Characterization of Microchannels Produced by Friction Stir Channeling: An Experimental Study

Friction Stir Channeling (FSC) is a recent and innovative solid state manufacturing technology that allows, in a single pass, the opening of continuous internal channels in monolithic components and can be used in the mold and heat exchanger industries. However, the development of reliable Non-Destructive Testing (NDT) for the characterization of the channels is a major challenge. The focus of this work is the non-destructive characterization of micro channels, and the main goal was to experimentally validate which NDT techniques can be used to identify the presence of microchannels, their regularity along the section, and also their location, size, and path. Five NDT techniques were studied: digital radiology; eddy currents; ultrasounds; thermography; and dye penetrants. These techniques were applied to specimens with linear and curvilinear channels. The specimens were produced using tool pins with 0.5 mm diameter which obtained channels with 0.4 mm width and depths of 0.53 mm. Digital radiology and ultrasounds were effective in detecting channels regardless of its dimensions. Eddy currents did not allow to confirm the exclusive presence of the channels due to microstructural changes caused by the FSC process. Thermography using cold fluid injection was not successful in the channel's characterization due to the extremely low flow. The dye penetrants confirmed the presence of the channels of all dimensions due to the liquid having traveled along the entire path of the curvilinear channel without reaching the surface.