On the role of interface imperfections in thermoelectric nondestructive materials characterization

This letter draws attention to a previously unnoticed artifact associated with the most common type of thermoelectric nondestructive materials characterization technique. It is shown that contact heating between the specimen to be tested and the reference electrode gives rise to a considerable offset in the measured thermoelectric voltage. The resulting bias significantly reduces the feasibility of thermoelectric measurements in nondestructive testing applications that require sensitive materials discrimination, for example, to sort metals of similar alloying content, to distinguish similar grades of heat treatment, and to detect slight variations in the thermoelectric power of metals due to hardening, texture, fatigue, etc. It is also suggested that the demonstrated intrinsic sensitivity of the thermoelectric contact technique to imperfect interfaces could be exploited for nondestructive detection of tightly compressed but metallurgically not bonded interfaces in spot welds, diffusion bonds, and other types of solid-state bonds. (C) 1998 American Institute of Physics.