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Determination of sub-surface microstructure states by micromagnetic NDT

: Altpeter, I.; Kern, R.; Theiner, W.

Bussiere, J.F.:
Nondestructive Characterization of Materials II
New York/N.Y.: Plenum Press, 1987
ISBN: 0-306-42610-2
International Symposium on Nondestructive Characterization of Materials <2, 1986, Montreal>
Fraunhofer IZFP ()
Barkhausen-Rauschen; Gefüge; Gefügegradiant; Induktionshärte; Magnetostriktion(dynamisch); Mikromagnetik; Spannung; überlagerungspermeabilität

The functional behaviour of many components is determined by the intrinsic properties - residual stresses and microstructure - of sub-surface near zones. Therefore, in order to improve the static and dynamic mechanical properties of these surface near states, mechanical and/or thermal treatments such as laser hardening, inductive hardening, case hardening, nitriding, grinding and shot peening are applied. Depending upon the workpiece/component and the employed technique and machining parameters, the residual stress- and microstructure states will be changed between a few micrometers and several millimeters. To control the quality of these subsurface near states, metallographic inspections, x-ray methods and hardness measurements have been applied. Because all these conventional testing methods are expensive, time consuming and not suitable for real time control, 1-4 there is a considerable need of nondestructive testing (ndt) methods. So far ndt procedures are mainly restricted to eddy current methods, 5,6 ultrasonic techniques 7,8 and - in the case of ferromagnetic materials - micromagnetic techniques 1,9-11. (IZFP)