Compressive Fracture Strength Research Articles

Effects of heat treatment on the microstructure, wear behavior and corrosion resistance of AlCoCrFeNiSi high-entropy alloy

The effects of heat treatment on the microstructure, wear behavior and corrosion resistance of AlCoCrFeNiSi high-entropy alloy were investigated. Results indicate that the phase composition of as-cast alloy includes disordered body-centered cubic (BCC) solid solution phase, ordered BCC phase (B2), Cr3Si and (Cr, Ni, Si)-phase. The system exhibits a good thermal stability and no phase transition occurs after heat treatment except the change of diffraction peak intensity and the appearance of weak peak. After heat treatment, the dendrites of B2 phase turns into discontinuous spherical particles, the BCC interdendrite region narrows, and the short rod-like precipitation Cr3Si phase is transformed into long needle-like microstructure. The highest compression fracture strength and strain are 1752 MPa and 11.8 % at 1150-2 h, which are 36 % and 19 % higher than the as-cast alloy, respectively. At 1150-2 h, the highest microhardness (1004.3 HV0.5) and lowest friction coefficient (0.115) are obtained, which are 1.2 times and 3.4 times better than that of as-cast alloy. A mixed mechanism of abrasive and oxidative wear are occurred during friction and deformation. Heat treatment of 1100–2 h possesses the optimal corrosion resistance with the Ecorr and Icorr of −330.776 mV and 637.587 nA due to the appearance of weak passivation phenomenon.

Synthesis of Cr50Fe6Co7Mo14C15B6Y2 bulk metallic glass with integrated merits by high-content solvent element substitution and the structural origin

Novel Cr50Fe6Co7Mo14C15B6Y2 bulk metallic glass (BMG) with a critical diameter of about 1.5 mm was developed using high-content solvent element Cr substitution for Fe from the precursor Fe41Cr15Co7Mo14C15B6Y2 BMG. The alloy possesses integrated advantages of superior glass transition temperature of 981 K, extraordinary high onset temperature of crystallization of 1018 K, dramatical high compressive fracture strength of 4.49 GPa and Vickers microhardness of 14.01 GPa, and prominent corrosion resistance of no detectable weight loss in 1 M HCl solution. The structural origin for the decreased glass-forming ability of the present alloy in comparison with its precursor Fe41Cr15Co7Mo14C15B6Y2 BMG results from the lower fraction of icosahedral-type structures (with bond pair indexes of 1551, 1541, and 1431) along with the higher fraction of crystal-like structures (with bond pair indexes of 1421, 1422, 1441 and 1661), and the covalent-like Cr–C and Cr–B bonds are responsible for the superior glass transition temperature, the onset temperature of crystallization, fracture strength and hardness, based on the ab-initio molecular dynamics simulation for the local structures. The present BMG can be a preferable alloy for industrial applications under the harsh environment of high temperature, wear and corrosion.

Fracture of Porous Ceramics: Application to the Mechanical Degradation of Solid Oxide Cell During Redox Cycling

Solid Oxide Cell (SOC) is a high-temperature electrochemical device that can be operated in both fuel and electrolysis modes. It is constituted of a dense electrolyte in Yttria Stabilized Zirconia (YSZ) sandwiched between two porous electrodes. The hydrogen electrode is classically made of a cermet composed of Nickel and YSZ (Ni-YSZ). Because of system failures in operation (e.g. a fuel shortage or air re-introduction during the system shutdown), the Nickel is liable to be re-oxidized inducing its volume expansion. The Ni swelling within the cermet leads to a mechanical damage in the YSZ backbone [1] resulting in a degradation of the overall cell performances [2]. Therefore, it is still required to enhance the hydrogen electrode robustness for a higher redox tolerance. For this purpose, it is essential to predict accurately the formation and distribution of micro-cracks in the YSZ network during the re-oxidation. Nevertheless, the modeling of the initiation and propagation of cracks in complex microstructures of porous ceramics is still a subject of investigation. Moreover, there is also a lack of data on fracture properties for the porous YSZ material. In this frame, the present study was focused to propose a relevant model for the initiation and the growth of cracks in porous ceramics in order to simulate the fracture induced by Ni re-oxidation. For this purpose, a coupled experimental and modeling approach has been adopted (Fig.1). For the experimental part, the mechanical characterizations have been performed on thin YSZ membranes of different porosities representative of SOC microstructures. The compression test has been chosen as it generates a quasi-uniform stress field in the tested samples. To this end, micro-pillars of few tens of micro-meters in section have been milled in the YSZ membrane using a xenon plasma focused ion beam. For each investigated porosity, the compressive fracture strength has been measured on several pillars. The tested samples have been carefully characterized to assess the damage in the microstructure. As expected, the compressive strength was found to decrease with increasing the porosity. Moreover, a transition has been observed from a brittle behaviour at low porosity towards a local damage at high porosity [3]. All these experimental data have been used to validate a numerical tool to simulate the fracture in porous microstructure. In this study, a model based on the Phase Field Method (PFM) has been developed. In this approach, the crack is modeled implicitly through a smooth scalar damage variable and its width is controlled by a length scale parameter. Therefore, this method is well adapted to solve the fracture problem in complex and heterogeneous materials since it is mesh independent. The implemented model corresponds to the one proposed by C. Miehe et al. [4] who proposed a staggered scheme for the numerical resolution. A special attention has been paid in this work to evaluate the model capability to accurately predict the crack initiation for porous electrode material. For this purpose, the results of the PFM simulations have been compared to the mixed criterion proposed by D. Leguillon [5]. The study has been conducted on notched samples with different opening angles and for macro-cracks blunted by different cavity sizes. It has been highlighted that the two approaches provide consistent predictions for the crack initiation. Moreover, it has been checked that the PFM model is able to reproduce accurately the expected decrease of the fracture toughness when increasing the material porosity. Once these studies completed, the PFM model has been used to simulate the micro-compression test using a multiscale approach. It has been found that the model is able to reproduce correctly the decrease of the measured compressive fracture strength with the sample porosity. Moreover, the distribution of cracks in the simulations has enabled analysing the transition from a brittle to a local damage detected during the experiments. The validated model has been applied to simulate the fracture induced by the Ni re-oxidation. The repartition and density of micro-cracks in the YSZ backbone has been computed during the Ni reoxidation and the results have been confronted with an available tomographic data set. Finally, the impact on the cermet redox tolerance of the Yttrium content in YSZ has been discussed thanks to the modelling. [1] Faes, A. et al. J. Power Sources 193, 55–64. [2] Laurencin, J. et al. J. Power Sources 192, 344–352. [3] Meille, S. Et al . J. Eur. Ceram. Soc. 32, 3959–3967. [4] Miehe, C. et al. Comput. Methods Appl. Mech. Eng. 199, 2765–2778. [5] Leguillon, D. J. Mech. – A/Solids 21, 61–72. Figure 1

Fracture of Porous Ceramics: Application to the Mechanical Degradation of Solid Oxide Cell During Redox Cycling

A model based on the Phase Field approach has been developed to simulate the local fracture in porous electrode microstructures. The model capacity to predict the crack nucleation and propagation has been studied with theoretical considerations. For the model validation, micro-compression tests have been performed on porous YSZ micro-pillars. As expected, the compressive fracture strength has been found to decrease with the material porosity. Moreover, a transition in fracture mode has been detected from a brittle behavior toward a local damage when increasing the porosity. It has been shown that the model is able to reproduce correctly the experimental results. The validated model has been used to simulate the fracture of the YSZ backbone induced by the Ni re-oxidation in a typical Ni-YSZ cermet. The generation and localization of the micro-cracks have been discussed according to the degree of Ni re-oxidation and the local morphology of the electrode microstructure.

Effects of heat treatment on the microstructure, mechanical properties and corrosion resistance of AlCoCrFeNiTi0.5 high-entropy alloy

AlCoCrFeNiTi0.5 high-entropy alloy was fabricated, and the effects of heat treatment on the microstructure, mechanical properties and corrosion resistance of this alloy were investigated. The results indicate that heat treatment can not only refine as-cast dendrites and change the morphology of precipitation from long strip to short rod-like structure but also control the ratio of BCC to FCC. The volume fraction of the BCC phase at 1100 °C is 34.8%, which is 9.2% higher than that under the as-cast conditions (25.6%). The highest compression fracture strength and fracture strain of 2785 MPa and 30.7%, respectively, are achieved when the heat treatment temperature and time are 1100 °C and 6 h, respectively. The highest Vickers hardness values of FCC and BCC are 687 HV0.5 and 782 HV0.5, respectively. The order of corrosion resistance is 800-2 h 900-2 h, as-cast, 1000-2 h, 1100-2 h, and 1200-2 h, which is contrary to the trend of the BCC volume fraction. The potential of dendritic FCC is higher than that of interdendritic BCC, and the potential difference is rising because of dendrite decomposition and atom diffusion. The corrosion mechanism is also discussed in this study. Corrosion occurs preferentially on the phase interface and interdendrites, and subsequently connects with each other. As the corrosion intensifies, dendritic FCC begins to be corroded and develops into a large corrosion area.

In-situ synthesis of Mg-based bulk metallic glass matrix composites with primary α-Mg phases

Herein, we systematically investigate the in-situ synthesis and mechanical properties of Mg-based bulk metallic glass matrix composites (BMGMCs). From a well-known Mg65Cu25Gd10 bulk glass former, a series of Mg65+xCu20–2x/3Zn5Gd10−x/3 (x = 0–18 at%) alloys are systematically designed and Mg-rich (>77 at% Mg) glassy/crystalline matrix composites containing primary α-Mg phases are successfully developed. Mg77Cu12Zn5Gd6 BMGMC (x = 12 at%) exhibits over two times higher compressive fracture strength (773 ± 20.6 MPa) and specific strength (2.6 × 105 N m kg−1) than commercial Mg alloys such as AZ31 or AZ91. In particular, compared with monolithic Mg-based BMGs, the BMGMC displays obvious yielding, serrated plastic flow and plastic strain of 0.22 ± 0.02%. This result is attributed to the dispersed primary α-Mg phases which prevent the rapid propagation of shear bands and promote the formation of multiple shear bands. The Mg-rich crystalline matrix composites (x = 14-18 at%) containing primary α-Mg phases exhibit an enhancement in the plastic strain (from 0% to 1.51%) and pronounced work hardening at the expense of yield strength (<500 MPa) due to the absence of the amorphous phase. These results would give us a promising strategy to fabricate Mg-based BMGMCs with high specific strength and enhanced plasticity for lightweight structural applications.

Microstructure and Mechanical Properties of Cu-Ni-Zr-Ti Bulk Metallic Glass Composites by Spark Plasma Sintering

In the present study, Cu54Ni6Zr22Ti18 bulk metallic glass composites were developed by spark plasma sintering(SPS) using gas atomized Cu54Ni6Zr22Ti18 metallic glass powders and Ta powders. Metallic glass composites with Ta phase were fabricated by SPS. The successful consolidation of Cu54Ni6Zr22Ti18 metallic glass matrix composites with the Ta phase was achieved through the strong bonding due to the plastic deformation of the Ta powder and the super-plastic behavior of the metallic glass powder in the supercooled liquid state during SPS. The deformed Ta phases were well distributed in the Cu54Ni6Zr22Ti18 metallic glass matrix. The compressive fracture strength and total strain were 1770 Mpa and 10.2%, respectively, for the Cu54Ni6Zr22Ti18 bulk metallic glass composite with 40 wt% Ta phases. The uniformly dispersed deformed Ta phase in the Cu54Ni6Zr22Ti18 metallic glass matrix effectively impedes the propagation of the first shear band and generates a second shear band, causing a crossing of the shear bands, resulting in an improvement in plastic strain. This increase in plastic deformation is related to the fact that the deformed Ta phase, uniformly distributed in the Cu54Ni6Zr22Ti18 metallic glass matrix, acts as a source of shear bands and at the same time effectively suppresses the movement of the shear bands, dispersing the stress and causing wide plastic deformation.

Dual phase equal-atomic NbTaTiZr high-entropy alloy with ultra-fine grain and excellent mechanical properties fabricated by spark plasma sintering

Super-high strength NbTaTiZr high-entropy alloys (NbTaTiZr HEAs) have been successfully fabricated by the mechanical alloying (MA) with spark plasma sintering (SPS) technology, which is 2-fold compared with that of NbTaTiZr HEAs prepared by vacuum arc melting (VAM). After the SPS process, the bulk NbTaTiZr alloy samples are provided with dual-phase body-centered cubic (BCC) structure and nanoscale grain size about 500 nm that is obviously smaller than that of NbTaTiZr HEA fabricated by VAM. When the sintering temperature is 800 °C, the compressive fracture strength is the highest reaching at 2511 ± 78 MPa. When the sintering temperature is 1000 °C, the fracture strain is the highest reaching at 12.8%, and compressive fracture strength and yield strength also reach at 2274 ± 91 MPa and 2172 ± 47 MPa, respectively. The excellent mechanical properties of bulk NbTaTiZr alloy samples are attributed to the merits of MA and SPS, and the collaboration effect of ultra-fine grains strengthening, solid solution strengthening and interstitial solid solution strengthening.

Additively manufacturing-enabled hierarchical NiTi-based shape memory alloys with high strength and toughness

ABSTRACT A hierarchical microstructure was obtained, including the unique interlaced dual-phase structure, the solidified molten pool, the coarse columnar B2 grains and fine equiaxed B19’ grains, and a great many nanoparticles, during laser powder bed fusion (LPBF) of NiTi alloys. The effect of laser processing parameter on the growth of nanoparticles was assessed. A combination of low laser power and high scanning speed was conducive to the formation of fine granular nanoparticles with a more uniform distribution. Subsequently, effects of rotation angle between adjacent layers on the compressive deformation behaviour of LPBF-processed NiTi alloys were studied. At a small rotation angle (6–36°), the samples could exhibit an excellent combination of high compressive fracture strength and ductility (e.g. 3094 MPa/39.85%). Meanwhile, samples with small rotation angle tended to get a large strain span for the martensite transformation stage and a large deformation capacity (e.g. 4.64% and 9.25% for θ = 6° and σmax = 800 MPa).

Influence of tungsten on microstructure evolution and mechanical properties of selected novel FeCoCrMnWx high entropy alloys

A novel equiatomic FeCoCrMnW-based High Entropy Alloy system has been designed with the help of well-established thermodynamic parameters as well as a unique learning strategy based on multi-criteria decision-making tool named ‘TOPSIS’. The present study describes the effect of W addition on as-cast FeCoCrMnWx HEAs on their phase identities and mechanical properties. The results showed that the as-cast FeCoCrMnWx (molar ratio x = 0.2, 0.4, 0.6, 0.8, 1) HEAs were composed of BCC, FCC and several minor Fe–Cr and Co–Cr type σ phases. Transmission Electron Microscopy (TEM) analysis confirms the formation of potentially-embrittling intermetallic phases in minor amounts. The designed HEAs exhibit desirable compressive fracture strength of 1771 MPa and compressive plasticity of 17.1% at room temperature. Hike in Vickers microhardness and compressive strength values could be attributed to a large atomic radius of ‘W’ which further plays a crucial role in grain refinement and solid solution strengthening. This work not only provides advancement in decision making studies of HEAs with new and essential perspectives but also reveals possibly concealed relationships amongst some critical belief in the field of material science.

CVD synthesis of nanometer SiC coating on diamond particles

Poor interfacial bonding between diamond and matrices has limited industrial applications of diamond-containing composites. Herein, continuous and dense nanometer SiC coatings were deposited on both large size (200 μm) and small size (1.0 μm) diamond particles to improve the wettability of diamond and protect it from oxidation and graphitization. Coating procedure consisted of first pretreating diamond particles followed by chemical vapor deposition (CVD) using methyltrichlorosilane (MTS: CH3SiCl3) as a precursor. Effects of deposition temperature, time, and gas flowing rate on microstructures of SiC coatings were all studied. Results showed that diamond surfaces were fully coated by SiC with thicknesses of 30 nm and 20 nm for large and small size diamond particles, respectively. Meanwhile, onset oxidation temperatures of large and small SiC-coated diamond particles increased by 250 and 130 °C, showing greatly enhanced oxidation resistance than that of raw diamond particles. The compressive fracture strength (CFS) of SiC-coated diamond (200 μm) is 226 N, improved by 8.5% compared with that of the raw diamond (201 N). In sum, CVD method is promising for the preparation of homogeneous nanometer SiC coatings on diamond particles for its modification and further application in composites.

Bio-based poly (γ-glutamic acid) hydrogels reinforced with bacterial cellulose nanofibers exhibiting superior mechanical properties and cytocompatibility

Natural polymer hydrogels are expected to be promising biomaterial because of its excellent biocompatibility and biodegradability, but they are soft and easily broken. Herein, the poly (γ-glutamic acid) (γ-PGA)/bacterial cellulose (BC) composite hydrogels with excellent mechanical properties were constructed by introducing bacterial cellulose. The γ-PGA/BC composite hydrogels were obtained by the covalent cross-linking of γ-PGA in the BC nanofibers suspensions. The γ-PGA/BC composite hydrogels exhibited excellent strength and toughness due to the more effective energy dissipation of hydrogen bonds network among BC nanofibers and γ-PGA hydrogel matrix and BC also acts as an enhancer. The compressive fracture strength and toughness of the γ-PGA/BC composite hydrogels could reach up to 5.72 MPa and 0.42 MJ/m3 respectively. Additionally, the tensile strength of γ-PGA/BC composite hydrogels were improved 8.16 times compared with γ-PGA single network hydrogels. More significantly, BC could disperse evenly in the γ-PGA hydrogels because of the hydrophilic nature of γ-PGA and BC nanofillers, which led to good interface compatibility. The result of cytotoxicity tests indicated that γ-PGA/BC composite hydrogels present excellent cytocompatibility, which suggested that the γ-PGA/BC composite hydrogels could serve as promising materials for many biomaterial related applications.

Effect of Deformation Conditions on Mechanical Properties of Zr-based Metallic Glasses

In this paper, the effects of different strain rate(1×10-5 s-1, 5×10-5 s-1, 1×10-4 s-1, 5×10-4 s-1, 1×10-3 s-1) and aspect ratio(1:1, 1.5:1, 2:1, 2.5:1, 3:1) on mechanical properties of Zr-based metallic glasses at room temperature were investigated. The results indicate that as the strain rate increases, the plastic strain and compressive strength of the specimens gradually decrease. The specimen with the strain rate of 1×10-5 s-1 exhibits the higher plastic strain of 10.25 %, compressive strength of 2002 MPa and fracture strength of 1999 MPa. In addition, accompanied with the increase in aspect ratio, the plastic strain of the specimens declines from 25.42 % to 1.97 %, meanwhile, the compressive strength and fracture strength of the specimens also present declining trend.

Microstructure and mechanical properties of the TiZrNbMoTa refractory high-entropy alloy produced by mechanical alloying and spark plasma sintering

The equiatomic refractory high entropy alloy (HEA) TiZrNbMoTa was investigated. The alloyed powders with face-centered cubic (FCC) structured solid solution phase were prepared by mechanical alloying (MA) and then sintered by spark plasma sintering (SPS) at 1300, 1400, 1500, and 1600 °C. The microstructure and mechanical properties of the bulk alloy were investigated. The body-centered cubic (BCC) structured solid solution phase and the ZrO2 phase precipitated from the FCC structured solid solution phase during cool-down from sintering. The highest compression fracture strength (3759 MPa) and fracture strain (12.1%) were obtained in the refractory HEA sintered at 1400 °C. The grain boundary strengthening, precipitation strengthening, solid solution strengthening, transformation-induced plastic (TRIP) effect, and toughening effect of the ZrO2 phase are the important factors for the high strength and ducitily of the refractory HEA prepared in this study.

3D Model of Bone Scaffolds Based on the Mechanical Behaviour for a Hybrid Nano Bio-composites

Ceramic/polymer Nano composites in the view of possessing design uniqueness and property combinations have gained a great attention and reported to be the materials of the 21st century that are not found in conventional composites. In the present work, an attempt has been made to study, develop and improve the bio-mechanic for a designed and fabricated Ceramic/polymer bio-composite for a human natural bone repair and replacement in the case of complex fracture and bone diseases by adding the Nano fillers ceramic particles to the Polymer Matrix Nano composites (PMNC) for fabricated a hybrid Titanium dioxide and yttria stabilized zirconia reinforced high density polyethylene (HDPE) matrix bio-composites properties. These bioactive composites have been investigated by using hot pressing technique at different compression pressures of (30, 60, and 90 MPa) at a compounding temperature of (180, 190, and 200 °C). The SOLIDWORKS 17.0 and the finite element ANSYS 15.7 software programs were used to the simulation, modelling and analysing of femur bone biomechanics that can withstand the highest stresses and strains. The response surface methodology (RSM) technique was used to improve and verify the results. For all the fabricated Nano bio-composites systems, the results showed that the obtained output parameters values were increased with increasing the process input parameters, also the vice versa for the strain energy and equivalent elastic strain values, also the Nano ceramic compositions represented the main factor influenced the results. The main investigates results of the current research deduced that for the increase of the Nano ceramic powder (TiO2) contain from 1% to 10%, the compression fracture strength and the micro-Vickers hardness values increased by 50% and by 8.45%, respectively, and when adding 2% of zirconia (ZrO2), an additional increase in the compression fracture strength and micro hardness by 28.21% and 40.19% achieved, respectively. When using 10% TiO2 + 2% ZrO2/HDPE bio-composite at highest compact temperature of 200 °C and compounding pressure of 90 MPa, the strain energy and the equivalent elastic strain reduced by 82.69% and 14.53% when compared with using of 1% TiO2 content. While when increasing the nano ceramic content from 1% to 10% without adding the ZrO2 nano filler, they reduced by 142.25% and 67.81%, respectively. The maximum equivalent von Misses stress obtained is equal to 39.957MPa and when increasing the nano ceramic content from 1% to 10%, the stress safety factors and fatigue live values increased by 58.38% and by 46.28%, respectively and when adding 2% of zirconia (ZrO2), the stress safety factor reached its maximum values, with an additional increase in its values by 21.42% and 69.40%, respectively. These results give great choices to use successful in vivo tests and for a better life performance with any age, patient status and degree of injury.

Modifications of microstructures and mechanical properties of CoCrFeMnNi high entropy alloy films by adding Ti element

The phase evolution, microstructure and mechanical properties of CoCrFeMnNiTix (x = 0, 0.2, 0.4, 0.6, and 0.8 in molar ratio, denoted as Tix hereafter) high entropy alloy films (HEAFs) were studied in this work. The films were prepared by co-sputtering of CoCrFeMnNi alloy and Ti targets. Abundant nanotwins were observed in the Ti0 and Ti0.2 films and the crystalline structures of both films were identified to be a single FCC phase. In Ti0.4 and Ti0.6, the matrix exhibited an amorphous structure, and both the nanocrystalline grains and nanotwins were embedded in the amorphous matrix. With further addition of Ti, the Ti0.8 film transformed to an amorphous structure. As a result, there was a phase transition from a single FCC to an amorphous structure with the increasing Ti content. Furthermore, nanoindentation tests showed that the hardness of the films increased from 6.62 GPa in Ti0 to 8.99 GPa in Ti0.8. Micropillar compression tests showed that the fracture strain decreased from >19.42% (no fracture) to 7.78% with the increasing Ti content. The best mechanical properties in compression were observed in Ti0.4, and the compressive yield and fracture strengths were 2.82 and 4.44 GPa, respectively, with the fracture strain of 12.4%, which was achieved by a balanced amount of nanocrystalline grains in the amorphous matrix.

Comparison of compressive fracture strength of small dog dental prosthesis along the direction of bite force

Comparison of compressive fracture strength of small dog dental prosthesis along the direction of bite force

Soft-Magnetic High-Entropy AlCoFeMnNi Alloys with Dual-Phase Microstructures Induced by Annealing

The simultaneous enhancement of magnetic and mechanical properties is desirable but challenging for soft-magnetic materials. A fabrication strategy to meet this requirement is therefore in high demand. Herein, bulk equiatomic dual-phase AlCoFeMnNi high-entropy alloys were fabricated via a magnetic levitation induction melting and casting process followed by annealing at 700–1000 °C, and their microstructures as well as mechanical and magnetic properties were investigated. The as-cast alloy possessed a single metastable B2-ordered solid solution that decomposed upon annealing into a dual-phase structure comprising an Al- and Ni-rich body-centered cubic (BCC) matrix and Fe- and Mn-rich face-centered cubic (FCC) precipitates both in the grain interior and along the grain boundaries. The magnetic and mechanical properties were closely related to the relative volume fraction of FCC in the alloy. The FCC volume fraction could be increased by increasing the annealing temperature, thereby offering tunable properties. The optimal annealing temperature for balanced magnetic and mechanical properties was found to be 800 °C. The alloy annealed at this temperature had an average BCC grain size of 12 ± 3 μm and FCC volume fraction of 41 ± 4%. Correspondingly, the saturation magnetization and coercivity reached 82.57 Am2/kg and 433 A/m, respectively. The compressive yield strength and fracture strength were 1022 and 2539 MPa, respectively, and the plasticity was 33%. Owing to its adjustable microstructure and properties, the AlCoFeMnNi alloy has potential for use as a multi-functional soft-magnetic material.

Comparação da resistência de pino intrarradicular de fibra de vidro com pino experimental confeccionado pela tecnologia CAD/CAM

Objetivo: O objetivo do presente estudo foi comparar a resistência à fratura de dentes causados pela restauração endodonticamente restaurada com pino de fibra de vidro e pino experimental de fibra de vidro usada pelo método auxiliado por computador / fabricação auxiliada por computador (CAD / CAM). Metodologia: Um total de 20 bovinos incisivos com coroas seccionadas e raízes foram preparadas com 15mm de comprimento foram divididos aleatoriamente em dois grupos (n = 10): G1 - fibra de vidro (controle) G1 - e G2 - fibra de vidro (experimental) . Em ambos os grupos, como peças que tiveram seus condutores radiculares usados endodonticamente.Como as raízes foram incluídas em resina acrílica, os pinos cimentados com cimento resinoso duplo e posteriormente, o teste de resistência à fratura por uma velocidade de 0,05 mm / min, sob uma pressão de 45 ° na máquina de ensaio universal até uma fratura . Os valores de resistência a fratura foram submetidos a teste t-Student com o programa SPSS com nível de significância de 5%. Resultados: acordo com testes, os resultados da força requerida para fratura foi menor no Grupo de pinos de fibra pré-fabricados personalizados (48,2kgf) do que Grupo de pinos fresados pelo sistema CAD / CAM (56,9kgf), porém não mostra diferença estatística entre eles (p = 0,26). Com média de DP ± 14,6 para o primeiro e de ± 19,0 para o segundo grupo. Conclusão: Os pinos de fibra expandida pela tecnologia CAD / CAM podem surgir como alternativa viável para restaurações intrarradiculares de elementos usados endodonticamente, uma vez que não apresentem diferenças estatísticas de resistência à fratura com fragmentos pré-fabricados.

Enhancing strength and plasticity of Zr-based bulk metallic glasses by Zr partially substituted Fe and isothermal annealing

Zr-based bulk metallic glasses (BMG) Zr65+xCu17.5Fe10-xAl7.5 (x = 0, 2.5, 5, 7.5) with high zirconium content were prepared by an injection copper-mold casting method. The influence of Zr partially substituted Fe and isothermal annealing on the microstructure and mechanical properties of the Zr65+xCu17.5Fe10-xAl7.5 BMGs has been systematically studied. The as-prepared BMG with a Zr content of 70 at.% achieves superior glass forming ability with a large supercooled liquid region width of 82 K and compressive performance. An optimized isothermal annealing (0.5 h) below the glass transition temperature of the as-cast Zr70Cu17.5Fe5Al7.5 BMG contributes significant enhancement in compressive fracture strength and plasticity, from 1845 MPa and 7.4% (as-cast) to 2096 MPa and 12.7% (annealed), respectively. The result of the present study provides a new strategy for designing high-performance BMG-based alloys.