Fabrication and characterization of Fe-based bulk metallic glass composites produced by additive manufacturing

Abstract

Additive Manufacturing (AM) are processes where a part is built layer by layer based on a 3D model. This definition is widely applicable to all classes of materials including metals, ceramics, polymers, composites and biological systems. Among the processes used in the additive manufacture of metallic parts, we can highlight the Selective Laser Melting (SLM), which is a promising technique because it allows the production of complex shape parts with a better surface quality than other AM processes. The high cooling rates applied during SLM allow obtaining materials with non-equilibrium microstructures as metallic glasses. These materials exhibit better mechanical properties and corrosion behaviour than traditional crystalline alloys but they show a brittle behaviour during tensile loading. The formation of crystalline phases in a glassy matrix to obtain Bulk Metallic Glass Composites (BMGCs) improves the ductility without considerably sacrifice the strength. These materials are promising in several applications as, for example, sensors, flowmeters, micrometer-sized gears and coatings. The high cooling rates required to form the glass structure limit the size of BMGCs parts produced by casting to mm size. Because the SLM process fabricates parts layer by layer applying high cooling rates, this allows the production of large bulk metallic glass parts, as already demonstrated in the literature. A very few works were carried out to produce BMGCs by additive manufacturing methods, even considering that they exhibit better mechanical properties than metallic glasses. In this context, the present project aims to produce and characterize BMGCs of the Fe-Ni-P-C system by Selective Laser Melting (SLM) and to correlate the microstructure with the mechanical properties. First, chemical compositions are going to be selected using calculations able to predict the Glass Forming Ability (GFA) for the alloys and also using thermodynamic calculations of phases in equilibrium. Then, with the composition determined the powders will be fabricated by gas atomization with equipment available at DEMa/UFSCar using iron-alloys and steel. The powders will be characterized by X-ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), chemical analysis by X-ray Spectroscopy (EDX) and Differential Scanning Calorimetry (DSC). Due to the specificities of each alloy, especially for those never processed by AM, as a first step it will be necessary to optimize the SLM parameters in order to have samples with good quality and integrity. It will be investigated and identified the best combination of processing parameters in order to have high density parts free of defects that compromise its properties. The samples will be then micro characterized by XRD, OM, SEM, TEM, EDX and DSC. For the mechanical characterization, the specimens will be evaluated in different directions of construction (0°, 45° and 90° with relation the tensile axis) by tensile tests, hardness and fracture toughness. (AU)