Surface porosity sealing effect of plasma nitrocarburizing on sintered unalloyed iron

The influence of pore size on the sealing of P/M superficial pores as a result of plasma nitrocarburizing has been studied. Samples with different particle size distributions were sintered, resulting in surfaces with different pore sizes. The samples were compacted at 600 MPa and sintered at 1150°C for 1 h. The plasma treatment was carried out in an atmosphere of 87.75% N2/9.75% H2/2.5% CH4 for 2 h at three temperatures: 540; 570; and 600°C. The characteristics of the compound layer and porosity sealing effect of unalloyed sintered iron has been evaluated as a function of treatment temperature. Sample characterization was carried out by means of standard optical metallographical techniques, scanning electron microscopy (SEM) and X-ray diffractometry. In order to quantify the presence of superficial pores on sintered iron and their sealing effect after plasma nitrocarburizing, image analysis was also performed. Plasma treatment resulted in a significant sealing of the pores, which is related with the compound layer formation.