Reduction Of Dislocation Density Research Articles

Exploring popped-out phenomena in large-scale silicon ingot growth

Silicon wafers are essential for the semiconductor industry, providing the foundation for most integrated circuits. As demand for microelectronics grows, larger silicon wafers, have become crucial for increasing chip production and reducing manufacturing costs. However, the crystal separation phase during Czochralski (CZ) ingot growth is particularly challenging for larger ingots, often resulting in defects due to premature detachment (“popped-out” tails). This study investigates the popping-out stage of 18-inch ingots under varying heater power and ingot pull-out speed conditions. Photoluminescence (PL) imaging and a convolutional neural network (CNN) were used to analyze dislocation density in the silicon wafers. Results show that increasing the pull-out speed after detachment can significantly increase dislocation density, while pausing the ingot near the melt surface minimizes dislocations. Additionally, increasing heater power after detachment reduces dislocation density. The optimal condition for minimizing dislocation was found when heater power was doubled, and the ingot was paused near the melt surface for 30 min.

The Annealing Temperature Effect Enhances the Structural and Optical Parameters of Bi2Te3 Thermally Evaporated Thin Films

The current work investigates the influence of the annealing temperature (373, 473 K) on the structural and optical properties of Bi2Te3 thin films produced by the thermal evaporation technique. The crystal structure of samples is examined using an X-ray diffraction, indicating that Bi2Te3 thin films have a Rhombohedral structure with space group R-3m. The crystallite size (D) increased from 10.85 to 14.46 nm by increasing the annealing temperature. Additionally, increasing the annealing temperature reduces the micro-strain and the dislocation density from (3.33 × 10−3 to 2.5 × 10−3) and (8.49 × 1015 to 4.78 × 1015) Lines / m 2 , respectively. These micro-strain and dislocation density reductions refer to the crystallinity enhancement of sample Bi2Te3 thin films. The transmittance and reflectance spectra were measured using an Fourier transform infrared spectrometer. All samples reveal direct and indirect transition types and both direct and indirect optical energy gap decreased with increased annealing temperature from (0.325 to 0.29 eV) and (0.24 to 0.274 eV), respectively. From transmittance and reflectance data, the refractive index is calculated. These results reveal the refractive index decreasing as temperature annealing increased from (2.45–1.79) at 3250 nm. Other optical parameters such as absorption index, dielectric constant, energy loss function, and optical conductivity were estimated.

Investigation of the Softening Resistance Behavior and Its Mechanism in Cu-Ni-Si Alloys with Discontinuous Precipitates.

In this study, isothermal annealing experiments were conducted on copper-nickel-silicon alloys containing continuous precipitates (CP) and discontinuous precipitates (DP) to investigate the effects of different types of precipitate phases on the microstructural evolution and softening temperature during annealing, as well as to analyze the differences in softening mechanisms. The experimental results revealed that the softening temperature of the CP alloy, subjected to 75% cold deformation, was 505 °C. In contrast, the DP alloy achieved softening temperatures of 575 °C and 515 °C after 75% and 97.5% cold deformation, respectively. This indicates that the DP alloy exhibits significantly superior softening resistance compared to the CP alloy, attributed to the distinct softening mechanisms of the two alloys. In the CP alloy, softening is primarily influenced by factors such as the coarsening of the precipitate phase, the occurrence of recrystallization, and the reduction in dislocation density. In the DP alloy, the balling phenomenon of the DP phase is more pronounced, and its unique microstructure exerts a stronger hindrance to dislocation and grain boundary motion. This hindrance effect reduces the extent of recrystallization and results in a smaller decrease in dislocation density. In summary, the DP alloy, due to its unique microstructure and softening mechanisms, demonstrates better softening resistance, providing higher durability and stability for high-temperature applications.

Study of the effect of SMAW welding speed on the microstructure and crystal stability of X70 steel using X-ray diffraction

This study investigates the impact of manual electric arc welding (SMAW) speed on the microstructure of X70 steel. Welding was performed at two distinct speeds: S1 = 20 mm/min and S2 = 35 mm/min, at the COSIDER BISKRA workshop in Algeria. X-ray diffraction (XRD) analysis was conducted on the welded zones to examine crystal orientation, size, dislocation density, and structural stability across different welding areas, including the base metal (MB), heat-affected zones (HAZ1 and HAZ2), and weld zones (WZ1 and WZ2). The XRD results revealed that key crystal peaks, such as {110} and {200}, retained their positions at both welding speeds, though variations in {110} peak intensity were noted. The lower welding speed (S1) resulted in a higher heat input, which enhanced crystal stability, increased crystal size, and reduced dislocation density. On the other hand, the higher speed (S2) produced lower heat input, leading to smaller crystal sizes, increased residual stresses, and a greater number of defects due to rapid cooling. These findings underscore the critical influence of welding speed on heat input, cooling rates, and their consequent effects on microstructure. The study highlights the importance of optimizing welding parameters to balance microstructural integrity, mechanical performance, and production efficiency.

Effect of Tempering Temperature on the Aqueous Corrosion Resistance of 9Cr Series Heat-Resistant Steel

In this investigation, the aqueous corrosion resistance of 9Cr series heat-resistant steel during tempering was investigated. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometer (EDS) were used to analyze the effect of tempering temperature on the microstructure and precipitation behavior of precipitates. The heat-resisting steel was heated to 1150 °C for 1 h, and then tempered at different temperatures between 680 °C and 760 °C for 2 h. The microstructure of the heat-resistant steel after tempering was composed of lath-tempered martensite and fine precipitates. The hardness decreased with increasing tempering temperature, ranging from HBW 261 to HBW 193. The aqueous corrosion resistance improved as the tempering temperatures increased from 680 °C to 720 °C but deteriorated at higher temperatures, such as 760 °C, which was obtained by an electrochemical corrosion performance test. The aqueous corrosion resistance was affected by the decrease in dislocation density and the decrease in Cr solution in the tempered martensite. With the increase in the tempering temperature, the aqueous corrosion potential first increases and then decreases, the self-corrosion current density first decreases and then increases, and the polarization resistance first increases and then decreases. Furthermore, the increase in corrosion resistance is attributed to the reduction in dislocation density and chromium depletion in the martensitic structure as the tempering temperature approaches 720 °C. This paper reveals the effect of tempering temperature on the corrosion resistance of 9Cr series heat-resistant steel, which is a further exploration of a known phenomenon.

Towards Strength–Ductility Synergy in Cold Spray for Manufacturing and Repair Application: A Review

Cold spray is a solid-state additive manufacturing technology and has significant potential in component fabrication and structural repair. However, the unfavourable strength–ductility synergy in cold spray due to the high work hardening, porosity and insufficient bonding strength makes it an obstacle for real application. In recent years, several methods have been proposed to improve the quality of the cold-sprayed deposits, and to achieve a balance between strength and ductility. According to the mechanism of how these methods work to enhance metallurgical bonding, decrease porosity and reduce dislocation densities, they can be divided into four groups: (i) thermal methods, (ii) mechanical methods, (iii) thermal–mechanical methods and (iv) optimisation of microstructure morphology. A comprehensive review of the strengthening mechanism, microstructure and mechanical properties of cold-sprayed deposits by these methods is conducted. The challenges towards strength–ductility synergy of cold-sprayed deposits are summarised. The possible research directions based on authors’ research experience are also proposed. This review article aims to help researchers and engineers understand the strengths and weaknesses of existing methods and provide pointers to develop new technologies that are easily adopted to improve the strength–ductility synergy of cold-sprayed deposits for real application.

Microstructure evolution and deformation mechanisms of service-exposed P91 steel via interrupted uniaxial creep tests at 660 °C

Creep degradation behaviour of service-exposed P91 steel is evaluated during interrupted creep tests at 660 °C and 80 MPa using a number of material characterization techniques including transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), energy dispersive spectroscopy (EDS) and optical microscopy (OM) to identify the microstructural evolution and the associated deformation mechanisms. Microhardness has also been measured in order to evaluate the softening mechanism. Under the creep conditions examined, microstructural degradation is found to be governed by the disappearance of the lath sub-structure, lath widening and recrystallization, as well as dislocation density reduction, coarsening of M23C6 and creep cavitation while MX and Laves phases are stable. Hardness evolution, extrapolated from hardness data obtained from uniaxial creep tests, is used to characterize the softening of the material. On this basis, hardness decrease is justified in term of the aforementioned microstructural changes. Implications of the findings for specific in-service life management in thermal plant piping systems are addressed.

Effect of trace grain boundary segregation element bismuth on stress relaxation behavior of copper

The stress relaxation resistance of copper-based materials determines the reliability of contact and stable transmission of connector plugs. This study investigates the effect of trace bismuth (110 wt ppm) on the stress relaxation resistance of pure copper at temperatures of 25 °C, 100 °C, and 200 °C. The relationship between microstructure and stress relaxation resistance was analyzed using SEM, EBSD, and HAADF-STEM. The results demonstrate that trace bismuth significantly enhances the stress relaxation resistance of pure copper, especially at higher temperatures of 100 °C and 200 °C, where the stress relaxation rates of Cu-0.011Bi samples after 48 h decreased by 21.36 % and 18.06 %, respectively, compared to Cu samples. Trace bismuth elements exist in copper mainly in the form of double atomic layers segregated at grain boundaries, which pin the grain boundaries, inhibit grain growth, and hinder dislocation slip. At room temperature (25 °C), bismuth mainly improves stress relaxation resistance by refining grains. At higher temperatures of 100 °C and 200 °C, the significant enhancement in stress relaxation resistance is primarily related to bismuth's inhibition of the reduction in dislocation density and recrystallization during the stress relaxation process.

Deformation and microregion fracture mechanisms in type 316L welded joint under isothermal and thermo-mechanical fatigue loadings

Isothermal (IF) and thermo-mechanical fatigue (TMF) tests were conducted on 316L welded joints to investigate the effects of phase angle (in-phase (IP), clockwise-diamond (CD), and out-of-phase (OP)) and mechanical strain amplitude (±0.4 %, ±0.5 %, ±0.6 %) on deformation and microregion fracture mechanisms. Results reveal that increasing strain amplitude induces a higher softening rate, reduced fatigue life, and more pronounced dynamic strain aging (DSA). Nevertheless, there is a complicated discrepancy in the cyclic deformation between various phase angles. At high strain amplitudes, local embrittlement along the austenite/δ-ferrite interface induces cracking in the weld metal (WM) under both IF and TMF loadings, with TMF life increasing with phase angle. At a lower strain amplitude of 0.4 %, however, fracture location migration and different TMF life were observed. Microstructural analysis reveals that during TMF a lower strain amplitude of 0.4 %, the microstructure in both base metal (BM) and WM evolves from simple planar structures to low-energy substructures, characterized by an increase in kernel average misorientation, geometrically necessary dislocations, and low-angle grain boundaries, together with a reduction in high-angle grain boundaries and twin boundaries. In the WM, increasing phase angle tends to reduce dislocation density and reproduces planar dislocation structures due to enhanced DSA, thereby lowering cellular structure maturity. Conversely, in the BM, dislocation proliferation and interaction intensify, enhancing cellular structure maturity and de-twinning effect, which reduces BM fracture resistance and causes fracture migration from the WM to the BM. Moreover, active DSA under CD loading improves deformation resistance in both microregions, prolonging fatigue life and contributing to the observed different TMF life.

Mechanical characterization of nanocrystalline Cu-Ag alloys subjected to shear deformation

ABSTRACT This study investigates the mechanical behaviour of nanocrystalline Cu-Ag alloys using molecular dynamics simulations combined with detailed analyses of dislocation densities, atomic populations, and deformation characteristics. Shear tests were conducted across three different atomic compositions at temperatures ranging from 10 K to 500 K. The influence of temperature and Ag impurities on the mechanical properties of nanocrystalline Cu is explored. Elevated temperatures are found to promote plastic deformation by increasing atomic mobility, resulting in reduced dislocation densities and flow stresses. Increasing Ag content correlates with lower dislocation densities, highlighting enhanced plastic activity between grain and grain boundaries. Structural population analysis underscores the significant impact of Ag species on the mechanical response of nanocrystalline Cu. Further investigations are warranted to explore additional deformation mechanisms. These findings contribute to a deeper understanding of nanocrystalline Cu-Ag alloys, informing the design of novel materials with tailored mechanical properties.

Breaking strength-plasticity trade-off in heterostructure CrFeNiAl0.28Si0.09Ti0.02Cu0.01 high entropy alloy by heat-treatment-induced nano-precipitation

In this study, heat treatment was employed to enhance the mechanical properties of an as-cast CrFeNiAl0.28Si0.09Ti0.02Cu0.01 high entropy alloy (HEA) with the heterostructure consisting of face-centered cubic (FCC), body-centered cubic (BCC) and B2 phases. It was observed that, after heat treatment at 873 K for 1 h followed by water-quenching, well-dispersed L12 and L21 nano-precipitates could be formed in FCC phase and BCC phase of this as-cast HEA, respectively. Furthermore, it is worth noting that despite a noticeable reduction in dislocation density, this heat treatment process significantly enhances yield strength, ultimate tensile strength, plasticity and hardness simultaneously, which could be attributed to the formation of nano-scale precipitates mentioned above. These findings provide a novel approach for fabricating high-performance HEAs by introducing complex multi-level heterogeneity.

Microstructure and mechanical properties of a low-alloyed Mg–Zn–Al–Ca alloy: Effect of extrusion speed

A low-alloyed Mg-1.2Zn-0.6Al-0.1Ca (wt.%) alloy was extruded at 200 °C with different ram speeds (0.5–4.0 mm/s), and the microstructure and mechanical properties were studied systematically. Heterostructures with fine dynamic recrystallized (DRXed) grains and coarse unDRXed grains were achieved at lower ram speeds of 0.5 mm/s and 1.0 mm/s, and fully-DRXed microstructure was attained at 4.0 mm/s. Increasing the extrusion speed resulted in an increase in DRXed grain size from 0.9 μm to 3.8 μm, and a transformation of the DRXed texture component from <10 to 10>−<11–20> to a new orientation that deviated by approximately 14°. The sample extruded at 0.5 mm/s presented an excellent tensile yield strength (TYS) of 369 MPa along with a 7.8% elongation, which was mainly due to the high hetero-deformation induced (HDI) strengthening provided by its heterostructures. Increasing ram speed resulted in an improved elongation despite a decreased TYS. The reasons for the decreased strength with increasing extrusion speed were mainly associated with grain growth, reduced dislocation density and weakened HDI strengthening. The reasons for the improved ductility with increasing extrusion speed were largely due to the increased DRXed grains fraction with soft orientations.

Eliminating the soft zone for grade 91 steel weldment via enhancing prior austenite grain size of the intercritical heat-affected zone

The soft zone is deemed unwanted for grade 91 steel weldments as it constitutes a cracking-sensitive region deleterious for long-term creep performance. In the present work, formation mechanisms of the soft zone in grade 91 steel weldments have been elucidated and an approach for its elimination has been proposed. It has been demonstrated that a soft zone forms within the intercritical heat-affected zone (ICHAZ) after post-weld tempering. Post-weld normalizing and tempering enables the elimination of the soft zone. Further analysis reveals that the ICHAZ of the as-welded specimen possesses a mixed structure, consisting of over-tempered martensite and fresh martensite with a fine prior austenite grain size. During post-weld tempering, the increase in grain size and the reduction in dislocation density are the main factors contributing to the decrease in hardness. The recrystallization rate of the ICHAZ is faster than that of other regions, resulting in a decrease in hardness from 350.8 HV0.3 to 204.6 HV0.3 and the formation of the soft zone. Increased prior austenite grain size in the ICHAZ, achieved through post-weld normalizing and subsequent tempering, facilitates the formation of tempered martensite and prevents the formation of the soft zone.

Improved mechanical properties and thermal conductivity of laser powder bed fused tungsten by using hot isostatic pressing

In this study, the microstructure evolution, mechanical properties and thermal conductivity of laser powder bed fused tungsten subjected to the subsequent hot isostatic pressing (HIP) processes with natural cooling (NC) and ultra-rapid quenching (URQ) were investigated. The results showed that the relative density was significantly improved after HIPping regardless of the cooling rates. The HIP-URQ treatment led to a near defect-free component with increased recrystallization and reduced dislocation density. The enhanced comprehensive mechanical properties, including the ultimate compressive strength of 1180 MPa without sacrificing microhardness was achieved for the HIP-URQ sample. Furthermore, the highest thermal conductivity of 168.6 W/(m·K) related to the densification behaviour and microstructure evolution during the HIP treatments was reported.

Atomic-scale understanding of microstructural evolution in electrochemical additive manufacturing of metallic nickel

Atomic-level manufacturing is fundamentally concerned with the precise removal, addition, and migration of material at the atomic and close-to-atomic scale (ACS). Tip-based electrochemical deposition, a quintessential ACS electrochemical additive manufacturing technique, offers promising prospects for achieving bottom-up fabrication of metallic micro/nano structures. However, the complex physicochemical reactions involved in electrodes lead to a limited understanding of the mechanisms underlying atomic electrodeposition and structural evolution. For the first time, this study proposes electric double-layer controlled electrochemical kinetics and investigates the effect of direct current (DC) and pulse current (PC) on nickel atomic electrodeposition using molecular dynamics (MD) simulations. The findings reveal that compared to DC electrodeposition, PC electrodeposition results in more orderly deposition morphology, improved surface smoothness, reduced dislocation density, and lower crystal distortion, with these effects being particularly pronounced under low pulse duty ratio conditions. In addition, the pulse frequency significantly influences the morphology and structure of the deposit. The high pulse frequency yields smoother surfaces with local protrusions, while the low frequency favors the formation of orderly and dense structures excepting slightly increased roughness. This study provides critical insights into understanding the microscopic mechanisms of atomic-scale electrodeposition processes and achieving atomically controlled tip-based electrochemical additive manufacturing of micro/nanodevices.

Microstructural evolution and mechanical properties of maraging steel by additive manufacturing

Laser powder bed fusion (LPBF) is a revolutionary and innovative technology that provides advanced technical support for the forming of parts with high precision and complex structures. In this work, a new type of Fe-Ni-Mo-Ti-Al-Y cobalt-free maraging steel was successfully fabricated by LPBF. The additive manufacturing parameters and the microstructural evolution of cobalt-free maraging steel under different heat treatment parameters were systematically studied. The results show that the parts without cracks and close to complete density can be fabricated under a wide LPBF process window. The dislocation cell with 500 nm in the printing state makes the material have good plasticity. After post-heat treatment, the preferred orientation of LPBF maraging steel is reduced, but the typical characteristics of molten pool and cellular structure in maraging steel disappeared, which is the result of local composition and microstructure homogenization. The elongation of LPBF maraging steel in solution annealed state is higher than that in as-printed state, which is due to the reduction of dislocation density and grain coarsening. However, after direct aging, due to the formation of nano-sized Ni3(Ti, Mo) precipitates in the matrix, the mechanical properties of the material were effectively enhanced, and the tensile strength increases from ∼1.1 GPa in as-printed state to ∼1.6 GPa in aging state. In contrast, the corrosion resistance of as-printed maraging steel is higher and comparable to that of traditional cobalt-containing maraging steel. However, the corrosion resistance of LPBF maraging steel after being aged is reduced, which is due to the existence of precipitates and dislocations. This study provides a theoretical reference for the composition design and strengthening mechanism of LPBF cobalt-free maraging steel.

Effect of dislocation density on microstructure and mechanical properties of cold-rolled medium Mn steel

This study investigated the effect of dislocation density on microstructural transformation and mechanical properties of Fe-7.23Mn-4.42Al-0.09C-1.99Si (wt.%) steel. By the tempering treatment, the dislocation density was reduced. The effect of of dislocation density on the plasticity of the steel was analyzed. The dislocation density was reduced from 2.3 × 10−16 m−2 to 1.6 10−16m−2 by tempering. Reducing dislocation density in the metastable austenite resulted in a higher metastable austenite transformation rate. And the low dislocation density steels exhibited a longer strain length during tensile deformation. It was obvserved that the dislocation density of the test steel decreased by 30% after tempering, the austenite transformation rate increased to 53.3%, and tensile strength and elongation increased to 1010 MPa and 44% respectively.

High-temperature oxidation behavior of a novel γ′-strengthened superalloy manufactured by laser-beam powder bed fusion: Effect of post-heat treatment

This study systematically researched the high-temperature oxidation behavior of a γ′-strengthened alloy based on Haynes 230 prepared by laser-beam powder bed fusion (PBF-LB). The results indicate that the experimental alloy showed a higher oxidation resistance than Haynes 230 at 1000 °C. The oxidation products mainly consisted of the outmost MnCr2O4-TiO2 layer, intermediate Cr2O3 layer and inner TiO2 layer. Branched Al2O3 oxides were formed in the interior oxidation zone. Post-heat treatment can increase oxidation resistance by reducing the oxidation rates from 0.0152 mg2cm−4h−1 to 0.0126 mg2cm−4h−1. The decrease in dislocation density and the precipitation of ordered γ' phases can slow down the short-circuit diffusion and lattice diffusion rate of oxygen, and are the main reasons for this improvement. Furthermore, the γ' phase precipitation and dislocation density reduction can provide more sites for Cr2O3 nucleation and reduce the Cr supply required for grain growth. As a result, the Cr2O3 grains on the heat-treated sample surface were smaller.

Electroplasticity mechanism of Ti2AlNb alloys under hot compression with the application of a lower electric current

In this study, a lower electric current (1.0–2.0 A/mm2) was applied during hot compression of Ti2AlNb alloys, and the mechanical response, microstructure evolution, and electroplasticity mechanism were investigated. The results showed that the maximum flow stress drop could reach 18.7 % after applying a lower electric current of 2.0 A/mm2, which confirms the existence of electroplasticity. The stress drop increased with increasing electric current density. However, the flow stresses of the samples in the isothermal compression test and those subjected to a 1.0 A/mm2 electric current compression test were similar, indicating that there is a threshold value for the electroplasticity effect on flow stress. The lower strain hardening rate caused by the electric current confirmed the electroplasticity effect, promoting the softening effect. Additionally, the lower average activation energy Q, affected by the electric current, implied the improvement of the deformability of the alloy due to the deformation mechanism of dynamic recovery (DRV), dynamic globularization, or dynamic recrystallization (DRX). The gradual reduction of dislocation density with increasing electric current density resulted in the stress drop, which can be ascribed to the directional drifting electrons colliding with dislocations, which promoted the movement of dislocations by arranging the dislocations in parallel. The local high temperature induced by the local Joule heating effect at the O lamella had a strong promoting effect on the globularization of the O lamella by producing uniform lattice distortion/local strain at the O/B2 interface. With increasing furnace temperature, the drifting electrons accelerated the transformation of LAGBs to HAGBs which promoted the appearance of dynamic recrystallization grains.

Record High Thermoelectric Figure of Merit of a III-V Semiconductor InGaSb by Defects Engineering via the Addition of Excess Constituent Elements.

Materials with enhanced electron and reduced phonon transport properties are preferred for thermoelectric applications. The defect engineering process can optimize the interrelated electron and phonon transport properties to enhance thermoelectric performance. As the influence of various crystalline defects on the functional properties of materials is diverse, it is crucial to scale, optimize, and understand them experimentally. With this perspective, crystalline defects in InGaSb ternary alloys were engineered and their influence on the thermoelectric properties was studied experimentally. Crystalline defects such as point defects, dislocations, and compositional segregations were induced in In0.95Ga0.05Sb crystals by the addition of excess constituent elements, In, Ga, or Sb. The addition of excess Ga increased point defects, whereas excess Sb reduced dislocation densities. The thermoelectric figure of merit value (ZT) of In0.95Ga0.05Sb+Ga0.02 was recorded to be 0.87 at 573 K, which is the highest among other reported values of III-V semiconductors. The collective interactions of compositional segregations, point defects, and dislocations with electrons and phonons enhanced the ZT in this study.