Obvious Grain Research Articles

Effects of Trace Amounts of Mn, Zr and Sc on the Recrystallization and Corrosion Resistance of Al-5Mg Alloys

This study aimed to explore the effects of trace amounts of Mn, Zr, and Sc on the recrystallization behavior and corrosion resistance of Al-5Mg alloys after process annealing by means of alloy design and microstructure analysis of electron backscatter diffraction (EBSD), electron microprobe (EPMA), and electron microscopes (TEM and SEM). The main objective was to obtain alloys with better corrosion resistance. The results show that the fine Al3Zr and Al3Sc precipitated particles were both superior to the MnAl6 particles in inhibiting grain and sub-grain boundary migrations. Therefore, the Zr-containing and Sc-containing alloys were better than the Mn-containing alloy in inhibiting recrystallization. For further comparison, the thermal stability of the Al3Sc particles was better than that of the Al3Zr particles, so the Sc-containing alloy at the high temperature above 350 °C inhibited grain growth better than the Zr-containing alloy. During the recovery stage of the alloy in the recrystallization process, the β-Mg2Al3 phase precipitated on the sub-grain boundary, thus reducing the occurrence of intergranular corrosion. However, in the initial stage of recrystallization, the β-Mg2Al3 phase continuously precipitated on the grain boundary, causing obvious intergranular corrosion. For the Sc-containing alloy, because there was no obvious grain growth stage, the β-Mg2Al3 phase continuously precipitated on the grain boundary, and thereby intergranular corrosion occurred. Therefore, its corrosion resistance was greatly reduced. By contrast, for the alloy containing Mn or Zr, because of obvious grain growth, magnesium atoms aggregated. As a result, the β-Mg2Al3 phase discontinuously precipitated on the grain boundary. The corrosion morphology was local pitting corrosion rather than intergranular corrosion, and thus the corrosion resistance of the alloy was enhanced. As a novelty, this study clearly observed the sensitized precipitation and corrosion morphology of the β-Mg2Al3 phase of Al-5Mg alloy under different recrystallization methods. This will be of benefit to the design of anti-corrosion measures for the future manufacturing and application of Al-5Mg alloy.

Effect of Minor Er Additions on the Microstructures and Mechanical Properties of Cast Al-Cu-Mg-Ag Alloys.

The microstructures and mechanical properties of novel cast Al-Cu-Mg-Ag alloys with and without minor additions of Er (0.09 and 0.2 wt %) are investigated by Vickers hardness tests, tensile tests, optical metallographic examination, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results reveal that the Er addition decreases the hardness value of peak-aged Al-Cu-Mg-Ag alloy but has little influence on the time required for achieving the peak aging condition. Meanwhile, the Ω phase is suppressed in Er-added alloys, leading to a lower tensile strength at room temperature, which causes the (Mg, Ag, Er, V, Ti)-rich phase in the matrix in Er-added alloys. This blocky phase consumes available Mg and Ag atoms for Ω nucleation, leading to the low number density of Ω plates. The strength properties of Er-added alloys at 300 °C are found to be enhanced, which benefits from the pinning effect of the Al8Cu4Er phase on grain boundaries. Meanwhile, the brittle fracture of Er-added alloys at room temperature is directly associated with the Al8Cu4Er phase and the blocky (Mg, Ag, Er, V, Ti)-rich phase, which acts as the source of microcracks during deformation. In addition, no obvious grain refinement effect can be observed in Er-added alloys.

Effect of electrification and chlorination on the microstructure and electrical properties of fine Al wires

In this study, Al-50 ppm Ni (AN0005) was fabricated into 15, 12, and 4 mil (375, 300, and 100 μm, respectively) wires through the wire drawing process. The thick 12 and 15 mil wires exhibited an isometric crystal structure. A large plastic deformation of the thin 4 mil wire resulted in obvious grain refinement. Thin 4 mil AN0005 wires exhibited the best mechanical performance. In the fusing test, the platform area in I–V curve, called the over resistance zone (OR Zone). The change of wire diameter obtained by the fusing test does not affect the occurrence of the OR Zone and all wire diameters appear incandescent. The change of the fusing current conforms to the empirical formula, which increases as the wire diameter increases. The OR zone decreased with the increase in the diameter of AN0005 wires. During the incandescent stage, the Ni-rich granular eutectic cladding structure caused holes and reduced the electrical effective cross-sectional area, which then affected the electrical properties of the AN0005 wires. In the chlorination test, AN0005 wires of three diameters were soaked in a saturated saline solution for various durations. The mechanical strength of the wires did not change considerably, but the cracks on the surface of the wire because of chlorination caused reduced ductility. The results of the study indicated that aluminum wires were resistant to chloride ion attacks.

Tuning nanostructure and mechanical property of Fe–Co–Ni–Cr–Mn high-entropy alloy thin films by substrate temperature

Improving the mechanical property of high-entropy alloys (HEAs) with face-centered cubic (fcc) structure is critical for their potential applications. In this study, the effects of substrate temperature, Tsub, on nanometer-sized structure and mechanical property of fcc-structured Fe–Co–Ni–Cr–Mn HEA thin films prepared by magnetron sputtering were systematically investigated. All films grow in a nanocolumnar manner and display a single fcc-structured solid solution phase with (111) preferential orientation in addition to the reduced amorphous phase fraction and increased average grain size with increasing Tsub. The top-surface cauliflower-like hierarchical microstructure with some voided boundaries for 293 K-film gradually disappears with increasing Tsub up to 573 K. For higher Tsub (673 K–773 K), the obvious grain growth occurs with significantly increased column size and roughness. The variations in normal hardness, H, and Young's modulus, Es, obtained from nanoindentation tests on the surface of Fe–Co–Ni–Cr–Mn HEA thin films experienced a process of first increasing and then decreasing with Tsub, with a maximum at Tsub = 573 K. The former increase is due to enhanced interfacial adhesion and the later decrease is ascribed to the weakened grain boundary strengthening caused by grain growth. The 573 K-film with a nanocomposite structure including hybrid nanocrystalline and amorphous phase exhibits the highest H (∼10.0 GPa) and Es (∼185.5 GPa) and is the strongest in terms of hardness among reported Fe–Co–Ni–Cr–Mn HEAs without post-treatment. In-situ micro-tensile tests alone the surface of Fe–Co–Ni–Cr–Mn HEA thin films uncovered the higher lateral yield strength (∼1.1 GPa), fracture strength (∼1.4 GPa), and Young's modulus (∼64.3 GPa) for 573 K-film than those of 293 K- and 773 K-films as well, consistent with nanoindentation results. Anisotropic mechanical responses normal to and along the surface were clearly found in Fe–Co–Ni–Cr–Mn HEA thin films, which are caused by the nanocolumnar morphology and the weakened columnar boundaries adhesion compared to the column itself.

Response of Microbial Consortia Culture Inoculation to Soil Moisture Status, Proline and Yield of Sorghum (Sorghum bicolar L.)

Plant secondary metabolites play vital role in plant stress response. In this study we investigated root colonization of sorghum (Sorghum bicolar) infected by two different types of microbial consortia culture (MC1 & MC2) leads to alteration in the biosynthesis of secondary plant metabolites including phytoharmones and osmolyte proline under drought stress. The promising microbial consortia procured from authentic sources (Department of Microbiology CRIDA, Hyderabad and that consortia culture contain mixture of effective beneficial microbes such as N-fixing bacteria, PGPR and mycorrhizal fungi). Application of microbial consortia culture through soil application and seed treatment to sorghum along with Recommended Dose Of Fertilizer (RDF) showed increased soil moisture content and chlorophyll pigments as compared to uninoculated controls as well as drought stressed plants. Proline content was increased in plants inoculated with microbial consortia under both normal as well as drought conditions. An obvious increase grain yield and dry matter yield through application of microbial consortia with soil application and seed treatments in normal and drought condition respectively.

Mechanical properties and microstructural evolution of pressureless sintered ceramics obtained from high-energy ball-milled TiB2–TiC powders

A series of TiB2–TiC composites were successfully fabricated through one-step and two-step pressureless sintering using powders obtained by high-energy ball-milling. Effects of ball-milling time on crystal size and morphology of powders as well as microstructural evolution and mechanical properties of TiB2–TiC composites were investigated. The crystal size of TiB2–TiC powders decreases to 14.7 nm after ball milling for 30 h. Two-step pressureless sintering is beneficial to the densification process without obvious grain coarsening. The core-rim structure of carbides in TiB2–TiC composites is formed by nonuniform diffusion of W atoms from the outside to the interior of TiC grains. The phenomenon of selective solution of WC into TiC grains was carried out through experiments and verification of first-principles DFT calculations. An in-situ TiB2 plate toughened microstructure is developed for TiB2-40 wt %TiC composites two-step sintered at 1500 °C for 4 h and 2000 °C for 1 h with excellent comprehensive performances.

Role of bimodal-grained structure with random texture on mechanical and corrosion properties of a Mg-Zn-Nd alloy

Fine grained ZN20 alloy was obtained by combining equal-channel angular pressing (ECAP) with extrusion. Microstructural observation showed an obvious grain refinement with an average grain size of 10 µm after ECAP. The original bimodal-grained structure composed of coarse grains with strong basal texture and fine grains with random texture was substituted by a new kind of bimodal-grained structure with finer grains and more random texture after 4 passes ECAP at 300 °C. The combination of grain refinement and texture weakening caused the ductility can be increased by 40% compared with the as-extruded alloy. Immersion test in simulated intestinal fluid revealed an improvement of corrosion resistance after ECAP. Grain refinement can stable the corrosion product layer and basal texture is more beneficial for the corrosion resistance than the non-basal texture.

Effect of extrusion parameters on microstructure, texture and mechanical property anisotropy of spray deposited 2195 Al–Li alloy profile

To study the effects of extrusion parameters on the microstructure, texture, and mechanical property of 2195 Al–Li alloy, several extrusion experiments were carried out at different extrusion temperatures and speeds. A profile with different aspect ratios was designed, and the corresponding extrusion die was also designed and manufactured. The effects of aspect ratio, extrusion temperature, and speed on the microstructure and mechanical properties were investigated. The results show that cylindrical fiber grains and strong fiber textures of <111> and <100>//ED can be formed in the symmetrical areas with a low aspect ratio, which makes the profile at the areas have higher tensile strength along the extrusion direction and cause greater anisotropy of mechanical property. With the increase of aspect ratio, the grain structure turns into flat shape, and the fiber textures also change to {011}<211> and {011}<311>, the proportion of the {011}<311> texture component is higher at the area with a larger aspect ratio. This change in texture reduces the longitudinal strength of the profile and improves the transverse strength, which thus reduces the degree of anisotropy. As the extrusion temperature increases, the tensile strength of the profile can be increased due to the enhanced solution strengthening. However, excessive extrusion temperature will lead to obvious recrystallization and grain coarsening, which seriously reduces the formability and plasticity of the profile. Increasing the extrusion speed is beneficial to the dissolution of secondary particles into the matrix, which improves the strength of the profile. The grain size and recrystallization are little influenced by the extrusion speed. The increase of extrusion speed promotes the formation of the texture of {011}<311>, which improves the transverse strength of the profile and reduces the anisotropy.

Effects of heat treatment on interfacial characteristics and mechanical properties of titanium matrix composites reinforced with discontinuous carbon fibers

Weak interfacial bonding was a significant problem in titanium matrix composites (TMCs) reinforced with carbon fibers (CFs). In this study, heat treatment (HT) up to 1000 °C was applied on powder metallurgy Ti-6Al-4V matrix composites reinforced with discontinuous CFs to obtain different interfacial structures. Mechanical tests at both room-temperature and 500 °C showed that the best mechanical properties were attained at HT temperature of 900 °C. To understand the underlying mechanism, the phase structure, grain morphology and interfacial microstructure were examined. It was found that as HT temperature was increased, the interface thickness increases continuously and obvious grain growth happens at 1000 °C. Suitable interfacial reaction and fine grain size are identified as critical structural parameters to obtain high-performance CFs/TMCs. This study may provide new insight into the role of interfacial structure played in the strengthening effect of CFs/TMCs.

Effect of a Tempering Treatment on the Microstructural Evolution and Mechanical Properties of an M2 HSS/Ta Alloy Fabricated by Laser Metal Direct Forming

In a previous work, M2 high‐speed steel consisting of Ta on #45 steel was prepared by a laser metal direct forming process. After the appropriate proportion of Ta powder is added, obvious grain refinement occurs, and the amount of retained austenite decreases. Furthermore, the microhardness, impact toughness, and wear resistance increase. On the basis of this work, the microstructure and mechanical properties of the samples are further studied after tempering at different temperatures. The phase, microstructure, hardness, and wear resistance of the two kinds of steels are characterized by X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and hardness and wear tests. The results show that compared with the deposition state, the microstructure of the samples after heat treatment shows grain refinement and carbide aggregation. In addition, the hardness and impact toughness of the samples increase to different degrees after tempering at an appropriate temperature. However, after tempering, the mesh structure of the grain boundaries is destroyed, and the anchoring effect of the carbides weakens; thus, the wear rate of the samples increases to a certain extent.

In-situ observation of grain growth and phase transformation in weld zone of Ti-6Al-4V titanium alloy by laser welding with filler wire

Through in situ observation at high temperature confocal laser scanning microscope, the microstructures and phase transformation of Ti-6Al-4V titanium alloy welded joint by laser welding with filler wire during heating, heat preservation and cooling process in simulating welding thermal cycle were studied. When the weld microstructure was heated to 380 °C, obvious grain growth was observed. After heating to 1 050 °C, weld microstructures were mostly composed of coarse β-columnar grains. During the heat preservation process of the weld metal, it could be found that the β phase boundary moved slowly. In the cooling process of weld microstructures, with the increase of the cooling rate, the transition temperature for new phase precipitation decreased gradually, and that for ending the precipitation increased gradually. The microstructures after cooling to room temperature at a rate of 0.5 °C/s and 5 °C s−1 were composed of α phases. At 20 °C s−1, acicular α′ martensite appeared in the microstructures. At 80 °C s−1, precipitated phases were all composed of acicular α′ martensite.The Ti-6Al-4V titanium alloy weld microstructure by laser welding with filler wire is completely hexagonal close packed (HCP) crystal structure.The hardness of the weld microstructures was improved with the cooling rate getting faster.

Effect of grain and phase boundaries on soft magnetic properties of FeCoNiAlSi high-entropy alloys

The impact of grain and phase boundaries on the magnetic domain structure and soft magnetic properties of the FeCoNi(AlSi)x (0.1 ≤ x ≤ 0.7) high-entropy alloys (HEAs) have been studied in this work. The x = 0.1 alloy with single FCC phase and the x = 0.5 alloy with single BCC phase show obvious grain and phase boundaries, while the x = 0.3 containing FCC plus BCC phase and x = 0.7 alloy containing single BCC phase only present phase boundaries. Besides, The magnetic domains can cross grain and phase boundaries when the exchange coupling interaction is stronger enough. However, the domains are blocked for x = 0.5 alloy due to the strong pinning effect of grain boundaries (GBs). Moreover, the x = 0.1 and x = 0.5 alloys display good statically soft magnetic properties with relatively low coervivity (Hc) and high maximum permeability (μmax), whereas the x = 0.3 and x = 0.7 alloys exhibit good dynamic magnetic parameters with low alternating current (AC) Hc and total loss (Ps).

Unraveling the Charge Transport Mechanism in Mechanochemically Processed Hybrid Perovskite Solar Cell.

The long-term operation of organic-inorganic hybrid perovskite solar cells is hampered by the microscopic strain introduced by the multiple thermal cycles during the synthesis of the material via a solution process route. This setback can be eliminated by a room temperature synthesis scheme. In this work, a mechanochemical synthesis technique at room temperature is employed to process CH3NH3PbI2Br films for fabricating perovskite solar cell devices. The solar cell device has produced a 957 mV Voc, a 16.92 mA/cm2 short circuit current density, and a 10.5% efficiency. These values are higher than the published values on mechanochemically synthesized CH3NH3PbI3. The charge transport properties of the devices are studied using DC conductivity and AC impedance spectroscopy, which show a multichannel transport mechanism having both ionic and electronic contributions. A much smaller defect density in the mechanochemically synthesized hybrid perovskite material is confirmed. A polarization assisted recombination mechanism is observed to have a dominant effect on the overall charge transport mechanism. However, no obvious grain boundary and intralayer lattice defect related responses are found in the perovskite layer. Interfacial charge transport and recombination are found to show major effects on both the temperature dependent and illumination dependent impedance spectra.

Properties and Mechanism of PEALD-In2O3 Thin Films Prepared by Different Precursor Reaction Energy.

Indium oxide (In2O3) film has excellent optical and electrical properties, which makes it useful for a multitude of applications. The preparation of In2O3 film via atomic layer deposition (ALD) method remains an issue as most of the available In-precursors are inactive and thermally unstable. In this work, In2O3 film was prepared by ALD using a remote O2 plasma as oxidant, which provides highly reactive oxygen radicals, and hence significantly enhancing the film growth. The substrate temperature that determines the adsorption state on the substrate and reaction energy of the precursor was investigated. At low substrate temperature (100–150 °C), the ratio of chemically adsorbed precursors is low, leading to a low growth rate and amorphous structure of the films. An amorphous-to-crystalline transition was observed at 150–200 °C. An ALD window with self-limiting reaction and a reasonable film growth rate was observed in the intermediate temperature range of 225–275 °C. At high substrate temperature (300–350 °C), the film growth rate further increases due to the decomposition of the precursors. The resulting film exhibits a rough surface which consists of coarse grains and obvious grain boundaries. The growth mode and properties of the In2O3 films prepared by plasma-enhanced ALD can be efficiently tuned by varying the substrate temperature.

Stabilizing a severely deformed Al–7Mg alloy with a multimodal grain structure via Mg solute segregation

Single-phase Al–Mg alloys processed by severe plastic deformation (SPD) usually suffer from unsatisfactory thermal stability at moderate to high temperatures with recrystallization occurring and obvious grain coarsening. In the present work, an Al–7Mg alloy prepared by equal-channel angular pressing (ECAP) possessed markedly enhanced thermal stability upon annealing at moderate to high temperatures (200–275 ℃), compared with those ultrafine-grained dilute Al–Mg alloys with a uniform microstructure. The enhanced thermal stability is due primarily to the multimodal grain structure consisting of nano-, ultrafine- and micron-sized grains, strong segregation and/or clusters of Mg solute along grain boundaries (GBs), and Al3Mg2 precipitates formed during annealing. First, extensive recovery predominates over recrystallization and consumes most of the stored energy in the ECAPed Al–7Mg alloy annealed at ≤ 275 ℃, leading to the recrystallization and growth of nano/ultrafine grains being retarded or postponed. Moreover, Mg solute segregation and/or clusters along GBs of nano/ultrafine grains could further suppress grain growth via diminishing GB energy and dragging GBs efficiently. In addition, Al3Mg2 precipitates formed with increasing annealing time could inhibit grain growth by pinning GBs. The present multimodal-grained Al–7Mg alloy with enhanced thermal stability is believed to be particularly attractive in potential engineering applications at moderate to high temperatures.

A hardening model considering grain size effect for ion-irradiated polycrystals under nanoindentation

In this work, a new hardening model is proposed for the depth-dependent hardness of ion-irradiated polycrystals with obvious grain size effect. Dominant hardening mechanisms are addressed in the model, including the contribution of dislocations, irradiation-induced defects and grain boundaries. Two versions of the hardening model are compared, including the linear and square superposition models. A succinct parameter calibration method is modified to parametrize the models based on experimentally obtained hardness vs. indentation depth curves. It is noticed that both models can well characterize the experimental data of unirradiated polycrystals; whereas, the square superposition model performs better for ion-irradiated materials, therefore, the square superposition model is recommended. In addition, the new model separates the grain size effect from the dislocation hardening contribution, which makes the physical meaning of fitted parameters more rational when compared with existing hardness analysis models.

Effect of Laser Strengthening on Electrochemical Corrosion of AA6082 Aluminum Alloy

In this study, the surface of 6082 aluminum alloy was machined by laser heat treatment, and the microstructure and properties of the affected zone of laser surface were discussed by scanning electron microscope (SEM). The experimental results show that the laser treatment has an obvious second phase fine grain strengthening effect on the surface of aluminum alloy. The local hardness of the surface laser action zone has been improved obviously. Combined with the polarization curve data and microscopic corrosion morphology, with the addition of laser, the corrosion resistance mechanism of aluminum alloy has been well optimized, and the number and continuity of pitting pits on the surface of aluminum alloy have been restrained. The intergranular corrosion and the maximum corrosion depth behavior decreased under the corrosion of Cl−. The comprehensive properties of aluminum alloy surface have been effectively optimized under the action of laser heat treatment.the effect of laser heat treatment on the corrosion resistance and the surface mechanical properties of AA6082 aluminum alloy was investigated.

Improved efficiency and carrier dynamic transportation behavior in perovskite solar cells with CuInS2 quantum dots as hole-transport materials.

Inorganic quantum dot (QD)-based hole-transport materials (HTMs) have proved their potential in perovskite solar cells (PSCs). In this work, CuInS2 quantum dots (CIS QDs) were applied as HTMs for PSCs with the architecture of TiO2/Cs0.17FA0.83Pb(Br0.2I0.8)3/HTM/Au. By optimizing the preparation process, a high-quality perovskite thin film could be obtained. When the speed was 5000 rpm, the speed acceleration was 3000 rpm per s and heat treated at 150 °C, the perovskite film had low surface roughness (15.26 nm) and obvious grain boundary. The photoelectric conversion efficiency (PCE) of PSCs was greatly improved from 2.83% to 12.33% utilizing CIS QDs at an optimal concentration and with surface ligands as HTMs. Surface ligands can control the size and shape of CIS QDs, and thus affect the performance of PSCs. The carrier dynamic transportation behaviour at the CIS/perovskite interface was studied, which showed that CIS QDs as HTMs in PSCs can strongly quench the fluorescence and increase the photobleaching recovery rate. Therefore, CIS QDs are promising inorganic HTMs for the fabrication of PSCs.

Effect of welding heat input on microstructure and properties of TC4 titanium alloy ultra-narrow gap welded joint by laser welding with filler wire

A 10 mm narrow gap TC4 titanium alloy welded joint by laser welding with filler wire was obtained by different welding heat inputs. The microstructures of the welded joint were analyzed by OM, SEM, XRD and EBSD. The mechanical properties of the welded joint were analyzed by microhardness test and tensile test. The results show that with the increase of laser welding heat input, the average grain size and width of the equiaxed crystal zone in the center of the weld increases, the grain angle in the columnar crystal zone gradually tends to be perpendicular to the center of the weld, and the width of the heat affected zone (HAZ) increases without obvious grain coarsening. The HAZ of the welded joint is softened, and its microhardness value is lower than that of the weld and the base metal. The tensile strength of the welded joint is slightly higher than those of the base metal, but the elongation after fracture is less than that of the base metal, and it decreases with the increase of laser welding heat input.

Experimental investigations on deformation characteristics in microstructure level during incremental forming of AA5052 sheet

Abstract Revealing the deformation mechanism of incremental sheet forming (ISF) in microstructure level is crucial in verifying the enhanced formability, which is helpful for fabricating the panels with low-ductility materials or with complex geometry. In the present work, grain fragmentation, grain orientation, void evolution and dislocation accumulation during ISF were observed by EBSD, SEM, TEM and X-Ray microscope. Results show that the grains are elongated along the meridianal direction with obvious grain fragmentation, and the special grain gradient along thickness direction was observed. The distinct grain orientation along {111} are gradually accumulated with the increasing of plastic deformation. Meanwhile, the voids are coalesced and elongated basically along meridianal direction into strip-shaped voids. The observation of TEM micrographs shows that coarse grains are transformed into fine sub-grains/grains with obvious misorientation. Multiple sets of dislocation pile-up stacked at the sub-grain boundaries is believed to increase stress concentration and tendency of micro-crack.