Equiaxed Structure Research Articles

Assessment of the impact of hydrogen on the stress developed ahead of a fatigue crack

The microstructure generated in a low carbon steel under cyclic loading in air and a 40 MPa gaseous hydrogen environment has been compared as a function of distance from the crack tip. The presence of hydrogen resulted in the formation of a smaller and more equiaxed dislocation cell structure that extended further from the crack tip than the one generated in air. This enhancement and extension of the dislocation structure by hydrogen is consistent with it modifying the generation rate and mobility of dislocations as well as dislocation interactions. Qualitative assessment of the dislocation structure ahead of the crack tip found the stress ahead of the crack tip to vary linearly as ln(1/x), where x is the distance from the crack tip irrespective of the test environment. Hydrogen caused a shift to higher stresses, implying the critical damage level for crack propagation will be achieved more rapidly with a concomitant increase in the crack propagation rate.

The Effect of Specific Energy Density on Microstructure and Corrosion Resistance of CoCrMo Alloy Fabricated by Laser Metal Deposition.

With the development of modern medical implants, there are significantly increasing demands for personalized prosthesis. Corrosion-resistance and dense cobalt alloy specimens have been successfully fabricated by laser metal deposition. The relationship between specific energy density, microstructure and corrosion resistance of the specimens is investigated. The results show that higher specific energy density promotes the formation of columnar grain and leads to coarse grain size. The evolution and distribution of deposited microstructure from bottom to top are summarized in a metallographic sketch. The corrosion current of deposited specimens increases from 2.071 × 10−6 A/cm2 to 6.86 × 10−5 A/cm2 and rapidly drops to 9.88 × 10−7 A/cm2 with increase of specific energy density from 318.8 J/g to 2752.3 J/g. The columnar and equiaxed structure of deposited specimens have lower corrosion current than mixed structure due to finer grain and less Mo segregation. The deposited have low level metal released because of passive film. The passive film have different formation routes in Hank’s solution and acidic saliva. The specific energy density has an important effect on the microstructure of deposited, which improves corrosion resistance and life span in implant.

Effect of Direct Laser Deposition on Microstructure and Mechanical Properties of 316L Stainless Steel

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Method of Changing the Structure of Cast Fe–Al Alloys By Inputting Titanium-containing Modifiers

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Effect of Pulse Frequency on Microstructural and Corrosion Properties of Inconel 718 Gas Tungsten Arc Weldments

A study has been carried out to understand the effect of pulse frequencies on the formation of laves phase, the microstructural and corrosion properties of Inconel 718. Bead on welds was made by using gas tungsten arc welding (GTAW) in pulsed mode at different frequencies such as 2, 4, 6, 8 and 10 Hz. Varying frequencies exhibit significant changes in weld surface ripples. Microstructural analysis revealed that the welds at 2, 4 and 6 Hz showed both columnar and equiaxed dendrite structure, while at 8 and 10 Hz, the welds predominantly had equiaxed dendrites. Scanning electron microscopy results showed a reduction in continuous laves phase with the increase in pulsing frequency. Corrosion studies confirmed that the pitting resistance was increased at a higher frequency due to the reduction in laves phase in welds.

Investigation of stamping and heat treatment processes on the microstructure and blanking characteristics of Au80Sn20 eutectic alloy

Au80Sn20 eutectic alloy solder is extensively used in high-end microelectronics and optoelectronics packaging because of its good liquidity, high thermal conductivity, excellent resistance to fatigue, corrosion and creep. However, the brittleness and hardness of the δ-AuSn phase and ζ’-Au5Sn phase and massive primary phase make the processing and molding of Au80Sn20 eutectic alloy very difficult leading to inevitably limitations of its application. To improve the blanking ability of Au80Sn20 eutectic alloy, effects of stamping temperature, heat treatment on blanking of Au80Sn20 eutectic alloy were studied in this paper. Results showed that Au80Sn20 eutectic alloy had poor blanking performance at room temperature. However, the hot blanking process can reduce the hardness of the alloy which could improve the blanking performance significantly. With the extension of annealing time, the high temperature hardness of the alloy decreased first and then increased, reflecting that, suitable annealing process can reduce the residual stress in the alloy and reduce the adverse effects of the annealing process in the anisotropy of the initial lamellar eutectic structure. At the same time, ultrathin Au80Sn20 solder ring with smooth edge, can be made from an equiaxed eutectic structure in which the grains are uniformly fine if annealed for 120 min at 260 °C.

Evolution of microstructure, texture, and mechanical properties in a multi-directionally forged ZK60 Mg alloy

Abstract An extruded ZK60 magnesium alloy with the nominal composition of Mg–6Zn–0.5Zr was processed by multi directional forging (MDF) for 2, 4, 6 and 8 passes at 473 K. Microstructural studies showed that the uniform microstructure of the as-extruded material transforms to a duplex structure consisting of fine recrystallized grains surrounding some patches of unrecrystallized grains after 2 and 4 passes of MDF. Further MDF passes, however, resulted in a homogeneous equiaxed structure in such a way that the as-extruded grain size of 12.7 μm was refined to 1.9 μm after 8 passes. Evaluation of crystallographic texture revealed that deformation by MDF changed the conventional fiber texture of the extruded condition to a new texture, in which the basal planes tend to align almost 45° to the transverse direction. Mechanical properties of the extruded and MDFed samples were studied by shear punch testing (SPT) at room temperature. The results indicated that the 182.6 MPa shear yield stress (SYS) and 184.9 MPa ultimate shear strength (USS) of the extruded condition were, respectively, reduced to 170.0 and 172.3 MPa after 2 passes of MDF. This drop in strength is attributed to the presence of coarse patches of unrecrystallized grains. Further pressing of the alloy was accompanied by a decrease in the volume fraction of coarse grains and an increase in the number density of fine grains. Textural softening that occurred at higher strain levels of the final MDF passes, however, offset the strengthening effect of these fine grains.

Annealing-Driven Microstructural Evolution and Its Effects on the Surface and Nanomechanical Properties of Cu-Doped NiO Thin Films

The effects of annealing temperature on the structural, surface morphological and nanomechanical properties of Cu-doped (Cu-10 at %) NiO thin films grown on glass substrates by radio-frequency magnetron sputtering are investigated in this study. The X-ray diffraction (XRD) results indicated that the as-deposited Cu-doped NiO (CNO) thin films predominantly consisted of highly defective (200)-oriented grains, as revealed by the broadened diffraction peaks. Progressively increasing the annealing temperature from 300 to 500 °C appeared to drive the films into a more equiaxed polycrystalline structure with enhanced film crystallinity, as manifested by the increased intensities and narrower peak widths of (111), (200) and even (220) diffraction peaks. The changes in the film microstructure appeared to result in significant effects on the surface energy, in particular the wettability of the films as revealed by the X-ray photoelectron spectroscopy and the contact angle of the water droplets on the film surface. The nanoindentation tests further revealed that both the hardness and Young’s modulus of the CNO thin films increased with the annealing temperature, suggesting that the strain state and/or grain boundaries may have played a prominent role in determining the film’s nanomechanical characterizations.

Relationship of Mechanical and Micromechanical Properties with Microstructural Evolution of Sn-3.0Ag-0.5Cu (SAC305) Solder Wire Under Varied Tensile Strain Rates and Temperatures

A characterization of mechanical and micromechanical properties of SAC305 solder wire under varied strain rates and temperatures was performed using tensile and nanoindentation tests. The evolution of SAC305 lead-free solder wire grains was compared in samples that were subjected to various strain rates and temperatures using tensile tests based on ASTM E12 standards. Different behaviours of mechanical properties, micromechanical properties, and microstructure evolution of SAC305 solder wire were observed when either temperature or strain rate was held constant and the other varied. Both tensile and nanoindentation tests produced qualitative results, such as dynamic recovery and occurrence of pop-in events, that reflected changes of microstructure. It was observed that some of the mechanical properties of SAC305 solder wire, namely yield strength (YS), ultimate tensile strength (UTS) and Young’s modulus, showed the same trends, but with lower values, compared to micromechanical properties obtained from nanoindentation tests based upon hardness and reduced modulus. Microstructure examination further confirms that the YS, UTS and hardness values increase with more solder wire grain refinement. SAC305 solder wire also maintained an equiaxed structure under various strain rates and temperatures.

Investigation for high accurate MPF-LBM model for prediction of equiaxed structures

Investigation for high accurate MPF-LBM model for prediction of equiaxed structures

Effect of Heat Processing Technique on Microstructure and Mechanical Properties of Extrusion Beta Titanium Alloy Tube Blank

The effects of extrusion temperature and heat treatment on the microstructure and mechanical properties of beta-CEZ titanium alloy tube blank were studied with an emphasis on the relationship between the heat processing technique and microscopic structure. The results show that the extruded tube blank of beta-CEZ titanium alloy at alpha-beta phase has better tensile strength and plasticity match, and the ductility of the alpha-beta phase extrusion is obviously better than that of the single beta-phase extrusion, especially the reduction of area. When the extruded tube is heat treated at 830°C and 860°C solid solution, with the increase of aging temperature, the strength of tube decreases and the plasticity increases. When the aging temperature is up to 600°C, the reduction of area of the tube increases obviously. When the extruding tube is aged at 550°C and 600°C, the strength of the tube increases and the plasticity decreases with the increase of the solid solution temperature. The titanium alloy of beta-CEZ is extruded below the phase transition point after low temperature solid solution and high temperature aging treatment, which can achieve good microstructure and performance matching. The tensile strength is greater than 1250MPa, the elongation is more than 15%, and the reduction of area is more than 40%. The microstructure was a fine and uniform equiaxed structure.

Effect of porosity on the structure and properties of β-SiAlON ceramics

Abstract Porous SiAlON ceramics were produced by incorporating starch in the range of 0–5 wt% in a commercial grade SYALON 101 powder and pressureless sintered at 1700 °C for 4 h in nitrogen atmosphere. The crystal phase formation, microstructure, dielectric- and mechanical properties of SiAlON ceramic composites thus produced were investigated thoroughly. XRD analysis of the porous SiAlONs showed the presence of major phase β-Si5.85Al0.15O0.15N7.85 corresponding to β-Si6-ZAlZOZN8-Z (Z = 0.15) phase, in addition to yttrium aluminum silicon oxynitride and/or yttrium silicates. Transmission electron microscopy revealed the spherical and rod-like structure for yttrium aluminum silicon oxynitride and yttrium silicates at the proximity of pores, while the elongated and equiaxial structure for β-Si5.85Al0.15O0.15N7.85. In addition, the influence of structural transition and porosity on the dielectric constant and mechanical properties are discussed in detail. The consolidated porous SiAlON showed a promising combination of mechanical and dielectric properties, making them useful as candidate material for applications like electro magnetic wave transmitter, microwave based reactor, heat exchanger and many other structural applications, where conductivity, density and dielectric constant are critical.

Dewetted nanostructures of gold, silver, copper, and palladium with enhanced faceting

Abstract At the foundation of nanoscience and nanotechnology is the ability to shape-engineer nanometric objects so as to exert control over their physical and chemical properties. Architectural control is achieved by manipulating thermodynamic and kinetic factors that are able to guide reactions along pathways that lead to the formation or elimination of particular crystal facets. While the dewetting of ultrathin metal films provides a straightforward method for generating substrate-based metallic nanostructures, the ability to shape-engineer these structures is limited to such an extent that even the formation of highly faceted equiaxed structures often proves challenging. This, however, is not the case for colloidal syntheses where the exquisite chemical controls and synthetic ease offered by liquid-phase chemistry has led to the generation of a diverse library of nanostructure architectures. Here, it is demonstrated that the faceting of dewetted structures of gold, silver, copper, and palladium can be enhanced by subjecting them to a liquid-phase chemical environment in which metal ions are reduced to a neutral state and deposited on the nanostructure surface in manner that leads to facet formation. The faceting procedure, which can be carried out in minutes, is also shown to be amenable to a templated dewetting approach in which lithographically-defined metal discs formed in an array each agglomerate to form a single nanostructure. The work has the potential to increase the functionality of dewetted nanostructures by enabling facet-dependent chemical reactivity and plasmonic hot spots.

Effect of the forced flow on the permeability of dendritic networks: A study using phase-field-lattice Boltzmann method

Abstract A phase-field-lattice-Boltzmann method, coupled with parallel computing and adaptive mesh refinement (Para-AMR), was employed to study the effect of forced flow on permeability of the mushy zone during solidification. Accuracy of the method was testified by comparing with predictions of conventional models, as well as other numerical investigations in literature. Results showed that the permeability of the mushy zone changed as the forced flow was imposed. For columnar dendritic networks, the permeability decreased exponentially either parallel or normal to the dendritic growth direction due to impinging and interlocking of secondary arms. The permeability of equiaxed dendritic networks decreased significantly when the flow was present. The permeability changed as a result of morphological transformation of the dendritic network, which became more columnar-like under a higher incoming velocity. Based on the numerical results and theoretical analysis, a new model was proposed for predicting permeability under the forced flow. Results showed that the model was suitable for describing the permeability of both columnar and equiaxed dendritic structures under a moderate forced flow, and could be used as a viable alternative to determine the permeability in a wide range of solid fraction during solidification.

Special features of the weldability of a new wrought VMD16 magnesium alloy

ABSTRACTThe results of the investigation of the weldability of a new VMD16 magnesium alloy by automatic argon-shielded arc welding and friction stir welding are presented. The friction stir welding technology was investigated for the first time for the Russian magnesium wrought alloy. The data obtained in the studies of the phase composition and structure of the VMD16 alloy are presented. The experimental results show that the intermetallic phases (Mg, Zn)5REE (REE = rare-earth elements) and Zn2(Zr, REE)3 and the Laves phases ZrZn2, together with the fine-grained and equiaxed structure (the grain size 8–12 µm), result in a high level of the strength characteristics of the alloy and of welded joints in the alloy. It is also shown that the alloy is characterized by higher (two to six times) resistance to the formation of cracks in welding than the standard magnesium alloys MA2-1, MA2-1pch and MA20. The strength of the welded joints in the VMD16 alloy equals 0.85–0.88 of the strength of the parent material. Postweld heat treatment is not required.

Effect of cold rolling and heat-treatment on the microstructure and mechanical properties of β-titanium Ti-25Nb-25Zr alloy

Abstract The present work describes a detailed investigation on the effect of cold deformation and subsequent heat treatment on a recently developed commercial β-type Ti-25Nb-25Zr (wt%) alloy. The β-type Ti-25Nb-25Zr alloy exhibited excellent phase stability against severe plastic deformation as well as after subsequent heat-treatments at elevated temperatures as primarily β-phase was retained. However, at low annealing temperatures, i.e. 673 K, a small amounts of metastable HCP-α phase precipitated, which inhibited any recrystallization and grain growth. Subsequent annealing at 873 K and 1073 K resulted in the gradual dissolution of HCP-α phase and recrystallized randomly oriented fine-grained equiaxed structure wherein average grain size increased with increasing temperature. High annealing temperatures, i.e. at 1273 K, resulted in extremely coarse-grained structure with preferential crystallographic orientation due to abnormal rapid grain growth. The average hardness, yield strength, and ultimate tensile strength increased whereas elongation-to-fracture, i.e. ductility, decreased after cold rolling due to strain hardening owing to large amounts of accumulated lattice defects. The retained deformed structure with α phase particles exhibited highest strength but lowest ductility. Increasing annealing temperatures from 873 K to 1273 K exhibited continuously decreasing strength values and increasing ductility due to the recrystallized structure and increasing grain size. The increasing grain size together with decreasing amounts of HCP-α phase also demonstrated a higher uniform plastic deformation and shifting of plastic instability point, i.e. UTS, towards higher strain values in the present beta Ti-25Nb-25Zr alloys.

Effect of a Traveling Magnetic Field on Micropore Formation in Al-Cu Alloys

The effect of traveling magnetic fields (TMFs) on the grain and micro-pore formation in an Al alloy was studied by scanning electron microscope and X-ray microtomography in this work. The results show that with the increasing magnetic flux density, the three-dimensional morphology of the micro-pores transformed from dendrite to a relatively equiaxed structure. Quantified results show that both the micro-pore volume fraction and the average grain size of the primary phase decreased as the TMF density increased. The analyses show that the forced convection induced by TMF can break the dendrites, refine the grain size, and promote the liquid feeding, leading to the decrease in the volume fraction of the porosity and improved mechanical property. The TMF performed at different stages during solidification reveal that the maximum effect of TMF on reducing the micro-pore formation was found when TMF was applied in the stage of nucleation and the early stage of grain growth during solidification.

Characterization of microstructure and mechanical properties of nickel based superalloy 617 by pulsed current gas tungsten arc welding technique

Nickel based superalloy (alloy 617) exhibits high strength and oxidation resistance at elevated temperatures. The major limitation of this alloy is microsegregation of alloying elements due to the formation of Molybdenum (Mo) rich secondary phases in the interdendritic region of the weldments. The present study investigates the possibilities to mitigate the microsegregation effect. In order to achieve this, weld joints were fabricated with pulsed current gas tungsten arc welding (PCGTAW) techniques with three different filler wires. The filler wires employed with present study are ERNiCrMo-4, ERNiCrMo-10 and ERNiCrMo-14. The macro examination was carried out to reveal the defects in the weld joints. Optical and Scanning electron microscope (SEM) analysis were performed to evaluate the micro structural changes in the fusion zone and Heat Affected Zone (HAZ). Microstructure shows the fine equiaxed dendrite structure in the fusion zone. Energy Dispersive x-ray Spectroscopy (EDS) analysis was also carried out in the weldments to quantify the level of microsegregation of alloying elements. Tensile test reveals the strength and ductility of the weld joints. Root and face bend test was carried out to check the ability of the weld joints to withstand bending forces. The result shows the defect free weld was achieved in all the welded joints. EDS analysis revealed the presence of Mo rich phases in the ERNiCrMo-4 filler wire. There is no evidence for the formation of secondary phases in the filler wires. The tensile strength of ERNiCrMo-14 filler shows the marginally higher strength compare to other filler wires. Root and Face bend test did not show the presence of cracks and other defects in the weldments.

Research on the forming quality and mechanical properties of cylindrical spun parts with ultrafine-grained structure during power spinning

The further power spinning (FS) on the cylindrical parts with ultrafine-grained (UFG) structure was carried out to further improve the mechanical properties of the cylindrical parts. The forming quality and microstructural evolution of the spun parts made of ASTM1020 steel during FS were investigated. The results show that the forming quality of the spun part is improved, the equiaxial structure of the grains is remained, and the grain size is increased slightly after FS. The mechanical properties of the cylindrical parts with UFG structure and the influence of the thinning ratio of wall thickness on the mechanical properties were also investigated, and the results show that the cylindrical parts with excellent comprehensive mechanical properties can be obtained by QSA method. The tensile strength and hardness of the parts with UFG structure are increased and the elongation is decreased with the increasing of the thinning ratio of wall thickness. The cylindrical parts made of ASTM1020 steel with high strength and hardness can be obtained by the method combining QSA with FS.

Alloying Behaviour and Microstructural Changes of a Ti-10%Mo-10%Cr Alloy on Sintering Process

This study aimed to investigate the effects of element diffusion on the alloying behaviour and microstructure of a Ti-10%Mo- 10%Cr alloy during sintering and furnace cooling. A theoretical calculation of the average diffusion distance for each element was performed to predict the alloying behaviour during sintering and furnace cooling. The Ti-10%Mo-10%Cr alloy was fabricated using a blended element powder metallurgy approach. Micrograph of the samples after sintering showed bright-circle structures and significantly decreased equiaxed structures. The number of plate-like structures increased with prolonged sintering time. Microstructural changes occurred because of element diffusion resulting from the prolonged sintering time. Moreover, the diffusion distance of each element also increased with prolonged sintering time. Although elements can sufficiently diffuse during both sintering and furnace cooling, the diffusion distance during sintering was considerably higher than that during furnace cooling for all elements. The diffusion distances of Cr and Mo were the highest and lowest, respectively, during sintering and furnace cooling. This study showed that alloying behaviour mostly occurred during sintering and was controlled by the diffusion of Mo atoms.