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Thin strips of electrochemically deposited nanocrystalline nickel-iron with thicknesses of 320 or 330 µm 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 µm 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 µm 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.

Nanocrystalline nickel-iron layers are produced electrochemically on copper discs by varying the current density and then annealed in a vacuum furnace at a temperature range between 200 and 800 °C. Grain size, iron content, texture and microstrain of the microstructure are primarily characterized by X-ray diffraction (XRD). Instrumented indentation tests and microbending tests for mechanical characterization are carried out. The iron contents of the investigated layers are 5.7, 8.8, 13.5 and 17.7 wt.-%. By varying the annealing temperature, the reduction of the microstrains is initiated at 200 °C and ends at a temperature of about 280 °C. Primary recrystallization starts slightly higher at 220 °C and is completed at 300 °C. With higher iron content, the indicated temperatures shift to slightly higher values. Indentation modulus, Young's modulus, indentation hardness and strength change considerably after the annealing treatment. Fracture strain at the edge, as a measure of ductility, decreases immediately after annealing at 200 °C to 0 %. Low annealing temperatures occurring before the beginning of primary recrystallization lead to an increase in indentation hardness and 0.01-% offset bending yield strength Rp0.01∗ as compared to the electrochemically deposited initial state. After annealing at high temperatures, the mechanical parameters are mostly below the initial values for electrochemical deposition. Hall-Petch (HP) behavior is observed for Rp0.01∗, both for the electrochemically deposited specimens down to almost 6 nm and for the specimens annealed at high temperatures. Specimens annealed at low temperatures deviate from the HP straight line to higher values. In this case, an increase in strength is assumed to be due to the very small nanocrystalline (nc) grain sizes, segregation at the grain boundaries and a decrease in dislocation density. Indentation hardness measurements show almost no dependence on D−0.5 for the electrochemically deposited specimens and also for annealed specimens below 30nm grain size. Above 30nm, the indentation hardness values are considerably higher than for the HP straight line. Overall, the hardness and strength values of the nc specimens, electrochemically deposited or additionally annealed, are significantly higher than those of the microcrystalline (mc) specimens.

Nanocrystalline nickel-iron microstructures, manufactured by means of an electrochemical deposition process via electrolyte solutions, were investigated to collect relevant information for the use of nickel-iron for micro-components. By varying the current density, nickel-iron coatings can be set to show specific grain sizes, iron content, lattice strains and textures. Uniform microstructures exist in each of the deposited nickel-iron coatings. The grain sizes determined using x-ray analysis (XRD) cover a range of 6 to 17 nm. XRD texture analyses parallel to the deposition plane resulted in {111} and {200} orientations. To characterize the material's mechanical properties indentation hardness measurements and micro-bending tests were performed. For a 0.01 %-offset bending yield strength (Rp0.01*), grain sizes of 6 to 17 nm clearly demonstrate Hall-Petch behavior. In addition, the investigations show lower work hardening and lower values for remaining edge strain at fracture for decreasing grain size. In contrast to Rp0.01*, the Young's modulus, indentation modulus, indentation hardness values and the bending strength, within their scatter bands, all remain largely unaffected by the different microstructures. Overall, all measured strength and hardness values of the considered nanocrystalline microstructures are very high in comparison to microcrystalline microstructures.