Barkhausen Noise Emission in Hard-Milled Surfaces

Abstract

This paper reports on an investigation treating a hard-milled surface as a surface undergoing severe plastic deformation at elevated temperatures. This surface exhibits remarkable magnetic anisotropy (expressed in term of Barkhausen noise). This paper also shows that Barkhausen noise emission in a hard-milled surface is a function of tool wear and the corresponding microstructure transformations initiated in the tool/machined surface interface. The paper discusses the specific character of Barkhausen noise bursts and the unusually high magnitude of Barkhausen noise pulses, especially at a low degree of tool wear. The main causes can be seen in specific structures and the corresponding domain configurations formed during rapid cooling following surface heating. Domains are not randomly but preferentially oriented in the direction of the cutting speed. Barkhausen noise signals (measured in two perpendicular directions such as cutting speed and feed direction) indicate that the mechanism of Bloch wall motion during cyclic magnetization in hard-milled surfaces differs from surfaces produced by grinding cycles or the raw surface after heat treatment.

Asymmetrical Barkhausen Noise of a Hard Milled Surface

“…A cutting depth of a p = 0.25 mm, a feed speed of v f = 112 mm·min −1 (the feed direction corresponds to the axial direction on the milled surface) and a cutting speed of v c = 78.5 m·min −1 (the cutting speed direction corresponds to the tangential direction on the milled surface) were used. More details regarding the process kinematics and MBN measurements can be found in previous publications [ 4 , 5 , 6 ]. MBN was measured by the use of RollScan 300 (Stresstech, Jyväskylä, Finland) and software µScan (version 5.4.1) (magnetising voltage in the range of 4 to 16 V, a magnetising frequency of 125 Hz, ten bursts and a frequency range of MBN signal from 10 to 1000 kHz).…”

“…However, the thickness of the HAZ and WLs after hard milling is about one order of magnitude lower than that induced by grinding. Furthermore, the ratio between the WL and HAZ thickness after hard machining (turning or milling) is much higher compared to grinding [ 3 , 4 ]. Hard turned or milled WLs are denser and more uniform with a severely strained matrix, whereas ground WLs retain their original appearance [ 2 , 4 , 5 ].…”

“…Furthermore, the ratio between the WL and HAZ thickness after hard machining (turning or milling) is much higher compared to grinding [ 3 , 4 ]. Hard turned or milled WLs are denser and more uniform with a severely strained matrix, whereas ground WLs retain their original appearance [ 2 , 4 , 5 ]. Compared to the bulk, the HAZ produces richer Barkhausen noise emissions (due to tensile stresses, reduced dislocation density and the modification of carbides, i.e., their size, density and morphology), whereas WLs induced by grinding cycles in the near-surface region emit poor Barkhausen noise due to the existence of a higher volume of retained austenite, compressive stresses and very fine grains [ 2 ].…”

Assessment of Tendon Prestressing after Long-Term Service via the Barkhausen Noise Technique

“…Domain walls are pinned by dislocation tangles, precipitates, grain boundaries, non-ferromagnetic particles, or phases, etc. [18,19,20,21]. On the other hand, the stress state strongly affects the domain walls’ alignment.…”

Surface Integrity after Turning a Duplex Stainless Steel with Respect to Tool Geometry

“…The MBN is sensitive to RSs as well as the microstructure. BWs interfere with lattice defects, whereas RSs affect mainly the BW alignment [15][16][17]. Therefore, the MBN is potentially a promising technique for monitoring the surface state of a duplex stainless steel.…”