Solid-state additive manufacturing of tantalum using high-pressure cold gas-dynamic spray

Abstract

Additive manufacturing (AM) of refractory metals, including tantalum (Ta), is highly valued due to the wide application of these materials in different industrial sectors where outstanding mechanical properties at elevated temperatures are required. Among metal AM processes, newly introduced cold gas-dynamic spray or, more commonly, cold spray (CS) offers a unique opportunity for solid-state consolidation of refractory metals. This research presents the CS process as a method for additive manufacturing of Ta. Following the successful manufacturing of free-standing Ta, an extensive mechanical characterization at the macro and nano levels has been carried out to evaluate the material's structural integrity. Anisotropy in the mechanical properties, which is one of the major concerns in the AM-produced materials, was extensively analyzed at both the macro and nano levels. The produced Ta's resistance against the pre-existing crack was studied by evaluating the far-field J-integral versus the crack extension (J-R curve). The influence of microstructural characteristics and process-induced defects such as pores and micro-cracks on the Ta's mechanical and fracture properties was studied to explain the performance-microstructure linkage. The macro and nanomechanical testing results indicated an elastic modulus and ultimate tensile strength in the range of vacuum-arc melted or electron-beam melted Ta ingots following cold-working. The microstructure analysis demonstrated a mixture of ultrafine grains and highly elongated coarse grains, explaining the CS-produced Ta high strength. Moreover, excellent isotropy in the mechanical properties was observed at both the macro and nano levels. This finding distinguishes the CS process from the laser-based AM process in which mechanical properties highly depend on the build direction. On the other hand, the CS-produced Ta exhibited brittle characteristics during uniaxial tensile loading and ductile behavior during the uniaxial compression test. Also, stable crack growth accompanied by crack branching was observed in the CS-produced Ta. The crack branching and formation of secondary cracks have been identified as the mechanisms retard crack extension. Overall, this research revealed that the CS process is a promising AM technique for producing tantalum-based components.