Steel Samples Research Articles

Enhancing high cycle fatigue performance of plasma nitrided AISI 4140 steel by post-aging treatment and direct current magnetic field

Machine elements become unable to perform their duties as a result of fatigue damage. In addition, machine elements that are subjected to fatigue under cyclic loads are exposed to electric and magnetic fields when they are close to electrical and magnetic field sources such as electric motors. Moreover, plasma nitriding is often used to increase the fatigue strength of materials. Although the fatigue properties of surface-treated materials are frequently studied, the fatigue behavior of these materials under a magnetic field is not fully known. Therefore, this study focuses on examining the effects of magnetic field on the fatigue properties of surface-treated materials. For this purpose, AISI 4140 steel samples were plasma nitrided and subsequently post-aged, and then they were tested using a rotating bending fatigue testing system by exposing them to a magnetic field for 30 % and 100 % of their fatigue life. ε-Fe2–3N and γ’-Fe4N phases were seen in surface-treated samples, in addition to these phases, peaks belonging to the α”-Fe16N2 phase were observed in post-aged samples. Plasma nitriding raised the hardness of the material because of nitride phases and α”-Fe16N2 caused an extra increase. The highest diffusion depth was seen in the post-aged samples because post-aging facilitated the diffusion of nitrogen. Surface treatments increased the fatigue strength of the material. All samples tested under a magnetic field exhibited higher fatigue strength than samples tested without a magnetic field because fatigue crack initiation was prolonged by the magnetic field. Compared to non-magnetic and 30 % magnetic samples, the fatigue strengths of the samples in a 100 % magnetic field were lower. Furthermore, it was observed that applying a magnetic field had no effect on the samples' fractographic structure.

STRENGTHENING OF THE SURFACE BY FRICTION

The study is devoted to the application of the method of surface hardening by friction Object of study - the process of surface hardening by friction.Subject of study - samples of 65G steel the method allows achieving high values of hardness, strength and wear resistance of materials in a short time and at much lower cost compared to other processing methods. The aim and objectives of the study are to investigate the nature of surface hardening of steel samples by friction. To achieve this goal, the following tasks are envisaged: manufacturing samples from 65G steel in the form of plates, preliminary heat treatment of samples for their maximum thermal hardening, hardening of the surface of samples by friction, analysis of the microstructure and microhardness of each sample, comparison of the microstructure, microhardness and depth of hardening of these samples, conclusions on the influence of processing factors on the hardening result. Based on the experimental data obtained, we constructed graphs of microhardness changes in the cross-section of the samples and studied the microstructures. It can be seen that after friction treatment, a layer with a modified structure is formed in the surface of the samples. The microhardness of the surface is significantly higher (approximately 2 times) than the microhardness of the main part in the samples. Metallographic analysis has shown that the layer formed in the samples has a martensitic structure characterized by a higher degree of dispersion and microhardness compared to the martensitic structure obtained during the previous heat treatment. Changes in the microstructure and microhardness of the samples that were surface hardened using different processing modes were compared. Certain differences in the characteristics of their hardened «white» layers were found. It is also shown that the hardened «white» layer is located along the entire length of the surface in the samples and is continuous and homogeneous.

Elevated temperature rusting characteristics of UNS 31254 weldments within the operational confines of fossil fuel-fired plants and municipal waste incinerator surroundings at 700 °C

ABSTRACT This study investigates the air oxidation and rusting traits of fully austenitic alloy 254 stainless steel samples at 700°C after pulse current gas tungsten arc welding (PCGTA) and CO2 laser beam welding (CO2 LBW), with or without molten salt, relevant to coal-fired plants and waste incinerator settings. Among the weldments studied, CO2 laser weldments demonstrate greater resilience to corrosive gas and salt amalgamation, as well as air oxidation, compared to gas tungsten arc weldments, possibly due to thermal disparities and microstructural differences inherent in the welding processes. Protective oxides enhance corrosion resistance in air-oxidised samples, while corrosive compounds like CrS, Cr2K2O7, etc., reduce corrosion resistance and promote spallation in salt-degraded material. A thermogravimetric approach was used to assess rusting effects, alongside microstructural analysis employing optical, Scanning electron microscopy/ Energy dispersive x-ray spectroscopy (SEM/EDS), and X-Ray diffraction analysis (XRD) techniques.

Investigations of corrosion inhibition of ethanolic extract of Dillenia suffruticosa leaves as a green corrosion inhibitor of mild steel in hydrochloric acid medium

The utilization of plant extracts as environmentally friendly corrosion inhibitors has garnered considerable interest in the field of metallic corrosion protection. The primary objective of this study was to explore a new approach for utilizing Dillenia suffruticosa leaves extract (DSLE) to provide corrosion protection for mild steel (MS) in a molar hydrochloric acid solution. The phytocompounds responsible for corrosion prevention were extracted using ethanol with Soxhlet apparatus. The effectiveness of the extract as a corrosion inhibitor was evaluated through gravimetric and electrochemical methods, along with surface analysis of the corroded steel samples. This analysis involved the use of scanning electron microscopy (SEM) and Fourier-transformed infrared spectroscopy (FTIR) to examine the specimens with and without addition of the extract as inhibitor. The findings demonstrate that DSLE exhibits notable efficacy as a corrosion inhibitor for MS in an acidic environment. The inhibition efficiency (IE) demonstrates a positive correlation with the concentration of the extract, ultimately reaching a maximum value of 81.4 % at the optimum concentration of 1000 mg/L of the extract investigated. Potentiodynamic polarization data revealed that the DSLE functions as a mixed-type inhibitor.

Measuring Dielectric Properties of MARDI 76 (MRQ76) Rice at the Frequency of 915 MHz and 2.45 GHz

The microwave heating system has been widely used in the food processing and postharvest handling of rice. However, to develop efficient heating energy for the heating and drying process, the knowledge of permittivity or dielectric properties of the MARDI 76 (MRQ76) rice is quite important. The penetration and power dissipation of microwave inside the MARDI 76 (MRQ76) rice is strongly dependent on its dielectric properties or permittivity. Furthermore, characterisation of changes in permittivity or dielectric properties of MARDI 76 rice at elevated temperatures is essential for designing the microwave heating device and system. The permittivity or dielectric properties of MARDI 76 rice (MRQ76) were measured using Agilent open-ended coaxial-line probe and Agilent E5071C Network Analyser. The temperature of the MRQ 76 rice sample was regulated using a WiswCircu Circulator Water bath between temperatures of 27ºC to 70ºC. MARDI MRQ 76 rice sample was placed into the temperature-controlled stainless steel sample holder with water jacket assembly which was designed for permittivity measurement at different temperatures. The effect of temperature on dielectric properties of MARDI 76 rice, power dissipation and penetration depth of microwave radiation at the Industrial, Scientific, and Medical (ISM) heating frequency of 915 MHz and 2.45 GHz was assessed. Results indicated that both dielectric constant and dielectric loss of MARDI 76 rice samples increased with increasing temperature. Power dissipation of microwave radiation inside MARDI 76 rice increases with an increase in temperature. On the other hand, the penetration depth of microwave radiation into the MARDI 76 rice decreased with the increase in temperature. The result of this study shows dielectric properties and heating temperature of MARDI MRQ 76 rice play an important role in designing the microwave heating system for MARDI MRQ 76 rice.

Effect of Calcium Addition on Oxide and Sulfide Inclusions in Heavy Steel Ingot Simulated by Lab Experiments

The effect of calcium addition on inclusions (oxides and sulfides) in heavy steel ingot is investigated via lab experiments and thermodynamic calculation. The characteristics (chemistry, size, morphology, and number) of inclusions in the steel samples are investigated by scanning electron microscope with an energy‐dispersive spectrometer. The three‐dimensional morphology of inclusions is investigated by the nonaqueous solution electrolysis method. Inclusions in the fast‐quenched steel are changed from Al2O3 to Al2O3–CaO, Al2O3–CaO–CaS, and CaS after Ca addition. After slow cooling, inclusions in the solid steels are changed from Al2O3, single MnS, and Al2O3–MnS complex inclusions to Al2O3–CaO–CaS–MnS and CaS–MnS. The evolution trajectory of inclusions is Al2O3→Al2O3–CaO→Al2O3–CaO–CaS→Al2O3–CaO–CaS–MnS. With increasing Ca content in the steel, the number density and proportion of single MnS inclusions decrease. The formation mechanism of inclusions after Ca addition is explained by thermodynamic calculation.

Prediction of case depth for deep carburising heat treatments based on the spatial gradient feature of the grain size profile

ABSTRACT Precise evaluation of carburising heat treatment is necessary to avoid failure and degradation of high-performance industrial mechanical components. In this work, a novel non-destructive detection method is proposed for the deep carburised case depth (>2 mm) combining spatial ultrasonic backscatter technique and linear regression model. To create various carburised case depths, three groups of cylindrical 20CrMnMo steel samples were heat-treated in various cycles (Carburising, diffusing, quenching at 850–870°C (holding in range of 2.5–3 h) and tempering). The carburising heat treatment results in a gradient microstructure within the surface region caused by changes in grain size. We employed a transverse-to-transverse scattering model to provide the gradient feature of the grain size profile in the depth direction. The extracted gradient profiles of different carburised case depths exhibit two overlapped growth rates with high- and low-slope factors, respectively. With the increase of the carburised case depth, the positions of the centre points increase and the slope factors decrease. Based on these observations, a modified double sigmoidal function was utilised to parametrise the gradient profile curve. The relationship among the selected gradient feature parameters and various carburised case depths has been established. The predicted results were compared to hardness measurements with good agreement.

УПРОЧНЕНИЕ РАБОЧИХ ОРГАНОВ СЕЛЬСКОХОЗЯЙСТВЕННЫХ МАШИН ВИБРОПЛАЗМЕННЫМ МЕТОДОМ

The task of increasing the service life of agricultural machinery by hardening the surfaces of its working parts has always been relevant. Currently, this problem is most successfully solved with the use of plasma technologies. In this paper, we present the results of some studies on the vibrating plasma treatment of the surface layer of samples made of steel 65G. (Research purpose) The research purpose is determining the possibilities of vibrating plasma methods for hardening the working parts of agricultural machinery and studying the physical and mechanical properties and structural changes in the surface layer of these products. (Materials and methods) Four samples of 65G steel were taken for research: the initial one; a sample with electric spark treatment; a sample with vibrating arc treatment with a single-rod electrode; a sample with vibrating arc treatment with a three-rod electrode. The morphology of the surface, the elemental composition of the samples and the microstructure of the coatings were studied using electron and metallographic microscopes. (Results and discussion) It has been shown that electric spark treatment in some modes increases the hardness of the surface of the material by more than four times. Vibrating arc treatment with a copper graphite electrode allows carburization of the surface layer of the material; the hardened layer has a hardness of more than three times the hardness of the base. (Conclusions) The results of the study are consistent with the results of studies by other authors on electric spark and vibrating arc discharges. The surface layer formed during the processing of the part with vibrating plasma is a new composite structure. Hardening of the base material along the depth of the part during electric spark processing occurs by 0.5-1.0 millimeters, during vibrating arc processing - up to 3-4 millimeters.

Study on the Tribological Properties of DIN 16MnCr5 Steel after Duplex Gas-Nitriding and Pack Boriding.

DIN 16MnCr5 is commonly used in mechanical engineering contact applications such as gears, joint parts, shafts, gear wheels, camshafts, bolts, pins, and cardan joints, among others. This study examined the microstructural and mechanical properties and tribological behavior of different surface treatments applied to DIN 16MnCr5 steel. The samples were hardened at 870 °C for 15 min and then quenched in water. The surface conditions evaluated were as follows: quenched and tempered DIN 16MnCr5 steel samples without surface treatments (control group), quenched and tempered DIN 16MnCr5 steel samples with gas-nitriding at 560 °C for 6 h, quenched and tempered DIN 16MnCr5 steel samples with pack boriding at 950 °C for 4 h, and quenched and tempered DIN 16MnCr5 steel samples with duplex gas-nitriding and pack boriding. Microstructure characterization was carried out using metallographic techniques, optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. The mechanical properties were assessed through microhardness and elastic modulus tests using nanoindentation. The tribological behavior was evaluated using pin-on-disc tests following the ASTM G99-17 standard procedure under dry sliding conditions. The results indicated that the surface treated with duplex gas-nitriding and pack boriding exhibited the highest wear resistance and a reduced coefficient of friction due to improved mechanical properties, leading to increased hardness and elastic modulus.

Progressive Induction Hardening: Measurement and Alteration of Residual Stresses

Progressive induction hardening is an in-line steel heat treatment method commonly used to surface harden powertrain components. It produces a martensitic case layer with a sharp transition zone to the base material. This rapid process will induce large residual stresses, where a compressive state in the case layer will shift to a tensile state in the transition zone. For fatigue performance, it is important to quantify the magnitude and distribution of these stresses, and moreover how they depend on material and processing parameters. In this work, x-ray diffraction in combination with a layer removal method is used for efficient and robust quantification of the subsurface stress state, which combines electropolishing with either turning or milling. Characterization is done on C45E steel samples that were progressively induction hardened using either a fast or slow (27.5 or 5 mm/s, respectively) scanning speed. The results show that although the hardening procedures will meet arbitrary requirements on surface hardness, case depth and microstructure, the subsurface tensile stress peak magnitude is doubled when using a fast scanning speed. However, the near-surface compressive residual stresses are comparable. In addition, the subsurface tensile residual stress peak is compared with the on-surface tensile stresses in the fade-out zone.

Electrodeposition of organic corrosion inhibitor prepared from eucalyptus robusta leaves

Eucalyptus Robusta leaves were used as raw material to develop a steel corrosion inhibitor. A straightforward approach was employed to extract organic molecules from Eucalyptus Robusta leaves, which were applied as a protective coating on steel surfaces to inhibit corrosion. The solution containing the organic inhibitor was electrodeposited onto the surfaces of ASTM A36 steel samples, and an investigation into the parameters of charge (positive or negative), voltage (5 or 20 V), and time (5 and 30 min) was conducted through a 23 factorial experiment. Electrodeposited wet and dry samples had their open circuit voltage (OCP) measured in an acid solution and compared with the OCP of samples in which the inhibitor was deposited by simple immersion (deposited samples) and samples without inhibitor (blank samples). All the samples that had contact with the inhibitor increased their OCP values, showing the effectiveness of the deposition of the inhibitor. Nevertheless, the electrodeposition process carried out for 30 min and with a positive charge (anodic) proved to be the most effective in increasing the OCP value. Optical and scanning electron microscopy analyses revealed that the inhibitor solution effectively formed a thin, uniform, compact film on the metal surface. However, occasional deposition anomalies resulted in the formation of protrusions with organic material accumulation. Electrochemical Impedance Spectroscopy and Tafel curves were used to evaluate the effectiveness of the organic inhibitors. Accelerated corrosion tests in an HCl solution indicated reduced corrosion and the formation of distinct corrosion products for samples with an inhibitor compared to a sample without an inhibitor.

Corrosion and erosion behaviour of TiC-TiB2 reinforced epoxy coatings

ABSTRACT This research investigates the impact of incorporating titanium carbide (TiC) and titanium diboride (TiB2) particles into epoxy coatings to enhance corrosion and erosion resistance. The targeted particles were synthesised by subjecting boron and titanium carbide powders to mechanical alloying for a duration of 20 hours. X-ray diffraction (XRD) analysis confirmed the successful formation of titanium diboride and titanium carbide particles. Subsequently, ceramic particles were integrated into the epoxy at concentrations of 0, 5, 10, and 15 wt.%, and the resultant coatings were applied to steel samples through an immersion method. Electrochemical impedance spectroscopy tests on the samples demonstrated a positive influence of TiC + TiB2 particles on enhancing the corrosion resistance of the coatings, with the 15 wt.% concentration exhibiting superior corrosion resistance compared to other formulations. Employing the Box–Behnken method, 13 samples were designed and subjected to erosion testing. The findings revealed that the coating containing 15 wt.% TiC + TiB2 particles exhibited the lowest erosion rate. Moreover, an increase in the speed and angle during the erosion test correlated with a rise in the erosion rate.

Study on the screening of marine beneficial bacteria and the inhibition of sulfate-reducing bacteria corrosion in marine oil field produced water

PurposeThe purpose of this study is to provide ideas and theoretical guidance for green, environmentally friendly and efficient “bacteriostasis with bacteria” technology.Design/methodology/approachIn this paper, a beneficial strain of bacteria was extracted and purified from marine mud. Weight-loss test, morphological observation and electrochemical test were used to systematically study the effect of sulfate-reducing bacteria (SRB)-induced corrosion inhibition on X65 steel in simulated offshore oil field production water.FindingsThe results showed that a beneficial strain was selected and identified as Vibrio alginolyticus. Under the condition of co-culture of SRB, the average corrosion rate of X65 steel was significantly reduced. In the mixed bacterial system, the surface of X65 steel samples was relatively flat, and the structure of biofilm and corrosion product film was dense. The number of corrosion pits, the average diameter and depth of corrosion pits were significantly reduced. The localized corrosion of X65 steel was significantly inhibited.Originality/valueThe complex and changing marine environment makes the corrosion problem of marine steel increasingly severe, and the microbiologically influenced corrosion (MIC) caused by SRB is particularly serious. The research and development of environmentally friendly corrosion protection technology is a long-term and difficult problem. The use of beneficial microorganisms to control MIC is a green and efficient anticorrosion measure. Compared with terrestrial microorganisms, marine microorganisms can adapt to complex environments, and their metabolites exhibit special biological activities. The use of marine beneficial bacteria can inhibit SRB activity to achieve the corrosion inhibition effect.

The utilization of ionic liquids as sustainable and eco-friendly inhibitors for corrosion protection of carbon steel in petroleum fields

Various ionic liquid compounds are synthesized from the combination of iminodiethanol and fatty acid of butyric (IL-4) caprylic (IL-8) and capric (IL-10). The composition of such compounds was confirmed by various spectroscopic techniques and was tested as mitigators for the destruction of carbon steel in 10 % diluted oil field-produced water. The measurements of electrochemical potentiodynamic polarization, impedance spectroscopy, and gravimetry were complemented by surface investigation of some corroded carbon steel samples utilizing scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX). The data indicated that the addition of IL-4, IL-8, and IL-10 inhibits the destruction of carbon steel in the 10 % diluted oil field-produced water by lowering the corrosion current density (Iorr) and the double-layer capacitance (Cdl). Tafel polarization data confirmed that the studied compounds acted as mixed inhibitors. The values of the cathodic Tafel slope, bc, are found to be close to each other confirming that the adsorbed compounds did not alter the mechanism of hydrogen evolution. The charge transfer resistance, Rct, for the blank solution is 1501 and increased with the addition of such compounds to reach 5332 at a concentration of 500 mg/l of IL-10 with a protection efficiency of 85.83 %, at 25 ◦C. The computed -ΔG°ads values varied between −18.11 and –23.98kJ mol/1 depending on the type of inhibitor and the temperature, which confirms the suggestion of the physisorption mechanism. The negative values of ΔG°ads explain the spontaneity of the adsorption process. The lowering in Kads values with T is attributed to the escaping of some of the adsorbed inhibitor molecules leaving the carbon steel surface. Theoretical quantum computation was used to confirm the adsorption ability of various ionic liquids on the examined metal.

Investigation of microstructure and mechanical properties of 45KH2NMFBA steel samples after thermal exposure

The analysis of the structure of ballistic materials was carried out and the optimal mechanical properties necessary to ensure the best bullet resistance and durability of armored steel were selected. A study of 45X2NMFBA armor steel was carried out under various heat treatment modes. The optimal modes of heat treatment have been determined to ensure an increase in mechanical properties. It was found that with an increase in the cooling rate of steel, a finer‑grained structure is formed, and an increase in the quenching temperature leads to an increase in the grain of primary austenite. The results of optical microscopy and mechanical properties of the studied steel samples are presented

Formation mechanism of large-sized CaO-SiO2-CaF2-Al2O3-MgO composite inclusions in super 304H stainless steel rods

Employing silicon deoxidation in the production of Super 304H stainless steel, large-sized CaO-SiO2-CaF2-Al2O3-MgO (CSFAM) composite inclusions are frequently observed in the rods, posing a substantial threat to product quality. This study delves into an analysis of the constituent phases of these large-sized inclusions, identifying the coexistence of liquid phase and spinel phase. Leveraging industrial experiments, systematic sampling of Super 304H stainless steel, and a comprehensive analysis involving dynamic and thermodynamic calculations, this study investigates the formation mechanism underlying such inclusions. The composition of inclusions in the sample before AOD tapping mirrors that of the slag, with high CaF2 content, indicating that they come from slag entrapment. Through kinetic calculations, it is indicated that the time of existence of the liquid film during the ascent of these inclusions is significantly longer than the collision time. This suggests that they are not easily removed and tend to persist in the steel. Despite LF refining, the predominant types of inclusions remain unchanged, and the decrease in temperature leads to the precipitation of solid-phase MgO within the inclusions. Solubility calculations for solid-phase MgO show a rising trend with temperature. Post-casting, MgO and Al2O3 content in inclusions increase, the solid-phase MgO region disappears, and in the subsequent cooling process, inclusions precipitate the stable spinel phase (MgAl2O4). Solubility calculations for solid-phase MgAl2O4 show a temperature-dependent increase. After the completion of casting, the steel ingot undergoes a deformation process through rolling, leading to the transformation of inclusions into large-sized, elongated, composite CSFAM inclusions.

Effect of gadolinium on the machinability of an Al-killed high sulfur steel

The effect of various gadolinium contents on the number density and morphology of sulfide in Al-killed high-sulfur steel was investigated. Meanwhile, the effect of characterization of sulfide inclusions, i.e., number density and morphology on the cutting performance of steel also were studied. The evolution process of sulfide inclusions with the increasing T.Gd content from 0 ppm to 198 ppm in steel samples could be described as follows: MnS → (Gd-O-S)-MnS→(Gd-S)-MnS →Gd-S. As the gadolinium content in the steel increased, sulfide inclusions with an aspect ratio of < 3 increased from 26.1 % to 99.7 % and the number density of sulfides decreased from 438 #/mm2 to 80.4 #/mm2. Spherical sulfides could form micro-holes during cutting, facilitating the chip-breaking process, whereas long-strip MnS tended to self-break during cutting. The higher the proportion of C-type chips in the cutting process, the better the cutting performance of the material. Therefore, spherical sulfides exhibited superior modification effects on surface finishes compared to long-strip sulfides. In low-speed cutting, sulfide morphology predominantly affected surface roughness, while in high-speed cutting, the number density of sulfides became the dominant factor. The addition of gadolinium can effectively decrease the surface roughness of the material at various cutting parameters. Moreover, the Gd-O film can be formed on the tool surface was observed after the addition of gadolinium in the steel, which can increase the lubrication during the cutting process and reduce the tool surface wear.

Classification of pitting corrosion damage in process facilities using supervised machine learning

AbstractCorrosion is widely known to be a major cause of the failures in process facilities. Prediction of corrosion damage is therefore essential for industries to manage the availability of their assets. This research aims to investigate the application of supervised machine learning methods for the classification of pitting corrosion damage. Several machine learning classifiers, namely ensemble methods, support vector machine (SVM), K‐nearest neighbours, and the decision tree are used to classify the extent of pitting corrosion damage in corroded steel samples. To simulate the corrosion of the steel samples, a series of laboratory experiments were conducted. After processing the results using appropriate statistical methods, the corrosion data was used to train the machine learning models. The trained models can predict the class of corrosion damage with acceptable accuracy using the material and environmental specifications of the samples. Additionally, a discussion on the selection of machine learning techniques which classify corrosion damage using a risk‐based approach is provided. With their optimal accuracy and lower risk of misclassification, the SVM and AdaBoost models perform better than the other studied models.

Green Alternatives for Archaeological Iron Stabilization

ABSTRACT One of the most challenging types of artifact occurring within museum collections is unstable chloride-contaminated archaeological iron. A high chloride concentration causes cracking, flaking and leads to full mineralization, in effect making objects fragile. Consequently, removal of chloride ions plays a key role in stabilization treatment, while preserving the integrity of the corroded iron object. Despite the variety of stabilization methods, all have significant disadvantages, including a lack of sustainability. Within the framework of the Horizon Europe project GoGreen the potential of microbial biosorption to stabilize archaeological iron artefacts is being investigated. Dry biomass of the fungi Meyerozyma sp. and Saccharomyces cerevisiae was studied to remove chloride ions. Preliminary tests were carried out on artificially-aged steel samples. To assess the activities of the microorganisms’ functional groups and biosorption capabilities as a potential green stabilization treatment, analytical techniques including FTIR, Raman spectroscopy, and SEM-EDX were used. The results demonstrate two promising paths for the development of green stabilization treatments based on fungal biomass: passive adsorption into the cell wall and conversion of reactive corrosion products into more stable compounds. The use of microbial biomass opens up promising perspectives for the development of more sustainable solutions in archaeological iron stabilization, while avoiding the generation of toxic waste in our environment.

A novel powder sheet laser additive manufacturing method using irregular morphology feedstock

Irregular (i.e. non-spherical) morphology powder is more cost-efficient to produce than spherical shaped powder. However, its reduced levels of flowability limit the wide application ranges of laser beam powder bed fusion (LPBF). To address this issue, a novel powder sheet additive manufacturing concept (MAPS) is proposed. Herein, a pre-manufactured metal particle-polymer binder composite (i.e. powder sheet) feedstock is employed as a raw material. The printability of irregularly shaped powder particles in sheet (MAPS) format was physically investigated using a range of different process parameters. The manufacturing process was observed by high-speed imaging. Microstructural and chemical element characterisations of the irregularly shaped powder particle print were then compared against those prints which were conducted using sheet-based (MAPS) spherical powder morphologies. The results indicated that the geometric accuracy and density of irregular powder morphology sheet printing improved when using a negative defocus strategy of the laser beam. A negative defocusing strategy allowed for the melting mode of the material to be transformed from keyhole to a more favourable conduction state. High speed imaging revealed that more spatter and vapour plume were observed with the increase in the magnitude of the negative defocus. The multi-morphology 304 L stainless steel (SS304) samples were printed in a single printer using an efficient method for the first time, i.e. printing spherical SS304 material on top of irregular SS304. EDX results indicated an insignificant change of chemical elements between the spherical and irregular prints. EBSD results revealed that columnar grains could grow through the irregular-spherical transition zone and similar grain size can form between spherical and irregular prints. The results of this study provide insights into the optimum printing configurations for powder sheet additive manufacturing using a cost-effective solution of irregular morphology material.