Mechanical Properties and Nanocrystallization Behavior of Al-Ni-La Alloys
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A number of Al-based amorphous alloys with Al content over 80 at. pct have been synthesized by rapid solidification techniques.[1,2] Among these, Al-Ni-Ln (Ln = Y, La, Ce, Nd, or Gd) amorphous alloys show good glass forming ability and wide glass formation range.[3] These amorphous alloys are ductile and possess tensile stress up to 2 to 2.5 times that of the best conventional precipitation-hardened Al alloy. By partially crystallizing the as-quenched Al-based amorphous alloys, nanosized crystals could homogeneously precipitate in the matrix. Such composite microstructure further enhances substantially the tensile stress, up to 1.5 times, without embrittlement.[3–5] For example, a tensile fracture stress as high as 1560 MPa has been reported in an Al88Ni9Ce2Fe1 amorphous alloy.[3] These favorable properties of the alloy deteriorate if the size of the precipitates exceeds the range by a few nanometers. RINA SAHU, Senior Research Fellow, and K.L. SAHOO, Scientist, are with the National Metallurgical Laboratory, Jamshedpur-831007, India. Contact e-mail: [email protected] S. CHATTERJEE, Professor, is with the Department of Metallurgical and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah-711103, India. This article is based on a presentation given in the symposium entitled ‘‘Mechanical Behavior of Nanostructured Materials,’’ which occurred during the TMS Spring Meeting in San Francisco, CA, February 15–19, 2009, under the auspices of TMS, the TMS Electronic, Magnetic, and Photonic Materials Division, the TMS Materials Processing and Manufacturing Division, the TMS Structural Materials Division, the TMS Nanomechanical Materials Behavior Committee, the TMS Chemistry and Physics of Materials Committee, and the TMS/ASM Mechanical Behavior of Materials Committee. Article published online February 6, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
It has been reported that the nanocrystalline materials can be consolidated and can retain useful strength at elevated temperatures.[6] The formation of nanometer size Al particles in amorphous Al-Ni-Ce,[7] Al-Ni-Y,[8,9] Al-Ni-Sm,[10] and Al-Ni-Mischmetal[11] alloys is mainly controlled by a grain growth process. Gangopadhyay and Kelton[12] investigated the crystallization process in Al-Ni-RE (RE = rare earth elements) amorphous alloys and found that crystallization products depend on the radius of the RE atoms. They showed that alloys containing smaller radius RE elements produce fcc-Al and larger radius RE elements produce metastable intermetallic phases as primary crystallization product. Zhuang et al.[13] reported the eutectic crystallization of fcc-Al and metastable bcc-(AlNi)11La3-like phase in Al89Ni5La6 alloy. Sahoo et al.[14] reported that the primary crystallization pathway depends not only on the atomic radius but also on the amount of La content in Al-Ni-La amorphous alloys. A number of publications[3,12] regarding the stability and the crystallization kinetics of various Al-TM-RE amorphous alloys are available; however, information
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