Evolution of microstructure in TiC/NiCr cermet induced by electropulsing
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M.L. Sui Shenyang National Laboratory for Materials Science and International Center for Materials Physics, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of China
Y.Z. Zhou, J.D. Guo, G.H. He, and D.X. Li Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, People’s Republic of China (Received 21 January 2003; accepted 1 April 2003)
Microstructures of a TiC/Ni80Cr20 cermet, subjected to single high-current-density electropulsing, were characterized by x-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. Under the electropulsing, the shift of NiCr peaks versus the reverse change of TiC counterparts illustrates that the treatment gives rise to strong thermal stress impacting on the cermet. The stress, accompanied by the transient rise of temperature, led to microstructural evolutions of the cermet. Some nanostructured TiC grains, consisting of many nanocrystallites with small-angle grain boundaries, developed during electropulsing. Also, many regions teemed with coexisting nanosized TiC and NiCr crystallites, which possessed good bonding. Within the NiCr regions, large amounts of deformation twins were produced by the electropulsing.
I. INTRODUCTION
The properties of materials depend strongly on their microstructures. Therefore, an understanding of the microstructural evolution of a material is essential for any processing activity. Electropulsing, or electrical discharge, is one of the increasingly important methods for materials processing. Published works on electropulsing include electroplasticity,1 electromigration,2 enhanced powder densification,3 accelerated mechanical milling,4 amorphous crystallization,5,6 and healing crack and damage.7,8 Despite the great importance of electropulsing in technology and nature, fundamental mechanisms by which they occur are generally not well understood.9 Therefore, it is important to reveal the microstructural evolution of conventional materials under electropulsing to gain insight into the essence of electropulsing. Recently, we have successively reported some new phenomena through which nanophases were formed in several different coarse-grained materials under highcurrent-density electropulsing. Under the electropulsing,
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 7, Jul 2003
␣–Cu(Zn) and ⬘–(CuZn) nanophases, 10 nanosized ␥–Fe,11 and nanostructured TiC12 were formed in the supersaturated solution ␣–Cu(Zn) alloy, low-carbon steel, and TiCp-reinforced NiCr alloy, respectively. These results reveal that high-current-density electropulsing can be a novel method to synthesize nanostructured materials directly from their coarse-grained counterparts. However, there currently exist few reports about detailed investigations of microstructures at the atomic level in the materials under the electropulsing. In the curren
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