Amplitude dependent damping in electrodeposited nano-crystalline nickel after various heat treatments

Abstract

Coercivity, hardness and amplitude dependence of damping of electrochemically deposited nickel layers were measured directly after electrochemical deposition and subsequently after isochronal heat treatments at various annealing temperatures. All as-electrodeposited nickel samples have ultrafine grains with mean grain sizes in the order of 300 nm. The co-deposition of nanoscaled ceramic SiO 2-particles led to a reduction of the grain size to 60 nm. The amplitude dependence of damping with and without saturating DC magnetic field, coercivity and microhardness was measured at room temperature after electrodeposition and after successive step by step isochronal heat treatments for increasing annealing temperatures. The heat treatments with increasing temperature led to progressive grain growth in the originally ultra fined grain material. By measuring the amplitude dependence of damping with and without magnetic field magneto-elastic and dislocation damping could be separated. It is shown that the increase in the grain size leads to smaller coercivity and therefore to higher damping, as expected. The amplitude dependent magneto-elastically caused damping was determined as the difference between the damping measurements without and with magnetic field for the same specimen. For annealing temperatures higher than 200 °C an inverse proportionality between the slope of logarithmic decrement versus strain amplitude and the square of coercivity was observed like expected from theory.