Study Of Multi-Element Materials With Immiscible Element On Liquid Sintering Mechanisms And Characteristics

Multi-element liguid-phase sintering gains its wide application in practical production of powder metallurgy, but its corresponding liquid-phase sintering theories lag behind the development of practical application. Specially in liquid-phase sintering containing immiscible element, there are still some problems needed to be clarified. Aim at these problems, further analysis and research are carried out by integrating three kinds of materials with immiscible elements which are respectively minor element, main one and one under chemical reaction.For materials with immiscible elements which are minor elements, sintering of powder metallurgy material Fe-Ni-Cu-C is on a typical example. The results of research show that the key problem of sintering the series of material is how to reduce the effect of mutual limit of diffusion between elements and immiscible element so as to ensure that immiscible element can be solid-solubilized into main element rapidly, effectively and uniformly. On the base of it, the diffusion model of infiltration sintering, by analyzing and comparing the mechanism of infiltration sintering of two kinds of traditional technics, was established, and another new sintering technics suitable to this kind of powder metallurgy was advanced.For materials with immiscible elements which are main elements, powder metallurgy material of W-based heavy alloy is on a typical example. Based on the preparation of W-basedheavy alloy, the factors to influence sintering densification of heavy alloy such as the content of elements Ni and Co, powder pre-treating system, and atmospheres including vacuum/Ar, N2, CO and H2 were studied. Further, by adding hydrogenated rare-earth compound to heavy alloy powder as activator, the behavior and mechanism of hydrogen-releasing compound to help activated liquid-phase sintering were studied. The results of research represent that the key problem of sintering the series of material is how main element diffuses to achieve sintering densification which is realized by accelerating to flat pressed or sintered neck between grains. The intensification of immiscible element in this process is the key to realize uniformization sintering and reach a higher shrinkage ratio.For materials with immiscible elements which are under chemical reaction, the key problem that it is difficult to control growth shape in Lanxide technology was studied, and the study found that the key factor which affects this problem was that cellular growers difficult to control their sizes and heights were formed by spraying molten alloy which goes through growth layer under the action of capillary attraction. According to these, a novel technology to realize the growth of composite material easy to control its shape was developed by diffusing oxygen through oxide layer to growth front and producing two chemical reactions as follows: C+[O]=CO and 36/31Al+4/31Si+2CO=18/31AI2O3+4/31SiO2+2C. Because this technology avoids spraying molten alloy, it is easy to ensure the shape in the course of growth of composite material.