Laser deposition of a Cu-based metallic glass powder on a Zr-based glass substrate

Abstract

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 Cu 47 Ti 33 Zr 11 Ni 8 Si 1 powder on a bulk metallic glass substrate, with nominal composition Zr 58.5 Nb 2.8 Cu 15.6 Ni 12.8 Al 10.3 , 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) 51.8 Cu 24.7 Ti 3.4 Ni 16.4 Al 3.7 . The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.

Microstructural Analysis of a Laser-Processed Zr-Based Bulk Metallic Glass

“…Prior work on metallic glasses has shown that the depth of the melt zone and the thickness of the HAZ both increase with increasing heat input. [12] The effect on the morphology of the HAZ is also observed in the present study, where increasing the laser travel speed, and thereby reducing the heat input, nearly eliminates the formation of a crystalline HAZ in the amorphous substrate (Figure 1(c)). Indeed, a combination of laser power at 150 W and travel speed at 21.2 mm/s, or a heat input of 7.1 J/mm 2 , appears to be close to ideal for successfully forming a melt pool, necessary for powder incorporation, without causing extensive crystallization in the underlying amorphous substrate.…”

“…Although the local cooling rate was not measured directly in the present work, finite element method (FEM) simulations of a moving heat source analogous to the laser heating process indicate that the maximum cooling rate of the center of the melt zone is approximately 8000 to 10,000 K/s. [12,15] This is orders of magnitude higher than the critical cooling rate required to avoid crystallization of the Zr-based BMG (~1.75 K/s [16] ) used in the present study. Moreover, the DSC data presented in Figure 5 reveal slightly higher glass transition temperatures in the deposited material than the as-cast glass.…”

“…The FEM analysis suggests that the HAZ is confined to a region where the peak temperature is 900 K or greater. [12] This higher temperature promotes the rapid growth of the spherulites in the amorphous substrate. Furthermore, the isothermal annealing condition allows time for diffusion-controlled phase separation to form the observed Zr 2 Cu and other phases.…”

“…Our recent investigation of laser deposition of a Cu-based amorphous powder on a Zr-based metallic glass substrate indicated that laser deposition can be used to produce amorphous coatings with intermediate glass forming compositions. [12] However, residual heating effects result in crystallization of the underlying amorphous material. It is therefore of interest to investigate the development of the HAZ in the amorphous substrate in order to identify optimal processing parameters.…”

Surface rippling on bulk metallic glass under nanosecond pulse laser ablation

“…Bulk metallic glasses (BMGs) with both glassy-state structure and metallic-bonding character show a series of intriguing mechanical, physical, and chemical properties, having wide range functional and structural applications. [8][9][10][11][12] Due to rapid heating and cooling, lasers have been widely used to welding, cutting, cladding, alloying, glazing, annealing, melting, or ablating the small-scaled amorphous alloys such as ribbons, films, and wires, [13][14][15][16][17] very recently extending to BMGs. 18,19 Through laser-processing, microstructures, 15-17 magnetic properties, 14 forming ability, 20 and mechanical properties 19 of this kind of glassy alloys can be significantly improved, whereas only few works have focused on the surface patterns.…”