The microstructures of Ni-containing P/M steels produced by admixed powders or diffusion alloyed powders are usually heterogeneous. To improve the microstructure homogeneity, the effects of Mo and Cr additions in the prealloyed powder form were examined. The results showed that the microstructural homogeneity was improved and superior mechanical properties were achieved with increases in the alloy content, particularly for the Cr. Such a beneficial effect was attained due to the reduction of the repelling effect between Ni and C, as was demonstrated through thermodynamic analysis using the Thermo-Calc software.

In this study, copper vapor chambers with built-in cooling fins, which eliminated the soldered or brazed joints in the conventional vapor chamber, were fabricated using the metal injection molding process. The results show that with optimized molding parameters, fins with an aspect ratio up to 18 could be produced. After sintering, the densities of the fin and chamber reached 96%. With only 32 cooling fins and a small fan installed, the thermal resistance of the heat sink was 1.156 ℃/W, and the power dissipation was 40W when the junction temperature was 70℃. When copper powder was sintered onto the chamber to make a vapor chamber, the thermal resistance decreased to 1.046℃/W.

The thermal dissipation performance of sintered heat pipes is usually determined by the capillarity and permeability of the Cu powder wicks. Since the capillary provided by the Cu powder is usually large enough to draw water from the condenser end to the evaporator end, the permeability has become the controlling factor. In this study, Cu powders with different particle sizes and shapes were loosely sintered, and their permeabilities were compared. The results show that more complicated shapes, finer particle sizes, lower porosities, and rougher pore surfaces give lower permeability and thermal dissipation.

To understand the effect of powder characteristics on the thermal debinding behavior, PIM parts produced with powders with different particle sizes and particle shapes were examined to determine their weight losses during thermal debinding. The results show that the average diameter of the pore channel in the compact increased when the temperature increased and when coarse powders were used. However, the weight loss rates did not increase proportionally with the pore size. This suggests that the different powders that are frequently used in PIM parts do not affect the thermal debinding rate significantly. This is because the pore size is much larger than the mean free path of the decomposed gas molecules. Thus, the diffusion rates of the gases are not rate-controlling in thermal debinding. The controlling mechanism of the thermal debinding rate is the decomposition of the backbone binder in the PIM parts.

To lower the cost of MIM products, the gate and runner materials and green parts with defects are usually recycled. It is necessary to understand what causes the recycled products to deteriorate. The results show that the viscosity of the 1R (recycled once) feedstock was slightly lower than that of the fresh material. However, as the number of recyclings increased, the viscosity increased, while the density decreased, and more defects were noticed duri ng solvent debinding. These deteriorations were mainly caused by the increase of the melting point of the backbone binder and the oxidation of the filler or paraffin wax.