AM of a precious bulk metallic glass shows promise for jewellery

A study conducted by Swiss researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) and ETH in Zurich has produced, for the first time via additive manufacturing, a high-density amorphous and crack-free bulk metallic glass (BMG) based on palladium alloy. The results show significant promise in the use of such material in the additive manufacturing of watches and jewelry.

Bulk Metallic Glasses, also commonly called BMGs (or glassy metals), represent the fringe of non-crystalline solid materials and advanced materials in general. Their high strength and hardness, combined with a surprising elasticity make them ideal for industrial innovation. 3D printing of metallic glass is being studied for use in the military sector and in space research, and they may also be able to replace conventional engineering materials in many more applications, including electronics, sports equipment and jewelry. Some early AM applications of metallic have emerged for the medical sector in particular.

In the EPFL-ETH study, Pd-based Pd43Cu27Ni10P20 bulk metallic glass (BMG) parts, manufactured via Laser Powder-Bed Fusion (LPBF) were characterized, looking in detail at the microstructure and mechanical properties of the bulk samples, and the crystallization kinetics of the amorphous powder particles.

The parts achieved a density of 99.6% and displayed excellent mechanical properties such as high hardness and compressive strength were achieved, overcoming the limitations usually found for precious metals in jewelry and watchmaking.

Furthermore, without any post-processing, a mirror-like smooth and brilliant surface was directly obtained, which is highly beneficial for applications where surface finish or aesthetics matters. The effect of the main processing parameters, such as laser power and laser scanning speed, on the shape of single tracks was investigated by laser confocal microscopy (LCM).

Following the single-track experiments, highly amorphous 3D printed samples were produced. The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM), conventional and synchrotron X-ray diffraction (XRD), micro-computed tomography (μ-CT), compression tests, and microhardness. The crystallization kinetics of the powder alloy was investigated via fast differential scanning calorimetry (FDSC).

A small quantity of the powder (< 70 g) was used for the fabrication of samples, alleviating the cost of the process. The study demonstrated the efficient production of precious metal parts with enhanced mechanical properties while highlighting that, despite the good glass-forming ability (GFA) of Pd-based BMG, the critical aspects in LPBF fabrication for avoiding crystallization are not so much the thermal conditions related to laser parameters, as much as the absence of impurities during the LPBF process.