Hall-Petch Research Articles

Enhanced microstructures, mechanical properties, and machinability of high performance ADC12/SiC composites fabricated through the integration of a master pellet feeding approach and ultrasonication-assisted stir casting

Integrating ceramic particles into aluminum matrices poses significant challenges due to their limited wettability and high specific volume ratio. This research focused on developing ADC12/SiC aluminum composites with varying SiC concentrations (1.5, 2.5, and 3.5 wt%) through an innovative fabrication process. Initially, ADC12/SiC master pellets containing a high concentration of homogenously dispersed 1-μm SiC particles were produced. Subsequently, these master pellets were introduced into the molten ADC12 alloy, followed by the dispersion of SiC particles via stir casting assisted by ultrasonication. The study assessed the impact of SiC weight fractions on the microstructures, mechanical properties, and machinability of the fabricated composites. The results revealed significant microstructural improvements and a more even distribution of SiC reinforcement inside the ADC12 matrix after the application of this innovative processing method. Increased SiC concentration led to notable refinement of α-aluminum grains and eutectic Si, as well as a more uniform dispersion of intermetallic phases. Additionally, a substantial increase in tensile properties and hardness was observed with the increment of SiC content. Particularly, the ADC12/3.5 wt%SiC composite exhibited a 46.73% increase in hardness and notable enhancements in yield strength, ultimate tensile strength, and elongation, denoted as 201.7 MPa, 241.1 MPa, and 3.40%, respectively, as compared with those of the unreinforced ADC12 alloy. Moreover, the ADC12/SiC composites demonstrated reduced surface roughness compared to the unmodified ADC12 alloy, indicative of a superior surface finish. With the addition of a high SiC content, the chip morphology was observed to change from continuous to discontinuous following a turning operation.

Effect of trace niobium on the microstructure and properties of full-pearlite steel used in the high-strength hypereutectoid wire rods

The present study investigated the impact of 20–80 ppm Nb on the microstructure and properties of hypereutectoid pearlite steel. Remarkably, even trace amounts of Nb exhibited a favorable effect on the refinement of austenite grain. The addition of the Nb element resulted in a reduction of pearlite transition temperature, leading to a decrease of approximately 13% in lamellar spacing and 11% in the size of pearlite colonies. Furthermore, the dragging effect of the Nb element on the carbon atoms in hypereutectoid steel facilitated the control and refinement of network carbides. These findings offer valuable theoretical guidance for the production of ultra-high-strength wire rods. When the Nb content reached 80 ppm, it promoted the precipitation of (Ti, V)C, while simultaneously improving the morphology of square carbides. The grain refining strengthening mechanism accounted for about 70% of the overall strengthening effect observed in high carbon wire rods, with the influence of the Nb element primarily targeting grain refinement. Consequently, the incorporation of minute quantities of Nb presents a promising avenue for the development of ultra-high-strength hypereutectoid wire rods, offering significant potential for enhancing their strength properties.

Effect of grain size on tensile behavior and the underlying deformation modes in a Mg-5Y sheet

This work aims to further understand the grain size effects on individual slip/twining activities at grain scale and their correlation with the tensile behavior, for a Mg-5Y sheet with mean grain size range of 3–130 μm, based on slip trace/electron backscatter diffraction (EBSD) analysis. The correlation between tensile yield strength and the corresponding grain size fitted well with the Hall-Petch relationship, i.e., the k value was 191 MPa·μm1/2, with an R2 of 0.96. According to the identified 1004 sets of slip traces in 2477 grains, basal <a> slip was always dominant and tended to increase (from 47.2% to 71.5%) with grain size increased from 3 to 85 μm. Meanwhile, the percentage of pyramidal II <c+a> slip exhibited a marked decline from 34.5% to 8.9%, while that of prismatic <a> and pyramidal I <c+a> slip changed slightly. The decreased pyramidal II <c+a> slip activity was consistent with the decreased tensile yield strength as grain size increased. The twinning activity was limited and insensitive to grain size. In addition, the geometrically necessary dislocation (GND) density was increased with increasing grain size. Based on the slip activity statistics, the critical resolved shear stress (CRSS) ratios were estimated, which exhibited a significant grain size effect. Specifically, CRSSpris/CRSSbas showed negative grain size dependence, while the opposite was true for CRSSpyrIICA/CRSSbas. This study provides valuable grain-scale experimental evidence for the grain size effect on individual slip activity and CRSS ratios, which contributes to a better understanding of the Hall-Petch relationship in Mg-Y alloy.

Intrinsic tensile brittleness of tilted grain boundaries and its shear toughening

In the endeavors of working with microstructures in polycrystalline metals for better strength and ductility, grain boundaries (GBs) are placed at the front burner for their pivotal roles in plastic deformation. Often the mechanical properties of polycrystalline metals are governed by mutual interactions among GBs and dislocations. A thorough comprehension of GB deformation is therefore critical for the design of metals of superb performance. In this research, we investigated the mechanical behavior of symmetric tilt grain boundaries in face-centered cubic (F.C.C.) nickel, which may be subject to tension, shearing, and mixing-mode load using molecular dynamics simulations. We observed that (1) there exist four types of micro deformation mechanisms in GBs, and illustrate at the atomistic scale their distinctions and their dependence on the activation of lattice slip in the crystal; (2) GBs are intrinsically brittle under tension but exhibit ductile behavior during shearing. Shifting from pure tension with increasing shear component during mixing-mode load leads to GB toughening; and (3) there lacks conceivable dependence of GB tensile strength on tilted GBs, in contrast to a relatively rough trend of greater shear strength in GBs of large misorientation. GB energy shows no direct connection with GB strength, as broadly reported in existing literature. This research enhances our mechanistic understanding of GB plasticity in crystalline metals, and points to a potential way of making strong-yet-tough polycrystalline metals through GB engineering: in addition to GB structure manipulation, tuning the loading mode of GBs may open another avenue for their better performance.

Microstructure, mechanical and tribological characteristics of AZ91D-HAp-TiB2 hybrid nanocomposites synthesized through the stir casting route

The aim of this study is to develop a novel magnesium-based nanohybrid composite for potential orthopaedic bioimplant applications. The hybrid nanocomposites were fabricated with AZ91D magnesium alloy as the matrix and hydroxyapatite (HAp) and TiB2 nanoparticles as reinforcements, through the stir casting route. The nanocomposites were synthesized with a fixed concentration of HAp (5 wt%) and different concentrations of TiB2 (2, 4 and 6 wt%). The microstructure of the fabricated composites revealed that the grains are significantly refined with the addition of nanoparticles. The AZ91D-5wt%HAp-2wt%TiB2 hybrid nanocomposite is observed with relatively low porosity, without significant agglomeration of the reinforcement particles, and exhibited the highest tensile and compressive strength with considerably higher ductility than the base AZ91D alloy and the nanocomposites with 4 and 6 wt% TiB2 (about 21% and 34% improvement in compressive and tensile strengths, respectively, compared to the AZ91D alloy). The refinement of grains due to the addition of nanoreinforcements and the alleviation of micro-strain up to a certain extent due to the presence of HAp nanoparticles together with the negligible porosity and agglomeration are the major reasons for the superior strength and ductility. The wear test results showed that the nanocomposite with 2 wt% TiB2 has superior tribological properties. The studies revealed that the AZ91D-5 wt% HAp-2 wt% TiB2 hybrid nanocomposite is a potential material for temporary orthopaedic bioimplants due to its superior strength, ductility, and tribological properties together with the possible enhanced biocompatibility and corrosion resistance due to the presence of HAp particles.

Effect of processing sequences in multi-pass friction stir processing on microstructure, microtexture and microhardness of 6063 aluminum alloy

ABSTRACT Single and double direction stir processing sequences were employed and investigated by fixing all other FSP parameters. Optical microscopy (OM) was utilised to assess the size and geometry of the processed zone. EBSD was also employed to evaluate the microstructure and microtexture development in different regions of the processed zones. In addition, Vickers microhardness measurements were made to evaluate the hardness evolution across the processed zone for the two processing sequences. The results show that using a single direction processing sequence is preferable due to better grain refinement, mainly in all regions of the processed samples. Gradual improvement was observed in microhardness with each additional pass, stronger refinement, and homogeneous grains in the processed regions (stir and overlapping zones). In the first pass’s stir zone (SZ), the microhardness is approximately 42.5Hv, while it increases to an average of 43.4Hv in SZ2 of the second pass and 44.3Hv in SZ3 of the third pass. Furthermore, more resistance to plastic deformation (slip) and lower intensity of heat distribution when compared to the double direction. Therefore, the application of a single direction processing sequence can be beneficial in the welding of such aluminium alloys.

Size-dependent mechanical responses of twinned Nanocrystalline HfNbZrTi refractory high-entropy alloy

Atomistic simulations are performed to study the size-dependent mechanical responses of HfNbZrTi refractory high-entropy alloy (RHEA) containing ultrafine grains and highly oriented twin boundaries (TBs). The strength and flow stress of nanocrystalline RHEA (NC-RHEA) under tensile loadings are explored versus decreasing grain size d. The transition from classical Hall-Petch (HP) strengthening to inverse HP softening at a critical grain size dc = 5.91 nm is attributed to the change of plastic deformation mechanisms from dislocation emission and phase transformation to grain boundary (GB) activities. Besides, the intragranular TBs considerably enhance the strength of nanotwinned RHEA (NT-RHEA); the enhancing effect reduces with decreasing twin thickness λ. As the volume fraction of GB increases with decreasing d, GB activities dominate the plasticity of NT-RHEA and cause comparable mechanical properties with NC-RHEA. Moreover, the influences of dislocation glide, phase transformation and twinning on the mechanical properties of RHEA are quantified and separately analyzed to further verify our simulation results. Findings of this study not only promote insights into the nanostructure-property relation of HfNbZrTi, but also shed the light on performance enhancement through nanostructural design.

Evolution of NbC during laser welding and its impacts on the performance of molybdenum alloy joint

Influences of addition of niobium carbide (NbC) in the fusion zone (FZ) on room-temperature and high-temperature mechanical properties of laser-welded joints of molybdenum (Mo) alloys were studied. Results show that after adding NbC powder, the average Vickers microhardness in the upper part of the FZ increases from 183.0 HV to 712.3 HV; the room-temperature tensile strength grows from 33.9 MPa to 323.1 MPa, reaching 45.4 % that of base metal (BM). In addition, the fracture mode of joints turns from intergranular fractures into transgranular fracture; at 1100 °C, the high-temperature tensile strength of joints added with NbC is 141.6 MPa, which is 65.9 % that of BM. Energy dispersive spectrometer (EDS) and electron backscattered diffraction (EBSD) results show that after adding NbC powder, the average grain size in the FZ diminishes from 40.3 μm to 32.9 μm, where the number of low-angle grain boundaries (LAGBs) increases; the FZ not only contains NbC phase but also a large quantity of Nb2O5 and Mo2C phases dispersed on grain boundaries (GBs), and the number of MoO2 phase on GBs decreases apparently. Therefore, physical mechanisms underlying significant improvement of room-temperature and high-temperature tensile strengths of laser-welded joints of Mo alloys added with NbC in the FZ mainly include fine-grain strengthening, GB purification, and GB strengthening.

Promoting grain refinement and nanocrystal generation in surface nanomachining by means of overlapping collisions

Surface nanostructuring effectively improves the mechanical properties and wear resistance of the moving parts, yet a thorough understanding of its formation mechanism remains elusive. This study examined the microstructure evolution of pure copper under various linear overlapping ratios (φ) using a self-made impact wear tester. The results revealed that high Smid factor grains activate the basal slip system to handle deformation during repeated impacts. Still, overlapping impacts can intensify plastic deformation by activating multiple slip systems and boosting dislocation proliferation. Moreover, overlapping collisions will generate Frank's incomplete dislocations, hindering dislocation slip and generating cross slip trajectories, resulting in the bending of slip-trajectories, the formation of uneven wrinkles, and the refinement of superficial grains.

Influence of spatial position of sound source on dual-frequency ultrasound-assisted preparation of magnesium alloy

In this work, a dual-frequency ultrasonic field was employed to improve the quality and mechanical properties of magnesium alloy ZW61 ingot. The effect of the spatial position of the sound source on the cavitation volume, microstructure size, and morphology was discussed in detail combined with numerical simulations and experiments. The mechanical properties were analyzed elaborately and the relationship between yield strength (YS), ultimate tensile strength (UTS), and average grain size (d) was established. The results showed that the dual-frequency ultrasonic field (DUF) had a larger cavitation range and superior grain refinement ability than the single-frequency ultrasonic field (SUF) at the same energy consumption, with the grain refining from 578 μm (untreated) and 395–433 μm (SUF) to 55.2 μm. The grain refining effect of DUF weakened with increasing sound source spacing, with d increasing from 55.2 μm to 163 μm. The radiating angle had little effect on the grain size. Too shallow or too deep inserting depth of the ultrasonic rods could seriously weaken the grain refinement. In this case, 30 mm source spacing, 60° radiating angle, and 30 mm inserting depth were the optimal process parameter combinations, and the ingot strength was increased from YS of 83 MPa and UTS of 151 MPa to 138 MPa and 241 MPa, respectively. YS and d for all conditions conformed to the Hall-Petch relationship, with σ0 and k values of 71.3 MPa and 503.9 MPa μm−1/2. The relationship between UTS and d could be expressed as UTS = 126.7 + 907.0 d−1/2.

Slip to twinning to slip transition in polycrystalline BCC-Fe: Effect of grain size

A slip-to-twinning-to-slip transition concerning grain size has not been reported in the literature on BCC-Fe so far. In the present investigation, we report slip-to-twinning and twinning-to-slip transitions at 8 nm and 20 nm grain sizes, respectively. For this purpose, we used molecular dynamics simulations to study ⟨110⟩ quasi-3D polycrystals of BCC-Fe with grain sizes ranging from 3 nm to 102 nm at 10 K. Hall-Petch and inverse Hall-Petch relations were obtained depending on the grain size. Grain boundaries (GBs) were converted to lower energy boundaries through twin-GB interactions. Nucleation of twin boundary through GB decomposition was observed even under the constraints of triple junctions. Various dislocation mechanisms were observed, like delayed slip transfer, slip absorption, dislocations from a twin boundary, and formation of debris/point defects/tubular-type cylindrical rods from the gliding dislocations. Dislocation activity was observed to increase with increasing grain size. Luster and Morris parameter was used to understand dislocation-GB interactions. Intergranular fracture was observed.

Driving forces of solid-state Cu-to-Cu direct bonding suppressing the work-hardening loss by refill friction stir spot welding

In this study, the solid-state bonding of the Cu-to-Cu parallel connection with no fusion zone and keyhole formation was achieved using the refill friction stir spot welding (RFSSW) process. During the refilling process, significant plastic flow and thermo-compressive behavior promoted geometric and continuous dynamic recrystallization behaviors and highly oriented (111) microstructures, serving as key mechanisms to prevent work-hardening loss and reinforce the joint. Furthermore, the refinement of the grain size without work-hardening loss, increased by 50.8 % which was from 61 Hv in the base material to 92 Hv in the thermo-mechanically affected zone (TMAZ). Even, the hardness of the TMAZ/stir zone interface noticeably increased up to 138 Hv as the reduction in the stacking fault energy (SFE) due to the infiltration of Al element at the trace from the tool. The contribution of microstructural features to the mechanical property was quantitatively investigated by a modified Hall-Petch relationship in terms of the grain size, sub-grain size, and dislocation density. This study systematically investigated the driving forces for the implementation of Cu-to-Cu direct bonding, where work-hardening loss can be suppressed, through the RFSSW process from the perspective of dynamic recrystallization behavior and SFE due to partial alloying of Al elements.

Hot compression recrystallization and processing characteristics of 18 %Cr lean duplex stainless steel with Mn addition

The deformation differences of hot compression tests for 18 % Cr lean duplex stainless steels, alloyed with 3.1 and 5.8 wt% Mn concentrations were comparatively investigated. The deformed microstructure revealed that more Mn promoted the formation of austenitic dislocation cells, inhibited the occurrence of dynamic recrystallization (DRX), and resulted in a decrease in the number of refined austenite grains at lower temperatures and strain rates. Meanwhile, more Mn addition promoted ferrite DRX, and delayed austenite DRX initiation deformed at higher strain rates and lower deformation temperatures. The nearly complete refinement of austenite grains formed due to DRX deformation at 950℃/0.01 s−1 with 3.1 % Mn addition, while fine grains caused by ferrite DRX mainly occurred at 850℃/1 s−1 with 5.8 wt% Mn addition. The relationships between the Zener–Hollomon parameter (Z) and critical strain (stress) were established using the power law relation. The stability processing domains with high power efficiency greater than 0.34 narrowed with increasing Mn content, are located in the temperature range of 1000–1150℃ and strain rate range of 0.01–0.03 s−1, and austenite DRX plays a significant role in compression deformation improvement. At a low deformation temperature of 850 ℃, the work hardening rate in the initial strain increased with increasing Mn addition, and a lower strain rate and deformation temperature contributed to the dynamic deformation softening caused by austenite DRX, but ferrite DRX slightly contributed to the improvement of compression deformation. The DRX kinetics models show that the trend of the volume fraction of DRX as a function of processing variables is in good agreement with experimental data.

Correlation of austenite grain size with ε-/α′-martensitic transformation and mechanical properties in a high-manganese damping steel

One of the core studies on low stacking fault energy (SFE) high-manganese steel is to maintain excellent damping capacity while achieving high strength and toughness. The austenite grain size (AGS) in high-Mn steel affects its SFE and even the strength-plasticity and damping capacity of the steel, but the detailed mechanism related to martensitic transformation has not been clarified. In this study, Fe-17Mn high-Mn damping steel is used as the material to obtain austenite grains of different sizes by controlling the cold rolling and annealing processes. By using in-situ tensile testing, damping capacity testing, and various microscopic analytical techniques, the influence of AGS on the thermal/deformation induced martensitic transformation, work hardening behavior, mechanical properties and damping capacity of the steel is mainly studied. The results indicate that the refinement of austenite grain increases the SFE of high-Mn damping steel and reduces the amount of thermal induced ε-martensite (εth) and stacking faults (SFs). The deformation induced martensitic transformations (DIMTs) in high-Mn damping steel during tensile deformation include γ→εD, εth→α′ and εD→α′ transformation. The deformation induced ε-martensitic transformation is more helpful to improve the work hardening rate than deformation induced α′-martensitic transformation. Due to the concentration of strain partitioning at grain boundaries, twin boundaries and phase boundaries, refinement of austenite grain can promote deformation induced ε-martensitic transformation and improve the steel strength. However, excessively small austenite grains can suppress deformation induced α′-martensitic transformation leading to a significant decrease in elongation. Under the synergetic effects of grain refinement strengthening and multiple martensitic transformations, when the average AGS is about 4.0 μm, the steel has high strength and high plasticity, with a tensile strength of 919 MPa, a yield strength of 518 MPa and an elongation of 46.4 %. The product of tensile strength and elongation is up to 42.6 GPa·%. At low or high strain amplitudes, the damping capacity of this steel shows an opposite trend with the refinement of AGS. The damping capacity of the steel gradually increases with grain refinement at low strain amplitudes of 0.01 %–0.065 %, mainly due to the reduction of the content of weak pinning points. At high strain amplitudes of 0.065 %–0.1 %, the damping capacity of the steel gradually decreases for the reduction of damping sources with the refinement of grain size.

Size-dependent deformation mechanisms in two-phase γ-TiAl/α2-Ti3Al alloys

Polysynthetic twinned (PST) TiAl single crystals, consisting of alternating layers of γ-TiAl and α2-Ti3Al, exhibit excellent mechanical properties. However, size-dependent deformation mechanisms have not yet been fully elucidated. In this work, we investigated the deformation process of two-phase γ-TiAl/α2-Ti3Al alloys with different layered sizes via uniaxial tensile loading using molecular dynamics simulations. The results show that with the decreasing phase boundary (PB) spacing λ or domain boundary (DB) spacing d, the excess free volume at the intersection of DB and PB decreases, leading to increased yield stress. We found that a higher interface density (smaller λ or d) can accommodate more dislocations, and the size-dependent ultimate strength follows an approximate Hall-Petch relation. These findings offer an essential understanding for the size-dependent PST TiAl single crystals with high strength.

Precipitation behavior and strengthening mechanism in a Cu-3.5Ti-0.1 Tm alloy

The study investigates the complex relationship between precipitation patterns, microstructural evolution, and mechanical properties in a Cu-3.5Ti-0.1 Tm alloy subjected to isothermal ageing. The results reveal that ageing at 450 °C leads to the formation of nanoscale β′-Cu4Ti phase particles within the grains and fibrous β-Cu4Ti precipitates along the grain boundaries. The precipitation microstructure of this aged alloy is predominantly characterised by tetragonal β′-Cu4Ti precipitates. During spinodal decomposition, Ti atoms segregate in rod-like Ti-rich Cu phases, facilitating their conversion into β′-Cu4Ti phase. The β′-Cu4Ti precipitates remain fully coherent with the Cu matrix, exhibiting a crystallographic orientation relationship of (001)Cu//(001)β′ and [100]Cu//[130]β′. As the precipitate radius exceeds approximately 11 nm, the elastic strain energy surpasses the energy at the precipitate/matrix interface. This leads to a shape transition from spherical to cuboidal for the β′-Cu4Ti precipitates. Moreover, the Ti solute atoms contribute significantly to the alloy's strength through solid solution hardening, with the dissolution of 1 at.% Ti solute increases the yield strength by 46.2 MPa. However, as ageing progresses from 1 to 20 h, the effect of solid solution strengthening decreases, while precipitation strengthening becomes more dominant, mainly due to the Orowan bypass mechanism. After 20 h of ageing, precipitation strengthening significantly increases the yield strength by about 436 MPa, exceeding the contributions from solid solution strengthening (78 MPa) and grain-boundary strengthening (14 MPa).

Influence of grain size and grain edge phase on the flexural strength of aluminum nitride ceramics with Y2O3 sintering additive

The necessity for efficient heat dissipation compels AlN packaging materials towards a thinner profile. In response to the ensuing concerns regarding the reliability of strength, the effects of the grain edge phases and grain size on flexural strength are investigated in this study. Different preparation processes, including (hot-pressed sintering, pressureless sintering, and annealing) are employed to prepare AlN ceramics with different grain edge phases and grain sizes. After classifying the morphology of the grain edge phases and fitting the Hall-Petch relationship, it is found that the grain edge phases had a more significant influence on the flexural strength. Depending on the morphology, the negative effects can be divided into three degrees. While the finer grain size proves advantageous for the flexural strength. Consequently, in the non-additive system, the flexural strength of AlN ceramic is 422 MPa, with an average grain size of 8.47 μm. For the additive-doped system, the maximum flexural strength can reach 532 MPa, which can be attributed to the limited average grain size resulting from the hot-pressed sintering process, approximately 1.32 μm. These results could potentially be employed in the microstructural design of high-strength AlN ceramics.

Effect of grain size, temperature, and tensile strain rate on mechanical response of CoCrNi medium-entropy alloys

Grain boundary (GB) strengthening of metallic materials faces limitations as grain sizes are reduced to the nanoscale, primarily due to the transition from the strengthening to the softening effects. Understanding the intrinsic mechanisms behind such pronounced transitions is essential for optimizing the mechanical properties of nanocrystalline (NC) alloys. In this work, the critical grain size responsible for this transition is determined for NC CoCrNi medium-entropy alloys using molecular dynamics simulation, and the underlying mechanisms concerning varying temperatures and strain rates are systematically investigated for the samples with the critical grain size. The transition from Hall-Petch (HP) strengthening to Inverse Hall-Petch (IHP) softening is established by decreasing the average grain sizes from 21 nm to 3 nm. The critical grain size for the current alloys is estimated to be 12 nm, and the underlying deformation mechanisms are illustrated as follows: In the IHP regime, GB-mediated deformation becomes dominant, leading to softening. Conversely, in the HP regime, dislocation slip dominates the deformation mode, contributing to strengthening. It is found that an increase in temperature from 77 K to 1100 K leads to a decrease in the average flow stress and Young's modulus. Meanwhile, the deformation mechanisms change from dislocation slip (77K–700K) to GB-mediated deformation (700 K–1100 K). Furthermore, the underlying mechanisms correlating to the critical strain rate are uncovered. It can be attributed to the shift in deformation mechanisms from dislocation slip at relatively low strain rate regimes (5 × 107 s−1-2 × 109 s−1) to dislocation drag at relatively high strain rate regimes (2 × 109 s−1-5 × 109 s−1). Our atomistic insights into the tensile response of NC CoCrNi may provide a crucial basis for designing superior properties to meet the growing demands of advanced engineering fields.

Effect of APMImBr ionic liquid on the migration of silver in copper electrorefining

As the grade of copper concentrate decreases and its composition becomes increasingly complex, the silver content in the anode plate casting after fire refining increases. This leads to a high silver content in the copper cathode during electrorefining and a substantial loss of precious metals. This study investigated the effect of 1-aminopropyl-3-methylimidazolium bromide (APMImBr) ionic liquid on the migration of silver during high-silver anode plate electrorefining. The results show that APMImBr is adsorbed on the anode surface by reacting with Ag+ released from the anode to form AgBr precipitates, thereby preventing Ag+ ions from entering the electrolyte. Simultaneously, agglomerates of fine Ag–Se compounds and AgBr particles form, resulting in anode slime particles that are sufficiently large to settle quickly to the bottom of the cell, thus inhibiting fine silver-containing particles from adhering to the cathode. Furthermore, APMImBr adsorbs onto the cathode surface, forming CuBr intermediates and inhibiting Cu2+ electrodeposition. This facilitates the refinement of the surface grains and flattens the copper cathode surface. The Ag content of the cathode decreased continuously as the concentration of APMImBr increased. The Ag content of the cathode decreased by 41.67% from 6.0 ppm (no additives) to 3.5 ppm upon the addition of the optimal concentration of 300 mg/L of APMImBr.

Effect of aging temperatures on the microstructure and mechanical properties of TC21 forgings with basket–weave microstructure

This study aims to explore the influence of various aging temperatures on the microstructure and mechanical properties of TC21 forgings. Basket-weave microstructures were prepared via quasi-β forging followed by annealed at 900 °C for 1.5 h and aged at 530 °C, 560 °C, and 590 °C for 4 h, and then their tensile performance, impact toughness, and fracture toughness were examined. Results indicate that higher aging temperatures not only facilitate the segregation of Al element, resulting in a reduction in the effective size (dαlaths, the width/length ratio) of primary α laths (αlaths) and their amount, but also promote phase transition, inducing an increase in the effective size (dαfine) of secondary fine α (αfine) lamellae. While both dαlaths−1/2 and dαfine−1/2 have a linear relationship with the strength, which was analyzed using the Hall–Petch relationship, the more pronounced interface strengthening effect and hindering crack propagation mainly results from the αlaths. Moreover, the plasticity declines significantly as the proportion of the αlaths phases decreases. Thus, for strength and plasticity, the αlaths are a much more important factor than the αfine lamellae. However, although the synergistic deformation and fracture of both the αlaths and αfine phases can consume a larger impact initiation energy, the enhancement of the impact energy of the alloy is primarily related to a high precipitation amount of the αfine lamellae. Furthermore, the decrease in dαlaths promotes the misorientation and accumulation of dislocations between αlaths interfaces, hindering the enhancement of KIC (fracture toughness) by forming transgranular fractures. Conversely, the increase in KIC attributed to the energy consumed in the plastic deformation region at the crack tip, due to the αfine lamellae compensates for the energy, resulting in a reduction in the crack propagation path. Therefore, the αfine lamellae may play a more crucial role in increasing the toughness of alloys, in particular the impact toughness of the TC21 alloy.