Hot Isostatic Pressing of Niobium-based Refractory Alloys.

다국어 초록 (Multilingual Abstract)

The period of niobium refractory alloy development in the 1950s-1970s was significant in metallurgical history because of its unique ability to operate at high temperatures (1200+°C). Marred by high costs and lack of processability through traditional industrial techniques, novel alloy development diminished, leaving behind a limited catalog of alloys and production methods. There is now a resurging interest in niobium alloys. However, the empirical metallurgy principles relied on for the development of the alloys in earlier research are no longer sufficient. Their exploration of alternative processing techniques such as metal powder consolidation was limited, at best.This work investigates hot isostatic pressing (HIP) of C103 (Nb-10Hf-1Ti wt%) and WC3009 (Nb-30Hf-9W wt%) powders into near net shapes. Subsequent isothermal heat treatments were conducted to better understand recrystallization behavior during HIP processing. This effort was performed to identify key alloy attributes that drive processability through HIP such that higher strength niobium alloys can be utilized. Dilute binary niobium alloys (Nb-1[Ti, Zr, Hf] at%) were fabricated and analyzed to elucidate variances in solute strengthening potency. Room-temperature mechanical tensile tests and nanoindentation were conducted to compare the relative strengths of alloys and to generate a deformed microstructure. Advanced SEM characterization of HIP-processed, pre-, and post-deformation structures was accomplished using electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI).The results shown in this study show that HIP processing of powder niobium alloys is a viable method to produce near-net shapes. Furthermore, the fact that alloys such as WC3009 can be consolidated indicates that this process is not limited to historically fabricable alloys like C103; It can also be applied to high-performance alloy systems that were previously thought impossible to use. The microstructures generated via HIP processing are heterogeneous compared with wrought material. Isothermal heat treatments of partially HIP processed materials revealed that recrystallization occurs heterogeneously throughout the microstructure where areas of comparatively high strain such as prior particle-particle interfaces are initially favored. The mechanical testing results for dilute binary niobium alloys confirm zirconium is the most potent and anomalous strengthener compared with titanium and hafnium.