Simulations describing the settling of suspensions of solid particles bounded by a rigid container are presented. Results are compared with previous simulations of homogeneous suspensions with periodic boundary conditions. Velocity fluctuations in vertically inhomogeneous suspensions are found to saturate under conditions similar to those found in laboratory experiments, while in vertically homogeneous suspensions, with or without side walls, the velocity fluctuations diverge. A mechanism for the establishment of a correlation length in sedimenting suspensions is proposed.

Effects of container walls on the velocity fluctuations of sedimenting spheres

The settling of a bidisperse suspension with small particles having different sizes and densities can be described by an initial value problem for a system of two non-linear, first-order conservation laws. Solutions to this problem are in general discontinuous and exhibit kinematic shocks that separate areas of different composition. The solution requires the construction of so-called elementary curves in phase space, which are determined from eigenvector fields of the Jacobian of the flux function. Differences in solution behavior to the previously analyzed equal-density case are due to an umbilic point, which appears for different densities only. The initial value problem is eventually solved by the front tracking method, which generates a series of Riemann problems. It turns out that the solution of the problem predicts a fairly complex process of sediment formation, and that the stationary solution can consist of non-constant smooth transitions. This observation is of interest for manufacturing of functionally graded materials.

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On the settling of a bidisperse suspension with particles having different sizes and densities

Commercially available polycrystalline diamond compacts (PCD), consisting of a polycrystalline diamond-cobalt layer on a WC-Co substrate are used in drilling and machining applications. The presence of a cobalt phase in the diamond layer has the effect of signicantly reducing thermal resistance. The thermal stability of a PCD material can be dened as its resistance to graphitization in an inert atmosphere at elevated temperatures. One of the possibilities to increase the thermal resistance of PCD materials is to reduce the cobalt content. The second one is the manufacturing of diamond compacts with a non-cobalt bonding phase. Presented in this paper are new trends for this type of material and my own experimental results of high-temperature sintering of diamond with carbides and/or silicides. The WC-Co layer allows for brazing of the PCD material to the tool body. Direct brazing of diamond materials to metal bodies is difcult and r equires special solders and special conditions. Due to differences in thermal and mechanical properties between diamond and WC-Co, residual stresses develop in the interface region during the cooling from sintering, brazing or cutting temperatures. In an effort to reduce residual stresses, functionally graded material (FGM) diamond compacts with a ceramic bonding phase were designed and obtained. The results of X-ray phase composition analysis, electron microscopy microstructure observations, and selected physical and mechanical properties together with thermal resistance studies are presented.

Diamond–ceramic bonding phase composites for application in cutting tools

Al2O3 and ZrO2 powders formed by centrifugal compaction using the ultra HCP method

Wpływ warunków zagęszczania wirówkowego proszków na kształtowanie struktury gradientowej spieków diamentowych

Purpose: Sedimentation of particles in a viscous fluid is a main physical problem in fluid mechanics. Sedimentation is benchmark of one of the technica; methods to produce the functionally graded materials (FGM) with a continuous spatial change of mechanical properties. The aim of the research was execution of mathematical calculations of the phases distribution for the phase graded diamond-Ti3SiC2 compacts which were verified with phases distribution in compacts after the high pressure – high temperature sintering process. Design/methodology/approach: In this paper, we construct a mathematical model of FGM basing on the modifications of the Stokes formula. We proposed an algorithm to describe sedimentation of the group of spherical particles of different sizes and different materials. Main calculations for this system and real conditions of the highspeed centrifugal compaction process are made using the Barnea-Mizrahi equation. Deposition process was carried out using the ultra centrifuge UP 65M with rotational speed of 15000 to 25000 rpm. Particle size distribution for the diamond and Ti3SiC2 powders were measured using Shimadzu apparatus. Findings: The results of calculations and microscopic analysis are compared. The obtained results of mathematical calculations demonstrate that for the considered diamond-Ti3SiC2 suspensions the obtained compact has the structure of the laminate what confirmed microscopic analysis. Practical implications: The mathematical simulations using our algorithm show that it is possible to obtain continuous concentrations of the both materials with appropriate initial suspensions. Thus our method allows to obtain graded materials. Originality/value: This mathematical model gives possibility of use to describe sedimentation of the group of spherical particles different materials and different sizes.

M. Rozmus

Papers

Compaction of the diamond-Ti3SiC2 graded material by the high-speed centrifugal compaction process

Kompozyty diamentowe z ceramiczną fazą wiążącą - modyfikacja mikrostruktury w aspekcie łączenia z korpusem narzędzia

of Achievements in Materials and Manufacturing Engineering of Achievements in Materials and Manufacturing Engineering