The use of generalized magnetic parameters for magnetic structural analysis and nondestructive testing

Abstract

The results of studies regarding the dependence of the product of the coercive force and the initial magnetic susceptibility of a nickel single crystal with an intermediate orientation on the shear stress are analyzed. It is concluded that an increase in the aforementioned product χ in H c for a nickel single crystal upon cold plastic deformation is due to refining of magnetic domains that is caused by formation of cells and subgrains within the single crystal. The tentative size of magnetic domains was determined based on the value of generalized magnetic parameter ( χ in H c )/ M s . The variations in the χ in H c product and in the calculated dimensions of magnetic domains in polycrystalline nickel are analyzed using data reported by Kersten-Gottschalt. It was also shown that, the density of dislocations being constant, the generalized magnetic parameter M Hr /( χ in H c ) is sensitive to changes in the sizes of nonferromagnetic inclusions, whereas in the case of small nonferromagnetic inclusions, an increase in the generalized parameter is due to an increase in the density of dislocations.We have calculated the relaxation magnetization M Hr for a ferromagnet with crystal-structure defects in the form of statistically distributed spherical nonferromagnetic inclusions with diameter d inc [1][2][3] ,(where M s is the saturation magnetization, L z is the magnetic-domain size along the displacement direction of a domain boundary of area S δ and thickness δ 180 , ν = L z /2 δ 180 , and ϕ is the angle between the magneticfield direction and the magnetization of the crystal. When the domain boundary motion is hindered by stresses appearing due to the presence of dislocations, ,where r is the density of dislocations, which is determined as the number of dislocations intersecting a unitarea surface (according to a different definition, r is the total length of all dislocations per unit volume [4]). From the expressions above, it follows that, in contrast to the coercive force that is sensitive to various structural changes , the relaxation magnetization is proportional to the average number of domains N ~ 1/ L z in the state H ≅ H c and to the average diameter of nonferromagnetic inclusions. The relaxation magnetization is inversely proportional to the square root of the density of dislocations. When nonferromagnetic inclusions and dislocation-induced stresses affect parameter M Hr , ;(M Hr (i) and χ r (i) are the relaxation magnetization and magnetic susceptibility attributed to nonferromagnetic inclusions, respectively, and M Hr ( r ) and χ r ( r ) are the same magnitudes attributed to dislocations, respectively.The dependences of M Hr of many steels on the heating temperature during quenching and tempering are described in [41][42][43], while the dependences on the degree of cold plastic deformation and the temperature during subsequent annealing are described in [44]. The M Hr parameter is used for the nondestructive testing of the quality of articles both as an independent characteristic [45][46][47] and along wit...

Materials Degradation and Detection (MD2): Deep Dive Final Report

“…Magnetization occurs via various processes, among them movement of magnetic domain walls. Domain wall motion is impeded by defects such as dislocations, precipitates, voids, and second phases (Bida 2004). Irradiation produces and/or destroys these types of defects, thus changing the local coercive fields of the material.…”