Mechanical and Conductive Properties of Cu Matrix Composites Reinforced by Oriented Carbon Nanotubes with Different Coatings

Because of the dilemma that the current industrial Cu enhancement methods lead to a significant decline in conductivity and ductility, Cu matrix composites reinforced by oriented multi-walled carbon nanotubes (MWCNTs) were prepared through sintering, hot extrusion, and cold drawing. Before sintering, Ni, Cu, and Ni&Cu coatings were electroless plated on MWCNTs as the intermediate transition layer, and then they were mixed with Cu powder through a nitrogen bubbling assisted ultrasonic process. By analyzing the composition, microstructure, and formation mechanism of the interface between MWCNTs and the matrix, the influence and mechanism of the interface on the mechanical properties, conductivity, and ductility of the composites were explored. The results indicated that MWCNTs maintained a highly dispersed and highly consistent orientation in the Cu matrix. The coating on Ni@CNT was the densest, continuous, and complete. The Ni@CNTs/Cu composite had the greatest effect, while the Cu composite reinforced by MWCNT without coating had the smallest reduction in elongation and conductivity. The comprehensive performance of the Cu@CNTs/Cu composite was the most balanced, with an ultimate tensile strength that reached 373 MPa, while the ductility and conductivity were not excessively reduced. The axial electrical and thermal conductivity were 79.9 IACS % (International Annealed Copper Standard) and 376 W/mK, respectively.

Innovative Technology for Stamping a Small-Sized Sleeve Blank

The work is devoted to the development of an innovative technology of stamping from low-carbon steel for small-size liner blanks. The sequence of punching transitions includes a cold back extrusion operation, two cold drawing operations with thinning, and a cold crimping operation. Simulation with the use of the finite element method established the forces and specific forces during operations, the thermal effect during shaping, the shape and size of semi-finished products with distributions of the intensity of deformations. An elastoplastic metal model was used, which made it possible to reveal the deformation forces, tool extraction from deformed semifinished products and the effort to remove semifinished products from the dies. A hollow semi-finished product is obtained by reverse extrusion. The possibility of carrying out the first drawing operation with thinning through two sequentially located dies with the formation of a hole in the bottom part is shown. After this operation, annealing of the semi-finished product is required to restore plasticity. In the second operation, thinning stretching. The shape and dimensions of the wall of the semi-finished product after the second drawing, the distribution of the intensity of deformations in it are determined from the condition of reaching the final dimensions and mechanical properties of the sleeve blank at the last crimping operation. For this, the deformations obtained as a result of the second drawing are taken into account when modeling the crimp. For each transition of stamping, a construction of stamping equipment has been developed. The proposed technology for stamping a sleeve blank can be implemented on a universal pressing equipment, has a high productivity due to a reduction in the number of transitions and minimizes mechanical processing.

Mechanical Properties and Degradation Behaviors of Zn-xMg Alloy Fine Wires for Biomedical Applications

Zn and Zn-based alloys exhibit biosafety and biodegradation, considered as candidates for biomedical implants. Zn-0.02 wt.% Mg (Zn-0.02 Mg), Zn-0.05 wt.% Mg (Zn-0.05 Mg), and Zn-0.2 wt.% Mg (Zn-0.2 Mg) wires (Φ 0.3 mm) were prepared for precision biomedical devices in this work. With the addition of Mg in Zn-xMg alloys, the grain size decreased along with the occurrence of Mg2Zn11 at the grain boundaries. Hot extrusion, cold drawing, and annealing treatment were introduced to further refining the grain size. Besides, the hot extrusion and cold drawing improved the tensile strength of Zn-xMg alloys to 240-270 MPa while elongation also increased but remained under 10%. Annealing treatment could improve the elongation of Zn alloys to 12% -28%, but decrease the tensile strength. Furthermore, Zn-xMg wires displayed an increase in degradation rate with Mg addition. The findings might provide a potential possibility of Zn-xMg alloy wires for biomedical applications.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF STEELS FOR SHAPED CHARGE LINERS AND PRELIMINARY ASSESSMENT OF THE EFFECTIVENESS OF EXPERIMENTAL SHAPED CHARGES INTENDED FOR USE IN THE MINING INDUSTRY

The paper presents the results of investigation of the microstructure and mechanical properties of Fe-based materials designed for the manufacture of semi-spherical liners for experimental shaped charges. The tests were carried out on material samples taken from two semi-finished products, i.e. a rod for the manufacture of charge liners with a diameter of 50 mm using machining, and sheets for the manufacture of liners with a diameter of 100 mm using cold drawing. Microstructure examination was also carried out on a test specimen obtained using the additive method (3D-WAAM), made of low-carbon unalloyed steel wire. Firing tests on concrete blocks were carried out in order to quantify the effects of drilling at the Experimental Mine Barbara. The scope of the tests consisted of firing at cylindrical concrete blocks using projectiles containing 50 mm diameter liners made of Fe-based alloys. Based on the results of the laboratory material, two experimental steel grades were selected for further testing. Plates made of the selected steels will be used to manufacture charge liners with a diameter of 100 mm.

Mechanical properties, crystallographic texture, and in vitro bio-corrosion of low-alloyed Zn–Mg, produced by hot and cold drawing for biodegradable surgical wires

The paper is devoted to the study of the mechanical, microstructural, and bio-corrosive behavior of low-alloyed Zn–Mg biodegradable surgical wires for bone reconstructions. Three biodegradable alloys with different magnesium content have been studied, their production technology has been developed and the product properties have been determined. The technology includes casting, extrusion, hot and cold drawing of the wire, and the product surface finishing. The paper shows the most important stages of the process (i.e., extrusion and drawing) in detail. The technological parameters have been selected based on the results of the computer modeling. The flow stress–strain curves of extruded materials have been obtained at various strain rates and temperatures. Two drawing technologies have been compared. The first one is the room temperature conventional wire drawing. In the second one, the first few passes have been made at an elevated temperature and the rest at room temperature. This allowed avoiding the breaking of the wire during the first passes (a typical issue of the conventional technology for these alloys) and increasing the ductility of the final product. Mechanical properties, bio-corrosion, and crystallographic texture of the material were determined at different stages of the processing. A simultaneous increase in the wire strength, the number of repeated bending until the rupture of the wire, and in the bio-corrosion rate due to drawing has been registered. This phenomenon coincided with a change in the crystallographic texture. It has been shown that the product tensile strength of about 250–300 MPa can be reduced by about 30% due to surgical knots tied on it.