Abstract
The detectability of small inclusions and subtle imperfections by magnetic measurements that senses thermoelectric currents produced by a temperature gradient is ultimately limited by the intrinsic thermoelectric anisotropy and inhomogeneity of the material to be inspected. The probability of detection (POD) of a given material flaw is determined by the resulting signal-to-noise ratio rather than by the absolute magnitude of the signal itself. The strength of the magnetic field to be detected greatly depends on the physical nature of the host medium and dimensions of the imperfection. This paper presents experimental data for the magnetic field produced by thermoelectric currents around tin inclusions in different host medium such as 316LVM stainless steel and Ti-6Al-4V titanium alloy under external thermal excitation. The diameter of the inclusions and the lift-off distance varied from 0.39 to 3.175 mm and from 1 to 10 mm, respectively. A 0.6 °C/cm temperature gradient in the samples produced peak magnetic flux densities ranging from 0.1 to 280 nT, that was measured by a fluxgate magnetometer. The numerical results were found to be in good agreement with theoretical predictions and demonstrated that both property anisotropy and gradient in thermoelectric materials can significantly influence the induced thermoelectric currents and magnetic fields.
Highlights
316 LVM and Ti-6Al-4V alloys are extensively used in the medical and engineering industries due to their intrinsic properties, such as corrosion resistance, biocompatibility, and excellent high temperature properties
The purpose of this investigation was to suggest an alternative non-destructive method of characterizing metallic inclusions embedded in a host medium that are free from cracks and voids
We present experimental and theoretical results of un-cracked tin inclusions in 316 LVM and Ti–6Al–4V under external thermal gradient which truthfully captures the
Summary
316 LVM (low carbon vacuum melt) and Ti-6Al-4V alloys are extensively used in the medical and engineering industries due to their intrinsic properties, such as corrosion resistance, biocompatibility, and excellent high temperature properties. Initiation sites for failure of titanium-base alloys and stainless steels in the components of interest can occur due to inclusions These inclusions are high interstitial defects and are regions of much higher hardness than the surrounding material. For ultrasonic detection of this type of inclusions includes a multizone system that uses multiple channels employing focused transducers of 5MHz and analog electronics.[1] Another current method for detection is photon induced positron annihilation (PIPA) developed by Positron Systems. This method promises to detect smaller, buried inclusions that other nondestructive methods cannot detect. We present experimental and theoretical results of un-cracked tin inclusions in 316 LVM and Ti–6Al–4V under external thermal gradient which truthfully captures the
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