Analysis Of Microstructure Evolution Research Articles

Grain disintegration and dynamic recrystallization during impact tests of additively manufactured nickel-based alloy 718

The high-temperature dynamic mechanical response of Alloy 718 produced via laser-powder bed fusion (LPBF) was investigated through compressive Split-Hopkinson Pressure Bar (SHPB) tests. Simulating the typical service conditions of Alloy 718, the tests were conducted at temperatures ranging from 298 K to 773 K and at strain rates of 1000 s−1 to 1500 s−1. Phenomenological material constitutive models, such as the modified versions of Johnson-Cook and Hensel-Spittel models, were developed based on the SHPB test results. Analysis of microstructural evolution under impact conditions highlighted that columnar grains with high Schmid factors tend to undergo preferential activation and dislocation pile-up. This process leads to the formation of adiabatic shear bands, grain disintegration, and intense lattice rotation, particularly at higher strain rates. Furthermore, increasing the dynamic deformation temperature facilitates the activation of discontinuous dynamic recrystallization (DRX), with strain accumulation promoting localized grain nucleation along heavily dislocated dendritic boundaries. Recognizing the limitations of phenomenological material constitutive models in accurately representing the underlying microstructural evolution, an artificial neural network (ANN)-based constitutive model employing a three-layer backpropagation learning algorithm was implemented, reducing the Average Absolute Relative Error (AARE) to 0.17%.

Evolution of microstructure and properties of nanocrystalline NiCo alloy under high-energy laser shock

In this study, nanocrystalline NiCo alloy was prepared through electrodeposition and subjected to high-energy laser shock (HELS) treatment to investigate the influence of laser shock on the microstructures and properties. An analysis of phase composition, microstructural evolution, texture evolution, and hardness was conducted. The results indicated that under HELS, there was no change in phase composition, while there was a slight reduction in grain size, as well as in the quantities of Low-angle grain boundaries (LAGBs) and twin boundaries (TBs). The texture evolution revealed that HELS led to a more uniform overall texture due to grain boundary (GB) mediate deformation mechanisms, along with the generation of a significant amount of 9R phases, causing a shift in texture orientation from (110) to (100). The internal structure of nanocrystalline NiCo showed an accumulation of numerous dislocations post-laser shock, with randomly oriented dislocations interacting to form Lomer-Cottrell Locks (L-C Locks) and 9R phases. Additionally, interactions with large stacking faults (SFs) also resulted in their dissociation into multiple 9R phases. The hardness enhancement was mainly attributed to the accumulation of dislocations within the grain and the generation of a significant quantity of 9R phases.

Atomic-scale insights into the effect of layer thickness ratio on the tensile properties of heterostructured nano-aluminum

Gradient-structured alloys with lamellar microstructures show extraordinary potential in breaking the strength-ductility trade-off dilemma. When partial grain size exceeds the Hall-Petch limit, the deformation mechanism is not fully understood. In this study, the competing relationship between grain boundary (GB) softening and hetero-deformation-induced (HDI) strengthening in laminated nano-grained aluminum was investigated under uniaxial tensile loading. In the soft domains, the high activity of grain boundaries results in pronounced GB softening. However, when the volume fraction of the soft layer exceeds 50 %, the flow stress surpasses the predicted values of the rule of mixtures (ROM), demonstrating a significant HDI strengthening. A detailed analysis of microstructural evolution is conducted, including strain gradients, GB migration, and dislocation distribution. The effects of mechanical incompatibility between soft and hard layers on the distribution of plastic strain and overall material strength are elucidated in gradient structures. The study provides critical theoretical insights into the design and development of high-performance gradient nanocrystalline aluminum alloys, particularly in applications where a balance between strength and ductility is of paramount importance.

A Study on Microstructure Evolution and Mechanical Properties of Inconel 690 Subjected to Milling Process

The metallic materials subjected to machining‐induced severe plastic deformation can experience alterations of microstructures and mechanical properties, affecting the functional performances of the components. This study concentrates on the microstructure evolution and mechanical properties analysis of Ni‐based superalloy Inconel 690 under severe plastic deformation induced by milling process. The obtained results show that the microstructures of the machined surface and subsurface exhibit the characteristic of gradient distribution. Plastic behaviors involving dislocation multiplication, grain deformation and refinement, increment of local misorientation and average intragranular misorientation, and transition from high‐angle grain boundaries to low‐angle grain boundaries occur in the superficial layer of the machined workpiece. Both the intensity and the affected depth of plastic deformation for the superficial layer are strengthened following the cutting speed and feed increase, which is attributed to higher cutting forces. No white layer and phase transformation is found under all cutting conditions. In addition, the nanohardness of the superficial layer shows the reduction tendency of hardening effect from the surface to the bulk of the machined workpiece material. With the increase in cutting speed and feed, the affected zones of residual stresses and work hardening below the machined surface become wider.

Effect of scanning strategy and laser peening on microstructure and fatigue properties of laser-directed energy deposition-built 15-5 PH stainless steel

PurposeThe aim of this paper is to study the effect of laser shock peening (LSP) on mechanical behaviour of the laser-directed energy deposition (LDED)-based printed 15-5 PH stainless steel with U and V notches. The study specifically concentrates on the evaluation of effect of scan strategy, machining and LSP processing on microstructural, texture evolution and fatigue behaviour of LDED-printed 15-5 PH steel.Design/methodology/approachFor LSP treatment, 15-5 PH steel was printed using LDED process with bidirectional scanning strategy (XX [θ = 0°) and XY [θ = 90°]) at optimised laser power of 600 W with a scanning speed of 300 mm/min and a powder feed rate of 3 g/min. Furthermore, LSP treatment was conducted on the V- and U-notched fatigue specimens extracted from LDED-built samples at laser energy of 3.5 J with a pulse width of 10 ns using laser spot diameter of 3 mm. Post to the LSP treatment, the surface roughness, fatigue life assessment and microstructural evolution analysis is performed. For this, different advanced characterisation techniques are used, such as scanning electron microscopy attached with electron backscatter diffraction for microstructure and texture, X-ray diffraction for residual stress (RS) and structure information, Vicker’s hardness tester for microhardness and universal testing machine for low-cycle fatigue.FindingsIt is observed that both scanning strategies during the LDED printing of 15-5 PH steel and laser peening have played significant role in fatigue life. Specimens with the XY printing strategy shows higher fatigue life as compared to XX with both U- and V-notched conditions. Furthermore, machining and LSP treatment led to a significant improvement of fatigue life for both scanning strategies with U and V notches. The extent of increase in fatigue life for both XX and XY scanning strategy with V notch is found to be higher than U notch after LSP treatment, though without LSP samples with U notch have a higher fatigue life. As fabricated sample is found to have the lowest fatigue life as compared to machines and laser peened with both scan strategies.Originality/valueThis study presents an innovative method to improve the fatigue life of 15-5 PH stainless steel by changing the microstructure, texture and RS with the adoption of a suitable scanning strategy, machining and LSP treatment as post-processing. The combination of preferred microstructure and compressive RS in LDED-printed 15-5 PH stainless steel achieved with a synergy between microstructure and RS, which is responsible to improve the fatigue life. This can be adopted for the futuristic application of LDED-printed 15-5 PH stainless steel for different applications in aerospace and other industries.Graphical abstract

Low cycle fatigue behavior of MAR-M247 nickel-based superalloy from 500 to 900 °C: Analysis of cyclic response, microstructure evolution and failure mechanism

Low cycle fatigue behaviors of MAR-M 247 superalloy were investigated at 500 °C, 700 °C and 900 °C. The detailed deformation mechanisms were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) and the critical resolved stress to active different deformation mechanisms were calculated. The results show that crack propagates along favorable {111} plane at 500 °C, and anti-phase boundary (APB) shearing is the main deformation mechanism. At intermediate temperatures, the cracking mode is similar to 500 °C. The dislocation pinning at L-C lock leads to premature failure. It is difficult for {111} 〈110〉 slip system to shear hard oriented grain with low Schmid factor at 900 °C. Dislocation movement is achieved by Orowan by pass process and thermal activated dislocation climb at high temperature. In addition, the improved life prediction model based on energy method has been constituted and discussed at different temperatures.

Neutron diffraction analysis of microstructural evolution and mechanical behavior in an additively manufactured multiphase alloy

Abstract Additive manufacturing (AM) involves an unprecedented thermal history during solidification and post-melt high-temperature exposure, leading to unique microstructural evolution. In this study, we employed neutron-diffraction-based microstructural analysis to better understand the microstructural evolution and mechanical behavior of AM alloys, with a particular focus on multiphase alloys. Samples of Ti−6Al−4V alloy used as a model material were prepared using electron beam powder bed fusion (EB-PBF) under varying building conditions. Time-of-flight neutron diffraction (TOF-ND) measurements were performed using an iMATERIA (BL20), J-PARC, Japan. Using Rietveld texture analysis (RTA), we revealed the textural evolution during hierarchical microstructural development from solidification to solid-state phase transformations in the EB-PBF process. The effects of building conditions on the textures in the as-built states and their evolution during subsequent tensile loading were analyzed.

Analysis of Microstructural Evolution during the Sintering Process of Aluminum Matrix Nanocomposites Reinforced with Al4C3, Using X-ray and HRTEM

Analysis of Microstructural Evolution during the Sintering Process of Aluminum Matrix Nanocomposites Reinforced with Al4C3, Using X-ray and HRTEM

Kinetics and mechanisms of high-temperature oxidation in BCC and FCC high-alloy Fe-based alloys with high volume fraction of carbides

This study conducts a detailed analysis of high-temperature oxidation and microstructural evolution in two high-alloy Fe-based alloys, each characterized by a high-volume fraction of carbides but differentiated by their matrices − body-centered cubic (BCC) and face-centered cubic (FCC), which was achieved by the addition of nickel. By investigating the intricate interplay of factors such as phase composition, nickel content, and the presence of carbides, this research aims to elucidate the diverse oxidation kinetics and underlying mechanisms specific to each alloy type. Results show that the BCC alloy exhibits slower oxidation kinetics compared to its FCC counterpart, suggesting better performance in high-temperature environments. Moreover, while both alloys develop strong adhesive oxide scales primarily composed of Cr2O3, the FCC alloy experiences more pronounced scale spallation and cracking. A faster progression of decarburization was observed in the BCC alloy. This comprehensive comparison highlights how variations in matrix structure, along with nickel content and carbide behavior, critically influence oxidation kinetics, scale adhesion, and the overall integrity of oxide scales. Understanding these nuanced interactions is crucial for designing high-performance alloys tailored for extreme operating conditions.

Zircoborate glass-ceramic composite reinforced with aluminum oxynitride: Microstructural evolution, physical properties, and charged radiation attenuation analysis

This study used the powder metallurgy method to create aluminum oxynitride (AlON)-reinforced zircoborate glass-ceramic composites. The solid-phase reaction method was used to synthesize AlON powder, which was then added to Zr-based glass-ceramic in different amounts (0, 4, and 8 % by weight) to make it stronger and harder. The prepared materials were characterized for their structural, physical, and radiation shielding properties. The density of GZr8 (AlON-free) had a value of 2.9 g/cm3, and the sintered glass-ceramic density with 4 % wt. AlON reinforcement (GZr8Al4) reached 3.05 g/cm3. The highest density of 3.11 g/cm3 was obtained for the GZr8Al8 sample with 8 % AlON wt. The Vickers hardness for GZr8, GZr8Al4, and GZr8Al8 was measured to be 4.89, 5.94, and 6.33 GPa, respectively. The AlON-reinforced GZr8 samples had fast neutron (FN) removal cross-sections of 0.0796 cm−1 and 0.0824 cm−1 for AlON content of 4 and 8 wt%, respectively. Generally, the coherent scattering cross-section (σcoh), incoherent scattering cross-section (σinc), and absorption cross-section (σabs) of thermal neutrons (TNs) increase from 0.047856 cm−1, 0.02072 cm−1, and 0.01498 cm−1, respectively for GZr8 to 0.53124 cm−1, 0.02074 cm−1, and 0.01795 cm−1, for GZr8Al8. AlON was proven to improve the ability of the Zr-based glass-ceramics to attenuate FNs and TNs. Stopping powers of electrons, protons, alpha particles and carbon ions increase with the AlON content of the materials. Comparatively, the range of charged radiation in AlON-rich samples is lower. The inclusion of AlON in the matrix of the Zr-based glass-ceramics makes it more efficient at absorbing charged radiation and can be used in ion beam or hadron therapy, ion beam analysis, or other charged radiation environments as an absorber.

Quantitative analysis of microstructural evolution in cold-sprayed CuCrZr: Understanding heat transfer mechanisms from room temperature to 600°C

Cold-sprayed CuCrZr coating offers interesting multifunctional properties with a combination of high mechanical property, good thermal stability and substantial deposition thickness. Despite these advantages, the incorporation of solid solution elements and the deposit’s unique microstructure often result in suboptimal heat transfer capabilities. This study delved into the thermal conductivity of cold-sprayed CuCrZr coatings over a temperature range from room temperature to 600 °C. Furthermore, it quantitatively analyzed their microstructural evolution post-thermal testing and its correlation with thermal properties, employing techniques such as FESEM, EBSD, TEM, and XRD. Findings indicate the CuCrZr coating exhibits significant thermal sensitivity, with conductivity increasing from 65.83±1.79 W/(m∙K) at 25 °C to 198.42±0.63 W/(m∙K) at 600 °C. The annealing effect during thermal testing significantly enhances the coatings’ room temperature thermal properties, chiefly through the enhancement of interparticle metallurgical bonding, grain enlargement, solid solution precipitation, and a reduction in dislocation density. The thermal conduction across the coating/substrate interface is intricately influenced by the interplay between electrons and phonons, with impediments at the interface becoming markedly pronounced beyond 300 °C. The investigation pinpointed interparticle interfaces as the predominant barriers to heat transfer, contributing to 73.77 % of the total resistance. Meanwhile, the effects of solid solution elements, grain boundaries, and dislocations on thermal conductivity were comparatively minor, contributing 9.36 %, 1.04 %, and 0.44 %, respectively. However, it is also noted that the annealing effect can induce the coalescence of microcracks into pores and promote the precipitation or oxidation of Cr at the interfaces, which, in turn, limits the potential for further enhancements in thermal conductivity.

Microstructural evolution and phase analysis of SS410–Al2O3–SiC multilayered functionally graded composite fabricated through laser cladding

In the present study, a functionally graded metal-ceramic composite structure comprising SS410, Al2O3, and SiC particles with varying composition, structure and properties in a single deposit was successfully fabricated using direct energy deposition (DED). The composition varied from 90 % SS410 with 10 % (xAl2O3 + ySiC) to 10 % SS410 with 90 % (xAl2O3 + ySiC), where x = 70 % and y = 30 % in a five-layered FGM design. The microstructure, phase evolution and mechanical properties of the components with different composition gradients were characterized by microscopy, energy dispersive spectroscopy, wavelength dispersive spectroscopy, X-ray diffraction and micro hardness. The investigation revealed that complex phases such as C0.12Fe0.79Si0.09, M7C3, Fe3C, and Fe3Si formed as a result of the interaction between SiC and SS410 during the cladding process. Microstructural analysis showed a transition from columnar dendrites at the bottom zone of the cladding to a typical cellular structure and carbide particle agglomerates in the middle zone, with finer grains at the top zone. This gradation in microstructure correlated with an increase in microhardness ranging from 299 HV at the bottom to 966 HV at the top. This enhancement in hardness is primarily attributed to solid solution strengthening from C and Si originating from the decomposition of SiC and the precipitation of intermetallic phases.

Friction stir welding of a rapidly solidified thin-strip continuous cast AA5182 Al–Mg alloy: analysis of microstructure evolution, mechanical properties, and corrosion resistance

Friction stir welding of a rapidly solidified thin-strip continuous cast AA5182 Al–Mg alloy: analysis of microstructure evolution, mechanical properties, and corrosion resistance

Effects of multi-axial compression and double-step aging on the microstructure and mechanical properties of Al alloy 7075

This study investigates the combined effect of severe plastic deformation via multi-axial compression (MAC) and subsequent double-step aging on the microstructure and mechanical properties of annealed 7075 Al alloy. Three distinct processes were employed: (1) double-step aging on the annealed sample, (2) double-step aging on the six-MAC pass processed sample, and (3) double-step aging without solutionization on the six-MAC pass sample. Process (2) yielded the most significant improvements in mechanical properties. Compared to the annealed sample, the six-MAC pass, double-step aged sample exhibited an average ultimate tensile strength increase of 134% and an average Vickers micro-hardness (HV) increase of 209%. This superior performance is likely attributable to the synergistic effect of grain refinement induced by MAC and precipitate hardening achieved through double-step aging. A comprehensive analysis of microstructure evolution, mechanical properties, fractography, and the relationship between them was conducted for all three processes. This in-depth examination provided valuable insights into the mechanisms governing the observed property enhancements, particularly in process (2). Additionally, a variety of characterization techniques were employed to comprehensively evaluate the material's mechanical and microstructural characteristics.

Multi-scale analysis of microstructural evolution and atomic bonding mechanisms in CoCrFeMnNi high-entropy alloys upon cold spray impact

Large interfacial strains in particles are crucial for promoting bonding in cold spraying (CS), initiated either by adiabatic shear instability (ASI) due to softening prevailing over strain hardening or by hydrostatic plasticity, which is claimed to promote bonding even without ASI. A thorough microstructural analysis is vital to fully understand the bonding mechanisms at play during microparticle impacts and throughout the CS process. In this study, the HEA CoCrFeMnNi, known for its relatively high strain hardening and resistance to softening, was selected to investigate the microstructure characteristics and bonding mechanisms in CS. This study used characterization techniques covering a range of length scales, including electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and high-resolution transmission microscopy (HR-TEM), to explore the microstructure characteristics of bonding and overall structure development of CoCrFeMnNi microparticles after impact in CS. HR-TEM lamellae were prepared using focused ion beam milling. Additionally, the effects of deformation field variables on microstructure development were determined through finite element modeling (FEM) of microparticle impacts. The ECCI, EBSD, and HR-TEM analyses revealed an interplay between dislocation-driven processes and twinning, leading to the development of four distinct deformation microstructures. Significant grain refinement occurs at the interface through continuous dynamic recrystallization (CDRX) due to high strain and temperature rise from adiabatic deformation, signs of softening, and ASI. Near the interface, a necklace-like structure of refined grains forms around grain boundaries, along with elongated grains, resulting from the coexistence of dynamic recovery and discontinuous dynamic recrystallization (DDRX) due to lower temperature rise and strain. Towards the particle or substrate interior, concurrent twinning and dislocation-mediated mechanisms refine the structure, forming straight, curved, and intersected twins. At the top of the particles, only deformed grains with a low dislocation density are observed. Our results showed that DRX induces microstructure softening in highly strained interface areas, facilitating atomic bonding in CoCrFeMnNi. HR-TEM investigation confirms the formation of atomic bonds between particles and substrate, with a gradual change in crystal lattice orientation from the particle to the substrate and the occurrence of some misfit dislocations and vacancies at the interface. Finally, the findings of this research suggest that softening and ASI, even in materials resistant to softening, are required to establish bonding in CS.

In situ neutron diffraction study and electron microscopy analysis of microstructure and texture evolution during annealing of rolled CoCrFeNi alloy doped with 1 at.%C

In situ neutron diffraction studies of changes in the dislocation density, volume fraction of carbides, and crystallographic texture have been performed during annealing of a cold-rolled multi-principal element CoCrFeNi alloy doped with 1 at.%C. In addition, microstructures of the as-rolled and several annealed samples of this alloy have been investigated using electron microscopy-based techniques. It is found that cold rolling to a thickness reduction of 74% results in a brass-type rolling texture with a spread of orientations between the Goss and brass components and with a pronounced 〈111〉//ND fiber. The deformed microstructure is characterized by a high density of dislocations and shows large variations in deformation structures in regions of different crystallographic orientations. In particular, bundles of deformation twins and high frequencies of shear bands are observed in regions having orientations along the 〈111〉//ND fiber. Annealing at 700 °C–1000 °C leads to recovery and recrystallization, during which shear bands and regions of mixed orientations act as preferential nucleation sites for recrystallized grains. Precipitation of M23C6 particles also takes place during annealing. The particles retard boundary migration, thus slowing down recrystallization and restricting grain growth. The average size of recrystallized grains does not exceed 5 μm even after annealing at 1000 °C for 60 min. While rolling textures are retained in some annealed samples, other samples demonstrate distinct recrystallization textures with new texture components. The results obtained in this work are compared with the literature data for several carbon-doped face-centered cubic multi-principal element alloys and for a carbon-free CoCrFeNi alloy.

Microstructure evolution and mechanical analysis of lithium battery electrode in calendering deformation zone

Microstructure evolution and mechanical analysis of lithium battery electrode in calendering deformation zone

In Situ Analysis of Stress and Microstructure Evolution during Welding of High-Alloy Steels Using Energy-Dispersive X-Ray Diffraction

Constrained thermal expansion and contraction during welding cause a compression-tension cycle and plastic deformation in the heat-affected zone, leading to work hardening. The nature of this hardening effect—isotropic or kinematic—determines the final local yield stress and thus affects the residual stress state. Therefore, mechanical hardening must be modeled correctly in welding simulations for accurately predicting welding residual stresses. Previous studies, relying on comparisons with experimental ex situ results, led to different recommendations regarding the choice of the hardening model and thus require clarification. In this work, the stress evolution in the heat-affected zone of a tungsten inert gas weld is studied in situ using energy-dispersive x-ray diffraction and a novel method of stress analysis based on crystallite anisotropy. Additionally, microstructural information is gathered through line profile analysis. Results are shown for both austenitic and ferritic high-alloy steels and compared to ex-situ results including a validation of the new method of stress analysis. Finally, conclusions on the nature of work hardening are drawn.

Comparative Analysis of Microstructure Evolution and Mechanical Properties of Dissimilar Welded Joints of AA7075/AA6061 via Friction Stir Welding, Tungsten Inert Gas Welding, and Tungsten Inert Gas + Friction Stir Processing

Comparative Analysis of Microstructure Evolution and Mechanical Properties of Dissimilar Welded Joints of AA7075/AA6061 via Friction Stir Welding, Tungsten Inert Gas Welding, and Tungsten Inert Gas + Friction Stir Processing

Microstructure evolution and mechanical properties analysis in dissimilar ultrasonic metal welding of aluminum to copper

Ultrasonic metal welding is a solid-state welding process being widely employed for joining the interconnections of lithium-ion batteries in hybrid and plug-in hybrid vehicles. Examining the microstructure of the joint is of crucial importance to evaluate the performance. This analysis allows a comprehensive understanding of the phenomena influencing the joint strength. In this study, ultrasonic welding was utilized to join copper to aluminum sheets of 0.3 mm thickness, and then the macro- and microstructural characteristics of the weld cross-section and interface were thoroughly investigated. Finally, the microstructural changes at different values of ultrasonic welding parameters were correlated with the mechanical strength characteristics. This research identified mechanical interlocking and interface diffusion as the primary welding mechanisms. With an increase in welding time from 0.2 to 0.8 s, the bond density rose, the post-weld thickness decreased, and the average Vickers hardness at various points along the weld interface decreased by 10%.