Design, Densification And Fabrication Of W-Mo-Ti Functionally Graded Material

In the present dissertation, the naissance and development of Functionally Graded Material (FGM) have been introduced, and the research actualities have been discussed from two aspects: preparation technique and application fields. Among these methods Particle Co-sedimentation is one of the most promising ways to fabricate large-scale profiles with continuous and smooth variations in composition and microstructure.From the particle settling point of view, the main factors affecting the compositional distributions of sediment have been analyzed. The result indicates that there exists quantitative relation between the compositional distributions of sediment and the settling quality ratio of the powders A and B. Only the ratio varies does the compositional distributions of sediment change. On the basis of the analysis abovementioned, the quantitative relation between the compositional distribution of sediment body and initial experiment parameters including powder characteristics (density, size and size distribution etc.) and settling parameters (density and viscosity of suspension, heights of suspension and liquid, etc.) have been established corresponding to the physical model selected. The qualities and size distributions of compositions corresponding to specified compositional distribution of FGM can be calculated via numerical simulations.Combining the characteristic of the fabrication of FGM by Particle Co-sedimentation, the densification of FGM has been designed from three aspects: the densification mechanism, the correlative parameters of the additives and the sintering schedule. Subsequently, the densification of the W-Mo-Ti system composites has been investigated. The experimental results illustrate that the powders Ni and Cu can promote the sintering densities of W and Mo alloys. In the processing of sintering, Cu powders melt to become liquid and Ni, dissolved in liquid Cu, shows more activating sintering feature than the solid Ni. The full density W and Mo alloys can be obtained under 1473K-30MPa-lh conditions in a vacuum furnace when the weight content of Ni is 3% and the weight content of Cu is 2%, and the W-Mo andMo-Ti alloys of diverse compositions can reach full densities at the same conditions. The Ni-Cu solid solution has the same function as Ni and Cu additives to promote the densification of W-Mo-Ti system composites. On the basis of the study, the condition of densifmg the W-Mo-Ti FGM is adding :5% Ni-Cu solid solution(Ni: Cu=3:2) and the sintering temperature is 1473K.The experimental techniques (such as sedimentation equipment, controlling the size and size distribution of powders, the concentration of suspension) have been devised subtly. On the basis of theoretical and densification design, the W-Mo-Ti FGM has been obtained by particle settling and hot pressing sintering. The structures of specimen were observed by electron probe. The results show that the compositional distributions along the thickness of the W-Mo-Ti FGM are in fair agreement with the designed values, and the element distributions along the vertical direction of the thickness are almost the same respectively. The W-Mo-Ti FGM also reaches the full density under the certain conditions.