Chemical Strengthening Research Articles

The effect of direct aging treatment on microstructure and mechanical properties of the GH4099 superalloys produced by selective laser melting

The effect of direct aging (DA) treatment on microstructure and mechanical properties of the GH4099 superalloys produced by selective laser melting (SLM) was investigated by the microhardness tests, room- (RT) and high-temperature (HT) tensile tests, field emission scanning electron microscopy (FE-SEM), and electron backscattered diffraction (EBSD) in this study. Both microhardness and RT tensile results show that DA treatment improves mechanical properties more than solution-aging (SA) treatment. By analyzing the effect of the microstructural features on the yield strength, we found that the dominant strengthening mechanisms responsible for higher yield strength of the DA specimens are the grain size hardening of fine γ matrix, high-density dislocation strengthening, Orowan dislocation bypass strengthening of smaller but dense M23C6-type carbides, and chemical strengthening of smaller but dense γ΄ nanoprecipitates. Furthermore, a transgranular fracture is a dominant fracture type for RT tensile specimens produced by DA treatment. Conversely, the failure type of SA tensile specimens is a typical intergranular fracture mechanism. The underlying mechanism for the above phenomenon is attributed to the effects of transgranular and intergranular M23C6-type carbides.

Chemical strengthening of glass powder particles

It is well known that chemical strengthening of glass brings the benefit of increased fracture strength. Despite extensive research on processing and mechanics at the macroscale, the effectiveness of chemical strengthening on glass elements with all three dimensions in the micrometer regime remains largely unexplored. Here, we develop a novel process for chemical strengthening of micrometer-sized spherical glass powder particles and study the fracture behavior of these particles with in-situ particle compression tests inside a scanning electron microscope. Cross-sectional microscopy and energy dispersive spectroscopy measurements confirm ion exchange and show an increase in diffusion depth with an increase in processing time and temperature. We report a higher fracture strength for chemically strengthened powder particles compared with the as-received ones. We show that the increase in fracture strength is associated to the compressive residual stress resulting from ion exchange during chemical strengthening.

Chemical Strengthening of Soda Lime Glasses via Ion Exchange Method

The aim of this study is to improve the mechanical properties of glasses by the chemical strengthening method via the ion-exchange technique. For this purpose, KNO3 salt baths were utilized for commercial soda-lime glasses. The diffusion-controlled strengthening mechanism is based on creating the compressive stress on the surface of glass by displacing the larger potassium ions with sodium ions. SEM-EDS line scan and XRF analysis, four-point bending, and Vickers hardness tests were performed for the structural and mechanical characterization of ion-exchanged glasses. The optimization of parameters led to a treatment duration of 24 hours at 400°C, resulting in a penetration depth of K+ ions reaching 85 µm. After ion exchange process, the improvement in the hardness, fracture toughness as well as bending strength values ​​of the glasses was observed. The strengthened glasses exhibited notable enhancements in mechanical properties, specifically, hardness increased from 517 HV to 612 HV, and the fracture toughness increased to 3.14 MPa.m1/2 compared to the untreated glass, which displayed the fracture toughness of 1.09 MPa.m1/2. Furthermore, the bending strength of treated specimens significantly improved to 421.6 MPa, representing a five-fold increase over the untreated sample's bending strength of 79 MPa.

Phase field modeling of fracture mechanics for ion-exchanged glass considering large viscoelastic deformation, mechanic–electrochemical coupling

A phase field model is proposed to investigate the fracture mechanics of ion-exchanged glass, which involves significant viscoelastic deformation and stress-diffusion interaction. Based on this theoretical model, the fracture behavior of both double-sided and single-sided ion exchange processes was studied. The results indicate that, compared to single-sided ion exchange, the double-sided process is more likely to induce crack initiation and propagation, ultimately resulting in a notable reduction in glass strength. For both cases, increasing the glass thickness and interfacial energy density will significantly improve the fracture resistance of the glass. Notably, when the glass thickness or interfacial energy density is large enough, the crack can be completely closed, ensuring the integrity of the glass during the ion exchange process. Furthermore, the study conducted a preliminary investigation of two industrially relevant conditions: edging and impurities. The impacts of edging parameters, glass interfacial energy density, and covering radius on glass stress evolution, mechanical deformation, crack initiation, and crack propagation during chemical strengthening were summarized. These findings offer valuable theoretical support and a reference for optimizing chemical strengthening process parameters and enhancing the strength of glass products.

Strength Increase of Alumina Foams by a Sodium Aluminosilicate Glass Coating with Subsequent Na+ ↔ K+ Ion Exchange (Gorilla Glass Coating)

Reticulated alumina ceramic foams manufactured by the Schwartzwalder technique are coated with a sodium aluminosilicate glass using an aqueous precursor containing alumina particles and sodium silicate. After a heat treatment, a well‐adhering glass layer with a thickness between 10 and 120 μm is obtained. Besides the strut surface, the glass phase also penetrates the hollow strut cavities as well as strut cracks. The total porosity of the glass‐coated foams is between 88% and 90%, and the open cellular structure is not negatively affected by the glass coating. The compressive strength increases by a factor of two under consideration of the decrease in total porosity; a compressive strength in the order of magnitude of 2 MPa is feasible. An ion exchange of Na+ by K+ into the glass coating layer (chemical strengthening) is successfully demonstrated, but does not result in an additional improvement of the compressive strength.

Effects of P2O5 content on the structure, stress distribution and vickers hardness of Na2O-MgO-Al2O3-SiO2 glasses with chemical strengthening treatments

In this work, effects of P2O5 content on the structure, stress distribution and vickers hardness of alkali aluminosilicate glasses with different chemical strengthening treatments were investigated. The results showed that the addition of P2O5 increased the degree of polymerization for glass network. The coefficient of thermal expansion, glass transition temperature and density of the parent glasses were all decreased. Meanwhile, the molar volume of the samples increased. The chemical strengthening experiments revealed that increasing P2O5 content promoted the diffusion of K+ ions, which resulted in an increase in the depth of stress layer. However, surface compressive stress of the glasses decreased with P2O5 content increasing, mainly attributed to stress relaxation of the glass structure. After chemical strengthening treatments at 370 °C and 390 °C respectively, the vickers hardness of the glasses decreased with the increase of P2O5, while an opposite trend was observed at 410 °C.

Enhancing bending performance of ultrathin flexible glass through chemical strengthening

AbstractFlexible glass with high bending strength is a remarkable component of flexible electronic displays. However, as a brittle material, its bending properties often do not meet requirements of application. To address this challenge, the application of chemical strengthening stands out as a viable approach to significantly bolster scratch resistance and bending strength in flexible glass. This study focuses on a conventional one‐step chemical strengthening method, employing molten potassium nitrate, to reinforce ultrathin aluminosilicate glass produced through the secondary down‐drawing thermoforming process. Effects of ion‐exchange temperature and time on mechanical properties of strengthened 110 µm flexible glass were investigated, and moreover, properties of strengthened ultrathin flexible glass with various thicknesses were compared. The results indicate that, after chemical strengthening at 380°C for 1 h, the compressive stress (CS) of 110 µm glass reaches 864.60 MPa, and the depth of layer is 15.86 µm, at which time the glass has the best bending performance and scratch resistance, and half of the faceplate spacing during glass breakage can be enhanced from 38.02 ± 2.7 to 8.40 ± 0.62 mm. For ultrathin flexible glass from 40 to 110 µm, after treatment at 380°C for 1 h, the CS of thick glass is higher than that of thin glass, and the enhancement of bending performance is better.

The treated recycled aggregates effects on workability, mechanical properties and microstructure of ultra-high performance concrete Co-reinforced with nano-silica and steel fibers

To promote the application of recycled aggregates (RA) in more high-performance engineering projects, it is necessary to scientifically modify and repair the RA, which is originally damaged by mechanical crushing and contains cracks and pores. This study investigates the influence of modified RA on the workability, mechanical properties, and microstructure of ultra-high-performance concrete (UHPC). Fresh state characteristic tests (slump and flowability), hardened mechanical property tests (compressive, axial tensile, elastic modulus, and four-point bending), and analysis of microstructure (SEM images and nuclear magnetic resonance (NMR) were performed on specimens with different modifications of RA. The results showed that after three different modifications (hydrochloric acid washing, cement slurry coating, and chemical strengthening) of RA, the apparent density increased and water absorption decreased. This resulted in improved workability and fluidity of the specimens containing modified RA, with increased compressive strength and elastic modulus by 15%, as well as enhanced bending performance indicators (flexural strength, toughness, and residual strength), while the axial tensile strength was not lower than that of specimens containing natural aggregates. Additionally, SEM analysis examined the pores between the cement matrix, interface transition zone (ITZ), and fibers, and how they were improved. The specimens with modified RA had a complete and continuous ITZ, with more thorough hydration reactions and better interface bonding. NMR analysis revealed a distinct "three-peak" structure in the T2 spectrum and showed the evolution of four types of pores in the microstructure, including an increase in the number of small pores and a decrease in the number of large and medium pores and microcracks. These research findings provide new insights into the application of modified RA and serve as a reference for the use of a suitable amount of modified RA in crack-resistant or other high-demand engineering projects.

Unravelling the extra-hardening in chemically architectured high entropy alloys

Chemically architectured high entropy alloys are a new concept of multi-scale microstructure originally including a 3D network of composition fluctuations, named interphase. To unravel the strengthening contribution of each entity of the microstructure, chemically architectured alloys were processed, their microstructure and mechanical properties were characterized and then they were modelled by the finite element method. Nanoindentation measurements reveal a local extra-hardening at the interphase. Conventional modelling, even when considering three phases in a full-field approach, could not reproduce the compression properties, indicating again the existence of an extra-hardening. Then, the chemical and plastic strain gradients effects were included in the model and an agreement was reached with experimental data. Both experimental and modelling results prove that chemical gradients are at the origin of a new strengthening mechanism. This chemical gradient strengthening depends on the many microstructural parameters of chemically architectured alloys and opens the way for tuning and optimization of mechanical properties.

Effect of alkali and alkaline-earth metal oxides on the chemical strengthening properties of sodium alumino-silicate glasses

Silicate based alumino-sodium (SAS) glasses were fabricated with various alkali (Li2O and K2O) and alkaline-earth metal (MgO and CaO) oxides to study their influence on chemical strengthening characteristics such as surface compression stress (CS) and depth of layer (DOL) after ion exchange of Na+ with K+. Introducing Li2O instead of Na2O decreased DOL while increasing CS up to 5.0 mol. % of Li2O. In contrast, replacing Na2O content with K2O increased DOL while decreasing CS. When alkaline-earth oxides such as MgO and CaO were substituted for Na2O, both CS and DOL decreased. Micro-Raman spectroscopy was used to study structural changes induced by alkali and alkaline-earth oxides and their impact on ion exchange properties. The inter-diffusion coefficients of K+ ions were predicted by employing the Boltzmann-Matano equation to support the chemical strengthening effect of various alkali and alkaline-earth elements in SAS glasses.

Second phase strengthening mechanism of 2219 aluminum alloy

Second phase particles have a decisive role in strengthening 2219 aluminum alloy, so it is important to study its strengthening mechanism. The different characteristics of the second phase particles of 2219 aluminum alloy were summarized, and the strengthening mechanism of deformable second phase particles (strain strengthening, chemical strengthening, order strengthening, modulus strengthening) and non-deformable second phase particles was analyzed. The strengthening mechanism model was established, the main application of the two particles was explained, and the guiding significance of the second phase particles on the coarse residual crystal phase breaking and the grain microstructure refinement of aluminum alloy was pointed out.

Research progress of high entropy alloy: Surface treatment improves friction and wear properties

High entropy alloy (HEA) has high hardness, strength and excellent friction and wear properties, which also has broad application prospects in wear-resistant and high temperature coating, aerospace and military fields. However, one third of the world's total energy is consumed by various forms of friction or wear and tear, causing untold economic losses each year. The important way to reduce the wear is to increase the hardness of materials. The surface modification of high entropy alloy is an effective way to improve the friction and wear properties. In this paper, the research progress of high entropy alloys at home and abroad in recent years is reviewed, especially the surface treatment technology which can improve the friction and wear properties of high entropy alloys is introduced, and the influence of surface strengthening treatment on the friction and wear properties and mechanism of high entropy alloys is discussed. Surface treatment mainly includes surface mechanical strengthening, surface heat treatment strengthening, chemical heat treatment strengthening, surface laser cladding treatment, surface plasma treatment, surface electron beam treatment, vapor deposition technology. The purpose of this work is to provide a reference for the research on the friction and wear property of high entropy alloy, to provide corresponding ideas for the possible industrial demand in the future, and to provide the key research direction for future application.

Assessing the results of work on strengthening the soils of the foundation of lock № 5 of the Volga-Don shipping canal and proposals for stabilizing the chamber position

The results of work to strengthen the soil foundation of the chamber of lock № 5 of the Volga-Don Shipping Canal, carried out in 2016–2017, are analyzed. The need to carry out work to strengthen the soil was caused by an increase in the intensity of sedimentation of the central sections of the lock chamber, which began in 2005. To stabilize the chamber position, the technology of two-component jet grouting is implemented. This technology assumes the formation of several longitudinal soil-cement walls in the soils of the lock chamber base, which would transfer the load from the weight of the chamber to the harder clay soils of the water-resistant layer. However, as a result of the work performed, the precipitation intensity has increased. Engineering-geological, hydrological and geophysical studies conducted in 2018–2020 recorded the absence of formed soil-cement elements in the soils of the chamber base. An analysis of the soil samples characteristics taken from the chamber base has showed that a layer of soils of 10–12 m thickness is composed of loess rocks, below which water-resistant clayey rocks lie. Initially, there were several confined and non-confined aquifers in the soils of the lock base, and the creation of a hydroelectric complex and the formation of a level difference between the upper and lower pools led to the formation of a filtration flow with a significant pressure gradient at the base of the chamber. An analysis of the properties and structure of loess soils has showed their predisposition to subsidence, transition to a floating state and liquefaction with an increase in water content. Under the conditions of weak water-saturated loess soils, the supply of a cement mixture into them under significant pressure did not lead to the formation of soil-cement elements. Thus, in accordance with the current regulatory documents, the technical condition of the gateway is defined as pre-emergency, and the security level is defined as unsatisfactory. Methods for reducing the intensity of the chamber sedimentation such as cutting through the loess layer with piles, physical and chemical strengthening of soils and water protection of the massif at the base of the chamber are considered and evaluated.

Investigation of chemical short range order strengthening in a model Fe–12Ni–18Cr (at. %) stainless steel alloy: A modeling and experimental study

Solid solution strengthening remains the basis for many industrial alloys, yet chemical short-range order (CSRO) can also play a significant role in the strengthening of alloys with appreciable alloying additions, such as in Austenitic stainless steels. In this work, we study the evolution of CSRO under various annealing temperatures and its role on the mechanical strength of a ternary Fe–12Ni–18Cr (at.%) alloy using molecular dynamics (MD) and Monte Carlo atomistic simulations and experimental measurements from mechanical microindentation and atom-probe tomography (APT). A general model that incorporates the role of CSRO into a solute–solution strengthening model is proposed, based on a family of analytical models due to Varvenne et al. (2016) which takes into account dislocation-solute misfit interaction, and a more recent extension due to Nag and Curtin (2020) which incorporates the role of solute–solute interactions during dislocation slip. Predictions of the modified model are validated against MD shearing simulations using two commonly used embedded atom model (EAM) interatomic potentials for Austenitic stainless steel alloys, and mechanical microindentation experiments on cast alloys of the same composition. Our results suggest that, while significant CSRO is predicted in the simulations, there is little experimental evidence in cast and annealed alloys analyzed by APT.

High tensile strength glass fiber with different ratios of Na2O and SiO2 prepared by chemical strengthening method

In this paper, chemical strengthening method was used to prepare high strength glass fiber with different Na2O/SiO2 molar ratios (N/S). The structure, viscosity and tensile strength of glass samples were investigated by Molecular dynamics (MD) simulation, Raman, rotational viscometer and tensile strength tests. Results showed that the variation trends of Qn units obtained by MD simulation and Raman spectra were consistent, both indicating the decrease of the degree of network polymerization (DNP) with N/S ratio increasing. Additionally, the DNP had excellent linear relationships with the glass forming temperature and tensile strength of fresh glass fiber, respectively. However, the tensile strength was significant improved after chemical strengthening. When N/S ratio increased or chemical strengthening time prolonged, the enhancement rate of tensile strength of treated glass fiber was increased. The optimal tensile strength of glass fiber was 3089.38 ± 7 MPa after chemical strengthening at 390 °C for 30 min with N/S ratio 0.17.

Surface Hardness and Abrasion Threshold of Chemically Strengthened Soda-Lime Silicate Glasses After Steam Processing

Chemical strengthening by diffusive ion exchange (IOX) is a common method to improve the mechanical performance of glass products. However, the process of ion-stuffing is often associated with an increase of surface hardness and a decrease of the resistance to abrasive wear during scratching, even when the thickness of the exchanged layer is low. Autoclave steam-treatment presents a way to compensate the enhanced surface brittleness accompanying IOX. It causes a notable shift in the load threshold for microabrasion to more abrasion-resistant glasses. Subject to the specific processing parameters, the softening effect is constrained to a surface layer of less than 500 nm in thickness; therefore, the overall compressive stress profile is not affected and the advantages of IOX strengthening are retained. In turn, ion-stuffing by IOX counteracts severe autoclave corrosion of soda-lime silicate glasses, making them suitable for a combination of both processes.

Review of Research on Coarse Aggregate Reinforcement of Recycled Concrete

In order to explore the effective method of strengthening recycled concrete coarse aggregate，improve the effective utilization rate of recycled concrete, respond to the development requirements of green buildings and green building materials. By reading a large number of existing research methods and documents, the advantages and disadvantages of various strengthening methods for recycled concrete coarse aggregate in recent years are analyzed and summarized. The main strengthening methods of reclaimed coarse aggregate are physical strengthening, chemical strengthening and gradation strengthening through comparative analysis, more effective strengthening methods are not single, but a combination of two or more methods. Effectively combine gradation strengthening and chemical strengthening, can better improve the mechanical properties of recycled concrete coarse aggregate and durability. There is little research on the failure mechanism of transition zone and strengthening the interface transition zone of recycled concrete, and there are few literatures about harmless treatment of chemically strengthened slurry. These two aspects can be explored and analyzed in the future research.

Structural relaxation dynamics of a silicate glass probed by refractive index and ionic conductivity

AbstractRelaxation occurs spontaneously in all glasses and is a fundamental step of important technological processes, such as annealing, crystal nucleation, and chemical strengthening by ion exchange. Despite extensive studies over the past decades, there are still conflicting results on whether the kinetics of structural relaxation depends on the analyzed property. Thus, in this study, we used a lithium disilicate glass as a model composition to determine the structural relaxation kinetics during physical aging experiments by measuring the time evolution of the refractive index and ionic conductivity down to 35 K below the initial fictive temperature. In all cases, variations in these properties were adequate to capture the structural changes throughout the aging experiments. At each temperature, the experimental relaxation data fit quite well with the classical stretched exponential relation. We also found that the relaxation process starts faster when probed by ionic conductivity than by refractive index; however, they show similar average relaxation times. These very small structural rearrangements are always the same, but ionic conductivity changes faster than refractive index at the beginning of the process. Our comprehensive results strongly indicate that relaxation dynamics is indeed dependent on the analyzed property.

14‐3: Drop Resistance Optimization Through Post‐Hoc Analysis of Chemically Strengthened Glass

In the market of the mobile cover glass, the development of chemically strengthened glass is focused on the drop resistance improvement. The cover glass which protects the display panel is a typical brittle material that the micro cracks tends to be occurred underneath a glass surface by physical impacts. The micro cracks tends to be propagated by tensile stress and it is known as a general procedures on glass breakage. In purpose of the cover glass strength improvement, compressive stress is applied to the glass surface using chemical strengthening method by ion exchange. However, since the central area of the glass is relatively subjected to tensile stress, the glass is instantly broken when the propagated cracks are reached on the tensile stress exerted area. The glass specifications have been managed for maintaining the strength using parameters of compressive stress (CS), depth of compression (DOC), and central tension (CT). However, there was no method to judge the most effective factor for impact drop resistance. In order to solve this problem, we developed a machine learning program for cover glass that can predict the breakage height based on stress and mapped evaluation data based on the measured stress profile data and the actual drop breakage simulated evaluation. Especially, eXplainable AI (XAI) method is used to identify the effective factors on drop breakage height. And the test and measurement data were applied to various chemically strengthened glass for analysis.In this study, it was possible to predict the drop breakage height only by measuring the stress profile of chemically strengthened glass. The feature value of chemically strengthened that has the most effect on the drop breakage resistance on rough surfaces was identified to be stress value at 30um in the case of alkali aluminosilicate glass. And it was proved that the drop breakage height was improved by 25% only by increasing the compressive stress at 30um depth.

Fractographic strength estimations of 1- and 2-step, ion-exchanged glass plates fractured in bending

Fractography is routinely applied to estimate the fracture strength of annealed brittle materials, however, it is rarely used in chemically strengthened (CS) glasses displaying significant residual stress. This work expands and improves upon a recently proposed fractographic strength estimation method applicable to CS glass plates with deep, 1-step residual stress profiles and no stress relaxation. In particular, the current work considers both CS soda-lime silicate glass with significant stress relaxation and 2-step, ion-exchanged lithium aluminosilicate glass plates. The proposed methodology and its limitations are discussed in light of extensive testing and analysis carried out on numerous CS glass plates. The accuracy of the proposed correlation between non-dimensional strength and mirror radius was validated on both 1-step and 2-step ion-exchanged glass plates with a relatively small case depth and relatively large, induced surface damage.