Microstructural Variations Research Articles

Investigation of fracture mechanical properties of a brass alloy with microstructural variations

This study investigates the effect of microstructural variations on the mechanical properties of CuZn35Mn2Al1Fe1-C-GS brass alloy. Specimens taken from positions with different cooling rates in a large cast component exhibit coarse-grained (approximately 5mm) and fine-grained (approximately 1mm) microstructures. Fine-grained samples demonstrate at least a 7% increase in Ultimate Tensile Strength (UTS) and up to a 33% higher long crack threshold ΔKth,lc. Hardness measurements are similar between microstructures. The NASGRO model and cyclic R-curve are applied to fit crack propagation data, and fractographic analysis reveals distinct fracture mechanisms. The results indicate that a fine-grained microstructure enhances tensile strength and crack resistance, providing valuable insights for the design and maintenance of heavy machinery components made from cast brass.

Repair effect of He+ ions in borosilicate glass by sequential irradiation

The structural variations from alpha decay in borosilicate glasses attract much attention. The glass samples were irradiated with single and sequential beams in Xe20+ and He+ ions. Sequential irradiation means the glasses, which were pre-irradiated with Xe20+ ions, were irradiated with He+ions. The variations in macroscopic properties and microstructure were analyzed by nanoindentation, Raman spectra, infrared spectra and XPS spectra, respectively. After He+ ion irradiation, the hardness of glasses decreases, and the BO4 units increase in the glasses, attributed to the migration of Na on the sample surface. The hardness recovery was observed in sequential irradiation. Combined with the results of single ion irradiation, a reason for hardness recovery is that the migration of Na in deep layer causes the BO3 structure to transform into BO4 structure after He+ions irradiation. The variation of boron structures in sequential irradiation could be considered as the superposition of two single irradiation effects.

Use of metakaolins from Eseka and Dibamba‐Cameroon as an optimization additive of CEM I Portland cement mortar

AbstractThe present study deals with two kaolins from Eseka and Dibamba‐Cameroon to determine their potential suitability as additive of CEM I 42.5R and to optimize the properties of cement in the sense to promote low‐carbon cement. X‐ray diffractometry was used to establish the mineralogical composition of two kaolins. X‐ray fluorescence was carried out to determine the chemical composition of kaolins and cement. Fine metakaolin powders obtained at 700°C were used as additive in CEM I 42.5R. Furthermore, consistency, setting time, water absorption, compressive and flexural test, and shrinkage test were evaluated. Scanning electron microscopy analysis was carried out to evaluate the microstructure variation. The substitution of CEM I with metakaolin resulted in a considerable increase in compressive and flexural strength from days 7 to 28 at optimum value. The compressive and flexural strengths at 28 days at optimum value of metakaolin increase to 52% and 44%, respectively, explaining the equilibrium oxides in the cement. The maximum values of strength with 20 wt.% MK1 and 30 wt.% MK2 at 7, 14, and 28 days appear in both cases when the ratio of SiO2/Al2O3 is between 2.8 and 2.9. The silica modulus and alumina modulus of cement–metakaolin improved when metakaolin was added. The properties of cement were optimized with a 52% increase in compressive strength at 28 days.

Residual stress prediction in Ti17 linear friction welds considering inhomogeneous mechanical properties of joints

Microstructural variations of joints occur in linear friction welding, resulting in inhomogeneous mechanical properties that affect the development of residual stress. The mathematical models for elastic moduli and yield strength of Ti17 were firstly developed to obtain the inhomogeneous mechanical properties of joints. Then, the influence of inhomogeneous mechanical properties on residual stress prediction was investigated. The results show that the finite element model considering inhomogeneous mechanical properties accurately captures the bimodal distribution of residual stress and the location of peak stress in joints. Numerically, the peak values of stress are ∼662 and ∼194 MPa along the direction of oscillation and forging, respectively, which is consistent with the result of the contour method.

Fatigue-thermal damage characteristics of red sandstone with a hole under high-temperature cyclic loading coupling and microstructural degradation

In underground coal gasification (UCG) projects, deeply buried subterranean projects are significantly influenced by high temperatures, alongside disruptive loads such as excavation, blasting, and drilling. Therefore, it is essential to study the fatigue behaviors of rocks under the coupled effects of thermal elevation and cyclic loads. This study performed uniaxial compression and cyclic loading-unloading tests on red sandstone specimens with cavities. The high-temperature fatigue behaviors of specimens were explored from various aspects, encompassing stress, deformation, energy, damage, and the microstructural variations of the specimens after high-temperature procedures were assessed by utilizing scanning electron microscopy (SEM). At temperatures below 600 °C, SEM images indicate a contraction of microcracks in the specimens, whereas temperatures above this threshold lead to their expansion. Notably, the total, elastic, and dissipated energy density of the specimens exhibit a curve of second degree with the upper limit stress. Additionally, elastic and dissipated energy densities linearly correlate with input energy density. Furthermore, the coupled damage and axial strain of the specimens positively correlate with the temperature. The damage mode of thermal fatigue is attributed to the accumulation and penetration of transgranular fractures within the red sandstone.

Influence on micro-geometry and surface characteristics of laser powder bed fusion built 17-4 PH miniature spur gears in laser shock peening

Micro-geometrical errors, surface roughness, and surface integrity (microstructure, residual stresses, microhardness) play an important role in defining the quality of the gears as they directly affect their noise, vibration characteristics and service life during their use. In the present work, underwater laser shock peening (LSP) is employed to improve the quality of the laser powder bed fusion built 17-4 PH small-size spur gears (12 mm outside diameter). LSP was employed near the spur gear root, and effects were measured in terms of residual stresses, variation in microgeometry errors, surface roughness, porosity, microstructure, and microhardness. It was observed that LSP could impart compressive residual stresses up to 0.4 mm of measured depth, while the surface roughness has improved by 32%. Microgeometry and microhardness of gears showed minor variations. Additionally, LSP has shown an impact on the microstructure as the grain orientation was altered and grain size reduced by 15.6% due to shock wave transmission. The study paves the way to use LSP as a post-processing technique to modify the surface characteristics of LPBF-built miniature spur gears with minimal impact on the gear microgeometry.

The effect of drying-wetting alternation on corrosion resistance of rusted weathering steel

In order to understand the effect of drying-wetting alternation on the corrosion resistance of rusted weathering steel, firstly, a rusted weathering steel was obtaioned through the preparation of stabilized rust layer on the surface of naked weathering steel; secondly, a cyclic corrosion test (CCT) of drying-wetting alternation with different cyclic periods was carried out for rusted weathering steel. With the extension of cyclic period in drying-wetting CCT, the corrosion resistance of rusted weathering steel increased from 0 cycle to 6 cycle and then decreased after 6 cycle, which was closely associated with the variations of composition and microstructure for stabilized rust layer during the process of drying-wetting CCT. From 0 cycle to 6 cycle, the increased corrosion resistance of rusted weathering steel was attributed to the abundance rise of α-FeOOH in the interior of stabilized rust layer; however, from 6 cycle to 20 cycle, the decreased corrosion resistance of rusted weathering steel was due to the partial destruction of crystal sturcuture for stabilized rust layer.

Microstructural and mechanical properties evolution for 9Cr[sbnd]Si heat resistant steel deposited metals under different heat treatment states

To develop the matched filler metal for the structural materials in Generation IV lead-cooled fast reactor (LFR), the microstructural evolution and mechanical property variation of 9CrSi heat resistant steels deposited metals were investigated both for the as-welded and as-aged (at 550 °C) weld metals. The experimental results indicate two precipitates in the as-welded deposited metals: the bigger M23C6 and the smaller MX. Si facilitates the nucleation of M23C6. The chain-like precipitates (consisting of M23C6) form at the boundaries of prior austenite and martensitic laths in high-Si specimens. They deteriorate not only the strength but also the impact energy. Meanwhile, a few δ ferrites form in high-Si deposited metal deteriorating the impact energy. Precipitates tend to nucleate at the interface between the δ ferrite and the martensite after aging. New types of precipitates (Mo-rich M6X and Laves) with rapid coarsening rate form in as-aged high-Si deposited metals as time increases. Coarse precipitates deteriorate the pinning effect, which causes the recovery of laths and dislocations. Subgrain pinned by M23C6 forms in deposited metals with post-weld heat treatment (PWHT) during aging. The structure hinders the formation of M6X and facilitates the formation of nano-sized MX. Therefore, the mechanical properties of deposited metals with PWHT are stable during long-term (up to 10,000 h) aging treatments.

Evolution of microstructure and mechanical property enhancement in wire-arc directed energy deposition with interlayer machining

Wire-Arc Directed Energy Deposition (Wire-Arc DED) has emerged as a promising additive manufacturing technique known for its high deposition rates. However, the variability in microstructure and mechanical properties (e.g., hardness) of the manufactured components poses significant challenges. This study delves into these issues, focusing on the influence of interlayer machining on the microstructural evolution and mechanical properties of thin-wall Wire-Arc DED structures. It is shown that as-built Wire-Arc DED structures exhibit a pronounced microstructure variation between different regions along the build direction, primarily governed by the differences in thermal history. In contrast, a Hybrid Wire-Arc DED process that integrates interlayer machining into the build process to induce severe plastic deformation leads to a microstructure characterized by refinement and homogenization, compared to a Wire-Arc DED process. This study provides insights into the impacts of plastic deformation due to machining and thermal cycling due to subsequent layer depositions on the microstructure and hardness obtained in Wire-Arc DED and Hybrid Wire-Arc DED processes, highlighting the potential of hybrid manufacturing to generate tailored microstructures to enhance the mechanical performance of functional components.

Analysis of High and Low Temperature Performance of Titanium Zirconium Molybdenum Alloy and High Temperature Alloy Brazed Joint

Abstract Using niobium as the intermediate layer and gold nickel (Au82-Ni) filler metal, TZM alloy and high-temperature alloy GH3128 were brazed. The brazed specimens were subjected to 400 cycles of high and low temperature cycling tests at temperatures ranging from 650 °C ∼ 680 °C (high temperature) to -196 °C (low temperature) for 10 minutes seperately. Then the microstructure variation before and after the experiment were observed and the shear strength of the specimens were tested at room temperature for 50 cycles of 400 high and low temperature testing.. The results show that the microstructure of the transition zone at the brazing interface after brazing is uniform and dense, with good wettability with the substrate and no defects such as cracks. The solder and substrate undergo diffusion reactions, and the molybdenum alloy, niobium, and niobium, high-temperature alloy had each form diffusion layers, formed intermetallic compounds on the brazing surface. After high and low temperature cycling, cracks exist in the braze seam between molybdenum alloy and niobium alloy. The cracking mode should be thermal fatigue based on the fracture morphology and phase analysis. The reasons of interface cracking are that due to different thermal expansion coefficients, low mutual solid solubility, and the formation of a large number of different types of intermetallic compounds, Mo and Nb materials have poor brazing compatibility and lower interface strength. Under cold and hot cycling conditions, brittle intermetallic compounds are prone to form crack source areas. As the number of cycles increases, the cracks gradually expand, ultimately leading to product leakage. In addition, the shear strength of brazed joints shows a decreasing trend with the increase of high and low temperature cycles in 400 high and low temperature tests.

Directed energy deposition of Ti6Al4V wire with continuous layer varied laser power

The laser-based directed energy deposition (DED) additive manufacturing enables the efficient fabrication of metallic parts. The layer-wise performance in DED-built metallic parts is challenging to remain consistent due to the intricate heat accumulation. As such, it is of significance to control the printing quality by adjusting the process settings with layers. In this work, we used DED to achieve Ti6Al4V wire deposition with continuously layer-varied laser power. Three laser power settings were selected to investigate the variation in defects, microstructure, and mechanical properties with layers. Our findings suggested that optimizing real-time laser power is critical for achieving desirable manufacturing efficiency and resultant performance in the DED of metallic materials. This research provides valuable guidelines for parameter optimization in DED processes, aiming to enhance the production quality and performance of high-strength metallic components, particularly in sectors demanding high-performance materials.

Improved gyromagnetic properties of LiZnTi ferrites co-fired with Bi2O3-La2O3 additives at low temperature

In this work, low temperature-sintered Li0.43Zn0.27Ti0.13Fe2.17O4 ferrites mixed with x wt.% (x = 0.00–0.30 wt%) of La2O3 and 1.5 wt% of Bi2O3 were successfully prepared by the solid-state reaction method. The variations in phase composition, microstructure, and gyromagnetic properties of the as-prepared samples were studied in detail. XRD patterns and refinement results show that La2O3 didn't affect the formation of the spinel phase, but a small amount of La3+ might enter into the lattice structure. The micro-morphological analysis and grain size statistics demonstrate that the addition of La2O3 significantly suppressed the grain growth, and the average grain size decreased from 2.19 μm (x = 0.00 wt%) to 1.14 μm (x = 0.15 wt%). The uniformity of the grain size distribution was improved, and the degree of densification was significantly increased. Meanwhile, the saturation magnetization (4πMs) increased from 3921 Gs to 3989 Gs, the coercivity (Hc) decreased from 457.5 A/m to 312.5 A/m, and the ferromagnetic resonance linewidth (ΔH) decreased from 328.5 Oe to 220.7 Oe. Our study indicates that the Bi2O3-La2O3 mixture is an effective sintering additive for low-temperature sintering of LiZnTi ferrite ceramics, which will play an important role in the development of low-temperature co-fired ferrites.

Stepwise oxidation of refractory pyrite using persulfate for efficient leaching of gold and silver by an eco-friendly copper(II)-glycine-thiosulfate system

Chemical oxidation is a promising pretreatment method for refractory pyrite enclosure to enhance Au/Ag extraction. Here, persulfate was employed for stepwise oxidation of a refractory pyrite concentrate with encapsulated Au/Ag: (i) pyrite oxidation began with heating-activation persulfate, where hydroxyl radical (•OH) acted as the primary oxidative species for fast-dissolving pyrite into Fe ions; (ii) pyrite self-dissolved Fe ions were in-suit used as a moderate activator of persulfate to generate •OH for sustainable oxidizing pyrite at room temperature. Mineralogical studies have confirmed that oxidation of the sulfide enclosure (FeS2) significantly reduced the particle size of pyrite, accompanied by pores creation and an increase in specific surface area. The variation of microstructure liberated Au and Ag particles to lixiviants for extraction, significantly improving leaching efficiency in an eco-friendly copper(II)-glycine-thiosulfate system to 92.2 % for Au and 88.6 % for Ag, respectively. This work provides a promising process for separating precious metals from refractory pyrite.

Experimental research on the glass fiber-reinforced effect and mechanisms of sand powder 3D-printed rock-like materials

Conducting laboratory tests on natural rocks has significant value for the scientific and practical advancement of various types of rock engineering. The investigation of a rock-like materials that is similar in characteristics and structure to natural rock is key to the further advancement of laboratory rock experiments. The rapid development of sand powder 3D printing technology in recent years has provided a solution for fabricating rock-like materials. However, the low strength and elastic modulus of sand powder 3D-printed materials limit their application in simulating natural rocks. Therefore, this paper proposes a method to enhance the mechanical properties of sand powder 3D-printed materials utilizing glass fiber reinforcement by incorporating glass fiber into sand powder 3D-printed rock-like specimens. The mechanical properties and microstructural variations of the specimens with varying glass fiber contents are investigated utilizing mechanical testing, acoustic emission, scanning electron microscopy, etc. The results indicate that (1) it is feasible to utilize glass fiber to enhance the mechanical properties of sand powder 3D-printed materials; (2) The mechanical properties of sand powder 3D printing materials are significantly enhanced by the addition of glass fiber; and (3) the mechanisms controlling the reinforcement effect of glass fiber addition on sand powder 3D-printed specimens are determined by analyzing the microstructural characteristics of the specimens. This study improves the applicability of sand powder 3D-printed materials in simulating natural rock, thereby promoting the further application of 3D printing in the field of rock mechanics.

Microstructural constituents in compositionally graded NiCrFeSiBC hardfacing alloy/316L SS additive manufactured deposits

Ni-Cr-Fe-Si-B-C hardfacing alloys (D50) provide excellent resistance to abrasive and adhesive wear, high temperature oxidation and corrosion. These alloys are candidate materials for hardface coatings on in-reactor components of fast breeder reactors. Conventionally these deposits are made on steels through the welding route. Due to high fluidity of the molten alloy, generation of residual stress and significant dilution of the deposit, achieving crack free deposits is often a very difficult and time consuming task. To address such issues arising out of conventional fabrication routes, compositionally graded coatings have been tried through laser additive manufacturing. A 3 layered compositionally graded deposit (D50/50D50-50SS/SS) was made on 316 L SS build plate and the phase constituents and possible correlation with micro hardness was analyzed. Uppermost D50 layer consisted of γ-Ni, γ-Ni + Ni3B and γ-Ni + Cr5B3 eutectics, CrB, Cr7C3, Cr23C6, Cr3C2 and Ni3Si precipitates. The middle layer consisted of γ-(Ni,Fe), γ-(Ni,Fe)+Cr5B3, Cr5B3, Cr3C2, Cr7C3,Cr23C6 and Ni3Si. The SS layer closest to the build plate had γ-Fe, Cr3C2 and Cr7C3 precipitates. Corresponding to the variation in microstructure a gradual change in hardness also can be seen starting from the top layer to SS build plate: 580 ± 35 HV0.1, 532 ± 17 HV0.1, 348 ± 21 HV0.1 and 230 ± 10 HV0.1, which is promising.

Solvothermal Polymerization of Diaminomaleonitrile Reveals Optimal Green Solvents for the Production of C=N-Based Polymers.

Solvothermal polymerization (STP) of diaminomaleonitrile (DAMN) was evaluated using a wide variety of solvents and in the temperature range from 80 to 170 °C. The highest yields, almost quantitative, were achieved with protic n-alcohols such as n-pentanol or n-hexanol at 130 and 150 °C, respectively. The kinetic behavior was studied by gravimetry and the DAMN consumption was monitored by UV-vis spectroscopy and HPLC. GC-MS identified byproducts of the DAMN hydrolysis and oxidation reactions, which were significantly reduced when n-pentanol or n-hexanol were used with respect to hydrothermal conditions. This led to an exploration of compositional changes and microstructural variations by FTIR and NMR spectroscopy and simultaneous thermal analysis. n-Hexanol appears to be an ideal eco-friendly solvent for the DAMN self-STP. The results presented here are not only of interest for the design of polymeric materials based on C=N structures but also show remarkable implications for prebiotic chemistry.

Multiscale modelling strategy for predicting fatigue performance of welded joints

This study predicts the fatigue performance of welded joints through a multiscale modelling strategy accounting for material and structural inhomogeneities. An S-N curve and detailed fracture surfaces with distinct beach marks were first derived by uniaxial fatigue tests utilising the designed cruciform welded joints. Considering the intrinsic features of welded joints, a multiscale modelling strategy was proposed to integrate multiple factors, including microstructural variations, strength distributions within the heat-affected zone (HAZ), and the diversity of three-dimensional weld toe shapes. Significantly, a modelling strategy was presented for the first time to simulate the simultaneous initiation, growth, and coalescence of multiple cracks, and was validated against experimental evidence. The results indicate that the proposed strategy can accurately predict both the fatigue strength and the overall crack growth process. Additionally, comparative assessments of single-crack and multiple-crack modelling strategies revealed notably shorter predicted fatigue lives when considering crack coalescence. Overall, this work establishes a multiscale framework for assessing the fatigue performance of welded joints considering both microscopic and macroscopic factors, offering substantial practical implications for engineering applications.

Understanding a new wrinkling behavior of annular grooved panel during flexible free incremental sheet forming

Wrinkling behavior of sheet metal by inappropriate process parameters and the resultant variation of thickness and microstructure during incremental sheet forming (ISF) have significant impact on forming stability and geometric profile. The wrinkling-related mechanism is yet to be well understood, which make it difficult to effectively control wrinkling defects during ISF. In the present work, the wrinkling behavior and related mechanism of a typical annular grooved panel are investigated during a novel flexible free ISF process. Experiments demonstrate that during this ISF process, the sheet material sequentially undergoes 4 deformation modes: contacting state under plane strain condition, contracting state with only elastic deflection, thickening state under uniaxial compression condition, and wrinkling state where the circumferential compressive stress exceeds the critical wrinkling stress. The evolution of these deformation modes is dominantly caused by the increasing of edge contraction and circumferential stress, which are induced by the bending moment from the forming tool and auxiliary sheets. Based on the mechanism, an analytical model is developed to predict the wrinkling behavior, by which the corresponded sheet thickness, bending moment, circumferential compressive stress and critical wrinkling stress during the wrinkling process could be comprehensively calculated. Experimental results validate that the analytical model can accurately predict the wrinkling behavior under different process parameters, material properties and auxiliary sheet materials. Through microstructural characterization, numerical simulation and analytical modeling, the influence of process parameter and material property on wrinkling behavior is systematically investigated, along with the variation of sheet thickness and microstructure under different wrinkling modes. This work enhance a deep understanding of wrinkling behavior during ISF process, thereby providing effective methods for process optimization and quality improvement.

The novel Vogel's approximation method integrated with a random forest algorithm in the vibration analysis of a two-directional functionally graded taper porous beam: Assessment

A functionally graded material is a class of composite materials characterized by gradual variations in composition and microstructure, which further induces the respective changes in the material properties. This study focuses on evaluating the vibration behavior of two directional functionally graded taper porous beams (FGTPB). This approach adopts a rectangular cross-section in order to deal with the challenges related to fluctuating material characteristics and geometric tapering in both thickness and width dimensions. The research employs a novel approach that merges Vogel's approximation technique with the Random Forest algorithm, an approach that has not been used in analyzing structural vibrations, establish boundary conditions and solve equations of motion. Comparative results of the suggested beam theory with the existing literature on FGTPB materials such as alumina and SUS304 at various taper, porosity, gradient and width ratios verified it. The material gradation and porosity developed a uniform pattern in the first three modes of fundamental frequencies. Higher gradient indices increased the rigidity and natural frequencies of the beams whereas the porosity index decreased the rigidity, resulting in lower natural frequencies. By combining Vogel's approximation method with machine learning techniques, the study improved vibration behavior analysis in FGTPB. The disciplines of materials and structural engineering are significantly impacted by this.

Effect of microstructure variation induced by processing on corrosion behavior of Zr-Sn-Nb alloy

In order to investigate the effect of microstructure variation induced by processing on corrosion behavior of zirconium alloys, Zr-Sn-Nb alloy original plates were processed by rolling and annealing, and the microstructure and corrosion behavior of both original plates and processed plates were analyzed. It was found that after the original plates were processed, the recrystallized microstructure in original plates was transformed to stress-relieved microstructure in processed plates, with second phase particles ripening. When exposed to pure water and water containing H3BO3 and LiOH, the original plates have better corrosion property than the processed plates, and the corrosion transition of the processed plates happened earlier than that of the original plates. The grain structure differences of original plates and processed plates have two aspects of influence on oxide cracking and corrosion transition. Firstly, there were more defects in processed plates which results in smaller grains and larger grain boundary areas in oxide. Secondly, the strength of processed plates is higher, and this will lead to less stress accommodation of the growing oxide by plastic deformation of the matrix, and higher stress in oxide layer formed during the corrosion process. Both factors caused more cracks in the oxide layer of processed plates, leading to earlier corrosion transition and decreasing corrosion property. Second phase particles and their surroundings are susceptible to cracks during corrosion process, and may become the original source of cracks. However, second phase particle ripening was not closely related to decreasing corrosion property of processed plates.