Deformation structures in zone-melted molybdenum

Lawley, A.; Gaigher, H.L.

doi:10.1080/14786436408224204

Cited by 105 publications

(15 citation statements)

References 18 publications

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“…A reduction of the mobility of screw dislocations seems to be caused by a high jog density. Transmission electron micrographs of Lawley and Gaigher [25] as well as of the authors [28] show a considerably high jog density in deformed molybdenum single crystals.…”

Section: Advantages Of Cylindrical Tensile Specimens For Slip System mentioning

confidence: 96%

“…Although work-hardening curves are lacking, Fig. 2 [25] concluded that several slip systems were active from the onset of plastic deformation. Preliminary results obtained with our weakly deformed molybdenum single crystals showed the existence of dislocations with different (111) Burgers-vectors A common explanation is that a t the onset of the plastic deformation only edge dislocations move over considerable distances thereby producing the long smooth slip traces at the side line.…”

Section: Advantages Of Cylindrical Tensile Specimens For Slip System mentioning

confidence: 99%

“…Besides, it is to be mentioned that Davidson and Brotzen [23] measured in direct shear a t molybdenum on (112) a higher flow stress than on { 110). [25] concluded that several slip systems were active from the onset of plastic deformation. Preliminary results obtained with our weakly deformed molybdenum single crystals showed the existence of dislocations with different (111) Burgers-vectors in comparable densities.…”

Section: Advantages Of Cylindrical Tensile Specimens For Slip System mentioning

confidence: 99%

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Slip Line Pattern and Active Slip Systems of Tungsten and Molybdenum Single Crystals Weakly Deformed in Tension at Room Temperature

Kaun

Luft

Richter

et al. 1968

Physica Status Solidi (b)

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Electron zone-refined tungsten and molybdenum single crystals are deformed in tension a t room temperature. The slip systems on the cylinder-shaped tensile specimens are determined using the light as well as the electron microscope. The slip line pattern depends sensitively on the orientation of the stress axis. Single slip on the crystals investigated is not observed. The slip occurs preferentially on planes of type { 110}, but usually further slip planes of the <111> zone are also active. The slip band structure is discussed in terms of elementary slip processes.Elektronenzonengeschmolzene Wolfram-und Molybdln-Einkristalle wurden bei Raumtemperatur im Zugversuch verformt. Mittels licht-und elektronenmikroskopischer Methoden wurden die Gleitsysteme an den zylinderformigen Zugproben bestimmt. Das Gleitlinienbild war stark abhiingig von der Achsenorientierung. An den untersuchten Kristallen konnte keine Einfachgleitung beobachtet werden. Die Abgleitung erfolgte auf Ebenen vom Typ { 1103, aber meistens waren auch noch andere Gleitebenen der (111)-Zone wirksam. Die Gleitlinienstruktur wird in Verbindung mit elementaren Gleitprozessen diskutiert.

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Section: Advantages Of Cylindrical Tensile Specimens For Slip System mentioning

confidence: 96%

Section: Advantages Of Cylindrical Tensile Specimens For Slip System mentioning

confidence: 99%

Section: Advantages Of Cylindrical Tensile Specimens For Slip System mentioning

confidence: 99%

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Slip Line Pattern and Active Slip Systems of Tungsten and Molybdenum Single Crystals Weakly Deformed in Tension at Room Temperature

Kaun

Luft

Richter

et al. 1968

Physica Status Solidi (b)

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“…Iron crystals indicate a similar behaviour [7, 301. Orava et al [ l l ] observed on niobium and Lawley and Gaigher [18] on molybdenum single crystals an increasing density of secondary dislocations as the temperature is decreased. However, it is hard t o accept that the increased secondary slip activity at low temperatures may be the result of increasing internal stresses due to the presence of many primary screws as presumed by Hirsch in the discussion to [ l l ] .…”

Section: Primary and Secondary Slip Activitiesmentioning

confidence: 99%

Electron Microscopic Investigation of the Dislocation Structure in Molybdenum Single Crystals Deformed in Tension at 293 and 493 °K

Luft¹,

Kaun²

1970

Physica Status Solidi (b)

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The dislocation structure of high purity molybdenum single crystals after weak tensile deformation a t 293 and 493 O K is studied b y transmission electron microscopy. The transition from parabolic stress-strain behaviour to three-stage hardening which occurs between the considered temperatures is associated with a basic change in the deformation substructure. Crystals deformed at 293 OK contain a uniform distribution of long primary and secondary screw dislocations. On the contrary, the dislocation structure in stage I at 493 O K consists mainly of isolated clusters of primary edge dipoles. It is concluded that the effect of temperature on the mobility of screw dislocations is responsible for the change observed both in work-hardening characteristics and related dislocation structures.

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“…The rapid increase in work hardening rate with decreasing temperature appears to be peculiar to the group VI metals, as it has also been observed in molybdenum as well (ref. 24). Other BCC metals, such as tantalum and iron, have a work-hardening rate which decreases with decreasing temperature below room temperature (ref.…”

Section: Work Hardeningmentioning

confidence: 99%

Yielding and fracture in tungsten and tungsten-rhenium alloys

Raffo

1969

Journal of the Less Common Metals

186

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A study was made of the mechanical properties of vacuum arc-melted tungsten and tungsten-rhenium alloys in the temperature range 77' to 810' K in order to elucidate the mechanism by which rhenium additions lower the ductile-brittle transition temperature of tungsten. The temperature and strain-rate dependency of the yield s t r e s s of tungsten is reduced by alloying with rhenium. This is shown to be because of a reduction in the Peierls s t r e s s . The reduction in the transition temperature is attributed to the reduced Peierls s t r e s s through its effect on the mobility and rate of multiplication of dislocations.ii I- ' YIELDING AND FRACTURE IN TUNGSTEN AND TUNGSTEN-RHENIUM ALLOYSby Peter L. Raffo Lewis Research Center SUMMARY A study was made of the mechanical properties of vacuum arc-melted tungsten and tungsten-rhenium alloys in the temperature range 7 7 O to 810' K. The ductile-brittle transition temperature of the unalloyed recrystallized tungsten prepared for this study was 490' K and was reduced to 430' and 350' K by additions of 2 and 25 percent rhenium (Re), respectively. The temperature and strain rate dependence of the yield stress of tungsten is decreased by alloying with rhenium. The work-hardening rate of l-percent plastic s t r a i n for unalloyed tungsten (W) increases rapidly with decreasing temperature, although it is relatively independent of temperature in the W-Re alloys. In unalloyed tungsten and dilute W-Re alloys, fracture was mainly by cleavage. In these materials, fracture is controlled by crack initiation; in the W-25-percent-Re alloy, failure is con trolled by crack propagation. The observations suggest that yielding of unalloyed tungsten is controlled by the nucleation of kink pairs over the Peierls b a r r i e r . Alloying with rhenium reduces the Peierls stress. The yielding of a W-25-percent-Re alloy is con trolled by a similar mechanism at low temperatures; at higher temperatures, an appar ent decrease in the s tacking-fault energy alters the yielding mechanism to one in which it is controlled by the recombination of dissociated screw dislocations. The reduction in the transition temperature in W-Re alloys is thought to be caused by the stress relax ation effect of an increased plastic-strain rate at the tip of a crack as a result of in creased dislocation mobilities and multiplication rates. Various theories have been advanced to explain the brittleness of these metals, with varying degrees of success. The fact that the transition temperature is sensitive to the presence of interstitial impurities has received the most attention and is supported by the fact that zone purification of molybdenum and tungsten has resulted i n significant decreases i n the transition temperature (refs. 3 and 4). The major effect of inter stitials appears to be related to their interaction with grain boundaries either in solid solution o r as Lxecipitate(ref. 5), since single crystals of the group VI metals are ductile at temperatures well below ambient. Other theories advanced t...

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Deformation structures in zone-melted molybdenum

Cited by 105 publications

References 18 publications

Slip Line Pattern and Active Slip Systems of Tungsten and Molybdenum Single Crystals Weakly Deformed in Tension at Room Temperature

Slip Line Pattern and Active Slip Systems of Tungsten and Molybdenum Single Crystals Weakly Deformed in Tension at Room Temperature

Electron Microscopic Investigation of the Dislocation Structure in Molybdenum Single Crystals Deformed in Tension at 293 and 493 °K

Yielding and fracture in tungsten and tungsten-rhenium alloys

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