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Abstract
Sintered iron specimens were prepared from -300 B.S. mesh electrolytic powder with porosities in the range 4-30%, by different combinations of compacting pressure, sintering temperature and atmosphere, and hot and cold deformation treatments. The fatigue behaviour has been investigated under push/pull axial stressing and alternating-torsion conditions. The fatigue strength tends to a limiting value between 106 and 107 cycles and depends primarily on the porosity in an approximately linear manner; the strength also decreases with decreasing testing frequency. The ratio of the 107 cycles fatigue strength in torsion, to that in push/pull, is higher than for fully dense materials, and increases with increasing porosity. The moduli of elasticity in torsion and tension also show linear dependence on the porosity. Metallographic observations indicate that fatigue cracks start from the external free surface and propagate in a mixed transgranular and intergranular fashion.
Notes
* Manuscript received 22 May 1963. Contribution to a symposium on “Residual Porosity in Powder Metallurgy” to be held in London on 21 and 22 October 1963.