Comparative measurement of residual stresses with the method based on the magnetic Barkhausen noise and the relaxation method
For an efficient prediction of residual stresses in a material or a machine part the non-destructive method based on the magnetic Barkhausen noise is, among others, employed in practice. An experimental system developed at home and including measuring and assessment units has proved to be very efficient in various applications of surface hardening or cold hardening, and heat treatment.
Determination of Residual Stresses Using Micromagnetic Parameters
All ferromagnetic NDE methods are sensitive to the mechanical stress- and microstructure state of the tested material. Therefore, residual stress measurements can only be made if the influence of microstructure can be separated by using two or three independent measuring quantities. Specimens with different microstructure- and residual stress states are tested by X-ray-, hardness-, Barkhausen noise-, and incremental permeability measuring devices. The state of development is demonstrated.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.