Dynamic Dislocation Mechanisms For the Anomalous Slip in a Single-Crystal BCC Metal Oriented for "Single Slip"

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Dislocation substructures of high-purity Mo single crystals deformed under uniaxial compression at room temperature to an axial strain of 0.6% were investigated in order to elucidate the underlying mechanisms for the {l_brace}0{bar 1}1{r_brace} anomalous slip in bcc metals [1], which is also known as the violation of Schmid law [2]. The test sample was oriented with the stress axis parallel to a nominal ''single-slip'' orientation of [{bar 2} 9 20], in which ({bar 1}01) [111] is the primary slip system that has a maximum Schmid factor (m = 0.5), which requires the lowest stress to operate among the twelve {l_brace}{bar ... continued below

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Hsiung, L & La Cruz, C January 11, 2007.

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Dislocation substructures of high-purity Mo single crystals deformed under uniaxial compression at room temperature to an axial strain of 0.6% were investigated in order to elucidate the underlying mechanisms for the {l_brace}0{bar 1}1{r_brace} anomalous slip in bcc metals [1], which is also known as the violation of Schmid law [2]. The test sample was oriented with the stress axis parallel to a nominal ''single-slip'' orientation of [{bar 2} 9 20], in which ({bar 1}01) [111] is the primary slip system that has a maximum Schmid factor (m = 0.5), which requires the lowest stress to operate among the twelve {l_brace}{bar 1}10{r_brace} <111> slip systems. Nevertheless, the recorded stress-strain curve reveals no easy-glide or single-slip stage; work hardening starts immediately after yielding. Moreover, the result of slip trace analysis indicates the occurrence of anomalous slip on both the (011) and (0{bar 1}1) planes, which according to the Schmid law requires relatively higher stresses to operate. TEM examinations of dislocation structures formed on the (101) primary slip plane reveal that in addition to the ({bar 1}01) [111] slip system, the coplanar ({bar 1}01) [1{bar 1}1] slip system which has a much smaller Schmid factor (m = 0.167) is also operative. Similarly, (0{bar 1}1) [111] (m = 0.25) is cooperative with the coplanar (0{bar 1}1) [{bar 1}11] slip system (m = 0.287) on the (0{bar 1}1) slip plane, and (011) [1{bar 1}1] (m = 0.222) is cooperative with the coplanar (011) [11{bar 1}] slip system (m = 0.32) on the (011) plane. The occurrence of {l_brace}0{bar 1}1{r_brace} anomalous slip is accordingly proposed to be originated from the cooperative dislocation motion of the {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] dislocations on the ({bar 1}01) slip plane; the mutual interaction and blocking of {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] dislocations not only cause an increase of glide resistance to the dislocation motion on the ({bar 1}01) plane but also render the {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] screw dislocations to cross slip and propagate from the ({bar 1}01) slip plane onto the (0{bar 1}1) and (011) intersecting slip planes. That is, the {+-} 1/2 [111] screw dislocations cross slip from (111) onto (011), and the {+-} 1/2 [1{bar 1}1] screw dislocations cross slip from (111) onto (011), which subsequently render another two slip systems, (0{bar 1}1) [{bar 1}11] and (011) [11{bar 1}], to become operative. As a result, all 1/2<111>-type dislocations, i.e. all <111> slip, take part in the plastic deformation of the [{bar 2} 9 20]-oriented single-crystal Mo.

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  • Report No.: UCRL-TR-227296
  • Grant Number: W-7405-ENG-48
  • DOI: 10.2172/900046 | External Link
  • Office of Scientific & Technical Information Report Number: 900046
  • Archival Resource Key: ark:/67531/metadc889565

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  • January 11, 2007

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  • Sept. 22, 2016, 2:13 a.m.

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  • Dec. 5, 2016, 2:32 p.m.

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Hsiung, L & La Cruz, C. Dynamic Dislocation Mechanisms For the Anomalous Slip in a Single-Crystal BCC Metal Oriented for "Single Slip", report, January 11, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc889565/: accessed November 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.