Nondestructive Determination of Case Depth

In order to increase wear resistance, many critical components such as shafts and gears are case hardened. Case hardening, such as induction hardening, carburizing or nitiriding, can create a hard wear-resistant surface layer The depth of the case hardened layer must be controlled to achieve optimum in-service performance of the component. There is currently no reliable nondestructive method of determining case depth. Eddy current offers the potential to provide that capability. JENTEK and others have shown correlations between electromagnetic properties, i.e., conductivity and permeability, and steel microstructure. Also, local electromagnetic properties, measured on a cross section, have been correlated with hardness in case hardened samples. In testing for a major automotive manufacturer, JENTEK has shown a preliminary correlation between case depth and magnetic permeability measured from the external surface. In this proposed Phase I program JENTEK will work with Bell Helicopter, Rolls-Royce and Sikorsky to adapt JENTEK’s Meandering Winding Magnetometer (MWM) and model based inverse methods for nondestructive determination of case depth. The MWM and MWM-Array are thin and conformable eddy current sensors that deliver superior materials characterization performance for challenging applications and have a strong potential to provide an effective tool for case depth measurement.