The effect of growth imperfections on the critical resolved shear stress is investigated for high-purity (99.99+%) aluminum single crystals as compared with strain-anneal crystals. An apparatus for measuring strains of the order of 0.2 μin. is described. Using etch pits as an index, the critical resolved shear stress is found to be inversely proportional to the growth imperfections for a range of etch pit density ρ of 5 to 25×104/cm2. An elastic range is demonstrated; and prior plastic deformation is found to lower Young's modulus. The results are interpreted in terms of dislocation theory.
An anomalous transient effect in Supermendur material is dramatically displayed when the magnetic properties of toroidal tape cores of the material are measured at temperatures between 500 and 600°C on a constant current flux reset tester. This test is designed to simulate the action of a half-wave self-saturating magnetic amplifier. Normally a steady-state cyclic flux change is achieved within one cycle of the applied alternating magnetizing field. A transient lasting several minutes (equivalent to several thousand cycles of alternating field) was observed instead for this alloy. When measured at room temperature after exposure to extreme temperatures the magnetic properties are observed to be degraded from the properties measured at room temperature before exposure. No direct evidence has been found to show that these two phenomena are related since specimens exposed to temperatures insufficient to cause the transient were observed to sustain some degradation in room temperature properties. The contributions of various mechanisms were investigated by environmental control. The most probable causes of the degradation of properties after high temperature exposure were concluded to be oxidation and relaxation of oriented domains.
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