Analysis of acoustic emission effect accompanying metal crystallization

Vorontsov, V. B.; Katalnikov, V V

doi:10.1088/1742-6596/98/5/052005

Cited by 9 publications

(2 citation statements)

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“…indium would only exhibit AE upon solidification. The exact cause of AE during melting and solidification is controversial [16], but may be due to frictional noise between solid crystals [17] or cluster addition/subtraction from the solid-liquid interface [18]. In polymers, AE during crystallization is due to cavitation in areas of occluded liquid where shrinkage stresses overwhelm the cohesive strength of the melt [19].…”

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Plastic strain accommodation and acoustic emission during melting of embedded particles

Kuba

Aken

2012

Materials Letters

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Melting point phenomena of micron-sized indium particles embedded in an aluminum matrix were studied by means of acoustic emission. The acoustic energy measured during melting increased with indium content. Acoustic emission during the melting transformation suggests a dislocation generation mechanism to accommodate the 2.5% volume strain required for melting of the embedded particles. A geometrically necessary increase in dislocation density of 4.1 x 10¹³ m⁻² was calculated for the 17 wt% indium composition.Embedding small particles (micron-sized) in a higher melting point matrix is known to increase the melting temperature of the particles. Numerous causes for the phenomenon have been proposed, including strain energy effects [1,2], interfacial energy effects [3][4][5], and kinetic barriers to nucleation [6].Malhotra and Van Aken studied the anelastic strain accommodation during melting of micron-sized indium particles embedded in an aluminum matrix [7][8][9]. By measuring internal friction and performing differential scanning calorimetry (DSC), they concluded that the noted increase in melting temperature was mainly a strain energy effect from the volume expansion during the melting transformation.Acoustic emission (AE) describes the propagation of elastic waves resulting from rapid energy release in a material [10]. Two qualitative types of AE exist: "burst," a discrete signal, and "continuous," a sustained signal usually caused by several bursts overlapping [10]. For example, crack growth tends to generate a burst emission, while dislocation movements result in a continuous emission [11]. Phase transformations that generate AE usually exhibit continuous emission due to time dependent nucleation [11].According to literature, displacive solid-state transformations exhibit AE; the shear mechanism results in rapid strain energy release in the form of AE. Diffusive transformations occur too slowly for this effect [12]. In steels, formation of allotriomorphic ferrite or pearlite would not generate AE [12], but martensite [12] and bainite [13] do. Widmanstätten ferrite may also exhibit AE [13]. AE is often recommended for use as a criterion in determining the displacive or martensitic-like qualities of a solidstate transformation [14]. However, solid-liquid transformations also exhibit AE as the material shrinks [15], e.g. indium would only exhibit AE upon solidification. The exact cause of AE during melting and solidification is controversial [16], but may be due to frictional noise between solid crystals [17] or cluster addition/subtraction from the solid-liquid interface [18]. In polymers, AE during crystallization is due to cavitation in areas of occluded liquid where shrinkage stresses overwhelm the cohesive strength of the melt [19].

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Plastic strain accommodation and acoustic emission during melting of embedded particles

Kuba

Aken

2012

Materials Letters

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“…most materials exhibit AE upon solidification but not melting [5]. The exact cause of solidification AE is debated [6], but may be due to frictional noise between solid crystals [7], cluster addition or subtraction from the solid-liquid interface [8], or perhaps casting separation from the mold wall. AE is detected in crystallizing polymers due to cavitation in areas of occluded liquid where shrinkage stresses overwhelm the cohesive strength of the melt and void formation occurs [9].…”

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Analysis of Acoustic Emission During the Melting of Embedded Indium Particles in an Aluminum Matrix: A Study of Plastic Strain Accommodation During Phase Transformation

Kuba

Aken

2012

Metall Mater Trans A

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Acoustic emission is used here to study melting and solidification of embedded indium particles in the size range of 0.2 to 3 µm in diameter and to show that dislocation generation occurs in the aluminum matrix to accommodate a 2.5% volume change. The volume averaged acoustic energy produced by indium particle melting is similar to that reported for bainite formation upon continuous cooling. A mechanism of prismatic loop generation is proposed to accommodate the volume change and an upper limit to the geometrically necessary increase in dislocation density is calculated as 4.1 x 10 9 cm -² for the Al-17In alloy. Thermomechanical processing is also used to change the size and distribution of the indium particles within the aluminum matrix. Dislocation generation with accompanied acoustic emission occurs when the melting indium particles are associated with grain boundaries or upon solidification where the solid-liquid interfaces act as free surfaces to facilitate dislocation generation. Acoustic emission is not observed for indium particles that require super heating and exhibit elevated melting temperatures. The acoustic emission work corroborates previously proposed relaxation mechanisms from prior internal friction studies and that the superheat observed for melting of these micron-sized particles is a result of matrix constraint. I. INTRODUCTIONRecent study of the aluminum-indium system has shown that equilibrium melting of the indium particles can be detected by acoustic emission (AE) techniques [1]. AE results from rapid energy release that creates elastic pressure waves in a material. According to literature, displacive solid-state transformations generate AE resulting from the shear mechanism of transformation and diffusive transformations normally occur too slowly to generate AE [2]. In steels, martensite [2] and bainite [3] generate AE, but formation of allotriomorphic ferrite or the eutectoid product pearlite does not [2]. Formation of Widmanstätten ferrite has been suggested to also generate AE [3]. Consequently, displacive or martensitic-like solid-state transformations are often distinguished from diffusion controlled phase transformations by the presence of AE [4]. However, liquid-solid transformations are also known to exhibit AE as the solid contracts, i.e. most materials exhibit AE upon solidification but not melting [5]. The exact cause of solidification AE is debated [6], but may be due to frictional noise between solid crystals [7], cluster addition or subtraction from the solid-liquid interface [8], or perhaps casting separation from the mold wall. AE is detected in crystallizing polymers due to cavitation in areas of occluded liquid where shrinkage stresses overwhelm the cohesive strength of the melt and void formation occurs [9].Acoustic emission is also detected during tensile tests for dislocation creation and motion associated with a yield point drop [10] and for void nucleation at nonmetallic inclusions during ductile fracture processes [11]. However, even a small amount of prior cold w...

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Experimental study of the structural characteristics of Al melts on the basis of Fourier analysis of acoustic emission signals

Vorontsov¹,

Zhuravlev²,

Cherepanov³

2014

Journal of Crystal Growth

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Analysis of acoustic emission effect accompanying metal crystallization

Cited by 9 publications

References 1 publication

Plastic strain accommodation and acoustic emission during melting of embedded particles

Plastic strain accommodation and acoustic emission during melting of embedded particles

Analysis of Acoustic Emission During the Melting of Embedded Indium Particles in an Aluminum Matrix: A Study of Plastic Strain Accommodation During Phase Transformation

Experimental study of the structural characteristics of Al melts on the basis of Fourier analysis of acoustic emission signals

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