Study of Compaction of the Titanium Powder by the Experimental-Analytical Method

详细

The dependence of porosity θ of the spongy titanium-based powder material on stress state coefficient k during the plastic deformation with the prevailing effect of the uniform compression is investigated. Based on the results found in previous works, the family of yield curves with a variable porosity is plotted on the σ–T plane. The yield criterion of the powder material is based on the Modified Drucker–Prager Cap Model. Straight lines corresponding to various values of stress-state coefficient k = σ/T, where σ is the average hydrostatic stress and T is the intensity of tangential stresses, are represented in the graph of the geometric interpretation of the accepted plasticity model. To formulate the relation of porosity (θ, %), average normal stress (\(\bar {\sigma }\)), expressed in the dimensionless form, and stress-state coefficient k, intersection points of the family of curves corresponding to generatrices of yield surfaces on the σ–T plane and radial straight lines, are used. This results in the derivation of the equation of the θ = θ (\(\bar {\sigma }\), k) form. To verify the adequacy of this relationship, the experimental part of the investigation is fulfilled. Powder billets preliminarily compacted at a pressure of 1000 MPa and temperature 325°C are subjected to electroerosion cutting along the axial section to form planar samples (templates). Several characteristic segments are selected on the template surface to determine the local surface porosity by quantitative metallography. The stress state was additionally determined in representative segments by the numerical simulation. Values of bulk plastic strain (\(\varepsilon _{{v}}^{{{\text{pl}}}}\)), intensities of tangential stresses (T), and hydrostatic normal stress (σ) are calculated in axial section zones corresponding to the regions under study. It is shown that the stress state coefficient insignificantly affects the porosity upon its variation in a rather broad range (k = –10 to –0.86).