The dimensional variations during the rearrangement stage of liquid phase sintering could have a detrimental effect on the dimensional tolerances of the sintered product. A numerical approach to model the liquid phase penetration into interparticle boundaries and the accompanied dimensional variations during the primary rearrangement stage of liquid phase sintering is presented. The coupled system of the Cahn-Hilliard and the Navier-Stokes equations is used to model the penetration of the liquid phase, whereas the rearrangement of the solid particles due to capillary forces is modeled using the equilibrium equation for a linear elastic material. The simulations are performed using realistic physical properties of the phases involved and the effect of green density, wettability and amount of liquid phase is also incorporated in the model. In the first step, the kinetics of the liquid phase penetration and the rearrangement of solid particles connected by a liquid bridge is modeled. The predicted and the calculated (analytical) results are compared in order to validate the numerical model. The numerical model is then extended to simulate the dimensional changes during primary rearrangement stage and a qualitative match with the published experimental data is achieved.

The addition of alloying elements in low alloyed PM steels in the form of a master alloy gives the advantage of introducing oxidation sensitive but less expensive elements and also allows manipulation in composition adjustment to achieve desired properties. In this work, interrupted sintering trials of the Fe-2MA-0.5C (%) (MA = Cu based master alloy) are performed. The behaviour of the liquid forming master alloy, for instance in terms of liquid phase formation, alloying element redistribution and effect on the dimensional changes, is investigated. The results show that master alloy particles melt over a range of temperature, which is also supported by the thermodynamic calculations. The low swelling in the master alloy system, compared to a reference system of Fe-2Cu-0.5C, is attributed to the progressive melting of the master alloy. The mean diffusion distance of Cu in Fe at the interparticle boundaries is 5.8 mu m after 34 min of isothermal holding.

The effective use of alloying elements in powder metallurgical steels requires a deep understanding of their redistribution kinetics during sintering. In this work, interrupted sintering trials of Fe–2Cu and Fe–2Cu–0·5C compacts were performed. Moreover, diffusion simulations of Cu in γ-Fe using Dictra were performed. It is found that transient liquid phase penetrates the Fe interparticle and grain boundaries in less than 3 min of holding time. However, C addition limits the penetration of liquid Cu, particularly into grain boundaries of large Fe particles. The results also show that the mean diffusion distance of Cu in γ-Fe in the C added system is slightly lower than that in the C-free system at 3 min of holding time; however, after 33 min, the mean diffusion distance is similar in both systems. The diffusion distances of Cu in γ-Fe, predicted by Dictra, are in good agreement with the measured values.

The initial rapid wetting of a solid surface by a liquid phase is an important step in many industrial processes. Liquid-phase sintering of powder metallurgical steels is one such industrial process, where metallic powders of micrometer size are used. Investigating the dynamic wetting of a high-temperature metallic drop of micrometer size experimentally is very challenging. Here, a phase-field-based numerical model is first implemented and verified by accurately capturing the initial dynamic wetting of millimeter-sized metal drops and then the model is extended to predict the dynamic wetting of a micrometer-sized metal drop. We found, in accordance with recent observations, that contact line friction is required for accurate simulation of dynamic wetting. Our results predict the wetting time for a micrometer-sized metal drop and also indicate that the dynamic wetting patterns at the micro- and millimeter length scales are qualitatively similar. We also found that the wetting process is much faster for a micrometer-sized metal drop compared to a millimeter-sized metal drop.

The distribution of the alloying element Cu in steel compacts is important in determining the properties of the sintered products. In this work, mixtures of Fe-2Cu and Fe-2Cu-0.5C were compacted at 600 MPa and sintered at 1120oC for the holding times of t_s= 3, 13, 23, and 33 min. Dilatometry and light optical microscopy is used to investigate porosity, Cu distribution and its effect on the dimensional changes during sintering. The result shows that the molten Cu penetrates into the Fe interparticle and grain boundaries in less then 3 min holding time at 1120°C, however C addition hinders the liquid penetration of Cu. Furthermore, it is found that the C-added compact has lower volume expansion and porosity compared to the C-free system, after 33 min of holding time at 1120°C.