Search Results (41)

As part of a comprehensive study on eco-friendly processing techniques, the influence of the heat treatment environment on the case hardening of AISI 1018 steel using pulverized cassava leaf was studied. The process was carried out at two different temperatures (850 °C and 950 °C) and under three environmental conditions: Process 1, the control experiment, was carried out in air only; in Process 2, the medium comprised pulverized cassava leaves; and in Process 3 a combination of pulverized cassava leaves plus barium carbonate (BaCO₃) was used as an energizer (CBC mixture). Vickers microhardness testing and scanning electron microscopy were used to evaluate the effect of the processing environment on the case hardening of the steel. As expected, regardless of the processing temperature, Process 1 resulted in little or no hardening of the steel surface. However, notable case hardening occurred when the steel specimens were subjected to either Process 2 or Process 3. Furthermore, the inclusion of barium carbonate in Process 3 significantly enhanced the case hardening effectiveness of the cassava leaf in terms of the rate of and maximum hardness achieved. A maximum enhancement was observed at 950 °C. After 1 h, the increase in hardness was 160% and 280% for Process 2 and Process 3, respectively. Upon increasing the processing time to 5 h, the increase in hardness due to Process 2 was raised to 254%, while that of Process 3 remained at approximately 280%. The diffusivity of AISI 1018 was calculated using the microhardness data. The diffusivity was highest in Process 2 samples with values of 1.568 × 10⁻⁹ m²/s at 850 °C and 1.893 × 10⁻⁹ m²/s at 950 °C. Effective case hardening of AISI 1018 steel was carried out using the medium of cassava leaf, without the addition of barium carbonate (BaCO₃) as an energizer. Full article

Integrated computational materials engineering (ICME) is emerging as an increasingly powerful approach to integrate computational materials science tools into a holistic system and address the multiscale modeling challenges in the processing of advanced steels. This work aims at incorporating macroscopic model (finite element-based thermal model) and microscopic model (CALPHAD-based microstructure model), building an industry-oriented computational tool (MICAST) for casting of steels. Two case studies were performed for solidification simulations of tool steel and stainless steel by using the CALPHAD approach (Thermo-Calc package and CALPHAD database). The predicted microsegregation results agree with the measured ones. In addition, two case studies were performed for continuous casting and ingot casting with selected steel grades, mold geometries and process conditions. The temperature distributions and histories in continuous casting and ingot casting process of steels were calculated using in-house finite-element code which is integrated in MICAST. The predicted temperature history from the casting process simulation was exported as input data for the DICTRA simulation of solidification. The resulting microsegregation by the DICTRA simulation can reflect the microstructure evolution in the real casting process. Current computational practice demonstrates that CALPHAD-based material models can be directly linked with casting process models to predict location-specific microstructures for smart material processing. Full article

A promising approach for producing parts with outstanding properties in directed energy deposition (DED-LB/M) provides the application of tailored powder mixtures processed by applying in situ alloying strategies. In this work, DED-LB/M was used to manufacture multilayer specimens from AISI H11 steel powders enriched with carbon nanoparticles (C-np) in concentrations of 0.1 wt.-% and 0.2 wt.-%. The scientific aim was to investigate the impact of C-np on the microstructural (particularly retained austenite content (RA-c) and grain size) and mechanical properties (specifically hardness and compression yield strength) of the manufactured specimens. It was shown that the addition of C-np to the H11 powder leads to a stronger distortion of martensite as well as significantly enhancing the RA-c. Furthermore, the C-np seem to favor the formation of finer martensite, as can be verified with XRD and EBSD. Under as-built conditions, the mean hardness increases from 653 ± 10 HV1 for the H11 sample to 770 ± 14 HV1 for the sample reinforced with 0.2 wt.-% C-np. At the same time, Y_0.2% rises up from 1839 ± 61 MPa to 2134 ± 68 MPa. The hardness- and strength-increasing effect of the added C-np is retained even after heat treatment, similarly to the industrial standard. Full article

This article presents a novel and feasible approach for researching the quantity of the ceramic phase and component optimization in high-temperature titanium alloys with small trace amounts of ceramic phases. Different near-α titanium alloys with varying yttrium and boron contents were prepared through the utilization of a vacuum non-consumable arc furnace melting method. The alloy used was a Ti-5.9Al-4Sn-3.9Zr-3.8Mo-0.4Si base. Its microstructure, texture, mechanical properties, and fracture behavior were studied. The observation of the as-cast structure shows that the addition of different doses of trace Y and B elements significantly refines both the original β grains and α grains. Moreover, the addition of the B element transforms the Widmanstätten structure in the titanium alloy structure into a basketweave structure. The addition of Y can refine the grain structure, improve the uniformity of the matrix structure, and act as a strong deoxidizer, which will take away the oxygen in the matrix and purify it. The TiB whiskers generated with the addition of B promotes dynamic recrystallization behavior and leads to more equiaxed α grains being precipitated around them, resulting in a significant refinement of the microstructure of the as-cast alloy. After adding a small amount of B, the texture strength of the α phase is significantly reduced, indicating that TiB whiskers inhibit the formation of texture. After conducting performance screening and structure analysis, the study supplements the analysis of Y’s regulation of the titanium alloy structure. The regulation is primarily explained by combining the results of the analysis of boron content, phase diagram analysis, mechanical properties, and fracture analysis. The mechanical analysis introduces the unique load transfer strengthening of TiB whiskers combined with an analysis of high-temperature mechanical properties, as the threshold for addition. The optimal amounts of Y and B additions are 0.6 wt% and 0.8 wt%, respectively. The optimized alloy obtained under this condition can achieve a tensile strength of 950 Mpa at 500 °C without any plastic deformation or heat treatment. Full article

Ultrasonic-assisted Ti6Al4V Directed Energy Deposition (DED) additive manufacturing technology can improve the problem of uneven microstructure caused by laser heating and sudden cooling of the molten pool. In this paper, the numerical analysis and experimental verification methods were adopted. The influencing factors, such as the cavitations’ effect, sound flow enhancement effect, and sound flow thermal effect related to the ultrasonic assistance in the molten pool, were analyzed. After equating the energy of the ultrasound, the model of additive manufacturing was introduced in the form of a heat source. The temperature gradient changes during the solidification process of the molten pool with the addition of ultrasound assistance and the effect of ultrasonic vibration during the manufacturing process on its deposited state and microstructure of solution-aged formed parts were studied. The results showed that when the wire feeding rate is 5 mm/s and the laser scanning speed is 5 mm/s, the optimal laser power is 1000 W~1100 W, corresponding to the optimal ultrasonic amplitude of 120 μm. Then, by comparing the temperature field with the same amplitude of 0 μm (i.e., no ultrasonic vibration) and the microstructure of the formed parts, it was verified that ultrasonic vibration facilitates fluid flow in the molten pool, which could lead to a more uniform temperature distribution. This optimized approach not only enhances the understanding of the process but also contributes significantly to the advancement of related research endeavors. Full article

The solubility of lanthanum in indium and Ga–In alloys containing 21.8, 40 and 70 wt. % In was determined experimentally at temperatures up to 1081 K. The low temperature limit depended on the melting point of the alloy. The solubility was measured using isothermal saturation and high-temperature filtration methods. The phase composition of solid intermetallic compounds formed in the ternary La–Ga–In systems of various compositions was determined by X-ray diffraction. Activity coefficients of lanthanum in the alloys based on gallium, indium and three Ga–In mixtures (21.8, 40 and 70 wt. % In) were calculated. Temperature dependencies of thermodynamically possible separation factors for the uranium/lanthanum couple in “LiCl–KCl–CsCl melt–liquid alloy” systems were derived for various gallium–indium alloys. Full article

In pressurized water reactors (PWRs), flow-induced vibration (FIV) induces the fretting wear of fuel rods and supporting grids, and the process is accompanied by corrosion, which is called fretting corrosion. In this paper, fretting corrosion experiments were carried out in a simulated cladding service environment, and the fretting corrosion performance of AlCrNbSiTi coating cladding, Cr coating cladding and uncoated cladding with the supporting grids were investigated using a three-dimensional white light interferometer and a scanning electron microscope (SEM). The results showed that the AlCrNbSiTi coating cladding has the strongest fretting corrosion performance, the Cr coating cladding has the second best fretting corrosion performance and the uncoated cladding has the worst fretting corrosion performance. The coating also changes the wear mechanism of the cladding and improves the corrosion resistance of the cladding, which is responsible for the improvement in the fretting corrosion performance of the cladding. By comparing the AlCrNbSiTi coating with the Cr coating, it was found that the AlCrNbSiTi coating has a better fretting corrosion performance than the Cr coating due to its higher hardness and stronger corrosion resistance. Full article

Al–Mg–Si alloys are used in aircraft, train, and car manufacturing industries due to their advantages, which include non-corrosivity, low density, relatively low cost, high thermal and electrical conductivity, formability, and weldability. This study investigates the bulk mechanical properties of Al–Mg–Si alloys and the influence of the Si/Mg ratio on these properties. The Al cell was used as the starting structure, and then nine structures were modeled with varying percentages of aluminium, magnesium, and silicon. Elastic constant calculations were conducted using the stress–strain method as implemented in the quantum espresso code. This study found that the optimum properties obtained were a density of 2.762 g/cm³, a bulk modulus of 83.3 GPa, a shear modulus of 34.4 GPa, a Vickers hardness of 2.79 GPa, a Poisson’s ratio of 0.413, a Pugh’s ratio of 5.42, and a yield strength of 8.38 GPa. The optimum Si/Mg ratio was found to be 4.5 for most of the mechanical properties. The study successfully established that the Si/Mg ratio is a critical factor when dealing with the mechanical properties of the Al–Mg–Si alloys. The alloys with the optimum Si/Mg ratio can be used for industrial applications such as plane skins and mining equipment where these properties are required. Full article

The paper is a personal perspective on the design of metallic ultra-high temperature materials (UHTMs). Specifically, the alloy design “landscape” of metallic UHTMs was considered from the viewpoint of the alloy design methodology NICE. The concepts of synergy, entanglement and self-regulation and their significance for alloy design/development were discussed. The risks, ecological challenges and material-environment interactions associated with the development of metallic UHTMs were highlighted. The “landscape” showed that beneath the complexities of alloy design lies an elegant and powerful unity of specific parameters that link logically and that progress can be made by recognising those interrelationships between parameters that generate interesting, diverse, and complex alloys. Full article

Case-hardening steels are gaining increasing interest in the field of laser powder bed fusion (PBF-LB/M) due to their excellent weldability. In combination with post-process carburization heat treatment, the surface properties can be improved to generate high-strength products. When manufacturing larger products by means of PBF-LB/M, the in situ heat accumulation and the altered cooling rates affect the resulting material properties. Therefore, the fabrication of larger products requires an understanding on the influencing factors that affect the material properties. This work investigates the effect of different volumetric energy densities (VED) on the resulting microstructural and mechanical properties. It is found that the hardness decreases continuously along the build direction. The gradient depends on the applied energy and is stronger for higher energy inputs due to heat accumulation and lowered cooling rates. Furthermore, countering strategies are investigated to avoid process-specific hardness reduction along the build direction. This includes a reduced number of parts within the build job as well as a modified inter-layer time (ILT) between consecutive layers of the specimen. Applying a moderate inter-layer time helps to counter process-specific overheating, which is indicated by an almost homogeneous material hardness and melt pool size along the build direction. Full article

This article presents the results of studies of the self-propagating high-temperature synthesis (SHS) for obtaining zirconium alloys with niobium by the method of calcium-thermal reduction of nuclear-grade zirconium tetrafluoride in the presence of niobium powder. The optimal heating temperature of the initial charge and the methods of charge mixture with different calcium content were determined. The safety of the SHS process is ensured by the formation of an optimal combustion front of the mixture to remove the released high-pressure gases. A setup for the furnace reduction of zirconium alloys with charge preheating, discharge of molten products into molds of various designs, and control of the time and rate of slag and alloy crystallization has been tested. The required performance of the installation, the degree of transition of zirconium from salt into the alloy, and the purity, structure, and uniformity of the alloy were achieved. Full article

A systematic study of the phase composition of quenched binary titanium alloys with d-metals of groups 5–11 from periods four to six was carried out using the methods of X-ray diffraction analysis. It was found that the formation of the orthorhombic α″-phase depends on the position of the alloying metal in the periodic table. The formation of the α″-phase occurs only in the systems Ti-V, Ti-Nb, Ti-Mo, Ti-Ru, Ti-Ta, Ti-W, Ti-Re, Ti-Os and Ti-Ir, and in other systems, it does not occur. It was found that the critical parameter for the formation of the α″-phase is the difference in the size of titanium atoms and those of the alloying metal {(r_Ti − r_Me)/r_Ti 100%}. The formation of the α″-phase occurs only in systems where this value is lower than 9 at.%. Full article

Laser materials processing includes rapid heating to possibly high temperatures and rapid cooling of the illuminated materials. The material reactions can show significant deviations from equilibrium processing. During processing of complex materials and material combinations, it is mainly unknown how the materials react and mix. However, it is important to know which chemical elements or compounds are present in the material to define the alloy. In addition, their distribution after rapid cooling needs to be better understood. Therefore, such alloy changes at rapid heating induced by laser illumination were created as pre-placed and pre-mixed powder nuggets. The energy input and the material ratio between the powder components were varied to identify characteristic responses. For the detection of reaction durations and mixing characteristics, the vapor plume content was assumed to contain the necessary information. Spectral measurements of the plume were used to identify indicators about process behaviors. It was seen that the spectral data give indications about the chemical reactions in the melt pool. The reactions of iron ore components with aluminum seem to require laser illumination to finish completely, although the thermite reaction should maintain the chemical reaction, likely due to the required melt mixing that enables the interaction of the reacting partners at all. Full article

Instead of a number of different approaches or a formal description of experimental data, a unified approach is proposed to consider failure and deformation as thermodynamic processes. Mathematical modeling of the processes is carried out using rheological models of the material. Parametric identification of structural models is carried out using minimal necessary experiments. Based on results of these experiments, the scope of applicability conditions for this material and test modes necessary for parametric identification of models are selected. One fracture criterion is used that formally corresponds to the achievement of a threshold concentration of micro-damage in any volume of the material. Calculations of durability under conditions of varying temperature and variable loads are based on the relationship of plastic flow and failure processes distributed over the volume of the material. They are performed numerically over time steps depending on the ratio of the rate of change of temperature and stresses. Full article

In this work, the influence of heat treatment on the corrosion resistance of shape memory stainless steel based on FeMnSiCrNiCo was evaluated. Deformed samples were annealed from 250 °C to 1050 °C for 1 h. Scanning electron microscopy (SEM-EDS) and a Vickers microhardness test were used to characterize the microstructure. Thermal analysis was performed to identify phase transformations. Corrosion resistance was evaluated in an electrochemical test in a 3.5% NaCl solution. FeMnSiCrNiCo in the deformed state had better corrosion resistance compared to other conditions. However, as the annealing temperature increased, the corrosion resistance decreased due to the formation of precipitates. Full article