(Invited) Design of Effective Pulse Deposition Process for Functional Cr Coatings from Cr3+ Electrolyte

Abstract

The presented work investigates the pulse current deposition as an approach for electrodeposition of functional Cr films. Our data suggest that observed growth stress during DC Cr deposition are negative, i.e. compressive with steady state values in the range below -100 MPa. The negative stress is associated with blistering in Cr films and accumulation of different defects on the Cr film surface during deposition which indicated significant amount of dissolved hydrogen either as interstitial impurity or as a part of chemically bonded H as Cr-hydride. Stress, impedance and optical results undoubtedly suggest that weakened structure of the Cr films by oxidation process has a true origin in Cr-hydride formation and subsequent oxidation of its degradation by-products (H and Cr). Therefore, the electrodeposition process that produces less Cr-hydride in the deposit should be more desirable when the crack free Cr films are the goal. Our pulse current function design is therefore driven by the goal to achieve Cr-films with minimum amount of Cr-hydride phase. The off time of the pulse current cycle is designed to allow break up and decomposition of hydride phase which has been formed in preceding current on part of the pulse cycle. Our in situ stress data show that using such approach, it is possible to completely change the sing of the insitu stress in Cr films during deposition from compressive to tensile. More importantly, we will show the first indications that pulse electrodeposited Cr films have similar micro-cracked structure as Cr films electrodeposited from Cr6+ solutions. This work is supported by Gift Grant from NASF-AESF Research Foundation.