The limits of glass formation by pulsed laser quenching in NbNi alloys

Bulk metallic glasses (BMGs) are non-crystalline class of advanced materials and have found potential applications in the biomedical field. Although there are numerous conventional manufacturing approaches for processing BMGs, the most commonly used like copper-mould casting have some limitations. It is not easy to manage and control the critical cooling rate, especially when the fabrication of complex BMG geometries is involved. Other limitations of these techniques include the size constraints, non-flexibility, and the tooling and accessories are costly. The emergence of additive manufacturing (AM) has opened another promising manufacturing route for processing BMGs. AM processes, particularly laser powder-bed fusion (PBF-LB/M) builds parts layer-by-layer and successively fused the powder-melted feedstocks using prescribed computer-controlled laser scanner system, thereby forming a BMGs part upon sufficiently rapid cooling to ensure the glass forming-ability. PBF-LB/M overcomes the limitations of the pre-existing BMGs processing techniques by not only improving the part size, but also produces exceptionally complex structures and patient-specific implants. This review article aims to summarise and discuss the mechanism of BMGs formation through PBF-LB/M for biomedical applications and to highlight the current scientific and technological challenges as well as the future research perspectives towards overcoming the pore-mediated microcracks, partial crystallisation, brittleness and BMG size constraint.

Amorphous Ni₅₀Nb₅₀/C multilayers with a period of 2.4 nm for the water window soft X-rays were prepared by pulsed laser ablation deposition. The structural stability of these multilayers was studied by grazing incidence X-ray scattering. The multilayers were found to be highly stable at room temperature for periods as long as 3 years. However, the Ni₅₀Nb₅₀ layer was found to undergo an amorphous – crystalline disorder – order transformation due to annealing while the carbon layer remained unchanged. The crystalline phase after transformation could be identified as the NiNb phase. The vertical layered structure, however, was found to be highly stable even after annealing the multilayers at 473 and 593 K under vacuum. The multilayer period remains unchanged till 473 K and increases by 7% on annealing at 593 K.

Amorphous NdFeB films prepared by sputtering technique were annealed by laser irradiation of a Nd:YAG pulse laser. Laser annealing yielded rapid precipitation of ferromagnetic Nd₂Fe₁₄B phase from the amorphous matrix. The magnetic properties and the microstructure of the annealed NdFeB materials could be controlled by the applied laser power.