Investigation on the Effect of Atmosphere on the Pores of Sintered Astaloy CrM Steel

Image analysis is used to study the effect of sintering atmosphere and sintering time on the pores morphology of Astaloy CrM. The pores morphology was described by means of some parameters,Circular Diameter (DC)- which shows the diameter of equivalent circle for comparing the pore size,FElongation and FShape- which have different geometrical meanings. The results were interpreted with reference to an elliptical geometry which represents the theoretical shape to which pores tend. Effect of different sintering atmospheres (N2, Cracked Ammonia (NH3), Ar, Vacuum and air) at 1200ºC wasinvestigated. The results showed 20% decrease of maximum DC in vacuum and cracked ammonia in comparison with other atmospheres. The pore size measurement by image analyses confirmed the variation of density measured by Archimedes method. Dc was affected by atmosphere more than Fshapeand FElongation. Furthermore, Fshape was more sensitive than Felongation to different sintering atmospheres.Mechanical properties of specimens have a significant relation with percentage of pores (porosity) and morphology. Vacuum atmosphere led to more spherical and finer pores. Sintering atmosphere has significant effect on pores size and pore distribution in comparison with other morphologicalparameters in Astaloy CrM. Differences in FShape and FElongation factors are more observable in large pores (over 75μm2 area) in comparison with smaller ones. Fshape seems to be more suitable than Felongation for evaluating the effect of sintering variables on the evolution of pores morphology

Keywords:

Image Analyses , Powder Metals , Sintering Process , Sintering Atmosphere , Pores Morphology