Microstructure and mechanical properties of NiAl-based hypereutectic alloy obtained by liquid metal cooling and zone mel
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Shen State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, China
Yunpeng Zhang and Hengxin Xu School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, Shaanxi, China
Hengzhi Fu State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, China (Received 8 December 2015; accepted 1 February 2016)
The microstructure, room temperature compressive property, and elevated temperature tensile property of directionally solidified NiAl–Cr(Mo)–(Hf,Dy) hypereutectic alloy were investigated. The directional solidifications of liquid metal cooling technique (LMC) and zone melted liquid metal cooling technique (ZMLMC) were adopted. In the LMC alloy, the well-aligned and fully eutectic lamellar structure parallel to the growth direction is obtained. The interlamellar spacing gradually decreases with increasing the withdrawal rate, and the compressive yield strength gradually increases. In the ZMLMC alloy, the eutectic lamellar structure is disordered and not parallel to the growth direction, and the quantities of Cr(Mo) primary phases are observed. Compared to the ZMLMC alloy, the LMC alloy has a better combination property because of the well-aligned lamellar structure. The observations of crack propagation and fracture surface are performed to better understand the fracture behavior.
I. INTRODUCTION
NiAl–Cr(Mo) eutectic alloy exhibits a promising room temperature and elevated temperature properties1 and possesses some advantages, such as a high melting point, good thermal conductivity, and excellent oxidation resistance.2 However, compared to Ni-based superalloy, NiAl–Cr(Mo) eutectic alloy is not satisfied for the application of aeroengine blade due to the lower elevated temperature strength. It was reported that the refractory Cr(Mo) phase can effectively improve the room temperature brittleness and elevated temperature strength of NiAl through the common bridging mechanism of Cr(Mo) phase,1,3–5 and the volume fraction of Cr(Mo) phase in NiAl–32Cr–6Mo hypereutectic alloy is higher than that of NiAl–Cr(Mo) eutectic alloy.6 Therefore, we take NiAl–32Cr–6Mo hypereutectic alloy as a matrix alloy in this paper. Guo and Cui et al.7–9 reported that the addition of Hf element (0.5 at.%) enhances the elevated temperature strength of NiAl–Cr(Mo) eutectic alloy, but
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.61
causes the room temperature brittleness due to the existence of Heusler phase at NiAl/Cr(Mo) interface. Thus, we attempt to reduce the additive content of Hf to maintain a good combination property in this paper. Furthermore, the rare earth element Dy may improve the property of the alloy by the microstructural refinement and interface purification (enhancing interface strength).10–14 In addition, the well-aligned lamellar structure can be obtained for NiAl–Cr(Mo) eutectic system alloy by directional so
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