Heat Treatment Regimes Research Articles

OPTIMIZATION OF HEAT TREATMENT REGIME FOR A NEW BIODEGRADABLE Mg-Zr-Nd ALLOY WITH ENHANCED MECHANICAL PROPERTIES

Purpose. To develop a rational heat treatment regime for a new biodegradable magnesium alloy of the Mg-Zr-Nd system, to ensure enhanced mechanical properties throughout the entire treatment period. Research methods. Differential thermal analysis (DTA) was used to determine phase transformation temperatures. Microstructure analysis was conducted using optical microscopy (“Neophot 32” and “OLYMPUS IX 70”) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SELMI RЕМ-106I). Mechanical properties were determined using an INSTRON 2801 testing machine. The influence of cooling rate on microstructure and properties was studied using ProCAST simulation software. Heat treatment was carried out in a Bellevue type shaft furnace and a PAP-4M furnace. X-ray analysis was used to detect internal defects in samples. Results. A new heat treatment regime was developed for the biodegradable Mg-3.15Nd-1.25Zr-0.6Zn (wt%) alloy. Using differential thermal analysis and microstructure studies at various quenching temperatures, the optimal quenching temperature was established at 560 °C. Empirical relationships describing the influence of heat treatment parameters on the alloy's microstructure were calculated. The new heat treatment regime (quenching from 560 °C for 8 hours, air cooling + aging at 200 °C for 16 hours) resulted in improved mechanical properties (UTS = 276–282 MPa, δ = 5.2–5.8%) compared to the standard T6 regime. Scientific novelty. For the first time, a comprehensive study of the influence of heat treatment parameters on the structure and properties of a new Mg-3.15Nd-1.25Zr-0.6Zn (wt%) alloy with increased content of alloying elements was conducted. New dependencies describing the influence of quenching temperature on the alloy's grain size were established. Practical value. A new heat treatment regime for the biodegradable magnesium alloy was developed, which ensures complete dissolution of the pseudoeutectic phase and formation of strengthening phases, resulting in improved mechanical properties compared to the standard alloy Mg-2.5Nd-0.4Zn-0.5Zr (wt%) and the standard T6 regime.

The first CICC-type Bi-2212 insert coil for high-field applications up to 20 T

Abstract As the need for high-magnetic field magnets, this article made the first cable-in-conduit conductor (CICC) -type Bi-2212 insert coil. The Bi-2212 conductor consists of 24 wires, an Ag tube, and a 316 LN jacket. With the optimized heat-treatment regime, the insert coil exhibited excellent current-carrying capacity under magnetic fields up to 20 T: the Ic of the coil was up to 5.4 kA under 20 T backfield. With the ‘Pre-OP before cabling’ process, the void fraction was precisely controlled. Besides, the insert coil exhibits excellent stability with the electromagnetic loads and quenching process: no obvious change in performance was detected even when the electromagnetic loads increased to 101 kN m−1; after the quench event where the voltage on the insert coil was up to ∼4000 times criterion, no degradation was detected. The excellent performance of the Bi-2212 insert coil gives a solid foundation for the development of full-size Bi-2212 CICC for high-field applications.

Optical properties and energy transfer of Tm3+ single-doped and Tm3+-Tb3+ co-doped transparent glass-ceramics containing NaGd(MoO4)2 single phase

Tm3+ single-doped and Tm3+-Tb3+ co-doped SiO2–B2O3–Na2O–ZnO–MoO3-Gd2O3 glasses were successfully prepared by the melt-quenching process. X-ray diffraction and transmittance measurements were used to determine that the optimal heat treatment regime consisted of crystallization at 620 °C for 5 h and transparent glass-ceramics containing the NaGd(MoO4)2 single phase were obtained. The characterization results by SEM confirmed that the size of the crystals precipitated in the glass matrix was on the nanometer level. The effects of different contents of Tm2O3 on the luminescent properties of glass-ceramics in this system were explored. The results showed that the emission peak at 453 nm (1D2→3F4) had the highest intensity when Tm2O3 was doped with 0.5 mol% under the wavelength at 359 nm excitation. In addition, with the gradual increase of Tb2O3 contents, the luminescence colour of the Tm2O3–Tb2O3 co-doped glass-ceramics gradually shifted from blue to green. This indicates its potential application in blue-green light display technologies and various other areas. The experimental results of the water resistance stability of the samples show that the co-doped glass-ceramic still has good luminescence stability after being immersed in water, which provides further favourable support for its application.

Crystallization behaviour, structure, and photocatalytic properties of SiO2-B2O3-Li2O-WO3-Bi2O3 glass-ceramics containing Bi2WO6 crystals

SiO2-B2O3-Li2O-WO3-Bi2O3 system parent glass was prepared by the melt-quenching method and glass-ceramics containing the Bi2WO6 crystals were obtained by a one-step heat treatment. The crystallization kinetics of the parent glass were investigated, and the effect of the different heat-treatment regimes on the microscopic morphology and optical bandgaps of the glass-ceramics was discussed. The results show that the crystallization activation energy of the parent glass is about 300 kJ/mol and the precipitated Bi2WO6 crystals exist in a columnar structure. As obtained from the UV-Vis spectra, the glass-ceramic with a heat treatment regime of 640 °C/2 h has the smallest optical bandgap (2.45 eV). During the photocatalytic degradation of methylene blue dye, the glass-ceramic with a heat treatment regime of 640 °C/2 h shows the best catalytic degradation performance, reaching a dye degradation rate of 76% at 120 min. The experimental results indicate that glass-ceramics containing Bi2WO6 crystals have promising applications in the field of sewage treatment.

Scientific and practical basis of cephalopods dehydration processes

Nowadays, it is relevant to solve the problems of adapting optimal resource- and energy-efficient modes to technologies for processing food raw materials. The work is focused on the analysis of the prerequisites to find similar features in the dehydration of food capillary-porous colloidal materials by means of various methods. The authors have studied the patterns of cephalopods dehydration using the example of octopus and squid under different heat treatment regimes. It has been proved that there is only one critical point characterizing the transition from moisture with a lower binding energy to moisture with a higher one, and an equation has been proposed for finding the critical humidity during dehydration of the objects been studied. A generalized mathematical model has been developed to determine the duration of the process at the current moisture content of the food material based on dimensionless similarity criteria characterizing the phenomena been investigated. The dependences of the moisture removal rate for different heat treatment methods of cephalopods are given according to their initial moisture content, the specific surface area of the material and the operating factors that determine the process. The obtained dependencies and patterns open up unique opportunities for labor-saving design in the food industry using rational operating modes of industrial enterprises, optimization of heat treatment processes in general and the creation of energy-efficient equipment new designs.

DEVELOPMENT OF INNOVATIVE TECHNOLOGY AND HARDENING EQUIPMENT FOR THE IMPLEMENTATION OF HARDENING HEAT TREATMENT OF METAL PRODUCTS USING FLUIDIZED BULK MATERIALS (PART 1)

Statement of the problem. One of the main problems faced by a modern enterprise is the search for ways to improve the efficiency of its activities. For the effective functioning of the thermal units of toolmaking industries, the simultaneous availability of heating and quenching devices with different heating and cooling media is required. This explains the desire of manufacturers and scientists to find technological, cheap, environmentally friendly heating and cooling media that can provide the required heat treatment parameters and high quality of the processed parts. The purpose of the article is to analyze the state-of-the-art of hardening thermal (combined) treatment methods using bulk materials as media for volumetric heating and forced cooling of metal products and the design and technological features of hardening devices that can ensure a rational structural state of metal parts of complex geometric shapes with a minimum level of their warping and deformation on the example of using vibro-fluidized bulk materials (in the technical literature, the term vibro-gravity particles of heat is used). Research results. To analyze the results of tests of bulk materials as quenching media for high-alloy steel grades and their effect on the structure and properties of the metal in comparison with the traditional oil quenching regime. To consider the features of quenching devices that use mechanical vibration to produce vibro-s bulk material and the possibility of their use in the implementation of quenching modes (including isothermal) of steel products of complex geometric shapes. Conclusion. The use of fluidized bulk materials in industry as media for volumetric heating and hardening of metal products and the design of devices for their use has been investigated. The advantages of the fluidized bed cooling method for the effective implementation of hardening heat treatment regimes are determined. It is shown that this method of forced volumetric cooling of toolmaking products is rational in terms of various indicators. The structural and technological parameters of devices for its implementation are analyzed, which can consistently provide the required level of properties of alloyed and high-alloy tool steels with a minimum level of warping and deformation.

Microstructure evolution in A356 alloy subjected to controlled heat treatment regimes processes

Aluminium–silicon alloys are highly regarded for their lightweight and unique mechanical properties, making them crucial for various industrial applications. Achieving optimal mechanical behavior in Al-Si-based alloys necessitates meticulous control over their microstructure. The research investigated the impacts of heat treatment regimes on the microstructure of A356 hypoeutectic alloys by light optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectroscope (EDS). The alloy, produced via stir-casting, underwent homogenization at 540 °C/5 h, one-step (200 °C for 0.5–8 h (T1)) and two-step (T2 (200 °C/0.5 h/180 °C/0.5–8 h)), and T2L (200 °C/0.5 h/160 °C/0.5–8 h)) aging processes. The findings revealed significant microstructural changes due to heat treatment. Homogenization reduced the average grain size of eutectic silicon by 20.5%. The T1 treatment increased the grain size and changed the grain morphology with prolonged aging, negatively impacting the mechanical properties. The T2 and T2L treatments resulted in finer, more uniform grain structures. The T2L treatment produced the finest eutectic silicon and the most uniform grain distribution, indicating the superior potential for mechanical performance. Overall, this study underscores the importance of tailored heat treatment regimes to optimize the microstructure and enhance the structural sensitive properties of Al-Si alloys, benefiting automotive and aerospace industries.

Investigation of the impact of non-magnetic Si element addition and heat treatment on the electromagnetic wave absorption properties of medium entropy FeCoNiSi alloy particles

Based on chemical liquid phase reduction and high temperature annealing, the effects of non-magnetic Si element addition and heat treatment regime on the microstructure, magnetic properties, and electromagnetic wave absorption properties of medium entropy alloy particles FeCoNiSi were studied. The results show that the prepared Fe1Co0.8Ni1Six alloy particles have a spherical structure, and with the increase of Si content, the particle size continuously decreases, with the average particle size decreasing from 150 to 200 nm to 20-50 nm. After high temperature annealing, the alloy particles undergo some agglomeration and growth. The as-prepared Fe1Co0.8Ni1Six alloy particles exhibit an amorphous state, and crystallization occurs during high temperature annealing, but the increase in Si element content has a certain inhibitory effect on the crystallization of the alloy particles. With the increase of Si element content and annealing temperature, the specific saturation magnetization intensity of the material shows a decreasing trend, while the residual magnetism and coercivity show an increasing trend. With the increase of Si element content, the real and imaginary parts of the permeability change alternately in different frequency ranges. The magnetic loss mechanism for the three alloy particles was eddy current loss in the frequency ranges of 10-14GHz and 16.5-18GHz. With the increase of Si element content, the magnetic loss shows an increasing trend, and the impedance matching shows a decreasing trend. The Fe1Co0.8Ni1Si0.5 alloy particle sample has the maximum reflection loss |RLmax| of 28.2 dB at thickness of 2.3 mm, and the Fe1Co0.8Ni1Si0.7 alloy particle sample has an effective absorption bandwidth of 1.7GHz at thickness of 1.9 mm. Eddy current loss was the main magnetic loss mechanism for Fe1Co0.8Ni1Si0.6 alloy particles under 400 °C and 600 °C annealing conditions, and for Fe1Co0.8Ni1Si0.7 alloy particles under 600 °C annealing conditions. With the increase of annealing temperature, the fluctuation of dielectric loss with frequency decreases in the low frequency range, and increases in the high frequency range, while annealing reduces the fluctuation of magnetic loss with frequency. Under 400 °C annealing conditions, the attenuation constant of the three alloy particles was lower than that of the unannealed alloy particles, and under 600 °C annealing conditions, the attenuation constant of Fe1Co0.8Ni1Si0.5 alloy particles in the frequency range of 6-15GHz was higher than that of unannealed and 400 °C annealed alloy particles, and that of Fe1Co0.8Ni1Si0.6 alloy particles in the frequency range of 7-14GHz was higher than that of unannealed and 400 °C annealed alloy particles. High temperature annealing was not able to effectively improve the impedance matching performance of Fe1Co0.8Ni1Six alloy particles. The maximum reflection loss |RLmax| of Fe1Co0.8Ni1Si0.6 alloy particles under 600 °C annealing conditions was 37.8 dB.

Isothermal β grain growth kinetics and mechanical properties of Ti-351 titanium alloy

The Ti-3.6Al-5.2Mo-4.6Cr-4.7 V-0.7Fe (Ti-351) alloy was developed based on the d-electron theory and the β grain growth behavior during isothermal heat treatment (IHT) was investigated. The nanoindentation analysis of β grain and the tensile properties with different IHT states were carried out. The results showed the grain coarsening temperature of Ti-351 alloy is 850 °C. The grain growth activation energy Q of 75.11–133.92 kJ/mol and the grain growth exponents n of 0.28–0.33 were calculated, indicating a competition between alloy atom diffusion and grain boundary migration. Due to the enhanced diffusion of solute atoms and lower substructure density at higher IHT temperature and longer holding time, the hardness and creep stiffness of β grain would decrease as indicated by nanoindentation test, while the total work W and the plastic deformation work Wp would increase, suggesting an improved toughness of the alloy. In order to achieve full recrystallization of β grains and a better balance between tensile strength and plasticity at room temperature, it is recommended to select a solution heat treatment regime at 850–900 ℃ for 2–4 h.

Effect of post-deposition heat treatments on the microstructure and tensile properties of wire-fed electron beam directed energy deposition GH4169 Ni-based alloy

The microstructure and tensile properties of GH4169 alloy fabricated by wire-fed electron beam directed energy deposition (EB-DED) were investigated in both as-deposited (As-Dep) and homogenization plus double aging heat treatment (HA) condition. The results show that thermal cycling caused an aging effect in the As-Dep samples, resulting in the precipitation of the γ’/γ” phases in close proximity to the Laves phase. The dissolution behavior of Laves phase in GH4169 alloy at various homogenization heat treatment temperatures and holding times was studied. Based on experimental results and Johnson-Mehl-Avramie-Kolmogorov (JMAK) analysis, the dissolution activation energy of Laves phase was calculated as 218.2 kJ/mol. The heat treatment regime utilized in HA treatment consisted of 1150 °C × 60 min/WC + 720 °C × 8 h/FC to 620 °C × 8 h/WC. After HA treatment, most of the Laves phases were dissolved and the γ’/γ” phases were precipitated. The mechanical properties of HA samples are superior to those of As-Dep samples. The morphology, distribution and evolutionary mechanism of the Laves phase, γ’/γ” phases are discussed and analyzed.

Підвищення тріщиностійкості чавунів з кулястим графітом та їх термічна обробка при виготовленні зносостійких виробів

Methods of achieving the maximum values of crack resistance of Spheroidal graphite cast irons (SGCI) due to the combination of strength of bainite with high plasticity of residual austenite (in the amount of 30-35%) are considered. The results of such studies are suitable for use, in particular, in the manufacture of teeth or crowns of buckets of excavators and other working bodies of mining, earthmoving or earth-moving machinery, as well as parts that function in extreme conditions. These data are comparable to the known results of work on increasing the wear resistance of SGCI for variable parts of agricultural machinery and transport. In addition to crack and wear resistance, the long-term performance and efficiency of the working organs depends on maintaining their pointed part or blade in a sharp condition. The creation of functional-gradient materials, which are characterized by the effect of self-sharpening during their operation and wear, is considered. This effect is proposed to be implemented through the use of gradient heat dissipation in the material of the sand mold, increasing these values by introducing a refrigerant near a specific surface of the casting to accelerate its cooling. For this, casting molds made of loose sand were used in the Lost Foam casting (LFC) process. The method of manufacturing metal working bodies is described on the example of casting by the LFC method of an excavator bucket tooth, it is proposed to obtain its gradient structure according to the regime of heat treatment of castings in a foundry mold due to intensive cooling of its given surface to increase its hardness. At the same time, such conditions were used for the construction and formation of the pattern cluster in the sand, which cause the cooling of the opposite surface to slow down with its lower hardness, which corresponds to the conditions of self-sharpening of the tooth under its operating conditions. Keywords: Spheroidal graphite cast iron, austempering, heat treatment, castings, austenite, Lost Foam casting, bainite.

Effect of heat treatment on microstructure evolution and strengthening-toughening behavior of high-strength Mg-Gd-Y-Zn-Zr alloy fabricated by wire-arc additive manufacturing

Mg-Gd-Y-Zn-Zr alloy is an important lightweight material in the aerospace field. Wire arc additive manufacturing (WAAM) provides a new route to fabricate large Mg alloy components. Here, a Mg-8Gd-4Y–1Zn-0.5Zr (wt.%) alloy was fabricated using WAAM based on the cold metal transfer (CMT) process. Subsequently, a short-time solid solution + aging treatment was designed to tailor the microstructure. In the as-fabricated condition, the microstructure mainly consisted of fine α-Mg, network (Mg,Zn)3(Gd,Y) eutectic phase, and lamellar γ′ basal precipitate. After 500 °C-1 h short-time solid solution, the eutectic phase rapidly dissolved, the long-period stacking ordered (LPSO) phase formed, and the fine grain was maintained. Due to the good deformation capacity of the fine grains and the kinking deformation capacity of the LPSO phase, the ductility was significantly improved from 5.2 ± 0.4% to 15.5 ± 1.1%. After further 200 °C-64 h artificial aging, dense β′ prismatic precipitates formed. Thanks to the synergistic strengthening of the fine grains and β′ prismatic precipitates, a yield strength of 242 ± 4 MPa was achieved. However, the kinking deformation of the LPSO phase was inhibited, resulting in a drastic decrease of ductility to 6.1 ± 0.5%. Overall, the combination of strength and ductility of the CMT-based WAAM-processed Mg-Gd-Y-Zn-Zr alloy under an optimized heat treatment regime can be superior to those of the cast Mg-Gd-Y-Zn-Zr alloys with similar contents of Gd and Y elements. This work can guide further performance optimization for WAAM-processed Mg-Gd-Y-Zn-Zr alloys.

ЗАВИСИМОСТЬ УДАРНО-АБРАЗИВНОЙ ИЗНОСОСТОЙКОСТИ СЛОИСТЫХ КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ ОТ ДЕФОРМИРОВАННОГО СОСТОЯНИЯ РЕЗИНОВОЙ ПРОСЛОЙКИ

It is established that during impact-abrasive testing of layered composite materials made of 40X, P40X and rubber steels, the amount of absorbed energy depends not only on the physical and mechanical properties of the materials, but also on the geometric parameters of the elastic-dissipative layer. The impact and abrasive wear resistance of layered composite materials is 1.5-2 times greater than when using wear-resistant steels. A method for determining the deformed state of a rubber elastic-dissipative substrate of layered composite materials is proposed and the effect of stress and strain intensity on the dissipation operation when testing structural steels for impact and abrasive wear resistance is shown. The influence of the heat treatment regime of the 40X steel working layer on the impact and abrasive wear of the SCM is investigated. The mechanism of destruction of the surface of sintered structural steels during impact and abrasive wear has been revealed.

The Effect of Heat Treatment on the Microstructure and Mechanical Properties of Powder Metallurgy Ti-48Al Alloy

Heat treatment is the critical step in achieving a refined microstructure and enhanced mechanical properties of TiAl-based alloys. This study investigated the influence of heat treatment temperature, cooling method, and heat treatment time on the microstructure and mechanical properties of an extruded powder metallurgy Ti-48Al alloy, and achieved the control of fully lamellar fine microstructures and the enhancement of performance through a simple heat treatment, rather than the traditional approach of homogenization followed by heat treatment. The results indicate that the heat treatment temperature determines the type of microstructure, while the cooling rate dictates the lamellar width. As the heat treatment temperature was increased from the two-phase region to the α single-phase region, the microstructure transitioned from duplex to near lamellar, and the alloy strength initially increased and then decreased, influenced by both the lamellar colony ratio and grain size. A rapid cooling rate (water quenching) induces a non-diffusive massive phase transformation, whereas a slow cooling rate (air cooling) gradually forms α2/γ lamellar colonies. Therefore, a suitable heat treatment regime for the powder metallurgy Ti-48Al alloy was determined to be 1340 °C/5 min/air cooling. The microstructure of the alloy was near lamellar, consisting of lamellar colonies approximately 50 μm and a small number of γ equiaxed grains of about 10 μm. Subsequently, the alloy exhibited a room temperature tensile strength of 784 MPa and a yield strength of 763 MPa, representing improvements of 17.0% and 38.7% over the extruded alloy, respectively. This research provides a reference for establishing a heat treatment process for powder metallurgy TiAl alloys.

STUDY OF ANTIBACTERIAL PROPERTIES OF A TiO2-SiO2-Ag COMPOSITE FILTER ON A GLASS FABRIC BASE

Composite films based on catalytically active forms of titanium dioxide synthesized on the fibrous structure of glass fabric are a promising solution for the creation of antibacterial filters for photocatalytic oxidation of microorganism cells under the influence of light radiation of the visible region of the spectrum. The filter obtained in the present work is a multilayer TiO2-SiO2-Ag composite film bonded to fibres of glass fibre carrier. This material has photocatalytic activity due to the presence of titanium dioxide in the anatase phase, which under the influence of light radiation is able to decompose organic compounds and microorganisms sorbed on the filter surface. Special attention was paid to thermal analysis, as a result of which the optimal mode of step-by-step heat treatment of materials was determined to obtain the required phase composition. The selected heat treatment regime allowed to increase the crystallinity of the anatase phase of TiO2, which significantly affected its optical characteristics such as refractive index and forbidden band width energy. The antimicrobial effect of TiO2-SiO2-Ag/glass material tested as a filter in the air purification process was demonstrated in this work. After applying this material as a filter, it was possible significantly reduce the number of E. coli colonies detected in the filter washes, reaching a level of 125 CFU m-3. This indicates the high oxidative capacity of the filter in relation to microorganisms and confirms its potential for use in the field of photocatalytic air purification. The authors note the possibility of application of the developed material in the field of water purification and surface treatment, which determines the prospects for further research. For citation: Buzaev A.A., Tkachuk V.A., Lyutova E.S., Borilo L.P. Study of antibacterial properties of A TiO2-SiO2-Ag composite filter on a glass fabric base. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 7. P. 63-71. DOI: 10.6060/ivkkt.20246707.7001.

Synthesis of transparent tin-doped indium oxide (ITO)-containing glass-ceramic coating by the sol-gel route for UV/NIR-shielding

Transparent glass-ceramic containing tin-doped indium oxide nano-crystalline phase was synthesized using the sol-gel method. The prepared sol, which was based on sodium aluminoborosilicate glass composition, was applied on soda-lime-silicate glass substrate through the dip-coating technique. Developing such glass-ceramics can offer several advantages, including reducing the total cost of production, enhanced chemical durability and a low-temperature synthesis process. The thermal behavior of the dried gels was investigated using simultaneous thermal analysis (STA), to determine the decomposition temperature of the nitrate salts in the gel, its glass crystallization temperature, and finally to optimize the heat treatment regime and optical properties as well. UV–Vis–NIR spectroscopy of the coated samples after heat treatment at 500 °C for 10 h revealed high visible transparency (T>70%) while indicating significant UV/NIR shielding, i.e. near zero and 10 % transmission, respectively. Phase analysis and crystallization behavior studies were conducted using XRD and FE-SEM to evaluate the morphology and size of the precipitated crystallites. According to the results, the optimum heating program for ITO crystallization was heating temperature and soaking time of 500 °C and 10 h, respectively. The undesirable crystalline phase of InBO3 was precipitated as the main crystalline phase by increasing the heat treating temperature to 550 °C. Furthermore, the glass structure was studied using FTIR spectroscopy demonstrating a highly polymerized glassy network for the coating. The effect of the precursors-to-solvent ratio during the synthesis process on the final optical properties was also investigated.

Prediction of martensite start temperature of steel combined with expert experience and machine learning

ABSTRACT The martensite start temperature (MS) plays a pivotal role in formulating heat treatment regimes for steel. This paper, through the compilation of experimental data from literature and the incorporation of expert knowledge to construct features, employs machine learning algorithms to predict the MS of steel. The study highlights that the ETR algorithm attains optimal prediction accuracy, and the inclusion of atomic features enhances the model’s performance. Feature selection is accomplished by evaluating linear and nonlinear relationships between data using the Pearson correlation coefficient (PCC), variance inflation factor (VIF), and maximum information coefficient (MIC). Subsequently, the performance of machine learning models on unknown data is compared to validate the model’s generalization ability. The introduction of SHAP values for model interpretability analysis unveils the influencing mechanisms between features and the target variable. Finally, utilizing a specific steel type as an illustration, the paper underscores the practical value of the model.

Delayed recrystallization behavior and deformation mechanism of IN738LC alloy prepared by laser powder bed fusion

The design and development of heat treatment regimes adapted to the laser powder bed fusion technology for specific service conditions have become a hot topic of research in the field of additive manufacturing. This paper systematically studies the microstructure changes of the L-PBFed IN738LC alloy, solution heat treated at 1250 °C for various durations (1 h, 3 h, 5 h) and then aged at 850 °C for 24 h. The delayed recrystallization behavior was revealed, and the selective precipitation pattern of the M23C6 carbide on different types of grain boundaries was discussed. Additionally, the tensile deformation mechanism of the alloy before and after heat treatment is clarified. The results indicate that grain boundary migration and transformation are impeded under 1250 °C/1 h conditions due to carbide particle pinning and solute atom segregation during the initial stage of solution treatment, which accounts for the delayed recrystallization behavior, and the microstructure is mainly undergoing recovery. At 1250 °C/5 h, M23C6 carbides selectively precipitate at twin boundaries, accompanied by recrystallization. The samples treated at 1250 °C/1 h exhibit the highest mechanical property (σYS=1305 ± 21 MPa, σUTS=1462 ± 11 MPa, εEL=5.4 ± 0.7 %) owing to the precipitation of γ′ phase and the presence of sub-grain boundaries. The deformation mechanism shows that the as-built samples mainly experience planar dislocations slipping, while the heat-treated samples undergo stacking faults shearing and anti-phase boundary shearing. The dominant mechanism among these is anti-phase boundary shearing.

Complex hydraulic studies of welded pipes with different visco-plastic characteristics

For the first time, complex hydraulic studies of pipes welded according to three different schemes were carried out, which made it possible to combine pipes of different viscosities, which affects the performance of welding joints. It was found that in the experimental temperature range, the zone of thermal influence of the second welding variant has the greatest resistance to the initiation of fractures under shock loading, and the lowest - the first variant. The static strength and ductility of the welded pipe joints of the second and third pipe welding options are approximately equivalent, and the resistance to the initiation of the thermally affected zone in all options is almost the same and not lower than that of the base metal. The results of the performed experimental studies indicate a weak correlation in the area of small values of impact viscosity with the characteristics of resistance to fracture propagation of welding joints in the conditions of full-scale pipe tests. The characteristics obtained from tests of full-thickness DWTT specimens are closer than the Charpy specimens to the actual performance characteristics of the weld joints in the pipe. In particular, it was established that the values of Az (-150C)=0.75 kJ and Ar (-150C)=0.45 kJ provide satisfactory resistance to the initiation and propagation of fractures in welding joints (at the base metal level). These characteristics correspond to KSU-60 = 0.5 MJ/m2, which is close to the impact toughness requirements for the base metal (0.55 MJ/m2). The use of optimal structural materials, that is, materials with high resistance to hydrogen destruction of both the base metal and zones of welding joints subjected to a thermo-deformation cycle of welding. A significant effect can be achieved by technological measures that will reduce residual welding stresses, as well as significantly reduce stress concentrators due to structural improvement of the shape of the welding unit. Application of such heat treatment regimes that restore the stability of metal with a coarse-grained and defective structure. Use improved pipe steels and welding materials, such as 06G2BAand 08 KhMCHA steels, which are characterized by increased resistance to hydrogen embrittlement and high crack resistance in aggressive environments, for the construction of pipelines of responsible purpose.

A novel under-aging design to improve the creep rupture life of a precipitation-strengthened Fe–Ni-based superalloy

The under-aging, peak-aging, and over-aging microstructures of a precipitation-strengthened Fe–Ni-based alloy were designed by applying different heat treatment procedures. Tensile creep tests were conducted at 700 °C and 250 MPa on samples exhibiting different strengthening γ′ precipitate volume fractions and diameters. The creep life of the alloy in the under-aged state was increased by more than 10% compared to the peak-aged condition, which provided a new approach to designing the heat treatment regime that improve the creep rupture life and plasticity of precipitation-strengthened alloys. The improvement in creep properties of the under-aged state was attributed to the transition from shearing to Orowan looping of γ′ particles by matrix dislocations during the dynamic precipitation and coarsening of γ′ phase, increasing intragranular deformation resistance. The under-aged microstructure design allowed reducing the grain boundary sliding contribution to overall strain during creep. As a result, the steady-state creep stage of the alloy in the under-aged state was extended. Additionally, relationships between applied stress and nucleation, growth, and coarsening of the γ′ phase have been evidenced.