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 res ult of plasma nitrocarburizing has been studied. Samples with different par ticle size distributions were sintered, resulting in surfaces with differen t pore sizes. The samples were compacted at 600 MPa and sintered at 1150 de greesC for 1 h. The plasma treatment was carried out in an atmosphere of 87 .75% N-2/9.75% H-2/2.5% CH4 for 2 h at three temperatures: 540; 570; and 60 0 degreesC. The characteristics of the compound layer and porosity sealing effect of unalloyed sintered iron has been evaluated as a function of treat ment temperature. Sample characterization was carried out by means of stand ard 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 nitrocarburiz ing, image analysis was also performed. Plasma treatment resulted in a sign ificant sealing of the pores, which is related with the compound layer form ation. (C) 2001 Elsevier Science B.V. All rights reserved.