Hall coefficient measurement for nondestructive materials characterization

Abstract

Articles you may be interested inNondestructive thermoelectric evaluation of the grit blasting induced effects in metallic biomaterials AIP Conf. Proc. 1511, 1504 (2013); 10.1063/1.4789220 Development of nondestructive non-contact acousto-thermal evaluation technique for damage detection in materials Rev. Sci. Instrum. 83, 095103 (2012); 10.1063/1.4749245Characterization of an epoxy bonded aluminum alloy sample applying dynamic acousto elastic testing AIP Conf.ABSTRACT. Although Hall detectors are widely used for magnetic flux density measurements in numerous electromagnetic NDE applications, measurement of the Hall coefficient of metals and their alloys for NDE purposes has not been successfully attempted before. While other intrinsic electric properties, such as electric conductivity and, to a lesser degree, thermoelectric power, are widely used for NDE, Hall coefficient measurements have never been really considered mainly because the measurements are rather difficult to carry out, especially in high-conductivity materials. In contrast to electric conductivity, the Hall coefficient is influenced mainly by the concentration density of the free charge carriers, i.e., electrons in metals, and not so much by their mobility, therefore it could be a valuable addition to our NDE arsenal. We modified the alternating current potential drop (ACPD) method with square-electrode configuration by adding an external bias magnetic field modulation to measure the Hall coefficient. The presence of such a bias field violates the Reciprocity Theorem unless the sign of the magnetic field is switched between the two measurements, which can be exploited to measure the Hall coefficient in the presence of other variations that would otherwise hide it. This new experimental method was tested on paramagnetic alloys and yielded a ±4% reproducibility that probably could be further improved by additional development efforts. As a first step towards illustrating some of the potential applications of this new technique, we have done reversible applied stress measurements in Al 1100 plates and found the sensitivity of the technique to elastic strain surprisingly high.

Stress dependence of Hall coefficient in a nickel-base superalloy

“…It is believed that the lack of selectivity of Eddy current technique to residual stress is mainly due to the sensitivity of carrier mobility to microstructure change while the carrier density (physically the only parameter that determines the Hall coefficient value) is much less influenced [7]. Recently the stress-dependence of Hall coefficient was measured on two Nickel-base superalloys such as IN718 and IN600 [8,11].…”

“…Therefore an ideal non-destructive technique for residual stress profiling should not only be sensitive to the residual stress state, but more importantly exhibit least sensitivity to the disturbing factors such as cold work and hardness. Hall coefficient method has been proposed recently and it is anticipated to be more selective to residual stress [1,7,8]. This paper presents the stress dependence of Hall coefficient in a Nickel-base superalloy Inconel 100 (IN100), which is the initial step to apply the Hall coefficient method to nondestructive measurement of subsurface residual stress.…”

Nondestructive hall coefficient measurements using ACPD techniques

“…In a first-order approximation, the total current density J can be written as the sum of [12]. To avoid this problem, Nagy used a permanent magnet of diameter D m ≈ d << D that resulted in a restricted nonuniform magnetic field and thereby in a measurable Hall voltage across the sensing points [5]. A unitless constant K was included in the expression for the Hall coefficient R H , where K depended on the D m /d ratio.…”

“…Without such cutting, no Hall potential is produced in case of a thin plate in the presence of a uniform normal magnetic field [2][3][4]. In the context of NDE of residual stress, a recent preliminary study demonstrated that the well-known alternating current potential drop (ACPD) method combined with magnetic modulation can be used to measure the Hall coefficient in nonmagnetic alloys and that this effect is highly sensitive to the presence of elastic strain in aluminum and copper alloys [5]. More recently, Kosaka et al found a strong dependence of the Hall coefficient on the applied stress in IN600 and IN718 nickel-base superalloys [6].…”

“…To answer this question, we will consider the feasibility of using square-electrode ACPD probes that were originally developed for directional conductivity measurements [8] and later successfully implemented in creep monitoring [9]. It has been shown that this technique could be modified to measure the Hall coefficient in thin plates of nonmagnetic alloys without any destructive sample preparation with current injection and voltage sensing along the orthogonal diagonals of the square probe [5]. It was reported without explanation that low-frequency measurements conducted with a square-configuration ACPD probe with springloaded electrodes and external bias magnetic field could be used to produce a measurable Hall voltage across the sensing electrodes when the diameter of the permanent magnet used to produce the external magnetic bias field matched the diagonal distance between the two sensing electrodes.…”