RELATION BETWEEN PORE STRUCTURE AND FATIGUE BEHAVIOR IN SINTERED IRON-COPPER-CARBON

A statistically designed study of the high cycle fatigue of an iron-co pper-carbon alloy (Fe-2w/oCu-0.8w/oC or FC-0208) was performed to isol ate the controlling pore microstructure factors with respect to endura nce strength. The study included four variations in powder characteris tics and three variations in density, with a sintering cycle of 30min at 1120-degrees-C in an atmosphere of 11v/o hydrogen and 89v/o nitroge n. Twenty samples were fatigue tested for each of the 12 powder-densit y test combinations to assess the fatigue strength distribution. Quant itative metallography provided insight to the controlling microstructu re effects on fatigue life. Regression analysis between the various me chanical properties and microstructure parameters shows that the fatig ue endurance strength is linked to the porosity, average pore curvatur e, and separation distance between pores. The powder characteristics o ptimal for fatigue resistance depend on the density level. At the lowe r density (6.65g/cm3), endurance is enhanced by increasing the proport ion of small particles, thereby generating smaller, smoother pores in sintering. But an increased proportion of large particles is desirable for fatigue resistance at the higher densities (7.15g/cm3).