Abstract
Residual porosity in ferrous powder metallurgical alloys induces the phenomenon of localized yielding, or first yielding, during tensile testing. This gives rise to the existence of a true ( E 1 ) and apparent ( E 2 ) Young’s modulus. The true Young’s modulus is similar to the dynamic modulus ( E d ) determined by the acoustic resonance method, whereas the apparent Young’s modulus is lower than both E 1 and E d . For alloys with hard microstructures the apparent Young’s modulus turned out to be about 6% lower than the true Young’s modulus and a negligible influence of matrix hardness and pore morphology was highlighted. However, for ferritic or ferritic–pearlitic materials this difference was higher, ranging between 14 and 31% and it decreases as pore roundness is increased. For austenitic AISI 316L alloys both E 1 and E 2 are lower than E d because of the presence of oxides on the powder surface, which favour early decohesion at the necks during tensile testing.
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