On the Formation of Nanoscale Intergranular Intermetallic Compound Films in a Cu-5 at. pct Zr Alloy
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ALLOYING has been shown to be highly effective in producing thermally stable nanocrystalline metallic materials.[1,2] The precipitation of an intermetallic compound associated with alloying additions has been the most widely used microstructural control and strengthening strategies in both coarse- and fine-grained polycrystalline metals.[3,4] In principle, intermetallic compounds in many alloys precipitate out preferentially at grain boundaries (GBs) as precipitating at GBs can often provide a lower system energy. This GB precipitation behavior would be a critical phenomenon in fine-grained alloys. Consequently, understanding the formation of intermetallic compounds along GBs and within grains is an important consideration as it can
DENGSHAN ZHOU, HAO WANG, and DELIANG ZHANG are with the Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China and also with the School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China. Contact e-mail: [email protected] ONDREJ MURA´NSKY is with the Australian Nuclear Science and Technology Organization, Lucas Heights, NSW 2234, Australia and also with the School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. CHARLIE KONG is with the Electron Microscope Unit, The University of New South Wales, Sydney, NSW 2052, Australia. CHAO YANG is with the Shanghai Key Laboratory of Advanced High-temperature Materials and Precision Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. Contact e-mail: [email protected] Manuscript submitted March 1, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
affect low and high-temperature mechanical properties.[3,5,6] It has been shown that uniformly distributed nanoscale particles are commonly pursued in developing precipitation-hardened ultrahigh strength alloys.[7] In some cases, however, second-phase particles are designed deliberately to distribute inhomogeneously and have different size ranges.[8] The intermetallic compounds in a binary alloy can also be engineered to have different morphologies as well as distribute within grain interiors and at GBs respectively. For example, within grain interiors, the intermetallic compounds are discrete nanoprecipitates, while at (along) GBs nanoscale intergranular intermetallic compound films (NIICFs) can be formed. As one type of GB complexions,[9,10] NIICFs are in principle able to be obtained by manipulating complexion transformation. Specifically, the formation of the NIICFs can be induced by segregation of solute atoms to GBs. This is analogous to nanophase separation/ decomposition process involved during annealing or sintering of supersaturated solid-solution nanocrystalline alloys in which solute species segregate to GBs and form solute-rich phases along the GBs.[11–13] Previous studies have shown that segregation of Zr atoms at GBs can thermodynamically stabilize nanos
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