Study of the process of titanium-containing furnace charging material compaction by an experimental-analytical method

The study covers the dependence of spongy titanium-based powder material porosity on the stress state coefficient during plastic deformation with the prevailing effect of all-round compression. Based on the results obtained in previous papers, an assemblage of yield curves with varying porosity is constructed on the σ —T plane. The yielding condition of the powder material is based on the Modified Drucker—Prager Cap model. The graph of geometrical interpretation of the accepted yielding condition contains straight lines corresponding to different values of the stress state coefficient k = σ/T where о is the average hydrostatic stress, and T is the shear stress intensity. In order to formulate the relationship of porosity (θ, %), average normal stress (σ) expressed in the nondimensional form, and the stress state coefficient (k), intersection points of the yield curve assemblage corresponding to yield surface generatrices on the o—T plane and radial straight lines were used. As a result, an equation of the θ = θ(σ, k) form was obtained. The experimental part of the study was performed in order to test the adequacy of this ratio. Powder blanks pre-compacted at a pressure of 1000 MPa and a temperature of 325 °C were subjected to electrical discharge sawing along the axial section to obtain flat samples (templates). Several characteristic areas were selected on the surface of templates to determine local surface porosity using quantitative metallography. The stress-strain state in representative areas was additionally determined by numerical simulation. The calculated values of the volumetric plastic strain, shear stress intensity and average normal stress were determined in axial section zones corresponding to the studied areas. It is shown that the stress state coefficient varying within a sufficiently wide range (k = —10...—0.86) does not affect significantly the porosity value.

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