PSI - Issue 50

Andrey Polyakov et al. / Procedia Structural Integrity 50 (2023) 228–235 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Therefore, when choosing the quantitative and qualitative composition of alloying additives in a powder composite with a content of the main component of approximately at least 93-95%, intended for obtaining blanks and products by extrusion, the following approach can be proposed: Calculation of extrusion pressure and residual porosity is carried out using dependencies (1)-(3). In order to determine the extrusion pressure of a real material, it is necessary to know the value of the yield strength τ s of the solid phase, which has different values τ s for the compaction stage and the extrusion stage. Therefore, it is necessary to obtain compaction curves during compaction and the dependence "pressure - relative density" depending on the drawing ratio at the stage of extrusion. For this, experimental studies of the processes of compaction and extrusion for the base material of the powder composite are carried out. Due to the small amount of alloying additives (wt. %, see above), the indicated dependences for a "pure" powder and compositions based on it with a content of alloying components in the range of 5-7 wt. % will differ slightly from each other. As a result of experiments on extrusion for the base material, it is necessary to determine not only the dependence "pressure - relative density", but also the minimum density of the briquette at which the bar did not collapse. Based on the results of tests for axial and radial compression of unsintered briquettes, we determine the numerical values in the Mohr-Coulomb strength condition and the minimum shear resistance d (and the blank density corresponding to this value) at which a bar suitable for subsequent machining is obtained. When choosing the parameters of the extrusion process of a new powder composition, it is necessary to perform axial and radial compression tests for a given composition to determine the numerical values in the Mohr-Coulomb strength condition, the dependence of the shear resistance value d on the relative density. Knowing the minimum value of the shear resistance of the base material, which ensures the integrity of the rod, we use this value d to determine the minimum required density of the briquette of the already studied composition, at which the rod will not collapse. Figures 4-5 show the results of studies of the strength properties of the studied samples depending on ρ rel (markers show the experimental points, lines show the calculated curves). Analyzing the results presented in Fig 4a, we see that the initial powder has the highest axial compressive strength. Somewhat less durable are the powder with the addition of copper. As for the powders with the addition of zinc and graphite, at a density of ρ rel  0.8  0.82, their strength in axial compression differs slightly from the strength of other compositions, while with increasing density, the value of σ c for these powders grows more slowly than for the initial composition and composition with copper.

Fig. 4. Dependence of stress at the time of crack initiation on density. a - uniaxial compression, b - diametral compression.