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Showing papers on "Grain boundary strengthening published in 2019"


Journal ArticleDOI
TL;DR: In this paper, the effect of elemental combinations on the friction stress and Hall-Petch relationship in medium entropy alloys (MEAs) and high entropy alloy (HEAs) was reported.

158 citations


Journal ArticleDOI
TL;DR: In this paper, the CoCrFeNiMn high entropy alloy (HEA) bulk alloy was successfully manufactured using laser aided additive manufacturing (LAAM) and the microstructure and mechanical behaviors of the as-fabricated HEAs were investigated.
Abstract: The CoCrFeNiMn high entropy alloy (HEA) bulk alloy was successfully manufactured using laser aided additive manufacturing (LAAM). The microstructure and mechanical behaviors of the as-fabricated HEAs were investigated. The as-built HEAs exhibit directional solidification at regions close to the melt-pool boundaries, forming dendritic columnar grains and transiting to equiaxed grains further away from the boundaries. Compared with the conventionally cast HEAs, the CoCrFeNiMn fabricated using LAAM possesses significantly higher yield strength (518 MPa) and ultimate tensile strength (660 MPa). The strengthening effect is attributed to finer grains and could be explained quantitatively through grain boundary strengthening. The as-built HEA shows a simultaneous enhancement in yield strength and ductility with decreasing testing temperature. The improved low temperature tensile properties could be ascribed to the formation of deformation twins at low temperature, which results in a steady strain hardening behavior. This work demonstrates the potential of using LAAM technology to extend the application of HEAs with fabrication of larger and more complex parts with good mechanical properties.

137 citations


Journal ArticleDOI
TL;DR: In this article, the effect of temperature variation on the microstructural evolution is particularly important to refractory high-entropy alloys (RHEAs), given their potential high-temperature applications.

112 citations


Journal ArticleDOI
TL;DR: In this article, an equiatomic AlCrCuFeNi high entropy alloy (HEA) is fabricated successfully from the alloy powders using selective laser melting (SLM), and the microstructural characteristics and mechanical behavior of SLMed AlCrcuFeNi samples under optimal SLM processing parameters are studied in detail.

102 citations


Journal ArticleDOI
Yan Chong1, Guanyu Deng1, Si Gao1, Jangho Yi1, Akinobu Shibata1, Nobuhiro Tsuji1 
TL;DR: In this paper, the Hall-Petch coefficient of a Ti-6Al-4V alloy with fully equiaxed and two different bimodal microstructures obtained by intercritical annealing at 850 and 950°C (BM850) was studied.

99 citations


Journal ArticleDOI
TL;DR: In this article, the microstructural evolution and mechanical properties of the TiC-reinforced CoCrFeMnNi high-entropy alloy (HEA) composite were investigated using electron backscatter diffraction, transmission electron microscopy, and room temperature compression tests.

96 citations


Journal ArticleDOI
TL;DR: In this article, the microstructural evolution and mechanical properties of sintered NbMoTaWVCr refractory high-entropy alloy powders were investigated.

89 citations


Journal ArticleDOI
TL;DR: In this paper, the MoNbTaTiV refractory high-entropy alloy (RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS).

71 citations


Journal ArticleDOI
TL;DR: In this article, the effect of grain size and grain shape on the flow stress in model copper grains was investigated and a simple model was proposed to account for the grain shape influence on the grain size effect.

68 citations


Journal ArticleDOI
TL;DR: In this paper, the superior mechanical properties of CoCrFeMnNi high-entropy alloy (HEA) at cryogenic temperatures were revealed, and the Hall-Petch relationship was well fitted and the fitting parameters had a negative relation with temperature.

65 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of samarium (Sm) content on microstructure and mechanical properties of Mg-0.5Zn-Zr alloy under as-cast and as-extruded states were thoroughly investigated.

Journal ArticleDOI
TL;DR: In this article, a high-strength AZ80 alloy was fabricated by multidirectional forging (MDF) under air-cooling condition, at an initial temperature of 360 °C, with an accumulative strain of 1.8, with no need of ageing treatment.

Journal ArticleDOI
TL;DR: In this article, relatively lightweight AlCoCrFeNi HEA ingots with different initial microstructures were fabricated by utilizing the cooling rate effect, and the associated mechanical properties and strengthening response are also reported.

Journal ArticleDOI
TL;DR: In this paper, selective laser melting (SLM) was employed to fabricate the aluminum alloy AlCu5MnCdVA in order to investigate the microstructure, mechanical behavior, anisotropy, and strengthening mechanisms.
Abstract: Selective laser melting (SLM) was employed to fabricate the aluminum alloy AlCu5MnCdVA in this work. The microstructure, mechanical behavior, anisotropy, and strengthening mechanisms were investigated. The results show that the main phases consist of α-Al and Al2Cu. In addition, the supersaturated solid solution with fine columnar grain, high dislocation density and weak texture has been obtained. There is little difference in mechanical properties when the scanning velocity changes if dense samples are obtained. The yield strength, the ultimate strength (UTS) and the elongation are 145.5–157.6 MPa, 309.1–319.7 MPa, 11.44%–14.34%, respectively. The anisotropy is weak, which results from the weak texture. The horizontal specimens show a little higher yield strength and lower elongation. The UTSs of the samples are nearly the same. The strongest anisotropy results from the lowest scanning velocity. The solid solution strengthening, grain boundary strengthening, dislocation strengthening, precipitate and dispersoid strengthening contribute to the strength of the specimens. The quantitative analyses show that all the four strengthening mechanisms dominant in the SLMed AlCu5MnCdVA alloys.

Journal ArticleDOI
TL;DR: In this paper, the grain growth kinetics of CoCrFeNi and CoCrMnNi high entropy alloys have been estimated by subjecting them to heat treatment in the temperature range 1073-1373 K. The strength coefficient (slope of Hall-Petch relation) is calculated as 1.92

Journal ArticleDOI
01 Jul 2019-Vacuum
TL;DR: In this article, the microstructure of bulk TiC10 alloy is mainly composed of FCC phase as the matrix phase and a small quantity of M23C6, M7C3 and TiMnO3 phases.

Journal ArticleDOI
TL;DR: In this paper, a weak elliptical texture was derived from the joint contributions of multiple dynamic recrystallization (DRX) mechanisms consisted of twin-, compound-and dislocation slip-induced DRX behaviors.
Abstract: All the time, it is difficult for magnesium alloys to equilibrate the relationship among strength, ductility and stretch formability at room temperature. Here, we added 0.6 wt% Zn into Mg-0.4Sn-0.7Y (TW00, wt%) alloy attempting to achieve a good combination among strength, ductility and stretch formability at room temperature. After extrusion, we found that Mg-0.4Sn-0.7Y-0.6Zn (TWZ000, wt%) alloy sheet exhibited a weak elliptical texture, accompanied with significant grain and second phase refinement. The formation of this weak elliptical texture was mainly originated from the joint contributions of multiple dynamic recrystallization (DRX) mechanisms consisted of twin-, compound- and dislocation slip-induced DRX behaviors. Grain boundary strengthening and second phase strengthening were mainly dedicated to the enhanced yield strength (~ 150.0 MPa) and ultimate tensile strength (~ 235.1 MPa), while non-basal slip, grain boundary cohesion, texture modification and twins commonly guaranteed the high ductility (~ 39.8%). Besides texture modification and non-basal slip, a large number of twins altered the initial microstructure along with the formation of new twinning textures during stretch forming. These new twinning texture facilitated the higher Schmid factor (SF) for basal slip beneficial to the enhancement in stretch formability (~ 7.0 mm). Therefore, TWZ000 alloy sheet provided an enormous potential to broaden magnesium alloys applications.

Journal ArticleDOI
19 Mar 2019-Entropy
TL;DR: The results demonstrate that the QG values of these H/MEAs are much higher than those of conventional alloys; most notable is FeCoNiCrPd HEA, which has an unusually lattice distortion effect that hinders grain growth.
Abstract: The recrystallization behavior, grain growth kinetics, and corresponding hardness variation of homogenized and 80% cold-rolled FeCoNiCrPd, FeCoNiCrMn, and their quaternary/ternary FCC-structured high/medium entropy alloys (H/MEAs) annealed under different conditions were investigated. Experimental results indicate that the grain size and hardness of these H/MEAs follow the Hall-Petch equation, with the Hall-Petch coefficient KH value being mainly dominated by the alloy's stacking fault energy and shear modulus. The FeCoNiCrPd alloy exhibits the highest hardness of the H/MEAs at the same grain size due to the largest Young's modulus difference between Cr and Pd. The grain growth exponent n, kinetic constant k, and activation energy for grain growth QG of all H/MEAs are calculated. The k can be expressed by the Arrhenius equation with QG, which is attributed to the diffusion rate. The results demonstrate that the QG values of these H/MEAs are much higher than those of conventional alloys; most notable is FeCoNiCrPd HEA, which has an unusually lattice distortion effect that hinders grain growth.

Journal ArticleDOI
TL;DR: In this article, the effect of strain-rate on tensile deformation behavior and strength properties was evaluated for two Cr-Ni-based austenitic stainless steels with different stacking fault energies.
Abstract: Using thermal-mechanical treatments, specimens with different grain sizes were produced for two Cr-Ni-based austenitic stainless steels with different stacking fault energies (analogues of AISI 316L and AISI 321 steels). The effect of strain-rate on the tensile deformation behavior and strength properties was evaluated for these steels. In given grain size interval, (3–73)μm for 316 steel and (0.2–32)μm for 321 steel, the yield strength σ 0.2 varies with grain size D in accordance with Hall-Petch relationship σ 0.2 = σ 0 + k H P D − 1 / 2 . The Hall-Petch coefficient kHP depends on steel composition (stacking fault energy) and possesses higher value for 321 steel as compared to 316 steel. Increase in strain-rate in the interval of 1.0 × 10−4 s−1 to 1.0 × 10−2 s−1 causes growth in stress σ0, but weakly changes coefficient kHP in Hall-Petch relationship: 322–327 MPa × m0.5 for 316 steel and 404–413 MPa × m0.5 for 321 steel. The strain-rate dependence of the constants in Hall-Petch relationship was discussed in terms of deformation mechanism and dislocation arrangement in both steels.

Journal ArticleDOI
Jiangtao Yang1, J.W. Qiao1, Shufang Ma1, G.Y. Wu1, D. Zhao1, Z.H. Wang1 
TL;DR: Al0.1CoCrFeNi high-entropy alloys with fully recrystallized single-phase structures and various grain sizes ranging from 4.7 to 59.5μm are fabricated through cold rolling and subsequent annealing as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of deformation experiments on olivine single crystals and aggregates conducted in a deformation-DIA at confining pressures of 5 to 9 GPa and temperatures of 298 to 1473 K.
Abstract: Plastic deformation of olivine at relatively low temperatures (i.e., low‐temperature plasticity) likely controls the strength of the lithospheric mantle in a variety of geodynamic contexts. Unfortunately, laboratory estimates of the strength of olivine deforming by low‐temperature plasticity vary considerably from study to study, limiting confidence in extrapolation to geological conditions. Here we present the results of deformation experiments on olivine single crystals and aggregates conducted in a deformation‐DIA at confining pressures of 5 to 9 GPa and temperatures of 298 to 1473 K. These results demonstrate that, under conditions in which low‐temperature plasticity is the dominant deformation mechanism, fine‐grained samples are stronger at yield than coarse‐grained samples, and the yield stress decreases with increasing temperature. All samples exhibited significant strain hardening until an approximately constant flow stress was reached. The magnitude of the increase in stress from the yield stress to the flow stress was independent of grain size and temperature. Cyclical loading experiments revealed a Bauschinger effect, wherein the initial yield strength is higher than the yield strength during subsequent cycles. Both strain hardening and the Bauschinger effect are interpreted to result from the development of back stresses associated with long‐range dislocation interactions. We calibrated a constitutive model based on these observations, and extrapolation of the model to geological conditions predicts that the strength of the lithosphere at yield is low compared to previous experimental predictions but increases significantly with increasing strain. Our results resolve apparent discrepancies in recent observational estimates of the strength of the oceanic lithosphere.

Journal ArticleDOI
TL;DR: In this paper, the effect of the volume fraction (0.6-8.4%) of the icosahedral phase (I-phase) on the microstructure, texture and mechanical properties of extruded Mg-Zn-Y alloys was examined.

Journal ArticleDOI
01 Jan 2019
TL;DR: In this article, the authors investigated the Hall-petch strengthening by grain and annealing twin boundaries in MnFeNi and found that 25% of the boundaries are anneal twin boundaries regardless of the grain size.
Abstract: Among equiatomic alloys of the Cr-Mn-Fe-Co-Ni system, MnFeNi was shown to exhibit a strong anti-invar behavior but little is known regarding its mechanical properties. The objective of the present study is to investigate Hall–Petch strengthening by grain and annealing twin boundaries in MnFeNi. For this purpose, seven different grain sizes between 17 and 216 µm were produced. Mean grain sizes (excluding annealing twin boundaries) and crystallite sizes (including them) were determined using the linear intercept method. Overall, 25% of the boundaries were found to be annealing twin boundaries regardless of the grain size. In some cases, two twin boundaries can be present in one grain forming an annealing twin, which thickness represents one quarter of the mean grain size. Based on a comparison of the mean twin thickness of different alloys with different stacking fault energy (SFE), we estimated an SFE of 80 ± 20 mJ/m2 for MnFeNi. Compression tests of MnFeNi with different grain sizes were performed between 77 and 873 K and revealed a parallel shift of the Hall–Petch lines with temperature. The interaction between dislocations and boundaries was investigated by scanning transmission electron microscopy (STEM) in a deformed specimen. It was found that a large number of dislocations are piling up against grain boundaries while the pile-ups at annealing twin boundaries contain much fewer dislocations. This indicates that annealing twin boundaries in this alloy are less effective obstacles to dislocation motion than grain boundaries.

Journal ArticleDOI
TL;DR: In this paper, the formation of a high density of nanoscale precipitates in an ultrafine-grained (UFG) FCC matrix was used to overcome the strength-ductility trade-off.
Abstract: FCC high- and medium-entropy alloys (HEAs and MEAs) have demonstrated high ductility and fracture toughness, but suffer from low strength. To overcome such strength-ductility trade-off, here, we present a strategy via the formation of a high density of nanoscale precipitates in an ultrafine-grained (UFG) FCC matrix. To realize this concept, we selected a cost-effective equiatomic CrFeNi MEA as our model system. The equimolar elemental powder mixture was first forced into the formation of a nanostructured supersaturated FCC solid solution, followed by densification via spark plasma sintering (SPS). During SPS, a high density of nanoscale Cr-rich precipitates were formed in the UFG FCC matrix (821 nm). Such a particular microstructure enabled the alloy to overcome the strength-ductility trade-off, with a high tensile strength of 826 MPa and elongation of 26%. Grain boundary strengthening and precipitation strengthening were found to be the main strengthening mechanisms. These results provide deep insight into the design of novel multi-principal element alloys with high strength and ductility for structural applications.

Journal ArticleDOI
TL;DR: In this paper, a new type of Cu-Cr alloy with Co and Si additions together with cryogenic rolling (CR) was designed and investigated, and the improvement of tensile properties of the Cu-1Cr-1Co-0.6Si alloy is mainly attributed to the precipitation strengthening and grain boundary strengthening, and also benefited from dislocation density strengthening, twin boundary strengthening and solid solution strengthening.
Abstract: Cu–Cr alloys have been widely used in industrial applications owing to their good combination of mechanical properties and electrical conductivity. However, the comprehensive performance of the alloy needs to be further improved to meet the harsh working environment. Hence, in this study, a new type of Cu–Cr alloy with Co and Si additions together with cryogenic rolling (CR) was designed and investigated. Microstructure analysis confirms that the Cr15Co9Si6 and Co2Si phases are formed with Co and Si additions into the Cu–Cr alloy. For the more, partial Cr15Co9Si6 phase decomposes during heat treatment process, and the Co2Si and Cr precipitates are precipitated from matrix during aging process. The improvement of tensile properties of the Cu–1Cr–1Co–0.6Si alloy is mainly attributed to the precipitation strengthening and grain boundary strengthening, and is also benefited from dislocation density strengthening, twin boundary strengthening, and solid solution strengthening. The electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy decreases dramatically mainly due to the increase of impurity scattering caused by surplus Si atoms. CR deformation is helpful for more solute atoms precipitated from the supersaturated solid solution during aging process, and thus the electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy increases with increasing deformation amount. After homogenizing treatment at 900 °C for 2 h, hot rolling by 60% at 900 °C, solution treating at 990 °C for 4 h, cold rolling by 90%, and aging at 440 °C for 1 h, the hardness, yield strength (YS), ultimate tensile strength (UTS), and electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy are 214.6 HV, 663.7 MPa, 745.9 MPa and 41.6%IACS, respectively, which exhibit good mechanical properties with a proper electrical conductivity. These results provide a feasible route for developing high performance Cu–Cr alloys.

Journal ArticleDOI
TL;DR: In this article, the influence of aging prior to extrusion (APE) on the tensile strength and ductility of as-extruded Mg 8.32Sn 1.85Zn 0.17Mn alloy was investigated.

Journal ArticleDOI
TL;DR: Graphene reinforced copper matrix (graphene/Cu) nanocomposite powders are fabricated by the molecular-level mixing process and consolidated by spark plasma sintering and pressureless sinting process followed by hot isostatic pressing for the full densification as mentioned in this paper.
Abstract: Graphene reinforced copper matrix (graphene/Cu) nanocomposite powders are fabricated by the molecular-level mixing process and consolidated by spark plasma sintering and pressureless sintering process followed by hot isostatic pressing for the full densification. The addition of 1.2% volume fraction of graphene in Cu matrix resulted in 1.9 and 1.3 times increase in yield strength and elastic modulus, respectively, in comparison to those of pure Cu fabricated by same sintering process. Homogeneous dispersion of graphene in Cu matrix and strong interfacial bonding between graphene and Cu matrix allowed outstanding mechanical properties which are similar to theoretically estimated values based on strengthening mechanisms. The strengthening mechanisms of graphene/Cu nanocomposites are quantitatively discussed in respect to grain boundary strengthening, load transfer and dislocation strengthening caused by mismatch in thermal expansion coefficient between graphene and Cu. It is demonstrated that graphene/Cu nanocomposites were strengthened mainly by load transfer mechanism and graphene induced grain boundary strengthening of Cu matrix. In addition, the rapid cooling rate during the spark plasma sintering process resulted in the dislocation strengthening in graphene/Cu nanocomposites.

Journal ArticleDOI
TL;DR: In this paper, Voronoi tessellation is used to model the hierarchical structure, prior austenite grain (PAG)/packet/block, of the martensitic steel and the effect of PAG/packet or block size on the macro and micro-scale mechanical response.

Journal ArticleDOI
TL;DR: In this article, different strengthening mechanisms including precipitation strengthening, grain boundary strengthening, solid solution strengthening, and Orowan strengthening were found to contribute to the yield strength in different degrees, which would help to further enhance the tensile properties of these alloys through composition design and processing optimization thereafter.

Journal ArticleDOI
TL;DR: In this paper, the performance of a high strength wear-proof alloy, which is fabricated by selective laser melting (SLM), was investigated and the strengthening mechanisms were discussed, and the incremental strength for heat-treated samples aged at 400°C was mainly due to the DO22 ordering and spinodal decomposition.
Abstract: As a high strength wearproof alloy, Cu–15Ni–8Sn alloy structures were fabricated by selective laser melting (SLM), while they possessed poor mechanical properties due to the absence of precipitated phase, and thus they are on the halfway to industrial application SLM-processed Cu–15Ni–8Sn alloy subjected to heat treatments is studied to further improve the performance Microstructure evolutions and mechanical properties variations were investigated, and the strengthening mechanisms are discussed SLM-processed matrix is a supersaturated solid solution with fine grains, leading to important yield strength contributions from solid solution strengthening The incremental strength for heat-treated samples aged at 400 °C is mainly due to the DO22 ordering and the spinodal decomposition The precipitation strengthening increased from 14% to above 70% after heat-treatment Among the three aging methods, directly aging (DA) samples showed highest strength than the other two methods The directly aged samples exhibit fine grains and high dislocation density, resulting in high grain boundary strengthening and dislocation strengthening Moreover, direct aging treatment is an economical and environment-friendly way to improve mechanical properties of SLM-processed precipitation-hardened alloy, which is a high strength conductive elastic material