Characterization of Nickel Diffusion and its Effect on the Microstructure of Nickel PM Steels

Effects of additions of nickel nanoparticles on sintering response of PM hybrid low alloy steels

“…9, martensite formation in FLN2 PM steels is promoted for a certain range of nickel concentrations. If too much is present, retained austenite will form instead, 3 as verified in Fig. 8.…”

“…Nickel diffusion was characterised with Suzuoka's instantaneous source model combined with an approach that was developed and presented elsewhere, which allows the measurement of grain boundary D GB and lattice diffusion D L coefficients. 3 Suzuoka's model consists of a finite source, perpendicular to a grain boundary in a polycrystal containing cubic grains as described in Fig. 5.…”

“…31 Therefore, this phenomenon explains the superior strength of the REF series and the fact that, although more dense, the specimens prepared using steel particles coated with nanoparticles of nickel show slightly inferior strength. Indeed, the latter specimens are less prone to strain induced transformation from retained austenite to martensite during plastic deformation since 9 Nickel concentration normally distributed intervals where each phase is favoured (base powder ATOMET 4901) 3 10 Microprobe nickel X-ray maps for a REF and b NANO sintered at 1050uC (1922uF) less NRAs are present, hence their lower strength. Moreover, the fact that the variation of TRS, at each temperature (REF versus NANO), decreases with increasing temperature concurs with this hypothesis since higher temperatures reduce the relative significance of the size of the particles on the diffusion rate.…”

“…1 However, the use of admixed nickel usually leads to the formation of nickel rich areas (NRAs) in sintered microstructures due to low solute diffusion coefficients of nickel into iron at conventional sintering. [2][3][4] Sintering is a crucial step in the production of PM components. It is at this stage that metallurgical bonds are created between neighbouring particles to give strength to PM parts.…”

Ultrasound-assisted drilling of copper and pre-alloyed powder metallurgy steels

“…This situation is reported to amplify the cyclic loading on the cutting tool as the cutting force varies quite significantly with the varying volume fraction of microstructural constituents [6]. In admixed PM steels for example, it is common to observe microstructures showing different volume fractions of pearlite, bainite, and martensite as well as retained austenite [7]. Furthermore, most PM parts are machined without the use of liquid coolant since the latter penetrates the pores by capillarity and generally requires a cleaning operation for its elimination, thus increasing manufacturing costs.…”