Dislocation Substructure In Single Crystals Of Hexagonal Ag Al Oriented For Prismatic Slip

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ISBN 13 :
Total Pages : 27 pages
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Download or read book Dynamic Dislocation Mechanisms For the Anomalous Slip in a Single-Crystal BCC Metal Oriented for "Single Slip." written by and published by . This book was released on 2007 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 1/2111-type dislocations, i.e. all 111 slip, take part in the plastic deformation of the [{bar 2} 9 20]-oriented single-crystal Mo.