Processing of nitinol medical devices has evolved over the years as manufacturers have identified methods of reducing surface defects such as inclusions. One recent method proposes to soak nitinol medical devices in a 6% sodium hypochlorite (NaClO) solution as a means of identifying surface inclusions. Devices with surface inclusions could in theory then be removed from production because inclusions would interact with NaClO to form a visible black material on the nitinol surface. To understand the effects of an NaClO soak on performance, we compared as-received and NaClO-soaked nitinol wires with two different surface finishes (black oxide and electropolished). Pitting corrosion susceptibility was equivalent between the as-received and NaClO-soaked groups for both surface finishes. Nickel ion release increased in the NaClO-soaked group for black oxide nitinol, but was equivalent for electropolished nitinol. Fatigue testing revealed a lower fatigue life for NaClO-soaked black oxide nitinol at all alternating strains. With the exception of 0.83% alternating strain, NaClO-soaked and as-received electropolished nitinol had similar average fatigue life, but the NaClO-soaked group showed higher variability. NaClO-soaked electropolished nitinol had specimens with the lowest number of cycles to fracture for all alternating strains tested with the exception of the highest alternating strain 1.2%. The NaClO treatment identified only one specimen with surface inclusions and caused readily identifiable surface damage to the black oxide nitinol. Damage from the NaClO soak to electropolished nitinol surface also appears to have occurred and is likely the cause of the increased variability of the fatigue results. Overall, the NaClO soak appears to not lead to an improvement in nitinol performance and seems to be damaging to the nitinol surface in ways that may not be detectable with a simple visual inspection for black material on the nitinol surface.

Microbiologically influenced corrosion (MIC) of carbon steel infrastructure is an emerging environmental and cost issue for the ethanol fuel industry, yet its examination lacks rigorous quantification of microbiological parameters that could reveal effective intervention strategies. To quantitatively characterize the effect of cell concentration on MIC of carbon steel, numbers of bacteria exposed to test coupons were systematically controlled to span four orders of magnitude throughout a seven-day test. The bacterium studied, , has been found in ethanol fuel environments, and can convert ethanol to the corrosive species acetic acid. biofilms formed during the test were qualitatively evaluated with fluorescence microscopy, and steel surfaces were characterized by scanning electron microscopy. During exposure, biofilms developed more quickly, and test reactor pH decreased at a faster rate, when cell exposure was higher. Resulting corrosion rates, however, were inversely proportional to cell exposure, indicating that biofilms are able to protect carbon steel surfaces from corrosion. This is a novel demonstration of corrosion inhibition by an acid-producing bacterium that occurs naturally in corrosive environments. Mitigation techniques for MIC that harness the power of microbial communities have the potential to be scalable, inexpensive, and green solutions to industrial problems.

Six different organizations participated in this interlaboratory study to quantify the variability in the tensile properties of Inconel 625 specimens manufactured using laser-powder-bed-fusion additive manufacturing machines. The tensile specimens were heat treated and tensile tests conducted until failure. The properties measured were yield strength, ultimate tensile strength, elastic modulus, and elongation. Statistical analysis revealed that between-participant variability for yield strength, ultimate tensile strength, and elastic modulus values were significantly higher (up to 4 times) than typical within-participant variations. Only between-participant and within-participant variability were both similar for elongation. A scanning electron microscope was used to examine one tensile specimen for fractography. The fracture surface does not have many secondary cracks or other features that would reduce the mechanical properties. In fact, the features largely consist of microvoid coalescence and are entirely consistent with ductile failure.

Given its relatively simple setup and ability to produce results quickly, rotary bend fatigue testing is becoming commonplace in the medical device industry and is the subject of a new standard test method ASTM E2948-14. Although some research has been conducted to determine if results differ for different rotary bend fatigue test setups or test speeds, these parameters have not been extensively studied together. In this work, we investigate the effects of these two parameters on the fatigue life of three commonly used medical device alloys (ASTM F2063 nitinol, ASTM F138 stainless steel, and ASTM F1058 cobalt chromium). Results with three different rotary bend fatigue test setups revealed no difference in fatigue life among those setups. Increasing test speed, however, between 100 and 35,000 RPM led to an increased fatigue life for all three alloys studied (average number of cycles to fracture increased between 2.0 and 5.1 times between slowest and fastest test speed). Supplemental uniaxial tension tests of stainless steel wire at varying strain rates showed a strain rate dependence in the mechanical response which could in part explain the increased fatigue life at faster test speeds. How exactly strain rate dependence might affect the fatigue properties of different alloys at different alternating strain values requires further study. Given the difference in loading rates between benchtop fatigue tests and in vivo deformations, the potential for strain rate dependence should be considered when designing durability tests for medical devices and in extrapolating results of those tests to in vivo performance.

Small punch (SP) testing is a methodology that uses tiny disks (generally 8 mm in diameter and 0.5 mm thick) to estimate mechanical properties of metallic materials, such as tensile properties, fracture toughness, and ductile-to-brittle transition temperature. Empirical correlations are typically used to infer conventional mechanical properties from characteristic forces and displacements obtained from the test record. The majority of the available literature relates to SP testing of steels, while relatively little is available for other metallic materials. At NIST in Boulder, Colorado, we conducted SP tests on additively manufactured (AM) Ti-6Al-4V with different processing parameters and heat treatment conditions. Force/punch displacement curves appeared different than those typically reported for conventionally manufactured steels, and correlations with tensile and fracture parameters were generally weaker than those published for steel samples. It appears that the application of the SP technique (characterized by a biaxial loading mode) to materials with high anisotropy such as AM materials may be somewhat problematic and therefore of limited applicability.

3D printing is a popular nonconventional manufacturing technique used to print 3D objects by using conventional and nonconventional materials. The application and uses of 3D printing are rapidly increasing in each dimension of the engineering and medical sectors. This article overviews the multipurpose applications of 3D printing based on current research. In the beginning, various popular methods including fused deposition method, stereolithography 3D printing method, powder bed fusion method, digital light processing method, and metal transfer dynamic method used in 3D printing are discussed. Popular materials utilized randomly in printing techniques such as hydrogel, ABS, steel, silver, and epoxy are overviewed. Engineering applications under the current development of the printing technique which include electrode, 4D printing technique, twisting object, photosensitive polymer, and engines are focused. Printing of medical equipment including artificial tissues, scaffolds, bioprinted model, prostheses, surgical instruments, COVID-19, skull, and heart is of major focus. Characterization techniques of the printed 3D products are mentioned. In addition, potential challenges and future prospects are evaluated based on the current scenario. This review article will work as a masterpiece for the researchers interested to work in this field.

This paper reports the effect of post-heat treatment (PHT) on laser-deposited WC + Ni-based composite thin walls. The PHT at 700, 800, and 900 °C was conducted to modify the microstructure and mechanical properties of the composite. The results showed that the as-deposited composite had a weak flexural strength and plasticity due to the brittle nature of the eutectic phase. The eutectic phase consisted of MC, MC, and a small amount of the γ phase. However, after PHT at a certain temperature (e.g., 700 or 800 °C), the eutectic phase gradually disappeared, and carbides, such as MC and MC, tended to be distributed uniformly in the γ matrix, which improved the flexural strength of the composite. Nevertheless, after the PHT at 900 °C, the flexural strength of the composite displayed a downward trend, which was mainly because of the severe softening of the γ phase. In addition, the plasticity of this composite continuously improved as the eutectic phase disappeared and the γ phase softened. Based on the above results, we proposed a PHT at 800 °C for 1 h as an optimal process for this WC + Ni-based composite.

Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process.

Nanocomposite Sn-Bi solders received noticeable attention for flexible electronics due to their improved mechanical properties. The main limitation is the dispersion of nanoparticles in the solder alloy. Accordingly, in this work, varying additions of ZnO nanoparticles were successfully dispersed into Sn57Bi solder via the liquid-state ultrasonic treatment. Nanocomposite solders were prepared using the melting and casting route. The solder alloys were then characterized for microstructure, spreading and mechanical properties. With increasing ZnO addition, the microstructure revealed significant refinement of Bi- and Sn-rich phases. Consequently, the eutectic lamellar spacing also decreases. The spreading improved up to 0.1 wt.% ZnO addition. For higher additions, nanocomposite solders experienced deterioration in spreading characteristics. The tensile strength of the solder increases with an increase in the amount of ZnO nanoparticles. High ductility is achieved for nanocomposite solder containing 0.05 wt.% ZnO. An attempt was made, to explain the effect of increasing ZnO nanoparticle addition on microstructural, spreading, and mechanical properties of Sn57Bi solder.

The size of copper precipitates is the main factor affecting the antibacterial performance of antibacterial stainless steel. To study the mechanism of copper precipitate growth in ferritic stainless steel, the shape coefficient and average specific interfacial energy of copper precipitate were calculated. The growth process of copper precipitate was observed by atomic probe tomography and transmission electron microscope. The results show that the shape coefficient of copper precipitate was 3.053, and the average specific interfacial energy was . The increase in the aging time resulted in an increase in the size of copper precipitates and a decrease in the number density. In addition, with the increase in the aspect ratio, the shape of the precipitated phase changed from an initial spherical shape to ellipsoid shape and finally to a rod shape. The increase in the annealing time enhanced the antibacterial activity of the tested steel until almost 100% of the bacteria were killed. Thus, the antibacterial performance is closely related to the size and total surface area per unit area of the precipitate.

The viscosity and electrical conductivity as structure-sensitive transport properties of the liquid metals and alloys are important for modeling of the melting and solidification processes. The viscosity and electrical conductivity data provide additional information about the influence of impurities on the structure and physicochemical properties of the liquid metal matrix, which is useful for understanding of structural transformations in the liquid state. In the present work, an impact of minor Co admixtures on the viscosity and electrical conductivity of liquid Sn-3.8Ag-0.7Cu alloy was studied. An increase in viscosity with minor Co admixtures is in a satisfactory agreement with model predicted data obtained from thermodynamic approaches and suggests a significant impact of interatomic interactions. Cobalt admixtures significantly affect the electrical conductivity, which gradually decreases with increasing the amount of Co. Additionally, the sample microstructure has been examined using x-ray diffraction and scanning electron microscopy analyses. The formation of Sn-based Co-Sn intermetallic compounds was detected in the alloys with more than 1 wt.% Co.

This work deals with the development of cyanide-free copper-silver electroplated coatings on AISI-1075 steel and its corrosion behavior under a 5% NaClO solution (commercial household bleach). A cyanide-free bath based on sodium thiosulfate was employed to obtain the silver coatings using current densities from 0.2 to 5.0 mA/cm and different concentrations of EDTA (additive). The evolution of the open circuit potential with time showed that silver is anodic with respect to copper, so there were no intense attacks in the silver pores. Adhesion measurements were made on both coatings by the tape test. The behavior against corrosion was evaluated by polarization resistance (Rp) in samples with the best coating adhesion. The best results were obtained with a silver coating of about 20 μm in thickness deposited on copper coating previously polished with colloidal silica. The best performance was attributed to the formation of AgCl as demonstrated by x-ray diffraction and scanning electron microscopy.

Additive manufacturing (AM) has attracted much attention due to its capability in building parts with complex geometries. Unfortunately, AM metals suffer from three major drawbacks, including high porosity, poor surface finish, and tensile residual stresses, all of which will significantly compromise the fatigue performance. These drawbacks present a major obstacle to the application of AM metals in industries that produce fatigue-sensitive components. Many post-processing methods, including heat treatment, hot isotropic pressing, laser shock peening, ultrasonic nanocrystal surface modification, advanced finishing and machining, and laser polishing, have been used to treat AM metals to decrease their porosity, improve the surface finish, and eliminate tensile residual stresses. As a result, significant improvement in fatigue performance has been observed. In this paper, the state of the art in utilizing post-processing techniques to treat AM metals and the effects of these treatments on the porosity, surface finish, and residual stresses of metal components and their resultant fatigue performance are reviewed.

Thermal joining can lead to high thermal stresses, undesired structural changes, and the associated loss of properties. In the turbine industry, monocrystalline materials are often used to take advantage of their high creep resistance and heat resistance. For process-related reasons, components are mechanically machined, and the contours usually have slightly work-hardened areas due to the mechanical processing. Downstream thermal processes at temperatures above 1100 °C can lead to recrystallization (x) at these areas, so that the properties are negatively affected. Usually, the joining temperatures for high-temperature brazing are in the range of 1200 °C, both in new installations and in the case of repairs. It is therefore desirable to reduce the joining temperature without changing the choice of filler material, which can lead to susceptibility to corrosion and oxidation. According to investigations of the last years, nanojoining with nanoparticles offers great potential. The joining temperature can be lowered due to the "surface effect." A considerable reduction in the size of the particles leads to a significant increase in surface atoms and thus in the specific surface area. The connection of the materials occurs predominantly due to sintering processes. After the joining process, the properties of a bulk material are available again. Mechanical properties comparable to those of brazing have already been achieved with silver nanoparticles (Hausner in WWA 56, 2015). Up to now, publications on the topic of nanojoining have largely referred to silver nanoparticles/silver sintering. Due to the temperature application range, silver filler material cannot be used in gas turbines. Therefore, the first results of nickel nanoparticles for joining of the nickel-based superalloy PWA 1483 using induction heating are described in this paper. During joining, the parameters brazing temperature, holding time and the surface treatment of the base materials were varied. It becomes clear that the microstructure of the joint is dependent on temperature and holding time. Moreover, if the temperature is too low and holding time too short, only insufficiently sintering occurs, which leads to sample failure during the metallographic preparation. On the other hand, samples with a tensile shear strength of up to 165 MPa can be achieved with convenient joining conditions.

This study aims to investigate the effects of annealing, quenching, and tempering (Q&T) heat treatments on the microstructure, crystallographic orientation, and electrochemical performance of a wall shaped 420 martensitic stainless steel part fabricated by wire arc additive manufacturing technology. The formation of a martensitic matrix with delta ferrite in the as-printed sample, islands of spherical chromium carbides embedded in a ferritic matrix in annealed sample, and intergranular chromium-rich carbides along the primary austenite grain boundaries in addition to intra-lath Fe-rich carbides in the quenching and tempering heat treated sample were detected. To characterize the corrosion performance of the fabricated samples, open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy tests were performed on all samples in aerated 3.5 wt.% NaCl electrolyte at room temperature. The corrosion morphology of the as-printed sample was characterized by localized corrosion attacks adjacent to the delta ferrite phase, while severe pitting occurred in the annealed sample due to the high susceptibility of ferritic matrix-carbide interface to pitting. In contrast to the as-printed and annealed sample, the electrochemical performance of the quenched and subsequently tempered samples was found to be significantly improved, ascribed to elimination of the chromium depleted regions adjacent to the delta ferrite phase, and enhanced protectiveness of the passive film on the alloy's surface.

Aim of this work is to improve the bond between a strain sensor and a device on which the strain shall be determined. As strain sensor, a CMOS-integrated chip featuring piezoresistive sensor elements was used which is capable of wireless energy and data transmission. The sensor chip was mounted on a standardized tensile test specimen of stainless steel by a bonding process using reactive multilayer systems (RMS). RMS provide a well-defined amount of heat within a very short reaction time of a few milliseconds and are placed in-between two bonding partners. RMS were combined with layers of solder which melt during the bonding process. Epoxy adhesive films were used as a reference bonding process. Under mechanical tensile loading, the sensor bonded with RMS shows a linear strain sensitivity in the whole range of tested forces whereas the adhesive-bonded sensor has slightly nonlinear behavior for low forces. Compared to the adhesive-bonded chips, the sensitivity of the reactively bonded chips is increased by a factor of about 2.5. This indicates a stronger mechanical coupling by reactive bonding as compared to adhesive bonding.

The paper reports high temperature resistance of ferritic steels in fireside corrosion regime in terms of temperature and deposits aggressiveness. Four candidate power plant steels: 15Mo3, T22, T23 and T91 were exposed under simulated air-fired combustion environment for 1000 h. The tests were conducted at 600, 650 and 700 °C according to deposit-recoat test method. Post-exposed samples were examined via dimensional metrology (the main route to quantify metal loss), and mass change data were recorded to perform the study of kinetic behavior at elevated temperatures. Microstructural investigations using ESEM-EDX were performed in order to investigate corrosion degradation and thickness of the scales. The ranking of the steels from most to the least damage was 15Mo3 > T22 > T23 > T91 in all three temperatures. The highest rate of corrosion in all temperatures occurred under the screening deposit.

In this work, we demonstrate on a new interconnection technology which can be used for bonding Flip-Chips with 5-µm-Bumps and fine pitches <5 µm. In this technology, the bumps on both joint partners are coated with metallic nanowires (in most cases copper, in rare cases gold), through an in situ electrochemical deposition process, the so-called NanoWiring process. The diameter of the wires can be adjusted between 30 and 4000 nm, and their length is ranged from 4 to 50 µm. The process is scaled up for 12 inch wafers. The bonding process can be performed directly at wafer level or also at Flip-Chip level. The nanowires overcome the dicing step. The diced chips can be bonded by adjusting and pressing the NanoWired bumps together at room temperature, using the standard bonding devices. The required bonding forces range from 5 to 50 MPa for flip chips, LEDs and sensors. The bonding with nanowires, the so-called KlettWelding, can be explained by diffusion of the nanowires in each other under compression and weaving of the wires as well. The measured shear strength of these connections yields 15-24 MPa. The very large achieved Surface/Volume quotient of NanoWired surface causes this strength. For a better performance, a prior copper oxide reducing step for the copper NanoWires is needed. This can be done by using standard processes like forming gas plasma or formic acid vapor. By heating during the pressing process up to 230 °C, the shear strength increases to 60 MPa. The nanowired interconnections have an electrical conduction in the range of bulk metal, because of their pure metallic nature. Beside microelectronic applications, the bonding of larger metallic plates like aluminium, copper, steel and also flexible polymers, glass, silicon and ceramics are also enabled.

Reactive joining with Ni/Al nanocomposites is an innovative technology that provides an alternative to more common bonding techniques. This work focuses on a class of energetic material, produced by high energy ball milling and cold rolling. The initial microstructure is more complex than that of reactive multilayer nanofoils, produced by magnetron sputtering, in which the bilayer thickness is constant. Typical samples are composed of reactive nanocomposite particles that are numerically modelized by randomly distributed layered grains. The self-propagating reaction was studied by means of molecular dynamics simulations. We determined the front characteristics and investigated the elemental mechanics that trigger propagation. Both dissolution of Ni in amorphous Al and sustained crystallization of the -NiAl intermetallic compound were found to contribute to the heat delivered during the process.

To improve the antibacterial properties of 304L austenitic stainless steel, copper is often added as an antibacterial agent, but the forming performance of the resulting material is poor, impacting its actual production and use. Therefore, this study investigated the influence of copper addition on the formability of 304L austenitic stainless steel with drawing, cupping and conical cup forming tests. Mechanical properties were determined with tensile and hardness tests. The microstructure and phase transformation were further characterized by metallographic microscopy, scanning electron microscopy and x-ray diffraction analysis. It was found that the addition of copper impaired the mechanical properties of 304L austenitic stainless steel, increased the stacking fault energy of the material and inhibited the occurrence of strain-induced martensite transformation, leading to a decrease in the formability of 304L austenitic stainless steel.