Thermally induced atomic diffusion at the interface between release agent coating and mould substrate in a glass moulding press

Abstract

In a glass moulding press (GMP) for refractive/diffractive hybrid lenses, to improve the service life of nickel-phosphorus (Ni-P) plated moulds, it is necessary to control the diffusion of constituent elements from the mould into the release agent coating. In this study, diffusion phenomena of constituents of NiP plating are investigated for two types of release agent coatings, iridium-platinum (Ir-Pt) and iridium-rhenium (Ir-Re), by cross-sectional observation, compositional analysis and stress measurements. The results show that Ni atoms in the plating layer flow from regions of compressive stress to regions of tensile stress. In the case of the Ir-Pt coated mould, the diffusion of Ni is promoted from the grain boundaries between the Ni and Ni 3 P phases in the plating towards the surface of the Ir-Pt coating. However, in the Ir-Re coated mould, the diffusion of Ni is suppressed because the diffusion coefficient of Ni in the Ir-Re alloy is smaller than that in the Ir-Pt alloy, although the stress state is similar in both cases. By controlling the diffusion of Ni atoms, the use of Ir-Re alloy as a release agent coating for NiP plated moulds is expected to lead to a high degree of durability.

Model of coating wear degradation in precision glass molding

“…Since EBSD and XRD measurements revealed average grain sizes of 70-90 nm and crystallite sizes of 20-30 nm, grain boundary diffusion is the most probable diffusion mechanism. This is supported by the diffusion analysis of Ni thin films in [8]. After sputtering by 20 nm, nickel oxide is removed and only metallic nickel is detected to be present in the PtIr layer, in agreement with external selective oxidation.…”

Precision glass molding: Toward an optimal fabrication of optical lenses

“…Thus, coating is often used for extending mold life and thereby leading to the cost reduction of the molded optical products. There are mainly three types of coatings available in the market, namely, ceramic coating (TiAlN, CrN, TiBCN or TiBC) [63], noble metal coating (Pt/Ir [64,65] and Re/Ir [66,67]), and carbon coating (diamondlike coating, amorphous carbon coating) [68]. Ceramic coatings have been widely used in making machining tools, and therefore are straightforward to apply to PGM molds.…”

“…Noble metal coatings, especially the Pt/Ir alloy coating, can avoid such adhesion [64,65]. Nevertheless, it has been found that the Pt/Ir layer is not stable [66,67], and that the substrate material can diffuse into the coating layer and reduce its quality. However, the noble metal coating of Re/Ir demonstrates very stable properties [66] and low wetting angle among various coating materials [67].…”

“…Nevertheless, it has been found that the Pt/Ir layer is not stable [66,67], and that the substrate material can diffuse into the coating layer and reduce its quality. However, the noble metal coating of Re/Ir demonstrates very stable properties [66] and low wetting angle among various coating materials [67]. Diamonds-like coatings require a vacuum environment to avoid oxidation at high temperature.…”

“…These include the investigations on the sticking behavior of mold materials/coatings with hot glass preforms by the frequent contact method [70], the performance of different coatings in PGM [66,71], and the anti-sticking ability of Pt/Ir and TiAlN coatings on tungsten carbide and silicon wafer substrates [65]. It was understood that compression hold time, cooling time and peak force can significantly affect the sticking.…”