Sook In Kwun

Threshold for fatigue macrocrack propagation in some aluminum alloys

Measurement of the threshold for fatigue macrocrack propagation, ΔKo, in a number of aluminum alloys has shown an increase with grain size and decrease with increase in strength as with steels. The results are not primarily due to environmental enhancement of fatigue crack growth because an even larger variation in ΔKo with microstructural change is noted at 77 K than at 300 K. In particular, ΔKo of high purity 2124-T4 increases much more on cooling from 300 to 77 K than does ΔKo of 2024-T4. It is suggested that ΔKo is determined by the stress necessary to operate a dislocation source near the crack tip. A Frank-Read type source is proposed for 2024-T4 with constituent particles acting as pinning points while double cross-slip, a thermally activated process, is proposed for the source in high purity 2124-T4.

Microstructure evolution in Zr under equal channel angular pressing

AbstractPure polycrystalline Zr was deformed by equal channel angular pressing (ECAP), and the microstructural characteristics were analyzed. By repeated alternating ECAP, it was possible to refine the grain size from 200 to 0.2 µm. Subsequent annealing heat treatment at 550 °C resulted in a grain growth of up to 6 µm. Mechanical twinning was an important deformation mechanism, particularly during the early stage of deformation. The most active twinning system was identified as 85.2 deg {10

Effects of grain shape and texture on the yield strength anisotropy of Al-Li alloy sheet

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Effect of Mo addition on the crystal texture and deformation twin formation in Zr-based alloys

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Abnormal grain growth of Zr-1wt.%Nb alloy and the effect of Mo addition

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Fatigue crack initiation and propagation in a quenched and tempered niobium bearing HSLA steel

011〉 tensile twinning, followed by 57.1 deg {10