Surface states by grinding thin strips of electrochemically deposited nanocrystalline nickel-iron

Thin strips of electrochemically deposited nanocrystalline nickel-iron with thicknesses of 320 or 330 mu m are modified by defined grinding. Small changes in the cutting depth and the variation of the grinding process, up cut or down cut, result in different surface states. X-ray diffraction provides the analyses of the microstructures and residual stresses on the surfaces. In the initial state, the grain sizes have an average value of 9.3 nm, the micro strains 0.74% and the residual stresses predominantly values in the low-pressure range. Up grinding with the smallest depth of cut 1 mu m causes the lowest compressive residual stresses at workpiece surface due to cold plastic deformation. Larger cutting depths and surface temperatures reduce the mechanical effects. Then prevailing thermal effects cause tensile residual stresses through thermoplastic deformation and through changes in the microstructure, which can be observed by grain enlargements and decreases in micro strains. However, the recovery and recrystallization processes are only partial. Down grinding with a cutting depth of 3 mu m thus leads to a maximum grain size increase to 23.4 nm and a maximum decrease in micro strain to 0.41% as well as to maximum residual stresses of 880 MPa.