Properties of electrodeposited invar Fe-Ni alloy/SiC composite film

Electrodeposited Invar Fe-Ni alloy/SiC composite films were obtained by the composite electroplating method, and the properties of the composite films were assessed correlated to their microstructure. Invar Fe-35 to 37 mass% Ni alloy/SiC composite films with the maximum SiC contents of 20.8 vol% were obtained. The co-deposition of SiC particles into the Invar Fe-35 to 37 mass% Ni alloy film increased the hardness of the as-deposited films, and suppressed the decrease in hardness by the heat treatment at 600 °C; the heat treatment is essential to reduce the coefficient of thermal expansion of the electrodeposited Invar films. The hardness of the composite films with around 20 vol% of SiC remained almost unchanged after 600 °C heat treatment. This was attributed to the inhibition of grain growth by SiC particle distribution. The electrodeposited Invar Fe-35 to 37 mass% Ni alloy/SiC (approximately 20 vol%) composite films after the heat treatment at 600 °C both exhibited sufficiently high hardness and low CTE, and therefore, these composite films can be used in the fabrication of MEMS elements where high mechanical strength and high thermal dimensional stability are required.