An improved wax-based binder was developed for the powder injection molding (PIM) of WC-TiC-Co cemented carbides.The critical powder loading and the rheologic behavior of the feedstock were determined. It was found that the critical powder loading could achieve up to 62.5% (volume fraction) and the feedstock exhibited a pseudo-plastic flow behavior. The injection molding,debinding and sintering processes were studied. The dimension deviation of the sintered samples could be controlled in the range of ±0.2% with the optimized processing parameters and the mechanical properties were better than or equivalent to those of the same alloy made by conventional press-sintering process.
The bonded NdFeB magnets prepared by injection molding meet with the development tendency of the magnet in small volume, light weight and high performance ,and have a good prospect.In this paper, a modified nylonbased binder was developed for powder injection molding of NdFeB bonded magnets.The effects of pretreatment of NdFeB anisotropic magnetic powder produced with HDDR processing on the anti-oxidation behaviors of powder and the final magnetic properties of the molded bonded magnets were studied.The optimal powder loading of 65 vol% was achieved with the modified binder.It was found that the properties of the bonded magnets were mainly affected by the powder surface pretreatment and the intensity of the applied alignment magnetic field during injection molding for a certain powder.Bonded magnets with remanence of 0.820 T, intrinsic coercivity of 1140.3 kA· m-1 and maximum energy product of 111 kJ · m-3 were produced with the optimal processing.
MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high tempera-ture synthesis (SHS). Pure MoSi2 was obtained and a compound of MoSi2 and WSi2 was synthesized in the form of pre-dominant solid solution (Mo,W)Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2 and hexagonal C40 Mo(Si,Al)2. The (Mo,W)Si2-Mo(Si,Al)2-W(Si,Al)2 composite mate-rials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.
The oxidation behavior of molybdenum disilicide (MoSi2) powders at 400, 500, and 600oC for 12 h in air were investi- gated by using X-ray diffraction (XRD) and transmission electron microscopic (TEM) techniques. Significant changes were observed in volume, mass, and color. Especially at 500oC, the volume expansion was found to be as high as 7-8 times, the color changed from black to yellow-white, and the mass gain was about 169.34% after 8 h, with SiO2 and MoO3 as main reaction products. The gains in volume and mass were less at 400 and 600oC compared with those at 500oC, probably due to the less reaction rate at 400oC and the formation of silica glass scale at 600oC, which would protect the matrix and restrain the diffusion of oxygen and molybdenum. Thus, the accelerated oxidation behavior of MoSi2 powder appeared at 500oC and the volume expansion was the sign of accelerated oxida- tion.
