Characterization of the distribution of the sintering activator boron in powder metallurgical steels with SIMS.
Powder metallurgy is a well-established method for manufacturing ferrous precision parts. A very important step is sintering, which can be strongly enhanced by the formation of a liquid phase during the sintering process. Boron activates this process by forming such a liquid phase at about 1200 degrees C. In this work, the sintering of Fe-B was performed under the protective atmospheres of hydrogen, argon or nitrogen. Using different grain sizes of the added ferroboron leads to different formations of pores and to the formation of secondary pores. The effect of boron was investigated by means of Secondary Ion Mass Spectrometry (SIMS) supported by Scanning Electron Microscopy (SEM) and Light Microscopy (LM). To verify the influence of the process parameters on the mechanical properties, the microstructure (pore shape) was examined and impact energy measurements were performed. The concentrations of B in different samples were varied from 0.03-0.6 weight percent (wt%). Higher boron concentrations are detectable by EPMA, whereas the distributions of boron in the samples with interesting overall concentration in the low wt% range are only detectable by means of SIMS. This work shows that the distribution of boron strongly depends on its concentration and the sintering atmosphere used. At low concentration (up to 0.1 wt%) there are boride precipitations; at higher concentration there is a eutectic iron-boron grain boundary network. There is a decrease of the impact energy observed that correlates with the amount of eutectic phase.
Institute for Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/164, 1060 Vienna, Austria.
Dragan
D
Krecar
Vassilka
V
Vassileva
Herbert
H
Danninger
Herbert
H
Hutter
D001128:Argon / Q000737:chemistry; D001895:Boron / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D008422:Materials Testing; D008669:Metallurgy; D009584:Nitrogen / Q000737:chemistry; D011208:Powders; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*; D013193:Stainless Steel / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
D011208:Powders; D013193:Stainless Steel; D001128:Argon; D006859:Hydrogen; D009584:Nitrogen; D001895:Boron