Research

12 pages, 8802 KiB

Open AccessArticle

A Novel Preparation Method of (Ti,Zr,Nb,Mo,W)B₂-SiC Composite Ceramic Based on Reactive Sintering of Pre-Alloyed Metals

by Yufei Zu, Zi Wang, Hongliang Tian, Fan Wu, Lianshen Fu, Jixiang Dai and Jianjun Sha

Crystals 2024, 14(1), 14; https://doi.org/10.3390/cryst14010014 - 22 Dec 2023

Viewed by 733

High-entropy diboride-based (MeB₂-based) ceramics are promising high-temperature structural materials because of their excellent mechanical properties, high-temperature stability, and oxidation resistance. In order to achieve low-temperature sintering of the high-entropy ceramics, a novel preparation method of high-entropy (Ti,Zr,Nb,Mo,W)B₂-SiC ceramics based [...] Read more.

High-entropy diboride-based (MeB₂-based) ceramics are promising high-temperature structural materials because of their excellent mechanical properties, high-temperature stability, and oxidation resistance. In order to achieve low-temperature sintering of the high-entropy ceramics, a novel preparation method of high-entropy (Ti,Zr,Nb,Mo,W)B₂-SiC ceramics based on reactive sintering of pre-alloyed solid-solution metals and nonmetals of Si, C, B₄C was conducted in the current work. Mechanical alloying behavior of the mixed metal powders, as well as the phase composition, microstructure, mechanical properties, and oxidation behavior of the as-sintered MeB₂-SiC ceramic were investigated. The XRD, SEM, and EPMA results indicated that the primary MeB₂ solid-solution and SiC phases could be successfully formed during reactive sintering at a relatively low temperature of 1650 °C. The as-sintered MeB₂-SiC ceramics had a high relative density of 97.8% and high mechanical properties (hardness of 19.74 ± 0.8 GPa, flexure strength of 533 ± 38 MPa, and fracture toughness of 6.01 ± 0.77 MPa·m^1/2). Combining the oxidation behavior and microstructure evolution of the oxidation layer, a continuous and relatively dense MeO_x-SiO₂ oxidation layer was gradually formed and covered on the external surface, leading to decelerating oxidation behavior after an oxidation exposure time of 10 min. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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18 pages, 6378 KiB

Open AccessArticle

Comparative Analysis of Three Constitutive Models and Microstructure Characteristics of Nb521 during Hot Deformation

by Baohui Zhu, Minghang Jia, Rui Zhao and Min Wan

Crystals 2023, 13(8), 1170; https://doi.org/10.3390/cryst13081170 - 27 Jul 2023

Viewed by 825

Abstract

This study presents an exploration of the flow stress constitutive model and the deformation mechanism of Nb521, both critical for its practical application. Hot-compression experiments were performed on Nb521 at temperatures ranging from 1523 K to 1723 K and strain rates ranging from [...] Read more.

This study presents an exploration of the flow stress constitutive model and the deformation mechanism of Nb521, both critical for its practical application. Hot-compression experiments were performed on Nb521 at temperatures ranging from 1523 K to 1723 K and strain rates ranging from 0.01 to 10

s^{- 1}

. In addition, the microstructure evolution was concurrently studied through scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The stress–strain behaviour of Nb521 was assessed, leading to the development of three constitutive models: the Johnson–Cook model, the modified Johnson–Cook model and the Arrhenius model. In the course of the deformation process, it is consistently observed that the hardening effect surpasses the softening effect during the plastic phase, with no observable occurrence of a steady-state phase. The modified Johnson–Cook model offers superior predictive accuracy. Both grain elongation and torsion are the main deformation mechanisms of Nb521 and specific texture forms during stretching. This study also reveals that fractures at both room temperature and high temperatures are brittle in nature. The elucidation of the constitutive model and underlying deformation mechanisms in this study offers indispensable insights into the hot-deformation behaviour of Nb521. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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18 pages, 48762 KiB

Open AccessArticle

A New, Precise Constitutive Model and Thermal Processing Map Based on the Hot Deformation Behavior of 2219 Aluminum Alloy

by Jing Wang, Guiqian Xiao and Jiansheng Zhang

Crystals 2023, 13(5), 732; https://doi.org/10.3390/cryst13050732 - 26 Apr 2023

Cited by 1 | Viewed by 865

Abstract

To study the hot deformation behavior of and obtain the optimal hot processing parameters for 2219 aluminum alloy, a new, precise constitutive model based on the partial derivative of flow data was constructed and hot processing maps were constructed based on the new [...] Read more.

To study the hot deformation behavior of and obtain the optimal hot processing parameters for 2219 aluminum alloy, a new, precise constitutive model based on the partial derivative of flow data was constructed and hot processing maps were constructed based on the new model. First, isothermal compression experiments were conducted at strain rates of 0.01–10 s⁻¹ and temperatures of 573–773 K, and the high-order differences of the logarithmic stress with respect to the temperature and logarithmic strain rate were calculated. Second, a new, precise constitutive model based on the high-order differences was constructed, and the predictive accuracies of the new model and the Arrhenius model were compared. Finally, the hot processing maps of 2219 aluminum alloy were constructed using the new model, and its optimal hot processing parameters were validated with metallographic experiments. The results showed that a first-order approximation between logarithmic stress and temperature and a third-order approximation between logarithmic stress and the logarithmic strain rate need to be considered to construct a high-precision constitutive model without significantly increasing material parameters. The new model exhibited a significantly higher prediction accuracy than the Arrhenius model at a high strain rate and low temperature levels. With an increase in temperature, the energy dissipation increased at a constant strain rate, and with an increase in the strain rate, the energy dissipation first increased and then decreased at constant temperature. The best region for hot processing was located in the temperature range of 673–773 K and the strain rate range of 0.1–1 s⁻¹. The results of microstructure analysis were in good agreement with the prediction results of hot processing maps. Hot processing maps can be used to guide the hot working process formulation of 2219 aluminum alloy. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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13 pages, 4330 KiB

Open AccessArticle

Spark Plasma Sintering (SPS) of Multi-Principal Element Alloys of Copper-Niobium-Titanium-Di-Boride-Graphite, Investigation of Microstructures, and Properties

by Azunna Agwo Eze, Emmanuel Rotimi Sadiku, Williams Kehinde Kupolati, Jacques Snyman, Julius Musyoka Ndambuki and Idowu David Ibrahim

Crystals 2022, 12(12), 1754; https://doi.org/10.3390/cryst12121754 - 03 Dec 2022

Viewed by 1143

Abstract

A near-equiatomic multi-principal element alloy of Cu₄₀Nb₃₀(TiB₂)₂₀C₁₀ with both nano-particle size (14 nm) and micron-particle sizes (−44 µm) of Nb was designed and made via the spark plasma sintering technique at two different sintered [...] Read more.

A near-equiatomic multi-principal element alloy of Cu₄₀Nb₃₀(TiB₂)₂₀C₁₀ with both nano-particle size (14 nm) and micron-particle sizes (−44 µm) of Nb was designed and made via the spark plasma sintering technique at two different sintered temperatures of 650 °C and 700 °C with other SPS parameters being constant. The sintering mode, microstructures, microhardness, density, relative density, wear behavior, and corrosion properties of the alloys were investigated and compared to ascertain the best for aerospace applications. The SPS technique was applied to produce the tested samples in this study. The results showed that the alloys with nano-particles of Nb sintered faster, with the lowest wear rate, and their microstructure shows a dendritic configuration with the existence of graphite-rich and niobium-rich nano-segregations in the inter-dendritic areas with the lowest coefficient of friction, Cu-NbTiB₂C with nano-particles of Nb sintered at 650 °C recorded the highest microhardness value (786.03 HV_0.2), and CuNbTiB₂C with micro-particles of Nb sintered at 700 °C exhibited the best anti-corrosion characteristics in a sulphuric acid environment. The results obtained in this study correspond to the requirements for high-performance engineering materials, which will make the novel materials relevant in the aerospace industry. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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12 pages, 2717 KiB

Open AccessFeature PaperArticle

Aero-TiO₂ Prepared on the Basis of Networks of ZnO Tetrapods

by Vladimir Ciobanu, Veaceslav V. Ursaki, Sebastian Lehmann, Tudor Braniste, Simion Raevschi, Victor V. Zalamai, Eduard V. Monaico, Pascal Colpo, Kornelius Nielsch and Ion M. Tiginyanu

Crystals 2022, 12(12), 1753; https://doi.org/10.3390/cryst12121753 - 03 Dec 2022

Cited by 4 | Viewed by 1712

Abstract

In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technology consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures [...] Read more.

In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technology consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures and etching of the sacrificial template. Two procedures are applied for etching, one of which is wet etching in a citric acid aqua solution, while the other one is etching in a hydride vapor phase epitaxy (HVPE) system with HCl and hydrogen chemicals. The morphology, composition, and crystal structure of the produced aeromaterials are investigated depending on the temperature of annealing and the sequence of the technological steps. The performed photoluminescence analysis suggests that the developed aeromaterials are potential candidates for photocatalytic applications. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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13 pages, 7865 KiB

Open AccessArticle

Investigating the β-Mg₁₇Al₁₂ Alloy under Pressure Using First-Principles Methods: Structure, Elastic Properties, and Mechanical Properties

by Chuncai Xiao, Zongxing Tu, Luliang Liao, Zhiwen Liu, Yufeng Wen and Xianshi Zeng

Crystals 2022, 12(12), 1741; https://doi.org/10.3390/cryst12121741 - 01 Dec 2022

Cited by 1 | Viewed by 1195

Abstract

Calculations of first principles were employed to explore the elastic constants of the

β

-Mg₁₇Al₁₂ intermetallic complex under pressure, along with several related physical parameters, including the bulk modulus, the shear modulus, Young’s modulus, Poisson’s ratio, and the anisotropy index. [...] Read more.

Calculations of first principles were employed to explore the elastic constants of the

β

-Mg₁₇Al₁₂ intermetallic complex under pressure, along with several related physical parameters, including the bulk modulus, the shear modulus, Young’s modulus, Poisson’s ratio, and the anisotropy index. The volume of the

β

-Mg

_{17}

Al

_{12}

crystal in the ground state was V₀ = 1180.353 Å

^{3}

, and the lattice parameter was 10.57 Å. This is in agreement with the available results in the literature, which indicate that the calculations were correct. The three independent elastic constants, C₁₁, C₁₂, and C₄₄, increased with increasing pressure. The bulk modulus B, shear modulus G, and Young’s modulus E increased with increasing pressure, indicating that the bulk deformation resistance, shear deformation resistance, and stiffness of the

β

-Mg

_{17}

Al

_{12}

phase increased with increasing pressure. The phase had a

B / G

> 1.75 and a Poisson’s ratio of

ν

> 0.26 and increased with pressure, indicating that the

β

-Mg

_{17}

Al

_{12}

crystals were ductile and that the ductility increased with pressure. The Cauchy pressure C

_{12}

–C

_{44}

increased with increasing pressure. The anisotropy coefficients A

_{(100)}

and A

_{(110)}

deviated further from 1, and the anisotropy increased. The electronic structure calculations showed that the total density of the states (TDOS) was achieved mainly by the Mg-3p and Al-3p states, and the total density of states moved toward the higher energy regions under pressure, with enhanced interatomic bonding, leading to an increase in the elastic constants and ultimately to an increase in each physical property with increasing pressure. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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10 pages, 2836 KiB

Open AccessArticle

Texture Evolution of a Single Crystal Cu-8% at. Al Subjected to the Drawing Process

by Tomasz Tokarski, Grzegorz Cios, Dorota Moszczynska, Boguslawa Adamczyk-Cieslak, Milena Koralnik and Jaroslaw Mizera

Crystals 2022, 12(10), 1435; https://doi.org/10.3390/cryst12101435 - 11 Oct 2022

Viewed by 1553

Abstract

Single crystals of Cu-8.% at. Al were subjected to cold drawing up to 1.1 true strain. Development of the crystallographic texture was analysed at various stages of the drawing process. Investigations revealed significant crystal rotation and reorientation due to a twinning process, while [...] Read more.

Single crystals of Cu-8.% at. Al were subjected to cold drawing up to 1.1 true strain. Development of the crystallographic texture was analysed at various stages of the drawing process. Investigations revealed significant crystal rotation and reorientation due to a twinning process, while general 4-fold symmetry around the drawing direction was preserved. Local texture analysis performed on cross-sections perpendicular to the drawing direction showed that due to crystal rotation, the original crystal was initially fragmented into four quadrants. However, within the volume near the central axis the initial cubic orientation was preserved. Subsequent deformation within dominating twinning systems led to further fragmentation which divided the crystal into sectors one eighth the size of the full circular cross-section. The obtained results also indicate that approximation of the drawing process stress state by the tensor having only normal components cannot be used during analysis of the activation of deformation systems. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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24 pages, 11106 KiB

Open AccessArticle

Mechanical Response and Fracture of Pultruded Carbon Fiber/Epoxy in Various Modes of Loading

by Arie Bussiba, Ilan Gilad, Snir Lugassi, Sigal David, Jacob Bortman and Zohar Yosibash

Crystals 2022, 12(6), 850; https://doi.org/10.3390/cryst12060850 - 16 Jun 2022

Cited by 3 | Viewed by 1788

Abstract

Pultrusion is a continuous process of forming constant cross-sections of unidirectional composites with a significant long length. This unique process is implemented widely in the composites industry due to its continuous, automated, and highly productive nature. The current research focused on mechanical response [...] Read more.

Pultrusion is a continuous process of forming constant cross-sections of unidirectional composites with a significant long length. This unique process is implemented widely in the composites industry due to its continuous, automated, and highly productive nature. The current research focused on mechanical response characterization at three modes of loading: tensile, compression, and shear loading of coupons made from a graphite/epoxy 1 mm sheet. In addition, the effects of holes and notches were examined in terms of mechanical properties. The mechanical behavior was assessed through stress–strain curves with careful attention on the curve profile, macroscopic fracture modes observations, and optical microscopic tracking with continuous video records. The mechanical tests follow standards with some critiques on the shear test. Finite element analysis (FEA) was used to accurately determine the shear modulus, and for other mechanical investigations. By nature, under tension, the unidirectional fiber composite at 0° orientation exhibits high strength (2800 MPa), with very low strength at 90° orientation (40 MPa). Both orientations display linear mechanical behavior. Under compression, 0° orientation exhibits low strength (1175 MPa), as compared to tension due to the kinking phenomena, which is the origin in the deviation from linear behavior. Under shear, both orientations exhibit approximately the same shear strength (45 MPa for 0° and 47 MPa for 90°), which is mainly related to the mechanical properties of the epoxy resin. In general, in the presence of holes, the remote fracture stress in the various modes of loading did not change significantly, as compared to uniform coupons; however, some localized delamination crack growth occurred at the vicinity of the holes, manifested by load drops up to the final fracture. This behavior is also attributed to the tension of notched coupons. FEA shows that the shear values were unaffected by manufacturing imperfections, coupon thickness, and by asymmetrical gripping up to 3 mm, with minor effect in the case of a small deviation from the load line. Selected experimental tests support the FEA tendencies. Full article

(This article belongs to the Special Issue Advanced Aerospace Materials: Processing, Microstructure, Mechanical Properties and Applications)

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