Eighteen as-cast binary Mg-Ni, Mg-Mm and ternary Mg-Ni-Mm and Mg-Ni-TM （TM=transition metals （Cu, Zn, Mn and Co）; Mm = mischmetal containing Ce, La, Nd and Pr） alloys were hydrided by an electrochemical process to...Eighteen as-cast binary Mg-Ni, Mg-Mm and ternary Mg-Ni-Mm and Mg-Ni-TM （TM=transition metals （Cu, Zn, Mn and Co）; Mm = mischmetal containing Ce, La, Nd and Pr） alloys were hydrided by an electrochemical process to determine the alloys with the most potential for electrochemical hydrogen storage. The alloys were hydrided in a 6 mol/L KOH solution at 80 °C for 480 min and at 100 A/m2. To assess the electrochemical hydriding performance of alloys, maximum hydrogen concentrations, hydrogen penetration depths and total mass of absorbed hydrogen in the alloys were measured by glow discharge spectrometry. In addition, the structures and phase compositions of the alloys both before and after hydriding were studied by optical and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. It was determined that the highest total amount of hydrogen was absorbed by the Mg-25Ni-12Mm and Mg-26Ni （mass fraction, %） alloys. The maximum hydrogen concentrations in the Mg-25Ni-12Mm and Mg-26Ni alloys were 1.0% and 1.6%, respectively. The main hydriding product was the binary MgH2 hydride, and the ternary Mg2NiH4 hydride was also detected in the Mg-25Ni-12Mm alloy. The electrochemical hydriding parameters achieved are discussed in relation to the structures of alloys, alloying elements and hydriding mechanisms.展开更多
Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were ...Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were studied. The alloys were studied in the as-cast state （cooling rate of 500 K/min） and after solution heat treatment （T4）. Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution （9 g/L NaCl） was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine a-Mg dendrites and eutectic Mg-RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg-Gd alloys. For this reason, the T4 heat treatment of the Mg-Gd alloy led to the formation of a new cuboidal Mg5Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg-Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg-Gd alloys. Its effect on the corrosion of Mg-Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.展开更多
This study describes the corrosion resistance of extruded,and extruded with post-processing annealing,Mg–7.5 Li–3 Al–1 Zn alloys.The results demonstrate that extrusion at 350°C with an extrusion speed 0.5 s^(-...This study describes the corrosion resistance of extruded,and extruded with post-processing annealing,Mg–7.5 Li–3 Al–1 Zn alloys.The results demonstrate that extrusion at 350°C with an extrusion speed 0.5 s^(-1) does not lead to the full recrystallization of the alloy,and the material still exhibits a dendritic microstructure.The post-processing annealing triggers the microstructure transformation,and the relative composition of the alloy changes.The ratio ofβ(Li)toα(Mg)in the extruded alloy was 29–71%;after annealing amount ofβ(Li)increased,and the ratio ofβ(Li)toα(Mg)in the annealed alloy was 35–65%.Corrosion testing shows that in 3.5 wt%Na Cl the extruded alloys immediately undergo strong dissolution.As a result of the subsequent annealing,an improvement of corrosion resistance is observed.The higher amount ofβ(Li)in the annealed alloy reduces the area ratio of cathodic to anodic sites of corrosion,and this makes the annealed alloy more resistive under the analyzed conditions.展开更多
The effects of beryllium (Be) on the microstructure, hardness and tensile properties of A380 aluminum alloy were investigated. The base and Be-containing A380 alloys were conventionally cast in a ductile iron mold. Th...The effects of beryllium (Be) on the microstructure, hardness and tensile properties of A380 aluminum alloy were investigated. The base and Be-containing A380 alloys were conventionally cast in a ductile iron mold. The microstructure evolution was investigated using SEM and optical microscope. The mechanical properties were assessed using tensile and hardness tests, finally the rapture surfaces of the used samples were studied to reveal the fracture mechanism in the presence of Be. The results revealed that the plateletβ intermetallic phases were transformed into relatively harmless Chinese script Be?Fe phase and eutectic Si phases changed from flake-like particles into fine ones. The corresponding ultimate tensile strength (UTS) and elongation values increased from 270 MPa to 295 MPa and 3.7% to 4.7%, respectively. Additionally, the hardness of A380 alloy decreased continuously with increasing Be content. While the fracture surfaces of the unmodified A380 alloy tensile samples showed a clear brittle fracture nature, while finer dimple and fewer brittle cleavage surfaces were seen in the alloys with Be addition. Moreover, in the presence of Be, due to the refined phases, there has been a decrease in the values of hardness.展开更多
The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavi...The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavior,fracture toughness and strain rate sensitivity(SRS)of materials within micro/nanoscale.Firstly,a nanomechanical model was developed for extracting hardness(H),young’s modulus(E)and yield stress(σY)from the characteristic load points which were subsequently analyzed by atomic force microscope(AFM)images.The elasticity data and AFM data were then utilized for determination of plastic deformation in constituent phases.The displacement of the indentation gets the highest value for Mg matrix and between precipitates,depth is more in LPSO rather than that of MgRE.The serrated flow or the behavior of shear bands may originate from the side effect of the interface region in Mg alloys with precipitates.It can be deduced that the KIC produced by both L method and energy-based calculation are both reliable for KIC approximation.The maximum load in simulation withμ=0.2 friction is marginally lesser than that of the frictionless(μ=0)one while elastic recovery of indentation withμ=0.2 is higher to some extent.展开更多
Powder metallurgy is a powerful method for the preparation of materials with superior properties.This work aimed to investigate the effect of powder size on the microstructure,mechanical,and corrosion properties of ad...Powder metallurgy is a powerful method for the preparation of materials with superior properties.This work aimed to investigate the effect of powder size on the microstructure,mechanical,and corrosion properties of advanced WE43(Mg-4Y-3REE-Zr)alloy prepared by spark plasma sintering(SPS).At the same time,the effect of HF pre-treatment of the powder on the properties of final compacted products is studied.Smaller powder particles yielded microstructure with more interfaces formed by Y_(2)O_(3),or MgF_(2) and YF_(3).These interfaces work as barriers against corrosion,which greatly improves corrosion resistance.The suggested pre-treatment of powder in HF further reduced the corrosion rate of the compacted materials.On the contrary,fragile interfaces of YF_(3) decreased mechanical properties as the crack primarily propagates through these interfaces.The original powder containing the mixture of all powder fractions exerted the best combination of mechanical properties.Powder size has also shown to affect ignition temperature.The highest ignition temperature was measured for the finest powder fraction.展开更多
The MgNi26 alloy was prepared by three different methods of gravity casting (GC), mechanical alloying (MA) and rapid solidification (RS). All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 ...The MgNi26 alloy was prepared by three different methods of gravity casting (GC), mechanical alloying (MA) and rapid solidification (RS). All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 °C for 240 min. The structures and phase compositions of the alloys were studied using optical microscopy and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. A temperature-programmed desorption technique was used to measure the absorbed hydrogen and study the dehydriding process. The content of hydrogen absorbed by the MgNi26-MA (approximately 1.3%, mass fraction) was 30 times higher than that of the MgNi26-GC. The MgNi26-RS sample absorbed only 0.1% of hydrogen. The lowest temperature for hydrogen evolution was exhibited by the MgNi26-MA. Compared with pure commercial MgH2, the decomposition temperature was reduced by more than 200 °C. The favourable phase and structural composition of the MgNi26-MA sample were the reasons for the best hydriding and dehydriding properties.展开更多
In this study, Al matrix composites reinforced by 7.5 and 15 vol.% B4C particles and also monolithic Al （Al without the B4C particles） were produced by wet attrition milling and subsequent hot forward extrusion proc...In this study, Al matrix composites reinforced by 7.5 and 15 vol.% B4C particles and also monolithic Al （Al without the B4C particles） were produced by wet attrition milling and subsequent hot forward extrusion processes. The microstructure of the composites, evaluated by scanning electron microscopy （SEM）, showed that the B4C particles were properly distributed in the Al matrix. Mechanical properties of the Al/B4C composites and monolithic Al were investigated by tensile, wear and hardness tests, The results revealed that with increasing content of B4C particles, the tensile strength and microhardness of composites increased but the elongation decreased. In addition, the tensile strength and microhardness of composite samples were higher than those of monolithic Al. The density measurements revealed that the density of composites decreased with increasing content of the B4C particles.展开更多
Magnesium alloys are important materials for application in the automotive and aviation industries. During the last few years, the number of possible applications as biodegradable implants in medicine has grown. Mg-RE...Magnesium alloys are important materials for application in the automotive and aviation industries. During the last few years, the number of possible applications as biodegradable implants in medicine has grown. Mg-RE（rare earth） alloys belong to the most advanced group of products, offering the best combination of mechanical properties and corrosion resistance. Among these materials, WE43（Mg-Y-Nd）is a very well-known commercial alloy that has been extensively studied for applications at increased temperatures and also in organisms. Although this material has been described, there are still possibilities to improve its properties and subsequently expand its applicability. Powder metallurgy has already been used for the preparation of magnesium alloys with superior mechanical properties and occasionally superior corrosion properties. Therefore, the present paper is oriented toward the preparation of Mg-4Y-3RE-Zr（WE43） alloy by the powder metallurgy technique（WE43-PM） and comparison of the final properties with the product of extrusion of as-cast ingot（WE43-IM）. Our processing leads to a partial improvement in the mechanical properties and superior corrosion resistance of WE43-PM. The texture strength of WE43-PM was low, and therefore, anisotropy of mechanical properties was suppressed.展开更多
A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity...A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.展开更多
The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly dev...The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly developed SPD method)at two different extrusion ratios.The fine-grained microstructures formed in the alloys were characterized,and the influence of grain refinement on corrosion resistance was analyzed.For fine-grained(α+β)Mg-Li alloys,a higher extrusion ratio led to more intensive grain refinement;however,this relationship did not improve their corrosion resistance in a chloride-containing solution.The corrosion resistance of the alloys was mainly controlled by the refinement ofα(Mg)andβ(Li),along with the distribution of second phases.The presence of MgLi_(2) Al at grain boundaries facilitated their dissolution.展开更多
Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications.Superior mechanical properties of these materials can be achieved by thermomechanical processing such as ...Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications.Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg–3 Nd–0.5 Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400 °C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall–Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall–Petch of extruded Mg–3Nd–0.5 Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall–Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg–3Nd–0.5 Zn alloys.展开更多
Most of dental implants are made from titanium or titanium based alloys.However, one of the drawback of such implants is high cost due to the technological difficulties in casting method or machining.In this work, pow...Most of dental implants are made from titanium or titanium based alloys.However, one of the drawback of such implants is high cost due to the technological difficulties in casting method or machining.In this work, powder injection moulding（PIM） method has been used in order to explore lower cost implants without minimising the biocorrosion resistance of the titanium.Corrosion resistance of titanium specimens, produced by powder injection moulding method（PIM-Ti）, in physiologic serum and artificial saliva was investigated.Commercially pure bulk Ti（CP-Ti） was used as control sample.Surface oxidation was also carried out to both PIMTi and CP-Ti samples.Microstructure and corrosion resistance were investigated using microhardness, X-ray diffraction（XRD）, scanning electron microscopy（SEM） and potentiodynamic polarization experiments.Resulting microstructure of PIM-Ti samples contained porosity as compared to CP-Ti control samples.Microhardness of PIM-Ti samples varied with varying applied load whereas it was free from applied load for CP-Ti control samples.Polarisation measurements and SEM analysis revealed that corrosion behaviour of PIM-Ti was reasonably as good as CP-Ti both in as-produced and oxidized conditions in physiologic serum and artificial saliva in spite of its porous structure.展开更多
A thermomechanical process （TMP） consisting of three cycles of cold pressing at 154 MPa and liquid-phase sintering at 600 ℃ for 30 min in each cycle was applied to modify the microstructure of nanostructured A1-Zn-...A thermomechanical process （TMP） consisting of three cycles of cold pressing at 154 MPa and liquid-phase sintering at 600 ℃ for 30 min in each cycle was applied to modify the microstructure of nanostructured A1-Zn-Mg alloy. The alloy powders were produced by mechanical alloying. Also, solid-state sintering at 550℃ for 90 min was done to compare the results with those obtained from the TMP. The powders and the thermomechanically （TM） processed samples were analyzed by XRD to reveal the present phases in addition to calculating the crystallite size changes by the Wil- liamson-Hall method. Moreover, scanning electron microscope was employed to observe the morphology of the powder and the microstructures of the sintered and the TM processed samples. The results revealed that the TMP affected the microstructure noticeably as well as the microhardness by removing the continuous grain boundary porosities and uniform distribution of the intermetallic phase particles as well as obtaining a near globular microstructure after the second cycle. Also, the average grain sizes in the first and the second cycles of the TMP were lower than those of the sintered sample. Furthermore, nanocrystalline grains were stable up to the second cycle of the TMP.展开更多
Molecular dynamics simulations of computer have been performed on the local structure and bond orientation order of liquid metal Pb at 623 K,Results show that,at point near melting temperature,the local structures of ...Molecular dynamics simulations of computer have been performed on the local structure and bond orientation order of liquid metal Pb at 623 K,Results show that,at point near melting temperature,the local structures of liquid metal Pb show cubic symmetry,and the long-range correlation of this symmetry is weak.展开更多
Besed on the embedded atom method,molecular dynamics simulations have been performed on microdynamics behavior of liquid transition metal.Cu and Ni.Mean-square displacement,self-diffusion coefficient and velocity self...Besed on the embedded atom method,molecular dynamics simulations have been performed on microdynamics behavior of liquid transition metal.Cu and Ni.Mean-square displacement,self-diffusion coefficient and velocity self-correlation function have been calculated.In addition,effects of many body interactions have been discussed.展开更多
The Mg-Y-Zn magnesium alloy system is commonly recognized for its remarkable combination of high strength and ductility,achieved even with minimal amounts of alloying elements.This exceptional performance is attribute...The Mg-Y-Zn magnesium alloy system is commonly recognized for its remarkable combination of high strength and ductility,achieved even with minimal amounts of alloying elements.This exceptional performance is attributed to its unique microstructure,which includes Long-Period Stacking Ordered(LPSO)phases or the distinctive microstructure derived from the LPSO phase,referred to as the Mille-Feuille structure(MFS).This study systematically compares the traditional ingot metallurgy method with the rapid solidification technique,coupled with diverse heat treatments and extrusion processes.Microscopic analyses reveal variations in the presence of LPSO phases,Mille-Feuille structure,and grain size,leading to divergent mechanical and corrosion properties.The rapid solidification approach stands out,ensuring superior mechanical properties alongside a reasonable corrosion rate.展开更多
The Mg-Y-Zn magnesium alloy system is known for the presence of Long-Period Stacking Ordered(LPSO)phases that improves strength and ductility with minimal amounts of alloying elements.Even better improvements are asso...The Mg-Y-Zn magnesium alloy system is known for the presence of Long-Period Stacking Ordered(LPSO)phases that improves strength and ductility with minimal amounts of alloying elements.Even better improvements are associated with the specific microstructure known as the Mille-Feuille(MF)structure that can occur in this alloy as well after proper heat treatment.This study systematically compares the traditional ingot metallurgy method with the Bridgman method(slow cooling),coupled with diverse heat treatments and extrusion process.Microscopic analyses reveal variations in the presence of LPSO phases,MF structure,and especially grain size,leading to divergent mechanical and corrosion properties.The Bridgman approach surprisingly stands out,ensuring superior mechanical properties due to kink and texture strengthening.展开更多
基金supported by the Czech Science Foundation(project no.P108/12/G043)
文摘Eighteen as-cast binary Mg-Ni, Mg-Mm and ternary Mg-Ni-Mm and Mg-Ni-TM （TM=transition metals （Cu, Zn, Mn and Co）; Mm = mischmetal containing Ce, La, Nd and Pr） alloys were hydrided by an electrochemical process to determine the alloys with the most potential for electrochemical hydrogen storage. The alloys were hydrided in a 6 mol/L KOH solution at 80 °C for 480 min and at 100 A/m2. To assess the electrochemical hydriding performance of alloys, maximum hydrogen concentrations, hydrogen penetration depths and total mass of absorbed hydrogen in the alloys were measured by glow discharge spectrometry. In addition, the structures and phase compositions of the alloys both before and after hydriding were studied by optical and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. It was determined that the highest total amount of hydrogen was absorbed by the Mg-25Ni-12Mm and Mg-26Ni （mass fraction, %） alloys. The maximum hydrogen concentrations in the Mg-25Ni-12Mm and Mg-26Ni alloys were 1.0% and 1.6%, respectively. The main hydriding product was the binary MgH2 hydride, and the ternary Mg2NiH4 hydride was also detected in the Mg-25Ni-12Mm alloy. The electrochemical hydriding parameters achieved are discussed in relation to the structures of alloys, alloying elements and hydriding mechanisms.
基金the Czech Science Foundation (P108/12/G043)the Academy of Sciences of the Czech Republic(KAN300100801)for the financial support
文摘Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were studied. The alloys were studied in the as-cast state （cooling rate of 500 K/min） and after solution heat treatment （T4）. Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution （9 g/L NaCl） was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine a-Mg dendrites and eutectic Mg-RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg-Gd alloys. For this reason, the T4 heat treatment of the Mg-Gd alloy led to the formation of a new cuboidal Mg5Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg-Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg-Gd alloys. Its effect on the corrosion of Mg-Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.
文摘This study describes the corrosion resistance of extruded,and extruded with post-processing annealing,Mg–7.5 Li–3 Al–1 Zn alloys.The results demonstrate that extrusion at 350°C with an extrusion speed 0.5 s^(-1) does not lead to the full recrystallization of the alloy,and the material still exhibits a dendritic microstructure.The post-processing annealing triggers the microstructure transformation,and the relative composition of the alloy changes.The ratio ofβ(Li)toα(Mg)in the extruded alloy was 29–71%;after annealing amount ofβ(Li)increased,and the ratio ofβ(Li)toα(Mg)in the annealed alloy was 35–65%.Corrosion testing shows that in 3.5 wt%Na Cl the extruded alloys immediately undergo strong dissolution.As a result of the subsequent annealing,an improvement of corrosion resistance is observed.The higher amount ofβ(Li)in the annealed alloy reduces the area ratio of cathodic to anodic sites of corrosion,and this makes the annealed alloy more resistive under the analyzed conditions.
基金University of Tehran and Graduate University of Advanced Technology for financial and mental support
文摘The effects of beryllium (Be) on the microstructure, hardness and tensile properties of A380 aluminum alloy were investigated. The base and Be-containing A380 alloys were conventionally cast in a ductile iron mold. The microstructure evolution was investigated using SEM and optical microscope. The mechanical properties were assessed using tensile and hardness tests, finally the rapture surfaces of the used samples were studied to reveal the fracture mechanism in the presence of Be. The results revealed that the plateletβ intermetallic phases were transformed into relatively harmless Chinese script Be?Fe phase and eutectic Si phases changed from flake-like particles into fine ones. The corresponding ultimate tensile strength (UTS) and elongation values increased from 270 MPa to 295 MPa and 3.7% to 4.7%, respectively. Additionally, the hardness of A380 alloy decreased continuously with increasing Be content. While the fracture surfaces of the unmodified A380 alloy tensile samples showed a clear brittle fracture nature, while finer dimple and fewer brittle cleavage surfaces were seen in the alloys with Be addition. Moreover, in the presence of Be, due to the refined phases, there has been a decrease in the values of hardness.
文摘The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavior,fracture toughness and strain rate sensitivity(SRS)of materials within micro/nanoscale.Firstly,a nanomechanical model was developed for extracting hardness(H),young’s modulus(E)and yield stress(σY)from the characteristic load points which were subsequently analyzed by atomic force microscope(AFM)images.The elasticity data and AFM data were then utilized for determination of plastic deformation in constituent phases.The displacement of the indentation gets the highest value for Mg matrix and between precipitates,depth is more in LPSO rather than that of MgRE.The serrated flow or the behavior of shear bands may originate from the side effect of the interface region in Mg alloys with precipitates.It can be deduced that the KIC produced by both L method and energy-based calculation are both reliable for KIC approximation.The maximum load in simulation withμ=0.2 friction is marginally lesser than that of the frictionless(μ=0)one while elastic recovery of indentation withμ=0.2 is higher to some extent.
基金The authors wish to thank the Czech Science Foundation(Project No.GA19-08937S)specific university research(A2_FCHT_2020_027 and A1_FCHT_2020_003)for the financial support of this research.
文摘Powder metallurgy is a powerful method for the preparation of materials with superior properties.This work aimed to investigate the effect of powder size on the microstructure,mechanical,and corrosion properties of advanced WE43(Mg-4Y-3REE-Zr)alloy prepared by spark plasma sintering(SPS).At the same time,the effect of HF pre-treatment of the powder on the properties of final compacted products is studied.Smaller powder particles yielded microstructure with more interfaces formed by Y_(2)O_(3),or MgF_(2) and YF_(3).These interfaces work as barriers against corrosion,which greatly improves corrosion resistance.The suggested pre-treatment of powder in HF further reduced the corrosion rate of the compacted materials.On the contrary,fragile interfaces of YF_(3) decreased mechanical properties as the crack primarily propagates through these interfaces.The original powder containing the mixture of all powder fractions exerted the best combination of mechanical properties.Powder size has also shown to affect ignition temperature.The highest ignition temperature was measured for the finest powder fraction.
基金the Czech Science Foundation (project No. P108/12/G043) for the financial support of this research
文摘The MgNi26 alloy was prepared by three different methods of gravity casting (GC), mechanical alloying (MA) and rapid solidification (RS). All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 °C for 240 min. The structures and phase compositions of the alloys were studied using optical microscopy and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. A temperature-programmed desorption technique was used to measure the absorbed hydrogen and study the dehydriding process. The content of hydrogen absorbed by the MgNi26-MA (approximately 1.3%, mass fraction) was 30 times higher than that of the MgNi26-GC. The MgNi26-RS sample absorbed only 0.1% of hydrogen. The lowest temperature for hydrogen evolution was exhibited by the MgNi26-MA. Compared with pure commercial MgH2, the decomposition temperature was reduced by more than 200 °C. The favourable phase and structural composition of the MgNi26-MA sample were the reasons for the best hydriding and dehydriding properties.
基金Shiraz University of Technology (Department of Materials Science and Engineering)for the support for this study
文摘In this study, Al matrix composites reinforced by 7.5 and 15 vol.% B4C particles and also monolithic Al （Al without the B4C particles） were produced by wet attrition milling and subsequent hot forward extrusion processes. The microstructure of the composites, evaluated by scanning electron microscopy （SEM）, showed that the B4C particles were properly distributed in the Al matrix. Mechanical properties of the Al/B4C composites and monolithic Al were investigated by tensile, wear and hardness tests, The results revealed that with increasing content of B4C particles, the tensile strength and microhardness of composites increased but the elongation decreased. In addition, the tensile strength and microhardness of composite samples were higher than those of monolithic Al. The density measurements revealed that the density of composites decreased with increasing content of the B4C particles.
基金financial support of this research by project No. GA16-08963S
文摘Magnesium alloys are important materials for application in the automotive and aviation industries. During the last few years, the number of possible applications as biodegradable implants in medicine has grown. Mg-RE（rare earth） alloys belong to the most advanced group of products, offering the best combination of mechanical properties and corrosion resistance. Among these materials, WE43（Mg-Y-Nd）is a very well-known commercial alloy that has been extensively studied for applications at increased temperatures and also in organisms. Although this material has been described, there are still possibilities to improve its properties and subsequently expand its applicability. Powder metallurgy has already been used for the preparation of magnesium alloys with superior mechanical properties and occasionally superior corrosion properties. Therefore, the present paper is oriented toward the preparation of Mg-4Y-3RE-Zr（WE43） alloy by the powder metallurgy technique（WE43-PM） and comparison of the final properties with the product of extrusion of as-cast ingot（WE43-IM）. Our processing leads to a partial improvement in the mechanical properties and superior corrosion resistance of WE43-PM. The texture strength of WE43-PM was low, and therefore, anisotropy of mechanical properties was suppressed.
基金financially supported by the Czech Science Foundation(No.P108/12/G043)
文摘A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.
文摘The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly developed SPD method)at two different extrusion ratios.The fine-grained microstructures formed in the alloys were characterized,and the influence of grain refinement on corrosion resistance was analyzed.For fine-grained(α+β)Mg-Li alloys,a higher extrusion ratio led to more intensive grain refinement;however,this relationship did not improve their corrosion resistance in a chloride-containing solution.The corrosion resistance of the alloys was mainly controlled by the refinement ofα(Mg)andβ(Li),along with the distribution of second phases.The presence of MgLi_(2) Al at grain boundaries facilitated their dissolution.
基金financially supported by the project Advanced magnesium alloys with tailored corrosion, biological and mechanical properties (No. GA16-08963S)
文摘Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications.Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg–3 Nd–0.5 Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400 °C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall–Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall–Petch of extruded Mg–3Nd–0.5 Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall–Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg–3Nd–0.5 Zn alloys.
文摘Most of dental implants are made from titanium or titanium based alloys.However, one of the drawback of such implants is high cost due to the technological difficulties in casting method or machining.In this work, powder injection moulding（PIM） method has been used in order to explore lower cost implants without minimising the biocorrosion resistance of the titanium.Corrosion resistance of titanium specimens, produced by powder injection moulding method（PIM-Ti）, in physiologic serum and artificial saliva was investigated.Commercially pure bulk Ti（CP-Ti） was used as control sample.Surface oxidation was also carried out to both PIMTi and CP-Ti samples.Microstructure and corrosion resistance were investigated using microhardness, X-ray diffraction（XRD）, scanning electron microscopy（SEM） and potentiodynamic polarization experiments.Resulting microstructure of PIM-Ti samples contained porosity as compared to CP-Ti control samples.Microhardness of PIM-Ti samples varied with varying applied load whereas it was free from applied load for CP-Ti control samples.Polarisation measurements and SEM analysis revealed that corrosion behaviour of PIM-Ti was reasonably as good as CP-Ti both in as-produced and oxidized conditions in physiologic serum and artificial saliva in spite of its porous structure.
基金Institute of Science,High Technology and Environmental Sciences, Graduate University of Advanced Technology and also INSF(the No. 92006471)
文摘A thermomechanical process （TMP） consisting of three cycles of cold pressing at 154 MPa and liquid-phase sintering at 600 ℃ for 30 min in each cycle was applied to modify the microstructure of nanostructured A1-Zn-Mg alloy. The alloy powders were produced by mechanical alloying. Also, solid-state sintering at 550℃ for 90 min was done to compare the results with those obtained from the TMP. The powders and the thermomechanically （TM） processed samples were analyzed by XRD to reveal the present phases in addition to calculating the crystallite size changes by the Wil- liamson-Hall method. Moreover, scanning electron microscope was employed to observe the morphology of the powder and the microstructures of the sintered and the TM processed samples. The results revealed that the TMP affected the microstructure noticeably as well as the microhardness by removing the continuous grain boundary porosities and uniform distribution of the intermetallic phase particles as well as obtaining a near globular microstructure after the second cycle. Also, the average grain sizes in the first and the second cycles of the TMP were lower than those of the sintered sample. Furthermore, nanocrystalline grains were stable up to the second cycle of the TMP.
基金Supported by the Laboratory of Rapidly Solidified Non-equilibrium Alloys,Institute of Metal Research,Academia Sinica.
文摘Molecular dynamics simulations of computer have been performed on the local structure and bond orientation order of liquid metal Pb at 623 K,Results show that,at point near melting temperature,the local structures of liquid metal Pb show cubic symmetry,and the long-range correlation of this symmetry is weak.
基金Supported by the Laboratory of Rapidly Solidified Non-equilibrium Alloys,Institute of Metal Research,Academia Sinica.
文摘Besed on the embedded atom method,molecular dynamics simulations have been performed on microdynamics behavior of liquid transition metal.Cu and Ni.Mean-square displacement,self-diffusion coefficient and velocity self-correlation function have been calculated.In addition,effects of many body interactions have been discussed.
基金supported by Japan Society for the Promotion of Science(KAKENHI Grant-in-Aid for Scientific Research18H05475,18H05476 and JP20H00312)+2 种基金MRC International Collaborative Research Grant.The authors would like to thank the Czech Science Foundation(Project No.22-22248S)specific university research(A1_FCHT_2024_007)for financial supportthe assistance provided by the Ferroic Multifunctionalities project,supported by the Ministry of Education,Youth,and Sports of the Czech Republic.Project No.CZ.02.01.01/00/22_008/0004591,co-funded by the European Union.CzechNanoLab project LM2023051 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements/sample fabrication at LNSM Research Infrastructure.
文摘The Mg-Y-Zn magnesium alloy system is commonly recognized for its remarkable combination of high strength and ductility,achieved even with minimal amounts of alloying elements.This exceptional performance is attributed to its unique microstructure,which includes Long-Period Stacking Ordered(LPSO)phases or the distinctive microstructure derived from the LPSO phase,referred to as the Mille-Feuille structure(MFS).This study systematically compares the traditional ingot metallurgy method with the rapid solidification technique,coupled with diverse heat treatments and extrusion processes.Microscopic analyses reveal variations in the presence of LPSO phases,Mille-Feuille structure,and grain size,leading to divergent mechanical and corrosion properties.The rapid solidification approach stands out,ensuring superior mechanical properties alongside a reasonable corrosion rate.
基金supported by Japan Society for the Promotion of Science(KAKENHI Grant-in-Aid for Scientific Research,18H05475,18H05476 and JP20H00312)MRC International Collaborative Research Grant+4 种基金The authors would like to thank the Czech Science Foundation(Project No.22-22248S)specific university research(A1_FCHT_2024_007)for financial supportsupported by the Ministry of Education,Youth,and Sports of the Czech Republic.Project No.CZ.02.01.01/00/22_008/0004591co-funded by the European UnionCzechNanoLab project LM2023051 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements/sample fabrication at LNSM Research Infrastructure。
文摘The Mg-Y-Zn magnesium alloy system is known for the presence of Long-Period Stacking Ordered(LPSO)phases that improves strength and ductility with minimal amounts of alloying elements.Even better improvements are associated with the specific microstructure known as the Mille-Feuille(MF)structure that can occur in this alloy as well after proper heat treatment.This study systematically compares the traditional ingot metallurgy method with the Bridgman method(slow cooling),coupled with diverse heat treatments and extrusion process.Microscopic analyses reveal variations in the presence of LPSO phases,MF structure,and especially grain size,leading to divergent mechanical and corrosion properties.The Bridgman approach surprisingly stands out,ensuring superior mechanical properties due to kink and texture strengthening.
