A. Piątkowski

Fracture behavior of Mg–Li matrix composites

Abstract Deformation and fracture of Saffil fiber (SF) reinforced Mg, Mg-8 wt.% Li and Mg-12 wt.% Li composites was monitored by means of in-situ scanning electron microscopy during 3-point bend tests. Mg and MgLi matrix composites (10 vol.% SF) were prepared by the melt infiltration technique. Poor interfacial bond causes premature failure of the SF/Mg composite that is usually triggered by the debonding of perpendicular fibers at the convex composite surface. Strong interfaces in SF/Mg12Li composite result in multiple cross-breakage of aligned fibers which is indicative of their participation in the composite strengthening. Resultant composite strengthening is frustrated by massive stress relaxation of the Mg12Li matrix. Strong interfaces and fairly high strength of the Mg8Li matrix cause remarkable strengthening of SF/Mg8Li composites. The cleavage of phases in two-phase Mg8Li matrix plays an insignificant role in the composite failure.

The Formation of New Orientations during Recrystallization of Silver Single Crystals with {112} Initial Orientation

The recrystallization mechanisms in high purity Ag crystals with C{112}<111> initial orientation, deformed by channel-die compression, have been studied by local orientation measurements using TEM and SEM/EBSD. The microtexture analysis clearly indicates the importance of a simple relation of 25-40o (<111> or <112>) type, which is frequently observed during the early stages of recrystallization between isolated nuclei of uniform orientation and one of the as-deformed groups of components. As recrystallization proceeds, recrystallization twinning increases radically. In C-oriented silver single crystals this latter mechanism also plays a decisive role in the formation of the cube orientation.

The Effect of Shear Bands on the Evolution of Rolling and Recrystallization Texture in Cold-Rolled Direct Chill Cast Strips of Brass

The texture of cold rolled and annealed cast strips of 70/30 brass was investigated. A delayed development of the main {110} component of brass type rolling texture was attributed to the intense deformation twinning which is associated with appearance of the strong {211} texture component at 50% reduction. The predominace of the {011} texture component in the range of 70%-90% reductions was related to the extensive shear banding. As for the rolling textures, the delay in development of the {236} component of brass type recrystallization texture was found.

Shear Banding in Twinned Structures and Their Influence on Brass-Type Texture

The local crystallography within shear bands (SB) has been examined in a single crystal of {112}<111> orientation of pure copper deformed at 77K by channel-die compression to strains of about 1. Setting up a system for making high-resolution orientation maps using transmission electron microscopy (TEM) has opened new advantageous circumstances for the analysis of orientation changes within SB. This method with spatial resolution higher than 10nm allows the examination of microstructure images composed of nanoscale subcells forming SB. It has been found that for well-developed shear bands, a crystal lattice rotation about <112> direction tends to dominate and this process is usually accompanied by activation of new slip systems. The present work shows that despite the plane strain deformation mode, the mechanism of lattice rotation within emerging SBs may lead to Goss and Brass texture components.