Self-healing Phenomenon Research Articles

Effect of Exposure Environment and Calcium Source on the Biologically Induced Self-Healing Phenomenon in a Cement-Based Material

Microbially induced calcium carbonate precipitation (MICP) presents a sustainable, environmentally friendly solution for repairing cracks in cement-based materials, such as mortar and concrete. This self-healing approach mechanism enables the matrix to autonomously close its own cracks over time. In this study, specimens (50 mm in diameter and 25 mm in height) were exposed to submersion and a wet–dry cycle environment. The solution considered a nutrient-rich suspension with calcium lactate, urea, calcium nitrate, and Bacillus subtilis or Sporosarcina pasteurii in a biomineralization approach. The self-healing efficiency was assessed through optical microscopy combined with image processing, focusing on the analysis of the superficial crack closure area. S. and B. subtilis exhibited notable capabilities in effectively healing cracks, respectively, 8 mm2 and 5 mm2 at 35 days. Healing was particularly effective in samples placed in a submerged environment, especially with a 69 mM concentration of calcium lactate in bacterial suspensions containing B. subtilis, where 87.5% of a 4 mm2 crack was closed within 21 days. In contrast, free calcium ions in the solution, resulting from anhydrous cement hydration, proved ineffective for S. pasteurii biomineralization in urea-rich environments. However, the addition of an external calcium source (calcium nitrate) significantly enhanced crack closure, emphasizing the critical role of calcium availability in optimizing MICP for bio-agents in cement-based materials. These findings highlight the potential of MICP to advance sustainable self-healing concrete technologies.

Advances in Self-Healing Perovskite Solar Cells Enabled by Dynamic Polymer Bonds.

This comprehensive review addresses the self-healing phenomenon in perovskite solar cells (PSCs), emphasizing the reversible reactions of dynamic bonds as the pivotal mechanism. The crucial role of polymers in both enhancing the inherent properties of perovskite and inducing self-healing phenomena in grain boundaries of perovskite films are exhibited. The review initiates with an exploration of the various stability problems that PSCs encounter, underscoring the imperative to develop PSCs with extended lifespans capable of self-heal following damage from moisture and mechanical stress. Owing to the strong compatibility brought by polymer characteristics, many additive strategies can be employed in self-healing PSCs through artful molecular design. These strategies aim to limit ion migration, prevent moisture ingress, alleviate mechanical stress, and enhance charge carrier transport. By scrutinizing the conditions, efficiency, and types of self-healing behavior, the review encapsulates the principles of dynamic bonds in the polymers of self-healing PSCs. The meticulously designed polymers not only improve the lifespan of PSCs through the action of dynamic bonds but also enhance their environmental stability through functional groups. In addition, an outlook on self-healing PSCs is provided, offering strategic guidance for future research directions in this specialized area.

Digital Twin-driven Health Operation and Maintenance Strategies for Complex Equipment with Self-healing Capabilities

With the development of the industrial level, the service-oriented transformation of the manufacturing industry has become a new growth point for the interests of the manufacturing industry recognized by all countries, and in this transformation process, the health operation and maintenance (HOM) of equipment has become a crucial link, especially for complex equipment, and its health operation and maintenance level directly affects the overall efficiency of the manufacturing industry. However, with the improvement of intelligence and complexity, a more general and complete set of methods and theories is needed for the healthy operation and maintenance of complex devices with self-healing states. Based on an in-depth analysis of the key issues of complex equipment health operation and maintenance, this paper introduces digital twin technology as a breakthrough. Digital twins provide new ideas for the healthy operation and maintenance of complex equipment. By defining a digital twin-driven PHM (Prediction and Health Management) framework, this paper not only solves the problem of mobility (i.e., virtual and real connection) of the cross-platform health operation and maintenance model, but also focuses on improving the accuracy and evaluation indicators of the model (the consistency between the virtual model and the entity). Addressing issues of strategy development and effectiveness evaluation. Based on the digital twin technology, a general model was established, and the self-healing phenomenon and different maintenance strategies were introduced to explore its impact on reliability. Based on the game idea, the reliability model is used to evaluate different maintenance strategies. So as to develop the optimal operation and maintenance strategy. This not only improves the accuracy and efficiency of O&M, but also provides a solid theoretical foundation and technical support for the intelligent and autonomous health O&M of complex equipment.

Emergent fault friction and supershear in a continuum model of geophysical rupture

Important physical observations in rupture dynamics such as static fault friction, short-slip, self-healing, and the supershear phenomenon in cracks are studied. A continuum model of rupture dynamics is developed using the field dislocation mechanics (FDM) theory. The energy density function in our model encodes accepted and simple physical facts related to rocks and granular materials under compression. We work within a 2-dimensional ansatz of FDM where the rupture front is allowed to move only in a horizontal fault layer sandwiched between elastic blocks. Damage via the degradation of elastic modulus is allowed to occur only in the fault layer, characterized by the amount of plastic slip. The theory dictates the evolution equation of the plastic shear strain to be a Hamilton–Jacobi (H-J) equation, resulting in the representation of a propagating rupture front. A Central-Upwind scheme is used to solve the H-J equation. The rupture propagation is fully coupled to elastodynamics in the whole domain, and our simulations recover static friction laws as emergent features of our continuum model, without putting in by hand any such discontinuous criteria in the formulation. Estimates of material parameters of cohesion and friction angle are deduced. Short-slip and slip-weakening (crack-like) behaviors are also reproduced as a function of the degree of damage behind the rupture front. The long-time behavior of a moving rupture front is probed, and it is deduced that equilibrium profiles under no shear stress are not traveling wave profiles under non-zero shear load in our model. However, it is shown that a traveling wave structure is likely attained in the limit of long times. Finally, a crack-like damage front is driven by an initial impact loading, and it is observed in our numerical simulations that an upper bound to the crack speed is the dilatational wave speed of the material unless the material is put under pre-stressed conditions, in which case supersonic motion can be obtained. Without pre-stress, intersonic (supershear) motion is recovered under appropriate conditions.

Characterization of combined blast- and fragments-induced synergetic damage in polyurea coated liquid-filled container

Liquid-filled containers (LFC) are widely used to store and transport petroleum, chemical reagents, and other resources. As an important target of military strikes and terrorist bombings, LFC are vulnerable to blast waves and fragments. To explore the protective effect of polyurea elastomer on LFC, the damage characteristics of polyurea coated liquid-filled container (PLFC) under the combined loading of blast shock wave and fragments were studied experimentally. The microstructure of the polyurea layer was observed by scanning electron microscopy, and the fracture and self-healing phenomena were analyzed. The simulation approach was used to explain the combined blast- and fragments-induced on the PLFC in detail. Finally, the effects of shock wave and fragment alone and in combination on the damage of PLFC were comprehensively compared. Results showed that the polyurea reduces the perforation rate of the fragment to the LFC, and the self-healing phenomenon could also reduce the liquid loss rate inside the container. The polyurea reduces the degree of depression in the center of the LFC, resulting in a decrease in the distance between adjacent fragments penetrating the LFC, and an increase in the probability of transfixion and fracture between holes. Under the close-in blast, the detonation shock wave reached the LFC before the fragment. Polyurea does not all have an enhanced effect on the protection of LFC. The presence of internal water enhances the anti-blast performance of the container, and the hydrodynamic ram (HRAM) formed by the fragment impacting the water aggravated the plastic deformation of the container. The combined action has an enhancement effect on the deformation of the LFC. The depth of the container depression was 27% higher than that of the blast shock wave alone; thus, it cannot be simply summarized as linear superposition.

Healing of Undisturbed Slide Zone Soil: Experimental Study on the Huaipa Landslide in Sanmenxia City

The occurrence and development of a landslide is a gradual process of destruction, causing huge losses to people’s lives and property. The shear strength of the shear zone gradually decreases to the residual state during the sliding process but it can recover to a certain extent during a relatively stable period. In a landslide, more than one slide usually occurs; however, after the first slide stops, it can enter a dormant period. The sliding surface can then experience a self-healing strength recovery phenomenon; this self-healing phenomenon has a significant impact on the reactivation of the landslide. Relevant studies have shown that the strength of the sliding surface is slightly greater than the residual strength when a landslide is reactivated; however, the explanations provided by these studies have not been sufficiently systematic. In this study, focusing on the undisturbed slide zone soil of the Huaipa landslide in Sanmenxia City, the “shear–pause–shear–pause–shear” test scheme is adopted. The soil is subjected to 3 h, 6 h, 12 h, 24 h, and 72 h healing shear tests, and combined with the SEM microstructure characteristics of the shear surface, to explore the internal mechanism of self-healing. The results show that the landslide soil exhibits strong self-healing strength recovery characteristics; however, these strength recovery characteristics decrease rapidly after experiencing a very small displacement. The strength recovery was strongly correlated with the vertical stress and healing time. With increasing vertical stress, the strength recovery value of the soil increases. Under low pressure, the strength recovery is small, and under high pressure, the strength recovery is obvious. With increasing healing time, the strength recovery increases; however, the increase in the amplitude diminishes and ultimately approaches zero with increasing healing time. A “healing phenomenon” occurs in the shear surface of slide zone soil after a short period of time. A shear strength value greater than the residual strength can be used to check the landslide design, which can effectively reduce costs.

The Effect of Self-Healing Microcapsules in Corrosion Testing on Magnesium AZ31 Alloy and Fibre Metal Laminates

Fibre metal laminates (FMLs) are the most interesting composite materials of the past decade. They possess the properties of both polymer composites and metallic alloys. However, there is a problem with corrosion when the outer layers are made of aluminium or magnesium. The electrochemical changes that occur during the corrosion process and the mechanisms associated with the corrosion phenomenon are still being investigated. Recently, self-healing phenomena have emerged as a useful approach to prevent corrosion. However, there is limited research on the combination of FMLs and self-healing layers. Therefore, the main purpose of this article is to evaluate the self-healing ability of a magnesium/PEO layer based on microcapsules in a corrosion environment. It was observed that the corrosion mechanism in magnesium alloys is very complex. However, the use of a barrier layer with PEO treatment and microcapsules yielded positive anti-corrosion results. The FML samples were subjected to a 6-week corrosion test, and the addition of microcapsules to the layers showed positive results. In contrast, the samples without microcapsules exhibited intergranular corrosion. In the future, comprehensive tests using self-healing microcapsules in FMLs could greatly enhance their anti-corrosion properties and improve the integrity of the structure.

Self-Healing Phenomenon at the Cut Edge of Zn-Al-Mg Alloy Coated Steel in Chloride Environments

This study explores the self-healing phenomenon at the cut edges of Zn-Al-Mg alloy coated steel in chloride environments, a critical consideration for materials exposed to marine conditions. Zn-Al-Mg coatings offer superior resistance to cut-edge corrosion. This research aims to unravel the self-healing properties observed in these coatings. Through cyclic corrosion tests (CCTs), we compared the corrosion resistance of Zn-Al-Mg coated steel with traditional zinc alloy coatings. Our findings show a notable reduction in corrosion with ZMA4 coatings after 120 CCT cycles. This is due to the formation of corrosion products, namely layered double hydroxides (LDHs) and Mg(OH)2. X-ray diffraction and X-ray photoelectron spectroscopy analyses were employed to confirm the presence of these products and elucidate their roles in the self-healing process. This study highlights the potential of Zn-Al-Mg coatings for enhancing the durability of steel structures in corrosive environments, suggesting a paradigm shift in corrosion protection strategies for marine applications. The development of coatings that exhibit self-healing capabilities in chloride-rich environments could significantly mitigate the challenges posed by cut-edge corrosion, promising extended service life and reduced maintenance costs.

Modified Bacteria Incorporated Geopolymer - A Qualitative Approach for an Eco-friendly, Energy-efficient and Self-healing Construction Material

Cement production consumes huge energy and creates environmental pollution. Cracks present in the cement-based concretes, deteriorate the structural longevity and requires costly repair. An eco-friendly and energy-efficient geopolymeric material is developed by incorporating modified bacterium cells, assuming that the developed material will be a cement-alternatives in construction industries in near future. Transformed Bacillus subtilis cells is incorporated to the alkali-activated fly ash only (100%) for making the geo-polymeric material. The mortar samples prepared by geopolymeric material are cured under various conditions to achieve the best possible energy-efficient curing process. Simulated cracks on mortars are developed by applying 50% (half) of predetermined breaking load for studying the self-healing phenomenon. Artificial cracks on mortars are created by introducing steel bar for studying crack-repairing activity. Mechanical strengths (compressive, tensile and flexural), water permeability, sulfate and chloride resistant activities along with the crack-repairing and the self-healing efficacy of the samples are characterized. Higher mechanical strengths and better longevity in terms of decreased water and chloride ions permeability and increased sulfate resistant activity are noted in the bacterium amended mortars. Ambient temperature modified heat curing process reveals the best possible energy-efficient curing condition. Images and micro-structures analyses show that several new phases (e.g., silicate, mullite, albite and alite etc.) are developed within the bacteria-amended mortars. Eco-friendliness of the bacterium is confirmed by toxicity study against rats models and human cell lines. We hypothesize that the developed geo-polymeric material is a suitable cement alternative in construction industries as well as an eco-friendly and energy efficient material.

The synergistic effect of microorganisms and multiple admixtures on improving the self-healing of cracks in biogenic mortar exposed to different marine environments

Existing research has inadequately addressed the synergistic effects of microorganisms and admixtures in promoting self-healing behavior and mechanisms of cracks in marine environments, including the atmospheric zone, tidal-splash zone, and submerged zone. This study primarily involved the incorporation of multiple admixtures and microorganisms into cement to prepare two types of biogenic mortars: Bacillus pasteurii-based mortar (BPM) and Bacillus subtilis-based mortar (BSM), with ordinary mortar (OM) serving as the control group. The mechanical properties, electrical flux, and pore structure of the mortars were investigated. Additionally, the self-healing behavior and mechanisms of cracks were studied under atmospheric, tidal-splash, and submerged conditions. The results indicate that with increasing curing age, the synergistic effect of admixtures and microorganisms continuously refined the pore structure of the specimens and enhanced their flexural strength, compressive strength, and resistance to chloride ion penetration. The atmospheric environment was found to be unfavorable for the self-healing of cracks in the specimens. However, in the submerged and tidal-splash zones, the combined action of microorganisms and admixtures led to more pronounced self-healing phenomena in the biogenic mortars compared to OM. Particularly, the self-healing effect of BSM cracks was more pronounced in the tidal-splash zone, with a 100% self-healing efficiency observed after 53 days. This was attributed to the ability of microorganisms in the tidal-splash zone to induce calcium carbonate precipitation on the surface of cracks in admixture-modified cementitious materials, thereby reducing the penetration of seawater, CO2, and O2 into the cracks, lowering the carbonation reaction of Ca(OH)2 crystals, and reducing the formation of brucite crystals inside the cracks, consequently enhancing the water permeability resistance of the specimens. These research findings hold significant engineering implications for improving the durability and service life of coastal self-healing concrete structures.

Impact of Tribological Conditions on Collagen Coating Self-Healing.

The study examined the correlation between collagen coating damage and self-healing under various tribological conditions. It confirmed that the friction coefficient and degree of damage on the collagen coating varied based on contact and sliding conditions. The friction coefficient, measured at 0.56 for a single sliding cycle under a 350 mN normal load, demonstrated a notable decrease to 0.46 for 2295 cycles under 30 mN, further reducing to 0.15 for 90 cycles under a 20 mN normal load. As the normal load increased, the friction coefficient decreased, and with repeated sliding cycles under the same load, the coefficient also decreased. Water droplets induced a self-healing effect on collagen coating, causing wear tracks to vanish as fibers absorbed water. Severe wear tracks, with broken fibers and peeled coating, showed limited self-healing. In contrast, mild wear tracks, with compressed yet connected fibers, exhibited the self-healing phenomenon, making the wear tracks disappear. Real-time observations during 90 cycles under a 20 mN normal load highlighted the formation of mild wear tracks with intact collagen fibers, providing quantitative insights into self-healing characteristics. To preserve the self-healing effect of the collagen coating, it is essential to ensure tribological conditions during contact and sliding that prevent the disconnection of collagen fibers.

Harnessing microbes for self-healing concrete – A review

This review explores the burgeoning field of microbially enhanced construction materials, with a special focus on self-healing concrete, through the lens of microbial biotechnology. Central to this discourse is the innovative use of bacteria, particularly Bacillus species, to address the pervasive issue of microcracks in concrete, a fundamental material in the construction industry. Traditional remedies, such as chemical admixtures and fiber reinforcements, offer partial solutions; however, self-healing concrete represents a paradigm shift, harnessing the natural calcite-precipitating ability of bacteria to autonomously repair cracks, thereby augmenting structural durability and longevity. Delving into the mechanics, the bacteria, embedded within the concrete matrix, remain dormant until crack formation triggers their metabolic pathways, leading to calcite production that effectively seals the fissures. This bio-mediated repair mechanism not only enhances the structural integrity of concrete but also aligns with sustainable construction practices by minimizing maintenance requirements and material wastage. The review extends beyond self-healing phenomena, encompassing broader applications of microbial technology in construction, including bio-concrete, bio-cement, and soil stabilization methods. These applications underscore the versatility of microbes in enhancing material properties such as compressive strength, tensile resilience, and water impermeability. Empirical evidence underscores the necessity of optimizing bacterial dosages and curing conditions to maximize the self-healing efficiency. Future research trajectories should aim to elucidate the complex interactions between microbial agents and concrete matrices, assess long-term performance, and evaluate the environmental and economic sustainability of microbial interventions in construction. The integration of microbial technology in construction materials heralds a new epoch of innovation, offering robust, sustainable, and resilient solutions to enduring challenges in the industry.

Alkali-Ion Batteries by Carbon Encapsulation of Liquid Metal Anode.

Gallium-based metallic liquids, exhibiting high theoretical capacity, are considered a promising anode material for room-temperature liquid metal alkali-ion batteries. However, electrochemical performances, especially the cyclic stability, of the liquid metal anode for alkali-ion batteries are strongly limited because of the volume expansion and unstable solid electrolyte interphase film of liquid metal. Here, the bottleneck problem is resolved by designing carbon encapsulation on gallium-indium liquid metal nanoparticles (EGaIn@C LMNPs). A superior cycling stability (644mAhg-1 after 800 cycles at 1.0Ag-1 ) is demonstrated for lithium-ion batteries, and excellent cycle stability (87mAhg-1 after 2500 cycles at 1.0Ag-1 ) is achieved for sodium-ion batteries by carbon encapsulation of the liquid metal anode. Morphological and phase changes of EGaIn@C LMNPs during the electrochemical reaction process are revealed by in situ transmission electron microscopy measurements in real-time. The origin for the excellent performance is uncovered, that is the EGaIn@C core-shell structure effectively suppresses the non-uniform volume expansion of LMNPs from ≈160% to 127%, improves the electrical conductivity of the LMNPs, and exhibits superior electrochemical kinetics and a self-healing phenomenon. This work paves the way for the applications of room-temperature liquid metal anodes for high-performance alkali-ion batteries.

Integration of FDM and self-healing technology: evaluation of crack sealing by durability and mechanical strength

The tensile zone of concrete is prone to cracking due to its limited ability to withstand tension. To address this issue, steel reinforcement is used in these specific regions. The occurrence of little cracks might potentially facilitate the ingress of liquids and gases into the reinforcing material, hence inducing corrosion. Self-healing concrete can repair and seal minuscule cracks, thus impeding the formation of corrosion. This study investigates the potential application of fused deposition modeling (FDM) for generating novel vascular networks and tubes using polylactic acid (PLA) as the material. Poly (lactic acid) (PLA) was fabricated using three-dimensional (3D) printing techniques, and its properties were compared to those of one-dimensional (1D) and two-dimensional (2D) networks. The external diameter measured 5.6 mm, while the internal diameter measured 4 mm. utilized a 10 ml volume to apply healing agents, specifically organic polyethylene glycol liquid and nano-powder (fly ash) derived from recycled materials, to all vascular structures (1D, 2D, and 3D). This application was carried out using a planetary ball mill. Following this, the prepared tubes were incorporated into a concrete beam to introduce self-healing capabilities. The water-to-cement ratio (W/C) utilized for all concrete mixtures was 0.6%, while the definite mixture proportions were 1:2.16:2.98. The quantification of the self-healing phenomenon was conducted by evaluating the restoration of load-carrying capacity following the application of a repaired specimen to a four-point bending test. Furthermore, these enhancements resulted in improved durability, increased compressive strength, and enhanced other physical characteristics. The pipes that are manufactured can be utilized to produce innovative concrete that possesses the ability to undergo self-healing processes by combining low-viscosity healing solutions (PEG) with powders (nano fly ash) that are appropriate for this application by injection into the vascular network , making it well-suited for various self-healing applications.

Shadows of structured beams in lenslike media.

The self-healing phenomenon of structured light beams has been comprehensively investigated for its important role in various applications including optical tweezing, superresolution imaging, and optical communication. However, for different structured beams, there are different explanations for the self-healing effect, and a unified theory has not yet been formed. Here we report both theoretically and experimentally a study of the self-healing effect of structured beams in lenslike media, this is, inhomogeneous lenslike media with a quadratic gradient index. By observing the appearance of a number of shadows of obstructed structured wave fields it has been demonstrated that their self-healing in inhomogeneous media are the result of superposition of fundamental traveling waves. We have found that self-healing of structured beams occurs in this medium and, interestingly enough, that the shadows created in the process present sinusoidal propagating characteristics as determined by the geometrical ray theory in lenslike media. This work provides what we believe to be a new inhomogenous environment to explain the self-healing effect and is expected to deepen understanding of the physical mechanism.

A Study on the Movement and Deformation Law of Overlying Strata and the Self-Healing Characteristics of Ground Fissures in Non-Pillar Mining in the Aeolian Sand Area

The mining area in western China is ecologically sensitive. Coal mining can cause the formation of ground fissures, leading to geological disasters and further accelerating the process of land desertification. In this study, the working face of non-coal-pillar mining in the aeolian sand area was considered as the research object. The movement and deformation law of overlying strata were investigated through field measurements, theoretical analysis, and numerical simulation, and the mechanism governing the self-healing characteristics of ground fissures was revealed. The results demonstrated that the surface angular parameters were lower. This implies that the surface movement and the degree of deformation in non-coal-pillar mining in the aeolian sand area are significant, with a large mining influence range and rapid surface subsidence speed. After the mining of the working face, the resulting failure form of the overlying rock was asymmetric. Boundary ground fissures are typically located within the boundary of the working face, and no outward expansion is primarily observed. Dynamic ground fissures have “waviness” morphological characteristics and asymmetric “M” type development characteristics. A location model as well as a development cycle model of dynamic ground fissures were established for the first time, which can be used to predict the location and period of ground fissures. Based on the motion characteristics of hinged rock block structures, the mechanical mechanism of the self-healing phenomenon of dynamic ground fissures was revealed. A partition monitoring mode of working faces without coal pillar mining was proposed for the first time, which can reduce a lot of manpower and material resources. The coal mining subsidence basin is divided into a natural restoration area and an artificial restoration area. The combination of natural restoration and artificial guidance was used to control the ground fissures and reduce the associated costs. The research conclusions can provide a basis for mining damage evaluation and ecological environment protection in the aeolian sand area.

Structural reconstruction of iron oxide induces stable catalytic performance in the oxidative dehydrogenation of n-butane to 1,3-butadiene

The CO2-assisted oxidative dehydrogenation of n-butane to 1,3-C4H6 offers a perspective process for producing valuable chemicals while simultaneously utilizing CO2. In this work, iron-based ZnFe2Ox and Fe2O3 catalysts with high 1,3-C4H6 selectivity were prepared and their corresponding structure–activity relationships were investigated in detail. On basis of the in situ spectroscopic characterization, hydrogen-assisted CO2 activation pathway was captured. Kinetic studies show that Fe2O3 catalyst displays a higher reaction order depending on CO2 concentration than that of ZnFe2Ox catalyst. Fe2O3 is evidenced to serve as an effective mediator for oxygen exchange between CO2 and n-butane based on temperature-programmed experiments and deactivation kinetics analysis. Rapid deactivation is observed over ZnFe2Ox due to its strong CO2 adsorption ability, which triggers the reforming reaction accompanied by severe coke deposition. Interestingly, self-healing phenomena for catalytic performance are found on Fe2O3 catalyst after several test cycles. The reaction/regeneration cycles are proved to drive the surface reconstruction which greatly enhance its resistance to over reduction and coking. This study provides a fundamental insight into Fe-based catalysts in the CO2-assisted oxidative dehydrogenation reactions.

Densification behaviour of laser powder bed fusion processed Ti6Al4V: Effects of customized heat treatment and build direction

The present work exploits the customized heat treatment, and laser powder bed fusion process to build direction effects on the densification behaviour and microstructural development in Ti6Al4V alloy. Optical microscopy evaluates the porosity and microstructure in different conditions. Further, the porosities are classified as inter-micropores (size < 10 µm) and super-micropores (size > 10 µm). Classification and quantifications of the porosities of laser powder bed fusion processed Ti6Al4V alloy under both directions due to customized heat treatment. The effect of customized heat treatment, the corresponding pore self-healing mechanism, and microstructure refinement on laser powder bed fusion-processed Ti6Al4V alloy were discussed. Moreover, the X-ray diffraction technique was used to analyse the different phases during laser powder bed fusion and customized heat treatment. The elevated customized heat treatment helps to reduce the overall porosity by two times that of as-printed samples due to the sintering self-healing phenomenon. Interestingly, the super micropores observed in as-printed samples are reduced via customized heat treatment ∼ 44% in a horizontal direction and ∼ 46% in a vertical direction, respectively, which is favourable for enhancing mechanical properties. This is because reducing these micropores leads to improved ductility. The ductility of the customized heat treatment executed sample was ∼ 68% in a horizontal orientation and ∼180% in a vertical orientation. The isotropic index for ductility in as-printed Ti6Al4V in the horizontal and vertical directions is 0.61. In contrast, it is 0.97 for customized heat treatment in both orientations showing high isotropy for customized heat treatment samples compared to as-printed samples. This study reveals that the customized heat treatment technique can be beneficial in introducing isotropic microstructure and densifying the distinctive laser powder bed fusion components.

The hot corrosion resistance of APS YSZ coatings micro glazed via an ultraviolet picosecond ultrashort pulsed laser

In this paper, yttria-stabilized zirconia (YSZ) was innovatively glazed via an ultraviolet picosecond ultrashort pulsed laser (laser micro glazing, LMG). A smooth LMGed layer (surface roughness: ∼0.714 µm) with incredibly narrow cracks (< 0.547 µm in width) was achieved. The hot corrosion tests of molten salt (V2O5 +Na2SO4) at 1100 °C for 20 h were performed. The results show that laser irradiation not only increased oxygen vacancies but also reduced the reaction area between the molten salt and coatings. During the hot corrosion test, the LMGed layer with ultra-fine grains also promoted a homogeneous redistribution of Y3+ during the segregation process. These factors greatly improved the phase and structural stability of t′-ZrO2 in the LMGed surface. Interestingly, the self-healing phenomenon of narrow cracks was found in the LMGed layer, which tremendously decreased the penetration channels of the molten salt. Compared with the original as-sprayed coatings, the corrosion product YVO4 on the LMGed coatings was not only reduced in number but also greatly diminished in size. Meanwhile, the m-ZrO2 content and penetration depth in the LMGed coatings were decreased by 80.336 % and 60.057 %, which demonstrated the excellent hot corrosion resistance of LMGed YSZ coatings.

A comprehensive review on the properties of engineered cementitious composite with a self- healing material

The most common types of cementitious materials used as building materials can be found all over the world. The fact remains, however, that deterioration is unavoidable right from the start of the service life, which is followed by maintenance and repair work. Since the cementitious materials have been observed to exhibit a self-healing phenomenon, which has been the subject of research for quite some time. This paper is focused on the review of the feasibility of (Engineered Cementitious Composite) ECC and its properties such as mechanical, physical, rheological, and chemical properties. ECC is considered to have a high self-healing potential and superior mechanical and durability performance. Self-healing concrete is typically employed for the purpose of minimizing cracks in concrete and enhancing the material's overall durability. These mechanisms are reviewed based on extensive experimental studies and practical experience. Self-healing concretes are typically employed for the purpose of mending cracks in concrete and enhancing the material's overall durability. There are many distinct varieties of self-healing processes, including natural, chemical, and biological ones. Studies were conducted with a primary emphasis on biological processes that are dependent on precipitation. In order to study the properties of self-healing with ECC, a transmission electron microscope (TEM), an environmental scanning electron microscope-energy dispersive spectroscopy system (ESEM-EDS), Fourier transform infrared spectroscopy, and X Ray Diffraction (XRD) were all implemented. To further understand the properties of self-healing, this research was conducted. This review offers a fresh perspective on the research done on the topic of treating unexpected cracking in concrete through the use of a self-healing process.