Microstructural Observations Research Articles

Feasibility study of an integrated pre‐curing and forming process for 6061 Al alloy and carbon fiber hybrid composites

AbstractThis article proposes a 6061‐T6 Al alloy and carbon fiber hybrid composite material pre‐curing and forming integrated new process, which can significantly reduce the hybrid composite material processing time, improve the production efficiency, and provide the possibility of hybrid composite materials in automotive parts applications. The process started by placing hand‐stacked carbon fiber reinforced plastic (CFRP) composites on the surface of 6061 Al alloy sheets, followed by bonding and pre‐curing of the CFRP to the Al alloy sheets through two different sets of dies in a hydraulic press, and ultimately full curing in an aging furnace. Mechanical properties of the CFRP/Al hybrid composite material were measured by flexural tests. The results show that the flexural strength of CFRP/Al hybrid composites with different layups ([90]12, [0/45/90/−45]3, and [0]12) was increased by 159%, 93.4%, and 67.9%, respectively, compared with the single 6061 Al alloy. According to the macro‐morphological observation, [90]12 lay‐up parts have the least thinning. According to the microstructure observation, no obvious cracks or voids were found in the [90]12 lay‐up parts. Elongated cracks and void defects could be found in the [0]12 lay‐up parts. For the [0/45/90/−45]3 lay‐up parts, voids are mainly exist in ±45°layups. The results of the spring‐back analysis show that the standard deviation of the formed parts obtained from the three lay‐up methods is within 1 mm, indicating that the forming effect is good.Highlights New process improves productivity and reduces production costs The flexural strength of CFRP/Al hybrid parts is greatly improved [90]°12 lay‐up parts have the least thinning and no cracks were found The forming precision of the three lay‐up parts is good

Assessing Modeled Mesoscale Stirring Using Microscale Observations

Abstract We assess the representation of mesoscale stirring in a suite of models against an estimate derived from microstructure data collected during the North Atlantic Tracer Release Experiment (NATRE). We draw heavily from the approximate temperature variance budget framework of Ferrari and Polzin. This framework assumes two sources of temperature variance away from boundaries: first, the vertical stirring of the large-scale mean vertical gradient by small-scale turbulence; and second, the lateral stirring of large-scale mean along-isopycnal gradients by mesoscale eddies. Temperature variance so produced is transformed and on average transferred down scales for ultimate dissipation at the microscale at a rate χ estimated using microstructure observations. Ocean models represent these pathways by a vertical mixing parameterization, and an along-isopycnal lateral mixing parameterization (if needed). We assess the rate of variance production by the latter as a residual from the NATRE dataset and compare against the parameterized representations in a suite of model simulations. We find that variance production due to lateral stirring in a Parallel Ocean Program version 2 (POP2) 1/10° simulation agrees well, to within the estimated error bars, with that inferred from the NATRE estimate. A POP2 1° simulation and the Estimating the Circulation and Climate of the Ocean Version 4 release 4 (ECCOV4r4) simulation appear to dissipate an order of magnitude too much variance by applying a lateral diffusivity, when compared to the NATRE estimate, particularly below 1250 m. The ECCOV4r4-adjusted lateral diffusivities are elevated where the microstructure suggests elevated χ sourced from mesoscale stirring. Such elevated values are absent in other diffusivity estimates suggesting the possibility of compensating errors and caution in interpreting ECCOV4r4’s adjusted lateral diffusivities. Significance Statement We look at whether microstructure turbulence observations can provide a useful metric for judging the fidelity of representation of mesoscale stirring in a suite of models. We focus on the region of the North Atlantic Tracer Release Experiment (NATRE), the site of a major ocean turbulence observation campaign, and use an approximate variance budget framework for the region with observational estimates from Ferrari and Polzin (2005). The approach provides a novel framework to evaluate the approximate representation of mesoscale stirring in a variety of models.

Development of TRIP phenomenon using power refining of retained austenite by niobium

AbstractThe illustrations above demonstrate that as the percentage of niobium increases, the grain size decreases, leading to an increase in the stability of transformation induced plasticity steel. This, in turn, results in improved mechanical strength. The optimal volume fraction of retained austenite for a significant transformation induced plasticity effect to occur is reported to be in the range of 10 vol. %–20 vol. %. The volume fraction of retained austenite directly determines the carbon content and grain size of the retained austenite, its two main stabilization factors. The stability of the retained austenite dictates when the strain‐induced martensite transformation (SIMT) occurs during straining of transformation induced plasticity high strength steel. Unstable retained austenite transforms almost immediately upon deformation, increasing work hardening rate and formability during the stamping process. At the appropriate stability of the retained austenite, the Strain‐Induced Martensite Transformation begins only at strain levels beyond those produced during stamping and forming, and the retained austenite is still present in the final part; it can transform into martensite in the event of a crash, providing greater crash energy absorption. The tensile strength level of micro‐alloyed transformation induced plasticity steels may exceed 1 GPa. Grain refinement mechanism is considered as the most applied mechanism used in increasing of steel strength without deterioration of ductility and toughness. Recently, it was proposed that the grain refinement could act positively on promoting the transformation induced plasticity effect of advanced high strength steel through improving the stability of retained austenite. In this research, quenching and partitioning heat treatment technique was applied to four grades of low carbon steel with different percentage of niobium. Then, the effect of niobium on grain refinement has been detected by microstructure observations. Mechanical properties and strain hardening properties of investigated steel have been determined. In addition, by using x‐ray diffraction, as well as a new electric resistance‐based sensor, it was possible to characterize the stability of the retained austenite through the plastic deformation of steel. Grain refinement by using of niobium has a great impact on promoting the stability of retained austenite against the plastic stress at the plastic deformation zone.

Selection strategy of curing depth for vat photopolymerization 3D printing of Al2O3 ceramics

Vat photopolymerization (VPP) 3D printing technology allows the fabrication of complex ceramic structure components through the layer-by-layer stacking strategy. The curing depth is a crucial parameter for the stacking process, as it directly impacts the printing quality. Furthermore, this parameter exerts a profound effect on the final quality of the printed part. However, there is currently a lack of comprehensive research on how the curing depth affects VPP ceramic 3D printing. This study aims to thoroughly evaluate the impact of curing depth parameters on critical aspects of the 3D printing process, including the forming accuracy, surface quality, monomer conversion, resin pyrolysis, interlayer defects, and mechanical properties. The results of our investigation clearly demonstrate the significant influence of curing depth on the precision and performance of VPP 3D printed ceramic parts. Ceramic samples produced with higher curing depth exhibited superior surface quality (Ra<1.6 μm) but lower forming accuracy. Increasing the curing depth improved interlayer adhesion but excessive depth led to a decreased monomer conversion content from 5.2 % to 2.0 % and an internal stress in the green body. Moreover, increasing the curing depth intensified the pyrolysis process and increased the propensity for cracks forming, as confirmed by simultaneous thermal analysis and microstructure observations. The flexural strength of the sintered samples reached its maximum value of 630 MPa at three times the printing layer thickness. This study provides valuable insights for selecting appropriate curing depth parameters in VPP ceramic 3D printing.

Microstructure and mechanical properties of heterogeneous-gradient composite plates with a sphere-array interlayer prepared using explosive welding

Composite structures with high strength and controllable fragments driven by implosions are valuable in weaponry. This study explored a technical approach to preparing heterogeneous-gradient composite plates with a sphere-array interlayer using explosive welding. TA1 and Q235B steel plates with various spherical grooves were employed as the flyer and base plates, respectively. The spherical grooves were filled with Q235 steel balls. Composite plates were formed by a single explosion using the parallel method, and the parameters adopted in the experiment were within a weldable window. The performance of the TA1/Q235 steel balls/Q235B composite plate was studied through microstructural observations and mechanical property testing. The results indicated that the two embedded spherical structure schemes (with steel balls protruding or not protruding from the plane of the base plate) created effective metallurgical bonding interfaces between the two plates and at the top of the spheres. Surface flatness plays a crucial role in forming wavy interfaces. The composite plates embedded with non-protruding spheres exhibited better mechanical properties, higher interface strength, and a more regular, wavy interface than those embedded with protruding spheres. The ultimate tensile strength of the composite plate containing a sphere with a diameter of 2 mm was similar to that of an intact composite plate. The fracture surfaces of the specimens embedded with spheres exhibited ductile and quasi-cleavage fracturing in the tensile and impact-toughness tests. The structure of the composite plates embedded with non-protruding spheres provides a strategy for preparing multifunctional warhead shells.

Analisa Komparasi Sifat Fisis dan Mekanis Piston Sepeda Motor dari Empat Pabrikan

The piston is an essential component in the internal combustion system. Unfortunately, most piston products on the market are of low quality, which is detrimental to consumers. Most pistons sold in spare parts shops in Medan City have varying prices and different quality. The study compares four manufacturers' chemical composition, microstructure and hardness of the pistons of 4-stroke motorcycles. The four types of pistons were purchased at an automotive component sales shop in Medan city. The pistons were cut by machine and then analyzed for chemical composition, microstructure and hardness. The research results show that the chemical composition of the four-piston manufacturers is almost similar, where the silicon content ranges from 2-3%, which is a hypoeutectic Al-Si aluminium alloy. Interestingly, the hardness values and microstructure of pistons are different. The hardness value for brand X is the highest compared to other products, at 41.16 VHN. Microstructural observations show that the microstructures of manufacturers W, X and Y are similar, where the Si particles are evenly distributed with almost uniform sizes. Meanwhile, the Z manufacturer shows a microstructure with fibrous Si particles with a coarse SDAS size.

Formation mechanism of the microstructural heterogeneity in a die-cast Al-Mg-Si alloy and its effect on mechanical properties

Al-Mg-Si series alloys fabricated by high pressure die casting (HPDC) have a broad application prospect in the production of large-scale and thin-walled die-castings. However, the die-cast Al-Mg-Si series alloys usually exhibit obvious microstructural heterogeneity. This study investigated the microstructural heterogeneity of the die-cast Al-7 Mg-3Si alloy along the thickness direction, and the corresponding formation mechanism was verified. In this study, the die-cast sample can be divided into four distinct regions (R1 ∼ R4) from the surface to the center in turn according to the area fraction of the primary α-Al. Two aspects were considered to be the main reasons for the formation of microstructural heterogeneity. On the one hand, the externally solidified crystals (ESCs) preferentially formed in the shot sleeve and aggregated in the casting center. On the other hand, the cooling rates were quite different in each region, leading to different solidification behaviors. Based on the combination of the microstructural observation and calculated cooling rates, a physical model has been proposed to describe the formation mechanism of the microstructural heterogeneity. The heterogeneous microstructure of the die-cast sample resulted in the inhomogeneity of mechanical properties along the thickness direction. The R2 exhibited the highest micro-hardness than the other regions because of its highest amount of eutectics. Moreover, the casting surface with fine grains (R1) is conducive to improving the EL, whereas the center (R4) showed the lowest tensile properties due to the existence of ESCs and porosity band.

Interface microstructural evolution, microhardness variation mechanism and 750 °C tensile behavior of the HIPed/FGed PM superalloy plastic bonded joints

In present research, a novel 3rd-generation powder metallurgy (PM) superalloys with different initial microstructures (hot isostatic pressed (HIPed) and fine grained (FGed)) were selected for plastic bonding (PB). Non-uniform deformation of the HIPed/FGed PB joint can be obtained due to the significant difference in flow behavior of the studied PM superalloys. Microstructure observation reveals that interface recrystallization dominates the successful healing of bonding interface. The lower dynamic recrystallization (DRX) degree accompanied with higher dislocation density can be detected in HIPed side, manifests that incomplete grain refinement would reduce the efficiency of interface healing and induce the generation of strain gradient at bonding interface. In addition, the microhardness variation of HIPed/FGed PB joint is fully dependent on the interface microstructural evolution. The average microhardness at the bonding interface about 501.0 HV is greatly associated with the neutralization effect of strain hardening from HIPed side and fine grain strengthening from FGed side. Special attention was focused on the fracture behavior and underlying mechanism of the HIPed/FGed PB joint in 750 °C tensile test. Owing to the grain size difference and huge strain gradient, the dislocations pile-up caused by localized stress concentration at bonding interface should be responsible for the brittle fracture of the HIPed/FGed PB joint. The whole process from damage initiation to final fracture includes the microvoids nucleation at grain boundaries, microvoids grow and coalesce into the microcracks, the extending microcracks aggregate to form main crack and then the brittle fracture occurs.

Recovery of dislocation cell structures in 316L stainless steel manufactured by selective laser melting

Understanding the recovery mechanism associated with the dislocation cell structure in 316L austenitic stainless steel produced by selective laser melting (SLM), as well as the role played by the accompanying segregation network, is crucial for tailoring the microstructures and mechanical properties of SLM-prepared components. In the present work, the evolution of the dislocation cells was investigated during isothermal annealing, and a recovery mechanism for the dislocation cell structure was proposed based on a combination of microstructural observations and recovery kinetics analysis. The results show that the high-density dislocations at the cell boundaries annihilate during prolonged annealing at 800 °C, resulting in the decomposition of the dislocation cells. The recovery kinetics analysis reveals that SLM-prepared 316L exhibits a lower recovery rate and requires significantly higher apparent activation energy during annealing compared to conventional 316L deformed by cold rolling. The segregation network plays an important role during the dislocation recovery process, which limits the dislocation reaction occurring within the cell boundaries at the early stage of recovery, impedes the dislocation motion after the decomposition of dislocation cells, and leads to a strong temperature dependence of recovery kinetics in SLM-prepared 316L.

Effect of heat input on the microstructure and hardness of AISI 321 stainless steel welds using ER 347 filler metal

Stainless steel is widely used in various fields, one of which is AISI 321, which is used for high-temperature applications because of its high resistance to creep and intergranular corrosion. The type of filler metal and heat input on stainless steel welds play an essential role in determining the microstructure and mechanical properties of the welded joints. The purpose of this experiment was to evaluate the microstructure and mechanical properties of AISI 321 stainless steel welds with variations in heat input. This study is expected to explore the performance of this weld joint, which can be anticipated in relevant fields. The welding method used in this experiment was Gas Tungsten Arc Welding (GTAW) with ER 347 as filler metal. Welding was carried out on three samples with a heat input of 0.92 kJ/mm, 0.64 kJ/mm, and 0.52 kJ/mm, respectively. The tests included tensile strength, Vickers microhardness, and microstructure observations. The tensile test results showed that a fracture occurred in the Base Metal (BM) area, indicating that the strength of the weld joint was higher than that in the BM. The Vickers microhardness test results showed that the Weld Metal's hardness (WM) was the highest, followed by the Heat-Affected Zone (HAZ) and BM. The welding experiment that used three variations in heat input demonstrated that higher heat input lowered the hardness of the weld joint. The microstructure observation results around the fusion line demonstrated the presence of step and ditch structures. The ditch structure indicates intergranular corrosion.

Sensitization characteristics for type 445 ultra-pure ferritic stainless steel with an electrochemical reactivation method

The sensitization characteristics of type 445 ultra-pure ferritic stainless steel (FSS) under different aging conditions were investigated by the optimized double loop electrochemical potentiodynamic reactivation (DL-EPR) test and microstructure observation. The solution 2 mol L−1 H2SO4 + 0.01 mol L−1 KSCN +0.5 mol L−1 NaCl and a scan rate of 100 mV min−1 are suitable for the DL-EPR test of 445 FSS. With the change of aging temperature from 500 to 900 °C, the degree of sensitization (DOS) slightly increases at first and then decreases, which reaches a maximum value at about 700 °C. Under the aging condition at 700 °C for 10 min to 2 h, the DOS value gradually increases, but it is less than 3% due to the low intergranular corrosion susceptibility. The aging treatment at 700 °C results in the precipitation of Laves phase and (Nb, Ti)(C, N), but no Cr-carbides. The sensitization may be related to the segregation of Cr atoms around (Nb, Ti)-precipitates at the grain boundaries.

Effect of the duplex aging on the phase constitute and antibacterial properties of Ti-13 Nb-13Zr-7Ag

Biomedical titanium alloy Ti-13 Nb-13Zr-7Ag (TNZ-7Ag) has a low elastic modulus, but its antibacterial ability is still not satisfied. In this paper, a duplex aging treatment was applied to TNZ-7Ag alloy to improve the antibacterial properties, and the effects of the duplex aging on the microstructure, antibacterial properties and mechanical properties of TNZ-7Ag were studied, and the corrosion resistance and cytotoxicity were assessed. Microstructure observation indicated that the chemical component segregation appeared in the alloy matrix after the pre-aging at 350℃, and two types of martensite α" phases, namely primary α"M and secondary α"T, appeared in the solute-rich areas. During the subsequent aging at 600℃, α"T promoted the precipitation of Ti2Ag, which enhanced the antibacterial properties. In the solute-poor areas, the spherical α phase precipitated, which significantly improved the ratio of strength-to-modulus. Finally, TNZ-7Ag treated by a duplex aging treatment of 350 ℃/2 h+600 ℃/2 h exhibited an antibacterial rate of 99.9 % and the ratio of strength-to-modulus of 18.59.

Study on the factors affecting the mechanical properties of antler under quasi-static compression.

In the natural environment, antlers have a significant mechanical structure that protects the deer head from injury. In this paper, the mechanical properties of antlers were evaluated through quasi-static compression tests and microstructural observation of samples from antlers, and the relationship between the sampling position, load direction, and microstructure and their mechanical properties were investigated. Compression experiments confirmed that the tines had the strongest mechanical properties, followed by the main beams and finally the brow tines. The mechanical properties of the test specimens subjected to axial compression were higher than those of lateral compression. The axial load test of the longitudinal sample of the tine of the antler has the best mechanical properties. Its specific energy absorption is 51.33 J/g, the peak crushing force is 1.26 kN, and the mean crushing force is 1.47 kN. There are many tubular structures in the transverse sections of antlers, and the distribution of fibers in the vertical direction is laminar with alternating rows forming a helical structure. Tubular structures were found to be prevalent in some of the better biomechanical structures by comparison. Numerical modeling simulations to describe the effect of tubular structures on the mechanical properties of antlers. The simulation results show that the increase in the size of the tubular structure improves its energy absorption within the variation of a 20% increase in the size of the long and short axis. These findings provide a theoretical and experimental basis for the design of energy-absorbing structures. RESEARCH HIGHLIGHTS: In this paper, transverse and longitudinal samples were taken from the main beam, tine, and brow tine of antlers, and axial and lateral compression were carried out, respectively. In this paper, quasi-static compression experiments were carried out on antler samples to study the effects of sampling position, loading direction, and microstructure on antler mechanical properties. By means of microstructure observation and numerical modeling, it is determined that the size of the antler Havel tube has an effect on its mechanical properties.

Effect of Heat Treatment Combined with TG Enzyme Cross-Linking on the Zein-Pea Protein Complex: Physicochemical and Gel Properties.

Plant proteins have the advantages of low cost and high yield, but they are still not comparable to animal proteins in processing due to factors such as gelation and solubility. How to enhance the processing performance of plant proteins by simple and green modification means has become a hot research topic nowadays. Based on the above problems, we studied the effect of gel induction on its properties. In this study, a pea protein-zein complex was prepared by the pH cycle method, and the effects of different induced gel methods on the gel properties of the complex protein were studied. The conclusions are as follows: All three gel induction methods can make the complex protein form a gel system, among which the gel strength of heat treatment and the TG enzyme-inducted group is the highest (372.84 g). Through the observation of the gel microstructure, the gel double network structure disappears and the structure becomes denser, which leads to a stronger water-binding state of the gel sample in the collaborative treatment group. In the simulated digestion experiment, heat treatment and enzyme-induced samples showed the best slow-release effect. This study provides a new method for the preparation of multi-vegetable protein gels and lays a theoretical foundation for their application in food processing.

Effect of Friction Pressure on the Mechanical Properties of CDFW Dissimilar Aluminium 6061-T6 and Stainless steel 304 Welding Joints

Welding technology has significantly developed in the industrial sector along with advances in manufacturing technology. The demand for joining methods combining dissimilar metals is increasing in the industrial sector. However, joining dissimilar metals is challenging because of differences in physical and mechanical properties. Continuous drive friction welding is a solid-state joining method widely used to join dissimilar metals. The research aimed to determine the effect of variations in friction pressure on the mechanical properties of continuous drive friction welding joints with dissimilar materials, Aluminum 6061 T6 and Stainless Steel 304. The process parameters used in this welding were the friction pressures used were 30 MPa, 35 MPa, and 45 MPa. The friction time is 2 seconds, the rotation speed is 1000 rpm, and the upset pressure is 50 MPa. Then, welded joints were evaluated for Vickers microhardness and microstructure observations. Based on the research results, it shows that the temperature distribution and microstructure results show that there is a change in the hardness value of the aluminum material. In contrast, the 304 stainless steel material experiences an insignificant change in the hardness value.

Growth characteristics and SHG properties of Li:SrB4O7

In this paper, high-quality Li:SrB4O7 (LSBO) crystals have been obtained and the distribution of domain structures induced by Li+-doped has a certain regularity. The crystal defects, domain structure morphology and growth characteristics are investigated by X-ray diffraction (XRD), microstructure observation, etc. The results prove that the derivation of domain structure depends on the growth direction of crystal and Li+-doping enhances this result. Further frequency-doubling effect tests show that the as-prepared crystal can realize the frequency-doubling conversion of laser from 532 nm to 266 nm, which provides the ideas and methods for the further development and application of SBO NLO crystals.

A cost-effective dual-layer grain boundary diffusion strategy to significantly enhance coercivity of sintered Nd-Ce-Fe-B magnets

In an attempt to obtain cost-effective sintered Nd-Ce-Fe-B magnet and overcome the coercivity-remanence trade-off challenge caused by heavy rare earth (HRE) diffusion, a novel dual-layer coating method has been proposed for the grain boundary diffusion process (GBDP). A high coercivity increment of 8.56 kOe is achieved by dual-layer coated DyHx/Pr80Al20 (DH/PA) diffusion with 0.8 wt% DyHx and a slight remanence reduction from 12.85 to 12.71 kG. Although the DyHx diffused magnet has a coercivity increment of 9.24 kOe, it consumes twice as much DyHx as the DH/PA diffused magnet at the great sacrifice of remanence. This can be attributed to the formation of continuous grain boundary phase and thin Dy-rich shell via microstructural observations. Further TEM characterization indicates that the amorphous triple junction grain boundary phase (TJP) gradually transforms into the crystalline Nd2O3 structure after GBDP. The coexistence of cubic-Nd2O3 phase and hexagonal-Nd2O3 phase found in the dual-layer coated Pr80Al20/DyHx (PA/DH) diffused magnet creates a more intricate grain boundary phase structure, hindering the diffusion of Dy. Comparably, the formation of single cubic-Nd2O3 (Ia3̅ structure) grain boundary phase in the DH/PA and DyHx diffused magnets is an important reason for the significant increase in coercivity. Based on the evaluation of magnetic performance and cost, the DH/PA diffused magnet achieves a higher price-performance ratio (PPR). This cost-effective bilayer grain boundary diffusion strategy provides a valuable reference for high PPR Nd-Ce-Fe-B magnet fabrication.

Study of the mechanism of the strength-ductility synergy of α-Ti at cryogenic temperature via experiment and atomistic simulation

Alpha titanium (α-Ti) is a promising material for making high-performance components for applications in aerospace, marine, energy and healthcare fields. The excellent strength-ductility synergy has been observed for α-Ti at cryogenic temperature. Twinning is generally considered a key mechanism of outstanding cryogenic ductility. The dislocation-grain boundaries (GBs) interaction and void nucleation usually play crucial roles in the plastic deformation of polycrystalline materials, but their effects on the cryogenic ductility of α-Ti are rarely considered. To eliminate this confusion and gain an in-depth insight into the mechanism of the cryogenic strength-ductility synergy of α-Ti, in this work, a series of characterization experiments and molecular dynamics (MD) simulations were designed and carried out. 1) From uniaxial tension tests of the coarse-grained α-Ti sheets at the temperature from 25 to -180 °C, the uniform elongation and post-necking elongation were increased by 92 % and 20 %, respectively. The material maintained a larger strain hardening rate within a greater range of strain at cryogenic temperature compared with room temperature. 2) Via microstructure and fractography observations and the analysis of slip and geometrically necessary dislocation (GND) activities, the uniform plastic deformation was mainly accomplished by prismatic slip, whether at room temperature or at cryogenic temperature. The significantly increased uniform elongation is mainly attributed to the more uniform distribution of GND pile-ups at cryogenic temperature. 3) The MD simulations revealed that cryogenic temperatures made the GBs present a stronger barrier effect on dislocation transmission compared with that at room temperature, contributing to the more uniform distribution of GNDs and lower densities of GND pile-ups. The GBs at cryogenic temperature show a greater ability to resist void nucleation due to the decreased accumulation rate of excess potential energy and increased energy required to void nucleation. The larger strains were thus required to increase the densities of GND pile-ups to induce large stress concentrations for driving void nucleation. This made the uniform elongation of α-Ti increase significantly at cryogenic temperature. This study revealed that the enhanced barrier effect of GBs on dislocation transmission and the improved ability of GBs to resist void nucleation are key mechanisms besides twinning governing the cryogenic strength-ductility synergy of α-Ti. The understanding developed in this work can be useful for the development of new high-performance materials and the precise forming of complex components with high quality.

Influence of tool geometry on mechanical and microstructural characteristics of friction stir welded cast alloys

Abstract Cast alloys find suitable applicability in aerospace sector owing to low porosity, high specific strength, corrosion resistance, fluidity and good machinability. The investigation focuses on friction stir welding (FSW) of cast A356 and A2014 alloys with varied range of process parameters, namely tool pin shape (cylinder, threaded cylinder, square, and conical), tool rotation speed (1800–2100 rpm) and welding speed (10–25 mm × min−1). Experimentation on stirwelding was performed based on selected tool pin shape between varied tool rotation and welding speed. The output responses, namely Ultimate tensile strength (UTS) and micro hardness, have been evaluated to study the effect of each tool. The microstructural characteristics of the weld samples were analyzed using optical microscope and scanning electron microscope (SEM) technique. The microstructural observation unveiled that complete fusion prevails between the parent alloys devoid of micro porosities and segregations. The re-crystallization effect resulted in the finer grains. The cylinder-shaped tool with a thread and square shaped tool rendered better strength and hardness properties of 136.6 MPa and 109.4 HV, respectively.

Effect of zein-pectin composite particles on the stability and rheological properties of gelatin/hydroxypropyl methylcellulose water-water systems

To improve the compatibility of gelatin (GA) and hydroxypropyl methylcellulose (HPMC), we investigated the effects of zein-pectin composite particles (ZCPs) with various zein/pectin ratios (1:0, 1:0.5, 1:1, 1:1.5, and 1:2) on the physical stability, microstructure, and rheological properties of the GA/HPMC water-water systems. With increasing pectin ratio, the particle size of the composite particles increased from 234.53 ± 1.48 nm to 1111.00 ± 26.91 nm, and their zeta potential decreased from 20.60 mV to below −34.77 mV. Macroscopic and microstructure observations indicated that pectin-modified ZCPs could effectively inhibit phase separation behavior between GA and HPMC. Compared to pure HPMC, the GA/HPMC water-water systems possessed a higher viscosity and dynamic modulus at room temperatures but lower gel temperatures (reduction of about 11 %). The viscosity and modulus of the water-water systems increased with increasing pectin ratio in ZCPs. However, the ratio had no impact on the gel-sol (sol-gel) transition temperatures (not statistically significant (P < 0.05)). This study may serve as a reference for advancing the processability of HPMC.