The structural feature and industrial application of metallic glasses have long been challenging topics. In this thesis, an atomic cluster packing model was proposed to predict alloy compositions of bulk metallic glasses (BMGs) based on the concept of efficient filling and the recent progress on medium range order in metallic glasses. On the other hand, due to the intrinsic nature of low plasticity in BMGs, much attention was focused on their good corrosion resistance and wear resistance, which make them more attractive to use as coatings than as bulk materials. Ni-based amorphous metallic coatings were fabricated by High Velocity Air Fuel (HVAF) thermal spraying and Kinetic Metallization (KM), and the effect of spraying parameters on the structure and corrosion behavior of coatings was investigated. The conclusions were summarized as follows:
1. An atomic clusters packing model was proposed for calculating alloy compositions with high glass forming ability (GFA) based on the concept of efficient filling. The chemical effect on atomic clusters packing was considered and the strain was calculated during the atomic filling. When the critical strain is reached, the dense packing of clusters is “collapsed” to amorphous state. This model provides an explanation to many BMGs found so far, and new Fe-B-Nb and Hf-Al-Cu BMGs are successfully predicted.
2. Miracle’s efficient cluster packing (ECP) model for metallic glasses and the topological instability criterion for multi-component alloy systems have been combined to formulate a design protocol for BMGs. A simple ternary Ni-Nb-Zr BMG with best GFA of 2 mm was successfully designed and fabricated. The new BMG exhibits excellent corrosion resistance in 1M HCl aqueous solution.
3. Ni-Zr-Ti-Si-Sn and Ni-Nb-Ti-Zr-Co-Cu partial amorphous metallic coatings with dense structure were prepared by HVAF thermal spraying. It was found that the porosity and amorphous phase fraction in coatings are sensitive to spraying parameters. The Ni-Zr-Ti-Si-Sn amorphous alloy and its coating present good corrosion resistance in 0.05M H2SO4 + 0.05M Na2SO4 aqueous solution, while the Ni-Nb-Ti-Zr-Co-Cu amorphous alloy and its coating exhibit high corrosion resistance in severely corrosive environment of 1 M HCl aqueous solution.
4. Ni-Nb-Ti-Zr-Co-Cu fully amorphous metallic coating with high corrosion resistance was fabricated by KM. The coating becomes much denser with increasing spraying temperature, and it exhibits higher corrosion resistance with increasing thickness due to the difficulty to form through-pores.
5. The corrosion behaviors of Ni-Zr-Ti-Si-Sn and Ni-Nb-Ti-Zr-Co-Cu amorphous alloy and their crystalline counterparts in 1M HCl aqueous solution were compared by potentiodynamic polarization curves and X-ray Photoelectron Spectroscopy (XPS) analysis. It was found that the corrosion resistance of Ni-based amorphous alloys is very sensitive to the compositions and the structural homogeneity only has a beneficial effect on the corrosion resistance.
修改评论