In Situ High-Energy X-Ray Diffraction Study of Load Partitioning in Nb/NiTi Nanocomposite Plate
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INTRODUCTION
EXTENSIVE research has been devoted to in situ metal matrix nanocomposites due to their remarkable mechanical properties and their great potential for widespread applications.[1–7] It has been demonstrated that the load-partitioning behavior between nano-reinforcements and metal matrix plays a dominant role in determining the mechanical properties of the metal matrix composites (MMCs). So far extensive knowledge has existed concerning the load-partitioning behavior in the MMCs where the metal matrix plastic flow occurs primarily by dislocation slip.[8–12] It is found that the intrinsic mechanical properties of reinforcement cannot be fully performed when the metal matrix plastically deforms by dislocation slip. As we know, some metals plastically deform by the atomic lattice shear plastic deformation mechanism without dislocation slip, such as stress-induced martensitic transformation (SIMT) and martensite reorientation (MR), rather than the dislocation slip plastic deformation mechanism. It can be speculated that the load transfer between nano-reinforcement and metal matrix during deformation by the atomic lattice shear will be different from that by dislocation slip. However, detailed knowl-
CUN YU, XIAOBIN SHI, and ZHENYANG LIU, Ph.D. Students, LISHAN CUI, Professor, and SHIJIE HAO and DAQIANG JIANG, Associate Professors, are with the State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, P.R. China. Contact e-mail: [email protected] ZUNPING LIU, Engineer, and YANG REN, Beam Scientist, are with the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. Contact e-mail: [email protected] DENNIS E. BROWN, Associate Professor, is with the Department of Physics, Northern Illinois University, De Kalb, IL. Manuscript submitted February 15, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
edge about the load transfer in nanocomposites during atomic lattice shear plastic deformation is limited. It is known that NiTi shape memory alloys are able to plastically deform by SIMT or MR during testing at different temperatures.[13,14] In this paper, the uniaxial tensile deformation of a nanocomposite plate consisting of Nb nanosheets embedded in a NiTi matrix was investigated at different temperatures by in situ highenergy X-ray diffraction. It is found that the Nb nanosheets, with a volume fraction of only 13 pct, can undertake an applied stress of ~90 pct as the NiTi matrix deforms by MR or SIMT, which is larger than that of the metal matrix plastically deforming by dislocation slip.
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EXPERIMENTAL
An alloy ingot of 27 kg in weight with a nominal composition of Ti44Ni47Nb9 (at. pct) was prepared by vacuum induction melting. The raw materials used were of commercial purity Ni (99.96 wt pct), Ti (99.90 wt pct), and Nb (99.99 wt pct). A plate 40 mm in thickness was cut from the ingot and was hot-rolled to 2 mm at 844 K (850 C). After hot-rolling, the plate was repeatedly cold-rolled into a thin plate 0.3 mm in thickness at room temperature with a short time (~5 minutes) int
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