Commercial purity aluminium at true strains 3 = 2 ∼ 5.5 was annealed in a wide temperature range (from room temperature to 220• C), and the evolution of microstructure was characterized using transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) techniques. Triple junctions in an ultrafine lamellar structure are classified into three categories based on the structural morphology, and a relationship is formulated between the density (length per unit volume) of triple junctions and the boundary spacing. The triple junction density increases with increasing strain during plastic deformation and decreases during isochronal and isothermal annealing. Based on TEM and EBSD observations, thermally activated triple junction motion is identified as the key process during the recovery of highly strained aluminium, leading to the removal of thin lamellae with small dihedral angles at the ends and structural coarsening. A mechanism for recovery by triple junction motion is proposed, which can underpin the general observation that a lamellar structure formed by plastic deformation during annealing can evolve into an equiaxed structure, preceding further structural coarsening and recrystallization. Within this framework, the grain boundary surface tension on triple junctions is discussed based on the structural parameters characterizing the deformed and annealed microstructure.

No abstract

Laminated Ti-Al composite sheets with different layer thickness ratios have been fabricated through hot pressing followed by multi-pass hot rolling at 500˚C. The laminated sheets show strong bonding with an intermetallic interfacial layer of nanoscale thickness between the layers of Ti and Al. The mechanical properties of the composites with different volume fraction of Al from 67% to 10% showed a good combination of strength and ductility. A constraint strain in the hot-rolled laminated structure between the 'hard' and 'soft' phases introduces an elastic-plastic deformation stage, more pronounced as the volume fraction of Al decreases. The thin intermetallic interfacial layer may also contribute to the strength of the composites. This effect increases with increasing volume fraction of the interface layer which thereby can contribute to the flow stress.

No abstract

No abstract