In Situ Growth Of Magnesium Borate Whiskers And Joining Process And Mechanism Of Magnesia Ceramics

Magnesium borate whisker is widely applied in the reinforce of metal, ceramic,composite materials with lots of advantages, such as the materials used to madewhiskers is easy getting, the cost of its production is in a low degree, the preparationprocess is simple. In this paper, the magnesium borate whisker was in situ grown on thesurface of magnesic ceramics in order to join magnesic ceramics, and this kind of jointsare formed by the weaving of magnesium borate whisker. Analysis the morphology ofmagnesium borate whisker and its joints by using SEM electron microscope, energyspectrum analysis, XRD, transmission electron microscope and other methods. Usingmechanical test methods to analysis joints of different joining temperature and holdingtime.Magnesium borate whiskers were generated with B2O3, MgO+B2O3,KCl+MgO+B2O3, K2SO4+MgO+B2O3, MnO2+MgO+B2O3as raw materials. All thisfive kinds of materials can make it. Using B2O3as raw material can successfullyachieve magnesium borate whisker in situ grown from MgO ceramic surface, whiskersare density on the surface of MgO ceramic, but the length of the whiskers ranges from2-10μm, the diameters of the whiskers were about1-2μm, and the direction with MgOceramic is under30°. Adding10%MgO powder to B2O3raw materials, the density ofwhiskers become larger, the ratio of length to diameter up to20:1, no powder and mixedresidue. But the angle between whiskers and ceramics is still small. Flux can solve thisproblem. When KCl was used as flux, the angle between whiskers and ceramicsincreases largely. When K2SO4was used as flux, the length of whiskers also increases.When MnO2was used as flux, the morphology of whiskers was more stable, and thedistribution density increased.Using KCl+MgO+B2O3powder as interlayer can successfully join the MgOceramic itself, The strength of joints was provided by whiskers. Analysis the influencesof parameters on microstructure and properties of the joints, The maximum bendingstrength of the joint reached62MPa with the heating temperature of850oC after fourhours’holding.Analysis the influence of parameters on the microstructure and properties of thejoint, found that with the increase of joining temperature, density of whiskers and thestrength of the joint increased. While the strength of the joint increased with the holdingtime, The maximum strength of the joint reaches62MPa after4~6h’s holding, then thestrength is no longer rising. When the holding time is less than1h, the growth process of whiskers did not complete in the system. When the holding time is greater than12h, thewhiskers disappeared in the system, but the strength is continue rising.