| This paper was built on the analysis of the methodology of infiltration,which was used to create a compound of molybdenum powder with high melting point(2623?)and copper with low melting point(1083?).This kind of composite owns the excellent properties of both molybdenum and copper.Mo-15 Cu composites possessing the specific performance of high strength,high hardness and better conductivity is regarded as a“pseudo-alloy”due to the immiscible characteristics of the molybdenum and copper chemical compositions.The application of optical microscope(OM),scanning electron microscope(SEM)and back scattered electron imaging(BSE)was introduced to analyze the effect that non-pressure melt infiltration impacted upon the microstructure of Mo-15 Cu composites.The results showed that the powder agglomeration existing in the non-pressure melt infiltration caused crack of Mo skeleton and reduces the uniformity of composites.Meanwhile,sintering necks formation have not been fully made,which affected the condition of melting infiltration and the distribution of liquid-state Cu of different regions.The volume of liquid-state Cu got shrunken when it was being frozen by flowing backwards to cluster in the capillary tube,which reduced the density of Mo-15 Cu composites.The new type of pressure driven melt infiltration has been designed to optimize the process aimed at settling the major problems which existed in the Mo-15 Cu composites in the conventional production of melting infiltration.And the sintering was carried out in the same temperature and time condition as non-pressure melt infiltration.The improvement of the microstructure of pressure driven melt infiltration composite was observed by using the OM and BSE.We found that crack was not generated for both the surface and inside of the composites composite prepared by the new type of melt infiltration method,that was pressing and melt-infiltrating composite under the pressure of 1.4×10~4Pa.Furthermore,pressure driven melt infiltration method had a noticeable effect on the improvement of holes shrinkage and reverse-flowing or reverse-sucking phenomenon of liquid-state Cu in comparison with the non-pressure melt infiltration method;thereby not merely uniformity of the liquid-state Cu melt-fluxing distribution but also uniformity of the constitution of Mo-15 Cu composites was greatly improved.During the process of pressure driven melt-infiltration sintering,the bonding between particles and the result of sintering necks were superior to the non-pressure infiltration,and the densification and homogeneity of Mo-15 Cu composites were improved as well.Moreover,in the process of pressure melting,the evaporation of liquid Cu was reduced by a factor of 1/2.Based on the physical performance testing and comparison between Mo-15 Cu composites made by pressure driven melt infiltration and non-pressure melt infiltration,we can conclude that the hardness of composites prepared by pressure driven melt infiltration has about 30%superiority over the one prepared by non-pressure melt infiltration and its density is about 10%higher than non-pressure melt infiltration composites.And each of the two density values was less than the theoretical density value of the composite.Meanwhile,with the continuous increasing pressure exerted on Mo skeleton,the changes of hardness and density of melt-infiltrating Mo-15 Cu composites shows a rising trend.Moreover,the electrical resistivity for composites prepared by pressure driven melt infiltration shows a 10%'s reduction of the one prepared by non-pressure melt infiltration,whatever the electrical resistivity for both the two are greater than their theoretical values.In conclusion,comparing with the non-pressure melt infiltration,there are obvious improvements in the melting behavior,sintering behavior and physical properties of the pressure driven melt Mo-15 Cu composites. |
PDF Full Text Request