Mechanical Properties of Pt-Ir and Ni-Ir Binary Alloys for Glass-Molding Dies Coating

Abstract

In this study, the different compositions of Pt-Ir and Ni-Ir alloys were deposited by utilizing ion source assisted magnetron sputtering system (ISAMSS). The surface roughness and crystallite size of the Pt-Ir and Ni-Ir coatings were analyzed by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. In addition, coatings were soaked at 700 degrees C and maintained 10 min under N(2) atmosphere using a glass-molding machine. The annealed coatings for oxidation test were examined by energy dispersive X-ray spectrometry (EDS) and for microhardness and reduced modulus test were evaluated by nanoindentation instrucment. The cross-sectional structures between the Pt-Ir and Ni-Ir coating layer and substrates were also examined by field emission scanning electron microscope (FESEM). The results show that surface roughness Ra from 1.25 nm to 3.426 nm was observed with increasing the Ni elements. However, the Ra is less than 2 nm measured in Ir-based coatings doped with Pt concentrations under this study. With increasing Pt and Ni doping, the microhardness of both coatings decreased significantly and the values of reduced modulus of Pt-Ir alloys are larger than that of Ni-Ir alloys. After oxidation process, the oxygen concentration of Pt-Ir coatings is less than that of Ni-Ir coatings and the Pt-Ir coatings exhibit superior properties including oxidation resistance, low surface roughness and high reduced modulus over Ni-Ir coatings, especially for the high Pt concentration coatings such as Pt-Ir 2 (55.25 at.% Pt) and Pt-Ir 3 (79.42 at.% Pt) coatings. The surface roughnesses of all specimens annealed at 700 degrees C were slightly larger than as-deposited coatings. Moreover, due to the serious oxidation occurred in Ni-Ir 3 (73.45 at.% Ni) coatings, the value of reduced modulus of this specimen coating is the lowest and the corrsponding Ra value is the largest compared with the rest of Ir-based coatings in the oxidation testing.