Analytical model of equal-channel angular pressing of titanium sponge

Abstract

Introduction. The use of equal-channel angular pressing (ECAP) of metal powder makes it possible to obtain practically non-porous blanks with high hardness, with a high level of accumulated deformation and with the formation of an ultra-fine-grained structure. A relevant issue for the study of the semi-continuous ECAP process remains a reliable assessment of the energy-power parameters of the process and the prediction of the porosity of compressed materials. This, in turn, is due to the need to develop sufficiently accurate, reliable and simple mathematical models for practical application. The purpose of the work is to develop an analytical model of the process of equal-channel angular pressing of porous material. Powdered screening of spongy titanium of the TG-100 brand was selected as a model of the material for the study. The object of the study is the process of semi-continuous equal-channel angular pressing of axisymmetric porous briquette of titanium sponge in the channel of the mold. It is assumed that the ECAP uses a punch to create back pressure. For the solution, a process scheme, a statically permissible load scheme on a layer of intense deformation and a kinematically permissible flow scheme of a plastically compressible medium in a layer are determined. A system of equations is constructed in accordance with the accepted schemes. The equation power balance is applied. The analytical equation is solved by the method of successive approximations. Finite element simulation of the porous titanium ECAP process was carried out at the angles of intersection of the mold channels at 45°, 50°, 55° and 60°. Results and Discussion. The porosity of the blank is determined at different stages of the ECAP process. A diagram of the change in pressure on the punch using the analytical solution and finite element simulation is obtained. It is revealed that the results of the analytical solution are consistent with the data of the finite element simulation. The highest stress level occurs in the process of equal-channel angular pressing at α = 45°, however, the distribution of relative density over the cross section is most uniform. The maximum value of the pressure on the working punch decreases with an increase in the angle α. Rational technological parameters of pressing porous blanks should provide the maximum permissible pressure on the deforming tool. From this condition, in each specific ECAP process, it is possible to determine the optimal angle value from the analytical solution.

Microstructure Evolution and Numerical Modeling of TC4 Titanium Alloy during Ultrasonic Shot Peening Process

“…Past studies have proven that surface nanocrystallization (SNC) is the most effective and promising method, which induces severe plastic deformation (SPD) on the surface of metallic materials [6,7],providing a very effective potential approach for achieving microstructure refinement and enhancing the overall properties of TC4 titanium alloy. Currently, surface nanocrystallization techniques such as laser shock peening (LSP) [8][9][10], surface mechanical attrition treatment (SMAT) [11][12][13], surface mechanical rolling treatment (SMRT) [14][15][16], equal-channel angular pressing (ECAP) [17][18][19] and ultrasonic shot peening (USP) [20] are widely used to achieve grain refinement and the surface integrity enhancement of materials, aiming to improve the fatigue resistance and wear resistance of titanium alloys during service. Li et al [21] investigated the strengthening effect of ultrasonic surface rolling at low temperatures, and demonstrated a significant enhancement of residual stress and wear properties at 120 • C. Liu et al [22] obtained an extremely strong surface nanocrystalline layer for Ti64 after laser-assisted ultrasonic nanocrystal surface modification (LA-UNSM), showing a 75.2% increase in hardness.…”