Tribological and mechanical properties of high power laser surface-treated metallic glasses

Abstract

The processing power of high power Nd:YAG laser has been utilised to achieve the inherently high cooling rates required to form many of today's bulk metallic glasses (BMGs). The production of thick (≥250 m) amorphous surface layers has been considered. Microstructural and chemical observation techniques including scanning electron microscopy (SEM) and transmission electron microscopy (both with energy-dispersive X-ray spectrometry, EDS), and X-ray diffraction (XRD), reveal that fully amorphous layers are attainable. Coating-to-substrate adherence is functionally graded by virtue of an amorphous matrix interlayer around 50 m in depth. Actual cladding and remelting to Ti substrates indicate that the process of laser cladding is a suitable technique for the application of metallic glasses as surface layers. Hardness and nanoindentation profiles reveal hardnesses up to 13 GPa over the full depth of a coating, coupled with elastic modulus around 150 GPa, which are comparable with bulk metallic glass melt-spun ribbons. Tribological tests have also been conducted which reveal good wear properties are attainable and shear banding has been seen in the contact region. Scratch testing shows the layers may exhibit extremely low coefficients of friction, and again shear band formation is witnessed.

Surface rippling on bulk metallic glass under nanosecond pulse laser ablation

“…[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. 13,21,22 Its underlying physics is still unclear and deserves further investigations.…”

Dry Sliding Wear Behavior of Spark Plasma Sintered Fe-Based Bulk Metallic Glass/Graphite Composites

“…It was also observed that, as the wear continues, the asperities of the shear bands break down, resulting in accumulation and compaction of micro-and nano-scale debris behind the shear bands. While the amorphous alloys showed a lower coefficient of friction, the wear rates were comparable to the steel specimens [15]. Prakash investigated abrasive two-body wear of Fe-, Co-, and Ni-based amorphous alloys and reported extensive micro-cutting and micro-cracking of the amorphous alloys [9].…”

“…As amorphous alloys lack general ductility, the wear behavior of these materials is characterized by shear banding and microcracking in the contact region [9,14,15]. Matthews et al investigated the dry sliding wear behavior of as-cast and laser remelted Cu-based amorphous alloys and observed formation of shear bands inclined to the sliding direction [15]. It was also observed that, as the wear continues, the asperities of the shear bands break down, resulting in accumulation and compaction of micro-and nano-scale debris behind the shear bands.…”

Layered Microstructure Distribution and Forming Mechanism of Laser-Processed Ni-Fe-B-Si-Nb-C Amorphous Composite Coatings

“…Laser processing techniques such as laser cladding and laser remelting have been utilized in producing various amorphous coatings. 9,10) In the last several years, studies have focused on the use of compositions based on (Fe, Ni, Co)-B-Si-Nb alloy systems. These compositions are mostly suitable for surface coatings on traditional steel substrates.…”