In fundamental physics, sensors operating below liquid helium temperatures are highly vulnerable to vibrations, which can affect the sensitivity, for example, of high-performance particle detectors. Pulse-tube refrigerators, while generating vibrations lower than those of conventional systems, may still introduce several disturbances. Hence, flexible thermal connections are a commonly used mechanical solution to mitigate these undesirable effects. Among the materials that can be used, ultra-high-purity aluminum (UHP-Al) has attracted the attention for low-amplitude-vibration cryogenic applications, including gravitational wave interferometry, quantum information systems, precision space instrumentation, and cryogenic resonators. Thus, the aim of the paper is the characterization of the mechanical and microstructure properties of three UHP-Als (i.e., 5N-99.999 wt%, 5N5-99.9995 wt% and 6N-99.9999 wt%) intended for the production of thermal flexible connections with low stiffness, specifically designed to reduce vibration transmission in cryogenic environments. Mechanical properties were evaluated through standard tensile tests from room (+25 °C) to low temperature (i.e., -150 °C), providing insights into yield strength, ultimate tensile strength, elongation and elastic modulus. In addition, the dynamic elastic modulus of material loads, at cryogenic conditions (i.e., about -180 °C), was determined by measuring the natural resonance frequency, thereby assessing the material's response to vibrational. Moreover, an extensive microstructural analysis was conducted using electron backscatter diffraction and x-ray diffraction. The correlation between the observed microstructure and the elastic properties was systematically examined. The results underscore the pivotal role of microstructural characteristics in dictating the elastic behavior of UHP Als. Eventually, the analysis provides valuable guidelines for the materials employment inside cryogenic systems, where severe vibration control is critical to maintain high operational performance.

With a volume fraction of austenite and ferrite that is roughly equal, duplex stainless steels (DSS) have good mechanical characteristics and a high level of corrosion resistance. On the other hand, for decades, laser welding of sheets has been adopted as a profitable technology for joining many metallic materials. Obtaining a balanced microstructure and ensuring its qualities and uses is the difficulty in DSS laser welding. Generally, when DSS is welded with a technique inherently associated with high cooling rates, a mostly ferritic microstructure results. The addition of austenite stabilizing elements or heat treatments is indicated to balance the microstructure. Before butt welding two UNS S32750 DSS sheets with a pulsed Nd:YAG laser, a 50-µm-thick cobalt layer was electro-deposited onto the edge of one of them with a Watts bath procedure. The microstructural characterization of the weld beads was performed using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The volume fractions were determined using two methods: (1) Image analysis software for SEM images and (2) computerized volume fraction computation from XRD spectra. As the volume fractions of austenite increased, the results demonstrated that adding cobalt in the fusion zone effectively resolved the unwanted unbalanced microstructure that resulted from autogenous laser welding of the DSS. Residual stresses were determined for the austenitic phase and the ferrite matrix in the weld bead, the former resulting affected by tensile stresses, while the latter by compressive stresses.

Recently carbide free bainitic steels, with microstructure consisting in nanoscaled bainitic ferrite plates and high carbon-enriched austenite, have been developed. These steels have found commercial use in manufacturing engineering components, nevertheless, their high carbon concentration poses a limitation as they cannot be welded, restricting their potential applications, therefore the actual research has shifted to the investigation to medium carbon steels. In this work, Butt weld – V groove weldment have been realized with a novel medium carbon high silicon carbide-free bainitic steel by means GMAW and GTAW. Optical microscopy, scanning and transmission electron microscopy and X-ray diffraction were used to characterize the microstructures of both the fusion and heat affected zone. Dilatometry was utilized to study the phase transformations during post-welding heat treatment. Tensile and micro-hardness tests were carried out to evaluate the mechanical properties in the as-weld state after post-welding heat treatment. The analysis shows the possibility to obtain high strength weldments with high integrity and high strength (>1 GPa) coupled with reasonable ductility and the absence of cold or hot cracking phenomena.

The cladding process reduces manufacturing costs by depositing super austenitic stainless steel onto low-carbon steel. Arc welding techniques, especially gas tungsten arc welding (GTAW), are commonly used for this purpose. This study evaluates the influence of heat input on cladding performance. Macroscopic analysis showed good fusion of the weld beads to the base metal with no defects. Higher heat input resulted in a lower dilution rate due to increased reinforcement. A microstructural analysis of the heat-affected zones revealed similar characteristics, with martensite formation attributed to cooling conditions. Increased microhardness was observed at the interface between the cladding and base metal, corroborating the microstructural findings. Additionally, a significant enhancement in corrosion resistance was noted in the deposited layers. This research contributes to optimizing cladding processes, ensuring better material performance in industrial applications.

Super-duplex stainless steel (SDSS) shows high mechanical and corrosion resistance because of the balanced structure of austenite and ferrite. However, maintaining this phase ratio after welding is a challenge. The use of austenite stabilizing components is recommended to balance the microstructure. The addition of alloying elements presents a challenge because of the characteristics of Nd:YAG pulsed laser welding. An approach, which has proven to be effective, is to use metal electroplating to prepare the surfaces of the mechanical SDSS components that will be welded, therefore promoting the phase balance in the fusion zone. While the effects of metals such as nickel as an austenite stabilizer are well recognized, cobalt’s effects require more research. The present work investigated the influence of the use of cobalt addition in the joining process by preliminary electroplating on UNS S32750 SDSS Nd: YAG pulsed laser welding, specifically regarding microstructure and microhardness. Three conditions were investigated, changing the thickness of the deposited cobalt layer. The addition of cobalt modified the morphology and increased the volume fraction of austenite. An austenite volume fraction of around 48% was obtained using a 35 μm thick cobalt coating. The microhardness was affected by austenite/ferrite proportions. The microhardness dropped from about 375 HV to 345 HV as the cobalt layer’s thickness rose, being similar to that of the base metal. The effect of cobalt as an austenite stabilizer was observed, and the cobalt electroplating technique was effective to correct the phase balance on UNS S32750 laser welding.

Super duplex stainless steel has a microstructure consisting of equal proportions of austenite and ferrite. However, welding with Nd:YAG pulsed laser results in an imbalanced microstructure that compromises the steel’s properties. This paper studied the effects of preheating the base metal on pulsed Nd:YAG laser welding. Four conditions were evaluated (no preheating and heating at 100 °C, 200 °C, and 300 °C). The analysis included studying the microstructure, microhardness, and corrosion resistance. Preheating the base metals was found to be an effective method for increasing the volume fractions of austenite. The preheated samples showed an improvement in corrosion resistance compared to the untreated sample. The microhardness varied, with the ferrite amount being higher in the untreated sample.

Super-duplex stainless steel (SDSS) exhibits an austenite-ferrite dual-phase structure, which promotes many benefits upon single-phase grades, such as high mechanical strength and corrosion resistance. Welding process results in an unbalanced microstructure, with large amount of ferrite, which compromise SDSS’s properties. This paper investigates the effect of using electrolytic nickel foils as an addition metal on UNS S32750 SDSS Nd:YAG pulsed laser welding, through the evaluation of the microstructure, hardness, tensile strength, and corrosion resistance of the weld bead. Six conditions were investigated: autogenous welding and with addition of nickel, varying the thickness of nickel foil added. Microstructural analysis reveals an increase in volume fraction of austenite for the conditions with addition of nickel. Using a 30 µm thick nickel foil, approximately equal amount of austenite and ferrite was obtained in the weld bead. The higher microhardness was obtained for the autogenous welding, 400 HV and decreased with the addition of nickel. The tensile strength decreased 4% in the experimental conditions with high nickel addition. The corrosion resistances were the same for all the conditions with addition on nickel, regardless of the nickel foil thickness added, but it compared to autogenous welding the CPT’s increased approximately 14 °C.

This study consists of a failure analysis of gear wheels mounted on an agricultural machine subject to several breakages in operation. Two gears were the subject of metallographic, compositional and photographic analyzes, as well as micro hardness tests and electron microscope observations. The photographic analyzes clearly highlighted a strong wear of the tooth surfaces. Although the failure mechanism is attributable to fatigue, the classic fatigue morphology patterns on the fracture surface were not visible and this was probably due to the low number of cycles that led to the failure of the gears. The analysis of the composition and microstructure of the steel did not reveal any critical issue. In fact, sulphides were present within the material but not in such quantities as to justify the failure. In conclusion, the material of the wheels did not present anomalies, therefore the causes of the failure of the analyzed parts were to be found in an incorrect design or in their incorrect assembly.

Obtaining a balanced microstructure in the fusion zone on a super duplex stainless steel (SDSS) weld is a challenge. The present work reports the use of the Watts bath to correct the phase balance on laser-welded SDSS. Three different Watts bath times were used, and the microstructure of the weld bead was evaluated. The Watts bath was efficient to correct the undesirable unbalanced microstructure resulting from SDSS laser welding as the austenite percentage increased.

Prestrained at 5% and 15% duplex stainless steel UNS S32750 specimens have been subjected to electropulsing treatments with current density of 100 A/mm2 and 200 A/mm2 and 100 and 500 pulses for each current density value. Corrosion tests, X-ray diffraction, microhardness and residual stresses were collected before and after the electropulsing treatments. Tensile tests were performed after the electropulsing treatments in order to compare the mechanical response to reference tensile tests performed before pulsing treatments. Increase in fracture strain was observed after pulsing treatment in comparison to the reference tensile tests. A decrease in microhardness was also observed after electropulsing treatments for both degrees of prestrain. Electropulsing treatment almost eliminates the work-hardened state in the 5% prestrained specimens while partially recovered the 15% prestrained material increasing both uniform and fracture strain. Bulk temperature of the samples remained the same for all treatments duration. The effect are to be addressed to a combined effect of increase in atomic flux due to the electrical current and local joule heating in correspondence of crystal defects. Electropulsing treatment applied to metallic alloys is a promising technique to reduce the work hardening state without the need of annealing treatments in a dedicated furnace.

Duplex and Super Duplex Stainless Steels are very prone to secondary phases formation related to ferrite decomposition at high temperatures. In the present paper the results on secondary phase precipitation in a 2510 Duplex Stainless Steel, heat-treated in the temperature range 850–1050 °C for 3–30 min are presented. The precipitation starts at grain boundaries with a consistent ferrite transformation for very short times. The noses of the Time–Temperature–Precipitation (TTP) curves are at 1000 °C for σ-phase and at 900 °C for χ-phase, respectively. The precipitation sequence involves a partial transformation of χ into σ, as previously evidenced in 2205 and 2507 grades. Furthermore, the experimental data were compared to the results of Thermo-Calc calculations. Understanding and ability to predict phase stability in 2510 duplex stainless steel is a key factor to design optimal welding processes that avoid any secondary phase precipitation in the weld bead as well as in the heat-affected zone.

During the production of forged metal components, the sequence of heat treatments that are carried out, as well as hot working, remarkably influences mechanical properties of the product, in particular impact toughness. It is possible to tailor impact toughness by varying tempering temperature and soaking time after hardening treatment, widening the application range of structural steels. In this work, we consider the effects of a second tempering treatment on the microstructural properties and impact toughness of a structural steel EN 10025-6 S690 (DIN StE690, W. n: 1.8931). The steel was first forged and quenched in water after austenitization at 890 °C for 4 h. After quenching different tempering treatments were performed, at 590 °C in single or multiple steps. The effect of these treatments was evaluated both in microstructural terms, by means of optical microscopy, scanning and transmission electron microscopy and X-ray diffraction, and in terms of impact toughness. The mechanical behavior was correlated with the microstructure and a remarkable increase in impact toughness was found after the second tempering treatment due to carbide shape change.

Duplex stainless steels (DSSs), a particular category of stainless steels, are employed in all kinds of industrial applications where excellent corrosion resistance and high strength are necessary. These good properties are provided by their biphasic microstructure, consisting of ferrite and austenite in almost equal volume fractions of phases. In the present work, Nd: YAG pulsed laser dissimilar welding of UNS S32750 super duplex stainless steel (SDSS) with 316L austenitic stainless steel (ASS), with different heat inputs, was investigated. The results showed that the fusion zone microstructure observed consisted of a ferrite matrix with grain boundary austenite (GBA), Widmanstätten austenite (WA) and intragranular austenite (IA), with the same proportion of ferrite and austenite phases. Changes in the heat input (between 45, 90 and 120 J/mm) did not significantly affect the ferrite/austenite phase balance and the microhardness in the fusion zone.

Il lavoro presenta i risultati di indagini svolte su campioni di Ag commercialmente puro sottoposti a deformazione plastica severa mediante tecnica ECAP e attraverso laminazione asimmetrica a freddo. E stata studiata l’evoluzione della microstruttura e delle proprieta meccaniche al variare della deformazione impartita, rispettivamente mediante tecniche SEM / TEM e attraverso misure di durezza e prove di trazione. L’argento e stato scelto come materiale rappresentativo dei metalli a struttura FCC con bassa energia dei difetti di impilamento e quindi elevata possibilita di deformazione assistita da geminati. In letteratura esistono limitate informazioni sull’evoluzione della struttura ultrafine di questi metalli nel regime di deformazione plastica severa. I dati vengono discussi considerando l’evoluzione della struttura derivante dalle specifiche tecniche di deformazione e le proprieta raggiunte.

Commercially pure silver has been subjected to severe plastic deformation (SPD) by ECAP and by asymmetric cold rolling (ASR). Microstructure evolution as a function of imparted equivalent strain (up to about 8) has been investigated mainly by SEM and TEM. Mechanical properties have also been measured by room-temperature tensile testing. Silver is here selected as a representative FCC metal with a low stacking fault energy featuring high probability of deformation by twinning. Limited information exists on its structure evolution in the ultrafine grain-size range after SPD. Due to its ductility, the silver samples could be successfully deformed by the two processing techniques up to strain values exceeding 8. The ECAP processed materials featured a submicrometer-size equiaxed grain structure with sharp grain boundaries. On the contrary, both symmetric and asymmetric rolling led to a subgrain structure with a higher dislocation density at grain interiors and less defined grain boundaries. The tensile properties achieved after the different processing routes consistently differed. In ECAP samples the strength improved at first passes and then showed a plateau for the whole range of imposed strain here considered. In asymmetrically and symmetrically rolled silver, the achieved strength almost continuously improved even at larger strains. An estimate of the work-hardening behaviour over the whole strain range of the silver samples was computed by adding the experienced strain supplied during processing to that experienced during tensile testing. It was confirmed that in the asymmetrically rolled samples, the overall work-hardening behaviour was higher with respect to ECAP samples, at least up to equivalent strains of around 8.

Pure silver has been rapidly quenched (RQ) in ribbon form by means of planar flow casting with different cooling rates, obtained with different velocities of the cooling wheel. Ingots of pure silver have been subjected to severe plastic deformation (SPD) using constrained groove pressing and equal-channel angular pressing. The grain size of RQ and SPD samples has been analysed using electron microscopy, showing that the higher the solidification rate and plastic deformation, the finer the microstructure. Preferred orientations and quenched-in defect concentration have been determined from X-ray diffraction analysis, showing a correlation between density of defects and cooling rate. Higher defect concentration was found in the samples processed via SPD. Vickers hardness numbers range from 135 for SPD, 70 for RQ and 45 for annealed samples. Differential scanning calorimetry analysis revealed multi-step coarsening of the microstructure at various temperatures for all samples.

CO2 laser welding was performed on AISI 904L superaustenitic stainless steel sheets, with optimised processing parameters determined by means of melt run trial evaluations.

Gas atomization can produce, besides a possible significant degree of undercooling, high cooling rates, whose extent depends on the size of the droplets, on their velocity with respect to the surrounding medium, on the thermo-physical properties of both the alloy and the gas, and of course on the operating conditions such as melt overheating and gas-to-metal flow ratio. In this respect it is well-known that the atomizing gas can play a significant role in determining both the powder size distribution and the kind and mix of phases which result from the solidification and cooling processes. The microstructures and solidification morphologies of powders obtained from nitrogen and helium sonic gas atomization of two iron-nickel base glass forming alloys, Fe50Ni30Si10B10 and Fe32Ni36Ta7Si8B17, were investigated by means of light microscopy, X-ray diffraction (XRD) and differential thermal analysis (DTA). The Fe32Ni36Ta7Si8B17 alloy exhibits a higher proneness to the development of amorphous phase than the Fe50Ni30Si10B10 alloy, while the effect of the higher speed attainable by the stream of helium with respect to that of nitrogen., affords not only to obtain a larger amount of particles in the finer size ranges, but also to affect the relative amounts of phases within the different size fractions. (C) 2003 Elsevier B.V. All rights reserved.