Al-Ni-Y alloys processed through the amorphous state exhibit significant improvements in strength over conventional crystalline Al Alloys. As such, they may offer some promise in highstrength, weight critical applications such as aerospace if their other property combinations are acceptable. However, amorphous metals are highly non-equilibrium and the issues associated with their thermal stability have stimulated considerable interest, especially in terms of the effects of any partial crystallization on their properties. In this work, the influence of controlled states of crystallization on the corrosion resistance of rapidly solidified Al-Ni-Y amorphous ribbons in 3.5 wt. % NaCl (pH 6.5) solution is studied. Differential scanning calorimetry and Xray diffraction are used to determine the thermal stability of amorphous Al-Ni-Y ribbons. Two types of crystallites, FCC-Al and intermetallic phases were produced and their effect on the corrosion rate was studied by potentiodynamic polarization. The results show that the primary crystallized ribbons exhibit improved corrosion resistance compared with the as-spun, fully amorphous, secondary crystallized (i.e. containing intermetallic phase) or fully crystallized states. Possible physical origins of these effects are discussed.
In common engineering alloys such as steel, aluminium and copper, the atoms are arranged in a regular three-dimensional periodic structure. Although this arrangement is well defined, the packing is not perfect and defects are always observed. The most important of these defects are vacancies (point defects), dislocations (line defects) and surfaces (free surfaces and grain boundaries). These defects strongly influence the physio-chemical properties of the materials. The mechanical properties of the materials, such as the yield strength, elongation and fracture toughness, are largely controlled by the motion of the dislocations and how they interact with the microstructure. The surface defects (external surfaces and grain boundaries) strongly influence the electrochemical properties of the material.