Void Formation Research Articles

Dimensional stability of poly(lactic acid) (PLA) parts fabricated using fused deposition modelling (FDM)

The dimensional accuracy of a 3D printed part produced using Fused Deposition Modeling (FDM) is an important issue. In this work, polylactic acid (PLA) parts were produced using FDM at different platform temperatures. The dimensional stability of the parts was assessed by measuring the shrinkage, warpage and layer thicknesses of the parts. A sample of four different blades for warpage, two samples with different shapes and parts with fixed contact surface area but different heights were printed at a fixed nozzle temperature of 210°C while platform temperatures were varied from 60°C to 80°C. Deformation angles of the blades decreased with increasing platform temperature suggesting lower warpage due to the enhanced capability to dissipate thermal stress. Meanwhile, shrinkage decreased as platform temperature increased irrespective of the shape of the sample due to the lower temperature difference between platform and nozzle temperature leading to lower thermal contraction. However, a thin sample tends to shrink more compared with a thick sample with bigger differences at higher platform temperatures. No significant trend in density were observed on samples of different height with increasing platform temperature due to competing effects of increasing crystallinity that would increase the density and increasing layer contraction that would increase porosity as shown by the variation in the thickness of the top and the bottom layers of the samples and the formation of voids.

Hygroscopic damage of fiber–matrix interface in unidirectional composites: A computational approach

The mechanical properties of fiber-reinforced composites are significantly affected by hygroscopic exposure. Recent experimental findings reveal that the diffusion of water molecules results in void formation at the fiber–matrix interface, contributing to ∼1% increase in porosity. This paper presents a computational micromechanics framework to analyze the damage behavior of unidirectional composites under hygroscopic aging and transverse loads. First, a mathematical relation for the porosity evolution with moisture content in the composite is obtained. Leveraging this correlation, the aged composite is modeled as a porous microstructure consisting of fiber, matrix, and voids at the fiber–matrix interface in finite element simulations. The fiber is considered elastic, and the matrix is modeled as an elastoplastic material using a pressure-dependent yield model to capture tension–compression asymmetry. A cohesive interface is considered between the fiber and matrix. Simulation results indicate that a void at the interface significantly influences plastic strain evolution and stress distribution, leading to early damage initiation and reduced strength. Previous works have indicated that matrix and inter-fiber voids do not have a significant impact on the strength of composites when their combined porosity is below 1%. On the contrary, this study demonstrates that a porosity of as low as 0.1% at the fiber–matrix interface can result in an 11% decrease in the transverse tensile strength of the composite. A parametric study is conducted to understand the fundamental effects of pore size, location, and relative position on the transverse tension, compression, and shear loading responses of a unidirectional composite. For a given moisture content, the predicted strength of the hygroscopic aged composite exhibits a lower and upper bound. The strengths observed in the experiments fall within the model-predicted range. Additionally, a computational method is proposed that incorporates the effects of porosity at the fiber–matrix interface into a modified cohesive strength. This method allows efficient computations and failure predictions for water or moisture-aged strength degradation of unidirectional composites.

Rheological, mechanical, and microscopic properties of polypropylene fiber reinforced-geopolymer concrete for additive manufacturing

This study focuses on developing fiber-reinforced geopolymer concrete (GPC) for 3D printing, utilizing construction waste materials and polypropylene fibers. The GPC, reinforced with 0.8 %, 1.0 %, and 1.2 % polypropylene fibers by volume, underwent comprehensive testing, including rheological, mechanical, and microstructural analyses for lab-cast and 3D-printed samples. The results indicated that the 0.8 % polypropylene fibers enhanced flexural and tensile strengths by 8.2 % and 71.7 %, respectively, albeit decreasing compressive strength by 26.2 %. Higher polypropylene percentages led to adverse effects on material properties. Microscopic analysis revealed the formation of voids around fibers and features associated with incomplete hydration. The study emphasizes the need for optimizing water content and the use of longer polypropylene fibers. It also highlights the benefits of using GPC in the 3D printing of structural components.

Influence of the thermal shrinkage-induced volume contraction on the yielding behavior of waxy oil

The present article investigates the effect of thermal shrinkage on the yielding behavior of waxy oil gel. The paper compares constant gap and constant normal force measurement protocols to examine the effect of measurement protocol on the rheological behavior of thermoreversible gel. The findings of this study reveal that the extent of stress overshoot and yield stress in a constant shear-rate start-up flow shows a lower magnitude in a constant gap protocol compared to a constant normal force protocol. The decrease in gel strength in the former protocol is mainly attributed to the formation of voids. These voids cause localized fractures within the crystal network. In contrast, in the constant normal force measurement protocol, gel contraction is compensated by utilizing a variable gap setting. Variable gaps compensate for the lower specific volume of the gel after crystallization, minimizing void formation and subsequent rupture of the crystal network. Hence, the gel network formed using the constant normal force protocol is more homogeneous, eliminating the uncertainties in yield stress measurement. Finally, the effect of thermal history, wax content, and aging period on the yield stress values highlights notable findings. Contrary to the conventionally accepted results, the aging period is found to impact the yield stress negatively, and a nonmonotonic relationship between the cooling rate and yield stress is noticed under the constant gap protocol. Thus, the results obtained under the constant normal force protocol are more reliable and can help in developing a fundamental understanding of the yielding behavior.

Microwave Welding of Thermoplastic using Silicon Carbide Nanowhiskers as Susceptor: Effect of Heating Duration

Microwave welding is becoming more popular than conventional joining methods due to its advantages such as rapid and localised heating as well as applicable to components with complicated geometry. Previously reported susceptor, such as carbonaceous materials and conductive polymers, are toxic and the welding process involving these susceptors is time-consuming. Because of its exceptional microwave absorption and biocompatibility, silicon carbide nanowhiskers (SiCNWs) was employed as the microwave susceptor for microwave welding. Microwave welding in this study comprises of only three simple steps: SiCNWs suspension preparation, SiCNWs application and microwave heating. The weld strength of welded joint was then characterised using tensile test and energy dispersive x-ray spectroscopy equipped scanning electron microscopy (EDS-SEM) to study its mechanical properties and cross-section microstructure. The influence of microwave irradiation time was studied in this study, and it is found that the weld strength rose with the extension of microwave irradiation time, until a maximum weld strength of 1.61 MPa was achieved by 17 s welded joint. The development of SiCNWs reinforced PP nanocomposite welded joint layer is responsible for the enhanced weld strength. Prolonged heating duration may also result in flaws such as void formation at the welded joint, which subsequently lowered the weld strength to 0.60 MPa when the heating duration was extended to 20 s. In sum, a strengthen welded joint can be formed with rapid microwave heating under the proper control of heating duration.

Study on the strain partitioning behavior in heterostructured complex-concentrated alloy via high-resolution digital image correlation

Here, we investigate the tensile deformation behavior in a Ni42Fe30Cr12Mn8Al5Ti3 complex-concentrated alloy with heterogeneously-grained structure consisting of fine and ultrafine grains containing nano-sized L12 precipitates. It is found that Lüders band initiation and propagation account for the early stage of deformation. High-resolution digital image correlation investigation reveals that there is strong strain partitioning between fine and ultrafine-grained domains upon plastic deformation. Significant strain gradient across the domain-interfaces is thus established. Strain partitioning promoted dense microshear bands are observed in the deformed alloy. They are uniformly distributed and interacted with each other, resulting in the formation of strain concentration zones, which are mostly evolved in fine-grained domains and some of them extend into ultrafine-grained domains at high strain levels. Thus, the global plastic deformation of the alloy is synergistically accommodated. Finally, local high stress in strain concentration zones in ultrafine-grained domains promotes the formation of voids at triple junctions of grain boundaries.

Dentinal Crack Formation and Quality of Obturation Using Two Single File Systems and Two Obturation Techniques: A micro-CT Study.

Background and objectives: Root canal preparation following obturation with rotary instruments and different obturation techniques may lead to formation of microcracks in the root canal wall, void and gaps between the canal wall and obturation material. Aim: This study aimed to evaluate dentinal microcracks and voids formation after using two different files TruNatomy (TRN) and Genius (GN) and two obturation techniques Single Cone (SC) and GuttaCore (GC) using Microcomputed tomography scan (micro-CT). Methods: 40 extracted mandibular premolars were decoronated, leaving 13mm roots. The roots were randomly divided into two main groups TRN and GN ((n=20)) according to instrumentation, afterwards each group subdivided into two subgroups ((n=10)) according to obturation techniques. The root canals instrumented with TRN and GN file and obturated with Single Cone (SC) and GuttaCore (GC) obturation techniques. AH Plus sealer was used in all groups. The specimens were scanned with Micro-CT before and after root canal preparation and after obturation. subsequently, all pre-and postoperative cross-sectional images of the roots were screened to identify the presence of dentinal defects. Furthermore, the percentage of voids volume calculated. Data were analyzed statistically to determine difference between groups, the level of statistical significance was at p < 0.05. Results: GN revealed the least number of microcracks. There were no significant differences between groups in the incidence of dentinal microcracks. The highest percentage of filling material was observed in GC groups. There were significant differences between the obturation groups in the number of voids present after obturation (P < 0.001). Conclusion: The instrumentation of root canals induces dentinal microcracks. Obturation have no effect on the formation of cracks. None of the root canal filling procedures yield fillings that are void-free. Keywords: Dentinal crack, Voids, Micro CT, Guttacore, Singlecone, TruNatomy, Genius.

Improving the light transmission of silica glass using silicone as an anti-reflection layer for solar panel applications

The anti-reflection (AR) technology currently used in photovoltaic (PV) glass has reached its operational limit as the refractive index of existing materials cannot be lowered further. To overcome this, in this study, we selected formed methylsiloxane as an AR layer for PV glass. Its low refractive index (∼1.37) originates from the high content of methyl groups and the formation of voids during crosslinking. We acquired and compared the refractive index curves, conducted structural analyses, characterizations (optical, thermal, and surface), and performance evaluations to confirm the advantages of silicone as an AR layer for PV panels. The spreading and subsequent room-temperature self-curing characteristics of silicone considerably enhanced its applicability for upscaling and repair. The hydrophobic nature of the silicone AR layer imparted a new self-cleaning function to the solar panels; further, the methyl-silicone coating enhanced light transmission, resulting in electrical gain. Furthermore, the addition of the methyl-silicone layer created a refractive index gradient on the glass surface, making it fully compatible for use with the mainstream AR process, namely, the sol-gel method employed for PV glass.

Effect of Yttrium Additions on the High-Temperature Oxidation Behavior of GH4169 Ni-Based Superalloy.

The effect of the active element yttrium and its content on the oxidation behavior of GH4169 Ni-based superalloy at extreme temperature was studied by isothermal oxidation experiments. The results show that the oxide scale of GH4169 alloy presents a multi-layer structure, in which the continuous and dense Cr2O3 oxide layer is located in the subouter layer (II layer) and the continuous Nb-rich layer is in the subinner layer (III layer). These layers can inhibit the diffusion of oxygen and alloying elements, preventing the further oxidation of the alloy. The appropriate addition of yttrium can promote the selective oxidation of Cr element, reduce the thickness of the oxide scale and the oxidation rate of the alloy, inhibit the formation of voids at the interface of the oxide scale/alloy matrix, improve the resistance of the alloy to spalling as well as the adhesion of the oxide scale, and improve the high-temperature oxidation resistance of the alloy. Of those tested, the alloy containing 0.04 wt.%Y has the lowest oxidation weight gain, the slowest oxidation rate, and less oxide scale spalling. Based on this, the effect of yttrium on the high-temperature oxidation behavior of GH4169 Ni-based superalloy and its mechanism were revealed.

Comparison of irradiation-induced void formations in tungsten with equiaxed and columnar structures

Comparison of irradiation-induced void formations in tungsten with equiaxed and columnar structures

Exploring high-temperature deformation and damage behaviour in high-performance ferritic (HiperFerSCR) steel with Laves phase particles

The mechanical behaviour at high temperatures and the corresponding microstructural characteristics of a newly developed high-performance ferritic, salt-corrosion-resistant (HiperFerSCR) steel containing Laves phase particles were studied to investigate the active deformation mechanisms and the evolution of damage. A series of tensile tests were conducted at both room temperature and elevated temperatures (550, 600, and 650 °C), along with detailed microstructural analyses using scanning electron microscopy and electron backscatter diffraction. The tensile flow characteristics of HiperFerSCR at room temperature exhibit significant strain hardening, which is due to the Laves phase particles that encourage planar slip, demonstrated by the formation of numerous slip bands and low-angle grain boundaries. The intersections of these slip bands with grain boundaries appear to be the initiation sites for cracks, which then propagate intergranularly as well as within grain interiors along the slip bands. At high temperatures, the flow characteristics show strain softening, which is attributed to a dynamic recovery (DRV) mechanism, evident in the formation of subgrain boundaries decorated with Laves phase particles. During high-temperature deformation, damage initiates in the particle-free zone (PFZ), which expands at higher temperatures, leading to strain localisation, void formation along the grains, and eventually, grain boundary decohesion.

Investigating the impact of different solder alloy materials during laser soldering process

PurposeThis study aims to investigate the influence of different solder alloy materials on passive devices during laser soldering process. Solder alloy material has been found to significantly influence the solder joint’s quality, such as void formation that can lead to cracks, filling time that affects productivity and fillet shape that determines the solder joint’s reliability.Design/methodology/approachFinite volume method (FVM)-based simulation that was validated using real laser soldering experiment is used to evaluate the effect of various solder alloy materials, including SAC305, SAC387, SAC396 and SAC405 in laser soldering. These solders are commonly used to assemble the pin-through hole (PTH) capacitor onto the printed circuit board.FindingsThe simulation results show how the void ratio, filling time and flow characteristics of different solder alloy materials affect the quality of the solder joint. The optimal solder alloy is SAC396 due to its low void ratio of 1.95%, fastest filling time (1.3 s) to fill a 98% PTH barrel and excellent flow characteristics. The results give the ideal setting for the parameters that can increase the effectiveness of the laser soldering process, which include reducing filling time from 2.2 s to less than 1.5 s while maintaining a high-quality solder joint with a void ratio of less than 2%. Industries that emphasize reliable soldering and effective joint formation gain the advantage of minimal occurrence of void formation, quick filling time and exceptional flowability offered by this solution.Practical implicationsThis research is expected not only to improve solder joint reliability but also to drive advancements in laser soldering technology, supporting the development of efficient and reliable microelectronics assembly processes for future electronic devices. The optimized laser soldering material will enable the production of superior passive devices, meeting the growing demands of the electronics market for smaller, high-performance electronic products.Originality/valueThe comparison of different solder alloy materials for PTH capacitor assembly during the laser soldering process has not been reported to date. Additionally, volume of fluid numerical analysis of the quality and reliability of different solder alloy joints has never been conducted on real PTH capacitor assemblies.

Additive-Assisted Hydrothermal Growth Enabling Defect Passivation and Void Remedy in Antimony Selenosulfide Solar Cells.

Antimony selenosulfide (Sb2(S,Se)3) has recently emerged as a promising light-absorbing material, attributed to its tunable photovoltaic properties, low toxicity, and robust environmental stability. However, despite these advantages, the current record efficiency for Sb2(S,Se)3 solar cells significantly lags behind their Shockley-Queisser limit, especially when compared to other well-established chalcogenide-based thin-film solar cells, such as CdTe and Cu(In,Ga)Se2. This underperformance primarily arises from the formation of unfavorable defects, predominately located at deep energy levels, which act as recombination centers, thereby limiting the potential for performance enhancement in Sb2(S,Se)3 solar cells. Specifically, deep-level defects, such as sulfur vacancy (VS), have a lower formation energy, leading to severe non-radiative recombination and compromising device performance. To address this challenge, thioacetamide (TA), a sulfur-containing additive is introduced, into the precursor solution for the hydrothermal deposition of Sb2(S,Se)3. This results indicate that the incorporation of TA helps in passivating deep-level defects such as sulfur vacancies and in suppressing the formation of large voids within the Sb2(S,Se)3 absorber. Consequently, Sb2(S,Se)3 solar cells, with reduced carrier recombination and improved film quality, achieved a power conversion efficiency of 9.04%, with notable improvements in open-circuit voltage and fill factor. This work provides deeper insights into the passivation of deep-level donor-like VS defects through the incorporation of a sulfur-containing additive, highlighting pathways to enhance the photovoltaic performance of Sb2(S,Se)3 solar cells.

Valorization of Tomato Agricultural Waste for 3D-Printed Polymer Composites Based on Poly(lactic acid).

Agricultural waste is a renewable source of lignocellulosic components, which can be processed in a variety of ways to yield added-value materials for various applications, e.g., polymer composites. However, most lignocellulosic biomass is incinerated for energy. Typically, agricultural waste is left to decompose in the fields, causing problems such as greenhouse gas release, attracting insects and rodents, and impacting soil fertility. This study aims to valorise nonedible tomato waste with no commercial value in Additive Manufacturing (AM) to create sustainable, cost-effective and added-value PLA composites. Fused Filament Fabrication (FFF) filaments with 5 and 10 wt.% tomato stem powder (TSP) were developed, and 3D-printed specimens were tested. Mechanical testing showed consistent tensile properties with 5% TSP addition, while flexural strength decreased, possibly due to void formation. Dynamic mechanical analysis (DMA) indicated changes in storage modulus and damping factor with TSP addition. Notably, the composites exhibited antioxidant activity, increasing with higher TSP content. These findings underscore the potential of agricultural waste utilization in FFF, offering insights into greener waste management practices and addressing challenges in mechanical performance and material compatibility. This research highlights the viability of integrating agricultural waste into filament-based AM, contributing to sustainable agricultural practices and promoting circular economy initiatives.

Microstructural evolution in doped high entropy alloys NiCoFeCr-3X (X=Pd/Al/Cu) under irradiation

Commonly studied equatomic single-phase FCC high entropy alloys based on 3d transition metals like NiCoFeCr do not provide adequate strength and radiation resistance at high doses for nuclear structural applications. In the current study, the major alloying effects like lattice distortion, ordering and clustering tendencies were investigated by adding low concentration of Pd, Al, or Cu respectively to study the doping effects on the ion irradiation response of NiCoFeCr alloy. The alloys were irradiated with 3 MeV Ni2+ ions at 500 °C to a fluence of 1 × 1017/cm2 at a beam flux of approximately 2.8 × 1012 ions/cm2/s. The microstructural evolution upon irradiation i.e., formation of dislocation networks, radiation induced segregation and precipitation, and void formation were studied in detail. Post-irradiation characterization results showed that a Pd addition leads to a high void nucleation rate but controlled void growth, which may be attributed to increased lattice distortion. In Al added HEA, our microstructural analysis indicates that radiation induced ordered L12 precipitates do not affect void swelling significantly. Cu addition led to Cu precipitation that drastically suppressed dislocation density and void swelling of the alloy. Additionally, a model was developed to qualitatively describe the trend in void swelling of typical FCC alloys under ion irradiation. This model was able to qualitatively explain the suppression and reappearance of void swelling in ion irradiated alloys that generally occurs near the region with peak implanted ion concentration.

Enhancing sustainability in polymer 3D printing via fusion filament fabrication through integration of by-products in powder form: mechanical and thermal characterization

FFF (fused filament fabrication) is a type of 3D printing that utilizes filament for part creation. This study proposes using by-products or waste to replace part of the plastic in FFF filament, reducing environmental impact. The aim is to maintain a simple manufacturing process involving extrusion on a single-screw desktop machine followed by printing. The plastic matrix comprises polylactic acid (PLA) and polyethylene glycol (PETG), with added powdered by-products: seashells, car glass and mill scale (metal). Additives will be incorporated at 10% and 20% by weight, with two grain sizes: up to 0.09 mm and up to 0.018 mm. Mechanical tests (tensile, flexural and hardness) and thermal characterization tests will be conducted. Findings suggest adding 10%w powder of any variety to PETG increases tensile strength up to 48%, with metal powder (mill scale) showing the highest enhancement, even at 20%w, resulting in a 41% increase. Conversely, adding powder to PLA worsens mechanical properties without stiffening the material; instead, the elastic modulus decreases. Metal grain size has minimal impact, with grain sizes lower than 0.09 mm optimal for PLA. Thermal conductivity in polymers blended with powder additives is lower than in virgin polymers, likely due to air void formation, supported by density and microscopic evaluations. This research underscores the potential of utilizing waste materials with a simple FFF filament production to enhance sustainability in 3D printing practices.

Effect of β phase size on the microstructure of thermally grown oxide in water vapor atmosphere at 1100 °C

The arc-melted and vacuum-casted CoNiCrAlHf alloys with a 7YSZ top coat were designed to develop a protective alumina scale at 1100 °C in water vapor content. Arc-melted CoNiCrAlHf alloys provided substantial improvements in oxidation resistance. In this work, the oxidation behavior and void distribution of thermally grown oxide (TGO) formed on CoNiCrAlHf alloys were analyzed. The Al2O3 crystal structure and void distribution were studied as a function of the grain size of the CoNiCrAlHf substrate. Numerous voids developed in the oxide scale, and coarse HfO2 particles segregated at the Al2O3 grain boundaries of vacuum-cast CoNiCrAlHf alloys. The uniformly distributed HfO2 particles prevented void formation in the oxide scale. As a result, the phase transformation of Al2O3 was effectively impeded in water vapor.

Recycling of waste silicon powder from the photovoltaic industry into high performance porous Si@void@carbon anodes for Li-ion battery

To enhance the performance of lithium-ion battery anodes, this study leverages recycled diamond wire-cut silicon particles, a byproduct of the photovoltaic sector. These particles undergo purification through acid wash and pyrolysis to eliminate contaminants, thereby serving as potential anode materials. The inherent challenge with silicon involves its significant volumetric expansion during lithiation and delithiation, which hampers its viability for commercial applications. Addressing this, the research introduces a facile approach by synthesizing porous silicon (pSi) via the Ag-assisted chemical etching method. Subsequently, a distinctive yolk-shell porous silicon@void@carbon (pSi@V@C) structure is created using a sacrificial template approach, ensuring the formation of voids between the porous silicon core and the carbon shell. This configuration mitigates the detrimental effects of silicon's volume expansion while enhancing electrical conductivity through the carbon shell. The pSi@V@C composite exhibits promising electrochemical performance, demonstrated by an initial discharge capacity of 1826 mAh g-1 and a Coulombic efficiency of 68.6% at 0.1 A g-1. Remarkably, it maintains a capacity of 821.8 mAh g-1 after 550 cycles at 1 A g-1, with a retention rate of 90.4%.

More severe surface relief but stronger fatigue resistance at small scales: Vacancy-assisted fatigue damage mechanism

Surface relief in forms of extrusions and intrusions as the substantial feature of early fatigue damage is one of the most important phenomena studied in metal fatigue. The most common surface relief models in bulk metals are agreed to be correlated with the formation of typical dislocation patterns as persistent slip bands (PSBs), while little is known about the fundamental mechanisms at submicron and even nanometer scales where dislocation pattern formation is fully inhibited. Here, as exampled with thin Au films, the underlying fatigue damage mechanism at small scales is investigated through the quantitative characterization of fatigue damages. Continuous generation and migration of vacancies is found to be crucial for the shape of extrusion/intrusions and kinetics of their growth at submicron and even nanometer scales. Due to the degraded dislocation interaction and intensified vacancy diffusion, the delayed vacancy accumulation in the small-scale metal interior suppresses the extrusion and interface void formation in thinner films, which finally leads to the superior ability to support tremendous surface relief and strong fatigue resistance. The finding of the vacancy-dominated fatigue mechanism at small scales extends our understanding of the metal fatigue mechanisms down to the submicron and even nanometer scales and suggests a novel interface engineering strategy by vacancy behavior modulation for fatigue-tolerance material design.

Effect of impurity elements on the creep rupture strength of Gr. 91 steel welded joints at 650 °C

The upper limits for Sb, As, and Sn in Gr. 91 steel are set by the recent standardized Gr. 91 Type 2 specification. To clarify how the three impurities impact the microstructures and creep rupture strength of Gr. 91 welded joints, two types of steel with varying impurity concentrations were prepared. The first contained high impurity concentrations (Steel 1), while the other had low impurity concentrations (Steel 2). The results of the creep tests on the welded joints showed that Steel 1 had lower creep rupture strength compared to Steel 2, indicating premature failure caused by the impurities. Comparing the microstructures in the as-welded joints, it was observed that Steel 1 had more M23C6 particles in the fine-grained heat affected zone (FGHAZ) than Steel 2. This finding indicates that M23C6 dissolution during the welding process was hindered in Steel 1. It is believed that M23C6 dissolution was reduced due to the segregation of impurities at the grain boundaries or the interface between the matrix and M23C6 particles. Consequently, the microstructure in FGHAZ of Steel 1 showed lower creep resistance because the pinning force by M23C6 was decreased due to the reduction of re-precipitation on the grain boundaries during post weld heat treatment. The degradation in the creep rupture strength due to the impurities was attributed to the earlier progression of recovery process in FGHAZ during creep, leading to premature creep void formation.