The microstructure and internal stress of Fe-Ni nanocrystalline alloys electrodeposited without a stress-reliever

Nanocrystalline Fe-Ni deposits with thicknesses up to 400 mu m were manufactured under conditions of high overpotential from an additive-free, simple chloride electrolyte. Fe-12 divided by 15% Ni alloys with a grain size of 5.5 divided by 7 nm and a microhardness between 637 and 711 HV, represented a strongly textured solid solution of Ni in alpha Fe. An increase in the current density led to a reduction of grain size and an increase of deposit hardness. The tensile stress generated, exceeding 1400 MPa during the early stages of electrodeposition, was drastically decreased to 70 divided by 90 MPa after deposit cracking and the higher current density caused faster stress reduction to the lower level. The microcracks, oriented perpendicularly to the substrate surface and distributed evenly across the deposit thickness, formed a network with a density of over 100 per 1 mm. A correlation between microhardness and grain size was found, which supports the Hall-Fetch strengthening of the deposit matrix by ultra-fine grains. (C) 1998 Elsevier Science Ltd. All rights reserved.