Research

15 pages, 10167 KiB

Open AccessFeature PaperArticle

Structural, Electrical and Corrosion Properties of Bulk Ti–Cu Alloys Produced by Mechanical Alloying and Powder Metallurgy

by Katarzyna Arkusz, Kamila Pasik, Marek Nowak and Mieczyslaw Jurczyk

Materials 2024, 17(7), 1473; https://doi.org/10.3390/ma17071473 - 23 Mar 2024

Viewed by 511

Abstract

Binary Ti_100-x–Cu_x (x = 1.6 and 3.0 wt.%) alloys were produced by the application of mechanical alloying and powder metallurgy processes. The influence of the copper concentration in titanium on the microstructure and properties of bulk alloys was investigated. The [...] Read more.

Binary Ti_100-x–Cu_x (x = 1.6 and 3.0 wt.%) alloys were produced by the application of mechanical alloying and powder metallurgy processes. The influence of the copper concentration in titanium on the microstructure and properties of bulk alloys was investigated. The synthesized materials were characterized by an X-ray diffraction technique, scanning electron microscopy, and chemical composition determination. The electrochemical and corrosion properties were also investigated. Cold compaction and sintering reduced the content of α-Ti content in Ti98.4–Cu1.6 and Ti97–Cu3 alloys to 92.4% and 83.7%, respectively. Open Circuit Potential measurements showed a positive shift after the addition of copper, suggesting a potential deterioration in the corrosion resistance of the Ti–Cu alloys compared to pure Ti. Electrochemical Impedance Spectroscopy analysis revealed significant improvement in electrical conductivity after the addition of copper. Corrosion testing results demonstrated compromised corrosion resistance of Ti–Cu alloys compared to pure Ti. In summary, the comprehensive investigation of Ti_100-x–Cu_x alloys provides valuable insights for potential applications in biosensing. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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21 pages, 8825 KiB

Open AccessArticle

Finite Element Analysis of Dynamic Recrystallization Model and Microstructural Evolution for GCr15 Bearing Steel Warm–Hot Deformation Process

by Xuewen Chen, Jiawei Sun, Yisi Yang, Bingqi Liu, Yahui Si and Junzhuo Zhou

Materials 2023, 16(13), 4806; https://doi.org/10.3390/ma16134806 - 04 Jul 2023

Cited by 1 | Viewed by 1290

Abstract

Warm deformation is a plastic-forming process that differs from traditional cold and hot forming techniques. At the macro level, it can effectively reduce the problem of high deformation resistance in cold deformation and improve the surface decarburization issues during the hot deformation process. [...] Read more.

Warm deformation is a plastic-forming process that differs from traditional cold and hot forming techniques. At the macro level, it can effectively reduce the problem of high deformation resistance in cold deformation and improve the surface decarburization issues during the hot deformation process. Microscopically, it has significant advantages in controlling product structure, refining grain size, and enhancing product mechanical properties. The Gleeble-1500D thermal–mechanical physical simulation system was used to conduct isothermal compression tests on GCr15 bearing steel. The tests were conducted at temperatures of 600–1050 °C and strain rates of 0.01–5 s⁻¹. Based on the experimental data, the critical strain model and dynamic recrystallization model for the warm–hot forming of GCr15 bearing steel were established in this paper. The model accuracy is evaluated using statistical indicators such as the correlation coefficient (R). The dynamic recrystallization model exhibits high predictive accuracy, as indicated by an R-value of 0.986. The established dynamic recrystallization model for GCr15 bearing steel was integrated into the Forge^® 3.2 numerical simulation software through secondary program development to simulate the compression process of GCr15 warm–hot forming. The dynamic recrystallization fraction was analyzed in various deformation regions. The grain size of the severe deformation zone, small deformation zone, and difficult deformation zone was compared based on simulated compression specimens under the conditions of 1050 °C and 0.1 s⁻¹ with the corresponding grain size obtained with measurement based on metallographic photos; the relative error between the two is 5.75%. This verifies the accuracy of the established dynamic recrystallization and critical strain models for warm–hot deformation of GCr15 bearing steel. These models provide a theoretical basis for the finite element method analysis and microstructure control of the warm–hot forming process in bearing races. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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18 pages, 5933 KiB

Open AccessArticle

An Inverse Optimization Method for the Parameter Determination of the High-Temperature Damage Model and High-Temperature Damage Graph of Ti6Al4V Alloy

by Xuewen Chen, Zhen Yang, Bo Zhang, Jiawei Sun, Zhiyi Su and Yiran Mao

Materials 2023, 16(13), 4770; https://doi.org/10.3390/ma16134770 - 01 Jul 2023

Cited by 1 | Viewed by 800

Abstract

Ti6AL4V alloy is widely used in the biomedical and energy vehicle industries, among others. Ti6Al4V alloy cannot be fabricated at ambient temperatures; hence, it requires hot forming. However, this method is susceptible to crack defects. The crack defect problem of Ti6AL4V alloy in [...] Read more.

Ti6AL4V alloy is widely used in the biomedical and energy vehicle industries, among others. Ti6Al4V alloy cannot be fabricated at ambient temperatures; hence, it requires hot forming. However, this method is susceptible to crack defects. The crack defect problem of Ti6AL4V alloy in the hot-forming process cannot be ignored, so we must develop a precise hot-forming damage prediction model. In this study, three high-temperature damage models of Ti6Al4V alloy were developed, considering the temperature and strain rate. These models were derived from the normalized Cockcroft and Latham (NCL), Oyane, and Rice and Tracey (RT) damage models. The damage parameters of the models were identified using a genetic algorithm combined with finite element simulation. The force accumulation error of the Ti6AL4V alloy specimen, which was obtained from a simulated thermal tensile test and an actual test, was used as an optimization target function. Then, the damage parameters were optimized using the genetic algorithm until the target function reached the minimum value. Finally, the optimal damage model parameter was obtained. Through program development, the three high-temperature damage models established in this paper were embedded into Forge^® NxT 2.1 finite element software. The simulated thermal tensile test of Ti6AL4V alloy was performed at a temperature of 800–1000 °C and a strain rate of 0.01–5 s⁻¹. The simulated and actual fracture displacements of the tensile specimens were compared. The correlation coefficients (R) were calculated, which were 0.997, 0.951, and 0.912. Of the high-temperature damage models, the normalized Cockcroft and Latham high-temperature damage model had higher accuracy in predicting crack defects of Ti6Al4V alloy during the hot-forming process. Finally, a fracture strain graph and a high-temperature damage graph of Ti6Al4V alloy were constructed. The Ti6Al4V alloy damage evolution and thermal formability were analyzed in relation to the temperature and strain rate. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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17 pages, 4246 KiB

Open AccessArticle

Genetic-Algorithm-Based Inverse Optimization Identification Method for Hot-Temperature Constitutive Model Parameters of Ti6Al4V Alloy

by Xuewen Chen, Zhiyi Su, Jiawei Sun, Zhen Yang, Bo Zhang and Zheng Zhou

Materials 2023, 16(13), 4726; https://doi.org/10.3390/ma16134726 - 29 Jun 2023

Viewed by 967

Abstract

A precise constitutive model is the foundation and key to finite element simulation in material volume forming and the optimization of the hot working process. Hence, to build a precise constitutive model, a method based on a genetic algorithm (GA) for the inverse [...] Read more.

A precise constitutive model is the foundation and key to finite element simulation in material volume forming and the optimization of the hot working process. Hence, to build a precise constitutive model, a method based on a genetic algorithm (GA) for the inverse optimization identification of parameters is presented in this paper. The idea of this method is to continuously adjust the model parameters through GA until the objective function reaches the minimum value. In this study, hot compression experiments were performed on the Gleeble-1500D thermal simulator at temperatures ranging from 800 °C to 1000 °C and strain rates of 0.01 s⁻¹ to 1 s⁻¹. The Arrhenius-type (A-T) model considering strain compensation and the Johnson–Cook (JC) model considering the coupling effects of strain, temperature and strain rate were constructed, respectively, by using the regression method and the parameter inverse optimization identification method. For the purposes of comparing and verifying the reliability of the predictions of the two established constitutive models, the correlation coefficient (R), average absolute relative error (AARE), and relative error (RE) were adopted. The results show that both the optimized A-T model and the optimized JC model have high prediction accuracy. Compared to the optimized JC model, the optimized A-T model demonstrated a higher correlation coefficient, by 0.003, and a lower average absolute relative error, by 1.43%. Furthermore, the relative error distribution of the optimized A-T model was found to be more concentrated than that of the optimized JC model. These results suggest that the A-T model is more appropriate than the JC model for characterizing the high-temperature deformation behavior of Ti6Al4V alloy. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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16 pages, 4045 KiB

Open AccessArticle

Formation of Twin Boundaries in Rapidly Solidified Metals through Deformation Twinning

by Binting Huang, Jishi Yang, Zhiheng Luo, Yang Wang and Nan Wang

Materials 2023, 16(13), 4503; https://doi.org/10.3390/ma16134503 - 21 Jun 2023

Viewed by 687

Abstract

The rapid solidification process is relevant to many emerging metallurgical technologies. Compared with conventional solidification processes, high-density microstructure defects and residual thermal stress are commonly seen in rapidly solidified metals. Among the various defects, potentially beneficial twin boundaries have been observed in the [...] Read more.

The rapid solidification process is relevant to many emerging metallurgical technologies. Compared with conventional solidification processes, high-density microstructure defects and residual thermal stress are commonly seen in rapidly solidified metals. Among the various defects, potentially beneficial twin boundaries have been observed in the rapidly solidified nanocrystalline microstructures of many alloy systems. In this work, a pathway for forming twin boundaries in rapid solidification processes is proposed. A detailed derivation of strain inhomogeneities upon thermal shrinkage and the deformation twinning phase field method is given. By calculating cooling-induced thermal strain inhomogeneity in nanocrystalline metals and growth thresholds for deformation twinning using the phase field method, it is shown that residual thermal strain hotspots in the microstructure can reach the threshold for deformation twinning when the shear elastic property of grain boundaries is significantly different from the bulk. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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12 pages, 9827 KiB

Open AccessArticle

Microstructure and Recrystallization Behavior of Heating Rate-Controlled Electrolytic Capacitor Aluminum Foil under Cold Forming and Annealing

by Yunlei Wang, Taibin Wu, Luchang Che and Guangjie Huang

Materials 2023, 16(11), 4128; https://doi.org/10.3390/ma16114128 - 01 Jun 2023

Cited by 2 | Viewed by 1043

Abstract

A novel annealing process of controlled heating rate is used to produce severe cold-formed aluminum plates, which are processed into aluminum foil and mainly used for high-voltage electrolytic capacitor anodes. The experiment in this study focused on various aspects such as microstructure, recrystallization [...] Read more.

A novel annealing process of controlled heating rate is used to produce severe cold-formed aluminum plates, which are processed into aluminum foil and mainly used for high-voltage electrolytic capacitor anodes. The experiment in this study focused on various aspects such as microstructure, recrystallization behavior, grain size, and grain boundary characteristics. The results revealed a comprehensive influence of cold-rolled reduction rate, annealing temperature, and heating rate on recrystallization behavior and grain boundary characteristics during the annealing process. The heating rate applied plays a crucial role in controlling the recrystallization process and the subsequent grain growth, which ultimately determines whether or not the grains will become larger. In addition, as the annealing temperature rises, the recrystallized fraction increases and the grains size decreases; conversely, the recrystallized fraction decreases as the heating rate increases. When the annealing temperature remains constant, the recrystallization fraction increases with a greater deformation degree. Once complete recrystallization occurs, the grain will undergo secondary growth and may even subsequently become coarser. If the deformation degree and annealing temperature remain constant, the increased heating rate will result in a lower recrystallization fraction. This is due to the inhibition of recrystallization, and most of the aluminum sheet even remains in a deformed state before recrystallization. This kind of microstructure evolution, grain characteristic revelation, and recrystallization behavior regulation can provide effective help for enterprise engineers and technicians to guide the production of capacitor aluminum foil to a certain extent, so as to improve the quality of aluminum foil and increase the electric storage performance. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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14 pages, 7255 KiB

Open AccessArticle

The Optimization of Mechanical Alloying Conditions of Powder for the Preparation of a Fe-10Al-4Cr-4Y₂O₃ ODS Nanocomposite

by Jiří Svoboda, Štepán Gamanov, Denisa Bártková, Natália Luptáková, Petr Bořil, Milan Jarý, Bohuslav Mašek, Jakub Holzer and Petr Dymáček

Materials 2022, 15(24), 9034; https://doi.org/10.3390/ma15249034 - 17 Dec 2022

Cited by 2 | Viewed by 1099

Abstract

Mechanical alloying (MA) of powders represents the first processing step in the production of oxide dispersion-strengthened (ODS) alloys. MA is a time and energy-consuming process also in the production of Fe-10Al-4Cr-4Y₂O₃ creep and oxidation-resistant ODS nanocomposite, denoted as the FeAlOY, [...] Read more.

Mechanical alloying (MA) of powders represents the first processing step in the production of oxide dispersion-strengthened (ODS) alloys. MA is a time and energy-consuming process also in the production of Fe-10Al-4Cr-4Y₂O₃ creep and oxidation-resistant ODS nanocomposite, denoted as the FeAlOY, and it deserves to be optimized. MA is performed at two different temperatures at different times. The powder after MA, as well as the microstructure and high-temperature strength of the final FeAlOY, are characterized and the optimal MA conditions are evaluated. The obtained results show that the size distribution of the powder particles, as well as the dissolution and homogenization of the Y₂O₃, becomes saturated quite soon, while the homogenization of the metallic components, such as Al and Cr, takes significantly more time. The high-temperature tensile tests and grain microstructures of the secondary recrystallized FeAlOY, however, indicate that the homogenization of the metallic components during MA does not influence the quality of the FeAlOY, as the matrix of the FeAlOY is sufficiently homogenized during recrystallization. Thus, the conditions of MA correspond to sufficient dissolution and homogenization of Y₂O₃ and can be considered the optimal ones. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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21 pages, 16574 KiB

Open AccessArticle

Corrosion Behavior of Cold-Rolled and Solution-Treated Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃ HEA in Different Acidic Solutions

by Essam R. I. Mahmoud, Lamiaa Z. Mohamed, Mohamed A. Gepreel, Saad Ebied and Aliaa Abdelfatah

Materials 2022, 15(20), 7319; https://doi.org/10.3390/ma15207319 - 19 Oct 2022

Cited by 1 | Viewed by 1265

Abstract

New high entropy alloys with good corrosion resistance in severe environment are receiving increasing attention. This work reports upon the microstructure and the corrosion resistance of the non-equiatomic Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃ alloy in different [...] Read more.

New high entropy alloys with good corrosion resistance in severe environment are receiving increasing attention. This work reports upon the microstructure and the corrosion resistance of the non-equiatomic Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃ alloy in different acidic solutions. This alloy was designed by thermodynamic calculations using CALPHAD SOFTWARE, fabricated through casting, subjected to cold-rolling and solution-treatment, and compared with SS304 stainless steel. The corrosion test was performed through electrochemical behavior in 0.6 M NaCl and 0.6 M NaCl with 0.5 M H₂SO₄ and 0.6 M NaCl with 1 M H₂SO₄ solutions. Experimental results indicate that the alloy is composed of FCC phase as the main constituent besides a small amount of other BCC/B2 phases and other intermetallics. The corrosion test measurements revealed that cold-rolled Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃ alloy is more resistant to corrosion in 0.6 M NaCl, while it is more susceptible to localized pits in H₂SO₄ to 0.6 M NaCl. Experimental results indicate that the pits are preferentially occurred in the areas of BCC/B2 phase precipitates. The solution-treated Fe₃₆Mn₂₀Ni₂₀Cr₁₆Al₅Si₃ HEA has the highest corrosion resistance compared to others with the addition of H₂SO₄ to 0.6 M NaCl. Surface morphologies of the different conditions were studied, and relevant results were reported. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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18 pages, 6663 KiB

Open AccessArticle

Removal Mechanism and Electrochemical Milling of (TiB+TiC)/TC4 Composites

by Shukai Fan, Xiaoyun Hu, Xin Ma, Yuting Lu and Hansong Li

Materials 2022, 15(20), 7046; https://doi.org/10.3390/ma15207046 - 11 Oct 2022

Viewed by 1206

Abstract

Titanium matrix composite (TiB+TiC)/TC4 has excellent physical properties and is a completely new composite material with great application prospects in the next generation of the aerospace field. However, there are problems, such as tool loss and material overheating, when using conventional processing methods. [...] Read more.

Titanium matrix composite (TiB+TiC)/TC4 has excellent physical properties and is a completely new composite material with great application prospects in the next generation of the aerospace field. However, there are problems, such as tool loss and material overheating, when using conventional processing methods. Electrochemical milling is a low-cost, high-efficiency processing method for difficult-to-machine metal materials with no tool wear. In this research, the feasibility of the electrochemical milling of (TiB+TiC)/TC4 and removal mechanisms during processing was reported for the first time. The feasibility of electrochemical milling is verified by the current efficiency experiment and basic processing experiment. Through the adjustment of the processing parameters, the final material removal rate increased by 52.5% compared to that obtained in the first processing, while the surface roughness decreased by 27.3%. The removal mechanism during processing was further performed based on the current efficiency experiment; three stages were observed and concluded during the electrolytic dissolution. This research proved that electrochemical milling is an excellent low-cost method for roughing and semi-finishing (TiB+TiC)/TC4 composites and provides guidance for better electrochemical milling in the titanium matrix composites. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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15 pages, 8729 KiB

Open AccessArticle

Effect of Cold-Rolling Reduction on Recrystallization Microstructure, Texture and Corrosion Properties of the X2CrNi12 Ferritic Stainless Steel

by Rui Li, Binguo Fu, Yufeng Wang, Jingkun Li, Tianshun Dong, Guolu Li, Guixian Zhang and Jinhai Liu

Materials 2022, 15(19), 6914; https://doi.org/10.3390/ma15196914 - 05 Oct 2022

Cited by 5 | Viewed by 1259

Abstract

X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose [...] Read more.

X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose of this work is to investigate the effect of cold-rolling reduction on the microstructure, texture and corrosion properties of the recrystallized X2CrNi12 ferritic stainless steel by using SEM, TEM, EBSD and electrochemical testing technology. The results show that the crystal orientation characteristics of the cold-rolled sheet could be inherited into the annealed sheet. The higher cold-rolling reduction could promote the deformed grains rotating into the {111}<uvw> orientation, increasing storage energy and driving force for recrystallization, which could reduce the recrystallized grain size. The orientation densities of α-fiber and γ-fiber were low at 50% cold-rolling reduction. After recrystallization annealing, a large number of grains with random orientation could be produced, and the texture strength was weakened. When the cold-rolling reduction rose to 90%, the γ-fiber texture at {111}<110> was strengthened and the α-fibers, particularly the {112}<110> component, were weakened after recrystallisation annealing, which could improve the formability of the steels. The proportions of special boundaries, i.e., low-angle grain boundaries and low-Σ CSL boundaries, among the grain boundary distribution of the recrystallized X2CrNi12 stainless steel were higher when the reduction was 90%, especially when the annealing temperature was 770 °C. Additionally, the proportion of LAGBs and low-Σ CSL boundaries were 53% and 7.43%, respectively, which improves the corrosion resistance of the matrix, showing the best corrosion resistance. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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17 pages, 5916 KiB

Open AccessArticle

Modeling of Dynamic Recrystallization Evolution for Cr8 Alloy Steel and Its Application in FEM

by Xuewen Chen, Bingqi Liu, Bo Zhang, Jiawei Sun, Zhen Yang, Xudong Zhou, Tao Huang and Danqing Yin

Materials 2022, 15(19), 6830; https://doi.org/10.3390/ma15196830 - 01 Oct 2022

Cited by 1 | Viewed by 1061

Abstract

In the process of Cr8 roller production, the phenomenon of coarse grain size and uneven grain size often appears, which makes the mechanical properties of the material decrease sharply. Accurate dynamic recrystallization model is the basis for predicting the change of grain size [...] Read more.

In the process of Cr8 roller production, the phenomenon of coarse grain size and uneven grain size often appears, which makes the mechanical properties of the material decrease sharply. Accurate dynamic recrystallization model is the basis for predicting the change of grain size during thermal processing, and is an important basis for refining grain and improving material properties. In this study, the isothermal compression experiment was carried out on Cr8 alloy steel at 900–1200 °C and 0.005–0.1 s⁻¹ by Gleeble –1500D thermal simulation compressor, and the stress dates of Cr8 alloy steel were obtained. According to experimental data, the Kopp dynamic recrystallization model of Cr8 alloy steel was established. The dynamic recrystallization volume fraction obtained by Kopp model was compared with that obtained by experiment at the same temperature and strain rate. The correlation value was 0.988, and the root mean square error (RMSE) was 0.053, which proved that the DRX model established was reliable. Through the secondary development of the program, the DRX model of Cr8 alloy steel was written into the software Forge^® to verify the microstructure evolution model. The compression process of a cylindrical specimen of Cr8 alloy steel at 0.1 s⁻¹ and 1050 °C was simulated, and the DRX microstructure evolution of the alloy was calculated. The comparison between the final grain size calculation results and the test metallographic photos of samples in different deformation zones shows the relative error of the grain size was less than 10.6%, indicating that the DRX model of Cr8 alloy steel can better predict the dynamic recrystallization of Cr8 alloy steel. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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26 pages, 7147 KiB

Open AccessArticle

Analysis and Modeling of Stress–Strain Curves in Microalloyed Steels Based on a Dislocation Density Evolution Model

by Evelyn Sobotka, Johannes Kreyca, Maria Cecilia Poletti and Erwin Povoden-Karadeniz

Materials 2022, 15(19), 6824; https://doi.org/10.3390/ma15196824 - 01 Oct 2022

Cited by 5 | Viewed by 1657

Abstract

Microalloyed steels offer a good combination of desirable mechanical properties by fine-tuning grain growth and recrystallization dynamics while keeping the carbon content low for good weldability. In this work, the dislocation density evolution during hot rolling was correlated by materials modeling with flow [...] Read more.

Microalloyed steels offer a good combination of desirable mechanical properties by fine-tuning grain growth and recrystallization dynamics while keeping the carbon content low for good weldability. In this work, the dislocation density evolution during hot rolling was correlated by materials modeling with flow curves. Single-hit compression tests at different temperatures and strain rates were performed with varying isothermal holding times prior to deformation to achieve different precipitation stages. On the basis of these experimental results, the dislocation density evolution was evaluated using a recently developed semi-empirical state-parameter model implemented in the software MatCalc. The yield stress at the beginning of the deformation σ₀, the initial strain hardening rate θ₀, and the saturation stress σ_∞—as derived from the experimental flow curves and corresponding Kocks plots—were used for the calibration of the model. The applicability for industrial processing of many microalloyed steels was assured by calibration of the model parameters as a function of temperature and strain rate. As a result, it turned out that a single set of empirical equations was sufficient to model all investigated microalloyed steels since the plastic stresses at high temperatures did not depend on the precipitation state. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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18 pages, 4454 KiB

Open AccessArticle

Forming Quality Research on the Variable-Diameter Section of the Hollow Axle in Three-Roll Skew Rolling

by Yingxiang Xia, Xuedao Shu, Jianan Shi, Ying Wang, Zbigniew Pater and Jitai Wang

Materials 2022, 15(16), 5614; https://doi.org/10.3390/ma15165614 - 16 Aug 2022

Cited by 2 | Viewed by 1235

Abstract

The hollow axle is the key component of the high-speed train, and the realization of high-quality forming is the key to ensure the safety of train operation. In this paper, the specimen of the variable-diameter section of the hollow axle is taken as [...] Read more.

The hollow axle is the key component of the high-speed train, and the realization of high-quality forming is the key to ensure the safety of train operation. In this paper, the specimen of the variable-diameter section of the hollow axle is taken as the research object, and the generation mechanism of surface spiral mark defects and the formula of spiral mark depth of variable-diameter section in the TRSR (three-roll skew rolling) process with variable roll spacing are explored. The external roundness error and the function C to measure the wall thickness uniformity of the cross-section were taken as the evaluation indexes and the single-factor simulation experiment was established and simulated in the software Simufact.forming16.0 to obtain the influence law of each process parameter on the external roundness error and wall thickness uniformity of the rolled piece. Orthogonal tests were designed and the order and optimal combination of process parameters on the forming quality were obtained by range analysis and ANOVA analysis. The research results provide theoretical guidance for improving the forming quality of the variable-diameter section of the hollow axle in three-roll skew rolling, and promote the transformation of the TRSR process to high performance and accurate forming. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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14 pages, 8042 KiB

Open AccessArticle

Surface Condition Evolution and Fatigue Evaluation after Different Surface Processes for TiAl₄₇Cr₂Nb₂ Alloy

by Wen Yu, Yajun Yin, Jianxin Zhou, Qian Xu, Xin Feng, Hai Nan, Jiabin Zuo, Xiangning Wang and Xianfei Ding

Materials 2022, 15(16), 5491; https://doi.org/10.3390/ma15165491 - 10 Aug 2022

Cited by 1 | Viewed by 983

Abstract

The TiAl₄₇Cr₂Nb₂ alloy fatigue specimens were prepared by investment casting, and three kinds of surface processes were applied to fatigue specimens. These three processes were sand-blasting (SB), sand-blasting and shot-peening (SBSP) and sand-blasting and mechanical grinding (SBMG). The [...] Read more.

The TiAl₄₇Cr₂Nb₂ alloy fatigue specimens were prepared by investment casting, and three kinds of surface processes were applied to fatigue specimens. These three processes were sand-blasting (SB), sand-blasting and shot-peening (SBSP) and sand-blasting and mechanical grinding (SBMG). The surface condition evolutions before and after thermal exposure at 700 °C for 24 h were investigated. The fatigue performances of specimens after thermal exposure were evaluated. The results show that the surface roughness Ra after SB, SBSP and SBMG processes were 3.14, 2.35 and 0.04 µm, respectively. After thermal exposure, they almost remained unchanged for all three processes. The SB process caused work hardening in the near-surface region and the work hardening reached saturation after the SB process. Due to the mechanical grinding (MG) process removing the uncertain thick hardening layer, the maximum hardness after SBMG process was noticeably lower than those after SB and SBSP processes. After thermal exposure, the maximum hardness after SB, SBSP and SBMG processes significantly recovered. The SBMG specimens had the highest fatigue limit of 350 MPa. This is attributed to the SBMG specimens having very smooth surfaces and some work hardening remaining near their surface layers. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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22 pages, 17538 KiB

Open AccessArticle

Hot Formability Study of Cr5 Alloy Steel by Integration of FEM and 3D Processing Maps

by Xuewen Chen, Yahui Si, Rongren Bai, Xiaopeng Zhang and Zhipeng Li

Materials 2022, 15(14), 4801; https://doi.org/10.3390/ma15144801 - 09 Jul 2022

Cited by 9 | Viewed by 1400

Abstract

Microstructure is an important factor that affects the mechanical properties and service life of forgings. Through the full study of the formability of the material, the internal microstructure of the material can be effectively controlled. In order to accurately describe the formability of [...] Read more.

Microstructure is an important factor that affects the mechanical properties and service life of forgings. Through the full study of the formability of the material, the internal microstructure of the material can be effectively controlled. In order to accurately describe the formability of materials during thermal processing, 3D hot processing maps containing strains were established in this paper, and the 3D hot processing maps were coupled with the finite element method for simulation calculation. The Cr5 alloy steel was subjected to unidirectional thermal compression at a strain rate of 0.005–5 s⁻¹ and temperature range of 900–1200 °C on a Gleeble-1500D thermal simulation machine, in order to obtain the date of true stress and strain. Based on the dynamic material model (DMM), the 3D processing maps of Cr5 alloy steel was established, and the 3D processing maps were associated with the analysis of microstructure evolution during hot deformation. The results show that the optimum thermal deformation conditions are as follows: temperature of 1000–1125 °C, strain rate of 0.01–0.2 s⁻¹, and peak power dissipation of 0.41. The 3D processing maps were coupled with the finite element software FORGE^® to simulate the hot working process, and the distribution and change of power dissipation and flow instability domain on the metal deformation under different thermal deformation conditions were obtained. The comparison between the simulation results and metallographic images of typical regions of metal deformation shows that they are in good agreement. This method can effectively predict and analyze the formability of materials during hot processing and provide guidance for practical industrial production. Full article

(This article belongs to the Special Issue Processing–Microstructure–Properties Loop in Materials and Metallurgical Engineering)

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