Crystals

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10 pages, 2526 KiB

Open AccessArticle

First Principle Study on Mg₂X (X = Si, Ge, Sn) Intermetallics by Bi Micro-Alloying

by Guoning Bai, Jinzhong Tian, Qingwei Guo, Zhiqiang Li and Yuhong Zhao

Crystals 2021, 11(2), 142; https://doi.org/10.3390/cryst11020142 - 29 Jan 2021

Cited by 8 | Viewed by 1796

Being a positive candidate reinforcement material for laminar composites, the Mg₂X (X = Si, Ge, Sn) based intermetallics have attracted much attention. The elastic properties, anisotropy, and electronic properties of intermetallic compounds with Bi-doped Mg₂X (X = Si, Ge, [...] Read more.

Being a positive candidate reinforcement material for laminar composites, the Mg₂X (X = Si, Ge, Sn) based intermetallics have attracted much attention. The elastic properties, anisotropy, and electronic properties of intermetallic compounds with Bi-doped Mg₂X (X = Si, Ge, Sn) are calculated by the first principles method. Results show that the lattice parameters of Mg₂X are smaller than those of Bi-doped Mg₂X. The element Bi preferentially occupies the position of the X (X = Si, Ge, Sn) atom than other positions. Mg₂X (X = Si, Ge, Sn), Mg₆₃X₃₂Bi, Mg₆₄X₃₁Bi, Mg₆₄Ge₃₂Bi, and Mg₆₄Sn₃₂Bi are mechanically stable, while Mg₆₄Si₃₂Bi indicates that it cannot exist stably. The doping of alloying element Bi reduces the shear deformation resistance of the Mg₂X (X = Si, Ge, Sn) alloy. The pure and Bi-doped Mg₂X (X = Si, Ge, Sn) exhibits elastic and anisotropic characteristics. The contribution of the Bi orbitals of Mg₆₃X₃₂Bi, Mg₆₄X₃₁Bi, and Mg₆₃X₃₂Bi are different, resulting in different hybridization effects in three types of Bi-doped Mg₂X. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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10 pages, 5300 KiB

Open AccessArticle

Effect of Modification on Microstructure and Properties of AZ91 Magnesium Alloy

by Andrzej Kiełbus, Robert Jarosz and Adam Gryc

Crystals 2020, 10(6), 536; https://doi.org/10.3390/cryst10060536 - 24 Jun 2020

Cited by 6 | Viewed by 3049

Abstract

Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. [...] Read more.

Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. Overheating, hexachloroethane and wax-CaF₂-carbon powder were applied. The research procedure comprised microstructure analysis by means of light microscopy, scanning electron microscopy and quantitative analysis with AnalySIS Pro^® software and mechanical properties’ investigation. The microstructure of AZ91 alloy in the as-cast condition consists of α-Mg solid solution with precipitates of Mg₁₇Al_12, Mg₂Si and Al₈Mn₅ phases. It was reported that all applied modifiers cause refinement of α-Mg solid solution grains and a decrease of the volume fraction of α-Mg+Mg₁₇Al₁₂ compound discontinuous precipitates. The best results were obtained in the case of wax-CaF₂-carbon powder. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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12 pages, 4517 KiB

Open AccessArticle

Microstructure and Texture Evolution during Twin-Roll Casting and Annealing of a Mg–6.8Y2.5Zn–0.4Zr Alloy (WZ73)

by Kristina Kittner, Madlen Ullmann, Falko Arndt, Rudolf Kawalla and Ulrich Prahl

Crystals 2020, 10(6), 513; https://doi.org/10.3390/cryst10060513 - 16 Jun 2020

Cited by 15 | Viewed by 2836

Abstract

In the present work, the microstructure and texture of a Mg–6.8Y–2.5Zn–0.4Zr sheet manufactured by twin-roll casting were investigated. The twin-roll cast state consisted of two apparent phases: the α-Mg matrix, which was made up of dobulites with an average grain size of approximately [...] Read more.

In the present work, the microstructure and texture of a Mg–6.8Y–2.5Zn–0.4Zr sheet manufactured by twin-roll casting were investigated. The twin-roll cast state consisted of two apparent phases: the α-Mg matrix, which was made up of dobulites with an average grain size of approximately 50 µm and the LPSO (long-period stacking ordered) phase, which formed network-like precipitates along the grain boundaries. After twin-roll casting, annealing was carried out under conditions of different temperatures ranging from 450 °C to 525 °C and holding times between 2 h and 24 h. It was found that heat treatment led to the formation of a microstructure in which grains were apparent. Furthermore, it could be observed that high temperatures > 500 °C led to changes in the morphology of the LPSO structures. On one hand, the network-like structure dissolved while, on the other hand, both rodlike and blocky LPSO phases precipitated predominantly at the grain boundaries of the α-Mg matrix. This process was fostered by high temperatures and long holding times. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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17 pages, 8097 KiB

Open AccessArticle

Stabilisation of a Segment of Autologous Vascularised Stomach as a Patch for Myocardial Reconstruction with Degradable Magnesium Alloy Scaffolds in a Swine Model

by Tobias Schilling, Michael Bauer, Dagmar Hartung, Gudrun Brandes, Igor Tudorache, Serghei Cebotari, Tanja Meyer, Frank Wacker, Axel Haverich and Thomas Hassel

Crystals 2020, 10(6), 438; https://doi.org/10.3390/cryst10060438 - 29 May 2020

Cited by 2 | Viewed by 2079

Abstract

In patients with severe heart failure, the surgical reconstruction of the damaged myocardium with regenerative biological grafts is an innovative therapeutic option. However, natural patch materials are often too delicate for a full wall repair of the left ventricle. A degradable magnesium scaffold [...] Read more.

In patients with severe heart failure, the surgical reconstruction of the damaged myocardium with regenerative biological grafts is an innovative therapeutic option. However, natural patch materials are often too delicate for a full wall repair of the left ventricle. A degradable magnesium scaffold could provide temporary mechanical stability until the sufficient physiological remodeling of such grafts. An autologous vascularised gastric patch was employed for the reconstruction of the left ventricular myocardium in a porcine model. Magnesium alloy (LA63) scaffolds were fixed over the biological patch. The function of the implant was assessed via magnetic resonance imaging. Angiography was carried out to detect a connection between the gastric and coronary vasculature. The explants were examined via µ-computer tomography and light microscopy. All the test animals survived. The prostheses integrated biologically and functionally into the myocardium. No rupture of the prostheses occurred. An anastomosis of the gastric and coronary vasculature had developed. The magnesium scaffolds degraded, on average, to 30.9% of their original volume. This novel technique responds to the increasing demand for regenerative myocardial grafts. The magnesium scaffolds’ biocompatibility and degradation kinetics, as well as their stabilizing effects, indicate their applicability in the surgical treatment of terminal heart failure. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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18 pages, 5218 KiB

Open AccessArticle

Enhanced Mechanical Properties of Surface Treated AZ31 Reinforced Polymer Composites

by Muhammad Shoaib Butt, Adnan Maqbool, Malik Adeel Umer, Mohsin Saleem, Rizwan Ahmed Malik, Ibrahim M. Alarifi and Hussein Alrobei

Crystals 2020, 10(5), 381; https://doi.org/10.3390/cryst10050381 - 08 May 2020

Cited by 10 | Viewed by 2491

Abstract

To enhance the potential application of naturally biodegradable polylactic acid (PLA)-based composites reinforced with magnesium alloy, anodized coatings between Mg and PLA were fabricated on AZ31 magnesium alloy rods. After anodizing (AO) at four different treatment times, the surface demonstrated a typical porous [...] Read more.

To enhance the potential application of naturally biodegradable polylactic acid (PLA)-based composites reinforced with magnesium alloy, anodized coatings between Mg and PLA were fabricated on AZ31 magnesium alloy rods. After anodizing (AO) at four different treatment times, the surface demonstrated a typical porous MgO ceramics morphology, which greatly improved the mechanical properties of composite rods compared to untreated pure Mg. This was attributed to the micro-anchoring effect, which increases interfacial binding forces significantly between the Mg rod and PLA. Additionally, the AO layer can also substantially improve the degradability of composite rods in Hank’s solution, due to good corrosion resistance and stronger bonding between PLA and Mg. With a prolonged immersion time of up to 30 days, the porous MgO coating was eventually found to be degraded, evolving to a comparatively smooth surface resulting in a decline in mechanical properties due to a decrease in interfacial bonding strength. According to the current findings, the PLA-clad surface treated Mg composite rod may hold promise for use as a bioresorbable implant material for orthopedic inner fixation. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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16 pages, 13348 KiB

Open AccessArticle

Effect of Necklace-Type Distribution of SiC Particles on Dry Sliding Wear Behavior of As-Cast AZ91D/SiC_p Composites

by Chao Sun, Nannan Lu, Huan Liu, Xiaojun Wang, Xiaoshi Hu and Deqiang Chen

Crystals 2020, 10(4), 296; https://doi.org/10.3390/cryst10040296 - 13 Apr 2020

Cited by 8 | Viewed by 2299

Abstract

In this study, the dry sliding wear behaviors of SiC particle reinforced AZ91D matrix composites fabricated by stirring casting method were systematically investigated. The SiC particles in as-cast composites exhibited typical necklace-type distribution, which caused the weak interface bonding between SiC particles and [...] Read more.

In this study, the dry sliding wear behaviors of SiC particle reinforced AZ91D matrix composites fabricated by stirring casting method were systematically investigated. The SiC particles in as-cast composites exhibited typical necklace-type distribution, which caused the weak interface bonding between SiC particles and matrix in particle-segregated zones. During dry sliding at higher applied loads, SiC particles were easy to debond from the matrix, which accelerated the wear rates of the composites. While at the lower load of 10 N, the presence of SiC particles improved the wear resistance. Moreover, the necklace-type distribution became more evident with the decrease of particle sizes and the increase of SiC volume fractions. Larger particles had better interface bonding with the matrix, which could delay the transition of wear mechanism from oxidation to delamination. Therefore, composites reinforced by larger SiC particles exhibited higher wear resistance. Similarly, owing to more weak interfaces in the composites with high content of SiC particles, more severe delamination occurred and the wear resistance of the composites was impaired. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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14 pages, 2276 KiB

Open AccessArticle

First Principles Study on the Thermodynamic and Elastic Mechanical Stability of Mg₂X (X = Si,Ge) Intermetallics with (anti) Vacancy Point Defects

by Yuhong Zhao, Jinzhong Tian, Guoning Bai, Leting Zhang and Hua Hou

Crystals 2020, 10(3), 234; https://doi.org/10.3390/cryst10030234 - 23 Mar 2020

Cited by 12 | Viewed by 3080

Abstract

In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus [...] Read more.

In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus of Mg₂X (X = Si, Ge) intermetallics with or without point defects are calculated. The results show that the difference in the atomic radius leads to the instability and distortion of crystal cells with point defects; Mg₂X are easier to form vacancy defects than anti-site defects on the X (X = Si, Ge) lattice site, and form anti-site defects on the Mg lattice site. Generally, the point defect is more likely to appear at the Mg position than at the Si or Ge position. Among the four kinds of point defects, the anti-site defect

x_{M g}

is the easiest to form. The structure of intermetallics without defects is more stable than that with defects, and the structure of the intermetallics with point defects at the Mg position is more stable than that at the Si/Ge position. The anti-site and vacancy defects will reduce the material’s resistance to volume deformation shear strain, and positive elastic deformation, and increase the mechanical instability of the elastic deformation of the material. Compared with the anti-site point defect, the void point defect can lead to the mechanical instability of the transverse deformation of the material and improve the plasticity of the material. The research in this paper is helpful for the analysis of the mechanical stability of the elastic deformation of Mg₂X (X = Si, Ge) intermetallics under the service condition that it is easy to produce vacancy and anti-site defects. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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10 pages, 7922 KiB

Open AccessArticle

Rheological Solidification Behavior and Mechanical Properties of AZ91-Sn Alloys

by Di Tie, Boyu Zhang, Lufei Yan, Renguo Guan, Zhaoshan Ji, Haifeng Liu, Deliang Zhang, Debao Liu and Minfang Chen

Crystals 2019, 9(12), 641; https://doi.org/10.3390/cryst9120641 - 03 Dec 2019

Cited by 10 | Viewed by 2286

Abstract

The solidification and tensile deformation behaviors of rheo-cast AZ91-Sn alloys were revealed to study the effects of Sn alloying on improvement of AZ91 alloy’s mechanical properties. Two kinds of Mg₁₇Al₁₂ phases precipitated from the supersaturated magnesium matrix during rheo-solidification were [...] Read more.

The solidification and tensile deformation behaviors of rheo-cast AZ91-Sn alloys were revealed to study the effects of Sn alloying on improvement of AZ91 alloy’s mechanical properties. Two kinds of Mg₁₇Al₁₂ phases precipitated from the supersaturated magnesium matrix during rheo-solidification were observed: coarse discontinuous precipitates (DP) at grain boundaries and small-sized continuous precipitates (CP) inside grains. With increasing Sn content, the amount of Mg₁₇Al₁₂ phases was increased whilst the amount of Al atoms in the matrix was decreased. Due to the higher melting point of Mg₂Sn than Mg₁₇Al₁₂, Mg₂Sn precipitated earlier from the melt, and therefore provided heterogeneous nuclei for Mg₁₇Al₁₂ during the eutectic reaction. Due to grain refinement and solid solution strengthening, AZ91-2.4Sn (mass%) gained 52% increase in tensile strength and 93% increase in elongation compared with pure AZ91 alloy. The higher-density twins and microcracks induced by Sn alloying relaxed stress concentration during plastic deformation, so the fracture mode was transformed from cleavage fracture of pure AZ91 alloy to ductile fracture of AZ91-Sn alloys. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Magnesium Alloys and Composites)

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