Enhanced thermal stability of the devitrified nanoscale icosahedral phase in novel multicomponent amorphous alloys
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P.J. Warren Department of Materials, Oxford University, Oxford, OX1 3PH Oxford, United Kingdom
B. Cantor Vice-Chancellor’s Office, University of York, Heslington, YO10 5DD York, United Kingdom
J. Eckertb) FG Physikalische Metallkunde, FB 11 Material- und Geowissenschaften, Technische Universität Darmstadt, D-64287 Darmstadt, Germany (Received 2 August 2005; accepted 3 October 2005)
In this paper, details are given for the structural evolution of (Ti33Zr33Hf33)70(Ni50Cu50)20Al10, (Ti25Zr25Hf25Nb25)70(Ni50Cu50)20Al10, and (Ti33Zr33Hf33)70(Ni33Cu33Ag33)20Al10 amorphous alloys, part of wider program of alloy development by equiatomic substitution. All three alloys initially crystallize by forming a nanoscale icosahedral phase. However, at higher temperatures, their decomposition sequences differ significantly. The nanoscale icosahedral phase in the (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy decomposes into a mixture of Zr2Cu-type and icosahedral phases. This icosahedral phase still exists after heating up to 970 K, indicating a high thermal stability of this phase. The nanoscale icosahedral phase in the (Ti33Zr33Hf33)70(Ni33Cu33Ag33)20Al10 alloy also transforms into a mixture of Zr2Cu-type and icosahedral phase during the second exothermic reaction but then transforms into a mixture of Zr2Cu-type and Ti2Ni-type phases. The nanoscale icosahedral phase in the (Ti25Zr25Hf25Nb25)70(Ni50Cu50)20Al10 alloy decomposes into a mixture of Ti2Ni-type and MgZn2-type phases during the second exothermic reaction. It is concluded that the formation of the Zr2Cu-type phase retards the decomposition of the nanoscale icosahedral phase, which increases the thermal stability. In contrast, formation of Ti2Ni-type and MgZn2-type phases accelerates the decomposition of the nanoscale icosahedral phase, which decreases its thermal stability.
I. INTRODUCTION
Many reports indicate that adding small amounts of Ag,1,2 Pd,3,4 Ti,5 or Nb6 to Zr–Ni–Cu–Al glass-forming alloys promotes formation of icosahedral phases. It has been suggested that the additional element (e.g., Ag, Pd, Ti, and Nb) plays a key role in triggering the formation of the icosahedral phase in Zr–Ni–Cu–Al-based amorphous alloys7 due to a nearly zero or positive heat of mixing with at least one of the major alloying elements, such as Ni. a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/publications/jmr/policy.html. DOI: 10.1557/JMR.2006.0103 J. Mater. Res., Vol. 21, No. 4, Apr 2006
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In previous papers, we reported on the development of novel multicomponent metallic glasses based on wellknown good glass-forming Zr–Ni–Cu–Al alloys using the principle of equiatomic substitution.8–11 Along this line, a variety of samples with different composition have been produced using melt-spinning8–12 and mechanic
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