Модель формування пористості брикетів губчастого титану на стадії спікання

Abstract

This article examines the peculiarities of the formation of interparticle connections in porous products based on titanium powders using sponge titanium as an example, which are used in the aviation industry and airfield management. The developed model is based on the results of a previous study, where the structure of cuboctahedral and inverse cuboctahedral clusters of packing spherical powder particles was determined at the most dense packing. During the study, a model of the fusion of particles at the points of pressing deformation due to recrystallization under the influence of high temperatures in a vacuum was developed. 4 main stages of powder briquette sintering were considered, and a mathematical model was developed for each of them. Thus, the stage of liquid evaporation is considered from the viewpoint of the cavitation effect of boiling on the surface of particles and boiling of plasticizers. Euler's film boiling formula was used to describe the forces acting on the particle surface; Tolubinsky's formula was used for bubble boiling; convective heat exchange was considered part of the final stage of sintering. The stage of the formation of metallic bonds is modeled on the basis of the results of practical studies in the REV 5.5 furnace, recrystallization based on differential scanning colorimetry on the NETZSCH STA 449F1 Proteus device, and determining the change in grain size according to the E19 ASTM scales using the Jeffers method. The diffusion stage is modeled on the basis of the approximation of the particle deformation model in the contact zones at the pressing stage using the Frenkel formula. Linear shrinkage is modeled based on direct measurement of sample sizes before and after sintering. The developed model has a certain versatility when applied to simulate the interaction of particles of metal powders under the conditions of the formation of porous briquettes, especially if the shape of the particles is close to round or spongy. The obtained result will make it possible to more accurately evaluate such a factor as the adhesion between the particles of the pressing and predict the tensile strength of the material. Additionally, due to the mathematical characterization of the peculiarities of the formation of corpuscular porosity under the conditions of sintering in a vacuum, we can design materials with differentiated porosity, as well as lay the foundations for powder 3D printing of such materials, by assembling grain by grain, or layer by layer with the adjustment of the force of particle compression one into the other.