Regensburg 2002 – wissenschaftliches Programm

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M: Metallphysik

M 2: Mechanische Eigenschaften II

M 2.4: Fachvortrag

Montag, 11. März 2002, 16:45–17:00, H16

Compressive Deformation and Yielding Process of Niobium Sandwich-Bonded to Alumina Determined by Surface Mapping — •Yonghe Liu, Dieter Brunner, and Manfred Ruehle — Max-Planck-Institut f. Metallforschung, Seestr. 92, 70174 Stuttgart

The yielding behavior of polycrystalline niobium with thickness 0.7 to 2.8mm sandwich-bonded to alumina was studied by using surface strain mapping during compressive deformations. A full field optical strain measurement technique was employed in determining the 3D displacement and strain fields for one side surface of the metal layer including the interfaces between niobium and alumina. The measured stress-strain curves show that the deformation is divided into three regimes, i.e. elastic, plastic with hardening and fracture of alumina. The yielding of niobium starts from the immediate vicinity of interfaces and extends to the whole metal layer. Obvious strain localization along the diagonals as well as the interfaces is observed from the strain maps. The yielding strength increases with decreasing niobium thickness, in contrast, Young’s modulus is not sensitive to the variation of the thickness. The results on yielding strength are discussed in the light of a macromechanic model for the forging of metals with the consideration of friction, whereas the strain localization is discussed with reference to the micromechanical effects on plastic heterogeneity.