Research On Creep Resistance Of Al₂O₃Nanoparticles Reinforced Electroplatingnickel

The electroplating nickel has been widely applied in the field of MEMS since ithas the advantages of good electrical conductivity and thermal conductivity,excellent toughness and strength, low residual stress and low coefficient of thermalexpansion, and can also obtain high-aspect-ratio microstructures by LIGA technique.However, the creep behavior of electroplating pure Nickel at room temperature,makes the MEMS devices （especially for power devices, high-temperature devices,long-term loading components, electric actuators etc.） have low reliability at risk fora long time.In order to improve the creep resistance of electroplating nickel, theAl₂O₃nanoparticles that could be added into nicel by composite electroplatingprocess, was choosed as the dispersion strengthened second phase. In this article, theeffect of Al₂O₃nanoparticle content on the coating composition, the properties ofcomponents, construction of parts,was presented. The relationship betweencomposite Al₂O₃nanoparticles and the deformation and crack of the matrix wasinvestigated through dynamic record of the deformation, the initiation andpropagation of crack,that come from pure electroplating nickel and composite nickel.This paper clarify the creep mechanism in detail and the creep properties of purenickel and composite nickel was studied.The results showed that with the increase of the amount of Al₂O₃nanoparticlesin solution, the nanoparticles in composite nickel film continued to increase untilreaching a maximum value, at the same time, the grain size of the nickel filmdecreased and the microhardness of that gradually increased.The Al₂O₃nanoparticles were uniformly dispersed through the metal matrix as a whole, but theagglomerate particles appeared in composite nickel film because of theconglomeration of nano-particles.The agglomerated particle was more loose, thebetter interface between particels and natrix was obtained.We reach the conclusion that the composite nickel had a higher yield strengthand tensile strength than pure nickel through the uniaxial tensile test. Especially, thetensile strength of specimen reached734Mpa and it was improved nearly34.2%comparing with pure nickel when the content of Al₂O₃nano-particles was7.9%.That the crack initiation easily occurred on the boundary between the largeagglomerated particles and the matrix and the crack extended along the microcracksbetween particles and matrix, was in-situ observed by SEM.Finally, in a range of temperature,the steady state creep rate of the composite nickel is lower than that of the pure nickel, and the creep resistance was improvedby adding Al₂O₃nanoparticles as the dispersion strengthened second-phase. Sizeand the crystalline structure of the deformed samples were investigated by TEM,and we found some dislocation cells and dislocation anarl in pure nickel by creeptreatment, but the main structure changes in the creep procees were high densitydislocation formation. In addition,the creep activation energy that was similar tocross-slip, was up to30KJ/mol in pure nickel. Therefore, we can say that creepbehavior is controled by cross-slip in pure nickel. For the composite nickel-basedcoating as electrodeposited, it’s creep activation energy was up to42KJ/mol.