Ultrahigh strength Al-based amorphous alloys containing Sc
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Amorphous metallic alloys possess high strength characteristics, which are superior to crystalline materials. Here we report an influence of Sc addition on glass-forming ability, glass-transition behavior, supercooled liquid region, and mechanical properties of an Al84Y9Ni5Co2 glassy alloy. This paper also aims to present a promising (Al0.84Y0.09Ni0.05Co0.02)95Sc5 amorphous alloy. This alloy has an ultrahigh tensile fracture strength exceeding 1500 MPa, which surpasses those for all the other Al-based fully crystalline and amorphous alloys reported to date, in addition to high Young’s modulus of 78 GPa. The fracture surface of this new alloy exhibited vein pattern typical for amorphous alloys with good ductility, and multiple shear bands were observed on the lateral surface. The ultrahigh tensile strength of the (Al0.84Y0.09Ni0.05Co0.02)95Sc5 amorphous alloy results from an increase in the interatomic constraint force by the addition of Sc, an element having highly negative enthalpy of mixing with Al, Ni, and Co and the highest chemical affinity with Al among the alloying elements.
I. INTRODUCTION
Technical progress requires strong and light materials. Al-based amorphous alloys possess high tensile strength as well as high specific strength due to low density of Al and hence have attracted increasing interest for a large number of technical applications as light and highstrength structural materials, for example for aerospace applications and so on. The most prominent group of Al-based amorphous alloys includes binary Al–RE (RE ⳱ rare earth metals)1 and ternary Al–RE–TM (TM ⳱ transition metals)2–4 system alloys that can be produced by the melt-spinning technique. These alloys have already been commercialized. The amorphous alloys in ternary Al–Y–TM system were found to possess high strength and good bending ductility (i.e., showing ability to be bent through 180° without fracture).5,6 The addition of Co to Al–Y–Ni alloys increased their mechanical strength. Fine precipitates of Al solid solution (␣–Al), almost pure Al, formed by devitrification of the glassy matrix were found to increase tensile strength without reducing bending ductility.7 The devitrification of Al– RE–Ni–Co amorphous alloys was found to be strongly influenced by the presence of supercooled liquid.8 Recently the influence of full or partial replacement of Y
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Address all correspondence to this author. e-mail: [email protected] Family name can also be spelled Luzgin DOI: 10.1557/JMR.2004.0206 J. Mater. Res., Vol. 19, No. 5, May 2004
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in the Al85Y8Ni5Co2 alloy [all alloy compositions are given in nominal atomic percents (at.%)] by other RE metals was investigated.9 It has also been reported that the Al–Y–Ni–Co and Al–Y–Nd–Ni–Co amorphous alloys exhibit different devitrification behavior above and below the glass-transition temperature.10 It was also shown that the electronegativity11 of the constituent RE metal is an important factor influencing glass formation and the temperature interval of th
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