Random Crystallographic Orientation Research Articles

New Approach to Produce a Nanocrystalline Layer on Surface of a Large Size Pure Titanium Plate

It was demonstrated that the mechanical shot peening (MSP) technique was a viable way to obtain a nanocrystalline layer on a large size pure titanium plate due to the MSP provided for severe plastic deformation (SPD) of surface high velocity balls impacting. The MSP effects of various durations in producing the surface nanocrystalline layer was characterized by optical microscope (OM), X-ray diffraction (XRD), transmission electron microscope (TEM), and Vickers micro-hardness tester. The results showed that the thickness of the SPD layer gradually increased with the MSP processing time increase, but saturated at 230 μm after 30 min. The average grain size was refined to about 18.48 nm in the nanocrystalline layer. There was equiaxed grain morphology with random crystallographic orientation in the topmost surface. By comparing with the nanocrystalline layer, acquired by surface mechanical attrition treatment (SMAT), the microstructure and properties of the nanocrystalline layer acquired by MSP was evidently superior to that of the SMAT, but the production time was cut to about a quarter of the time used for the SMAT method.

A comparative study on microstructure and mechanical properties of HG785D steel joint produced by hybrid laser-MAG welding and laser welding

Hybrid Laser-arc welding (HLAW) and laser beam welding (LBW) of HG785D steel were investigated by comparing microstructure, mechanical properties and heat source melting efficiency. Same microstructure of lath martensite (LM) was observed in fusion zone (FZ) of the two welded joints. However, coarser grain size and more random crystallographic orientations of FZ in HLAW joint were investigated via electron back-scatter diffraction (EBSD) analysis. M-A constituent and equiaxed ferrite (EF) were observed in finer-grain HAZ of HLAW joint, whereas fine martensite was obtained in LBW joint. More M-A constituent and granular bainite (GB) appeared in coarse-grain HAZ of HLAW joint. Higher heat input and lower cooling rate of HLAW compared to LBW resulted in presence of different microstructure. All the tensile specimen in both cases fractured at the base metal, while distinct difference in microhardness and low-temperature impact property was observed. Lower microhardness and higher impact energy of fusion zone were obtained in HLAW joint. Moreover, heat source melting efficiency of HLAW for 6-mm-thick HG785D steel plate could be improved by 26% compared to LBW.

Effect of process parameters on the microstructure, tensile strength and productivity of 316L parts produced by laser powder bed fusion

The influence of process parameters during laser-powder bed fusion on the microstructure, tensile strength and build time of 316L parts is studied. By increasing both, scan speed and hatch distance, an improved productivity while maintaining acceptable properties were achieved. The samples were evaluated using volumetric energy density. The microstructure characterization showed that all produced samples had elongated grains aligned with the building direction independent on energy density that was used, whereas the grain size was strongly affected by the different energy densities. A high energy density resulted in larger grains with a very strong 〈101〉 crystallographic orientation while the lower energy generated small grains with a random crystallographic orientation. This indicates how both, crystallographic orientation and grain size, can be tailored by altering the energy density. Even if a large variance in microstructure was observed, the tensile test results only showed about 5% difference in yield strength between standard process parameters and the samples produced with the lowest energy density but with a 20% faster build time. Due to the decreased energy density, the amount of defects was increased which had a negative effect on the elongation. The samples produced with the lowest energy density had 32% elongation compared to 45% for the samples produced with standard process parameters. This study clearly indicates that the build time can be improved while maintaining good mechanical properties by adjusting the process parameters.

Influence of nettle extract on zinc electrodeposition in an acidic bath: Electrochemical effect and coating morphology

The electrodeposition of zinc from an acidic sulphate bath was studied in the presence of nettle (Urtica dioica L.) extract at room temperature and with relative low zinc concentration. Different electrochemical measurements show that the nettle extract allows a reduction of hydrogen adsorption on steel and zinc and therefore a decrease in hydrogen evolution, due to the specific adsorption of molecules of the extract. Scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) measurements reveal that the addition of nettle extract induces a very fine grain size with a random crystallographic orientation. Finally, the nettle extract constitutes an interesting and low cost additive for all processes based on zinc electrochemical reduction in acidic sulphate electrolytes.

Microstructure evolution and strengthening mechanisms in friction-stir welded Al–Mg–Sc alloy

The present work was undertaken to evaluate the effect of second-phase particles on microstructure evolution during friction-stir welding (FSW). To this end, Al-6.0Mg-0.35Mn-0.2Sc-0.1Zr alloy containing insoluble nano-scale Al3(Sc,Zr) dispersoids was used as a program material. A particular emphasis was given to an establishment of a microstructure-strength relationship in the welded material.It was found that pinning effect of the Al3(Sc,Zr) precipitates efficiently suppressed grain-boundary migration and promoted a concentration of slip activity in heavily-stressed near-grain-boundary regions. This gave rise to a preferential development of deformation-induced boundaries in the latter areas. Due to a complex character of slip at the grain boundaries, the newly evolved grains had nearly random crystallographic orientations. As a result, the final microstructure evolved in stir zone was characterized by relatively-fine grain size, poorly-developed texture and large fraction of high-angle boundaries.The retention of the coherent dispersoids as well as considerable grain refinement occurring during FSW resulted in substantial material hardening in the stir zone.

An experimental calibration of a sulfur-in-apatite oxybarometer for mafic systems

The incorporation of sulfur (S) into the apatite structure and the partitioning of S between apatite and silicate melt (DSap/m) have been proposed to vary systematically as a function of prevailing redox conditions. In this study, we experimentally equilibrated apatite with mafic silicate melt at 1000 °C, 300 MPa and a range of oxygen fugacity (fO2; log fO2 [ΔFMQ] = −1, 0, +0.3, +1.2, and +3 where FMQ is the fayalite-magnetite-quartz mineral redox buffer) to explore the partitioning behavior of S, including different oxidation states of S, between apatite and silicate melt. The data reveal that DSap/m values increase systematically with increasing fO2, from 0.02± 0.01 at log fO2 [ΔFMQ] of −1 to 3.20 ± 0.19 at log fO2 [ΔFMQ] of +3. The bulk S content (∼0.37 and ∼0.28 wt.% S added) imparts a minor influence on DSap/m at reducing conditions.Micro X-ray absorption near edge structure (μ-XANES) spectroscopy at the S K-edge was used to measure, in situ, the oxidation states of S in experimentally crystallized apatite. The S-XANES analyses reveal that with increasing fO2, apatite progressively incorporates S6+ ≫ S2− > S4+ > S1+. The integrated S6+/ΣS peak area ratios and centroid energies (eV) were determined for apatite crystals in apatite from experiments at all fO2 conditions. The orientation effects occurring during S-XANES analyses of apatite were considered by merging spectra from multiple grains with random crystallographic orientation. The S-XANES data reveal that S6+/ΣS peak area ratios and the centroid energies increase systematically with fO2, demonstrating that the S6+/ΣS ratio in apatite can be used as an oxybarometer.The results demonstrate that both the S6+/ΣS and CeV calibration methods are highly sensitive in the redox range of ∼FMQ to ∼FMQ + 1.2 at the conditions and compositions evaluated in this study. As a result, the S-in-apatite oxybarometer is particularly applicable to mafic systems such as mid ocean ridge basalts (MORB), relatively reduced ocean island basalts (OIB), and back-arc basin basalt (BABB). Owing to the ubiquity of apatite in magmatic and magmatic-hydrothermal systems, measuring the concentration and oxidations state(s) of S-in-apatite has the potential to serve as a powerful sulfo- and oxy-barometer for a broad range of natural systems.

Low-temperature superplastic deformation mechanism in Ti–6Al–4V alloy processed by friction stir processing

The rolled Ti–6Al–4V alloy plates with ~2.3 mm in thickness were processed by Friction stir processing (FSP), and ultrafine (~0.57 μm) and equiaxed microstructure was successfully obtained in the stir zone (SZ). Superplastic tensile tests of this microstructure were conducted in the strain rate range of 1 × 10−4-3 × 10−3 s−1 with the tensile testing temperature of 550–600 °C and an extremely excellent low-temperature superplasticity (LTSP) with an elongation of 1400% was obtained at 3 × 10−4 s−1 and 600 °C. Such a large elongation was owing to the presence of a large proportion of high angle grain boundaries (90.7%) and random crystallographic orientation in the SZ of the friction stir processed (FSPed) Ti–6Al–4V alloy. Furthermore, the precipitated β phase during tensile deformation also made a contribution to the enhancement of LTSP. In addition, a slight grain growth from initial 0.57 μm in the FSPed microstructure to 1.07 μm in the gauge section of the tensile fractured sample at 3 × 10−4 s−1 and 600 °C proved the excellent microstructure stability of the FSPed Ti–6Al–4V alloy. The grain boundary sliding (GBS) was recognized as the dominant superplastic deformation mechanism. The grain rotation (GR) and dynamic recrystallization (DRX), especially the discontinuous dynamic recrystallization (DDRX), acted as the coordination mechanisms that could relax the stress concentration generated during GBS, and thereby promoted the continuous operation of GBS and the achievement of the enhanced LTSP.

High-strain-rate superplasticity and tensile behavior of fine-grained Mg97Zn1Y2 alloys fabricated by chip/ribbon-consolidation

A new combined processing procedure is applied to a Mg97Zn1Y2 alloy with a long-period stacking ordered (LPSO) phase. The procedure involves three processes: cooling-rate-controlled solidification, chipping of the solidified master alloy, and extrusion for chip/ribbon-consolidation. Three types of chip/ribbon-consolidated alloys are fabricated from gravity-cast ingots, twin-roll-cast sheets, and melt-spun ribbons using this procedure and are denoted as GCC, TCC, and RRC, respectively. The cooling rate in the cooling-rate-controlled solidification process strongly affects the grain size of the α-Mg matrix and the morphology of the LPSO phase; increasing the cooling rate promotes reduction of the dendrite arm spacing in addition to grain refinement. Extrusion during chip/ribbon-consolidation promotes dynamic recrystallization of α-Mg grains, resulting in the formation of fine equiaxed grains with random crystallographic orientation. The GCC alloy and the TCC alloy consist of fine dynamically recrystallized α-Mg grains and a small amount of worked LPSO grains. The RRC alloy has fine dynamically recrystallized α-Mg grains with thin basal plate-shaped LPSO phase precipitates in their interior. The GCC alloy and the TCC alloy show large elongation with reasonable strength and slight work-hardening after yielding. By contrast, the RRC alloy shows a high strength of more than 450 MPa, but the flow stress decreases with increasing strain during tensile testing. The TCC alloy and the RRC alloy exhibit high-strain-rate superplasticity at a strain rate of 3 × 10-2 s-1 and extremely large elongation values of ~600% and ~1000%, respectively.

Rutile inclusions in garnet from a dissolution‐reprecipitation mechanism

AbstractMetamorphic garnet commonly contains needle‐like rutile inclusions as well as equant rutile inclusions that surround quartz inclusions and range in size from submicrometer to nanometer. Although the origin of these equant rutile inclusions, that is, exsolution or non‐exsolution, has important implications for petrological and tectonic processes, the crystallographic characteristics of these inclusions have rarely been studied because of the small sizes and analytical difficulties involved. Here, we report the crystallographic characteristics pertinent to the genetic origin of minute equant rutile inclusions in cloudy, nearly spherically shaped garnet domains with Ti‐depleted compositions surrounding quartz inclusions in ultrahigh‐pressure garnet from several diamondiferous Erzgebirge quartzofeldspathic gneissic rock samples. TEM analyses show that the equant rutile crystals in cloudy garnet domains are partially bounded by the low‐energy {100}rt ± {110}rt ± {101}rt facets and have rather random crystallographic orientation relationships (CORs) with the garnet host, with preferential alignment of low‐energy lattice planes, for example, {100}rt//{112}grt, for some rutile crystals. Although the rather random CORs are unlikely to be attributed to solid‐state exsolution subjected to the stringent topotactic garnet lattice constraints, the characteristic subhedral {100}rt ± {110}rt ± {101}rt crystal forms of rutile can be rationalized by a metasomatic dissolution‐reprecipitation mechanism via a fluid phase. In this scenario, the quartz+fluid inclusions in garnet were first subjected to decompression microcracking during rock exhumation, followed by dissolution of Ti‐bearing garnet matrix at the crack tips or along the crack surfaces and subsequent reprecipitation of rutile, apatite, gahnite, akdalaite, and Ti‐depleted garnet. The rapid coalescence between rutile and garnet crystals in fluid or direct attachment of rutile crystals onto the dissolving crack surfaces would then yield the rather random CORs as reported here. These results, along with previous work on rutile needles, indicate rather diverse genesis of rutile inclusions in various crystal forms, thus shedding light on the controversial exsolution origin for other inclusion suite/microstructure in minerals.

The gradient structure in the surface layer of an Al-Zn-Mg-Cu alloy subjected to sliding friction treatment

Abstract A surface gradient structure can be obtained by sliding friction treatment (SFT). This work studied the effects of SFT parameters on the microstructure evolution in the surface layer of a 7475-T7351 Al alloy. The results show that both applied load and cycle number are conducive to the surface deformation, but the former is more pronounced. Based on transmission electron microscopy (TEM) analyses, grain refinement process induced by SFT treated at a load of 300 N for 200 cycles was discussed. The grain refinement process involves the development of dense dislocation cell walls (DDWs), the formation of microbands with a high dislocation density, the formation of dislocation lines (DLs), dislocation tangles (DTs) and DDWs inside the microbands, the development of equiaxed dislocation cells in the microbands, the transformation of DDWs into ultrafine grains along the direction of the microbands and the development of ultrafine grains with random crystallographic orientations. In addition, from the substrate to the topmost surface, the matrix precipitates dissolved gradually and the grain boundary precipitates grew larger, which was mainly attributed to the severe shear plastic deformation and the formation of a large number of grain boundaries.

Structural, magnetic, optical, and magneto-optical properties of CoFe2O4 thin films fabricated by a chemical approach

Homogeneous, smooth, and partially transparent nanocrystalline thin films of CoFe2O4 were fabricated using a chemical solution approach with additional annealing for 2 h in a temperature range of 300 °C to 600 °C. Structural properties investigated by X-ray diffraction showed a single-phase spinel structure with a random crystallographic orientation for samples annealed above 400 °C. The ferromagnetic nature of prepared films was established from combined substrate with film hysteresis loops measured using a vibrating sample magnetometer. Optical and magneto-optical spectroscopic measurements revealed an improvement in the structural quality of the films after annealing up to 600 °C.

Surface grain nanocrystallization of Fe-Cr-Ni alloy steel by plasma thermochemical treatment

The Fe-Cr-Ni alloy (17-4PH steel) with metastable state was plasma thermochemical treated with and without rare earths (RE) addition. The experimental results show that after plasma thermochemical treatments, the initial coarse-grained structure with 20–40 μm grain size of 17-4PH steel could change into composition gradient nanoscale grains (as small as 5 nm) with random crystallographic orientations in plasma nitrocarburized layer. The hardness, modulus and wear resistance properties of nitrocarburized layer with nanoscale grains could be improved apparently. The present surface nanocrystallizaion method demonstrates the technological significance of metal alloy in improving traditional processing techniques and provides a new approach for surface nanocrystallizing of metal alloys.

Structural characterization of poly-Si Films crystallized by Ni Metal Induced Lateral Crystallization

The growth of the poly-Si films was studied by Transmission Electron Microscopy (TEM) after Ni Metal Induced Lateral Crystallization (Ni-MILC) of amorphous Si films at 413 °C. Significant differences in the morphology and the mode of growth of the films were observed, in comparison to films grown at temperatures above 500 °C. It was shown that at 413 °C the Solid Phase Crystallization (SPC), which acts in parallel with the Ni-MILC process at temperatures above 500 °C is suppressed. The suppression of SPC results in substantial change in the mode of growth. The poly-Si film grown at 413 °C consists of whiskers, which can be classified into two categories. Those growing fast along the <111> direction, which were already observed in conventional Ni-MILC above 500 °C and whiskers grown along random crystallographic orientations having significantly slower growth rates. Because of the large difference in growth rates of the whiskers, significant orientation filtering due to growth-velocity competition is observed. The uniform poly-Si films consist of a mixture of fast <111> type whiskers and slow ones, grown in other orientations, resulting in a tweed-like structure.

Effect of heat treatment on microstructure and mechanical properties of 316L steel synthesized by selective laser melting

The influence of annealing at different temperatures (573, 873, 1273, 1373 and 1673 K) on the stability of phases, composition and microstructure of 316L stainless steel fabricated by SLM has been investigated and the changes induced by the heat treatment have been used to understand the corresponding variations of the mechanical properties of the specimens under tensile loading. Annealing has no effect on phase formation: a single-phase austenite is observed in all specimens investigated here. In addition, annealing does not change the random crystallographic orientation observed in the as-synthesized material. The complex cellular microstructure with fine subgrain structures characteristic of the as-SLM specimens is stable up to 873 K. The cell size increases with increasing annealing temperature until the cellular microstructure can no longer be observed at high temperatures (T ≥ 1273 K). The strength of the specimens decreases with increasing annealing temperature as a result of the microstructural coarsening. The excellent combination of strength and ductility exhibited by the as-synthesized material can be ascribed to the complex cellular microstructure and subgrains along with the misorientation between grains, cells, cell walls and subgrains.

Effect of TiB2 particles on microstructure and crystallographic texture of Al-12Si fabricated by selective laser melting

Pronounced crystallographic texture, characteristic for the parts manufactured by selective laser melting, is eliminated upon addition of TiB2 microparticles to Al-12Si powder. Due to the wetting of TiB2 ceramic by Al-12Si melt and a high inoculation efficiency, a homogeneous microstructure consisting of fine equiaxed grains with random crystallographic orientation is formed by SLM processing of the Al-12Si/TiB2 powder mixture. The Al-12Si/TiB2 samples exhibit enhanced yield strength and microhardness, compared to the TiB2-free Al-12Si samples produced at the same SLM conditions.

Modeling of finite deformation of pseudoelastic NiTi shape memory alloy considering various inelasticity mechanisms

A crystal plasticity finite element (CPFE) model is developed for pseudoelastic NiTi shape memory alloy (SMA). The model includes various inelastic mechanisms of deformation such as martensite transformation, dislocation glide in austenite phase and twinning in the martensite phase. This model is based on the finite deformation theory and predicts phase transformation, stress field and residual strain due to slip and twinning. Following the work of Anand and Gurtin (2003), the Helmholtz free energy is derived and further the thermodynamic driving forces for slip, twin and phase transformation are obtained by using Clausius-Duhem inequality. The developed constitutive model has been implemented within a user material subroutine interface VUMAT in ABAQUS™/Explicit. The activation of different inelasticity mechanisms at different temperatures and strains are first verified by performing various simulations of uniaxial tensile deformation. Then the model is calibrated and validated against the experimental stress-strain response of NiTi single crystal as reported in the literature. The single crystal constitutive model is extended for modeling the response of a polycrystal with both initial random and textured crystallographic orientations using Taylor scale transition technique. A series of simulations are performed on polycrystalline representative volume element (RVE) at various temperatures and strains. The effect of temperature and imposed strain on phase transformation and residual strain is investigated systematically. The residual strain increases due to slip in austenite phase and twinning in the martensite phases that are activated as temperature and imposed strain increase respectively. Further the uniaxial loading conditions are extended to multiaxial loading and the results are compared against the experimental data.

Multiple precipitation pathways in an Al-7Si-0.6Mg alloy fabricated by selective laser melting

The ageing responses of selective laser melted Al-7Si-0.6Mg alloy with different solid solution treatment times are investigated in this work. Silicon particles with random crystallographic orientations are the dominant precipitates at the direct aged condition. With 1 or 8 h solid solution treatment, the precipitation sequence resembles that of cast/wrought Al-Si-Mg alloys. However, the main precipitates at the peak-aged condition are different and are premature B′ (1 h) and β″ (8 h), respectively. These unusual precipitation pathways are attributed to the uniaxial strains in the Al matrix, suggesting new heat treatment procedures required for selective laser melted alloys.

A spatial periodicity of microstructural evolution and anti-indentation properties of wire-arc additive manufacturing 2Cr13 thin-wall part

Based on cold metal transfer (CMT) welding, wire-arc additive manufacturing (WAAM) technology was adopted to manufacture 2Cr13 part. The spatial periodicity of the microstructural evolution and the anti-indentation properties was explored. The results show that the as-deposited part was featured by periodic martensite laths within the block-shaped ferrite matrix in the inner layers, followed by epitaxial ferrite grains containing ultra-fine acicular martensite in the top layer only. A slightly decreased Fe intensity was caused by local elemental segregation during the re-melting process; the homogeneity of Fe and Cr was attributed to similar cooling conditions in the top layer. The martensite size gradually coarsened from the fine grain zone to the coarse grain zone and the shape transformed correspondingly from irregularly short bar-like to orderly long rod-like due to the location-related thermal history. Elongated ferrite grains exhibited a slight fiber texture in the top layer and a random crystallographic orientation in the middle region. The anti-indentation properties evolved periodically due to the periodic microstructural characteristics. The obtained experimental results confirmed higher anti-indentation properties of the as-deposited part following comparison with the as-annealed base metal, while the elastic moduli of samples were not significantly different.

Embedding of hybrid MWCNT-Al2O3 particles in Ni matrix: Structural, tribological and corrosion studies

Composite nickel coatings, were produced under direct (DC) and pulse current (PC) from a Watt's type bath, containing 0.5 g/L hybrid MWCNT-Al2O3, in presence and absence of additive Sodium Dodecyl Sulfate - SDS. Surface morphology, crystallographic orientation, wear resistance and corrosion resistance were studied. Micro-Raman measurements revealed that MWCNT-Al2O3 particles are distributed at the whole depth of the cross-section profile analysis. The application of pulse current, favored a random crystallographic orientation of Ni crystallites with reduced grain sizes in comparison with pure Ni. The evaluation of the tribological data demonstrated that the composite coatings produced under pulse conditions in presence of additive, exhibited lower coefficient of friction, higher resistance to dry sliding accompanied by the presence of increased amounts of nickel oxide in wear tracks compared to pure Ni coatings. The behavior of pure and composite coatings in corrosive environment was evaluated by electrochemical impedance spectroscopy. It was found that composite coatings attained their corrosion resistance characteristics for 60 h in 0.6 M NaCl solution. Differences between pure nickel and composite coatings were attributed mainly to morphological differences rather than differences on corrosion performance.

Effect of Initial Microstructure on Grain Refinement and Enhanced Low Temperature Superplaticity in Friction Stir Processed Ti-6Al-4V Alloy

Ti-6Al-4V alloy sheet with two kinds of initial microstructure (base material (BM) and heat-treated material) was subjected to friction stir processing (FSP). These two kinds of friction stir processed (FSPed) materials show similar characteristics that the microstructure exhibited equiaxed ultrafine-grained (UFG) structure with high fraction of high angle grain boundaries (HAGBs) and random crystallographic orientations. Furthermore, slightly finer grains were observed in FSPed heat-treated material than that in FSPed BM. Superplastic tensile tests were conducted utilizing the FSPed heat-treated material in the strain rates range from 1×10-2 to 1×10-4 s-1 at 650°C, and the optimal superplasciticy with an elongation of 1220% was achieved at 1×10-3 s-1. The superplastic deformation mechanism appears to be grain boundary sliding.