Mechanism Of Void Formation Research Articles

On the nature of nano twin-induced shear band formation in a dispersion strengthened copper alloy under micro-mechanical loading

A key challenge in metallic alloys with high ductility is understanding how microstructural inhomogeneities influence shear localization, leading to localized plastic deformation and material failure. In this study, we explore the phenomenon of shear localization in coarse-grained copper, a material traditionally regarded as having low susceptibility to such behavior. Contrary to conventional understanding, our findings reveal that microstructural inhomogeneities play a pivotal role in inducing extensive strain localization during low strain rate micro-mechanical loading. The presence of fine precipitate particles leads to strain localization at small strains and low strain rates by activating shear localization driven by void formation mechanisms. Furthermore, nanoscale precipitates act as sites for dislocation pile-up within deformed structures of shear bands, leading to the formation of nano twins within these bands. Consequently, precipitate particles serve a dual role: contributing to strain localization and potential cracking, while also enhancing the alloy’s strength and ductility through nano-twinning mechanisms. This investigation offers a novel perspective on the interplay between material microstructure and deformation behavior, challenging existing paradigms in materials science.

4D-XCT monitoring of void formation in thick methacrylic composites produced by infusion

Void formation in fibre-reinforced polymer composites processed by liquid moulding is a persistent issue in composite research and development. Not only may several void formation mechanisms come into play, but these defects can also accumulate and grow over the course of the manufacturing process. Mitigation methods can be applied once the underlying causes of voiding are identified, which is impossible through post-mortem characterisation. Here, void formation is dynamically monitored in miniaturised glass fibre-reinforced thermoplastic polymer composite samples manufactured by vacuum infusion and in-situ polymerisation, using laboratory-based X-ray computed tomography (XCT). The method allows the characterisation of the evolution of void patterns as the resin polymerises and cools down within the fibre preform. With a time resolution of 2 min and a voxel size close to 20 µm, this first-of-a-kind XCT experiment provides insights into the evolution of the void volume fraction, void size and location. The root causes leading to void formation in the system of interest were successfully identified as a combination of flow-related air entrapment during preform filling and, mostly, of chemical shrinkage of the matrix upon polymerisation. Additionally, thermal shrinkage during the cooling of the preform results in a slight decrease in the final void volume fraction.

Dynamics of non-Newtonian fluid–fiber interactions and void formation mechanism based on fused filament fabrication

Due to the presence of internal defects such as voids in the composites manufactured by material extrusion additive manufacturing (MEX AM), the mechanical properties of the composites are significantly below the theoretical optimum. Under this circumstance, this paper is intended to investigate the effects of nozzle feeding angles and to analyze the void formation and evolution of multiphase flow, in which systematic computational fluid dynamics numerical simulations are conducted. The volume of fluid model and overset grid method are used to simulate the extrusion deposition process of carbon fiber-reinforced polymer composites, and the Carreau model is used to represent the shear-thinning behavior of molten polymer. The numerical method is validated against previously experimental and numerical simulation data. The numerical results show that the key factor leading to void formation is the vortices caused by fiber oscillation. The intense vortex at the front end of the fibers disrupts the interface between molten polymer and air, creating a beneficial condition for air to enter. Nozzle tilting can effectively reduce the probability of void formation by decreasing the fiber oscillation velocity. The results of the present study provide insights into the development and optimization of printer nozzles to enable the printing of longer fibers with less probability of potential void formation.

Influence of thermal history and consolidation force on wedge peel strength of CF/PEEK laminates manufactured by laser‐radiated in‐situ consolidation

AbstractProcessing parameters during the laser‐radiated in‐situ manufacturing process change the thermal history of the thermoplastic composite, which affects porosity and fiber‐resin interfacial bonding quality, and hence the wedge peel strength of the laminate. The effect of different laser powers and consolidation forces on the wedge peel strength of the specimens was investigated. Due to the fiber‐rich area on the tape surface during the laser heating phase as well as the insufficient consolidation force and consolidation length during the consolidation phase, the wedge peel strength decreased due to increased porosity and weak fiber‐resin bonding at the interlayer bonding interface. A conformable consolidation roller of lower hardness was used to improve the wedge peel strength of the laminates, which reduced the initial temperature of the cooling phase, thus inhibiting the void rebound and increasing the bonding strength at the fiber‐resin interface. The cross‐section and peeling surface were characterized by optical microscope and scanning electron microscope. The wedge peel strength of the laminates, with reduced voids and increased interfacial bonding strength between the fibers and the resin, is improved.Highlights Mechanism of void formation and evolution in different phases of laser‐radiated in‐situ consolidated laminate. Effect of consolidation roller hardness and deformation on wedge peel strength.

The formation mechanism of void in thin-walled capsule welding joint induced by HIP

Thin-walled capsule significantly impacts the overall quality of hot isostatic pressing (HIP）products, with capsule reliability being a crucial factor in determining the success or failure of the HIP process. High-temperature creep is essential for the densification of HIP powder. However, the capsule, made of dense metal, undergoes its own creep process. High temperature and high pressure may induce void formation in the capsule due to diffusion and creep. The integrity of the capsule typically relies on the welding process, and void formation at welded joints poses a significant challenge to the capsule’s reliability, increasing the likelihood of failure. This study investigates the mechanisms of void formation in welded joints during the HIP process. Results indicate that high temperature and high pressure during HIP promote the formation of two types of voids in mild steel: Kirkendall voids and creep voids. Kirkendall voids are driven by diffusion and influenced by the HIP insulation temperature, which affects their state but not their formation. Creep voids, however, originate from stress concentration at grain boundaries during creep deformation. Their distribution density is positively correlated with the degree of creep deformation, which is primarily controlled by HIP pressure and temperature.

The role of printing parameters on the short beam strength of 3D-printed continuous carbon fibre reinforced epoxy-PETG composites

It is well known that printing parameters strongly affect the mechanical performance of 3D printed parts. This work explores the role of i) extruder temperature, ii) print speed, and iii) layer height on the interlaminar strength of 3D-printed continuous fibre-reinforced composites. The carbon fibre-reinforced thermoset filament is printed concomitantly with polyethylene terephthalate glycol (PETG) thermoplastic filament in a single nozzle, characterising a continuous fibre co-extrusion (CFC) process. There is a significant variation in the short beam strength for composites printed with different parameters. The load–displacement curves have a similar pattern, with clear load peaks followed by a plastic zone. Optical micrographs and computed tomography (CT) scans reveal that the microstructure is dependent on the printing parameters. Image analysis elucidates the various mechanisms of void formation. Following the application of a three-way ANOVA and statistical tests to quantify the effects and interactions among variables, the analysis concludes that the extruder temperature has the highest influence, followed by print speed and layer height. When considering all possible interactions between the factors, the interaction between print speed and layer height is the most impactful.

Revealing the Void Formation Mechanism during Superplastic Deformation of a Fine-Grained Ni–Co-Base Superalloy

Revealing the Void Formation Mechanism during Superplastic Deformation of a Fine-Grained Ni–Co-Base Superalloy

Void formation and suppression in CFRP laminate using newly designed ultrasonic vibration assisted RTM technique

This study introduces an ultrasonic vibration assisted resin transfer molding (RTM) technique as an innovative approach to address the inherent challenges associated with traditional methods for producing CFRP laminates. It investigates the mechanism of void formation in CFRP composites under ultrasonic vibration using 3D X-ray microscopy. Numerical calculations and simulation analyses are also employed to validate the impact of ultrasonic vibration on mechanical properties of CFRP. The findings indicate that ultrasonic vibration results in CFRP laminates with more uniform thickness, leading to a substantial increase in fiber volume fraction up to ∼16 %. Concurrently, there are significant improvements in flexural strength (∼20 %) and fracture energy (∼90 %). Ultrasonic vibration also effectively reduces CFRP porosity by at least 25 %, resulting in a more consistent distribution of voids, primarily consisting of small circular voids. This porosity reduction is attributed to the cavitation effect and enhancing wettability, consequently improving the mechanical properties of CFRP. Moreover, simulations and numerical calculations demonstrate the significant occurrence of cavitation effect within the resin under specific process conditions. The intensity of cavitation is influenced by factors such as the initial bubble radius, acoustic pressure amplitude, and static pressure of the resin. The ultrasonic-assisted RTM process is proved as a promising method for producing CFRP laminates with superior properties.

3D CT scan metrology for solder void formation analysis in ball grid array electronic chips

The miniaturization of silicon chips and the complexity of device functionality has driven the electronic packaging industry to find new methods to enhance the reliability of chips at a smaller size. Solutions such as Ball Grid Array (BGA) packages have contributed to the miniaturization of integrated circuits (ICs) and the reduction in their overall size. However, void formation in the solder joint is a weakness that can affect the robustness of the solder joint integrity, both mechanically and electrically. To detect these voids, metrology methods such as 3D Computed tomography (CT)-scan are used. 3D CT-scans can identify submicron-sized void defects in real-time during thermal tests, which can be utilized to help improve the quality control lines in the electronic chip manufacturing industries. In this paper, two types of BGA packages will be evaluated for solder joint properties. The prepared samples will be subject to high temperature stress conditions to assess the mechanism of void formation in solder joint. The prepared samples will be heated at 260 °C four times where the heating lasts 0, 5, 10, and 15 min, respectively. The prepared samples will be mounted on a PCB board and the results of the thermal stress tests will be analyzed using 3D X-ray CT scans. These 3D-CT scans used in tandem with a reconstruction and visualization software suite, will be utilized to observe changes such as void formation in the solder joint after each heating time. Unexpectedly, void size reduced between the first and second heat cycles on both samples but increased for the third and fourth heat cycles then.

Origin of Voids at the SiO2/SiO2 and SiCN/SiCN Bonding Interface Using Positron Annihilation Spectroscopy and Electron Spin Resonance

To obtain reliable 3D stacking, a void-free bonding interface should be obtained during wafer-to-wafer direct bonding. Historically, SiO2 is the most studied dielectric layer for direct bonding applications, and it is reported to form voids at the interface. Recently, SiCN has raised as a new candidate for bonding layer. Further understanding of the mechanism behind void formation at the interface would allow to avoid bonding voids on different dielectrics. In this study, the void formation at the bonding interface was studied for a wafer pair of SiO2 and SiCN deposited by plasma enhanced chemical vapor deposition (PECVD). The presence of voids for SiO2 was confirmed after the post-bond anneal (PBA) at 350 °C by Scanning Acoustic Microscopy. Alternatively, SiCN deposited by PECVD has demonstrated a void-free interface after post bond annealing. To better understand the mechanism of void formation at the SiO2 bonding interface, we used Positron Annihilation Spectroscopy (PAS) to inspect the atomic-level open spaces and Electron Spin Resonance (ESR) to evaluate the dangling bond formation by N2 plasma activation. By correlating these results with previous results, a model for void formation mechanism at the SiO2 and the absence of for SiCN bonding interface is proposed.

Identification of the Kirkendall effect as a mechanism responsible for thermal decomposition of the InGaN/GaN MQWs system

A drop in the efficiency of light-emitting diodes based on InGaN/GaN QWs known as the ‘green gap’ has been studied intensively over the past dozen years. Several factors were revealed to contribute to its origin, such as random fluctuations in the indium concentration or the diffusion of point defects during the growth of QWs. The aim of this paper is to demonstrate that the Kirkendall effect can be the mechanism responsible for the thermal decomposition of InGaN/GaN MQWs structures, contributing to the green gap problem. By applying density functional theory, harmonic approximation, and harmonic transition state theory, we calculated the heights of the migration energy barriers of In and Ga atoms diffusing in alloys (), the vibrational frequencies of alloys in the presence of migrating point defects, the temperature dependencies of the defect migration energy barriers and diffusion coefficients of Ga and In atoms migrating in alloys. We demonstrated the presence of unbalanced diffusion rates of In and Ga atoms at the interfaces and finally explained the experimentally observed mechanism of void formation at the interfaces by means of the Kirkendall effect.

Optical Detection of Void Formation Mechanisms during Impregnation of Composites by UV-Reactive Resin Systems

During the impregnation of reinforcement fabrics in liquid composite molding processes, the flow within fiber bundles and the channels between the fiber bundles usually advances at different velocities. This so-called “dual-scale flow” results in void formation inside the composite material and has a negative effect on its mechanical properties. Semi-empirical models can be applied to calculate the extent of the dual-scale flow. In this study, a methodology is presented that stops the impregnation of reinforcement fabrics at different filling levels by using a photo-reactive resin system. By means of optical evaluation, the theoretical calculation models of the dual-scale flow are validated metrologically. The results show increasingly distinct dual-scale flow effects with increasing pressure gradients. The methodology enables the measurability of microscopic differences in flow front progression to validate renowned theoretical models and compare simulations to measurements of applied injection processes.

Mechanism of Void Formation in Lithium Metal Solid-State Batteries

Solid-state batteries (SSBs) with lithium metal anodes promise higher energy and power density over conventional lithium-ion batteries. But the development of SSBs faces fundamental challenges related to the electro-chemo-mechanics and stability of solid-solid interfaces. Among these, the formation and growth of voids at the lithium metal-solid electrolyte interface during stripping persists to be a major limitation. In this work, we analyze the nature of metal electro-dissolution and its critical implication on the evolution of solid-solid point contacts. The competing nature of lithium self-diffusion, reaction kinetics and ionic transport at the solid-solid interface, dependent on factors such as temperature and surface roughness are examined. Hotspots in the dissolution morphologies are identified and systematically connected to the electrochemical signature and onset of failure in SSBs.

(Invited) Computational Modeling of Void Formation Mechanism at the Lithium/Solid-Electrolyte Interface

Stabilization of the lithium deposition by the introduction of solid electrolytes was attempted in the past with partial success. However, electrochemical dissolution of lithium from the metal electrode to the solid electrolyte introduces unique challenges, such as, formation of micron sized voids at the electrode/electrolyte interface. These interfacial pores form due to stripping of lithium at a rate higher than they can actually be replenished from the bulk. Presence of these porous domains will minimize the electrochemically active surface area, dramatically increase the interfacial resistance, and effectively render the cell unusable. In the present research, a phase field based computational framework is developed that can capture the evolution of these micron sized voids at the lithium/solid-electrolyte interface during the electrochemical dissolution of lithium. Importance of lithium surface diffusion in determining the pore morphology is introduced for the first time. Impact of applied current density, external pressure, and operating temperature on the dynamics of void evolution is investigated in detail. Figure 1

Al-Si contact formation involving back surface field and voids of PERC

Local Al–Si contacts are a vital part of passivated emitter and rear cell (PERC) solar cells. They are generally fabricated using laser ablation to open the passivation dielectric layers, which is followed by Al paste printing and high-temperature alloying. However, the alloying process of Al–Si contacts and the formation mechanism of voids remain unclear in parts. In this study, based on the Al–Si binary phase diagram, we revealed the formation path associated with the back surface field (BSF) of the Al–Si alloying process and elucidated the formation mechanism of voids for dashed shape local contact openings. Also, a calculation model is proposed to determine and verify the Si concentration at the peak temperature. During peak-temperature firing, an equilibrium is established between the dissolution and diffusion of Si; subsequently, Si in the melt reaches its saturation concentration and laterally diffuses into the Al layer, thereby causing the net outflow of Si with the contact trench expansion and forming partial voids. During cooling, supersaturated Si precipitates to form BSF, while the degree of precipitated Si limits the thickness and forms the hypereutectic alloy. After the BSF formation, the melt was redistributed along the contact trench, resulting in partial voids turning into complete voids and fully filled contacts. This study also provides a new approach for regulating and optimizing Al–Si contacts. • The formation path of the back surface field of Al Si contact is revealed from the phase diagram. • Silicon saturated at peak temperature and BSF thickness is limited by the degree of silicon precipitation. • The contact of Hypereutectic component Al Si will affect the electrical properties. • The formation of voids is related to the lateral diffusion of silicon and the redistribution of melt. • The redistribution of melt transforms partial voids into complete voids.

Analysis of the voids formation mechanisms in CF/PEKK blank by water absorption behavior

The internal defects formed during infrared (IR) heating of carbon fiber-polyetherketoneketone thermoplastic composites at different temperatures and dwell times were analyzed based on the water absorption characteristics. IR heating generates internal defects such as voids, which affect the water absorption behavior of the composites; lesser voids were generated under higher heating temperatures and longer dwell times. A void formation mechanism consisting of growth, transfer, and removal of voids was proposed based on the difference in the standard deviation of the water absorption content. The reduction in the water absorption content of the composite after reforming confirmed the recovery of voids. All the specimens, except those heated at 420[Formula: see text]C for 5 min or more, showed good recovery.

Void Formation Mechanism Related to Particles During Wafer-to-Wafer Direct Bonding

Achieving a void-free bonding interface is an important requirement for the wafer-to-wafer direct bonding process. The two main potential mechanisms for void formation at the interface are (i) void formation induced by gas, such as condensation by-products caused by the bonding process or outgassing of trapped precursors, and (ii) void formation induced by physical obstacles, such as particles. In this work, emphasis is on the latter process. Particles were intentionally deposited on the wafer prior to bonding to study the kinetics of the physical void formation process. Void formations induced by particles deposited on different dielectrics bonding materials were analyzed using scanning acoustic microscopy and image software. The void formation mechanism is then discussed along with the wafer bonding dynamics at room temperature.

Effect of ZrO2 on crystallization behavior and mechanical property of Dy2O3–Al2O3–SiO2 glasses

Effects of ZrO2 content on the crystallization kinetics, formation mechanism of voids and mechanical property of Dy2O3–Al2O3–SiO2 glass were studied. The crystallization method of DAS glasses transforms from surface crystallization into bulk crystallization with an increase in ZrO2 content from 0-3% to 6–9%. When ZrO2 content is 0–3%, the crystalline phases of DAS glass ceramics are Dy2Si2O7 and Al2O3, accompanied by formation of voids. When ZrO2 content is 6–9%, the DAS glass ceramics consist of Dy2Si2O7, Al2O3 and ZrO2. At the same time, no voids are found in the glass ceramics. Therefore, formation of voids during crystallization can be attributed to combined effect of the crystallization method and the density difference before and after crystallization. In addition, for glassy samples, the flexural strength increases from 80.4 MPa to 219.3 MPa with an increase in ZrO2 content from 0% to 9%. Moreover, crystallization further improves the mechanical properties of the DAS glass ceramics with bulk crystallization method.

Microstructural evolution and performance of high-tin-content Cu40Sn60 (wt. %) core/shell powder TLPS bonding joints

This paper investigated the microstructure evolution and performance of high tin content Cu@Sn core/shell (60 wt% Sn) powder transient liquid phase sintering bonding. The formation and evolution mechanism of voids were analyzed. Results showed that, after consuming Sn, the joint was mainly composed of Cu6Sn5, Cu3Sn, and Cu, raising the remelting temperature of the joint to 400 °C. The porosity in the joint was decreased firstly, then increased, and finally decreased with bonding time. The maximum porosity was 0.876% and 1.052% at 300 °C for 150 min and 340 °C for 120 min. With the bonding time increased, the room temperature (RT) shear strength was increased first, then decreased, and finally remained stable. In contrast, the high-temperature (350 °C) shear strength was increased first, then remained stable with bonding time. The joint was possessed excellent RT (20.79 MPa) and high-temperature (18.46 MPa) shear strength. The electrical resistivity of joints was increased first, then remained stable with bonding time. The electrical resistivity was reached its maximum value of 1.83 × 10−5 Ω·cm at 300 °C for 150 min. The thermal conductivity of the joint was 28.72 W/(m·K), 26.83 W/(m·K), and 25.99 W/(m·K) at 30 °C, 250 °C, and 350 °C, respectively.

Nano-voids formation at the interaction sites of shear bands in a Zr-based metallic glass

Understanding the formation mechanism of voids is a significant issue in controlling the catastrophic fracture in the form of shear bands in metallic glasses. Here, using an amplitude-modulation atomic force microscope, we investigated the nano-voids formation at the mutual interaction of shear bands in a Cu50Zr50metallic glass. The results of phase shift revealed higher energy dissipation and more soft zones for the nano-voids. The formation of these nano-voids results from tensile stress concentration caused by the interaction of shear bands, based on the results of finite element simulation. The appearance of nano-voids and stress distribution at the site of shear band interaction is essential in understanding the plastic deformation and fracture of metallic glasses.