Alloy Wires Research Articles

Fabrication and Mechanical Property Evaluation of Peripheral Stent Made from Shape Memory Alloys

This study proposes to design and fabricate the peripheral stent using NiTi shape memory alloy wires by braiding technique. The 0.2 mm diameter NiTi wire was attached to the automatic braiding machine and fabricated the braided stent under the different height of circular rod holder. Heat-treatment was carried out at 450°C, 500°C, 550°C and 600°C for 10 and 20 minutes, respectively. Then transformation temperature, the shape of cell area, and mechanical properties were evaluated. The results show that complete superelasticity can be confirmed under body temperature in stent prototypes with heat-treatment temperature over 500°C irrespective of heat-treatment time. The prototype with the height of circular mold of 70 mm shown a good braiding pattern with high kink resistance. The radial force shown no significant difference at any section along the length profile. It is noted that stent with the height of circular mold at 70 mm, carrier speed of 30 rad/sec and take-up speed of 4.86 mm/s which shown radial resistive force (ROF) of 2.44 ± 0.05 N/mm, and chronic outward force (COF) of 0.533 ± 0.03 N/mm which is sufficient for vessel expansion.

Near-Net Forging of Titanium and Titanium Alloys with Low Friction and Low Work Hardening by Using Carbon-Supersaturated SKD11 Dies

A new near-net forging procedure of titanium and titanium alloys was proposed by using a carbon-supersaturated punch and die. Due to the in situ formation of carbon-based tribofilm on the contact interface between the dies and work materials, a low frictional state was sustained through the forging process even in a high reduction in thickness. The work hardening was suppressed during forging; an additional annealing process was unnecessary through the whole process of near-net forging. Pure titanium and β-phase titanium alloy wires were utilized to describe their galling-free forging behavior when increasing the reduction in thickness. Wires with a diameter of 3 mm were upset in a single-shot forging. The reduction in thickness reached 58% when upsetting the pure titanium wire and 45% when upsetting the β-phase titanium alloys, without lubricating materials or oils at room temperature. The friction coefficient on the contact interface was estimated to be 0.05 by inverse analysis. The work-hardening behavior was described by the hardness mapping on the work cross section. The formation of carbon tribofilms was explained by microstructural analysis, element mapping, and Raman spectroscopy. This tribofilm was formed from the isolated carbon solute from the carbon-supersaturated punch and die to sustain the in situ solid lubrication on the contact interface.

Effect of Cu and Mg addition on the mechanical and degradation properties of Zn alloy wires.

In this study, Zn-xCu (-0.1Mg) wires with a diameter of 0.3mm were obtained by hot extrusion and cold drawing. The microstructures, mechanical properties, and degradation behaviour were investigated to evaluate their feasibility as biodegradable metals. During the drawing process of the Zn-xCu alloys, many granular CuZn5 phases were dynamically precipitated, and the grains were significantly refined, along with a significant work softening with the tensile strength decreasing and the elongation increasing (from 161MPa to 92MPa and 22%-103% for Zn-0.2Cu). With the increase of Cu additions, the phenomenon of work softening was more intense and there was an opposite trend in the strength changes between the as-extruded rods (increase) and as-drawn wires (decrease). With 0.1 wt.% Mg added, the stable rod-like Mg2Zn11 phase was formed in as-extruded Zn-xCu-0.1Mg rods, which obviously improved the strength, and inhibited the dynamic precipitation of granular CuZn5 phase and work softening phenomenon in the drawing process (from 332MPa to 313MPa and 11%-46% for Zn-0.2Cu-0.1Mg). In addition, due to the micro-galvanic effect induced by the precipitates, alloying accelerated the degradation of Zn alloy wires, especially Zn-1Cu-0.1Mg, which was related to the shape, distribution, and potential of the phases.

Influence of Filler Metal on Electrochemical Characteristics of a Laser-Welded CoCrMoW Alloy Used in Prosthodontics.

This paper sought to determine corrosion resistance changes in the artificial saliva of a CoCrMoW-based alloy used for dental prostheses under Nd:YAG laser welding with CoCr alloy and stainless steel wire filler metals. The paper presents the corrosion characteristics of such joints, including the next stage of porcelain-fused-to-metal (PFM) firing. Corrosion tests were performed by electrochemical methods registering anodic polarization curves and electrochemical impedance spectroscopy (EIS). The microstructures were assessed by scanning microscopy (SEM) and chemical composition analysis (EDS) at the connection and heat-affected zones. Welding CoCrMoW alloy with and without a filler material increased the open circuit potential of the samples by 40–100 mV compared to unwelded base alloy. At the same time, a potentiodynamic test showed a polarization resistance Rpol reduction in welded samples, both for CoCr and stainless steel wires, as compared to the base CoCrMoW material. On the other hand, when comparing the current density and polarization resistance between materials welded with two different filler metals, better results were obtained for samples welded with stainless steel wire. The polarization resistance Rpol for the base alloy was 402 kΩ·cm2, for the CoCr wire weld it was 436 kΩ·cm2, and the value was 452 kΩ·cm2 for stainless steel wire welds. Comparing polarization resistance Rpol from the Tafel analysis and the total charge transfer resistance from Rp(EIS) from EIS, the CoCrMoW alloy welded with a stainless steel wire after heat treatment equaled or even slightly exceeded the corrosion resistance of the base alloy and alloy welded with dedicated CoCr wire after heat treatment. These results indicated the possibility of using stainless steel wire for the laser welding of CoCrMoW alloys dental prostheses, including the next stage of PFM, without sacrificing the corrosion resistance of such connections, and this was confirmed by most electrochemical parameters.

Influence of arc mode on the microstructure and mechanical properties of 5356 aluminum alloy fabricated by wire arc additive manufacturing

In this paper, two arc modes of gas shielded metal arc welding (GMAW), a new pulsed mode (microMIG) and a non-pulsed mode (microMIG-CC), were used to melt ER5356 aluminum alloy wire for thin-wall fabrication. The influence of both arc modes on the melt–drop transition pattern, thin–wall properties, porosity, microstructure and mechanical properties was investigated at the same heat input. The microMIG mode adds SKS-based current time based on conventional pulsed GMAW for short-circuiting the transition, which leads to a faster spread of melt pool temperature. The rapid cooling of the melt pool contributed to the increase of grain nucleation rate and inhibited grain growth, resulting in smaller grain size in the microMIG mode specimens. In addition, the low porosity of microMIG specimens is attributed to the high voltage of the micro-MIG mode resulting in an unfocused heat source, which leads to a shallow penetration depth of the specimens and a reduced hydrogen escape distance. Compared with the microMIG-CC mode, the microMIG mode specimens have smaller grain size and lower porosity, therefore higher tensile strength is obtained. The isotropic property of thin walls is due to the existence of equiaxed grains and the random distribution of grain orientation. However, the aggregation of dislocations and the increase of precipitates make microMIG-CC have higher hardness. Overall, the mechanical properties of the thin wall specimens of WAAM 5356 aluminum alloy are higher than those of the as-cast specimens.

The Development and Verification of a Simulation Model of Shape-Memory Alloy Wires for Strain Prediction

One of the greatest challenges in the design of shape-memory elements (mostly binary Nickel-Titanium wires) is to ensure that the required travel (stroke) is achieved, as this is subject to variation due to various influencing factors. One way of predicting the stroke is to use a suitable energy model. In the past, for example, a model was developed by Oelschläger with which the stroke can be calculated on the basis of the electrical energy. However, so far no model takes into account the change of the phase transformation temperature. In this study, the model of Oelschläger is extended and verified to consider the degradation behavior over the whole lifetime. For this purpose, fatigue tests of 52 wires (2 different load scenarios) were performed. Based on these tests and the application of statistical methods (distribution models, goodnes-of-fit tests etc.), a target model was developed for each load scenario, which is used to verify the extended energy model. The energy model was applied to wires of both load scenarios to simulate the stroke progression. The verification of the extended simulation model shows that it is possible to simulate the longterm behavior of the stroke for one of the two load scenarios. The second load scenario shows deviations between the target model and the simulation, which is due to problems in the area of measurement equipment, convection, and temperature distribution in the wire. Nevertheless, a decisive modeling approach could be developed, which can be used to consider the long-term behavior of the phase transformation temperature of wires in simulations.

Achieving exceptional improvement of yield strength in Mg–Zn–Ca alloy wire by nanoparticles induced by extreme plastic deformation

The size and distribution of second phase particles have an important influence on the mechanical properties of Mg alloys and further determine their application. In this study, extreme plastic deformation was employed to control the microstructure and tune the corresponding mechanical properties of Mg–Zn–Ca alloy. The uniformly dispersed nanoparticles (average diameter of ∼14.3 nm) could be successfully introduced into the Mg–Zn–Ca alloy wire after cold drawing with an area reduction of ∼99.8%, and the high yield strength of ∼285 MPa was obtained. When compared to the as-extruded alloy with yield strength of ∼171 MPa, the exceptional improvement in yield strength (∼114 MPa) for the Mg–Zn–Ca alloy wire is mainly attributed to the formation of nanoparticles. Moreover, the Mg wire also exhibited a good ductility of ∼11.8%. The results indicate that extreme plastic deformation can enable a refined microstructure to enhance the mechanical properties of Mg–Zn–Ca alloys.

A Computational Geometric Parameter Optimization of the Thermomechanical Deicing Concept

Ice formation on aerodynamic surfaces is a safety-related issue in aviation. Thermal, mechanical, or hybrid systems are used to prevent or eliminate ice formation. To increase energy efficiency, new methods are being researched and tested, using new materials. This article aims to investigate in detail the geometrical parameters of a novel thermomechanical deicing concept based on the shape memory effect. The thermomechanical behavior of a shape memory alloy wire embedded in an elastomer can be described, using the transformation expansion coefficient. The approach includes the nonlinear phase transformation and the linear expansion of the alloy. Simulation results using the above approach are compared with experimental results. In addition, a parameter study of the geometric quantities is presented, where the individual effects of these quantities are investigated assuming that there is a block-like ice layer on the surface. The results for the behavior of the SMA show promising results in terms of describing the thermomechanical behavior of the wire. However, deviations are still observed in the thermal behavior of the embedding matrix.

Quasi in-situ analysis of compressive creep behaviors and microstructure evolutions in Al–Zr alloys with Sc and Er additions

Al–Zr series alloy wires are not in a state of constant temperature and stress during service, thus the compressive stress and aging effects on the creep response in a changing state should be clarified. In this study, the quasi in-situ compressive creep behaviors and microstructure evolutions of Al–Zr alloys with Sc and Er additions have been studied. It is found that CCA curves of Al–Zr alloy were severely deformed at 120 °C for 40 h/90 MPa, for Al–Zr–Er alloy, the CCA curves sharply increased at 150 °C for 40 h/90 MPa, and that of Al–Zr-Sc alloy always kept stable at different stages. Moreover, different creep mechanisms were found in these alloys. After different CCA stages, the fibrous grains are always existing in the Al–Zr-Sc alloy, while equiaxed grains appear in the Al–Zr and Al–Zr–Er alloys, indicating the better compressive creep resistance with Sc additions. Discontinuous dynamic recrystallization (DDRX) is the dominant nucleation mechanism in the three alloys, and secondary dynamic recrystallization (SDRX) is the subordinate nucleation mechanism for the Al–Zr and Al–Zr–Er alloys. Additionally, Sc rich precipitation makes the stacking energy and lattice strain field obviously fluctuate and promotes the effective diffusion and storage of dislocations with Lomer–Cottrell locks, therefore, the compressive creep resistance of the material is improved.

Shear behaviour of beams strengthened using different Ni-Ti-Nb shape memory alloy wire configurations and design proposal based on the compression chord Capacity model (CCCM)

Shear strengthening of existing structures is often required in cases where shear strength is deficient because shear failures in RC members are associated with brittle collapse. In previous papers, the authors presented an innovative system for active strengthening shear critical-reinforced concrete (RC) beams using shape memory alloys (SMA) to take advantage of the shape memory effect. The authors also presented an approach to design this type of reinforcement based on the Compression Chord Capacity Model (CCCM). This model considers several shear transfer actions, including increased shear strength of the concrete compressed chord due to its confinement.This article presents an experimental study of RC beams with new types of SMA strengthening systems that also improve the shear behaviour of beams.The new types of tested shear strengthening systems are U-shaped external wires to facilitate the construction process by reducing initial imperfections; spiral active SMA wire implanted into a groove in the lower RC specimen part to see if it improves the dowel action effect; spiral active SMA wire only confining the compressed chord to check whether the CCCM predictions in this regard are adequate.

Near-Net Forging of Titanium and Titanium Alloys by the Plasma Carburized SKD11 Dies

The carbon supersaturated SKD11 punch and core-die were prepared by the plasma carburizing at 673 K for 14.4 ks. The upsetting experiment was performed by using this punch to describe the plastic flow of pure titanium and β-titanium works in higher reduction of thickness than 50%. The measured load – stroke relationship was utilized to describe the frictional behavior on the contact interface of punch to work materials and their work hardening process. The contact interface of carbon supersaturated punch to work was analyzed to investigate the formation of isolated carbon tribofilms from punch material and to describe the in situ solid lubrication on the contact interface. The micro-hardness mapping technique was also utilized to investigate how to suppress the work-hardening behavior by this in-situ solid lubrication. Free near-net forging experiments were performed to shape the circular β-titanium alloy wires to triangular bars.

Thin Wire Casting Using Twin Wheel Caster Equipped with Horizontal Wheels

solidification, process shortening and energy saving. A twin-wheel caster equipped with two additional horizontal wheels was proposed to cast thin aluminum alloy wire at higher speed. In the proposed twin-wheel caster, a groove was machined on the lower wheel. Two small horizontal wheels were positioned between the molten-metal-pouring launder and the upper wheel to assist the solidification of poured molten metal and to prevent burr formation. The alignment of the horizontal wheel sensitively affected the occurrence of wire defects. An Al-1.2%Fe wire with a cross section of 6.2 mm2 was cast at 15 m/min. Thinner wires without burring could be cast at a speed higher than that of the twin-wheel caster without the horizontal wheels. The surface condition of the as-cast wire cast by the twin-wheel caster equipped with horizontal wheels was worse than that of the casting using the twin-wheel caster without horizontal wheels.

MBFA algorithm based optimization of tungsten carbide alloy wire cut machining process

MBFA algorithm based optimization of tungsten carbide alloy wire cut machining process

Estimation of heat transfer model parameters by using recursive least square (RLS) method for a shape memory alloy wire

The thermal model of shape memory alloy (SMA) wires is improved by identifying the convectional heat transfer model (htm) parameters. Recursive Least Square (RLS) Method is used to estimate heat transfer coefficient, specific heat and latent heat coefficient. The parameters are estimated altogether with the surface area, volume and density of the wire. Also, after measuring the resistance by using multimeter, the value of each parameter was separately determined. Heat transfer coefficient is ambient dependent and dominant in the heat transfer model. The estimation of heat transfer coefficient is important and this is shown in this study. The proposed method builds an improved heat transfer model for SMA wire by using a single set of experimental data. Performance of the estimation with RLS is validated by using the measured data. It is shown that heat convection coefficient can be estimated with high accuracy. Thus, it is revealed that addition of the latent heat term during phase transformation into the model resulted in a more accurate model. The accuracy of the model can be enhanced by 28% by the addition of latent heat term.

The Post-Buckling Analysis of Porous Sandwich Cylindrical Shells with Shape Memory Alloy Wires Reinforced Layers Under Mechanical Loads

The main purpose of this paper is to analyze the nonlinear post-buckling behavior of three-layer porous sandwich cylindrical shells with shape memory alloy (SMA) wires reinforced outer layers under the mechanical loads. Considering the large deformations, the governing differential equations were extracted and then, using the Ritz energy method and considering the Airy function, the analytical expression for the critical stress of the system was extracted. Three types of porosity distributions were considered in the shell core and the mechanical properties of SMA-reinforced layers were determined using the law of mixtures. After validating the results, the effect of various parameters such as porosity distribution, volume fraction of SMA wires and geometric characteristics on nonlinear buckling loads and post-buckling behavior of these structures has been investigated. According to the results, it can be seen that the difference in critical buckling stress for three different porosity distribution types is significant, which reveals the need to determine the optimal porosity distribution for composite shells reinforced with SMA wires. The results show that the SMA wires increase the equivalent stiffness of the structure and their presence has a significant effect on improving the critical axial stress of the shells. According to the results, for the use of 1% volume fraction of SMA wires, the axial stress of sandwich shells can be increased up to about 51%. Therefore, the use of SMA wires is a good method to increase the load-bearing capacity of this type of structures.

Vibration control and trajectory tracking for nonlinear aeroelastic system based on adaptive iterative learning control

Vibration control and trajectory tracking for nonlinear aeroelastic system of 2D airfoil of wind turbine subjected to flap-wise vibration and independent pitch motion, are investigated based on hydraulic pitch control and adaptive iterative learning (AIL) control. The aeroelastic system is simplified by an external slubber, the host material of which is a composite material with shape memory alloy (SMA) wires embedded in. The independent pitch motion is driven by two-way-rack cylinder and hydraulic servo valve. The control of divergent unstable motions is implemented by tracking the vibrations of the preset displacements. The control law of AIL algorithm combines iterative algorithm and proportional-derivative (PD) control. The control parameters of PD controller are adjusted by proportional-derivative control based on single neuron (PDC/SN) algorithm. Based on the convergence analysis of the iterative algorithm, the tracking results (including position tracking and speed tracking) of the iterative process are shown, and the convergence of the absolute values of the relative errors during tracking is verified. The experiment based on process control and a refined OPC Technology verifies the feasibility of the engineering application of the proposed algorithm in nonlinear aeroelasticity. The consistency between the real-time dynamic tracking process shown on the experimental panel and the theoretical tracking process illustrated by simulation verifies the effectiveness of the control algorithm for engineering application. The research implication for the design of current turbine manufacturers is that it provides a design idea of blade buffer based on smart materials, and an implementation idea for the engineering application of adaptive AIL algorithm.

Preparation of functional coating on magnesium alloy with hydrophilic polymers and bioactive peptides for improved corrosion resistance and biocompatibility

• A multifunctional coating was constructed on ZE21B alloy for biodegradable vascular stents. • MgF 2 layer and hydrophilic polymers in the functional coating could effectively protect ZE21B alloy from overfast degradation. • Anticoagulant ACH 11 peptides and ECs-selective REDV peptides in the functional coating could dramatically enhance the hemocompatibility and pro-endothelialization capacity of ZE21B alloy. • The functional coating systematically improved the corrosion resistance and biocompatibility of ZE21B alloy in vitro and in vivo . Biodegradable magnesium alloy stents (MAS) have great potential in the treatment of cardiovascular diseases. However, too fast degradation and the poor biocompatibility are still two key problems for the clinical utility of MAS. In the present work, a functional coating composed of hydrophilic polymers and bioactive peptides was constructed on magnesium alloy to improve its corrosion resistance and biocompatibility in vitro and in vivo . Mg-Zn-Y-Nd (ZE21B) alloy modified with the functional coating exhibited moderate surface hydrophilicity and enhanced corrosion resistance. The favourable hemocompatibility of ZE21B alloy with the functional coating was confirmed by the in vitro blood experiments. Moreover, the modified ZE21B alloy could selectively promote the adhesion, proliferation, and migration of endothelial cells (ECs), but suppress these behaviors of smooth muscle cells (SMCs). Furthermore, the modified ZE21B alloy wires could alleviate intimal hyperplasia, enhance corrosion resistance and re-endothelialization in vivo transplantation experiment. These results collectively demonstrated that the functional coating improved the corrosion resistance and biocompatibility of ZE21B alloy. This functional coating provides new insight into the design and development of novel biodegradable stents for biomedical engineering.

Microstructure and properties of cold-drawn Cu and Cu-Fe alloy wires

Copper and Cu-Fe alloy wires were cold drawn at room temperature, and the microstructure and properties were characterized and analyzed. The results show that, at the same drawing strain, the strength and ductility of Cu-Fe wires are higher than those of copper wires. At a drawing strain of 4, the tensile elongation of Cu-Fe alloy wires is about 5%, much higher than 2% for pure copper wires. For Cu-Fe wires, with increasing drawing strain, the Fe phase is elongated along the drawing direction and forms a fiber structure with a <110> texture. In addition to the <111> and <100> fiber textures in the copper wire, a high-intensity of texture with a <112> orientation forms in Cu-Fe alloy wires. The ductility of the Cu-Fe alloy wires is greatly preserved due to dynamic recrystallization. Moreover, with the additional refining effect of nano-copper fibers in the Fe phase, the strength of the material is greatly improved.

Microstructural evolution of AA7050 alloy wires during tandem hot rolling (THR) and cold-drawing process

A novel processing route, the combination of two-step tandem hot rolling (THR) and cold drawing, was recently developed to produce AA7050 wire products. The evolution of second phases, grain microstructures, and micropores during the whole process was thoroughly studied. The specific effect of second phases on continuous dynamic recrystallization (CDRX) and grain refinement was also systematically investigated, which was of great significance to optimize the processing parameters and further improve the mechanical properties of AA7050 wires. Firstly, both the strip-shaped microscale and tens-of-nanometer MgZn2 primary phases are observed in the as-received extruded sample. The strip-shaped primary MgZn2 phases break and gradually spheroidize throughout the THR process, with some of them redissolving into the Al matrix. However, the nanoscale MgZn2 phases are obviously coarsened and equiaxed only during the second-step THR process. After the first-step THR process, the coarse columnar grains are refined to thin fibrous grains due to the occurrence of CDRX, and a high number of dislocations are stored in the recrystallized structures. During the second-step THR process, only dynamic recovery occurs and no obvious CDRX is observable. This may be due to the coarsening of nanoscale MgZn2 phases, which reduces the driving force of recrystallization by attracting and combining with other solute atoms. The following two-step cold-drawing process has little influence on the primary MgZn2 phases, but promotes the formation of refined and equiaxed grains due to the recurrence of CDRX. This may be because the larger coarsened MgZn2 phases accelerate the recrystallization nucleation and increase the driving force of recrystallization.

Experiment Validation Protocol for Flux Wire Measurements in the Advanced Test Reactor

One of the Advanced Test Reactor’s (ATR’s) functions is to irradiate and qualify nuclear fuels and materials. Due to the large number of experiment or test positions, the cost, and the limited number of vessel penetrations for instrumentation, in-core instrumentation for most experiments is not feasible. In such instances, modeling of experiment conditions using high-fidelity neutron transport codes can quantify such conditions as fission power density and fissile material burnup during irradiation. Validation of fissile material burnup can only be performed during post-irradiation examination, which typically occurs months—or even years—following irradiation. In most experiments, fission power density and fissile material burnup are directly proportional to the thermal neutron flux in the ATR. Additionally, fast neutrons are born from fission in the ATR core, affording a validation of power distribution within the reactor’s experiment locations. During each irradiation cycle, flux wires installed throughout the ATR can be used to validate computational models and determine an adjusted neutron flux for many of the experiment positions. The flux wires are installed as requested by the experiment sponsors in several of the ATR flux traps and consist of cobalt-aluminum alloy and nickel wires. Both kinds of wire enable measurements of the thermal and fast neutron flux in each experiment position. This paper presents the protocol for validating computational models for experiments using flux wires installed in the experiment positions, as well as the results for flux wires placed in the ATR safety rod guide tubes. The best estimate is typically referred to as the adjusted neutron flux. The calculated unadjusted neutron flux is referred to as the a priori neutron flux. The methods presented here provide the adjusted neutron flux, given both the measured and a prior fluxes. The adjusted flux is compared to the a priori flux to provide a bias in the calculated results and the adjusted results. Two model types are evaluated; an eigenvalue case and fixed-source case. Both conditions demonstrate relatively good agreement. The uncertainty for the adjusted flux ranges from 5% to 6% for all three energy ranges. For the eigenvalue case, the bias between the a priori and the adjusted neutron flux is within the statistical uncertainty in all but two wire pairs. For the fixed-source model, four wire pairs are outside of the uncertainty of the adjusted flux. The bias between the a priori and adjusted fast neutron flux is outside of the statistical range for four wires in the eigenvalue case and nine wires in the fixed-source model. As the differences are not contained to one flux trap, it can be assumed that the biases in the calculated models are attributed to localized effects in modeling. An additional evaluation was performed for the ATF-1 experiment in the ATR “I” positions. The differences between the adjusted and a priori are more pronounced in two of the test positions, indicating that additional model evaluation is needed, in particular in the region near the boundary of the ATR model. It is also noted that the eigenvalue model provides slightly better results in the flux trap positions. The fixed-source model is more computationally efficient though produces less accurate results; the differences in some cases are negligible. The work documented in this paper provides a methodology that extends the validation protocol established at the ATR for flux measurements to validate computational models with limited measurement capability during a cycle.