Synthesis and characterization of NbCr 2 Laves phase produced by spark plasma sintering
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S.M. Li State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China
K. Gao School of Mechatronics Engineering, Zhengzhou Institute of Aeronautical Industry Management, Zhengzhou, Henan 450000, China
D.Q. Gong College of Material Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China (Received 9 November 2015; accepted 30 December 2015)
The NbCr2 Laves phase was fabricated by spark plasma sintering (SPS) using spherical Nb and Cr powders. The experimental results revealed that increasing the sintering temperature to 1773 K can result in the formation of NbCr2 Laves phase as major phase, but it always appeared with trace amounts of Nb and Cr solid solutions. Based on the theoretical calculations, the residual of Nb and Cr solid solutions was attributed to the inhomogeneous distribution of temperature increase from the particle-contacting surface to the center of particle when pulsed current passed through. Moreover, the hardness and fracture toughness of the SPS-processed NbCr2 attained 14.05 6 0.67 GPa and 8.9 MPam1/2, which were 1.6 and 7.4 times of the as-cast NbCr2 Laves phase (1.2 MPam1/2). The formation of ductile Nb and Cr solid solutions and fine grains were considered to be the reason for the remarkable enhancements in mechanical properties.
I. INTRODUCTION
Laves-phase intermetallics are of great potential to be used as high-temperature structural materials.1–3 The NbCr2 is a typical Laves phase compound, and is of particular interest for such application due to its highmelting point (2003 K), high creep resistance, and excellent high-temperature strength.4–8 However, the NbCr2 Laves phase by itself generally has poor ductility and fracture toughness at room temperatures. Therefore, substantial attempts have been conducted to improve the fracture toughness of NbCr2 by composition designing and preparing method optimizing,4,5,9–11 and these works showed that the powder metallurgy route has a beneficial effect on the room temperature fracture toughness of NbCr2 Laves phase.4,5,8,9,11 The room-temperature fracture toughness of NbCr2 Laves phase was increased to 4.7 MPam1/2 by hot pressing,11 which is increased remarkably compared to the alloy prepared by conventional arc melting. However, the traditional powder metallurgy routes often produce relatively low sintered density, coarsen microstructure, and consequently degrade the desired mechanical properties.5,11 Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.6 380
J. Mater. Res., Vol. 31, No. 3, Feb 15, 2016
These problems can be alleviated by spark plasma sintering (hereafter abbreviated as SPS),12,13 which is a comparatively novel sintering process characterized by the synthesis of bulk materials from powders at low temperature with short heating, holding and cooling time when compared to conventional sintering processes.14–16 It is now successfully used to prepare advanced alloys, ceramics, c
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