Interstitial chemistry in sintering of metallic materials – often overlooked but decisive

Abstract

Sintering is a process by which particulate materials – loose or compacted – are transformed into a body that may be fully dense or may still contain pores, but in any case has structural integrity and load-bearing capacity. The physical mechanisms – especially the transport processes – that are responsible for these changes have been studied since the 1950s. However, the chemical part of sintering also is of decisive importance in particular for metallic systems, especially concerning the interstitial elements O and C. Any metal powder that has ever been exposed to air bears oxygen on the surface, and this oxygen has to be removed in the early stages of sintering to enable the physical transport processes to become effective. In the present work, various chemical reactions involving oxygen and/or carbon are described, and it is shown how the alloying system selected as well as the starting powder grade affect these reactions and the properties of the final products.