Electrochemically deposited nickel membranes; process–microstructure–property relationships

This paper reports on the manufacturing, surface morphology, internal structure and mechanical properties of Ni-foils used as membranes in reference-microphones. Two types of foils, referred to as S-type and 0-type foils, were electrochemically deposited from a Watts-type electrolyte, with (S-type) or without (0-type) the use of the sulfur-containing additive sodium saccharin. Both types of Ni-foils appeared perfectly smooth when investigated with scanning electron microscopy (SEM), while atomic force microscopy (AFM) and transmission electron microscopy (TEM) revealed differences in the surface morphologies and a smaller grain-size in the S-type foils. X-Ray diffraction showed a 〈311〉 texture component in both types of Ni-foils, most pronounced for 0-type foils. A minor 〈111〉 texture component observed in both foil types was strongest in the S-type foils. Mechanically 0-type foils proved more ductile than S-type foils during thin film tensile testing, due to microstructural defects caused by sodium saccharin during deposition. Tensile strengths in the order of 700–1000 MPa were observed—highest for the more ductile 0-type foils. A hardness in the order of 6 GPa (590 HV) was found by nanoindentation.