Effect of Cu and powder mixing with Cu-free (Nd, Dy)-Fe-B jet-milled powder on the magnetic properties of sintered magnets was investigated. The coercivity of a magnet prepared from the Cu-free (Nd, Dy)-Fe-B powder was about 10 kOe even though the alloy powder already contained some Dy (3.5 wt%). When small copper powder was blended, however, the coercivity of the magnet increased almost 100%, exhibiting about 20 kOe. On the contrary, the coercivity enhancement was moderate, about 4 kOe, when dysprosium content in the sintered magnet was simply increased to 4.9 wt% by the addition of small 3 powder.

In order to increase the coercivity of (Nd, Dy)-Fe-B sintered magnets without much reduction of remanence, small amount of Dy compounds such as and was mixed with (Nd, Dy)-Fe-B powder. After mixing, the coercivity of (Nd, Dy)-Fe-B sintered magnets apparently increased with the increase of Dy compound in the mixture. Addition of was more effective than for the improvement of coercivity. Reduction of the remanence by the addition of Dy compound, however, was larger than expected mostly due to unresolved coarse Dy compound in the magnet. EPMA analysis revealed that Dy was diffused throughout the grains in the magnet mixed with whereas Dy was rather concentrated around grain boundaries in the magnet mixed with .

Sintering behavior of 2xxx series Al alloy was investigated to obtain full densification and sound microstructure. The commercial 2xxx series Al alloy powder. AMB2712, was used as a starting powder. The mixing powder was characterized by using particle size analyzer, SEM and XRD. The optimum compacting pressure was 200 MPa, which was the starting point of the "homogeneous deformation" stage. The powder compacts were sintered at after burn-off process at . Swelling phenomenon caused by transient liquid phase sintering was observed below of sintering temperature. At , sintering density was increased by effect of remained liquid phase. Further densification was not observed above . Therefore, it was determined that the optimum sintering temperature of AMB2712 powder was .C.

Densificationbehavior of conventional austenitic stainless steel powder compacts was studied by comparing the relative density of sintered compact(Ds)with that of green compacts(Dg)prepared with various catbon contents and P/M process. Dg of 304and 316 powders by warm compaction under pressure of 686 MPa at heating temperature of powder(553K) and dies (573K) were 80% and 81%, repectively, whichwere 2 and 3% higher than those of conventional green compacts at the same pressure. Ds of 304 compacts sintered at 1373K in H2 gas has the same value of 84% max. regardless of compacting temperature, and Ds of 316 compacts at the same sintering conditions were 80% by conventional compaction and 83% by warm compaction. Oxygen contents of 304 and 316 sintered compacts were increased 1.43∼2.94% and 0.010∼0.921% higher than those of raw powders and warm green compacts, respectively. In other case, Ds of 316 compacts sintered at 1573K in vacuum had the same value of 86%max. And Ds of 316 compacts at the same sintering conditions were 83% and 86% by conventional and warm compaction, respectively. Oxygen contents of 304 sintered compacts were 0.321% and 0.360%, and in case of 316, they were 0.419% and 0.182% by the respective compating condition. With carbon additions in the range 0.1∼0.6% Ds increased to the extent of 86∼89% in 304 sintered compacts, and to 82∼84% and 85∼87% in 316 according to different two compacting peocesses compared to those of sintered compacts without carbon addition.

The densification of the compacts of Co+32%Cr+20%W+l.5%C, Co+32%Cr+20%W+3.0%C and Co+32%Cr+20%W+4.5%C sintered under gas or vacuum was investigated. The effect of V and B addition on the densification was also investigated. The densification of these compacts were always incomplete regardless of sintering atmosphere, temperature and time. The amounts of oxygen and carbon in compacts sintered in for 3.6ks at 1523K were 0.105~0.160 mass% and 0.33~0.89 mass%, respectively. And those in vacuum were 0.028~0.032% and 0.957~4.08%, respectively. Relative density(Ds) of Co+29%Cr+17%W+3.0%C compact containing 6%V and Co+32%Cr+20%W+2.97%C compact containing 0.03%B were 99 and 100%, respectively, indicating complete densification by solid phase sintering. Victors hardness of sintered compacts containing 6%V or 0.03%B were 632 and 568, showing 50~60% increase in comparison to those without V or B. These results can be explained in terms of oxidation/reduction of oxides and equilibrium pressure of CO in isolated pore, instead of presence of liquid formation and grain boundary separation from pores due to large grain growth.

The densification of the compacts of pure Co, Fe+50%.Co and Fe+25% Co sintered under H gas or in vacuum was investigated. The effects of AL, Nb, Ti, and V additions on the densification were also studied. The sintered compact of Co was fully-dense when the density of the compact was lower than . However, above , it was never fully-dense regardless of sintering atmosphere, temperature, and time. The densification of sintered compacts of Fe-50% Co and Fe-25% Co were always incomplete. While the addition of AL made all compacts fully-dense, the addition of Ti was effective for the compacts of Co and Fe-25% Co. V was effective only for the Fe-25% Co. These results tell us that the particle size of Co powder, the amount of Fe, and the amount of additives forming stable oxides play on important role for the complete densification. Therefore it is desirable to reduce or eliminate the equilibrium pressure of HO or CO in isolated pores to obtain a fully-dense sintered compact.