EFFECTIVE THERMOPHYSICAL PROPERTIES OF POWDER MATERIALS DURING SINTERING UNDER ELECTRONBEAM HEATING

Abstract

Background. Development of the consolidation processes of powder products using highly concentrated energy sources is impossible without a detailed analysis of the processes of thermal conditions arising in these products. Objective. The aim of the study is to select a method for calculating the thermal conductivity of a porous body, which will be established under various conditions of electron-beam sintering of molybdenum compacts, and to study the effect of the parameters of the porous structure on the thermal conductivity. Methods. An analysis of the sintering process in finite element calculations, in problems of thermal conductivity for two-dimensional and three-dimensional domains, simulating the real porous structure of molybdenum compaction and a regular porous structure with dense packing of spheres is proposed. Results. Mathematical analysis of the contribution of re-radiation to the total thermal conductivity of the porous material is performed. The obtained dependences of the relative thermal conductivity on the porosity of the material and the relative radius of contacts between its particles are presented. Conclusions. According to the results of the mathematical analysis of the conditions of heat transfer in a porous compact of molybdenum for the case of electron-beam heating, it was found that the radiant component of the thermal conductivity of a porous body with pores of the order of 2.5 μm is four orders of magnitude less than the conductive component of its thermal conductivity. Based on the results of finite element modeling of two-dimensional and three-dimensional porous objects, a significant effect of the contact area between particles on their integral thermal conductivity has been established, especially at small sizes of these contacts. At the same time, almost linear effect of porosity on thermal conductivity was established at contact radii between particles > 0.1 Rparticles. A significant influence of the uniformity of the distribution of contacts in aporous material on the uniformity of the temperature field in it is shown.