Annealing Step Research Articles

Stability of forming induced residual stresses in stainless steel components under mechanical load

Cold forward extrusion leads to the generation of residual stresses, which can have an advantageous or detrimental effect on the operating behavior of the formed components. In industrial practice, energy-intensive annealing steps are often used to remove unknown stress states and thus prevent unexpected failures. Residual stress-related knowledge can therefore help to save energy and resources. To be able to estimate the effects, not only sign and magnitude need to be known, but also the residual stress stability under typical operating loads. In this paper, stainless steel X6Cr17 (DIN 1.4016, AISI 430) is formed by forward rod extrusion at room temperature. The forming process leads to residual stresses in the formed components, which are subsequently subjected to mechanical testing. To represent different initial states, components with varied die opening angles are produced and tested. A modified 3-point bending setup is used to generate a defined tensile load stress in the part surface. The results show a behavior of the residual stresses, which is depending on the load magnitude, the initial stress state and the work hardening distribution in the part. While the number of cycles has an influence, the largest changes occur in the first stroke.

Poly‐SiOx Passivating Contacts with Plasma‐Assisted N2O Oxidation of Silicon (PANO‐SiOx)

Passivating contacts are crucial for realizing high‐performance crystalline silicon solar cells. Herein, contact formation by plasma‐enhanced chemical vapor deposition (PECVD) followed by an annealing step is focused on. Poly‐SiOx passivating contacts by combining plasma‐assisted N2O‐based oxidation of silicon (PANO‐SiOx) with a thin film of phosphorus (n+) or boron (p+)‐doped hydrogenated amorphous silicon oxide (a‐SiOx:H) are manufactured. Postannealing is conducted for transitioning a‐SiOx:H into poly‐SiOx. The aim is to achieve a contact with low absorption and high‐quality passivation. It is demonstrated that by tuning the plasma oxidation process time and power, the PANO‐SiOx thickness and its passivation quality can be controlled. A higher SiO2 content is observed in PANO‐SiOx than in the nitric acid oxidation of silicon (NAOS‐SiOx) counterpart. PANO‐SiOx acts as a stronger diffusion barrier for both boron and phosphorus atoms compared to NAOS‐SiOx, affecting the dopant distribution during annealing. Implied open‐circuit voltages up to 751 and 710 mV for n+ and p+ flat symmetric samples, respectively, are demonstrated. With respect to standard thermally grown SiO2 tunneling oxide combined with (in/ex )situ‐doped low‐pressure chemical vapor deposition poly‐Si, this study presents a simple alternative for manufacturing passivating contact fully based on PECVD processes.

Atomic Layer Deposition Route to Scalable, Electronic-Grade van der Waals Te Thin Films.

Scalable production and integration techniques for van der Waals (vdW) layered materials are vital for their implementation in next-generation nanoelectronics. Among available approaches, perhaps the most well-received is atomic layer deposition (ALD) due to its self-limiting layer-by-layer growth mode. However, ALD-grown vdW materials generally require high processing temperatures and/or additional postdeposition annealing steps for crystallization. Also, the collection of ALD-producible vdW materials is rather limited by the lack of a material-specific tailored process design. Here, we report the annealing-free wafer-scale growth of monoelemental vdW tellurium (Te) thin films using a rationally designed ALD process at temperatures as low as 50 °C. They exhibit exceptional homogeneity/crystallinity, precise layer controllability, and 100% step coverage, all of which are enabled by introducing a dual-function co-reactant and adopting a so-called repeating dosing technique. Electronically, vdW-coupled and mixed-dimensional vertical p-n heterojunctions with MoS2 and n-Si, respectively, are demonstrated with well-defined current rectification as well as spatial uniformity. Additionally, we showcase an ALD-Te-based threshold switching selector with fast switching time (∼40 ns), selectivity (∼104), and low Vth (∼1.3 V). This synthetic strategy allows the low-thermal-budget production of vdW semiconducting materials in a scalable fashion, thereby providing a promising approach for monolithic integration into arbitrary 3D device architectures.

Block length distribution, morphology, and property of thermoplastic polyurethanes affected by production method: A polymer‐by‐process investigation

AbstractTwo thermoplastic polyurethanes (TPUs) based on the same monomers and composition were produced by two different production methods – hand mix batch process and continuous band casting. The soft segment was poly(hydrofuran) (PTHF) with a molar mass of 1000 and the hard segment was made of 1,4‐butanediol (BD) and 4,4′‐methylene diphenyl diisocyanate (MDI). The hard segment content amounted to 42%. The distinctions in crystallization and thermal behavior and mechanical properties of the two TPUs were ascribed to differences in the hard and soft block length distribution caused by the different production methods. Using thermal fractionation – a series of successive self‐nucleation and annealing steps – the minor differences in hard block length distribution could be shown and quantified. The length distribution of the hard and soft blocks of the machine‐produced sample was narrower than that of the hand‐cast sample. The former with the narrow block distribution showed thicker and mechanically and thermally more stable hard domains. The more uniform block length distribution facilitated crystallization and resulted in improved tensile recovery behavior and elasticity. The second with the broader distribution, however, showed the highest tensile strength at break, which was ascribed to an improved strain‐induced hardening of the soft phase.

Improved corrosion resistance of cathodic arc evaporated Al0.7Cr0.3−xVxN coatings in NaCl-rich media

The corrosion resistance of cathodic arc evaporated Al0.7Cr0.3−xVxN coatings with a vanadium content up to 22.3 at% has been electrochemically tested in a 0.1 M NaCl-solution. Significant improvement in the open porosity and corrosion rate was observed for coatings with higher V-contents, due to a denser and more refined coating morphology. Further reduction in the open porosity rate was achieved through an annealing step in air at 700 °C. Here, the formation of an AlVO4 top-oxide and underlying oxygen-rich V-depletion zone provides additional sealing of the coating surface, whilst reducing the corrosion current density to a final 1.59 × 10−9 A/cm2.

High-density monodispersed nickel nanoparticles as highly functional and thermally robust catalysts for solid oxide fuel cells

In this study, we have explored the deposition of highly monodispersed nickel nanoparticles on various supports using a two-step metal–organic precursor thermolysis and reductive annealing process. The process allowed flexible tunability of application-relevant properties, such as nanoparticle size, density and distribution, via the process pressure and deposition cycle control. Ex-situ characterization revealed the presence of carbon in the nanoparticles, necessitating the reductive annealing step to remove residual carbon. The impurities-free nanoparticles were subsequently deposited onto Pr0.5Ba0.5MnO3−δ anodes of solid oxide fuel cells and used to promote the electrochemical oxidation of methane. Impedance spectroscopy of the symmetric cells (Pr0.5Ba0.5MnO3−δ Yttria-stabilized ZrO2 Pr0.5Ba0.5MnO3−δ) revealed a significant enhancement in the catalytic activity of the Ni nanoparticle-coated electrode relative to the bare reference. Moreover, compared to conventional infiltration, the Ni nanoparticles deposited with the strategy outlined in this work showed over a 4-fold improvement in performance with an initial electrode resistance of only 2.1 Ω cm2. This highlights the important role of the deposition method on catalytic performance and the potential of developing highly active electrode materials for direct-hydrocarbon utilization.

Colloidal Silver Nanoparticle Plasmonic Arrays for Versatile Lasing Architectures via Template‐Assisted Self‐Assembly

AbstractThe characteristic narrow spectral features of surface lattice resonances emerge as great candidates for the rational design of optical nanocavities targeting enhanced light‐matter interaction, ultrasensitive detection, or efficient light‐energy conversion. Traditional fabrication of metal arrays involves thermal evaporation and annealing steps, limiting scalability and adaptability. In contrast, template‐assisted self‐assembly provides a high‐throughput all‐around approach for implementing colloidal plasmonic metasurfaces on a variety of different materials. Here, the use of pre‐synthesized silver nanoparticles is designed and tested for the construction of versatile lasing architectures. Plasmonic arrays are prepared directly on top of the gain media (a photoresist thin film doped with Rhodamine B), creating optical nanocavities with quality factors as high as 85. The proposed architecture circumvents the need for an index‐matching superstrate to promote the generation of collective resonances, leaving the plasmonic surface accessible for post‐assembly modification. Additionally, the angular dispersion of the metasurfaces is used to modify the angle of the lasing emission, achieving both normal and off‐normal lasing upon modification of the lattice parameter of the array. The results demonstrate how state‐of‐the‐art colloidal self‐assembly techniques offer a scalable and versatile alternative for the fabrication of plasmonic and photonic devices targeting advanced and non‐linear optical phenomena.

Comprehensive characterization of Al-doped ZnO thin films deposited in confocal radio frequency magnetron co-sputtering

Al-doped ZnO thin films with varying Aluminium (Al) content were deposited by radio frequency magnetron co-sputtering of two ZnO and Al targets in confocal configuration. A comprehensive study of the effect of Al content variation on the structural, optical and electrical properties were studied for as-deposited films and after an annealing step under controlled argon atmosphere. Chemical composition analyses, performed by both X-ray photoelectron spectroscopy and energy dispersive X-ray spectrometry, show an Al content variation in the deposited films in the 0-14 at.% range by varying the Al target power from 0 to 30 W, while the Zn target power was kept constant at 200 W. All deposited films exhibit a wurtzite crystalline structure and a decreasing crystalline quality for Al content above 5 at.% as shown by grazing incidence X-ray diffraction patterns. Atomic Force Microscopy analysis revealed films with homogeneous and dense surface morphology with roughness in the one nm range. Carrier concentration, resistivity and photoluminescence vary significantly with Al content in the ZnO films and appear optimized for an Al content window ranging from 1.5 to 5.5 at. %. Both optical and electrical properties are improved by a post-annealing at 300°C under argon. A high figure of merit of 43.6 × 10-4 sq.Ω-1 was obtained for the ZnO film with Al content of 3.6 at.% after annealing at 300°C. Optimized properties are obtained for a higher Al content than the standard value of 2 at. % widely used in published works.

Co-evaporated p-i-n perovskite solar cells with sputtered NiOx hole transport layer

Metal oxides have long been used as charge transport layers in thin film solar cells due to their suitable energy band levels, high charge carrier mobilities, and excellent long-term stability. One example is non-stoichiometric nickel oxide (NiOx), a hole transport material which can be deposited in a conformal, scalable, and solvent-free manner via sputtering. However, sputtered NiOx has only ever been combined with spin-coated perovskite films in perovskite solar cells (PSCs). Here we report the fabrication of the first co-evaporated PSCs with sputtered NiOx as the hole transport layer. We reveal how the amount of argon gas used during sputtering affects important physical properties such as hole conductivity, visible light transmittance, and suitability of the NiOx surface for perovskite nucleation and growth. Optimized sputtering conditions led to CH3NH3PbI3 (MAPbI3) PSCs with an 18.6% power conversion efficiency (PCE), which was further increased to 19.5% by adding a spiro-TTB interlayer between NiOx and MAPbI3. We also show that removing the NiOx annealing step only reduced the device PCE by 1%, paving the way toward low-temperature deposition of metal oxide transport layers. This work exhibits the versatility of NiOx sputtering and perovskite evaporation as a powerful combination for solvent-free and low-temperature fabrication of highly efficient PSCs.

Carburization behavior at elevated temperatures and mechanical properties of a hot stamped complex phase steel

As a lightweight construction strategy, hot stamped parts of ultra-high-strength steels with tailored properties are increasingly used for crash relevant components in car bodies, e.g., as B-pillars. With the process of tailored carburization, parts can be reinforced locally without increasing the sheet metal thickness. Thus, this process has the potential to be applied to lightweight components for no deformation zones, e.g., in the battery housings. Standardly, carburization is performed at 950 °C, with the highest strengths achieved at long times of up to 6 h, which prolongs the total process time. By raising the temperature, the carbon diffusion increases, which enables a reduced heat treatment time and, consequently, a shorter process time. Therefore, the objective of this study is to investigate the influence of elevated carburization temperatures on the mechanical properties of a carburized and hardened complex phase steel, CP-W® 800. A single carburization step at the enhanced temperatures leads to an embrittlement of the samples. Hence, an additional diffusion-annealing step is implemented to homogenize the carbon content, without enlarging the total heat treatment time. Depending on the time allocation of carburization and diffusion, the application of the diffusion annealing step results in higher strengths and ductility compared to only carburized samples.

The study of mutations of CDK4 and TP53 genes in selected breast lesions

Lesions are abnormal changes in tissue. The theories behind tumorigenesis can be genetic epigenetic, immune surveillance and monoclonal hypothesis, which led to genetic changes. The genetic change can be the inactivation of tumor suppressor genes or the activation of oncogenes in the cell cycle. This study investigated the presence of gene mutation in CDK4 and TP53 genes in breast lesions. Ten (10) formalin fixed paraffin embedded tissue block, which includes 5 cases of fibroadenoma and 5 cases of invasive ductal carcinoma from the pathological archives were used. The nuclei amplification technique was carried out on the formalin fixed paraffin embedded tissue blocks. DNA extraction involves lysing the cells and solubilizing DNA, which is followed by chemical or enzymatic methods to remove macromolecules, lipids, RNA or proteins. Thereafter, the DNA is amplified using reagents and heated (denaturing) and cooling (annealing) steps. PCR requires free nucleotide (dNTPs), template DNA to amplify and unique single-stranded DNA primers that bind upstream (5') and downstream (3') of the DNA region of the tissue blocks. The integrity of the DNA is assessed by loading approximately 100 ng per sample on a 1.5% agarose gel and the sizes of PCR products were estimated by comparison with the mobility of a 100bp molecular weight ladder that was run alongside the samples in the gel. However, the amplified fragment was purified to remove PCR reagents and thereafter it was sequenced. The sequence of single nucleotide polymorphism of each gene was analyzed, and the results were reported. In mutation was more in both genes compared to the sequence of FA and IDC. From this study, both genes showed segments of mutation which were either SNPs or functional mutation. It showed that both genes were modified from a proto-oncogene to an oncogene and the protein it produces is an oncoprotein and as such it favours the alteration of both genes led to cell proliferation. The data generated from this research has highlighted the importance of carrying out further studies in assessing both genes to understand their involvement in the etiology of carcinogenesis which will help in clinical information about breast cancer. In line with the findings, there is an urgent need to understand carcinogenesis which may serve in early diagnosis and understanding of breast conditions and further help prevent or delay the onset of chronic complications and reduce morbidity and mortality rates to improve and assure the health of individuals.

Mechanical properties and fracture surface of Al-Al2O3 nano/micro-composites produced by accumulative roll bonding

ABSTRACT The accumulative roll bonding (ARB) process has been utilised to produce layered materials and composites with high strength without intermediate annealing steps. This study focused on the size of reinforced particles (Al2O3) with an average size of 3 µm (m) and 80 nm (n) in aluminum matrix composites. Three different samples of monolithic Al, Al-1 vol.% (m)Al2O3, and Al-1 vol.% (n)Al2O3 particulate composites were produced by ARB. The SEM results revealed that the distribution of alumina particles in the fabricated composites was improved with increasing ARB cycles, while the Al-1 vol.% (m)Al2O3 composite presented the proper distribution of particles at higher cycles in contrast with the Al-1 vol.% (n)Al2O3 composite. The tensile strength of the produced composites was enhanced, and their ductility decreased with the increase in ARB cycles, while Al-1 vol.% (m)Al2O3 with a tensile strength of 253 MPa showed higher strength than Al-1 vol.% (n)Al2O3 with 229 MPa at the sixth cycle. By adding Al2O3 microparticles, the yield strength and tensile strength of the microcomposite sheet were increased to about 5 and 2.1 times, respectively, compared to the Al sheet.

Unusual Micro Carbon Rods Formed from PET Plastic via Pyrolysis and Annealing in CO2/He Co-Gas

This study investigates the transformation of activated carbon (AC) powder, derived from polyethylene terephthalate (PET) through pyrolysis, into a specific type of short cylindrical carbon. This carbon-to-carbon (C-C) transformation was completed by annealing the AC powder in a co-gas atmosphere of He and CO2. This produces low-porous, amorphous, and micro carbon rods (MCR) in micron size. It is suggested that a so-far unknown growth mechanism originates from the oxidation role of CO2, initiating the curving of polycyclic aromatic hydrocarbons (PAHs) sheets. This annealing step was followed by layer-by-layer sheet stacking steps to render the thick rods. This thickness is also created by the simultaneous occurrence of rare carbon nanotubes, supposedly formed initially from curling a small sheet of PAH surrounding carbon nanoparticles to create a tube template for subsequent cylindrical growth. This is the first example of CNT growth through C-C transformation rather than the other vapor deposition routes. As the main product, MCR is amorphous and fairly porous, with an average aspect ratio greater than 10, which possesses potential applications as a mechanical reinforcing or energy-attenuation filler for different composites.

Study on the Application of Nitrogen-Doped Holey Graphene in Supercapacitors with Organic Electrolyte.

We present a facile low-cost method to produce nitrogen-doped holey graphene (N-HGE) and its application to supercapacitors. A composite of N-HGE and activated carbon (AC) was used as the electrode active material in organic-electrolyte supercapacitors, and the performances were evaluated. Melamine was mixed into graphite oxide (GO) as the N source, and an ultra-rapid heating method was used to create numerous holes during the reduction process of GO. X-ray photoelectron spectra confirmed the successful doping with 2.9-4.5 at.% of nitrogen on all samples. Scanning electron micrographs and Raman spectra revealed that a higher heating rate resulted in more holes and defects on the reduced graphene sheets. An extra annealing step at 1000 °C for 1 h was carried out to further eliminate residual oxygen functional groups, which are undesirable in the organic electrolyte system. Compared to the low-heating-rate counterpart (N-GE-15), N-HGE boosted the specific capacity of the supercapacitor by 42 and 22% at current densities of 0.5 and 20 A/g, respectively. The effects of annealing time (0.5, 1, and 2 h) at 1000 °C were also studied. Longer annealing time resulted in higher capacitance values at all current densities due to the minimized oxygen content. Volumetric specific capacitances of 49 and 24 F/cm3 were achieved at current densities of 0.5 and 20 A/g, respectively. For the high-power-density operation at 31,000 W/kg (or 10,000 W/L), an energy density as high as 11 Wh/kg (or 3.5 Wh/L) was achieved. The results indicated that N-HGE not only improved the conductivity of the composite supercapacitors but also accelerated ion transport by way of shortened diffusion paths through the numerous holes all over the graphene sheets.

Mechanical Properties of Ti–5Al–5V–5Mo–3Cr Alloy Sintered From Blended Elemental Powders

The field-assisted sintering technique (FAST) was successfully used to sinter, homogenize, and age the Ti–5Al–5V–5Mo–3Cr (Ti-5553) aerospace alloy from blended elemental powders in a single processing run. Sintering at a comparatively high temperature of 1500 °C assured chemical homogeneity of the material. Subsequently, without cooling to the room temperature, the temperature was lowered to 600 °C for 30 min to provide annealing treatment and to produce a desired lamellar α + β microstructure. Using an in-house designed assembly, a fully dense rod of 15 mm in diameter and 70 mm in length was successfully sintered. Microstructural and mechanical properties of the alloy were investigated and compared with the conventionally processed Ti-5553 alloy. A good combination of strength (1183 MPa) and ductility (6 pct) was achieved; these values are fully comparable to the conventional cast, forged, and aged Ti-5553 alloy. It was shown that homogeneous Ti-5553 alloy can be produced by FAST, FAST can instantly provide necessary annealing steps, and the FAST process can be upscaled to produce homogeneous rods.

In Situ Observations of the Microstructural Evolution during Heat Treatment of a PH 13‐8 Mo Maraging Steel

The standard heat treatment of PH 13‐8 Mo maraging steels consists of solution annealing and subsequent aging. Herein, it is investigated how an additional intercritical annealing step prior to aging affects the microstructure, and, consequently, the mechanical properties of a PH 13‐8 Mo maraging steel. In situ techniques by means of high‐temperature electron backscatter diffraction and high‐temperature X‐ray diffraction are applied to study the microstructural changes during intercritical annealing and subsequent aging. In addition, high‐resolution investigation methods, such as transmission electron microscopy and atom probe tomography supplemented by transmission Kikuchi diffraction, are used for an in‐depth characterization of the microstructure. The results reveal that a diffusion‐controlled martensite to austenite transformation accompanied by partitioning of the substitutional atoms Cr, Ni, and Mo takes place during intercritical annealing. As a result of partitioning during intercritical annealing, an inhomogeneous distribution of Ni remains in the microstructure after the martensitic transformation. Consequently, the formation of reverted austenite is facilitated during subsequent aging due to existing Ni‐enriched zones in martensite. Since the fracture toughness is significantly enhanced compared to the standard heat treatment, it is suggested that this improvement is related to the increased phase fraction of reverted austenite.

Defect engineering of silicon with ion pulses from laser acceleration

Defect engineering is foundational to classical electronic device development and for emerging quantum devices. Here, we report on defect engineering of silicon with ion pulses from a laser accelerator in the laser intensity range of 1019 W cm−2 and ion flux levels of up to 1022 ions cm−2 s−1, about five orders of magnitude higher than conventional ion implanters. Low energy ions from plasma expansion of the laser-foil target are implanted near the surface and then diffuse into silicon samples locally pre-heated by high energy ions from the same laser-ion pulse. Silicon crystals exfoliate in the areas of highest energy deposition. Color centers, predominantly W and G-centers, form directly in response to ion pulses without a subsequent annealing step. We find that the linewidth of G-centers increases with high ion flux faster than the linewidth of W-centers, consistent with density functional theory calculations of their electronic structure. Intense ion pulses from a laser-accelerator drive materials far from equilibrium and enable direct local defect engineering and high flux doping of semiconductors.

Tailoring of morphology and microstructure dependent optical properties of solution processed Ge23Sb7S70 chalcogenide glass films

This paper presents an extensive study carried out to understand the process of tailoring the morphology of solution processed nanostructured Ge23Sb7S70 Chalcogenide glass thin films and to analyze their microstructure dependent optical properties. To tailor the desired morphology of the solution processed ChG films different synthesis parameters have been optimized, step by step. It has been observed that the dissolution time and concentration of Chalcogenide glass precursor solution used for the deposition of solution processed films have the major role in determining their morphology. Annealing of solution processed chalcogenide glass film is an important step to get rid of residual solvent from the film. This study reveals that annealing may disturb the morphological uniformity of solution processed chalcogenide glass films and a careful optimization of annealing step is required to maintain the morphological uniformity. Microstructure dependent optical properties such as refractive index and optical bandgap of solution processed chalcogenide glass films have also been analyzed in this study. It has been observed the size of the microstructures insolution processed chalcogenide glass films greatly influences the optical properties of these films.

Enhanced grain growth and dielectric properties in aerosol deposited BaTiO3

Piezoelectric ceramics are envisioned as cell stimulating materials for in-vivo, load-bearing applications. To compensate for their brittle nature developing ceramic films on medically accredited metals is a promising approach. However, high temperature consolidation is often required to achieve highly dense ceramics with suitable functional properties, which can compromise the metal substrate integrity. With aerosol deposition highly dense thick films can be produced at room temperature. Still, an annealing step is required to enhance the functional properties of piezoelectric ceramics. Thermal annealing of dense, aerosol deposited BaTiO3 thick films on 304SUS stainless steel gave a clear enhancement of the dielectric properties. An increase in saturation polarization and the adoption of ferroelectric hysteresis at 750 °C coincided with a significant reduction in mechanical properties. The simultaneous appearance of grain growth and diffusion of chromium from the substrate at 750 °C suggests that chromium acts as a sintering aid.

Inkjet Printing Bio‐Inspired Electrochromic Pixels

AbstractIn this report the design, fabrication, and testing of inkjet‐printed electrochromic pixels (ECPs) incorporating the biochrome, xanthommatin (Xa) as programmable display units is described. As a redox sensitive chromophore, Xa is present in some species as a physiological indicator with red (reduced) or yellow (oxidized) colors associated with different behavioral or developmental stages. These features have been recently leveraged in some materials applications, illustrating a bio‐inspired design solution to color‐changing sensors and displays. This paper describes an extension of these applications to print individually addressable ECPs that can be processed in a mild annealing step to introduce localized conductivity on initially nonconductive substrates. When formulated together with a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) carrier ink, an addition of 0.19 wt% Xa is enough to generate dynamic ECPs which can be batch printed as lateral electrodes on any substrate to serve as both conductors and display units across electrically isolated boundaries. Application of low potentials triggers reversible color changes that span the red/yellow color space and can cycle for days. These results represent an important step towards the incorporation of alternative active materials like Xa to manufacture and scale low‐power, color‐changing pixels and patterns.