True and apparent Young's modulus in ferrous porous alloys

Residual porosity in ferrous powder metallurgical alloys induces the phenom enon 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 mod ulus. The true Young's modulus is similar to the dynamic modulus (E-d) dete rmined by the acoustic resonance method, whereas the apparent Young's modul us 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 You ng's modulus and a negligible influence of matrix hardness and pore morphol ogy 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 surfa ce, which favour early decohesion at the necks during tensile testing. (C) 1999 Elsevier Science S.A. All rights reserved.