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This research paper presents an analysis of the corrosion properties of steel-reinforced concrete samples during immersion in 3.5 wt. % NaCl aqueous solution by measuring their response both cathodic and anodic polarization in order to determine the corrosion rates in the function of their calcium nitrate inhibitor content. This cheap inorganic inhibitor was added to the concrete mix in concentrations of 1% and 3% by weight of cement in addition to two different superplasticizers (MapeiDynamon SR 31 and Oxydtron). The compressive strengths of the so prepared samples were also checked according to the relevant European standard and were within the acceptable limits, so this inhibitor does not weaken this important property of the concrete samples. The test results on steel reinforced samples immersed in 3.5 wt. % NaCl aqueous solutions at room temperature showed promising corrosion mitigating effects just after 6 months testing period. After 6 months the lower corrosion currents (i.e. better corrosion resistance) for both types of superplasticizers were observed with those samples which contained 3% calcium nitrate inhibitor. The best result was observed with sample C4 (in this case 3% calcium nitrate was added to the mixture of cement+Oxydtron superplasticizer). The advantageous inhibition mechanism of nitrate anions is also discussed and interpreted. more...

A four-component equimolar high-entropy alloy (HEA) with the composition of HfNbTiZr and body-centered cubic (bcc) structure was processed by HPT at RT. The evolution of the dislocation density, the grain size and the hardness was monitored along the HPT-processed disk radius for different numbers of turns between ¼ and 20. It was found that most of the increase of the dislocation density and the refinement of the grain structure occurred up to the shear strain of ∼40. Between the strains of ∼40 and ∼700, only a slight grain size reduction was observed. The saturated dislocation density and grain size were ∼2.1 × 1016 m−2 and ∼30 nm, respectively. The saturation in hardness was obtained at ∼4450 MPa. These values were similar to the parameters determined in the literature for five-component HEAs processed by HPT. The analysis confirmed that the main component in the strength was given by the friction stress in the HPT-processed bcc HfNbTiZr HEA. It was also revealed that the contribution of the high dislocation density to the strength was significantly higher than the effect of the small grain size. more...

A Cu&ndash, 1.1%Cr&ndash, 0.04%Zr (wt.%) alloy was processed by severe plastic deformation (SPD) using the equal channel angular pressing (ECAP) technique at room temperature (RT). It was found that when the number of passes increased from one to four, the dislocation density significantly increased by 35% while the crystallite size decreased by 32%. Subsequent rolling at RT did not influence considerably the crystallite size and dislocation density. At the same time, cryorolling at liquid nitrogen temperature yielded a much higher dislocation density. All the samples contained Cr particles with an average size of 1 &micro, m. Both the size and fraction of the Cr particles did not change during the increase in ECAP passes and the application of rolling after ECAP. The hardness of the severely deformed Cu alloy samples can be well correlated to the dislocation density using the Taylor equation. Heat treatment at 430 &deg, C for 30 min in air caused a significant reduction in the dislocation density for all the deformed samples, while the hardness considerably increased. This apparent contradiction can be explained by the solute oxygen hardening, but the annihilation of mobile dislocations during annealing may also contribute to hardening. more...

Extruded AM60 Mg alloy samples were processed by two different severe plastic deformation (SPD) techniques, equal-channel angular pressing (ECAP) and multi-directional forging (MDF) at 220 °C for 2, 4 and 6 passes. The evolutions of the microstructure during ECAP and MDF were compared. It was found that although the main trends were similar for the two processing methods, the changes in the microstructure were more pronounced for ECAP. This effect was explained by the higher imposed strain and the different loading conditions applied during ECAP, which resulted in a much larger dislocation density and precipitate fraction for 2 passes compared to MDF. Between 2 and 6 passes, the dislocation density decreased, while the diffraction domain size increased due to recovery/recrystallization. The present study demonstrates that for the two SPD-processing methods the microstructural evolutions do not coincide either as a function of the number of passes or the equivalent strain. more...

The correlation between the strength, ductility and phase structures of two new NiFeCrMoW type alloys is investigated. The ductile or brittle behavior is strongly influenced by the volume fraction of FCC and BCC phases. The results may allow for a concept to optimize the combination of strength and ductility by varying the alloy composition. more...

The effect of the chemical inhomogeneities on the local mechanical behavior was studied in a CoCrFeMnNi high-entropy alloy. Micropillar compression revealed that, despite the difference in the chemical composition, the stress-strain behaviors in the two regions were almost identical. The size effect was negligible in the micropillar compression experiments. more...

The lattice defect structure developed during plastic deformation in a High-Entropy Alloy (HEA) with the composition of Ti35Zr27.5Hf27.5Nb5Ta5 was investigated. The crystallite size as well as the density and types of dislocations in a disk processed by High-Pressure Torsion (HPT) were determined by X-ray profile line analysis (XLPA). Additional transmission electron microscopy (TEM) investigations were carried out to monitor the grain size evolution during deformation. It was found that the dislocation density in the HPT-processed sample was very high compared to conventional materials. In addition, in Ti35Zr27.5Hf27.5Nb5Ta5 HEA the initial body-centered cubic structure transformed into a martensitic phase during HPT. The hardness of this HEA was investigated along the HPT-processed disk radius and correlated to the microstructure. more...

The microstructure and the mechanical behavior of equimolar Ti 20 Hf 20 Zr 20 Ta 20 Nb 20 high-entropy alloy in a wide range of initial strain rates between ~ 10 − 3 s − 1 and ~ 3.4 × 10 3 s − 1 were studied. A significant increment in the yield strength with increasing strain rate was observed. The yield strength at ~ 3.4 × 10 3 s − 1 was about 40% higher than that measured at ~ 10 − 3 s − 1 . Analysis by electron backscatter diffraction shows that in the low strain rate regime (up to ~ 10 s − 1 ) the deformation occurs mainly in evenly distributed bands, while in the dynamic regime the deformation is strongly localized in macroscopic shear bands accompanied by softening even after the onset of yielding. The Kernel Average Misorientation technique reveals a high level of lattice rotation within these bands that also carries intense shear. In addition, X-ray diffraction line profile analysis indicates that the sharp increase in the flow stress is mostly related to an increase of the dislocation density. more...

The present study focuses on the corrosion behavior of a single-phase FCC high entropy alloy (VCrNiCoFeCu) casted by two different methods: induction melting and spark plasma sintering. The corrosion resistance has been evaluated using immersion tests in 3.5% NaCl solution, the potentiodynamic polarization measurements and the results are compared how is dependent the corrosion rate as a function of the production methods. Our results show that induction melted sample is stable in salty environment. On the other hand, based on the changes of polarization curves, there must be an evolution of oxide films on the SPSed sample until reaching the stable oxide layer. more...

This study investigates the correlation between the microstructure and the mechanical strength of AM60 magnesium alloy processed by equal channel angular pressing (ECAP) and multi-directional forging (MDF) at a constant temperature of 220 °C. The maximum number of passes was six for both severe plastic deformation (SPD) techniques. The minimum achievable grain size was ~1.9 μm for ECAP while it was only ~2.7 μm for MDF. Despite the monotonous reduction of the grain size, the yield and the ultimate tensile strength values decreased for high equivalent strains which was attributed to the decrease of the dislocation density. The maximum achievable strength was higher for ECAP than that for MDF mainly due to the higher dislocation density. Both ECAP and MDF processing led to an improvement of ductility. Based on the strength results, it is evident that the ECAP process is more effective in improving the mechanical properties of AM60 alloy at 220 °C, compared to the MDF process. more...

The recrystallization behavior of a well-known non-equiatomic high entropy alloy by the nominal chemical composition of Fe–27Mn–10Cr–10Co, at.% was investigated. The compression tests were performed in the temperature range of 400–1000 °C by the interval of 200 °C under the strain rate of 0.001 s−1. Initial microstructure consist of face centered cubic and hexagonal phases by the average grain size of 90, and 11 μm, respectively. Interestingly, the occurrence of dynamic recrystallization was observed during compression testing at warm temperature regime (400 and 600 °C). The appreciable grain refinement, the corresponding flow curve softening, and the detailed analysis of the hardening curves according to the Poliak and Jonas method, verified the occurrence of dynamic recrystallization at such warm temperature regime. The required stored energy was provided through the shear reversion of thermally induced martensite before any straining. In contrast, the softening mechanisms was not strong enough to compensate the strain hardening of the single phase microstructure. This further approved the significant role of the martensite phase to trigger the occurrence of dynamic recrystallization. The intensified substructure development and the random microtexture of the recrystallized grains well indicate the contribution of continuous recrystallization mechanism. The microstructure was also considerably refined (by the mean grain size of ∼1.7 μm) through compressive deformation at 1000 °C. In fact, the deformation temperature was high enough to compensate the inhibitory effects of sluggish diffusion and severe lattice distortion. more...

An investigation was conducted on aluminum samples (AA1050) to study the microstructure and hardness evolution during processing by High Pressure Torsion Extrusion (HPTE). The equivalent strain accumulated in the samples after one pass of HPTE varied in a wide range between 0.9 and 65.5, depending on the processing parameters. HPTE led to the formation of a gradient microstructure in which the grain size decreased by increasing the distance from the central axis of the billets. This gradient decreased significantly by increasing the ratio of rotational speed to extrusion speed. Most of the grain refinement and hardness-increase occurred up to the equivalent strain of ~5 but saturation level was achieved at the strain of ~20. Saturation levels in grain size and hardness were ~0.7 μm and ~67 HV, respectively. HPTE technique can provide similar saturation in microstructure and hardness as those obtained by HPT but in much larger samples. Therefore, HPTE can be a named as a suitable candidate for practical applications to produce bulk ultrafine-grained materials with considerable enhancement in hardness. more...

The effects of V, Cr, and Mn on the magnetic, elastic, and thermal properties of FeCoNiCu high-entropy alloy are studied by using the exact muffin-tin orbitals method in combination with the coherent potential approximation. The calculated lattice parameters and Curie temperatures in the face-centered-cubic structure are in line with the available experimental and theoretical data. A significant change in the magnetic behavior is revealed when adding equimolar V, Cr, and Mn to the host composition. The three independent single-crystal elastic constants are computed using a finite strain technique, and the polycrystalline elasticity parameters including shear modulus, Young's modulus, Pugh ratio, Poisson's ratio, and elastic anisotropy are derived and discussed. The effects of temperature on the structural parameters are determined by making use of the Debye-Gruneisen model. It is found that FeCoNiCuCr possesses a slightly larger thermal expansion coefficient than do the other alloys considered here. A Correction to this article was published on 12 February 2018. Correction in: JOM, vol. 70, issue 6, pages 1037-1037. DOI: 10.1007/s11837-018-2775-6 more...

High-Pressure Torsion (HPT) is one of the most effective severe plastic deformation techniques in grain refinement. The goal of this study was to investigate the influence of HPT on the microstructure and hardness of a Ti-rich High-Entropy Alloy (HEA). The evolution of the grain size due to 1 turn of HPT was studied by transmission electron microscopy. Besides the refinement of the microstructure, a phase transition also occurred during HPT, as revealed by X-ray diffraction. The initial bcc structure transformed into a martensitic phase throughout the material. The features of this phase transformation were studied on a sample compressed to low strain values. The hardness as a function of the distance from the center in the HPT-processed disk was measured and correlated to the microstructure. more...