Cracks In Coatings Research Articles

Identification and validation of major QTLs associated with low seed coat deficiency of natto soybean seeds (Glycine max L.)

Key messageTwo major QTLs associated with low seed coat deficiency of soybean seeds were identified in two biparental populations, and three SNP markers were validated to assist low-SCD natto soybean breeding selection.Soybean seed coat deficiency (SCD), known as seed coat cracking during soaking in the natto production process, is problematic because split or broken beans clog production lines and increases production costs. Development of natto soybean cultivars with low SCD is crucial to support the growth of the natto industry. Unfortunately, information on the genetic control of SCD in soybean, which is desperately needed to facilitate breeding selection, remains sparse. In this study, two F2 populations derived from V11-0883 × V12-1626 (Pop 1) and V11-0883 × V12-1885 (Pop 2) were developed and genotyped with BARCSoySNP6K Beadchips and F2-derived lines were evaluated for SCD in three consecutive years (2016–2018) in order to identify quantitative trait loci (QTLs) associated with low SCD in soybean. A total of 17 QTLs underlying SCD were identified in two populations. Among these, two major and stable QTLs, qSCD15 on chromosome 15 and qSCD20 on chromosome 20, were detected across multiple years. These QTLs explained up to 30.3% of the phenotypic variation for SCD in Pop 1 and 6.1% in Pop 2 across years. Three SNP markers associated with the qSCD20 were validated in additional four biparental populations. The average selection efficiency of low-SCD soybean was 77% based on two tightly linked markers, Gm20_34626867 and Gm20_34942502, and 64% based on the marker Gm20_35625615. The novel and stable QTLs identified in this study will facilitate elucidation of the genetic mechanism controlling SCD in soybean, and the markers will significantly accelerate breeding for low-SCD soybean through marker-assisted selection.

Preparation of Microcapsules of Urea Formaldehyde Resin Coated Waterborne Coatings and Their Effect on Properties of Wood Crackle Coating

Urea formaldehyde coated waterborne acrylic resin microcapsules with core-wall ratios of 0.30, 0.45, 0.60, 0.67, and 0.75, and mass fractions of 1.0%, 4.0%, 7.0%, 10.0%, 13.0%, and 16.0% were prepared by in situ polymerization. Their micro morphology was examined by scanning electron microscope and infrared spectrum measurements. The gloss, color difference, adhesion, hardness, and impact resistance of the coating surface were investigated in detail. The influence of the core-wall ratio on the performance of the waterborne crackle coating on the wood surface and the self-healing performance were examined. The results showed that when the core-wall ratio of microcapsules was 0.67, an evenly dispersed powder state with particle size of about 3 μm microcapsules was obtained, and the highest coverage was achieved. When the mass fraction of the microcapsule was 4.0%, it had the optimum effect on surface performance. The adhesion was grade two, gloss was 10.9%, impact resistance was 15 kg·cm, chromatic aberration was 1.0, hardness was H, and it had the best effect on the healing of microcracks in the wood coating. As the coating added with microcapsules can inhibit the microcracks of the coating and plays a protective role for the substrate to achieve a self-healing effect, this study lays a technical foundation for the self-healing of surface cracks in coatings for wood.

Optical properties of sol-gel coatings containing silver nanoparticles

The technology of receiving the antireflective coating increasing efficiency of use of sunlight in various service conditions is described. Suspensions of nanodimensional silicon dioxide with tetraethoxysilane as a precursor were synthesized to solve the assigned task. The received suspensions were applied by a dipping method on glass samples followed by the coating formation on a surface of the substrates at various temperatures. As a result of a cure of the received samples under natural conditions transparent film of about 500 nanometers thick having very low strength properties on the surface of glass were formed. Heat treatment led to the improvement of strength of coatings in process with increase of temperature up to 600 °C. Exceeding of this temperature resulted in cracking of coatings. In the course of heat treatment higher than 300 °C formation of a coating was accompanied by the thermolysis of silver nitrate that was introduced into silicon dioxide suspension with a formation of silver particles which size was in the nanoscale distance limits according to the results of Auger electron spectroscopy. Presence of evenly distributed silver nanoparticles provided an antireflective effect to coatings which at visual observation found expression in the form of the interference phenomenon. The obtained data confirmed prospects of use of nanosilver as a component of coatings on the basis of silicon dioxide in order to confer the antireflective properties.

Failure behaviour of Y2O3-ZrO2 thermal barrier coatings under the combined effects of hot corrosion and thermal shock

ABSTRACT Y2O3-ZrO2 thermal barrier coatings on a GH2132 alloy were fabricated by atmospheric plasma spraying method. Failure behaviours of the thermal barrier coatings under the combined condition of hot corrosion and thermal shock were investigated. Surface and cross-sectional morphologies of thermal barrier coatings before and after exposures were assessed by using scanning electron microscopy. It was established that the main failure mode was the formation of net-like cracks in coatings and penetrating cracks to the bond coat/substrate interface. By detailed consideration to the analysis of X-ray diffraction and morphologies, the effect of hot corrosion on the failure of thermal barrier coatings was inferred to be due to the induced stress during the cooling stage of the combined condition, which was prone to induce the crack formation.

Computational Model of Rib-Reinforced Plate

The article provides a methodology for constructing a calculation model that allows determining displacements in rectangular plates, reinforced by transverse and longitudinal stiffeners. The calculation model is based on the solution of the Sophie Germain’s equation by the Bubnov-Galerkin methods and successive approximations with the representation of the reactive action of the ribs on the plate in the form of a concentrated forces system. Based on the described computational model, the results of the corresponding algorithm implementation and estimation of its convergence are presented. The need to develop a calculation model is explained by the fact that the main cause of cracks in the asphalt concrete coatings of metal bridges with an orthotropic plate is the wheel load. It reaches its maximum values for short periods of time and does not allow the stresses arising in asphalt concrete to relax. At this stage of the development of the calculation model a single-layer plate is considered supported by longitudinal stiffeners. However, since the bridge bed is a multilayer structure, further development of the design model of the multilayer slab reinforced by longitudinal and transverse stiffeners will be necessary. It will help in the joint work of metal flooring and pavement. In addition, it is necessary to take into account the temperature stress factor.

THE INFLUENCE OF THE MULTILAYER STRUCTURE OF HARD COATINGS ON THEIR RESISTANCE TO MICRO-IMPACT FATIGUE WEAR

Fatigue cracking of thin hard anti-wear coatings occurs, among others, in the tribological contact of sliding friction pairs, in the top layers of cutting tools coatings, as well as in the surface of elements subjected to erosion processes. Coating fatigue wear is initiated as a result of cyclic interactions with micro-roughness of counterpart or other elements or particles that repeatedly impact the surface. The selection of appropriate coatings can increase the durability of machine components that are subjected to fatigue impact loads. The paper presents the results of tests on micro-impact fatigue wear of elements covered with single TiN and DLC coatings, as well as multi-layer (Ti/TiN)×8 type. Fatigue tests were carried out using the micro-impact method by cyclic impact of the surface of the coating with a diamond ball. The experiments were performed using a special laboratory stand. The correlation between fatigue life of coatings and their micromechanical properties such as Young's modulus and hardness were also examined. The hardness and Young's modulus were determined by an instrumented indentation method. The test results proved that the (Ti/TiN)×8 multilayer coating demonstrates wear 1.4 times smaller than the sample with the TiN coating and 1.2 than the sample with the DLC coating.

Crystallinity, Stresses, and Cracks of YSZ Coatings Characterized by SEM–EBSD–Raman Spectroscopy

Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying (APS). SEM–EBSD–Raman spectroscopy evaluated the relationship between the crystallinity, stresses, and cracks in YSZ coatings. Cracks were more likely to form in locations having poor crystallinity, due to the tensile stresses. Analysis between the formation of cracks and stresses shows that transgranular cracks are more likely created in areas with poor crystallinity. Moreover, intergranular cracks are more likely to occur around columnar grains, because the tensile stresses of columnar grains are greater than those of equiaxed grains. Resultantly, the formation and propagation of cracks can be controlled by controlling the cooling rate and grain shape.

Block cracking in surface coatings of polymeric substrates

Block cracking is commonly observed in form of a series of interconnected cracks that divide the surface of multilayered materials into approximately rectangular or square pieces. A three-dimensional (3D) elastic fracture model is developed to study the block cracking in thin film/substrate structures which consist of a thin protective metal oxide coating fully bonded to a polymer substrate. Under a temperature change, fracture occurs in the coating due to the thermal stress caused by the material mismatch. Using the plane assumption and non-shearing assumptions, the displacement and stress fields in this substrate-coating system under thermal loading are explicitly solved and verified with the finite element (FE) simulation results. Therefore, the energy release rate (ERR) can be calculated from the work done by the stress on the crack opening before crack and has been used to study the fracture initiation, infilling and saturation. Additionally, the theoretical fracture analysis results are verified by FE simulation using the cohesive zone model (CZM) and experimental data from literature. The results show that the fracture model presented in this study is able to capture the displacement and stress distributions in the thin hard oxide film fully bonded to a polymer substrate accurately and predicts the fracture initiation, infilling and saturation successfully.

Preparation of smart coatings with self-healing and anti-wear properties by embedding PU-fly ash absorbing linseed oil microcapsules

The wear resistance of self-healing coatings embedded microcapsules, an important indicator to determine whether it can be used industrially, has received little attention. Herein, an innovative method has been developed to synthesize Polyurea (PU) microcapsules containing inorganic porous fly ash absorbing linseed oil (FA-oil) as core materials by interfacial polymerization to enhance the mechanical property of the microcapsules, thereby preparing the smart self-healing coatings with and wear resistance properties. Compared with the coatings embedded PU-linseed oil microcapsules without fly ash, the wear loss of the smart coatings embedded PU-FA-oil microcapsules was 2.4 mg/8 h, which was 61.5 times lower than the former. Moreover, it was 161.7 times lower than pure epoxy coatings without any microcapsules in anti-wear test. The results showed the addition of PU-FA-oil microcapsules significantly improved the wear resistance of the smart coatings. This main reason was that the inorganic porous fly ash had the characteristics of high hardness, super wear resistance, and the slow-release effect of FA-oil in friction. In self-healing of smart coatings test, the impedance modulus at 0.01 Hz of the cured region was very close to 109 Ω·cm2, which was further higher than the uncured region of 106 Ω·cm2 and only lower an order of magnitude than unscratched region of 1010 Ω·cm2. It indicated that the linseed oil released from PU-FA-oil microcapsules could still form film, healing the microcracks and cracks in smart coatings, and self-healing property of the smart coatings embedded PU-FA-oil microcapsules was unaffected.

Effect of interlayer design on the mechanical properties of AlTiCrN and multilayered AlTiCrN/TiSiN hard coatings

The adhesion strength and mechanical properties of hard coatings on substrates can be improved by adding an interlayer, which is also known as an adhesion, buffer, or seed layer. Cathodic-arc deposition (CAD) of hard coating often results in residual stresses, and the optimized design of the hard coating interlayer helps to reduce residual stress and improve mechanical properties, which is expected to extend the useful life of high speed precision stamping die applications. AlTiCrN transition metal nitride has been used as a protective hard coating because of its high hardness (~36 GPa) and resistance to high temperature oxidation up to 1100 °C. In this study, multicomponent hard coatings of AlTiCrN and AlTiCrN/TiSiN, which in the form of AlTiCrN/TiSiN multilayers, were deposited by cathodic-arc deposition. During the coating process, gradient TiN and CrN were deposited, respectively, as interlayers with different structures to control the residual stress and adhesion strength between the coatings and substrates. AlTiCr and TiSi alloy targets were used to deposit hard AlTiCrN/TiSiN coatings. The multicomponent AlTiCrN/Ti and AlTiCrN/Cr with Ti and Cr interlayers showed high residual stresses of −8 GPa and −8.4 GPa, respectively. The multilayered AlTiCrN/TiSiN coating with intermediate CrN and transition AlTiN/CrN multilayers under the top AlTiCrN/TiSiN multilayers possessed the lowest residual stress (−3 GPa). The residual stress changed by modifying interlayer configuration before the top AlTiCrN/TiSiN multilayers. The design of AlTiCrN/TiSiN multilayered coatings with interlayers of CrN and AlTiCrN/CrN can decrease residual stress and possessed good impact fatigue performance, which can be effective to reduce damage and cracking of hard coatings during cyclic impact loading.

Effect of interfacial delamination on coating crack in thick diamond-like carbon coatings under indentation

Coating crack and interfacial delamination are recognized as two critical factors inducing spallation of thick diamond-like carbon (DLC) coatings. The effect of the two factors is found to dramatically accelerate the failure of thick DLC coatings. However, there are few reports on the effect of interfacial delamination on coating crack. In this work, in order to investigate the evolution of the coating crack and interfacial delamination, as well as the effect of interfacial delamination on coating crack, a finite element model that combines the bilinear cohesive zone model and the extended finite element method (XFEM) is established. It is found that the occurrence of interfacial delamination triggers a second expansion of coating crack. Factors influencing the degree of interfacial delamination on coating crack can be modulated by coating thickness and coating elastic modulus. As the coating thickness increases, the length of interfacial delamination increases, and thus the propagation of coating crack is accelerated. In contrast, the increase of coating elastic modulus could reduce the length of interfacial delamination, which consequently weakens its influence on the propagation of coating crack.

Discrete element simulation of damage evolution in coatings

This paper aims to use discrete element method (DEM) to investigate the cracking and interfacial delamination in ceramic coatings under uniaxial substrate tension. In DEM, the domain of the problem is discretized with a set of dense packing random arrangement of particles bonded together with springs or beam elements. In this method, partial damages can be well described which gives new insights into the qualitative description of damages in ceramic coating/substrate structures. A DEM solver code and dense particle packing generator has been developed by the authors. Yttria-stabilized zirconia is considered as an example of ceramic coatings which is usually used as a thermal insulator for superalloy substrates. A unit cell of ceramic coating/substrate structure was considered with three coating thicknesses and the effect of coating thickness was investigated on damage initiation and propagation. The results showed that the coating thickness affects the damage initiation mechanism. In addition, the structures with thick coatings are more susceptible to interfacial delamination.

Mechanism of vertical crack formation in Yb2SiO5 coatings deposited via plasma spray-physical vapor deposition

Plasma spray-physical vapor deposition (i.e., PS-PVD) is a promising method for obtaining advanced environmental barrier coatings (EBCs). The EBCs must meet some requirements in the application, in which the thermal cycle performance affects the service lifetime. The preparation of artificial vertical cracks in Yb2SiO5 coatings is an effective approach for meeting the requirements above because vertical cracks provide a strain tolerance. To clarify the formation mechanism of vertical cracks during the PS-PVD, the effects of coating thickness and substrate temperature on the formation of vertical cracks were investigated. In addition, the interactions of spray powder and plasma flame during coating deposition were also characterized by optical spectroscopy. It is indicated that vertical cracks are formed due to a thermal expansion mismatch between Yb2SiO5 and mullite coating, transient cooling after deposition and the nucleation of evaporated Yb2SiO5 as well.

Influence of moisture on the durability of protective and decorative coatings of external walls of buildings

The article presents the results of a study of the effect of air pressure in the pores of a cement substrate, which occurs when the wall material is moistened, on the crack resistance of protective and decorative coatings. It is shown that the value of air pressure in the pores of the material, provided that the moisture content of the wall material does not exceed the sorption limit, does not pose a threat to the integrity of most coatings. When the moisture content of concrete is higher than the sorption air pressure, it is comparable to the long-term cohesive strength of some protective and decorative coatings (lime, polymer-lime, KhSPE, etc.). When finishing external wall panels with a paint composition based on organic solvents (toluene, xylene, etc.), a saturated vapor-gas mixture is formed in the pores, which helps to reduce the rate of surface condensation. The destruction (peeling, cracking) of coatings from the action of air pressure in the pores of the substrate begins later in comparison with coatings based on aqueous paint formulations.

Genesis and mechanism of microstructural scale deformation and cracking in ZnAlMg coatings

In-depth investigation of the microscale deformation behavior of ZnAlMg coatings is essential to reveal the origin and mechanism of cracking in these coatings. In this work anisotropic microstructural damage and cracking of multiphase Zn1.8Al1.8Mg alloy coatings produced by hot-dip galvanization process on a steel substrate have been studied extensively. Nanoindentation coupled with orientation image microscopy (OIM) is utilized to determine the local micro ductility/strength of the existing phases as well as the orientation dependent micromechanical properties of primary zinc grains. Plastic deformation and damage behavior of the coating are evaluated through in-situ tensile/bending tests, micro-digital image correlation and in-situ OIM analyses. Stress distribution fields and nucleation sites of cracks within the coating microstructure are investigated using extended finite element method. Three quantitative plastic deformation-based criteria are revealed to correlate the coating microstructure to micro-mechanical properties to comprehend the cracking phenomenon. In particular, the binary eutectic is identified as the most detrimental constituent for compatible plastic deformation. Local strain hardening exponent and Schmid factor of primary zinc grains are found to play a significant role in clarifying the cracking behavior. The results of this study are considered as an important step towards designing microstructure controlled ZnAlMg coatings with superior formability.

Investigation on the effective parameters of through-the-width crack propagation in ceramic coatings due to substrate tension using discrete element method

This paper aims to simulate surface cracking and interfacial delamination in ceramic coatings due to their application in different industries. For this purpose, one of the most widely used ceramics, yttrium-stabilized zirconia, which is used as a thermal insulator for superalloy substrate is considered as a case study. Discrete element method was used, due to its great ability to capture the damages at the microscale, to investigate the effect of crack spacing and coating thickness on crack initiation and propagation. Discrete element method solver code is provided by the authors. To investigate damages, a unit cell of the structure between two successive surface cracks was considered. The length of the unit cell represents the crack density in the structure. In addition, for each unit cell length, three coating thicknesses were considered. The results of the current study were compared and validated with those experiments and numerical simulation results presented in the open literature. Good agreement was found. Finally, the effect of interface roughness on stress distribution and damage initiation was examined.

Gradient stiffening induced interfacial cracking and strain tolerant design in thermal barrier coatings

Strain tolerant structures endow thermal barrier coatings (TBCs) with exceptional capability to bear various strains generated during service. However, the strain tolerance of TBCs inevitably degrades when stiffening occurs at high temperatures. Herein, we tailored a strain tolerant structure to resist degradation based on an understanding of the unique stiffening behavior and consequent failure mechanism of TBCs. The degree of gradient stiffening across the thickness of TBCs is caused by temperature-dependent sintering kinetics of ceramic coatings. As a result, vertical and in-plane cracks are formed in a scale-progressive way. Simulation results reveal that the differential degree of stiffening is a main cause of interfacial cracking. Subsequently, we proposed a strain tolerant structure that is tailored by lowering the stiffening rate of regions exposed to higher temperatures. Due to the weakened differential stiffening effect, the driving force that extends the interfacial cracks was significantly lowered. Thus, this strain tolerant TBC is expected to be able to resist degradation caused by sintering. These results will guide advanced design of TBCs for future applications.

Свойства и склонность к образованию трещин покрытий сплавом Co—Cr—W

Свойства и склонность к образованию трещин покрытий сплавом Co—Cr—W

Qualitative description on channel cracking in ceramic type coatings due to substrate tension using 3D discrete element method

The objective of this work is to simulate qualitatively the initiation and propagation mechanism of channeling cracks in ceramic coatings due to uniaxial and biaxial substrate tension. Most of the previous simulations on damage evolution in coating/substrate structures were performed in 2D; however, in the current study, to demonstrate the damage evolution both in coating thickness and surface, several numerical simulation was performed in the 3D space frame. To this end, a FORTRAN code of Discrete Element Method (DEM) with Euler-Bernoulli beam bond elements and the random spherical arrangement was developed. Furthermore, the brittle fracture criterion was assigned for the coating while the substrate was considered to have linear elastic and isotropic behavior and to remain intact during loading. Three unit cells with the same dimensions and different coating thicknesses were considered. It was found that the coating thickness affects the damage initiation mechanism. In both uniaxial and biaxial tension, the increase of the coating thickness resulted in damage initiation near the interface and propagation to the top surface. At the surface view, the results showed that the free surfaces and edges could be susceptible to damage initiation in thin coatings.

A New Grating Thermography for Nondestructive Detection of Cracks in Coatings: Fundamental Principle

It is important to detect the surface and/or subsurface cracks in coatings because the cracks usually indicate the failure of the system. Conventional detection techniques face two main challenges. One is the locating of the shallow cracks or defects in thin coatings. The other is the detection of the vertical cracks. Conventional infrared thermography can efficiently detect the horizontal cracks or defects. However, when locating the shallow cracks, it requires a high sampling frequency which is unrealistic for most of the infrared cameras. In terms of the vertical cracks, it is invalid since the propagation of its detecting signal is parallel to the cracks and does not interact with them. We introduce a new grating thermography method to overcome the two difficulties. In this paper we mainly illustrate its fundamental principle, which is validated by numerical simulations and a simple experiment. Overall, the principle analysis shows that grating thermography is highly effective in detecting cracks in coatings.