Vol 52, No 11 (2016)

A novel primary attachable transducer has been developed. The transducer makes it possible to estimate the level of residual mechanical stresses at local spots of articles that are made of lowcarbon steels. The critical fields of displacement of 90-degree domain boundaries have been determined experimentally by using a technique that allows one to separate contributions from two types of domain boundaries to the magnetization reversal by means of simultaneous action of two orthogonal magnetic fields. Optimum operating parameters of the primary transducer have been established.

The possibilities are studied for using an electromagnetic eddy-current technique of monitoring the phase composition and hardness of austenitic chromium–nickel steel that has been subjected to hardening frictional treatment in different technological regimes. It is shown that an eddy-current structuroscope and a Vektor eddy-current defectoscope make it possible to control the amount of straininduced martensite and the microhardness of the surface of metastable austenitic steel after nanostructuring frictional treatment with different numbers of gliding indenter scans (passes). The Vektor eddycurrent defectoscope allows one to monitor the phase composition of austenitic steel that has been subjected to nanostructuring frictional treatment in a temperature range from −196 to +250°C.

Principles of measuring magnetoimpedance effect in samples that are intended for constructing electronic circuits that contain sensing elements for detecting weak magnetic fields, including stray fields, are described. Special attention is paid to those existent techniques of measuring magnetoimpedance effect in magnetic structures with distinctly manifested magnetic anisotropy that have already been used in or look promising for systems of magnetic nondestructive testing. The merits and drawbacks of a computer-aided magnetoimpedance-spectroscopy facility that has been designed at Ural Federal University are discussed in detail. The facility is based on an Agilent E4991a impedance analyzer that has been adapted for studying a wide class of magnetic structures.

An acoustic signal that is excited without acoustic contact by an excitation electrode in a metal sample has been studied. A constant electric voltage close to the breakdown value was applied between the electrode and the sample. A video pulse of electric field with a duration of 0.4 μs was used to excite sound in the sample. The ratio k of signals that were registered with noncontact and contact excitation proved surprisingly large (k = 0.14) when compared to the value expected from the literature data. A strong dependence of the noncontact acoustic signal on the filling frequency f of the excitation pulse has been observed. For f > 10 MHZ, the signal dropped to the level of noises. An explanation for this frequency dependence is proposed. It is based on the assumption of quasi-atomic thickness of the charged metal layer that is created by the electric field.

The effectiveness of Kelvin probe force microscopy, which is one of the scanning probe techniques, is demonstrated for assessing plastic-deformation induced changes in the phase composition of 08Kh21N6M2T austenite–martensite chromium–nickel steel. Changes in the numerical values of surface potentials of different phase components of two- and three-phase stainless steels versus sample deformation extent have been established. Dependence of surface electric potentials as measured with Kelvin probe force microscopy on the presence and amount of newly formed deformationmartensite phase has been discovered.