Low Alloy Research Articles

Diffusion kinetics of borided of low entropy soft magnetic FeCo alloy

Abstract The growth kinetics of boride layers were investigated by boronizing the FeCo low entropy alloy produced by arc melting reverse vacuum system with the pack boriding method at temperatures of 1173 K, 1223 K, 1273 K and for 2, 4, 6 h. FeCo alloy has a single-phase FCC crystal structure and there are linear cracks and homogeneously distributed point voids in its microstructure. The hardness of FeCo alloy is between 170 HV0.05 and 265 HV0.05. The boride layer appearance has a sawtooth appearance, and the layer thickness varies between 62 µm and 172 µm depending on temperature and time. According to the XRD pattern, (CoFe)B and (CoFe)B2 triple phases are present on the boride layer surface. With pack boriding, the hardness of the boride layer increased up to 2262 HV0.05, and the surface hardness of the alloy improved by 8–10 times. The boride layer activation energy of the FeCo alloy boronized with pack boriding was calculated as 89.065 kJ mol−1.

Effect of cyclic loading on microstructure and plastic deformation in heat-treated Co–28Cr–6Mo alloy fabricated via laser powder bed fusion: an in situ synchrotron X-ray diffraction study.

We present a systematic microstructure-oriented plasticity investigation of an additively manufactured cobalt-based alloy aiming to relate microstructural changes to the fatigue resistance. A load-controlled cyclic test in the low-cycle fatigue regime was utilized to study mechanical response and microstructural changes in the alloy after reverse phase transformation heat treatment. Deformation-induced FCC → HCP phase transformation was followed using in situ synchrotron X-ray diffraction combined with ex situ electron backscatter diffraction and scanning electron microscopy. Scanning transmission electron microscopy provided experimental evidence of the presence of precipitates in the solution annealed sample. It was found, that a stepwise increase in plastic deformation is attributed to nucleation and growth of different martensitic crystallographic variants. These insights into plasticity and microstructural changes suggest that the reverse phase transformation heat treatment is an effective approach for improving the fatigue resistance of low stacking fault energy alloys, that are susceptible to deformation-induced martensitic transformation.

Effects of water content on the corrosion behavior of NiCu low alloy steel embedded in compacted GMZ bentonite

Buffer material and metal disposal containers are the key engineering barriers in the geological disposal of high-level radioactive waste. The durability of disposal containers largely depends on the water content in buffer material. This work focused on investigating the corrosion evolution of NiCu low alloy steel in compacted GMZ bentonite with different water contents for 270 d by using weight loss, electrochemical measurements, and various methods for analyzing corrosion products. As the water content increased from 13% to 20%, the water in the bentonite transformed from an unsaturated to a critical saturated state, and the corrosion rate of NiCu steel clearly increased. In these two systems, the oxygen could migrate to the thin liquid film on the steel surface through the air pores in the bentonite in the gas phase and undergo cathodic reduction. Meanwhile, it oxidized the ferrous hydrolysis products into ferric corrosion products and formed a rust layer, which could block the diffusion of oxygen. At that moment, the cathodic process of NiCu steel corrosion changed to rust reduction. When the water content continually increased to 30% and 40%, the compacted bentonite was in a saturation state, and the corrosion rate of NiCu steel was significantly decreased. This was because most pores among the bentonite particles were occupied by a large amount of free water, which hindered the diffusion of oxygen and inhibited its cathodic reduction. Furthermore, it restrained the oxidation of ferrous corrosion products, which greatly weakened the cathodic depolarization of rust, leading to the cathodic process being dominated by the hydrogen evolution reaction.

Application of ANN Concepts for Prediction of Crack Growth and Remaining Life of Circumferentially Cracked Piping Components under Different Loading Scenarios

This paper presents the details of Artificial Neural Network (ANN) based models to predict crack depth and remaining life of circumferentially part-through cracked piping components used in the nuclear industry. Crack growth data from experimental studies on (i) straight pipes made up of SA 312 Type 304LN stainless steel having part-through circumferential notch under combined bending and torsion and (ii) dissimilar metal pipe weld joints having circumferential through-wall crack in the weld were used. The dissimilar metal pipe weld joint is made up of SA312 Type 304LN austenitic stainless steel and SA508 Gr. 3 Cl. 1 low alloy carbon steel and joined by Nickel-rich Inconel alloy weld. About 75% of the mixed experimental data has been used for development of model and the remaining data for validation. For the development of ANN model, (i) back propagation technique (ii) sigmoidal transfer functions and (iii) Levenberg-Marquardt algorithm are used. The maximum percentage difference observed between the predicted and the experimental results for crack depth and remaining life was 19.59% and 15.78% respectively. The efficiency of the developed model was verified using several statistical parameters. The developed models are useful for the structural integrity assessment of piping components under different loading scenarios.

Non-destructive ultrasonic measurement of residual stress in metallic materials

<p>The relationship between the applied stress σ, and the measured shear wave birefringence <b>B</b> was measured in the laboratory for several low alloy steel. The birefringence response was measured with a dual polarization electromagnetic transducer comparing the time of flight for the two polarizations, in the rolling direction and the transverse direction. This stress-birefringence relationship showed a linear dependence and can be described with the relation σ = <b>K</b> * <b>B</b> + σ<sub>0</sub>. The slope of this relationship when applying a tensile stress in the transverse direction of the sample, <b>K</b>, was measured to − 1280 MPa/<b>B</b>(%) and was independent of material chemistry, whereas the position/offset of the curves, i.e., σ<sub>0</sub> , varied in between steel grades, assumed to be due to microstructural texture. A non-contact EMAT probe has been installed in a levelling mill at SSAB Special Steel in Oxelösund, Sweden, to measure the residual stress dependence on the levelling process, in daily production of steel plates. The EMAT probe has been provided by Nordinkraft AG, Remchingen, Germany. This single EMAT probe has been applied along the centerline of plates. Measurements have been made on more than 2000 plates. The responsive or reactive residual stress was successfully measured and calculated for all plates using the above stress-birefringence relationship, showing typical residual stress difference values on the production plates after levelling in the range of less than ± 100 MPa.

Investigation of Lanthanum Content on Nonmetallic Inclusions and Mechanical Properties of Low Alloy Wear-Resistant Steel Containing P and As Elements Through In Situ Tensile Test

Investigation of Lanthanum Content on Nonmetallic Inclusions and Mechanical Properties of Low Alloy Wear-Resistant Steel Containing P and As Elements Through In Situ Tensile Test

Experimental Study on Enhancement in the Tribological Behaviour of Military Grade Lubricant Using Titanium Dioxide Nanoadditives for Aerospace Applications

ABSTRACTThe coefficient of friction of low carbon chromium alloy steel with military grade lubricant was high, resulting in increased heat generation and temperature rise of the lubricant in the aircraft power transmission units such as engine gearbox, accessory gearbox and so on. To address this, the current research proposes the addition of TiO2 nanoparticles to MIL grade lubricant as an additive to enhance the tribological performance. In this experimental study, TiO2 nanolubricant was prepared using various surfactants for better suspension of TiO2 nanoparticles, and properties were evaluated for both base lubricant and nanolubricant. The tribological experiments were conducted using a four ball tester, a shear stability tester and a reichert tester. In a four ball test, TiO2 nanolubricant resulted in a 27.3% reduction in wear scar diameter by the addition of TiO2 nanoparticles to the base lubricant. In a shear stability test, TiO2 nanolubricant showed 80% better shear stability than the base lubricant. In the reichert test, the coefficient of friction was reduced by 13% with the TiO2 nanolubricant. The experimental findings demonstrated that the TiO2 nanoparticles, as an additive to a military grade lubricant, have superior tribological properties for aerospace applications.

Synergism of Computational Simulation Technique and Machine Learning Algorithm for Prediction of Anticorrosion Properties of Some Antipyrine Derivatives.

This study aimed to predict the selected antipyrine compounds' inhibitory efficiencies and anticorrosion properties in a hydrochloric acid (HCl) environment. Molecular descriptors and input variables were obtained using density functional theory (DFT), and the variance inflation factor (VIF) was employed to reduce redundant variables, leading to the selection of seven quantum chemical descriptors as input variables. Using machine learning techniques such as K-nearest neighbor (KNN) and artificial neural network (ANN), a predictive model was built for 39 antipyrine compounds with known corrosion inhibition efficiencies for carbon and low alloy steel in hydrochloric acid solutions. The models' predictive capability was assessed using cross-validation, with the ANN model showing superior performance, achieving a coefficient of determination (R2) value of 0.715 compared to 0.548 for the KNN model. Performance metrics such as the mean square error (MSE), mean absolute error (MAE), and root-mean-square error (RMSE) further confirmed the superiority of the ANN model over the KNN model. The corrosion inhibition efficiencies (CIEs) of the selected antipyrine compounds ranged from 68.78 to 99.79%, with compound A1 demonstrating the highest CIE of 99.79% and compound A3 the lowest, as evaluated by the ANN model. Analysis of Fukui index parameters obtained from the Mulliken population analysis suggested that the nucleophilic and electrophilic sites play a crucial role in the interactions between the inhibitor and the metal atom through electron donor-acceptor interactions. Moreover, the energy of adsorption (Eads) in kcal·mol-1 decreased in the order of A1 (-187.8) > A2 (-132.0) > A2 (-84.4), with the high negative value of Eads indicating strong and spontaneous adsorption. Further analysis using radial distribution functions and molecular dynamics simulations revealed that inhibitor A1 exhibited predominantly chemisorption, inhibitor A2 showed a mixed type, and inhibitor A3 demonstrated predominantly physisorption, aligning well with the results of the predictive studies.

Evolution of carbides and Charpy toughness in a low alloy bainitic steel during step-up aging process

The low alloy bainitic steel used in reactor pressure vessels deteriorates during thermal service while the macroscopic thermodynamic parameters that cause thermal aging remains unknown. In this work, a thermal aging restructuring scheme was proposed by step-up aging the steel from 350 °C to 490 °C, with a total duration of 7500 hours. Samples from varied thickness of the steel were characterized in terms of carbides evolution and Charpy impact toughness at 20 °C. The carbide size and its fraction were statistically analyzed showing partial coarsening and dissolution during aging, while the carbide fraction was found linearly correlated with the impact energy for the first time. The critical transition temperature parameter of the aging process was found to be 470 °C for the steel. The macroscopic thermodynamic parameters, including the thermal aging time and temperature, facilitate a comprehensive understanding of the material degradation mechanism and provide a basis for long-term safety of equipment.

On the role of the retained porosity on the shock response of additively manufactured high-performance steel: Experiments, constitutive model and finite-element predictions

Experiments have shown that for quasi-static and moderate strain-rates (of the order of 102–103/s) the mechanical response of additively manufactured (AM) and traditionally processed high-strength steels is similar whereas the impact behavior is markedly different. In this paper, we reveal that the main reason for this difference is the retained porosity in the AM material. Fully-implicit finite element calculations are presented in which we simulate both the launching of the impact plate and the impact between the two plates. The constitutive model used is the elastic/plastic model for porous ductile materials with matrix displaying tension-compression asymmetry and Johnson-Cook hardening law that accounts for both strain-rate effects and plastic history. It is shown that even a very small initial porosity changes the wave front, decreases the Hugoniot while increasing the shock rise time, when compared to a void free material. Furthermore, quantitative comparisons between simulation results and plate impact data for both the AM and the wrought AF9628 steel are provided. The good agreement show that the model captures the impact response and illustrates the model capabilities to provide information on field variables that cannot be directly measured.Additive manufacturing (AM) of metals is rapidly advancing as a robust method for production of geometrically complex parts. To enhance understanding of material performance and open up additional application opportunities, dynamic characterization of newly printed alloys is required to validate their effectiveness. In this paper, we present results from plate impact testing of AF9628 steel, a newly developed high-strength low alloy martensitic steel for structural applications which require resistance to high-rate deformation. We put into evidence differences in the shock structure between the AM and the traditionally processed material. To gain understanding, we conduct fully-implicit finite element (FE) calculations in which we model both the launching of the impact plate and the impact between the two plates, respectively. An elastic/plastic damage model that accounts for the effects of the tension-compression asymmetry in plastic deformation and its influence on porosity evolution is used. The FE results reveal that even a very small amount of initial porosity leads to an increase in the shock rise time, explaining the observed trends. Furthermore, quantitative comparisons between simulation results and plate impact data for both the AM and the wrought AF9628 are provided. The good agreement show that the model captures the impact response and illustrates the model capabilities to provide information on field variables that cannot be directly measured.

Fatigue life modeling for a low alloy steel after long-term thermal aging

Fatigue failure of materials has a considerable impact on the safety of equipment in service. In this study, axially tensile and low cycle fatigue tests were conducted on a low alloy steel after accelerated thermal aged at 450 °C for 10,000 h. The experimental results indicate that the ultimate and yield strengths increase moderately, while the fatigue life of specimens experience a slight decrease in this circumstance. The fracture analysis demonstrates that the bainite breaking facilitates the fatigue crack initiation and propagation after thermal aging, which is accompanied by a decrease in plastic strain amplitude. Therefore, the plastic strain amplitude is considered as an indicator of thermal aging in fatigue life modeling for the low alloy steel. Finally, a novel life model that incorporates both aging time and temperature was proposed for rapid prediction of low cycle fatigue life. It is assumed that this model promotes reliable fatigue life prediction in low alloy steels under various thermal aging circumstances, as well as the extrapolation of fatigue performance of the material in service.

Verification and Refinement of Local Difference in TC4 Hollow Blade Pressing with Low Melting Point Alloy Mandrel

Verification and Refinement of Local Difference in TC4 Hollow Blade Pressing with Low Melting Point Alloy Mandrel

High Temperature Corrosion Study on NiCr Coated Low Alloy and Mild Steel

Cyclic hot corrosion behaviour of bare and D-gun sprayed NiCr coated low alloy and mild steel sample having dissimilar coating thicknesses viz. 0.2-0.25 mm and 0.25-0.30 mm have been studied in molten salt environment mixture of Na2SO4 - 25wt. % NaCl at temperature of 750 ̊C. Corrosion kinetics were analysed and parabolic rate constants (Kp) for both bare and coated sample were calculated and observed that 0.2-0.25 mm thick NiCr coated specimen showed better resistance against high temperature corrosion for both materials. SEM/EDX analysis was carried out to examine scale formed on the bare and coated sample after hot corrosion.

HyStor: An experimental database of hydrogen storage properties for various metal alloy classes

In this work, we introduce the HyStor database, consisting of 1282 metal alloys along with their maximum hydrogen storage capacity (H2wt%) at a given absorption temperature. The curated HydPark database consist of 831 entries. We sourced compositions from research articles and various patent documents, resulting in addition of 451 compositions to the HydPark database. The addition is reflected in the data across all existing classes of alloys. Further, low entropy alloys (LEA), medium entropy alloys (MEA) and high entropy alloys (HEA) have been newly included classes. This has broadened the scope of the database to encompass the latest materials of interest for hydrogen storage. HyStor contains representation of 54 elements, with a temperature range of 200–800 K, and H2wt% ranging from 0.1 to 7.19. We conducted thorough checks for duplicate entries, erroneous data, and conflicting compositions within the database to ensure data quality. Furthermore, we conducted multiple tests to identify potential outlier compositions. The data curation and updation reflects into slight improved error metrics of the HYST model, reducing the Mean Absolute Error (MAE) from 0.31 to 0.29 and increasing the R2 score from 0.77 to 0.79.

Fabrication of Die Sink Electrochemical Machining Tools Using Low Melting Fusible Alloy and Polymer Based Additive Manufacturing

Fabrication of Die Sink Electrochemical Machining Tools Using Low Melting Fusible Alloy and Polymer Based Additive Manufacturing

Applicability of microcapillary electrochemical droplet cell for monitoring microbiologically induced corrosion

Formed biofilms can induce corrosion of metallic substrates through the secretion of corrosive chemical species, changes in local acidity, and the creation of galvanic oxygen concentration cells. Electrochemical testing is useful to study and monitor the growth of biofilms on metallic substrates. Macroelectrochemical testing gives an average measurement of all the chemical interactions and processes in the sampled area which is typically on the mm2 to cm2 scale. Microcapillary electrochemical droplet cell testing can perform AC and DC electrochemical measurements on the µm2 scale, allowing measurements of local electrochemical processes in the picoampere range. Adapting this technique for use in studying microbiologically induced corrosion could provide high-resolution in-situ characterization of biofilm growth. Low alloy steel coupons were subjected to macro- and microelectrochemical techniques to characterize the influence of microbiological entities on the corrosion process.

Impact of Boron and Titanium on the Mechanical Properties and Recrystallization Behaviour of Low Carbon Cold Rolled and Batch Annealed HSLA Steels

This study investigates the impact of boron (B) on the mechanical properties and recrystallization behavior of cold rolled and batch-annealed titanium (Ti) microalloyed high-strength low-alloy (HSLA) steels. HSLA steels are essential in industries such as automotive and construction due to their superior mechanical properties and cost-effectiveness. The addition of microalloying elements, particularly Ti, has shown significant promise in enhancing these properties through mechanisms like precipitation strengthening and controlled recrystallization. However, the role of B in this context remains underexplored. Here, three alloy compositions were systematically examined: a reference low carbon steel base alloy with no Ti or B (Ref), the base alloy with added Ti (Ref+Ti), and the base alloy with both Ti and B additions (Ref+Ti+B). The findings showed that microalloying with Ti+B can provide excellent strength improvements in the hot rolled strip, mainly due to increased hardenability that promotes the formation of finer ferrite grains with a high dislocation density. However, the recovery and recrystallisation behavior is such that it is not possible to reproduce these benefits after cold rolling and batch annealing, highlighting the complexity of optimizing microalloying strategies for cold-rolled and batch annealed products. The insights gained from this study provide a deeper understanding of the mechanisms governing the recrystallization of Ti and B microalloyed HSLA steels, paving the way for the development of advanced materials with tailored properties for critical applications.

The effect of athermal omega on the transformation behaviour of Ti-24Nb-4Zr-8Sn (wt%)

Ti-Nb based alloys are candidate materials for orthopaedic and orthodontic applications due to a low elastic modulus and superelastic properties. However, many of these alloys are also susceptible to a transformation to the hexagonal ⍵ phase. When ⍵ is formed isothermally it can stiffen and embrittle the alloy, however, there is a limited understanding of the role it plays when formed athermally on cooling, with many conflicting statements made within the literature. As such, this study assesses the role of athermally formed ⍵ on the superelastic behaviour and elastic modulus of the exemplar superelastic alloy, Ti-24Nb-4Zr-8Sn. It was found that the ⍵ phase raised the modulus and the stress required for superelastic behaviour. This highlights the need to design alloys resistant to both forms of the ⍵ phase, for low modulus superelastic alloys to be produced.

Design, preparation and properties of biomedical Ti-Nb quaternary alloys with high strength and low modulus: insights from first-principles calculations

In this paper, we designed and developed biomedical β-type Ti-Nb quaternary alloy materials with high strength and low modulus. Building upon the d-electron alloy design method and the valence electron concentration e/a method, we use a Python program and thermodynamic theoretical parameters to determine a Ti-Nb quaternary alloy with the characteristics of a single-phase solid solution. Subsequently, we engage in theoretical and experimental investigations on the low modulus alloys identified through first-principles calculations. The results show that both Ti7Nb6Zr1Al2 and Ti11Nb2Ta2Al1 maintain a single β phase before and after cold rolling, which is related to the strong electronic density of states of s and p orbitals at low energy levels in the crystal structure of the two alloys. Ti11Nb2Ta2Al1 has a strong charge distribution on the (001) crystal plane, which causes a large amount of internal stress under large deformation conditions to promote grain crushing and weaken the intensity of the (001)[1-10] texture in the ODF diagram of 2 = 45°. The cold-rolled Ti11Nb2Ta2Al1 exhibits better corrosion resistance and biocompatibility than the cold-rolled Ti7Nb6Zr1Al2, and the good biocompatibility is related to the strong covalent bond between Al and Ta that inhibits the diffusion of Al ions. 90% cold-rolled Ti11Nb2Ta2Al1 stands out as an exceptionally promising orthopedic implant material due to its high elastic allowable strain (ReH/E), good corrosion resistance and biocompatibility.

Modeling of Dynamic Recrystallization Kinetics of a High Strength Low Alloy Steel During Hot Rolling

Modeling of Dynamic Recrystallization Kinetics of a High Strength Low Alloy Steel During Hot Rolling