Advanced NDT Inspection Tools for Titanium Surfaces Based on High-Performance Magnetoresistive Sensors

Abstract

Eddy current testing (ECT) is a high impact technology to detect surface flaws. However, its reliability is reduced for low conductive titanium alloys, which are broadly integrated into the industry. ECT tools based on magnetoresistive (MR) sensors offer advantages over inductive sensors due to an enhanced spatial resolution, high sensitivity, and bandwidth. In this paper, we demonstrate successful non-destructive testing inspection of titanium surfaces, not achieved by other ECT tools. Here, single surface defect (length = 0.6 mm; width $=100~\mu \text{m}$ ; depth $=50~\mu \text{m}$ ) in a non-polished TA6V $\alpha $ titanium mock-up was measured using an MR-ECT probe. The detection was made by an array of magnetic tunnel junctions with $50 \times 50~\mu \text{m}^{\mathrm { {2}}}$ with optimized field detectivity. A differential measurement employing a heterodyne technique isolated the magnetic field component ( $f_{H}- f_{\mathrm { {bias}}} = 1$ kHz) from the electric biasing component ( $f_{\mathrm { {bias}}} = 4999$ kHz) and electromagnetic coupling ( $f_{H} = 5$ MHz), revealing a bipolar defect signature of $6.01~\mu \text{V}_{\text {0-p}}$ amplitude.