In-situ study of the microstructure evolution during tension of a Mg-Y-Zn-Al alloy processed by rapidly solidified ribbon consolidation technique

Mg-Y-Zn-Al alloys processed by rapidly solidified ribbon consolidation(RSRC)technique exhibit an exceptional mechanical performance indicating promising application potential.This material has a bimodal microstructure consisting of fine recrystallized and coarse non-recrystallized grains with solute-rich stacking faults forming cluster arranged layers(CALs)and nanoplates(CANaPs),or complete long period stacking ordered(LPSO)phase.In order to reveal the deformation mechanisms,in-situ synchrotron X-ray diffraction line profile analysis was employed for a detailed study of the dislocation arrangement created during tension in Mg-0.9%Zn-2.05%Y-0.15%Al(at%)alloy.For uncovering the effect of the initial microstructure on the mechanical performance,additional samples were obtained by annealing of the as-consolidated specimen at 300 and 400℃ for 2 h.The heat treatment at 300℃ had no significant effect on the initial microstructure,its evolution during tension and,thus,the overall deformation behavior under tensile loading.On the other hand,annealing at 400℃ resulted in a significant increase of the recrystallized grains fraction and a decrease of the dislocation density,leading to only minor degradation of the mechanical strength.The maximum dislocation density at the failure of the samples corresponding to the plastic strain of 10-25% was estimated to be about 16-20×10^(14)m^(-2).The diffraction profile analysis indicated that most dislocations formed during tension were of non-basal and pyramidal types,what was also in agreement with the Schmid factor values revealed independently from orientation maps.It was also shown that the dislocation-induced Taylor hardening was much lower below the plastic strain of 3% than above this value,which was explained by a model of the interaction between prismatic dislocations and CANaPs/LPSO plates.

The slip activity during the transition from elastic to plastic tensile deformation of the Mg-Al-Mn sheet

The deformation behavior of the Mg-Al-Mn sheet was investigated during tensile loading along the rolling(RD)and transversal direction(TD)with special attention to the early stage of deformation.The activity of dislocation slip systems during the transition from elastic to plastic deformation was revealed by the acoustic emission(AE)technique.The parametrization and statistical AE analysis using the adaptive sequential k-mean(ASK)clustering provided necessary information about the individual deformation mechanisms and their evolution.The AE findings were supported by microstructural analyses,including in-situ secondary electron(SE)imaging and Schmid factor estimation for the activity of particular dislocation slip systems with respect to the loading direction.It was found that basal slip is the dominating mechanism up to the stress of~80 MPa in both loading directions with an absolute dominance during the RD-loading,while during the TD-loading,the contribution of prismatic slip to the deformation at stresses above 50 MPa was determined.Below the yielding in both loading directions,the predominance of prismatic over pyramidal slip was found at the stress in the range of 80-110 MPa and the opposite tendency occurred at stresses between 110 and 140 MPa.

The effect of powder size on the mechanical and corrosion properties and the ignition temperature of WE43 alloy prepared by spark plasma sintering

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.

Hot deformation of Mg-Y-Zn alloy with a low content of the LPSO phase studied by in-situ synchrotron radiation diffraction

The compressive deformation behavior of the extruded WZ42(Mg98.5Y1Zn0.5 in at.%)magnesium alloy containing a low amount of long-period stacking ordered(LPSO)phase was studied by in-situ synchrotron radiation diffraction technique.Tests were conducted at temperatures between room temperature and 350℃.Detailed microstructure investigation was provided by scanning electron microscopy,particularly the backscattered electron imaging and electron backscatter diffraction technique.The results show that twinning lost its dominance and kinking of the LPSO phase became more pronounced with increasing deformation temperature.No cracks of the LPSO phase and no debonding r at the interface between the LPSO phase and the Mg matrix were observed at temperatures above 200℃.At 350℃,the LPSO phase lost its strengthening effect and the deformation of the alloy was mainly realized by the dynamic recrystallization of the Mg matrix.

Individual effect of Y and Nd on the microstructure formation of Mg-Y-Nd alloys processed by severe plastic deformation and their effect on the subsequent mechanical and corrosion properties

This work investigated the effect of sole yttrium and neodymium alloying on the microstructure formation during severe plastic deformation by equal channel angular pressing(ECAP) and an impact on the mechanical strength and corrosion resistance of binary Mg-3Y and Mg-3Nd alloys.The results are compared with a ternary Mg-4Y-3Nd alloy,which represents a simplified version of the commercially successful WE43 alloy.The extensive study comprises a thorough microstructural analysis performed by scanning and transmission electron microscopy,including electron backscatter diffraction and texture analysis performed by X-ray diffraction.It is shown that the presence of Nd primarily caused precipitation during the processing of the Mg-3Nd alloy,while Y remained dissolved in the magnesium matrix in the Mg-3Y alloy.This difference resulted in a significantly smaller average grain size in the Mg-3Y alloy(~0.77 nm) than in the Mg-3Nd alloy(~1.3 μm) after the final step of the processing and formation of a slightly different texture.Consequently,the composition and the processing affected the mechanical and corrosion properties of the investigated materials,measured by compression deformation tests,microhardness measurement,and electrochemical impedance spectroscopy.This study shows that the ECAP-processed W3 sample exhibits a surprisingly good combination of ultrafine-grain structure,weak crystallographic texture,high strength,and high corrosion resistance compared with the other investigated samples.These attributes make this material very interesting for utilisation in the industry and/or medicine.

Three-dimensional crystal plasticity and HR-EBSD analysis of the local stress-strain fields induced during twin propagation and thickening in magnesium alloys

Present work focuses on analysis of the stress and strain fields inside and around the individual {10–12} twin in magnesium alloy. The 3D crystal plasticity model represents twin as an ellipsoidal inclusion surrounded by the matrix. Five different twin thicknesses and three different lateral twin lengths are used for stress/strain analysis. The simulations are complemented with experimental observations using high-resolution electron backscattered diffraction. The simulations and experiments show a similar distribution of the shear stress and the spatial activity of individual slip systems(basal, prismatic, pyramidal). Plasticity induced inside the twin is dominantly caused by the prismatic dislocations slip and does not influence twin back stress which is identical to pure elastic twin. The twin with larger lateral dimension requires lower equilibrium stress which suggests anisotropic twin propagation and increased thickness of such twins. The lateral twin propagation is mostly influenced by prismatic and pyramidal slip in the twin vicinity. The twin thickness can reach a maximal level that is driven by the critical resolved shear stress values for dislocation slip with the significant influence of basal slip.

In Vitro Evaluation of Polyurethane-Chitosan Scaffolds for Tissue Engineering

In this work the use of Polyurethane (PU)-Chitosan(CH) scaffolds prepared by thermal induced phase separation (TIPS) for osteoblast proliferation and bone mineralization is described. Primary rat calvaria osteoblasts were seeded in the scaffolds and it was shown that supported cell adhesion and growth. The behavior osteoblast cells growing in the scaffold in function of the different ratio of PU and CH is presented. The results showed that TIPS is an appropriate technique for the production of PU-CH scaffolds with high potential for application as cell scaffolds in bone tissue engineering.

Sc元素添加对双辊铸轧Al−Cu−Li−Mg−Zr基合金热处理的影响

提出制备含Sc的Al−Cu−Li−Mg−Zr基合金带材的工艺方案。即先采用双辊铸轧技术制备近净形状的3 mm厚带材,再对其进行均匀化/固溶处理。研究两种Al−Cu−Li−Mg−Zr基双辊铸轧合金,其中一种添加质量分数为0.17%的Sc,另一种未添加Sc。两种合金均先在300℃下退火30 min,然后在450℃下退火30 min以及530℃下退火30 min,随后进行室温水淬。前两段退火后组织中生成了细小、弥散的Al_(3)Zr/Al_(3)(Sc,Zr)颗粒。最后的退火步骤起到了均匀化/固溶处理的作用。双辊铸轧材料的细小晶粒结构使含有主要合金元素的原始颗粒在较短的退火时间内溶解。缩短保温时间可以限制表面层中Li的耗尽和Al_(3)Zr/Al_(3)(Sc,Zr)弥散相的明显粗化。铸态含Sc材料已经具有明显细小的晶粒结构,而经均匀化/固溶处理后生成的Al_(3)(Sc,Zr)弥散相抑制了晶粒在高温下发生粗化。在后续180℃下时效处理后,形成了θʹ(Al_(2)Cu)、T1(Al_(2)CuLi)和S'(Al_(2)CuMg)强化相。在峰值时效状态下,屈服强度提高了200 MPa,这一数值与类似直接冷却铸造材料的相当,从而证实了所提方案的合理性。

Tribological Characterization of Commercial Pure Titanium Processed by Multi-Directional Forging

This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.

Structural,morphological and photoluminescence characterizations of Sm^(3+) doped Y_(2)O_(3) nano-sized phosphors synthesized by ultrasound assisted sol-gel method

Nanosized 1 at% Sm^(3+)doped Y_(2)O_(3)powders were prepared by an ultrasound assisted sol-gel method.Y_(2)O_(3):Sm^(3+)powders crystallize in Y_(2)O_(3)pure cubic phase and XRD analysis shows that the as-used agitation protocol affects strongly the crystallite’s shape and mean size.The recorded emission spectra under λ_(em)=600 nm exhibit two absorption bands;the first one is assigned to O^(2-)→Sm^(3+)charge transfer state(CTS) with a maximum absorption at 223 nm,and the second is due to intraconfigurational transition 4f^(5)-4f^(5) of Sm^(3+) with a maximum absorption at 407 nm.The 223 and 407 nm transitions are attributed to characteristics intra-configurational transitions of Sm^(3+).All emission spectra are dominated by reddish/orange luminescence located at 606 nm and assigned to ^(4)G_(5/2)→^(6)H_(7/2) transition.It is found that the photoluminescence intensity of samples obtained under excitation at 407 nm is 60 times smaller than that obtained under 223 nm excitation.Decay time measurements of the ^(4)G_(5/2)→^(6)H_(7/2) luminescence transition indicate that decay time of nano-sized powder is significantly shorter than bulk material one.

Characterization of the High-Strength Mg–3Nd–0.5Zn Alloy Prepared by Thermomechanical Processing

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.

Shear banding-inducedslip enables unprecedented strength-ductility combination of laminated metallic composites

Shear bands in metallic materials have been reported to be catastrophic because they normally lead to non-uniform plastic deformation. Ductility of laminated metallic composites deteriorates with increasing processing strain, particularly for those having hexagonal-close-packed(hcp) constituents due to inadequate slip systems and consequently prominent shear banding. Here, we propose a design strategy that counterintuitively tolerates the bands with localized strains, i.e. the shear banded laminar(SBL) structure, which promotes <c+a> dislocation activation in hcp metals and renders unprecedented strengthductility combination in hcp-metal-based composites fabricated by accumulative roll bonding(ARB). The SBL structure is characterized with one soft hcp metal constrained by adjacent hard metal in which dislocations have been accumulated near the bimetal interfaces. High-energy X-ray diffraction astonishingly reveals that more than 90% of dislocations are non-basal in Ti layers of the SBL Ti/Nb composite processed by eight ARB cycles. Moreover, <c+a> dislocations occupy a high fraction of ~30%, promoting further <c+a>cross slip. The unique stress field tailored by both shear banding and heterophase interface-mediated deformation accommodation triggers important <c+a> slip. This SBL design is of significance for developing hcp-based laminates and other heterostructured materials with high performances.