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11 pages, 6950 KiB

Open AccessArticle

The Variation Patterns of the Martensitic Hierarchical Microstructure and Mechanical Properties of 35Si2MnCr2Ni3MoV Steel at Different Austenitizing Temperatures

by Zhipeng Wu, Chao Yang, Guangyao Chen, Yang Li, Xin Cao, Pengmin Cao, Han Dong and Chundong Hu

Materials 2024, 17(5), 1099; https://doi.org/10.3390/ma17051099 - 28 Feb 2024

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Abstract

This study investigates the influence of varying austenitizing temperatures on the microstructure and mechanical properties of 35Si2MnCr2Ni3MoV steel, utilizing Charpy impact testing and microscopic analysis techniques such as scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The findings reveal that optimal combination [...] Read more.

This study investigates the influence of varying austenitizing temperatures on the microstructure and mechanical properties of 35Si2MnCr2Ni3MoV steel, utilizing Charpy impact testing and microscopic analysis techniques such as scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The findings reveal that optimal combination of strength and toughness is achieved at an austenitizing temperature of 980 °C, resulting in an impact toughness of 67.2 J and a tensile strength of 2032 MPa. The prior austenite grain size initially decreases slightly with increasing temperature, then enlarges significantly beyond 1100 °C. The martensite blocks’ and packets’ structures exhibit a similar trend. The proportion of high–angle grain boundaries, determined by the density of the packets, peaks at 980 °C, providing maximal resistance to crack propagation. The amount of retained austenite increases noticeably after 980 °C; beyond 1200 °C, the coarsening of packets and a decrease in density reduce the likelihood of trapping retained austenite. Across different austenitizing temperatures, the steel demonstrates superior crack initiation resistance compared to crack propagation resistance, with the fracture mode transitioning from ductile dimple fracture to quasi–cleavage fracture as the austenitizing temperature increases. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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22 pages, 55376 KiB

Open AccessArticle

Effects of Thermal Exposure on the Microstructure and Mechanical Properties of a Ti–48Al–3Nb–1.5Ta Alloy via Powder Hot Isostatic Pressing

by Zhenbo Zuo, Rui Hu, Qingxiang Wang, Zitong Gao, Xian Luo, Yunjin Lai, Sa Xue, Min Xiang, Xiaohao Zhao and Shaoqiang Li

Materials 2024, 17(4), 794; https://doi.org/10.3390/ma17040794 - 07 Feb 2024

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Abstract

Research on how thermal exposure affects the microstructure and mechanical properties of the Ti–48Al–3Nb–1.5Ta (at. %) alloy, which is prepared via powder hot isostatic pressing (P–HIP), is essential since this low-density alloy shows promise for use in high-temperature applications, particularly for aero-engines, which [...] Read more.

Research on how thermal exposure affects the microstructure and mechanical properties of the Ti–48Al–3Nb–1.5Ta (at. %) alloy, which is prepared via powder hot isostatic pressing (P–HIP), is essential since this low-density alloy shows promise for use in high-temperature applications, particularly for aero-engines, which require long-term stable service. In this study, a P–HIP Ti–48Al–3Nb–1.5Ta (at. %) alloy was exposed to high temperatures for long durations. The phase, microstructure and mechanical properties of the P–HIP Ti–48Al–3Nb–1.5Ta alloy after thermal exposure under different conditions were analyzed using XRD, SEM, EBSD, EPMA, TEM, nanomechanical testing and tensile testing. The surface scale is composed of oxides and nitrides, primarily Al₂O₃, TiO₂, and TiN, among which Al₂O₃ is preferentially generated and then covered by rapidly growing TiO₂ as the thermal exposure duration increases. The nitrides appear later than the oxides and exist between the oxides and the substrate. With increasing exposure temperature and duration, the surface scale becomes more continuous, TiO₂ particles grow larger, and the oxide layer thickens or even falls off. The addition of Ta and Nb can improve the oxidation resistance because Ta⁵⁺ and Nb⁵⁺ replace Ti⁴⁺ in the rutile lattice and weaken O diffusion. Compared with the P–HIP Ti–48Al–3Nb–1.5Ta alloy, after thermal exposure, the grain size does not increase significantly, and the γ phase increases slightly (by less than 3%) with the decomposition of the α₂ phase. With increasing thermal exposure duration, the γ phase exhibits discontinuous coarsening (DC). Compared with the P–HIP Ti–48Al–3Nb–1.5Ta alloy, the hardness increases by about 2 GPa, the tensile strength increases by more than 50 MPa, and the fracture strain decreases by about 0.1% after thermal exposure. When the depth extends from the edge of the thermally exposed specimens, the hardness decreases overall. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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12 pages, 17293 KiB

Open AccessArticle

Regulation Law of Tempering Cooling Rate on Toughness of Medium-Carbon Medium-Alloy Steel

by Chao Yang, Tingting Xu, Hongshan Zhao, Chundong Hu and Han Dong

Materials 2024, 17(1), 205; https://doi.org/10.3390/ma17010205 - 30 Dec 2023

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Abstract

Temper embrittlement is a major challenge encountered during the heat treatment of high-performance steels for large forgings. This study investigates the microstructural evolution and mechanical properties of Cr-Ni-Mo-V thick-walled steel, designed for large forgings with a tensile strength of 1500 MPa, under different [...] Read more.

Temper embrittlement is a major challenge encountered during the heat treatment of high-performance steels for large forgings. This study investigates the microstructural evolution and mechanical properties of Cr-Ni-Mo-V thick-walled steel, designed for large forgings with a tensile strength of 1500 MPa, under different tempering cooling rates. Optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural features. The results demonstrate that the embrittlement occurring during air cooling after tempering is attributed to the concentration of impurities near Fe₃C at the grain boundaries. The low-temperature impact toughness at −40 °C after water quenching reaches 29 J due to the accelerated cooling rate during tempering, which slows down the diffusion of impurity elements towards the grain boundaries, resulting in a reduced concentration and dislocation density and an increased stability of the grain boundaries, thereby enhancing toughness. The bainite content decreases and the interface between martensite and bainite undergoes changes after water quenching during tempering. These alterations influence the crack propagation direction within the two-phase microstructure, further modifying the toughness. These findings contribute to the understanding of temper embrittlement and provide valuable guidance for optimizing heat treatment processes to enhance the performance of high-performance steels in large forgings. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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11 pages, 15869 KiB

Open AccessArticle

Preparation of Sr₂CeZrO₆ Refractory and Its Interaction with TiAl Alloy

by Fuli Bian, Zheyu Cai, Jian Liu, Yu Liu, Man Zhang, Yixin Fu, Kailiang Zhu, Guangyao Chen and Chonghe Li

Materials 2023, 16(23), 7298; https://doi.org/10.3390/ma16237298 - 23 Nov 2023

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Abstract

Vacuum induction melting in a refractory crucible is an economical method to produce TiAl-based alloys, aiming to reduce the preparation cost. In this paper, a Sr₂CeZrO₆ refractory was synthesized by a solid-state reaction method using SrCO₃, CeO₂ [...] Read more.

Vacuum induction melting in a refractory crucible is an economical method to produce TiAl-based alloys, aiming to reduce the preparation cost. In this paper, a Sr₂CeZrO₆ refractory was synthesized by a solid-state reaction method using SrCO₃, CeO₂ and ZrO₂ as raw materials, and its interaction with TiAl alloy melt was investigated. The results showed that a single-phase Sr₂CeZrO₆ refractory could be fabricated at 1400 °C for 12 h, and its space group was Pnma with a = 5.9742(3) Å, b = 8.3910(5) Å and c = 5.9069(5) Å. An interaction layer with a 40μm thickness and dense structure could be observed in Sr₂CeZrO₆ crucible after melting TiAl alloy. Additionally, the interaction mechanism showed that the Sr₂CeZrO₆ refractory dissolved in the alloy melt, resulting in the generation of Sr₃Zr₂O₇, SrAl₂O₄ and CeO_2−x, which attached to the surface of the crucible. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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9 pages, 7073 KiB

Open AccessCommunication

Dissolution Behavior of Eutectic Carbides in Medium-Alloy Steels for Heavy Forgings

by Yu Ji, Tingting Xu, Caiyan Zhao, Guangyao Chen, Hongshan Zhao, Chundong Hu and Han Dong

Materials 2023, 16(20), 6763; https://doi.org/10.3390/ma16206763 - 19 Oct 2023

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Abstract

In this study, we investigate the dissolution behavior of eutectic carbides in heavy forgings. High-temperature diffusion treatment was conducted on 35Cr3Ni3MoVW2 (MoVW2) and 35Cr2Ni3MoV (MoV) steels at 1230 °C for a duration ranging from 0 to 100 h. The dissolution of eutectic carbides [...] Read more.

In this study, we investigate the dissolution behavior of eutectic carbides in heavy forgings. High-temperature diffusion treatment was conducted on 35Cr3Ni3MoVW2 (MoVW2) and 35Cr2Ni3MoV (MoV) steels at 1230 °C for a duration ranging from 0 to 100 h. The dissolution of eutectic carbides and its effects on the microstructure and hardness of the steels were characterized and analyzed via SEM+EBSD, ImageJ, and Thermo-Calc. The results show that the coarse eutectic carbides in both steels gradually dissolved. The distribution and morphology tend to be uniform and spherical, respectively. For holding 50 h, the hardness of both steels significantly exhibited an increasing trend, and it was attributed to the combined effects of solid solution strengthening. Thermodynamic calculations indicated that the higher W content in MoVW2 steel promoted the precipitation of M₆C eutectic carbides. Moreover, both MoVW2 and MoV steels exhibited the precipitation of M₇C₃ eutectic carbides in the final stage of solidification, facilitated by the enrichment of C and Cr in the liquid steels. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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16 pages, 8072 KiB

Open AccessArticle

Achieving High Strength and Creep Resistance in Inconel 740H Superalloy through Wire-Arc Additive Manufacturing and Thermodynamic-Guided Heat Treatment

by Soumya Sridar, Luis Fernando Ladinos Pizano, Michael A. Klecka and Wei Xiong

Materials 2023, 16(19), 6388; https://doi.org/10.3390/ma16196388 - 25 Sep 2023

Cited by 1 | Viewed by 1026

Abstract

Inconel 740H superalloy is commonly used in advanced ultra-supercritical power plants since it possesses excellent strength and creep resistance. This study investigates the microstructure and mechanical properties of Inconel 740H superalloy fabricated using wire-arc additive manufacturing. The as-printed microstructure consisted of columnar γ [...] Read more.

Inconel 740H superalloy is commonly used in advanced ultra-supercritical power plants since it possesses excellent strength and creep resistance. This study investigates the microstructure and mechanical properties of Inconel 740H superalloy fabricated using wire-arc additive manufacturing. The as-printed microstructure consisted of columnar γ grains with the Laves phase and (Nb, Ti)C carbides as secondary phases. The anisotropy in grain structure increased from the bottom to the top regions, while the hardness was highest in the middle portion of the build. To guide the post-heat treatment design, thermodynamic and kinetic simulations were employed to predict the temperature and time. Complete recrystallization with the Laves phase dissolution occurred throughout the build after homogenization at 1200 °C for 2 h. The peak hardness was achieved after aging at 760 °C for 12 h with the M₂₃C₆ carbides decorating the grain boundaries and γ’ precipitates in the grain interior. The yield strength (655 MPa) and ductility (29.5%) in the post-heat treated condition exceeded the design targets (620 MPa, 20%). Stress rupture tests at 750 °C showed that the high-temperature performance was at par with the wrought counterparts. The fracture mode after rupture was identified to be intergranular with the presence of grain boundary cavities along with grain boundary sliding. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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14 pages, 9555 KiB

Open AccessArticle

Hot Deformation Behavior and Dynamic Softening Mechanism in 7B50 Aluminum Alloy

by Ming Li, Yong Li, Yu Liu, Zhengbing Xiao and Yuanchun Huang

Materials 2023, 16(16), 5590; https://doi.org/10.3390/ma16165590 - 12 Aug 2023

Viewed by 780

Abstract

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320–460 °C/0.001–1.0 s⁻¹. According to the flow curves obtained from the experiments, the flow behavior of this alloy was [...] Read more.

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320–460 °C/0.001–1.0 s⁻¹. According to the flow curves obtained from the experiments, the flow behavior of this alloy was analyzed, and the Zener–Hollomon (Z) parameter equation was established. The hot processing maps of this alloy were developed based on the dynamic material model, and the optimal hot working region was determined to be 410–460 °C/0.01–0.001 s⁻¹. The electron backscattered diffraction (EBSD) microstructure analysis of the deformed sample shows that the dynamic softening mechanism and microstructure evolution strongly depend on the Z parameter. Meanwhile, a correlation between the dynamic softening mechanism and the lnZ value was established. Dynamic recovery (DRV) was the only softening mechanism during isothermal compression with lnZ ≥ 20. Discontinuous dynamic recrystallization (DDRX) becomes the dominant dynamic recrystallization (DRX) mechanism under deformation conditions of 15 < lnZ < 20. Meanwhile, the size and percentage of DDRXed grains increased with decreasing lnZ values. The geometric dynamic recrystallization (GDRX) mechanism and continuous dynamic recrystallization (CDRX) mechanism coexist under deformation conditions with lnZ ≤ 15. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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17 pages, 10956 KiB

Open AccessArticle

He-ion Irradiation Effects on the Microstructures and Mechanical Properties of the Ti-Zr-Hf-V-Ta Low-Activation High-Entropy Alloys

by Huanzhi Zhang, Qianqian Wang, Chunhui Li, Zhenbo Zhu, Hefei Huang and Yiping Lu

Materials 2023, 16(16), 5530; https://doi.org/10.3390/ma16165530 - 09 Aug 2023

Cited by 2 | Viewed by 1027

Abstract

High-entropy alloys (HEAs) have shown promising potential applications in advanced reactors due to the outstanding mechanical properties and irradiation tolerance at elevated temperatures. In this work, the novel low-activation Ti₂ZrHf_xV_0.5Ta_0.2 HEAs were designed and prepared to [...] Read more.

High-entropy alloys (HEAs) have shown promising potential applications in advanced reactors due to the outstanding mechanical properties and irradiation tolerance at elevated temperatures. In this work, the novel low-activation Ti₂ZrHf_xV_0.5Ta_0.2 HEAs were designed and prepared to explore high-performance HEAs under irradiation. The microstructures and mechanical properties of the Ti₂ZrHf_xV_0.5Ta_0.2 HEAs before and after irradiation were investigated. The results showed that the unirradiated Ti₂ZrHf_xV_0.5Ta_0.2 HEAs displayed a single-phase BCC structure. The yield strength of the Ti₂ZrHf_xV_0.5Ta_0.2 HEAs increased gradually with the increase of Hf content without decreasing the plasticity at room and elevated temperatures. After irradiation, no obvious radiation-induced segregations or precipitations were found in the transmission electron microscope results of the representative Ti₂ZrHfV_0.5Ta_0.2 HEA. The size and number density of the He bubbles in the Ti₂ZrHfV_0.5Ta_0.2 HEA increased with the improvement of fluence at 1023 K. At the fluences of 1 × 10¹⁶ and 3 × 10¹⁶ ions/cm², the irradiation hardening fractions of the Ti₂ZrHfV_0.5Ta_0.2 HEA were 17.7% and 34.1%, respectively, which were lower than those of most reported conventional low-activation materials at similar He ion irradiation fluences. The Ti₂ZrHfV_0.5Ta_0.2 HEA showed good comprehensive mechanical properties, structural stability, and irradiation hardening resistance at elevated temperatures, making it a promising structural material candidate for advanced nuclear energy systems. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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22 pages, 8876 KiB

Open AccessArticle

Characterization of Complex Concentrated Alloys and Their Potential in Car Brake Manufacturing

by Ioana Anasiei, Dumitru Mitrica, Ioana-Cristina Badea, Beatrice-Adriana Șerban, Johannes Trapp, Andreas Storz, Ioan Carcea, Mihai Tudor Olaru, Marian Burada, Nicolae Constantin, Alexandru Cristian Matei, Ana-Maria Julieta Popescu and Mihai Ghiță

Materials 2023, 16(14), 5067; https://doi.org/10.3390/ma16145067 - 18 Jul 2023

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Abstract

The paper studies new materials for brake disks used in car manufacturing. The materials used in the manufacturing of the brake disc must adapt and correlate with the challenges of current society. There is a tremendous interest in the development of a material [...] Read more.

The paper studies new materials for brake disks used in car manufacturing. The materials used in the manufacturing of the brake disc must adapt and correlate with the challenges of current society. There is a tremendous interest in the development of a material that has high strength, good heat transfer, corrosion resistance and low density, in order to withstand high-breaking forces, high heat and various adverse environment. Low-density materials improve fuel efficiency and environmental impact. Complex concentrated alloys (CCA) are metallic element mixtures with multi-principal elements, which can respond promisingly to this challenge with their variety of properties. Several compositions were studied through thermodynamic criteria calculations (entropy of mixing, enthalpy of mixing, lambda coefficient, etc.) and CALPHAD modeling, in order to determine appropriate structures. The selected compositions were obtained in an induction furnace with a protective atmosphere and then subjected to an annealing process. Alloy samples presented uniform phase distribution, a high-melting temperature (over 1000 °C), high hardness (1000–1400 HV), good corrosion resistance in 3.5 wt.% NaCl solution (under 0.2 mm/year) and a low density (under 6 g/cm³). Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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13 pages, 4472 KiB

Open AccessArticle

Effects of Homogenization Heat Treatment on the Fe Micro-Segregation in Ti-1023 Titanium Alloy

by Jian-Bo Tong, Chao-Jie Zhang, Jun-Shu Chen, Meng-Qi Yan, Rui-Lin Xu and Li-Jun Huang

Materials 2023, 16(14), 4911; https://doi.org/10.3390/ma16144911 - 09 Jul 2023

Viewed by 765

Abstract

The segregation of the Fe element in Ti-10V-2Fe-3Al titanium alloy (Ti-1023) can lead to the generation of beta flecks, which seriously affects the performance of Ti-1023 products. During the heat treatment (HT) process at a high temperature, the Fe element in Ti-1023 ingots [...] Read more.

The segregation of the Fe element in Ti-10V-2Fe-3Al titanium alloy (Ti-1023) can lead to the generation of beta flecks, which seriously affects the performance of Ti-1023 products. During the heat treatment (HT) process at a high temperature, the Fe element in Ti-1023 ingots will migrate, making its distribution more uniform and reducing the segregation index. In this paper, the control of Fe micro-segregation in Ti-1023 ingots by homogenization HT was investigated. Firstly, dissection sampling and SEM-EDS analysis methods were used to study the distribution pattern of the Fe element in the equiaxed grains in the core of Ti-1023 ingots. It was found that the Fe content in the grain gradually increased along with the radial direction from the core to the grain boundary. Then, the homogenization HT experiments and numerical simulations of Ti-1023 at different HT temperatures from 1050 °C to 1200 °C were carried out. The results showed that the uniformity of Fe element distribution within grain can be significantly improved by the homogenization HT. With increasing HT temperature, Fe atoms migration ability increases, and the uniformity of Fe element distribution improves. Homogenization HT at 1150 °C and 1200 °C for 12 h can effectively reduce the degree of Fe element segregation. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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10 pages, 9239 KiB

Open AccessArticle

Estimation of Cooling Rate of High-Strength Thick Plate Steel during Water Quenching Based on a Dilatometric Experiment

by Hyo-Haeng Jo, Kyeong-Won Kim, Hyungkwon Park, Joonoh Moon, Young-Woo Kim, Hyun-Bo Shim and Chang-Hoon Lee

Materials 2023, 16(13), 4792; https://doi.org/10.3390/ma16134792 - 03 Jul 2023

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Abstract

The microstructure and hardness along the thickness direction of a water-quenched, high-strength thick plate with a thickness of 40 mm were investigated with three specimens from the thick plate: surface, 1/4t, and 1/2t (center) thickness, and the phase transformation behavior of the thick [...] Read more.

The microstructure and hardness along the thickness direction of a water-quenched, high-strength thick plate with a thickness of 40 mm were investigated with three specimens from the thick plate: surface, 1/4t, and 1/2t (center) thickness, and the phase transformation behavior of the thick plate according to the cooling rate was analyzed through dilatometric experiments. Finally, the cooling rate for each thickness of the thick plate was estimated by comparing the microstructure and hardness of the thick plate along with the thickness with those of the dilatometric specimens. Martensite microstructure was observed on the surface of the water-quenched thick plate due to the fast cooling rate. On the other hand, an inhomogeneous microstructure was transformed inside the thick plate due to the relatively slow cooling rate and central segregation of Mn. A small fraction of bainite was shown at 1/4t thickness. A banded microstructure with martensite and bainite resulting from Mn segregation was developed at 1/2t; that is, the full martensite microstructure was transformed in the Mn-enriched area even at a slow cooling rate due to high hardenability, but a bainite microstructure was formed in the Mn-depleted area owing to relatively low hardenability. A portion of martensite with fine cementite at the surface and 1/4t was identified as auto-tempered martensite with a Bagaryatskii orientation relationship between the ferrite matrix and cementite. The microstructure and hardness as well as dilatation were investigated at various cooling rates through a dilatometric experiment, and a continuous cooling transformation (CCT) diagram was finally presented for the thick plate. Comparing the microstructure and hardness at the surface, 1/4t, and 1/2t of the thick plate with those of dilatometric specimens cooled at various cooling rates, it was estimated that the surface of the thick plate was cooled at more than 20 °C/s, whereas the 1/4t region was cooled at approximately 5~10 °C/s during water quenching. Despite the difficulty in estimation of the cooling rate of 1/2t due to the banded structure, the cooling rate of 1/2t was estimated between 3 and 5 °C/s based on the results of an Mn-depleted zone. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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18 pages, 5154 KiB

Open AccessArticle

A Modified Constitutive Model and Microstructure Characterization for 2195 Al-Li Alloy Hot Extrusion

by Hui Li, Jian Wang, Yuanchun Huang and Rong Fu

Materials 2023, 16(10), 3826; https://doi.org/10.3390/ma16103826 - 18 May 2023

Cited by 1 | Viewed by 1021

Abstract

The quality of extruded profiles depends largely on accurate constitutive models and thermal processing maps. In this study, a modified Arrhenius constitutive model for homogenized 2195 Al-Li alloy with multi-parameter co-compensation was developed and further enhanced the prediction accuracy of flow stresses. Through [...] Read more.

The quality of extruded profiles depends largely on accurate constitutive models and thermal processing maps. In this study, a modified Arrhenius constitutive model for homogenized 2195 Al-Li alloy with multi-parameter co-compensation was developed and further enhanced the prediction accuracy of flow stresses. Through the processing map and microstructure characterization, the 2195 Al-Li alloy could be deformed optimally at the temperature range of 710~783 K and strain rate of 0.001~0.12 s⁻¹, preventing the occurrence of local plastic flow and abnormal growth of recrystallized grains. The accuracy of the constitutive model was verified through numerical simulation of 2195 Al-Li alloy extruded profiles with large shaped cross-sections. Dynamic recrystallization occurred at different regions during the practical extrusion process, resulting in slight variations in the microstructure. The differences in microstructure were due to the varying degrees of temperature and stress experienced by the material in different regions. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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17 pages, 15325 KiB

Open AccessArticle

Microstructure, Mechanical Properties and Oxidation Resistance of Nb-Si Based Ultrahigh-Temperature Alloys Prepared by Hot Press Sintering

by Lijing Zhang, Ping Guan and Xiping Guo

Materials 2023, 16(10), 3809; https://doi.org/10.3390/ma16103809 - 18 May 2023

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Abstract

Nb-Si based ultrahigh-temperature alloys with the composition of Nb-22Ti-15Si-5Cr-3Al (atomic percentage, at. %) were prepared by hot press sintering (HPS) at 1250, 1350, 1400, 1450 and 1500 °C. The effects of HPS temperatures on the microstructure, room temperature fracture toughness, hardness and isothermal [...] Read more.

Nb-Si based ultrahigh-temperature alloys with the composition of Nb-22Ti-15Si-5Cr-3Al (atomic percentage, at. %) were prepared by hot press sintering (HPS) at 1250, 1350, 1400, 1450 and 1500 °C. The effects of HPS temperatures on the microstructure, room temperature fracture toughness, hardness and isothermal oxidation behavior of the alloys were investigated. The results showed that the microstructures of the alloys prepared by HPS at different temperatures were composed of Nbss, βTiss and γ(Nb,X)₅Si₃ phases. When the HPS temperature was 1450 °C, the microstructure was fine and nearly equiaxed. When the HPS temperature was lower than 1450 °C, the supersaturated Nbss with insufficient diffusion reaction still existed. When the HPS temperature exceeded 1450 °C, the microstructure coarsened obviously. Both the room temperature fracture toughness and Vickers hardness of the alloys prepared by HPS at 1450 °C were the highest. The alloy prepared by HPS at 1450 °C exhibited the lowest mass gain upon oxidation at 1250 °C for 20 h. The oxide film was mainly composed of Nb₂O₅, TiNb₂O₇, TiO₂ and a small amount of amorphous silicate. The formation mechanism of oxide film is concluded as follows: TiO₂ forms by the preferential reaction of βTiss and O in the alloy; after that, a stable oxide film composed of TiO₂ and Nb₂O₅ forms; then, TiNb₂O₇ is formed by the reaction of TiO₂ and Nb₂O₅. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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11 pages, 3192 KiB

Open AccessArticle

In-Situ Synchrotron HEXRD Study on the Micro-Stress Evolution Behavior of a Superalloy during Room-Temperature Compression

by Hao Wang, Ruolan Tong, Guangxu Liu, Aixue Sha, Lin Song and Tiebang Zhang

Materials 2023, 16(10), 3761; https://doi.org/10.3390/ma16103761 - 16 May 2023

Viewed by 936

Abstract

The residual stress generated during heat treatment of nickel-base superalloys will affect their service performance and introduce primary cracks. In a component with high residual stress, a tiny amount of plastic deformation at room temperature can release the stress to a certain extent. [...] Read more.

The residual stress generated during heat treatment of nickel-base superalloys will affect their service performance and introduce primary cracks. In a component with high residual stress, a tiny amount of plastic deformation at room temperature can release the stress to a certain extent. However, the stress-releasing mechanism is still unclear. In the present study, the micro-mechanical behavior of the FGH96 nickel-base superalloy during room temperature compression was studied using in situ synchrotron radiation high-energy X-ray diffraction. The in situ evolution of the lattice strain was observed during deformation. The stress distribution mechanism of grains and phases with different orientations was clarified. The results show that at the elastic deformation stage, the (200) lattice plane of γ′ phase bears more stress after the stress reaches 900 MPa. When the stress exceeds 1160 MPa, the load is redistributed to the grains with their <200> crystal directions aligned with the loading direction. After yielding, the γ′ phase still bears the main stress. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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17 pages, 20474 KiB

Open AccessArticle

Improving Precipitation in Cryogenic Rolling 6016 Aluminum Alloys during Aging Treatment

by Xucheng Wang, Yu Liu and Yuanchun Huang

Materials 2023, 16(9), 3336; https://doi.org/10.3390/ma16093336 - 24 Apr 2023

Cited by 3 | Viewed by 861

Abstract

This study systematically investigated the performance and microstructure characterization of cryogenic rolling (CR) and room-temperature rolling (RTR) Al–Mg–Si alloys. The result showed that the hardness of the CR alloys decreased at the early aging stage, but that the hardness of the RTR alloys [...] Read more.

This study systematically investigated the performance and microstructure characterization of cryogenic rolling (CR) and room-temperature rolling (RTR) Al–Mg–Si alloys. The result showed that the hardness of the CR alloys decreased at the early aging stage, but that the hardness of the RTR alloys increased at the early aging stage. Retrogression phenomena were apparent in the CR alloys at the early aging stage. Despite undergoing the same solid solution treatment, a few substructures were still observed in the CR alloys, and the degree of recrystallization in the CR alloys was significantly inferior to that in the RTR alloys. After aging for 50 h, the strength and precipitates’ density in the CR 75 alloy were higher than that in the other alloys; this indicated that the substructures were beneficial to precipitation and precipitate growth. A precipitation strength model was employed to illustrate the precipitation contribution at different aging stages. The results showed that the CR 75 alloy obtained the strongest precipitation strengthening. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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20 pages, 10730 KiB

Open AccessArticle

On the Role of Microstructure and Defects in the Room and High-Temperature Tensile Behavior of the PBF-LB A357 (AlSi7Mg) Alloy in As-Built and Peak-Aged Conditions

by Lavinia Tonelli, Erica Liverani, Gianluca Di Egidio, Alessandro Fortunato, Alessandro Morri and Lorella Ceschini

Materials 2023, 16(7), 2721; https://doi.org/10.3390/ma16072721 - 29 Mar 2023

Cited by 3 | Viewed by 1117

Abstract

Additive processes like Laser Beam Powder Bed Fusion (PBF-LB) result in a distinctive microstructure characterized by metastability, supersaturation, and finesse. Post-process heat treatments modify microstructural features and tune mechanical behavior. However, the exposition at high temperatures can induce changes in the microstructure. Therefore, [...] Read more.

Additive processes like Laser Beam Powder Bed Fusion (PBF-LB) result in a distinctive microstructure characterized by metastability, supersaturation, and finesse. Post-process heat treatments modify microstructural features and tune mechanical behavior. However, the exposition at high temperatures can induce changes in the microstructure. Therefore, the present work focuses on the analyses of the tensile response at room and high (200 °C) temperature of the A357 (AlSi7Mg0.6) alloy processed by PBF-LB and subjected to tailored T5 (direct aging) and T6R (rapid solution treatment, quenching, and aging) treatments. Along with the effect of microstructural features in the as-built T5 and T6R alloy, the role of typical process-related defects is also considered. In this view, the structural integrity of the alloy is evaluated by a deep analysis of the work-hardening behavior, and quality indexes have been compared. Results show that T5 increases tensile strength at room temperature without compromising ductility. T6R homogenizes the microstructure and enhances the structural integrity by reducing the detrimental effect of defects, resulting in the best trade-off between strength and ductility. At 200 °C, tensile properties are comparable, but if resilience and toughness moduli are considered, as-built and T5 alloys show the best overall mechanical performance. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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15 pages, 5893 KiB

Open AccessArticle

Homogenization of Extrusion Billets of a Novel Al-Mg-Si-Cu Alloy with Increased Copper Content

by Antoni Woźnicki, Beata Leszczyńska-Madej, Grzegorz Włoch, Jacek Madura, Marek Bogusz and Dariusz Leśniak

Materials 2023, 16(5), 2091; https://doi.org/10.3390/ma16052091 - 03 Mar 2023

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Abstract

Within the present work the homogenization of DC-cast (direct chill-cast) extrusion billets of Al-Mg-Si-Cu alloy was investigated. The alloy is characterized by higher Cu content than currently applied in 6xxx series. The aim of the work was analysis of billets homogenization conditions enabling [...] Read more.

Within the present work the homogenization of DC-cast (direct chill-cast) extrusion billets of Al-Mg-Si-Cu alloy was investigated. The alloy is characterized by higher Cu content than currently applied in 6xxx series. The aim of the work was analysis of billets homogenization conditions enabling maximum dissolution of soluble phases during heating and soaking as well as their re-precipitation during cooling in form of particles capable for rapid dissolution during subsequent processes. The material was subjected to laboratory homogenization and the microstructural effects were assessed on the basis of DSC (differential scanning calorimetry) tests, SEM/EDS (scanning electron microscopy/energy-dispersive spectroscopy) investigations and XRD (X-ray diffraction) analyses. The proposed homogenization scheme with three soaking stages enabled full dissolution of Q-Al₅Cu₂Mg₈Si₆ and θ-Al₂Cu phases. The β-Mg₂Si phase was not dissolved completely during soaking, but its amount was significantly reduced. Fast cooling from homogenization was needed to refine β-Mg₂Si phase particles, but despite this in the microstructure coarse Q-Al₅Cu₂Mg₈Si₆ phase particles were found. Thus, rapid billets heating may lead to incipient melting at the temperature of about 545 °C and the careful selection of billets preheating and extrusion conditions was found necessary. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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10 pages, 2076 KiB

Open AccessArticle

A Machine Learning Method for Predicting Corrosion Weight Gain of Uranium and Uranium Alloys

by Xiaoyuan Wang, Wanying Zhang, Weidong Zhang and Yibo Ai

Materials 2023, 16(2), 631; https://doi.org/10.3390/ma16020631 - 09 Jan 2023

Cited by 2 | Viewed by 1238

Abstract

As an irreplaceable structural and functional material in strategic equipment, uranium and uranium alloys are generally susceptible to corrosion reactions during service, and predicting corrosion behavior has important research significance. There have been substantial studies conducted on metal corrosion research. Accelerated experiments can [...] Read more.

As an irreplaceable structural and functional material in strategic equipment, uranium and uranium alloys are generally susceptible to corrosion reactions during service, and predicting corrosion behavior has important research significance. There have been substantial studies conducted on metal corrosion research. Accelerated experiments can shorten the test time, but there are still differences in real corrosion processes. Numerical simulation methods can avoid radioactive experiments, but it is difficult to fully simulate a real corrosion environment. The modeling of real corrosion data using machine learning methods allows for effective corrosion prediction. This research used machine learning methods to study the corrosion of uranium and uranium alloys in air and established a corrosion weight gain prediction model. Eleven classic machine learning algorithms for regression were compared and a ten-fold cross validation method was used to choose the highest accuracy algorithm, which was the extra trees algorithm. Feature selection methods, including the extra trees and Pearson correlation analysis methods, were used to select the most important four factors in corrosion weight gain. As a result, the prediction accuracy of the corrosion weight gain prediction model was 96.8%, which could determine a good prediction of corrosion for uranium and uranium alloys. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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Review

Jump to: Research

15 pages, 3035 KiB

Open AccessReview

Review on Progress of Lamellar Orientation Control in Directionally Solidified TiAl Alloys

by Han Liu, Xianfei Ding, Xiao Zong, Hong Huang, Hai Nan, Yongfeng Liang and Junpin Lin

Materials 2023, 16(13), 4829; https://doi.org/10.3390/ma16134829 - 05 Jul 2023

Viewed by 868

Abstract

TiAl alloys have excellent high-temperature performance and are potentially used in the aerospace industry. By controlling the lamellar orientation through directional solidification (DS) technology, the plasticity and strength of TiAl alloy at room temperature and high temperatures can be effectively improved. However, various [...] Read more.

TiAl alloys have excellent high-temperature performance and are potentially used in the aerospace industry. By controlling the lamellar orientation through directional solidification (DS) technology, the plasticity and strength of TiAl alloy at room temperature and high temperatures can be effectively improved. However, various difficulties lie in ensuring the lamellar orientation is parallel to the growth direction. This paper reviews two fundamental thoughts for lamellar orientation control: using seed crystals and controlling the solidification path. Multiple specific methods and their progress are introduced, including α seed crystal method, the self-seeding method, the double DS self-seeding method, the quasi-seeding method, the pure metal seeding method, and controlling solidification parameters. The advantages and disadvantages of different methods are analyzed. This paper also introduces novel ways of controlling the lamellar orientation and discusses future development. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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18 pages, 27334 KiB

Open AccessReview

An Overview of Thermal Exposure on Microstructural Degradation and Mechanical Properties in Ni-Based Single Crystal Superalloys

by Jian Zhang, Fan Lu and Longfei Li

Materials 2023, 16(5), 1787; https://doi.org/10.3390/ma16051787 - 22 Feb 2023

Cited by 1 | Viewed by 1268

Abstract

Microstructural stability at elevated temperatures is one of the main concerns for the service reliability of aero-engine turbine blades. Thermal exposure, as an important approach to examine the microstructural degradation, has been widely studied in Ni-based single crystal (SX) superalloys for decades. This [...] Read more.

Microstructural stability at elevated temperatures is one of the main concerns for the service reliability of aero-engine turbine blades. Thermal exposure, as an important approach to examine the microstructural degradation, has been widely studied in Ni-based single crystal (SX) superalloys for decades. This paper presents a review on the microstructural degradation induced by high-temperature thermal exposure and the associated damage in mechanical properties in some typical Ni-based SX superalloys. The main factors affecting the microstructural evolution during thermal exposure and the influencing factors in the degradation of mechanical properties are also summarized. Insights into the quantitative estimation of the thermal exposure-affected microstructural evolution and the mechanical properties will be beneficial for the understanding and improvement of reliable service in Ni-based SX superalloys. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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18 pages, 3615 KiB

Open AccessEditor’s ChoiceReview

Research Progress on Multi-Component Alloying and Heat Treatment of High Strength and Toughness Al–Si–Cu–Mg Cast Aluminum Alloys

by Mingshan Zhang, Yaqiang Tian, Xiaoping Zheng, Yuan Zhang, Liansheng Chen and Junsheng Wang

Materials 2023, 16(3), 1065; https://doi.org/10.3390/ma16031065 - 25 Jan 2023

Cited by 15 | Viewed by 2556

Abstract

Al–Si–Cu–Mg cast aluminum alloys have important applications in automobile lightweight due to their advantages such as high strength-to-weight ratio, good heat resistance and excellent casting performance. With the increasing demand for strength and toughness of automotive parts, the development of high strength and [...] Read more.

Al–Si–Cu–Mg cast aluminum alloys have important applications in automobile lightweight due to their advantages such as high strength-to-weight ratio, good heat resistance and excellent casting performance. With the increasing demand for strength and toughness of automotive parts, the development of high strength and toughness Al–Si–Cu–Mg cast aluminum alloys is one of the effective measures to promote the application of cast aluminum alloys in the automotive industry. In this paper, the research progress of improving the strength and toughness of Al–Si–Cu–Mg cast aluminum alloys was described from the aspects of multi-component alloying and heat treatment based on the strengthening mechanism of Al–Si–Cu–Mg cast aluminum alloys. Finally, the development prospects of automotive lightweight Al–Si–Cu–Mg cast aluminum alloys is presented. Full article

(This article belongs to the Special Issue Heat Treatments and Performance of Alloy and Metal)

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