Deformation Processing of Anisotropic Metals

Avery, Donald H.; Backofen, W. A.

doi:10.21236/ad0463896

Cited by 11 publications

(19 citation statements)

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“…The presence of coarsened shear bands in the crept specimens is documented in Figure 8b, which shows a coarsened band parallel to the wetted interface, note that the coarsened band is nearly straight A higher magnification photograph, Figure 9, shows c that the material within the coarsened band consists of relatively large, equiaxed grains which resemble the grains formed by recrystallization of mechanically worked Pb-Sn · eutectics [10,11]. This is the normal microstructure within a coarsened band.…”

Section: The Formation Of Coarsened Bands During Creep In Shearmentioning

confidence: 81%

“…It is well known [10] that the replacement of the eutectic microstructure by a coarse microstructure of more equiaxed gains weakens the solder. Hence the cyclic shear strain is expected to concentrate in the coarsened band and induce fatigue there.…”

Section: Page3mentioning

confidence: 99%

“…The coarsened band that leads to fracture in the sample is always coincident with the parallel deformation band described above, and forms first at the terminus of the deformation band at the free surface, Figure The mechanism that initiates the coarsened band seems straightforward. It is well known [ 10,11] that the eutectic microstructure in the Pb-Sn system is unstable with respect to recrystallization if it is deformed at a high homologous temperature or exposed to high temperature after deformation. The inhomogeneous shear strain that develops during creep creates a band of concentrated plastic deformation, which is greatest at the free surface near the stress concentration point The eutectic recrystallizes there to relieve the accumulated deformation.…”

Section: The Formation Of Coarsened Bands During Creep In Shearmentioning

confidence: 99%

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Observations on the Mechanisms of Fatigue in Eutectic Pb-Sn Solder Joints

Tribula

Grivas

Frear

et al. 1989

Journal of Electronic Packaging

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Near-eutectic Pb-Sn solders are widely used for joints in electrical devices. These are liable to failure by thermal fatigue during operation of the device. Since the thermal fatigue load is often in shear, mechanisms of thermal fatigue in shear are of particular interest. Recent research has shown that the thermal fatigue of eutectic solders in shear is preceded by the formation of bands of coarsened material in the eutectic microstructure, which concentrate the deformation and cause the nucleation of fatigue cracks. Such coarsened bands are also observed in isothermal fatigue and unidirectional creep in shear. Since creep experiments are relatively simple to conduct and analyze, these have been used to study the formation and growth of coarsened bands. The mechanism includes three steps: the formation of inhomogeneous shear bands, the onset of recrystallization in the shear band to create a planar region of coarsened material, and the propagation of the coarsened band by progressive recrystallization at its tip. The results are applied to thermal fatigue and some of their implications are discussed.

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Section: The Formation Of Coarsened Bands During Creep In Shearmentioning

confidence: 81%

Section: Page3mentioning

confidence: 99%

Section: The Formation Of Coarsened Bands During Creep In Shearmentioning

confidence: 99%

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Observations on the Mechanisms of Fatigue in Eutectic Pb-Sn Solder Joints

Tribula

Grivas

Frear

et al. 1989

Journal of Electronic Packaging

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“…Although Grosskreutz(3) and others (18) suggested that the sub-boundaries be a preferred path of fatigue crack, no experimental evidence to support this has so far been presented. The present experiment offers some evidence to support this view.…”

Section: Transmission Electron Microscopymentioning

confidence: 99%

Studies on Substructures around a Fatigue Crack in <I>fcc</I> Metals and Alloys

Karashima

Ogura

1968

Trans. JIM

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To establish the relationship between the substructure formation and fatigue crack propagation, substructures around a fatigue crack in aluminium, copper, a-brass and aluminium-bronze have been examined by means of an X-ray microbeam technique and transmission electron microscopy.The results are: (1) So-called plastic zones have been observed in the vicinity of fatigue cracks in all the metals and aluminium, subgrains in the plastic zones are smaller than those in the matrix. (4) The higher the stacking-fault energy, the more pronounced becomes the substructure formation. (5) Fatigue cracks in aluminium have been found to propagate through a specimen of the well-developed substructure more easily than through a specimen of the less developed substructure. Direct evidence that fatigue cracks propagate along sub-boundaries has been obtained. (6) Strain-concentrated regions as well as the plastic zones have been observed around fatigue cracks by an electron microscope. In view of the above experimental results, the substructure formation is concluded to play an important role in the propagation of fatigue cracks.

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“…This superplasticity was attributed to the stable, equiaxed microstructure that results from recrystallization at room temperature. Others [5][6][7][8][9][10][11][12][13][14][15][16][17][18] have explored the dependence of superplasticity in cold-worked Sn-Pb alloys on variables, such as testing temperature, grain size, stress, and strain rate. In contrast to the extensive studies on the cold-worked and recrystallized Sn-Pb alloys, little attention has been paid to the alloys in the as-cast condition, beyond the repeated observation that as-cast alloys are not superplastic 3,4,6,19. But the recent works by Solomon 20, and by Seyyedi, Arsenault, and Keller 21 have shown that as-solidified solder joints exhibit some superplastic characteristics: the stress exponent, n, in the relation, ' Y = A cr 0 , is between 2 and 3 in a certain strain rate range.…”

Section: Introductionmentioning

confidence: 99%