scholarly journals Dislocation versus grain boundary strengthening in SPD processed metals: Non-causal relation between grain size and strength of deformed polycrystals

2017 ◽  
Vol 705 ◽  
pp. 42-45 ◽  
Author(s):  
M.J. Starink
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Causal Relation ◽  
Grain Boundary Strengthening

scholarly journals Microstructure and Enhanced Properties of Copper-Vanadium Nanocomposites Obtained by Powder Metallurgy

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 339 ◽  
Author(s):  
Yong Wang ◽  
Jinguo Wang ◽  
Haohao Zou ◽  
Yutong Wang ◽  
Xu Ran
Keyword(s):  
Electrical Conductivity ◽  
Grain Size ◽  
Yield Strength ◽  
Grain Boundary ◽  
High Strength ◽  
Strengthening Mechanism ◽  
Copper Matrix ◽  
Dispersion Strengthening ◽  
Annealed Copper ◽  
Grain Boundary Strengthening

Cu-2.4 wt.%V nanocomposite has been prepared by mechanical alloy and vacuum hot-pressed sintering technology. The composites were sintered at 800 °C, 850 °C, 900 °C, and 950 °C respectively. The microstructure and properties of composites were investigated. The results show that the Cu-2.4 wt.%V composite presents high strength and high electrical conductivity. The composite sintered at 900 °C has a microhardness of 205 HV, a yield strength of 404.41 MPa, and an electrical conductivity of 79.5% International Annealed Copper Standard (IACS); the microhardness and yield strength reduce gradually with the increasing consolidation temperature, which is mainly due to the growth of copper grain size. After sintering, copper grain size and V nanoparticle both maintain in nanoscale; the strengthening mechanism is related to grain boundary strengthening and dispersion strengthening, while the grain boundary strengthening mechanism plays the most important role. This study indicates that the addition of small amounts of V element could enhance the copper matrix markedly with the little sacrifice of electrical conductivity.

scholarly journals Effects of Sc and Zr Addition on Microstructure and Mechanical Properties of AA5182

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4753
Author(s):  
Jingxiao Li ◽  
Xiaofang Yang ◽  
Shihua Xiang ◽  
Yongfa Zhang ◽  
Jie Shi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundary ◽  
Tensile Properties ◽  
Isothermal Annealing ◽  
Zr Addition ◽  
Microstructure And Mechanical Properties ◽  
Alloy Microstructure ◽  
Zr Alloy ◽  
Grain Boundary Strengthening

The effects of 0.1 wt.% Sc and 0.1 wt.% Zr addition in AA5182 on microstructure and mechanical properties were investigated. Results show that Al3(ScxZr1−x) dispersoids formed in AA5182. Observation of ingots microstructures showed that the grain size of 5182-Sc-Zr alloy was 56% lower than that of based AA5182. Isothermal annealing between 230 °C and 500 °C for 2 h was performed to study the recrystallization, tensile properties and dispersoid coarsening. The recrystallization was inhibited by the dispersoids, and the alloy microstructure remained deformed after annealing. Al3(ScxZr1−x) in AA5182 was stable when annealing below 400 °C, while parts of dispersoids coarsened significantly when heating at 500 °C. The addition of Sc and Zr allowed YS of 5182 alloy to achieve 247.8 MPa, which is 100 MPa higher than the corresponding AA5182. The contributions of Orowan strengthening and grain boundary strengthening were obtained by calculation.

Improvement of Strength of Mg-12Gd-3Y-0.5Zr Alloys Processed by Combination of ECAP and Extrusion

2011 ◽  
Vol 682 ◽  
pp. 211-216
Author(s):  
Rong Zhu ◽  
Jin Qiang Liu ◽  
Jing Tao Wang ◽  
Ping Huang ◽  
Yan Jun Wu ◽  
...  
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Grain Boundary ◽  
Low Temperatures ◽  
Basal Slip ◽  
Extrusion Direction ◽  
Strengthening Mechanisms ◽  
Step Process ◽  
Angular Pressing ◽  
Peak Intensity

Equal channel angular pressing (ECAP) has been used to refine the grain size of Mg-12Gd-3Y-0.5Zr billet at about 400°C because it lacks sufficient ductility at low temperatures. However, <0001> peak intensity is oriented about 50º from the extrusion direction, which facilitates the basal slip, and decreases the yield strength. We have employed conventional extrusion at 300°C following ECAP to modify the texture in hard orientation. This two-step process makes use of two strengthening mechanisms a) grain boundary strengthening due to small grain size, and (b) texture strengthening due to grains in hard orientation. The samples processed by the two-step show the yield and ultimate strength to 283 and 308 MPa, respectively. Moreover, the activation of <c+a> slip and fine grains resulted from the ECAP helped to maintain a good ductility even after significant straining from conventional extrusion.

EFFECT OF GRAIN SIZE ON THE ELECTRON WORK FUNCTION OF Cu AND Al

2004 ◽  
Vol 11 (02) ◽  
pp. 173-178 ◽  
Author(s):  
WEN LI ◽  
D. Y. LI
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Grain Boundary ◽  
Work Function ◽  
Electron Work Function ◽  
Deformation Texture ◽  
Kelvin Probe ◽  
Surface Conditions ◽  
The Mean ◽  
Sophisticated Instrument

The Kelvin probe is a sophisticated instrument which is very sensitive to changes in surface conditions, such as deformation, texture, phase transformation and contamination. Efforts have been made to use this technique to diagnose wear. In this study, the effect of the grain boundary (GB) on the electron work function (EWF) was examined with the aim of investigating the contribution of changes in grain size to total changes in the EWF during wear. Copper and aluminum were studied as examples. It was demonstrated that the EWF dropped in the vicinity of GB's and the mean EWF decreased as the grain size decreased. The mechanism responsible for the changes in the EWF with respect to the GB is discussed.

Structural and thermodynamic properties of nanocrystalline fcc metals prepared by mechanical attrition

1992 ◽  
Vol 7 (7) ◽  
pp. 1751-1761 ◽  
Author(s):  
J. Eckert ◽  
J.C. Holzer ◽  
C.E. Krill ◽  
W.L. Johnson
Keyword(s):  
Thermal Analysis ◽  
Grain Size ◽  
Melting Point ◽  
Grain Boundary ◽  
Bulk Modulus ◽  
Atomic Level ◽  
X Ray Diffraction ◽  
X Ray ◽  
Fcc Metals ◽  
Mechanical Attrition

Nanocrystalline fcc metals have been synthesized by mechanical attrition. The crystal refinement and the development of the microstructure have been investigated in detail by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The deformation process causes a decrease of the grain size of the fcc metals to 6–22 nm for the different elements. The final grain size scales with the melting point and the bulk modulus of the respective metal: the higher the melting point and the bulk modulus, the smaller the final grain size of the powder. Thus, the ultimate grain size achievable by this technique is determined by the competition between the heavy mechanical deformation introduced during milling and the recovery behavior of the metal. X-ray diffraction and thermal analysis of the nanocrystalline powders reveal that the crystal size refinement is accompanied by an increase in atomic-level strain and in the mechanically stored enthalpy in comparison to the undeformed state. The excess stored enthalpies of 10–40% of the heat of fusion exceed by far the values known for conventional deformation processes. The contributions of the atomic-level strain and the excess enthalpy of the grain boundaries to the stored enthalpies are critically assessed. The kinetics of grain growth in the nanocrystalline fcc metals are investigated by thermal analysis. The activation energy for grain boundary migration is derived from a modified Kissinger analysis, and estimates of the grain boundary enthalpy are given.

Solid-phase crystallization of ultra-thin amorphous Ge layers on insulators

2021 ◽  
Author(s):  
Ryo Oishi ◽  
Koji ASAKA ◽  
Bolotov Leonid ◽  
Noriyuki Uchida ◽  
Masashi Kurosawa ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Barrier Height ◽  
Carrier Mobility ◽  
Solid Phase ◽  
Hole Mobility ◽  
Solid Phase Crystallization ◽  
Simple Method ◽  
20 Nm ◽  
Grain Boundary Barrier

Abstract A simple method to form ultra-thin (< 20 nm) semiconductor layers with a higher mobility on a 3D-structured insulating surface is required for next-generation nanoelectronics. We have investigated the solid-phase crystallization of amorphous Ge layers with thicknesses of 10−80 nm on insulators of SiO2 and Si3N4. We found that decreasing the Ge thickness reduces the grain size and increases the grain boundary barrier height, causing the carrier mobility degradation. We examined two methods, known effective to enhance the grain size in the thicker Ge (>100 nm). As a result, a relatively high Hall hole mobility (59 cm2/Vs) has been achieved with a 20-nm-thick polycrystalline Ge layer on Si3N4, which is the highest value among the previously reported works.

Creep Deformation / Oxidation Behavior of Re-Cr-Ni Diffusion Barrier Coated Hastelloy-X at 970°C in Air

2008 ◽  
Vol 595-598 ◽  
pp. 107-116 ◽  
Author(s):  
Shigenari Hayashi ◽  
Mikihiro Sakata ◽  
Shigeharu Ukai ◽  
Toshio Narita
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Barrier Layer ◽  
Creep Deformation ◽  
Diffusion Barrier ◽  
Hastelloy X ◽  
Alloy Substrate ◽  
Barrier Coating ◽  
Diffusion Barrier Layer ◽  
Coated Alloy

High temperature oxidation / creep deformation behavior of a diffusion barrier coated Hastelloy-X alloy, with large grain size ~500μm, was investigated at 970°C in air with external tensile stress of 22.5, 27.5, 32, and 40MPa. The diffusion barrier coating formed on Hastelloy-X consisted of a duplex structure with an inner diffusion barrier layer of Re-Cr-Ni alloy, and an outer oxidation resistant layer of β-NiAl. Un coated bare Hastelloy-X alloy with same grain size was also examined under the same conditions for comparison. The composition of the as-coated diffusion barrier coating was (15~21)Ni, (33~37)Cr, (30~33)Re, (11~15)Mo, and (9~14)Fe. This composition corresponds to σ-phase in the Ni-Cr-Re ternary system, which is known as a topologically close packed, TCP phase. The composition of this diffusion barrier layer did not change during the experiment. The oxide scales formed after creep testing on the coated and un-coated alloy surfaces were needle-like θ-Al2O3, and Cr2O3 with small amount of FeCr2O4, respectively. Grain boundary oxidation was also found in the subsurface region of the un-coated alloy. The Al2O3 scale exhibited severe spallation, and many cracks were formed perpendicular to the stress direction. However, no spallation or cracks were observed in the Cr2O3. The creep rupture times for the diffusion barrier coated alloy were about 1.5 times longer than those for bare alloy at all creep stress conditions. The fracture surface after rupture indicates that fracture occurred along alloy grain boundaries in both the coated and un-coated alloy substrate. Many cavities and cracks were observed within the diffusion barrier coated alloy substrate. These cavities and cracks tended to propagate from the substrate toward the diffusion barrier layer, and then stopped at the Re-Cr-Ni / β-NiAl interface. Cracks formed in the un-coated alloy initiated at the tip of grain boundary oxides, and propagated into alloy substrate. However no major cavities were observed inside the alloy substrate. The stress index, n, for both specimens was about 6, and this indicates that the deformation mechanism of both samples was dislocation creep. These results suggest that the Re-Cr-Ni diffusion barrier layer acts as a barrier against the movement of dislocations at the interface with the alloy surface.

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