A combinatorial strategy for metallic glass design via laser deposition Peter Tsai,Katharine M.Flores*
Department of Mechanical Engineering and Materials Science,Institute of Materials Science and Engineering,Washington University in St.Louis,
One Brookings Drive,Campus Box1185,St.Louis,MO63130,United States
a r t i c l e i n f o
Received21May2014 Received in revised form
B.Glass forming ability
http://m.wendangku.net/doc/8a739c36910ef12d2bf9e7bf.html ser processing and cladding
D.Microstructure a b s t r a c t
In this work,compositionally-graded Cu x Zr100Àx specimens with x ranging61e76were fabricated by a direct laser additive manufacturing process.Topographically featureless surface regions,which suggest the possibility of a non-crystalline structure,were observed over the range62e67at%Cu using differ-ential interference contrast light microscopy.Electron diffraction and differential scanning calorimetry veriﬁed that these regions were primarily amorphous.By varying the laser power and thereby the heating and cooling rate of the specimen,we show that the most stable glass-forming composition within the explored range is Cu64.7Zr35.3,in excellent agreement with the previously reported optimum composition of Cu64.5Zr35.5that was identiﬁed by trial and error.
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Despite the attractive properties of metallic glass(MG)alloys, relatively few bulk-scale MG alloys(BMGs),which can be vitriﬁed with dimensions of several millimeters or larger,have been iden-tiﬁed.This limitation reﬂects the lack of reliable criteria for pre-dicting good glass formers.For example,although the reduced glass transition temperature has been prevalently used as an indicator of high glass forming ability(GFA),its reliability is not universal[1,2], nor is it truly predictive of glass formation a priori since it requires knowledge of the glass transition temperature(T g).The same holds true for other parameters that are based on characteristic temper-atures[3e6].Recent structural models for MGs have identiﬁed efﬁcient packing conditions that are necessary,but not sufﬁcient, criteria for glass formation[7e10],and have primarily focused on binary and ternary systems,where determining cluster packing efﬁciency is a tractable problem.Without reliable predictive criteria,efforts to discover new,multicomponent BMGs still depend heavily on“trial and error”experimental methods.
Experimental evaluation of GFA is conventionally accomplished by casting discrete compositions,followed by application of diffraction techniques to verify amorphous structure.Because GFA is highly sensitive to chemical composition,a thorough investigation of multicomponent systems by casting,with each composition separated by no more than1at%,requires fabrication of an impractically large number of specimens.This shortcoming of conventional techniques has motivated the development of combinatorial approaches for BMG discovery and design[12e18]. For example,Ding et al.recently reported magnetron sputtering as a combinatorial tool for identifying chemical compositions with optimum GFA and thermoplastic formability in ternary alloy sys-tems[17,18].While the thinﬁlm libraries produced by sputtering techniques provide valuable information,notably through the ability to rapidly evaluate several properties using“lab on a chip”methods,the extreme quench rates achieved by such vapor depo-sition techniques result in atomic structures that are potentially quite different from those achieved by cooling from the liquid.
Alternatively,in this paper we demonstrate a novel,high-throughput combinatorial methodology for the identiﬁcation of BMG alloys by vitriﬁcation from the liquid,using a laser deposition technique.Previous studies have applied laser technologies to metallic glasses[19e27].Our group has also in prior studies depos-ited pre-alloyed powders of known Zr-,Cu-,and Fe-glass forming compositions[30,31].Continuous amorphous deposits were ach-ieved with varying degrees of a crystalline heat affected zone(HAZ) observed in the substrate.The extent of the HAZ was well-controlled by proper selection of the laser processing parameters.
In the present work,compositional libraries of the binary Cu e Zr system were fabricated using the Laser Engineered Net Shaping (LENS™)process.Glass-forming compositions were quickly identiﬁed by observing the surface topography of the deposit with differential
E-mail addresses:firstname.lastname@example.org(P.Tsai),ﬂoresk@wustl.edu,ﬂoresk@seas. wustl.edu,kmﬂores72@http://m.wendangku.net/doc/8a739c36910ef12d2bf9e7bf.html (K.M.
Flores).Contents lists available at ScienceDirect Intermetallics
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