INFLUENCE OF AXISYMMETRIC DEFORMATION PROCESSING METHODS ON THE MECHANICAL PROPERTIES OF Cu-Nb COMPOSITES

It has been shown that deformation processed Cu-19% Nb alloys with good strength and electrical conductivity can be developed in sizes that are useful for engineering applications. Mot extrusion of bundled sub-elemental Cu-19% Nb wires followed by cold drawing to make a composite wire of diameter equal to that of the initial sub-elemental wires resulted in a 67% increase in the ultimate tensile stress. However, on subsequent cold drawing of this composite wire the strength increased at a slower rate than that obtained on continuing cold drawing of the sub-elemental wire and the strength differential decreased. In addition, after cold drawing to equivalent diameters the electrical conductivity of the composite wire was less than that of the sub-elemental wire. These results indicate that while high strengths and good electrical conductivities can be produced in larger size deformation processed Cu-Nb composites by a process of bundling, extrusion and cold drawing of sub-elemental wires, there appears to be a limit to the amount of subsequent cold drawing feasible before the benefit in properties ceases.     

Neuartige Faserverbunddrähte für die Leistungselektronik

Novel fibre reinforced wires for power electronics The use of power electronics within the scope of mechatronic applications as well as the increasing integration of components lead to increased requirements concerning their mechanical and thermal reliability. Today contact making in power electronics is mostly done by aluminum thick wire bonding. This process is highly productive, however the life time of power electronic components is meanwhile predominantly limited by the durability of these wire bonds. The thermal mismatch between the wire material and the connected components is one cause. A new starting point, in order to improve the reliability, is the application of new fibre reinforced metal matrix composite (MMC) wires with increased reliability under thermo‐mechanical stress. In the context of a research project MMC bond wires of different material combinations and arrangements were manufactured. Aluminum wires with copper fiber reinforcement as well as Copper wires containing FeNi36 fibre reinforcement have successfully be drawn to a final diameter of 300 μm. The fibre reinforcements should reduce the coefficient of thermal expansion and improve the mechanical strength. By aluminium copper MMC the electrical conductivity is increased as well. Measurements of the produced MMC wires confirmed these expectations. The manufacturing of the MMC took place on the basis of wire material of different diameters. These wires were stacked in capsules in different arrangements and material combinations. Subsequently, the capsules were either hot‐isostatically pressed or directly extruded. In such a way produced composites have been manufactured by rotary swaging and wire drawing into bond wires and after that tested.     

Damascene Light‐Weight Metals

Besides widely investigated severely plastically deformed materials that are available in laboratory scale and size only, there is a high demand for semi‐finished products such as sheets and wires with similar mechanical properties. A damascene‐like technology applying swaging and bundling/swaging allows to deform Ti? Nb? Al composites up to a log. deformation strain of 8.4. Here, Al and Ti are used because of their low density, while Nb acts as diffusion barrier to prevent the formation of hardly deformable intermetallic phases. The obtained wires show an ufg microstructure with grain sizes of Ti and Al between 100 and 200 nm. In the cold‐worked condition the wires with a density of 4.0 g cm^?3 reveal an ultimate tensile strength of 790 MPa.     

Processing and property assessment of NiTi and NiTiCu shape memory actuator springs

Among the multifarious engineering applications of NiTi shape memory alloys (SMAs), their use in actuator applications stands out. In actuator applications, where the one‐way effect (1WE) of NiTi SMAs is exploited, SM components are often applied as helical coil springs. Ingots are generally used as starting materials for the production of springs. But before SM actuator springs can be manufactured, the processing of appropriate wires from NiTi ingots poses a challenge because cold and hot working of NiTi SMAs strongly affect microstructure, and it is well known that the functional properties of NiTi SMAs are strongly dependent on their microstructure. The objective of the present paper is therefore to produce binary Ni₅₀Ti₅₀ and ternary Ni₄₀Ti₅₀Cu₁₀ SMA actuator springs, starting from ingots produced by vacuum induction melting. From these ingots springs are produced using swaging, rolling, wire drawing and a shape‐constraining procedure in combination with appropriate heat treatments. The evolution of microstructure during processing is characterized and the mechanical properties of the wires prior to spring‐making are documented. The mechanical and functional characteristics of the wires are investigated in the stress‐strain‐temperature space. Finally, functional fatigue testing of actuator springs is briefly described and preliminary results for NiTi and NiTiCu actuator springs are reported.     

In situ strengthening of titanium with yttrium: texture analysis

In situ processing consists of heavily deforming a two-phase alloy of mutually immiscible elements to produce composite sheet or wire. In the well-studied Cu(fcc)-Nb(bcc) system, severe deformation by swaging and drawing reduces as-cast Nb filament phase thicknesses several hundred-fold after deformation. Cu-20 vol % Nb ultimate tensile strengths exceed 2000 MPa for material deformed to a true strain of η = 12, where η = ln (area_original/area_final). In an earlier study of in situ strengthening in immiscible hexagonal close-packed metals, Ti-50 vol % Y and Ti-20 vol % Y alloys were deformed by hot extrusion, hot and cold swaging. The composites were deformation processed to true strains as high as η = 7.6 to form a filamentary microstructure with filament thicknesses on the order of 0.1 μm. The deformation processing of these composites increased their ultimate tensile strengths from 318 to 945 MPa, but the specimens' original diameters were too small to allow deformation processing to the very high true strains achieved with the Cu-Nb composites. In this study, a larger casting of Ti-20 vol % Y was deformation processed to η = 12.8 in an attempt to achieve further refinement of the filament thickness. This composite formed the same filamentary microstructure up to η=7.27 observed in the earlier study of Ti-Y composites; however, at higher η values the filaments recrystallized into equiaxed grains, decreasing the ultimate tensile strength. X-ray texture analysis of the composite specimens showed a strong 〈10ˉ10〉 fibre texture in both the Ti and Y phases in the deformation processing range 2.25 ≤ η ≤ 7.27. This texturing is thought to constrain both the Ti and Y phases to deform by plane strain, which produces severe geometric restrictions on the ability of the plane straining filaments to achieve high η values without fracturing or recrystallizing.     

Development of Ag-Sheathed Bi(2223) Tapes with Improved Microstructure and Homogeneity

The development of the fabrication process of Ag-sheathed Bi(2223) tapes has been carried out in order to improve their transport and mechanical properties, as required by the power applications which are so far under study. Critical current density values of 28 kA/cm² at 77 K have been achieved on long multifilamentary Bi(2223) tapes, with a fabrication process that has been successfully employed in the fabrication of samples longer than 50 m. The microstructure and homogeneity of Ag-sheathed multifilamentary Bi(2223) tapes has been markedly improved by employing an alternative deformation technique. In a substantial part of the fabrication process, swaging, drawing, and rolling have been replaced by deformation with an active turks-head machine, which allows the deformation of rectangular shaped wires. At present, critical current densities in excess of 25 kA/cm² at 77 K have been achieved on long samples prepared with this technique. Moreover, innovative filament configurations have been employed for the fabrication of square-shaped Bi(2223) wires with reduced anisotropy and with critical current densities exceeding 20 kA/cm² at 77 K.     

Comparison of microstructure and strength in wire-drawn and rolled Cu-9 Fe-1.2 Ag filamentary microcomposite

Comparison of microstructure and strength of Cu-9 Fe-1.2 Ag microcomposite wires and sheets obtained by cold drawing or cold rolling combined with intermediate heat treatments has been made. The primary and secondary dendrite arms are aligned along the drawing or rolling direction and elongated into filaments after cold working. The microstructural scale of wire-drawn microcomposites was found to be finer than that of rolled microcomposites at the same drawing strain. The more effective microstructural refinement induced by unidirectional metallic flow and co-deformation of filament and Cu matrix resulted in finer microstructure in microcomposite wires. The ultimate tensile strength and the conductivity of wire-drawin Cu-Fe-Ag microcomposite were higher than those of rolled Cu-Fe-Ag microcomposites. The strength of Cu-Fe-Ag microcomposites is dependent on the spacing of the Fe filaments in accord with a Hall-Petch relationship. The good mechanical and electrical properties of wires may be associated with the more uniform distribution of fine filaments. The fracture surfaces of Cu-Fe-Ag wires and sheets showed ductile-type fracture and iron filaments were occasionally observed on the fracture surfaces. The fracture surface of Cu-Fe-Ag wires showed generally finer microstructural morphology than that of Cu-Fe-Ag sheets, consistent with the finer microstructural scale in Cu-Fe-Ag wires.     

Mechanical and electrical properties of heavily drawn Cu-Nb microcomposites with various Nb contents

The mechanical and electrical properties of Cu-Nb filamentary microcomposite fabricated by the bundling and drawing process were examined. The strength increased gradually with increasing Nb content while the ductility was insensitive to Nb content. The ratios of yield stresses are found to be close to that of Young's moduli in various Cu-Nb microcomposites, suggesting that athermal obstacles primarily control the strength. The fracture morphologies show ductile fractures irrespective of Nb contents. Secondary cracking along the interfaces between subelemental wires was occasionally observed and the frequency of secondary cracking increased with increasing Nb content. The conductivity and the resistivity ratio (_{295 K}/_{75 K}) decreased with increasing Nb content. The decrease of the conductivity and the resistivity ratio can be explained by the increasing contribution of interface scattering.     

铜包钢线材室温拉变形后的显微组织和力学性能

研究了经室温拉变形后的纯铜包覆Q195钢的不同线径的线材的显微组织及力学性能.结果表明,显微组织自原始的等轴晶变为细长条纤维状,纤维长度与形变量的平方近似地成正比,纤维直径与形变量近似地成反比.经室温拉变形的包覆线材的抗拉强度,随形变量增大而增大,与形变量平方根呈直线关系;但延伸率降低,延伸率波动偏高与晶界融合及Q195钢的渗碳体球化现象吻合.根据原始纯铜和Q195钢的抗拉强度值,可以用复合材料强度的混合法则来近似地预测不同线径的包覆线材的抗拉强度.     

Medium carbon fully pearlitic steel: microstructures and properties after wire drawing

In the current work, fully pearlitic microstructure was initially developed in a medium carbon steel by isothermal holding at different temperatures. Subsequently, these samples were drawn in laboratory scale wire-drawing machine without any intermediate heat treatment. Microstructures and mechanical properties of as-heat-treated and heat-treated plus drawn samples were characterised. The results were also compared with some commercially produced steel. It was found that the new steel can offer a very good wire drawing behaviour. The steel possesses a good combination of strength and ductility along with a high-value torsion, bending and reverse bending properties after drawn condition as well.     

Pass schedule of wire drawing process to prevent delamination for high strength steel cord wire

The high-speed drawing of high carbon content steel wires is usually conducted at room temperature employing a number of passes or reductions through several dies. In the multipass drawing process, the temperature rise at each pass affects the mechanical properties of the final product (such as its bending and torsion properties, and its tensile strength). This temperature rise during deformation encourages delamination in the wire, which has a deleterious influence on the torsional properties and durability of the wire. In this study, we investigated the delamination of wires using torsion tests and evaluated the wire temperature during drawing. Our data shows that one of the main reasons for delamination was an excessive rise in wire temperature. Based on our experimental results, in order to prevent delamination due to an excessive rise in wire temperature, a new isothermal pass schedule that could control the wire temperature was designed. The pass redesign for the conventional high carbon (0.75 wt%C) steel cord wire drawing process with delamination was carried out by using the isothermal pass schedule to control the wire temperature. In order to verify the effectiveness of the proposed method, wire drawing and torsion test were conducted. From the results of experiments, it was possible to produce high carbon steel cord wire without delamination.     

In situ strengthening of titanium with yttrium

In situ processing consists of heavily deforming a two-phase alloy of mutually immiscible elements to produce composite sheet or wire. In the well-studied Cu(fcc)-Nb(bcc) system, severe deformation by swaging and drawing reduces niobium filament phase thicknesses from 1–5 m (as-cast) to 0.007–0.030 m (after deformation). Cu-20% (vol.) Nb ultimate tensile strengths exceed 2000 MPa for material deformed to a true strain of =12, where =In (area_original/area_final). In a study on in situ strengthening in immiscible hexagonal close-packed metals, Ti-50 wt % Y and Ti-20 wt % Y alloys were deformed by hot extrusion, hot swaging, and cold swaging. As deformation progressed, samples were taken for tensile testing and examination by SEM and TEM. Ti-Y alloys deformed to final true strains of 6.6 (Ti-50Y) and 7.6 (Ti-20Y) contain nanofilaments (100 nm phase spacing) similar to those of deformation-processed Cu-20Nb at comparable strains. The ultimate tensile strengths of the alloys approximately tripled as deformation progressed from the as-cast condition to these final true strains, although the exponential strength increase seen in Cu-Nb alloys was not observed.     

Study of the martensitic transformation in NiTi–epoxy smart composite and its effect on the overall behavior

In this work, the effect of wire phase transformation on the overall thermo-mechanical behavior of NiTi–epoxy composites has been investigated. The shape memory wire received in as drawn condition was subjected to three heat treatments which results to different transformation characteristics. Composite specimens were manufactured by casting followed by curing and post curing process. The mechanical behavior of samples has been determined using standard tensile test. The effect of wire volume fraction and test temperature was investigated as well.It is found that the martensitic transformation occurring in the wire affects the mechanical behavior of the composite specimens. In this way, using the wire with higher transformation stress improves the composite tensile strength. This is achieved either by increasing the test temperature or by using the wires heat treated at lower temperatures. From the experimental results, the martensitic transformation can change the debonding mode. It seems that on the constraint of matrix, the transformation occurs simultaneously at several points in wires that result in regular debonded/undebonded pattern.     

Ultrahigh strength steel wires processed by severe plastic deformation for ultrafine grained microstructure

Abstract

A comprehensive review of recent literature on high strength, fine grained steels has been conducted. While relevant technologies in alloy design, processing and heat treating are included in the present review, the emphasis has been on high carbon steel wire processing technology that can be achieved with ‘conventional’ wire rolling and drawing processes. The thermomechanical processing of a pearlitic microstructure, followed by cold drawing, is recommended as the process of choice to efficiently produce an ultrafine grained ferrite–cementite microstructure for ultrahigh strength, ultrahigh carbon steel wires.     

Sigma Phase in Tungsten-Rhenium Alloys. II

This second part of the paper on sigma (a) phase in tungsten-rhenium alloys deals with experimental evaluation of the influence of a phase development on microstructure and mechanical properties during processing of powder metallurgy sintered bars of W-25%Re alloys into various shapes. The processing steps may include warm rolling, forging, swaging and drawing when producing sheet, rod and wire products. In addition, intermediate heat treatments have a decisive influence on the structure and hence the properties of the final product. The characteristics of the products at different stages in the processing route have been evaluated using optical microscopy, electron probe microanalysis and hardness testing to determine the effect of the presence of sigma phase in varying quantities. By controlling the appearance and minimizing the quantity of sigma phase in the microstructure the product quality can be greatly improved.     

电子束熔丝沉积4043/4074铝合金的组织与力学性能

目的 研究电子束熔丝沉积Al-Si合金的微观组织与力学性能以及后续热处理的影响。方法 采用电子束熔丝沉积快速成形技术,分别对直径2 mm的4043和4047铝合金丝材进行增材制造成形,研究样品在不同方向上的微观组织与力学性能以及后续热处理的影响。结果 打印态的4043和4047合金的致密度分别为99.81%和99.88%,热处理后略有降低,分别为98.94%和99.77%。打印态样品中含有一些由硅颗粒和杂质相组成的条带状微观组织。打印态样品中含有近似等轴状与棒状的两类细小Si颗粒。打印态样品在长、宽、高3个方向上的拉伸强度相当,4043合金的抗拉强度为120~127 MPa,伸长率为12%~30%;4047合金的抗拉强度为151~155 MPa,伸长率为15%~30%。经热处理后,样品的强度略有降低,但伸长率显著提升。结论 通过控制EBF3参数,可以获得致密无缺陷的具有良好力学性能的块体Al-Si合金样品,其力学性能可通过后续热处理进一步调控。     

Structure-sensitive properties during room-temperature wire drawing at various speeds in nickel 200

The effects of drawing speed, cell size and grain size on the yield strength of nickel 200 wires drawn at room temperature up to a true strain of 2.09 have been investigated. The wire drawing speeds in the range from 17 to 140 mm s^–1 do not show any effect on the yield strength, cell size and grain size of drawn wires. However, the cell sizes as well as grain sizes decrease with increase in true wire drawing strain when their values are averaged over all the wire drawing speeds at a given strain. Even though the Hall-Petch equation is valid for all the grain diameters observed in this study, the graph suggests that two distinct linear regimes may be more appropriate to properly describe the strengthening mechanisms during wire drawing. The cell diameter has been correlated with the yield strengths of drawn wires by an inverse relationship.     

Fabrication and mechanical properties of steel–steel composites

Metal matrix composites based on a low carbon steel matrix reinforced with high carbon steel wires have been fabricated by a combined cold and hot rolling process. Both continuously and discontinuously aligned composites have been produced. A subsequent heat treatment allowed the formation of martenisitc, bainitic or pearlitic wires in a ferrite predominantly matrix. The optimum wire microstructure giving a composite with high strength and reasonable ductility was found to be bainitic — martensitic wires were found to contain microcracks that gave poor composite strengths and ductilities. The discontinuous wire composites produced similar strengths to the continuous composites only when they were deformed to give a wire aspect ratio greater than 20. The strengths of both types of composites showed a good fit to the rule of mixtures as the volume fraction of fibers was increased.     

Cold drawn steel wires—processing, residual stresses and ductility—part I: metallography and finite element analyses

Cold drawing steel wires lead to an increase of their mechanical strength and to a drop of their ductility. The increase of their mechanical strength has long been related to the reduction of the various material scales by plastic deformation, but the mechanisms controlling their elongation to failure have received relatively little attention. It is usually found that heavily deformed materials show a tendency to plastic strain localization and necking. However, in this paper it is shown that, though the steel wires are plastically deformed up to strain levels as high as 3.5, a significant capability of plastic deformation is preserved in as‐drawn wires. This apparent contradiction is resolved by the existence of residual stresses inside the wire. Finite element analyses have been conducted in order to show that residual stresses, inherited from the drawing process, are sufficient to produce a significant hardening effect during a post‐drawing tensile test, without introducing any hardening in the local material behaviour. The main conclusion of this paper is that once the material has lost its hardening capabilities, residual stresses, inherited from the process, control the elongation of cold drawn wires. The finite element method allowed also the determination of the residual stress field that would lead to the best agreement between the simulated and the experimental stress strain curve of as‐drawn wires.     

A parametric study on residual stresses and loads in drawing process with idle rolls

A comprehensive study of drawing process with flat idle rolls of round wires is presented through 3D mechanical finite element simulations. An elastic–plastic model is used for the wire material and contact behavior is simulated by a sliding–sticking friction model. The results of numerical simulations are compared with measurements on wires produced with a laboratory equipment. The comparison of drawing load and some geometrical characteristics of experimental samples with numerical model predictions allowed to establish a good correspondence of model with experimental findings, thus validating the numerical model. Residual stress of flat roll drawn wires, pressure distribution on the forming rolls and drawing load are studied. The effects of main process parameters such as initial workpiece diameter, forming rolls diameter and percentage of deformation are investigated. The results present a helpful insight into the process parameters effect in wire drawing with flat idle rolls thus furnishing the basic guidelines for process design and optimization.