Average Grain Research Articles

The Microstructure Characterization of a Titanium Alloy Based on a Laser Ultrasonic Random Forest Regression

The traditional microstructure detecting methods such as metallography and electron backscatter diffraction are destructive to the sample and time-consuming and they cannot meet the needs of rapid online inspection. In this paper, a random forest regression microstructure characterization method based on a laser ultrasound technique is investigated for evaluating the microstructure of a titanium alloy (Ti-6Al-4V). Based on the high correlation between the longitudinal wave velocity of ultrasonic waves, the average grain size of the primary α phase, and the volume fraction of the transformed β matrix of the titanium alloy, and with the longitudinal wave velocity as the input feature and the average grain size of the primary α phase and the volume fraction of the transformed β matrix as the output features, prediction models for the average grain size of the primary α phase and the volume fraction of the transformed β matrix were developed based on a random forest regression. The results show that the mean values of the mean relative errors of the predicted mean grain size of the native α phase and the volume fraction of the transformed β matrix for the six samples in the two prediction models were 11.55% and 10.19%, respectively, and the RMSE and MAE obtained from both prediction models were relatively small, which indicates that the two established random forest regression models have a high prediction accuracy.

Growth and yield response of four bread wheat cultivars, (Triticum aestivum L.), to spraying with NPK nano fertilizer

Abstract A field experiment was carried out during the agricultural season 2021-2022 in two locations within the administrative borders of Nineveh Governorate, the first location in the Gleokhan area within the borders of Mosul Center and the second location within the administrative borders of Namrod district, which is 45 km from the center of Mosul district, in order to know the effect of the balanced NPK 20:20:20 compound fertilizer nano the growth and yield of four varieties of bread wheat. The global experiment was carried out, which consisted of two factors, a randomized complete block design, and three replications. The first factor was fertilizer levels with four levels (1, 2, and 3 gm.L-1) added in two phases. The first is in the tillers stage (Z 2-1) and the second stage is at the beginning of the boating stage (Z 4-0) on the Zadoks scale, in addition to the comparison treatment, which was the traditional farmer’s method of fertilization (adding urea and dab fertilizer according to the times and quantities recommended by the Ministry Iraqi Agriculture), the second factor, four varieties of local bread wheat (Bhoth 22, Abu Ghraib, Rashid and Jihan), the following characteristics were studied: plant height, number of tillers, flag leaf area, total chlorophyll content of flag leaf, number of days up to 50% flowering, number of spikes, spike length, number of grains per spike, grain yield, weight of 1000 grains. The most important results of the study were as follows: The comparison treatment (the traditional farmer's method) excelled in the total chlorophyll content of the Gleokhan site and in the number of spikes and weight of 1000 grains in the Namrod site, with values of (28.41 Spad, 267.75 spikes.m-2, and 44.91 g), respectively. The 1 g spray treatment excelled in the characteristics of the number of tillers, number of spikes, length of spike, grain yield, and weight of 1000 grains at the Gleokhan site, and in the two characteristics of leaf area and spike length at the Namrod site, with averages of (178.17 tiller.m-2, 100.08 spikes.m-2, 8.58 cm , 128.83 g.m-2, 35.20 g, 34.46 cm2 and 10.85 cm) in the aforementioned order. The 3 g spray treatment was superior in the characteristics of plant height for both sites, the number of days up to 50% flowering, and grain yield of the Namrod site, with rates of (54.42 cm, 80.77 cm, 135.83 days, and 332.17 g.m-2), respectively. No significant differences were recorded between the levels of fertilizer in terms of flag leaf area and number of days up to 50% flowering for Gleokhan site and number of grains per spike for both sites. The cultivar Bhoth 22 excelled in terms of total chlorophyll content and the weight of 1000 grains at the Gleokhan site, and for the characteristics of the number of tillers, number of days up to 50% flowering, number of spikes, and grain yield of the Namrod site, as averages were recorded (27.29 Spad, 34.23 g, 302.75 tiller.m-2, 134.92 days, 290.17 spike.m-2 and 405.42 g m-2) respectively. The Abu Ghraib cultivar achieved superiority in the number of grains per spike at Al-Namrod site, with an average of (46.43 grains.spike-1). The cultivar Rashid excelled in the characteristics of the number of tillers, number of spikes, and spike length at the Gleokhan site, and for the two characteristics of the flag leaf area and spike length at the Namrod site, where the rates were recorded (169.08 tiller.m-2, 104.58 spike.m-2, 8.56 cm, 34.55 cm2 and 12.98 cm), respectively. The cultivar Jihan achieved superiority in the two characteristics of the number of days up to 50% flowering and grain yield at Gleokhan site, with values of (131 days and 108.08 g.m-2), respectively. No significant differences were recorded between the cultivars included in the study in the characteristics of plant height, flag leaf area, number of grains per spike for Gleokhan site, and for the two characteristics of total chlorophyll content and weight of 1000 grains for Namrod site. The interaction of 1 g spray treatment with Jihan cultivar recorded the highest average grain yield at Gleokhan site, and the 3 g spray treatment with Bhoth 22 cultivar had the highest average grain yield at Namrod site with values of (301 and 487.67 g.m-2), respectively.

Effect of rolling on the microstructure and mechanical properties of (FeCrNi)94Ti3Al3 medium entropy alloy fabricated via selective laser melting

The microstructure evolution and mechanical properties of the (FeCrNi)94Ti3Al3 medium entropy alloy, fabricated through selective laser melting, were investigated after warm-rolling. The as-built (FeCrNi)94Ti3Al3 alloy exhibited a heterogeneous microstructure with alternating coarse face-centered cubic (FCC) phase grains (∼20 μm) and fine body-centered cubic (BCC) phase grains (∼1 μm). However, after warm-rolling and subsequent recrystallization, the alloy transformed into a dual-phase equiaxed grains structure consisting of FCC and BCC phases with an average grain size of approximately 2.8 μm. Additionally, the previously banded distribution of the BCC phase changed to a random distribution. Notably, during the deformation process, a twinning-induced plasticity (TWIP) effect was observed in the warm-rolled and recrystallized (FeCrNi)94Ti3Al3 alloy, resulting in excellent ductility and a wide work-hardening platform.

Comparison of the microstructure and properties of 19Al–24Cr–19Ti–37Ni–1Y high-entropy alloy fabricated through conventional and ultrahigh-speed laser cladding methods

Compared with conventional laser cladding (CLC), ultrahigh-speed laser cladding (UHSLC) can dramatically increase cladding efficiency. In this study, a new 19Al–24Cr–19Ti–37Ni–1Y eutectic high-entropy alloy coating was prepared through CLC and UHSLC, tested, and characterized. Results showed that the dilution rate of the UHSLC-HEA coating was 20.2 %, which was only half that of the CLC-HEA coating. The UHSLC-HEA coating had a lamellar spacing of 100 nm and an average grain size of 2.2 μm, which was only one-third of the average grain size of the CLC-HEA coating. The microhardness of the UHSLC-HEA coating was 210 HV0.5 higher than that of the CLC-HEA coating. The coefficient of friction and wear rate of the UHSLC-HEA coating had reduced by 43 % and 34 %, respectively, relative to those of the CLC-HEA coating. UHSLC enhances the wear resistance of coatings by reducing dilution rate, refining grain size, and promoting the formation of a second phase.

Achieved strength-plastic trade-off in HfMoNbTaTi refractory high-entropy alloy via powder metallurgy process

The practical application of refractory high-entropy alloys (RHEAs) has been limited by their brittleness at room temperature. This study prepared fine-grained HfMoNbTaTi refractory high-entropy alloys using a powder metallurgy process combining mechanical alloying (MA) and spark plasma sintering (SPS). This method effectively addresses the issue of room temperature brittleness and achieves a favorable balance between strength and plasticity. The resulting sintered alloy comprises two body-centered cubic (BCC) solid solution matrices and a range of nanoprecipitates, including the γ-phase, σ-phase, and α-phase. With increasing sintering temperature, the average grain size increased from 0.45 μm (at 1400 °C) to 4.56 μm (at 1700 °C). Simultaneously, the content of the γ-phase gradually decreases due to the greater influence of mixing entropy. Under quasi-static loading, the fine-grained multiphase structure not only benefits from grain boundary strengthening and precipitation strengthening effects, but also enhances the deformation uniformity, ultimately improving both the strength and plasticity. At 1450 °C, the sintered alloy exhibited a compressive yield strength of 2325 ± 8.40 MPa and a plastic strain of 26.44 ± 1.17 %. These values represent a 35.73 % increase in yield strength and a 120.33 % increase in plastic strain compared to those of the as-cast alloy. The deformation process at room temperature is mainly governed by the multiplication of screw dislocations and cross-slips. In the middle and late stages of deformation, the grains exhibit a preferred orientation, further enhancing the plastic strain. In summary, this study presents a practical approach for overcoming the issue of room temperature embrittlement in RHEAs.

Microstructures and mechanical properties of additively manufactured Fe–21Mn-0.6C TWIP steel using laser powder bed fusion

Twinning induced plasticity (TWIP) high manganese steel exhibits high ultimate tensile strength (UTS) and ductility, but its low yield strength restricts its applications. This research presents a Fe–21Mn-0.6C TWIP steel with enhanced mechanical properties additively manufactured using laser powder bed fusion (LPBF). The average grain size of the LPBF-fabricated Fe–21Mn-0.6C was 17.1 μm in the vertical direction, which was a quarter of that of a wrought one. The tensile yield strength was 657 MPa and the UTS was 1089 MPa with an elongation of 47.9% for the vertical direction. Compared to the wrought Fe–21Mn-0.6C, the yield strength increased by 110%. The high strength of LPBF-fabricated Fe–21Mn-0.6C is primarily attributed to solution, grain boundary and dislocation strengthening. Serrations were observed in the stress-strain curves at the initial stage of deformation, showing large stress drops. In the annealed sample, serrations appeared at a later stage of deformation with little stress drops. This difference in serration phenomenon is attributed to the varying dislocation density in the two samples.

Improved mechanical behavior of friction stir drilled 6082 aluminum alloy via T6 treatment

6082 Al-alloy underwent a friction stir drilling (FSD) processing. Subsequently, a two-stage post-heat treatment (PHT) procedure, i.e., solution treatment at 550 °C for 2 h, followed by artificial aging at 175 °C for 18 h, was implemented to significantly enhance microstructure and mechanical performance of the alloy. The microstructure was characterized by optical, laser, scanning electron and electron backscattered diffraction microscopes, while the mechanical behavior was assessed by a micro-indentation hardness tester, employing the indentation hardness (HIT) technique. Corrosion behavior of FSD as well as PHT specimens was investigated through electrochemical techniques.The microstructure of the base metal (BM) manifested an α-Al matrix with an average grain size of approximately 50 μm. FSD resulted in the creation of stirring zone (SZ) and thermo-mechanical affected zone (TMAZ), with respective widths of 400 ± 50 and 950 ± 100 μm. The SZ exhibited a very fine structure with an average grain size of 0.5 μm, thereby displaying increased hardness. The PHT microstructure displayed the formation of fine βʹ and βʺ second phase precipitate types, whereas the HIT hardness of the PHT α-aluminum matrix in the SZ, was lower than TMAZ and BM, due to reductions of βʹ in the SZ compared to TMAZ and BM. Moreover, the corrosion rate of the SZ decreased after the heat-treatment cycle, attributed to the recovery of strain energy induced during friction drilling and the increased solubility of solute atoms within the α-Al matrix.

Impacts of SiO2 on phase composition, microstructure, and electrical properties of ZnO-SrCO3-Co2O3 ceramics

ZnO-SrCO3-Co2O3-SiO2 varistor ceramics were fabricated using the solid state method. Structural, morphological characterizations and varistor characteristics of samples were systematically studied. Average grain size is gradually reduced from 13.74 to 6.67 μm, resulting in a simultaneous increase of breakdown gradient E1 mA from 157.14 to 339.29 V mm−1. An increase of doping amount of SiO2 from 0 to 0.50 mol% contributes to the positive influences on double Schottky barrier of ZnO-SrCO3-Co2O3 varistors. The sample doped by 0.50 mol% SiO2 exhibits the highest height of double Schottky barrier φB of 2.99 eV resulting in the high nonlinear coefficient α equal to 76.83 and small value of leakage current density IL less than 0.29 μA cm−2 among the samples, which may be attributed to the solid solution reactions of SiO2 and Co2O3 in grain boundaries. The fabrication of ZnO-SrCO3-Co2O3-SiO2 represents the low-cost, sustainable development and environmental friendliness, providing a high performance candidate material for dominant ZnO-Bi2O3 based varistor ceramics.

Uniaxial tensile behaviors and Hall-Petch relationship of polycrystalline 316LN stainless steel via molecular dynamics simulation

A molecular dynamics (MD) simulation method was used to investigate the effects of element position, tensile strain rate (ε̇) and average grain diameter (d) on the uniaxial tensile properties of 316LN stainless steel at room temperature. It was found that the mechanical properties (elastic modulus, yield strength and tensile strength) of 316LN stainless steel were independent of the random position of the elements used in the model. Since the time of atoms relaxing to the equilibrium position was determined by the tensile strain rate, the mechanical properties deeply depended on the tensile strain rate. The fluctuations of simulated mechanical properties decreased with the increase number of randomly oriented grains in the molecular dynamics model, and the minimum number of grains should not be less than 500. Intragranular dislocation movement and grain boundary sliding were the main factors leading to plastic deformation, and their competition led to the normal to inverse Hall-Petch (HP) transformation of yield strength at the critical average grain diameter of 17 nm. When d was bigger than 17 nm, the relationship between yield strength and d was a normal HP relationship, σy(MPa) = 162 + 465.5d −0.5; while d was smaller than 17 nm, the forgoing relationship transformed into an inverse HP relationship, σy(MPa) = 3930-25d−0.5.

Experimental investigation of creep behavior along the build height of stainless-steel 316L fabricated via selective laser melting

The aim of this study was to contribute to the existing knowledge on the creep behavior of 316L stainless steel (SS) produced through selective laser melting (SLM). Creep tests were conducted on samples extracted from the wall in the build direction at 650 °C under various load conditions using a small punch (SP) creep test machine. The results revealed that the creep response was anisotropic and strongly dependent on the building height of the cubic block. Specifically, the average creep life was approximately three and five times higher in the bottom region than that in the top and middle regions, respectively. This indicates that the middle region was more susceptible to creep damage, resulting in inferior creep resistance, whereas the bottom region exhibited higher creep resistance. Interrupted tests were performed to elucidate variations in the internal creep damage level. The creep-damage mechanism was assessed based on the geometrically-necessary dislocations (GNDs) density and characteristics of the melt pool boundary (MPB). Additionally, creep tests demonstrated that SS316L stainless steel manufactured by SLM processing has an inferior creep life compared with conventional SS316L material, a phenomenon that can be attributed to the nano-sized cell structure and average grain size boundaries.

Effects of La-Co Co-Substitution and Magnetic Field Pressing on the Structural and Magnetic Properties of SrM Hexaferrites

We carefully investigated the effects of La-Co co-substitution and magnetic field pressing (MFP) on the structural and magnetic properties of SrM hexaferrites. Samples composed of Sr1−xLaxFe12−xCoxO19 were sintered at 1230 °C for 2 h in air with sintering additives composed of 0.7 wt% CaCO3 and 0.7 wt% SiO2. A single M-type phase was confirmed to exist up to x = 0.3. Rietveld refinement revealed a slight decrease in lattice parameter a and the unit cell volume (Vcell) with an increasing x, while parameter c showed a significant decrease. The saturation magnetization (Ms) values increased from 70.90 to 72.40 emu/g with an increasing x from 0.0 to 0.15 and then decreased to 71.38 emu/g with further increasing of x to 0.3, while the anisotropy field (Ha) increased from 17.7 to 25.9 kOe, leading to a continuous increase in the intrinsic coercivity (Hci), from 3.52 to 5.00 kOe, respectively. Using the MFP process, the c-axis of M-type hexaferrite grains could be effectively aligned to the applied field direction, which significantly affected the microstructures and, thus, magnetic properties of samples. Unlike non-MFP samples, exhibiting a significant increase in the average grain size (davg) but almost unaltered average thickness (tavg) with an increasing x from 0.0 to 0.3, MFP-processed samples exhibited almost unaltered davg values but a continuous decrease in tavg. Consequently, the variation in remanent flux density (Br) versus x followed that of Ms versus x and thus exhibited the highest Br of 4.05 kG for x = 0.15, leading to the highest maximum energy product {(BH)max} of 3.62 MGOe. With an increasing x from 0.0 to 0.3, the Hci values continuously increased from 3.14 to 3.84 kOe mainly due to a continuous increase in Ha, although they were significantly lowered in comparison with those of non-MFP samples because of a large increase in Br for a given composition x. A higher Mr/Ms ratio always resulted in a larger (BH)max in our samples regardless of x. A careful comparison of the microstructures and magnetic properties between MFP and non-MFP samples provided valuable insights into a broad area of permanent magnet optimization.

Green preparation of tertiary-phase titanium oxide nanopowder using Chlorella sp. aqueous extract

Herein, a novel green synthesis of tertiary-phase titanium dioxide nanoparticles (TiO2 NPs) using an aqueous extract of Chlorella sp. was reported for the first time. The TiO2 NPs were prepared using various extract volume concentrations (0, 5, 10, 15 and 20 % v/v) and subsequently calcinated at 600 °C. The X-ray diffraction (XRD) results revealed that the concentration ranging from 5 to 15 % v/v algae extract resulted in mixed phases of anatase, brookite, and rutile, while the extract concentration of 20 % v/v yielded mixed phases of anatase and brookite. The phase transformation from anatase to rutile decreased with increasing extract concentration. Transmission electron microscopy (TEM) images showed that the average grain size of the control TiO2 was 90 nm, whereas that of algae mediated TiO2 NPs was 10–20 nm. The concentration of algae extract was a very significant parameter for the phase transformation and particle size reduction of TiO2 NPs. The tertiary phase 10 % and 15 % algae mediated TiO2 powder also exhibited reaction rate constants (k) similar to the binary phase 20 % TiO2, despite containing lower anatase content. The present work demonstrated the successful synthesis of tertiary phases TiO2 nanopowder using microalgae Chlorella extract as a biogenic capping agent.

Microstructure and mechanical properties of Cu–Cr–Zr–ZrB2 composites by novel fabrication process of ultrasonic vibration treatment

Copper matrix composites with dual-scale particles were fabricated through casting with reaction. Ultrasonic vibration has been successfully introduced into the melt at about 1523 K while the microstructural development and mechanism of copper matrix composites with high-performance through a novel method of casting with ultrasonic vibration treatment are investigated. When ultrasonic vibration is applied, the distribution of micro-scale particles is greatly improved. Primary Cr phase convents to non-dendrite and large aggregates of ZrB2 particles are disrupted into small clusters because of acoustic cavitation and acoustic streaming. The ultimate tensile strength and elongation of Cu-1wt%Cr-0.3 wt%Zr-1wt%ZrB2 composite in as-cast state were 321 MPa and 14.37 %, recording a 28.4 % and 14 % increment respectively compared with the sample without treatment. After solution treatment, deformation and aging subsequently, the uniform distribution of reinforcements also decreases the average transverse grain thickness and increases the dislocation density which improve the comprehensive properties.

Solving the Annealing of Mo Interconnects for Next‐Gen Integrated Circuits

AbstractRecent surge in demand for computational power combined with strict constraints on energy consumption requires persistent increase in the density of transistors and memory cells in integrated circuits. Metal interconnects in their current form struggle to follow the size downscaling due to materials limitations at the nanoscale, causing severe performance losses. Next‐generation interconnects need new materials, and molybdenum (Mo) is considered the best choice, offering low resistivity, good scalability, and barrierless integration at a low cost. However, it requires annealing at temperatures far exceeding the currently accepted limit. In this work, the challenges of high‐temperature annealing of patterned Mo nanowires are looked into, and a new approach is presented to overcome them. It is demonstrated that while a conventional annealing process improves the average grain size, it can also reduce the cross‐section area, thus increasing the resistivity. Using high‐resolution transmission electron microscopy (TEM) with in situ heating, the evolution of structural features in real time is directly observed. Using insights from these experiments, a cyclic pulsed annealing method is developed, and it is shown that the desired grain structure is achieved in only a few seconds, without forming the surface grooves. These findings can radically facilitate Mo integration, boosting the efficiency of future integrated circuits.

Optimizing fertilization depth to promote yield performance and economic benefit in maize for hybrid seed production

Fertilization depth adjustment is a well-known strategy for increasing crop yields. However, the precise mechanism associated with this strategy remains unclear, particularly regarding increased nutrient absorption and utilization, and maize seed production. Thus, we examined the effects of different nitrogen fertilization depths [0 cm (L0), 5 cm (L5), 15 cm (L15), and 25 cm (L25)] on maize crop growth, nutrient uptake and distribution, fertilizer use efficiency, grain yield, and economic benefits in a field study conducted for two years (2021–2022) in Hexi Oasis Irrigation Area, northwest China. The optimal nitrogen fertilization depth was crucial for enhancing growth, dry matter production, and the grain yield. In particular, compared with L15 and L5, L25 significantly (P < 0.05) increased the average plant height by 5.00 % and 10.36 %, respectively, and dry matter accumulation by 2.65 % and 3.39 %. Furthermore, compared with L5 and L15, the total nutrient uptake was 19.17 % (P < 0.05) and 7.11 % higher under L25, respectively, and the average grain nutrient uptake was 23.33 % higher (P < 0.05). Moreover, L25 significantly increased the N, P, and K fertilizer utilization efficiency compared with L5 and L15, and the highest dry matter to grain translocation occurred under L25. Structural equation modeling confirmed that deep nitrogen fertilization promoted growth, dry matter translocation to grain, and the uptake and distribution of nutrients in maize plants to significantly improve the fertilizer use efficiency and yield. These findings are important for guiding fertilization management practices to increase maize seed production in regions with similar climate conditions.

High cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing

In this work, the high cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing (CFAM) was studied for the first time. The microstructure and fatigue fracture morphology of CFAM sample were characterized by scanning electron microscopy equipped with electron backscattering diffraction. The stress versus number of cycles of failure (S-N) curve for CFAM sample was established, and the fatigue crack growth behavior of CFAM sample was analyzed. The results showed that the microstructure of CFAM sample was denser and more homogeneous compared with cold spray (CS) sample, and the average grain size was refined to 3.3 μm due to dynamic recrystallisation. The dense, homogeneous and fine microstructure delayed the initiation and growth of fatigue cracks, and thus resulted in a 178% increase in fatigue strength in the CFAM sample over CS sample. The fatigue surface of the CFAM sample could be divided into fatigue source zone, crack growth zone, and transient fracture zone, showing typical fatigue fracture characteristics. The fatigue crack growth rate in the CFAM sample was significantly lower than that of CS sample for the same stress intensity factor range (ΔK). This was because the fine grains uniformly distributed in CFAM sample increased the proportion of grain boundaries and hindered the fatigue cracks growth. Therefore, CFAM is a promising technology for preparing bulk 6061 Al with excellent fatigue properties.

Microstructures and dielectric properties analysis of BaTiO3–Bi0.5Na0.5TiO3–Nb2O5–MgO-based dielectric ceramics

9BT1BNTss–x Nb2O5–y MgO ceramics, with a molar ratio of 1: x: y, were synthesized, and their microstructure, bonding, and dielectric properties were analyzed (9BT1BNTss refers to a solid solution containing 0.9 mol BaTiO3 and 0.1 mol Bi0.5Na0.5TiO3). The results showed that all samples sintered at 1200 °C for 2 h exhibited core-shell structures with tetragonal and cubic phases, as well as secondary phases of Ba4Ti13O30 and Ba6Ti14Nb2O39. In this study, all five formulation samples (x = 0.02–0.04; y = 0.005–0.015) had a dense structure, with average grain sizes ranging from approximately 441±19 to 594±79 nm. The dielectric properties of the 9BT1BNTss–0.04 Nb2O5–0.015 MgO sample are as follows: εr = 998 (25 °C) and 1118 (200 °C); tanδ = 1.41% (25 °C) and 33.33% (200 °C); and ΔC/C25°C = 10.98% (TC) and 12.09% (200 °C). These values met the Electronic Industries Association (EIA) X9R specifications.

Controlling the columnar-to-equiaxed transition and crack propagation behavior of laser welded Al–Li alloy reinforced with TiC nanoparticles

The predominant method for improving the mechanical characteristics of aluminum-lithium (Al–Li) alloys during laser welding is by regulating the transition from columnar crystals to equiaxed crystals. The transition is facilitated through the incorporation of TiC particles, which play a crucial role in augmenting the strength and toughness of the aluminum alloy. The inclusion of TiC particles offers a new opportunity to enhance the utilization of Al–Li alloys in laser welding procedures. The main aim of this study is to control the transition from columnar to equiaxed crystal structures by creating a TiC nanoparticle-reinforced aluminum alloy filler wire. This is intended to improve the properties of laser-welded joints. The study investigates the impact of different TiC particle contents on the microstructural characteristics. The presence of TiC particles is noted to enhance the transformation of columnar crystals into equiaxed crystals in the welded joints, resulting in a refined microstructure. The augmentation of particle content results in a notable reduction in the average grain size, decreasing from 78.25 μm to 37.15 μm. This alteration shifts the directional growth preference from specific crystallographic axes to a stochastic trajectory. Significantly, when the particle content reaches 0.6 wt%, remarkable enhancements in both tensile strength and elongation are evident, resulting in an ultimate tensile strength of 318 MPa and an elongation of 4.8 %. The dispersed configuration of TiC particles plays a pivotal role in hindering the movement of dislocations, consequently increasing the energy necessary for this mechanism. Moreover, the existence of these particles at grain boundaries impedes the propagation of cracks by altering the direction of the crack path, absorbing additional energy, and consequently improving toughness. An evident pattern emerges when examining higher particle concentrations, indicating that a decrease in ultimate tensile strength is concomitant with an increase in elongation.

Influence of microstructure evolution and element segregation on high temperature tensile behaviors in GH4706 alloy

This work systematically investigated the influence of microstructure evolution and element segregation on tensile properties and fracture behaviors of GH4706 superalloy under different temperatures (25 °C, 400 °C, 500 °C, 600 °C and 650 °C). The advanced methods of TEM, AES and SIMS were conducted to characterize the variation of microstructure and element distribution. Experimental results showed that the yield and tensile strength of the test alloy decreased while the corresponding elongation increased as the increment of test temperature. The dominated fracture mode was intergranular brittle fracture at the temperature of 25 °C, gradually transforming to ductile dimple fracture as the temperature increased. This phenomenon was determined to be closely related to the increment of average grain size and size of γ'/γ″ coprecipitates as temperature rose. It was worth noticing that the elongation performed abnormally low (16.3%) at the temperature of 500 °C, exhibiting intermediate temperature brittleness (ITB) phenomenon. The SIMS analysis showed that the segregation of S towards grain boundary was the most obvious at the temperature of 500 °C, which was considered as the main factor leading to ITB. In addition, the coarsening of carbides at grain boundaries and local strain non-uniformity caused by dislocations could also resulted in ITB. The main reason for maintaining good strength and plasticity at the temperature of 650 °C was contributed to the softening of γ' phases by repeated cutting of dislocations and deformation twins, reducing the hindrance to the movement of dislocations. Moreover, composite strengthening effect of P and B could improve bonding strength, stabilize grain boundaries, and effectively suppress the initiation of intergranular cracks.

Bimodal grain sized barium titanate dielectrics enabled under the cold sintering process

In barium titanate (BaTiO3) the relative permittivity varies as a function of grain size due to the influence of various sizes and scaling effects. The cold sintering process (CSP) has been applied to sinter nanocrystalline BaTiO3 (<200 nm), however in conventionally sintered BaTiO3 a maximum relative permittivity is achieved at average grain sizes around 0.8 μm. In this work the feasibility of cold sintering 1 μm BaTiO3 inclusions in ratios of fine-grained BaTiO3 matrixes from 50 to 200 nm is investigated. Occurrences of both conformal sintering of inclusions into the matrix and constrained sintering with residual porosity are observed. Subsequently, electrical resistivities increased from 1 × 108 Ω cm to approximately 1 × 1012 Ω cm by a post CSP heat treatment of 500 °C. Relative permittivity of annealed samples increases systematically following a logarithmic mixing law as a function of matrix grain size and increasing the ratio of inclusions to matrix.