Powder Technology, Vol.329, 12-18, 2018
Effects of oxygen contents on sintering mechanism and sintering-neck growth behaviour of Fe-Cr powder
The effects of oxygen contents and sintering time on the sintering-neck growth behaviour of Fe-15Cr powder were studied. The oxygen content was increased from 0.029 to 0.059 wt% by heat-treating the powder under air at different temperatures. SEM observations revealed that the length of the neck decreased as the oxygen content increased. The sintering-neck growth rate decreased most significantly when the oxygen content was increased from 0.029 to 0.034 wt%. The results of electron probe microanalysis suggested that the increase in oxygen content led to encapsulation of the powder particles by oxide films, but the oxygen content inside the sintering neck remained similar to that of the matrix. Theoretical analysis indicated that the growth of sintering necks was hindered by surface oxides and interstitial oxygen in the matrix. When the oxygen content was 0.029 wt%, the sintering necks grew via surface diffusion; when the oxygen content exceeded 0.034 wt%, the dominant sintering mechanism changed to grain-boundary diffusion. The diffusion coefficient of surface diffusion was 2.41 x 10(-7) m(2)/s, which far exceeded that of grain-boundary diffusion; when the oxygen content was 0.034 wt%, the diffusion coefficient of grain-boundary diffusion was only 5.79 x 10(-9) m(2)/s. It was also found that grain-boundary diffusion required the breaking of Fe-O bonds, so the diffusion coefficient gradually decreased to 1.12 x 10(-9) m(2)/s when the oxygen content was 0.059 wt%. The findings of this work will provide a theoretical basis for the optimisation of sintering processes of stainless steel with high oxygen level, such as the metal injection moulding process. (C) 2018 Elsevier B.V. All rights reserved.