Powder Rod Research Articles

Rotary Friction Welding of Dissimilar Polymer Rods Containing Metal Powder.

Three-dimensional printing is widely used for manufacturing a variety of functional components. However, the 3D printing machine substantially limits the size of the functional components. Rotary friction welding (RFW) is a possible solution to this problem. In addition, there is a notable scarcity of research directed toward the domain knowledge of RFW involving dissimilar polymer rods containing metal powder. In this study, two welding specimens fabricated by polylactic acid (PLA)-containing copper powder and PLA-containing aluminum powder were joined using a turning machine. After RFW, a bending test and a Shore A surface hardness test were performed to investigate the weld quality. It was found that the bending strength of the welded parts fabricated by RFW of PLA and PLA-containing Al powder rods can be enhanced by about 57.5% when the welded part is placed at 45 °C. Surface hardness test results showed that the surface hardness of the weld interface is better than that of the 3D printed parts, and the average surface hardness of the weld interface from RFW of PLA and PLA is the highest. The surface hardness of the weld joint is about 3% higher than that of the base material. The surface hardness of the heat-affected zone is about 3% lower than that of the base material. The average peak temperature of the welded joint is the highest in the RFW of PLA-containing Al powder and PLA-containing Al powder rods. The average peak temperature of the weld joint can be as high as 160 °C. The average peak temperature of the welded joint is the highest in the RFW of PLA-containing Cu powder and PLA-containing Cu powder rods. The average peak temperature of the welded joint can be as high as 144 °C. A technical database was built for the selection of ambient temperatures used for the RFW of dissimilar polymer rods containing metal powder and three base materials.

Деформируемость пористого материала при прокатке в четырехвалковом калибре

Rolling in four-roll passes offers a lot of technological and ecological advantages over swaging which is presently used for working of sintered powder rods from tungsten and molybdenum. It explains the necessity of thorough experimental and theoretical investigations of such processes as plastic shaping and compacting of sintered powder materials at the zone of their deformation in rol­ling with four-side reduction. Authors have carried out numerous experimental investigations of compacting of powder rods in the process of their rolling in four-side passes. There exist several empirical formulae describing rod density change in the process of rolling. The present paper gives complex experimental details and justification of the proposed analytic function allowing the evaluation of powder strip density by measuring its geometric parameters. This analytic function is based on the law of constant rod mass in plastic shaping and compacting.

Influence of cobalt on the properties of load-sensitive magnesium alloys.

In this study, magnesium is alloyed with varying amounts of the ferromagnetic alloying element cobalt in order to obtain lightweight load-sensitive materials with sensory properties which allow an online-monitoring of mechanical forces applied to components made from Mg-Co alloys. An optimized casting process with the use of extruded Mg-Co powder rods is utilized which enables the production of magnetic magnesium alloys with a reproducible Co concentration. The efficiency of the casting process is confirmed by SEM analyses. Microstructures and Co-rich precipitations of various Mg-Co alloys are investigated by means of EDS and XRD analyses. The Mg-Co alloys' mechanical strengths are determined by tensile tests. Magnetic properties of the Mg-Co sensor alloys depending on the cobalt content and the acting mechanical load are measured utilizing the harmonic analysis of eddy-current signals. Within the scope of this work, the influence of the element cobalt on magnesium is investigated in detail and an optimal cobalt concentration is defined based on the performed examinations.

Growth characteristics and potential applications in optical sensors of composite Cr4+:yttrium–aluminum–garnet (YAG)–Nd3+:YAG crystal fiber

Composite Cr4+:yttrium–aluminum–garnet (YAG)–Nd3+:YAG crystal fiber was grown by means of the laser heated pedestal growth method. By using a high quality Nd3+:YAG as the seed and a sintered powder rod as the source rod, it was shown that Cr4+:YAG can be readily grown on a Nd3+:YAG end surface. The crystal fiber thus produced was processed and preliminary results showed that the crystal fiber demonstrated laser performance as a compact passively Q-switched laser device. A Q-switched laser output showing a 9 ns pulse duration, a 19 mW average output and a 10 kHz repetition rate was achieved. The use of the fiber in high temperature optical sensor application is discussed.

The Use of Utilizable Explosives to Increase the Efficiency of an Explosion

The possibility of using the utilizable explosives to increase the efficiency of an explosion of industrial high–explosive (HE) charges is studied under laboratory and working conditions. To do this, the explosive charges were used as linear initiators of the elongated charges of industrial HE. It is shown that the placing of an NB–40 ballistite powder rod of diameter 10 mm in a bulk–density TNT charge of diameter 40 mm increases the velocity of acceleration of an aluminum shell by 14% (the ratio between the detonation velocities of the powder and TNT is 1.8 : 1.0). The use of ShZ–1 TNT–based and ShZ–2 RDX–based hose charges in well charges of industrial HE, such as 79/21 Grammonit (79% granular ammonium nitrate/21% scale–shaped TNT), 30/70 Grammonit (30% granular ammonium nitrate/70% granular TNT), and ammonium nitrate, as linear initiators leads to a decrease in the output of bulky rock by 15—20% and allows one to increase the grid of the wells of diameters 160 and 220 mm by 20—25% with preservation of the rock output. The ratio of the detonation velocities of ShZ–1 and ShZ–2 and industrial HE charges is within 1.5—1.7 in the case of 79/21 Grammonit and 2.2—2.6 in the case of ammonium nitrate. The results obtained are explained by the fact that the detonation of a linear initiator from utilizable materials changes the form of the detonation wave front of the basic charge; as a result, it arrives at the surface of an ambient medium at a large angle and a more intense shock wave “enters” the medium compared to the case without a linear initiator.

A study of the growth mechanism of bismuth silicon oxide during LHPG method

Single-crystal fibers of Bi 12SiO 20 were grown by a laser-heated pedestal growth (LHPG) method. The thermal radiative emissions during the growth were monitored by a thermal imaging radiometer with a 5 μm bandpass filter. The variation in thermal emissions in the 5 μm spectrum during the growth process reflects the interior structure of re-crystallized Bi 12SiO 20. When a crystal fiber was grown upward from a sintered powder rod, bubbles oscillate in the upper floating zone and may be caught within the grown crystal, which may cause the inclusions, color fragments, voids or other defects inside the grown crystal. When we grew a crystal downward to minimize the effects of the bubbles, the defects were reduced, but could still be observed inside the crystal. In order to solve this problem, we used a two-pass method that is during the first pass, we grew downward to obtain an almost bubble-free polycrystalline rod. In the second pass, we grew the single-crystal fiber upward using the polycrystal source rod obtained in the first pass. The grown fiber has uniform luster and higher transmissivity.

Enhancement of growth rate for BSO crystals by improving thermal conditions

Effects of various thermal conditions on growth of single crystal of Bi 12SiO 20 (BSO) with a floating zone method were systematically investigated. The following are the main results: (1) Change of heating source from an infrared heater to a CO 2-laser system could have increased the temperature gradient in the grown crystal near the solid-liquid interface about 3 to 4 times, which gives rise to a dramatic increase of the critical transparent growth rate more than 3 times. (2) A single crystal seed with high thermal conductivity (e.g., Al 2O 3) can dramatically increase the critical transparent growth rates. (3) For a source rod of the multi-sintered powder rod, an increase of growth rate from 18.8 mm/h to 100 mm/h can decrease the diameter fluctuation of the grown crystal from 2~3%/cm to less than 0.5%/cm.

Fracture patterns in explosively compacted copper/graphite powder rods

Static and dynamic powder compaction and forming processes have been used for fabricating engineering components from powders of metals, ceramics, polymers and composite materials. The principal advantages of powder-metallurgy processing are its versatility for making parts in a wide range of sizes close to the final dimensions and finish, with little or no subsequent machining, as well as that an increased homogeneity of resulting metallurgical structure is secured. In the present investigation the explosive-compaction technique has been employed for producing cylindrical rods of copper/graphite powders using a steel container. In this paper, experimental observations of fracture-damage developments and microstructural changes which occur during the direct explosive-compaction process are outlined. The microhardness distribution was measured and damage “regions” are indicated. An attempt was made to explain qualitatively some modes of fracture in terms of stress wave-front developments.

Preparation of NbN single crystals

NbN single crystals were prepared for measurements of the phonon dispersion by inelastic neutron scattering and as starting material for ion implantation experiments. Series of experiments have been done to study three different possibilities to obtain crystals of the required size: (i) RF zone melting of NbN powder rods, (ii) nitriding of Nb single crystals by a graphite heating element under a N 2 pressure up to 100 bar, (iii) nitriding of Nb single crystals in a tungsten crucible by RF-heating. The crystals were characterized by chemical analysis, X-ray- and neutron diffraction and also by determination of the superconducting transition temperature.

Directional Solidification of Unstabilized HfO2‐Ta

Aligned eutectic composites of unstabilized ZrO/sub 2/ and Ta can be prepared crack-free even though the matrix has been completely transformed into the monoclinic lattice, i.e. the transformation-induced volume change does not result in the excessive cracking which is usually observed. Composites with Y/sub 2/O/sub 3/-stabilized ZrO/sub 2/, however, crack extensively and exhibit inhomogeneous eutectic structures. Similar results are obtained with directionally solidified, stabilized ZrO/sub 2/--W and stabilized HfO/sub 2/--W. The fact that ZrO/sub 2/ and HfO/sub 2/ have modifications with identical crystal structures suggested that compositions of unstabilized HfO/sub 2/ with Ta would also exhibit an improved solidification behavior compared with mixtures containing Y/sub 2/O/sub 3/-stabilized HfO/sub 2/. Eutectic areas of HfO/sub 2/--Ta sintered powder rods exhibited almost no cracking. There are two possible explanations for the fact that the composites with unstabilized ZrO/sub 2/ and HfO/sub 2/ survive the tetragonal..-->..monoclinic transformation without cracking: (1) the matrix is prestressed by the Ta fibers when expanding at the lattice tranformation; or (2) since the composites are sintered in vacuum, ZrO/sub 2/ or HfO/sub 2/ are substoichiometric. This condition, together with Ta in solid solution, may cause the monoclinic lattice cell to exhibit a density similar to that of the tetragonalmore » form. Both hypotheses, however, must be carefully investigated. (JRD)« less