In-situ hardness evaluation of hard-faced coatings through eddy current NDE

In order to improve galling resistance of nuclear components that are made of AISI type 316 (LN) stainless steel, Plasma Transferred Arc Welding (PTAW) is being followed for hard facing of nickel based alloys. However, the change in welding deposition parameters highly influences the required property of coatings. The quality of coating is assessed widely through chemical composition and hardness in production stage. The assessment on the inner diameter side of smaller diameter tubes due to inaccessibility of those measurements demand for the requirement of a quality control tool. In view of this, Eddy current (EC) non-destructive technique, which is sensitive to change in electrical conductivity and magnetic permeability of the material is utilised. EC phase angle measurement shows good sensitivity to the increase in iron content on the top surface of the coating resulted due to the increase in deposition current. Quadratic relationship between iron content in the coating and measured EC phase angle has been established. Hardness is observed to decrease with increasing iron content in the coating. Well correlated response between measured hardness and phase angle measurement promises a good in-situ tool for hardness evaluation of hard-faced coatings on small diameter tubes.