Microstructural and topographical changes of Ni-P plated moulds in glass lens pressing

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

“…However, since very little research has been carried out on the use of a mould comprising a Ni-P-plated substrate for the production of glass lenses, the most suitable release agent material is unknown at present. In our previous work [7], we found that when a combination of a Ni-P-plated substrate and an Ir-Pt coating were heated above 500 • C, Ni from the mould diffused into the Ir-Pt coating, which resulted in adhesion of the glass to the mould. Therefore, the choice of the release agent composition should be carefully considered in order to inhibit such diffusion and extend the mould lifetime above 500 • C.…”

“…We previously clarified that interdiffusion of the elements of the release agent and the Ni-P plating could occur at the moulding temperature of a glass lens [7]. Such interdiffusion causes an increase in the mould surface roughness and makes it difficult to remove the lens following moulding.…”

“…In contrast, in the case of Ir-Re-coated mould, the surface roughness shows almost no dependence on heating time. In the Ir-Pt-coated mould, it is thought that Ni diffuses from the Ni-P layer and the interlayer into the release agent layer and the mould surface swells locally due to non-uniform diffusion rates [7], thus leading to an increase in the surface roughness. If this is the case, it appears that such diffusion is suppressed in the case of the Ir-Re-coated mould.…”

“…Fine microstructures can be easily generated on the surface of the Ni-P plated mould using a single-crystal diamond cutting tool, and the moulds can be used to mould refractive/diffractive hybrid glass lenses and other microstructures at a temperature of 387 • C [4,5]. However, in higher temperature moulding tests, we found that the constituent elements of the Ni-P plating diffuse into the release agent coating, resulting in mould surface roughening and adhesion of glass to the mould [6,7].…”

Development of polycrystalline Ni–P mold by heat treatment for glass microgroove forming

“…As the hardness of the amorphous nickel-phosphorus (a-Ni-P) decreases rapidly with the increase of temperature, the microgrooves on the a-Ni-P layer were easily deformed under the repeated pressing load at the glass molding temperature. At the same time, the amorphous Ni-P alloy undergoes a self-crystalline transformation to Ni and Ni 3 P at temperature above 300 • C [20,21], which increases the uncertain factors during the molding process. In this research, polycrystalline nickel-phosphorus (c-Ni-P) mold was developed to apply to the molding process directly.…”