Dislocations, kink bands, and room-temperature plasticity of Ti 3 SiC 2
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I. INTRODUCTION
RECENTLY, we reported on the fabrication and characterization of the ternary compound Ti3SiC2.[1–5] This compound is a layered hexagonal material in which almost closepacked planes of Ti are separated from each other by hexagonal nets of Si; every fourth layer is a Si layer. The C atoms occupy the octahedral sites between the Ti layers. This compound combines an unusual set of properties. Like metals, it is a good electric and thermal conductor, readily machinable, relatively soft (with a Vickers hardness of 4 GPa), and highly thermal-shock resistant. Above 1200 8C, the material deforms in a pseudoplastic manner, with significant ductility. At 1300 8C, its “yield” stresses in flexure and compression are 100 and 500 MPa, respectively. Like ceramics, it is elastically rigid, oxidation resistant,[3] and stable to at least 1700 8C in inert atmospheres and in vacuum.[2] Basal-plane dislocation arrays of limited extent are observed in undeformed Ti3SiC2 samples.[6] However, roomtemperature deformation significantly increases their extent, indicating that dislocations multiply and are mobile at room temperature. The arrays are composed of perfect basal-plane dislocations with a Burgers vector of 1/3 ^112 0&. A key characteristic of the Ti3SiC2 structure, the appreciation of which is important in understanding the atomistics of its mechanical properties, is that the basal interatomic vector is by far the shortest full translation vector in this structure. Thus, nonbasal dislocations are very unlikely, and, indeed, none are observed. Oriented coarse-grained (1 to 3 mm) polycrystalline samples of Ti3SiC2, loaded in compression at room temperature, deform plastically.[5] When the basal planes are oriented
M.W. BARSOUM, Professor, L. FARBER, Postdoctoral Fellow, and T. EL-RAGHY, Research Assistant Professor, are with the Department of Materials Engineering, Drexel University, Philadelphia, PA 19104. Manuscript submitted November 3, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
favorably to the applied stress, substantial (.20 pct) deformation occurs by shearing along those planes. When the basal planes are parallel to the applied load, deformation occurs by a combination of delamination of individual grains and the formation of shear and kink bands. The buckling and kink-band formation initiates at the corners of the cubic samples.[5] Kink-band formation has been invoked to explain the deformation of numerous materials and structures such as highly constrained rocks,[7] organic crystals,[8] card decks,[9] rubber laminates,[10] oriented polymer fibers,[11–15] wood,[16] graphite fibers,[17,18] and laminated C-C and C-epoxy composites,[19,20,21] among others. The formation of kink bands in crystalline solids, however, is an uncommon deformation mechanism. As first reported by Orowan,[22] kink-band formation is a deformation mode typically observed in hexagonal metals such as zinc and cadmium. Typically, singlecrystal rods with the c-axis almost parallel to the rod axis undergo local collapse under compressio
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