons, revealed the presence of at least three main structures: i) β-(Ni, Cu)Al, ii) β-(Ni, Cu)Al + martensite (Ni, Cu)Al and iii) (Ni, Cu)3Al + martensite (Ni, Cu)Al. Microhardness Vickers and tensile test data indicated that alloys with a β-(Ni, Cu)Al + martensite (Ni, Cu)Al microstructure have improved room temperature ductility, reaching values of elongation up to 3.28 %. INTRODUCTION It is well known, that NiAl intermetallic compound possesses high melting temperature, low density, good oxidation resistance, metal-like properties, attractive modulus, high thermal conductivity and low raw material cost. These characteristics place it, as an interesting and potential structural material, for a wide range of applications, including those for high temperature in aerospace structures. The NiAl intermetallic compound shows a simple ordered B2 (cP2) CsCl crystal structure and a wide range of composition stability [1-3]. This B2 structure is stable for large deviations from stoichiometry with a significant long-range order [4]. In intermetallic compounds, different atomic species occupy different regular lattice sites and the strong bonds between their atoms result in attractive properties. In the NiAl intermetallic compound, the strong bonds and the lack of five independent slip systems, on the basis of ordered structure, give rise to low temperature embrittlement [5] and inadequate strength and inadequate creep resistance at elevated temperature [6]. Most ordered B2 intermetallic compounds exhibit at room temperature, a minima in both their yield strength and hardness at, or close to their stoichiometric composition [7]. In the NiAl intermetallic compound, the strength increases on either side of the stoichiometry composition [8]. Polycrystalline NiAl is generally referred as an intermetallic compound which is brittle at room temperature [9], and limited elongation of about 2% has been observed in stoichiometric composition. Since intermetallic compounds possesses a
Data Loading...
