Laser deposition of a Cu-based metallic glass powder on a Zr-based glass substrate
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Laser Engineered Net Shaping (LENS™) is a laser-assisted manufacturing process that offers the possibility of producing metallic coatings and components with highly nonequilibrium microstructures. In this work, the microstructure developed by LENS deposition of Cu47Ti33Zr11Ni8Si1 powder on a bulk metallic glass substrate, with nominal composition Zr58.5Nb2.8Cu15.6Ni12.8Al10.3, is investigated. Single-layer deposition results in the formation of an inhomogeneous but partially amorphous layer above a crystalline heat-affected zone. Elemental analysis of the deposited layer indicates incomplete mixing of the powder with the melt pool. The as-deposited alloy exhibits a single glass transition event and its primary crystallization event is consistent with the first crystallization temperature of the Cu-based powder. Subsequent remelting of this layer results in a still partially amorphous deposit with a uniform composition of (Zr + Nb)51.8Cu24.7Ti3.4Ni16.4Al3.7. The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.
I. INTRODUCTION
Bulk metallic glasses (BMGs) exhibit a number of extraordinary properties, including high hardness, corrosion resistance, and near-theoretical elastic limits, and thus have attracted tremendous interest.1–7 However, the dimensions of as-cast BMG components are limited by the compositionally-dependent critical cooling rates necessary to produce fully amorphous structures, thus restricting their widespread use in structural applications.1–3 Applications are further limited by the catastrophic nature of failure in BMGs, associated with the rapid propagation of highly localized shear bands.8–11 To limit shear band propagation and thereby improve reliability, techniques for manufacturing unique BMG composite microstructures are of interest.12,13 Laser-assisted materials processing is a novel manufacturing technology for the creation or repair of metallic coatings and components with highly nonequilibrium microstructures.14–16 Several previous studies have applied laser technologies to metallic glasses. Laser welding has been used to join Cu- and Zr-based BMG plates at a welding speed sufficient to avoid crystallization in both the bead and the heat-affected zone (HAZ).17,18 Laser surface melting and cladding techniques have also been a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0329 2692
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 10, Oct 2008 Downloaded: 18 Mar 2015
investigated to synthesize amorphous coatings, taking advantage of the inherent high cooling rate of small melt volumes to minimize crystallization.19–25 For example, Wu et al. cladded Fe- and Ni-based metallic glasses on steel substrates and obtained amorphous coatings with thicknesses of ∼1 mm.22,23 Additionally, several Zr-based amorphous coatings have been produced on aluminum,21 titanium,25 and magnesium24 substrates. While these prior stu
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