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Abstract
Groups of specimens with nominally 4% and 12% porosity have been prepared from fine (−240 + 300), medium (−200 + 240), and coarse (−150 − 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally sintering at 1573K (1300°C). Irrespective of porosity content and the powder fraction from which they were prepared, all specimens exhibited a mixture of rounded and film-like porosity. The film-like porosity was more extensive in the more porous specimens, but in all specimens markedly influenced the fatigue behaviour. The development of persistent film-like porosity is attributed to the botryoidal form of the powder particles. The endurance limits of the less-porous specimens were almost identical, irrespective of the powder fractions from which they were prepared. However, the endurance limits of the more-porous specimens made from the coarse powder fraction were significantly lower than those made from the fine and medium powder fractions. The endurance limits of the less-porous specimens were much higher than those of the more-porous specimens and the endurance ratios were significantly higher. In all specimens, fatigue fractures were intergranular. The influence of film-like porosity on the fatigue behaviour is discussed.
Notes
* Manuscript received 21 May 1973. Contribution to a Symposium on ‘PM Alloys and Properties’, to be held in Eastbourne on 19–21 November 1973.