Brittle Manner Research Articles

A Comparative Study of the Impact of La2O3 and La2Zr2O7 Dispersions on Molybdenum Microstructure, Mechanical Properties, and Fracture

AbstractWe report, for the first time, the effect of lanthanum zirconate (La2Zr2O7) particles on the microstructure and mechanical behavior of an experimental molybdenum oxide dispersion-strengthened alloy. The focus was on the preparation of the novel Mo–La2Zr2O7 composite using high-energy ball milling and spark plasma sintering and on the comparison of its microstructural and mechanical properties with pure Mo and Mo–La2O3 ODS alloy counterparts. Mechanical properties were assessed using a Vickers hardness test at room temperature and a three-point flexural test in the temperature range from − 150 to 150 °C. The microstructure of the studied materials and their fracture behavior were evaluated using x-ray diffraction, energy-dispersive x-ray spectroscopy, and scanning electron and transmission electron microscopy. The strengthening effect of La2Zr2O7 particles was found to be lower than that of La2O3 particles, resulting in a 30-35% lower yield stress and flexural strength of the Mo–La2Zr2O7 alloy compared to the Mo–La2O3 alloy. The experimental Mo–La2Zr2O7 alloy exhibited low plasticity and no distinct ductile-to-brittle transition temperature (DBTT) in the tested temperature range, unlike pure Mo and the Mo–La2O3 alloy, which had the DBTT of 63 and 1 °C, respectively. Fracture occurred mainly in a brittle intergranular manner in the entire testing temperature range, while the counterpart materials showed localized plastic stretching at grain boundaries and within grains at and above the transition region. The observed behavior was primarily related to lower strengthening and brittleness as well as less effective grain boundary purification.

Post irradiation examinations of FeCrAl cladding in PWR conditions

FeCrAl alloys have been one of the prominent Accident Tolerant Fuel (ATF) cladding material candidates, primarily due to their excellent oxidation resistance in high-temperature steam conditions when compared to Zr-based alloys. Prototypic irradiation of fueled FeCrAl rods is a fundamental step in confirming the integral performance behavior during in-pile conditions. Early generation C26M cladding, fabricated through wrought metallurgy techniques, was fueled with UO2 fuel pellets and irradiated in a pressurized water loop in the Advanced Test Reactor (ATR) at the Idaho National Lab (INL) to a burnup (BU) of ∼25 GWd/tHM. After irradiation, the rodlets were nondestructively and destructively examined. Nondestructive examinations included visual exams, profilometry, and gamma scanning. These examinations highlight the unique deposits, BU profile of the rodlets as well as the migration path of fission gases within the rodlet, and typical diametrical morphology of fuel rodlets. During handling, brittle failure of one end cap on one pin occurred. Destructive examinations included microscopy and mechanical testing. Radial cross sections of the cladding were analyzed metallographically through light optical microscopy (LOM), scanning electron microscopy (SEM) highlighting a unique corrosion morphology and micro-cracking (∼20–30 μm past the main oxide layer) at the metal-oxide interface. Ring compression testing (RCT) was used to elucidate the mechanical property change of the FeCrAl cladding after neutron irradiation. In contrast to the non-irradiated material, which remained ductile at all test temperatures between 25 °C and 250 °C, the irradiated cladding fractured in a brittle manner at 50 °C and below. The results of the tests show that some challenges remain in the development of FeCrAl cladding for LWR cladding applications including improvement of in-reactor waterside corrosion performance and the retention of ductility after neutron irradiation.

The role of collagen and crystallinity in the physicochemical properties of naturally derived bone grafts

Abstract Xenografts are commonly used for bone regeneration in dental and orthopaedic domains to repair bone voids and other defects. The first-generation xenografts were made through sintering, which deproteinises them and alters their crystallinity, while later xenografts are produced using cold-temperature chemical treatments to maintain the structural collagen phase. However, the impact of collagen and the crystalline phase on physicochemical properties have not been elucidated. We hypothesized that understanding these factors could explain why the latter provides improved bone regeneration clinically. In this study, we compared two types of xenografts, one prepared through a low-temperature chemical process (Treated) and another subsequently sintered at 1100 °C (Sintered) using advanced microscopy, spectroscopy, x-ray analysis, and compressive testing. Our investigation showed that the Treated bone graft was free of residual blood, lipids, or cell debris, mitigating the risk of pathogen transmission. Meanwhile, the sintering process removed collagen and the carbonate phase of the Sintered graft, leaving only calcium phosphate and increased mineral crystallinity. Micro computed tomography revealed that the Treated graft exhibited an increased high porosity (81%) and pore size compared to untreated bone, whereas the Sintered graft exhibited shrinkage, which reduced the porosity (72%), pore size, and strut size. Additionally, scanning electron microscopy (SEM) displayed crack formation around the pores of the Sintered graft. The Treated graft displayed median mechanical properties comparable to native cancellous bone and clinically available solutions, with an apparent modulus of 166 MPa, yield stress of 5.5 MPa, and yield strain of 4.9%. In contrast, the Sintered graft exhibited a lower median apparent modulus of 57 MPa. It failed in a brittle manner at a median stress of 1.7 MPa and strain level of 2.9%, demonstrating the structural importance of the collagen phase. This indicates why bone grafts prepared through cold-temperature processes are clinically favourable.

Experimental Investigations on the Application of Natural Plant Fibers in Ultra-High-Performance Concrete.

Due to its high strength, the use of ultra-high-performance concrete (UHPC) is particularly suitable for components subjected to compressive loads. Combined with its excellent durability, UHPC can be used to produce highly resource-efficient components that represent a sustainable alternative to conventional load-bearing structures. Since UHPC fails in a brittle manner without the addition of fibers, it is typically used in conjunction with micro steel fibers. The production of these steel fibers is both expensive and energy-intensive. Natural plant fibers, due to their good mechanical properties, cost-effective availability, and inherent CO2 neutrality, can provide a sustainable alternative to conventional steel fibers. Thanks to the low alkaline environment and dense matrix of UHPC, the use of natural plant fibers in terms of durability and bond is possible in principle. For the application of natural plant fibers in UHPC, however, knowledge of the load-bearing and post-cracking behavior or the performance of UHPC reinforced with natural plant fibers is essential. Currently, there are no tests available on the influence of different types of natural plant fibers on the load-bearing behavior of UHPC. Therefore, five series of compression and bending tensile tests were conducted. Three series were reinforced with natural plant fibers (bamboo, coir, and flax), one series without fibers, and one series with steel fibers as a reference. Under compression loads, the test specimens reinforced with natural plant fibers did not fail abruptly and exhibited a comparable post-failure behavior and damage pattern to the reference specimens reinforced with steel fibers. In contrast, the natural plant fibers did not perform as well as the steel fibers under bending tensile stress but did show a certain post-cracking bending tensile strength. A final life cycle assessment demonstrates the superiority of natural plant fibers and shows their positive impact on the environment.

Shear capacity of interlocking compressed stabilized earth block masonry panels

An experimental study was conducted to investigate the shear performance of reinforced and unreinforced interlocking compressed stabilized earth block (ICSEB) masonry wall panels. Forty-eight wall panels were fabricated using Auram 295 blocks and subjected to diagonal-compression. The influence of coir fibres, channel block, type of reinforcement (steel and bamboo) and arrangement (mesh and vertical) on wall shear behavior were studied. Cracking patterns, failure modes, load-deformation response and shear capacity were analyzed and discussed. The feasibility of using conventional masonry analytical equations in estimating the shear load capacity of wall panels was also evaluated. The test results demonstrated that wall panels without bamboo/steel reinforcement failed suddenly in a brittle manner and split into two parts, whilst bamboo/steel reinforced grouted wall panels behaved in a more ductile manner and remained intact after the failure, irrespective of presence of fibres. The incorporation of fibres effectively increased the shear load and deformation ability of wall panels, irrespective of the variables examined. The panels reinforced with steel/bamboo showed a significant improvement in shear load capacity of about 20.33% to 162.94% and in deformation capacity of around 48.47% to 258.29% when compared to the panels without reinforcement. The adopted analytical equations inaccurately predicted the shear capacity of wall panels.

Brittle initiation of dissolution–precipitation creep in plagioclase-rich rocks: insights from the Bergen arcs, Norway

The initiation of ductile shear zones commonly occurs spatially associated with fluid-rock reactions along brittle precursors. In many cases the relative timing of fracturing, fluid infiltration, reaction, and recrystallisation is unclear, making it difficult to disentangle mechanisms of shear zone initiation from subsequent deformation and recrystallisation. Here we present the study of the transition from a dry plagioclase-diopside-garnet-scapolite host granulite-facies lithology to (1) a low strain amphibolite-facies rock, and (2) a transition from low strain to high strain amphibolite-facies lithologies. Hydration of the granulite-facies precursor at amphibolite-facies conditions produces an assemblage comprised dominantly of plagioclase-amphibole-zoisite-clinozoisite-kyanite-scapolite-quartz. Detailed study of plagioclase chemistry and microstructures across these two transitions using Electron Backscatter Diffraction (EBSD) and Wavelength Dispersive Spectrometry (WDS) allows us to assess the degree of coupling between deformation and fluid-rock reaction across the outcrop. Plagioclase behaves dominantly in a brittle manner at the hydration interface and so the initial weakening of the rock is attributed to grain size reduction caused by fracture damage and fluid infiltration at amphibolite-facies conditions. Extensive fracturing-induced grain size reduction locally increases permeability and allows for continuing plagioclase and secondary mineral growth during shear. Based on plagioclase microstructures, such as, an inherited but dispersed crystallographic preferred orientation (CPO), truncation of chemical zoning, and the dominance of fine (5–150 µm), slightly elongate, polygonal grains we conclude that deformation is dominantly facilitated by dissolution–precipitation creep assisted by grain boundary sliding in the shear zone.

Experimental and theoretical evaluation of inclined screws in glued laminated bamboo and timber-concrete composite beams

In the timber-concrete composite beam, the timber beam in tension tends to fail in a brittle manner, which results in insufficient utilization of material strength in the compression zone and significant deformation problems. To improve the mechanical performance of the weak sections in the composite beam, a novel type of glued laminated bamboo and timber (GLBT)-concrete composite beam is proposed in which the bamboo layers are placed in the tension and compression zones of the beam. In this paper, thirty-six shear experiments were conducted to investigate the shear behavior of inclined screws in GLBT-concrete composite beams. The test results showed that the failure modes of diagonally positioned screws in GLBT-concrete composite beams involved pull-out failure of the screw and cone expulsion failure of the concrete. The pure tensile-shear loaded screws experienced the pull-out failure and single-hinge bending failure. For bamboo thicknesses of 30, 60, and 300 mm, the shear capacity of diagonally positioned screws increased by 27.9 %, 34.7 %, and 40.7 %, respectively, compared to the screws in pure wood members. Besides, the shear stiffness was improved by 40.4 %, 78.1 %, and 88.7 %, respectively. It was found that as bamboo thickness increased, the shear capacity and stiffness of diagonally positioned screws gradually improved, although the rate of increase gradually diminished. Among the four types of embedding methods, the ±45° diagonal screw connectors exhibited the highest shear stiffness, while the 135° unidirectional inclined screws (pure compressive-shear screws) had the lowest shear capacity and stiffness. This paper presented a theoretical model for estimating the shear capacity of inclined screw connectors in GLBT-concrete composite beams, which considered the various stress distributions of the screw connectors embedded in bamboo and timber layers.

Tensile characteristics of ultra-high-performance fibre-reinforced concrete with and without longitudinal steel rebars

Ultra-high-performance fibre-reinforced concrete (UHPFRC) specimens with and without longitudinal reinforcement were experimentally tested under direct tensile loading. The variables considered were the volume fraction of fibres (1.0% and 2.0%), the type of steel fibres (straight and hooked end) and the longitudinal steel reinforcement ratio (none and 1.2%). All of the specimens were tested using a servo-controlled fatigue testing machine in displacement control mode. The changes in displacement were monitored using linear variable displacement transducers and the digital image correlation technique. The strain profiles at different loading stages were used to identify the crack evolution process. The average localised strain was found to be 0.2–0.36%, with corresponding crack widths of 0.3–0.6 mm. A uniaxial tensile stress–strain model was developed based on the test results and data from the literature. Longitudinally steel-reinforced specimens showed both stiffening and strengthening effects. Tension-stiffened specimens with 1.0% fibres failed at a higher strain due to the formation of multiple macrocracks. In the specimens with 2.0% fibres, the rebar fractured in a brittle manner due to crack localisation. It is concluded that a higher longitudinal reinforcement ratio is needed to utilise UHPFRC effectively under tension-dominant loads.

Effect of titanium on microstructure and mechanical behaviour of additively manufactured 1.2709 maraging steel

The effect of titanium on the microstructure and properties of additively manufactured 1.2709 maraging steel is thoroughly studied in this work. For this purpose, a standardized alloy with 0.84 wt% Ti and a model alloy with 0.02 wt% of Ti were prepared by laser powder bed fusion. The microstructures and mechanical behaviour (tensile properties and hardness) of the alloys are described and compared here. It is shown that in contrast to the standardized alloy, the model alloy cracks along grain boundaries in a brittle manner. The effect of Ti is further completed by investigations of (i) an alloy with an addition of 0.7 wt% Ti prepared by laser powder bed fusion and (ii) a low-Ti alloy produced by conventional casting. It is unambiguously shown that the cracking is primarily caused by the interplay of steep temperature changes during laser powder bed fusion of the steel powder and of the low Ti content in the model alloy causing the absence of retained austenite at grain boundaries. Additionally, the tendency of grain boundaries to crack during additive manufacturing is shown to depend on the grain boundary character.

Mechanical Properties of Irradiated U-10 wt. %Mo Alloy Degraded by Porosity Development

Abstract A plate-type nuclear fuel consisting of a solid monolithic foil of U-10 wt. %Mo is under development for use in the United States' high-performance research reactors. In support of developing this fuel, the fuel has been fabricated for the first time by a commercial fuel vendor and subsequently irradiated in a test reactor. This provides an opportunity to evaluate postirradiation mechanical properties of the commercially fabricated fuel. Four-point bend testing was conducted on the irradiated U-10Mo samples to generate the fuel material properties, including the modulus of elasticity and the bending strength. Although the material behaves in a brittle manner due to the accumulated porosity, a general trend of strength and modulus reduction was found as fission density increases. The data produced was evaluated using both Weibull statistics and a modulus degradation model with recommendations provided.

Hydrological constraints on the potential of enhanced geothermal systems in the ductile crust

Continental crust at temperatures > 400 °C and depths > 10–20 km normally deforms in a ductile manner, but can become brittle and permeable in response to changes in temperature or stress state induced by fluid injection. In this study, we quantify the theoretical power generation potential of an enhanced geothermal system (EGS) at 15–17 km depth using a numerical model considering the dynamic response of the rock to injection-induced pressurization and cooling. Our simulations suggest that an EGS circulating 80 kg s−1 of water through initially 425 ℃ hot rock can produce thermal energy at a rate of ~ 120 MWth (~ 20 MWe) for up to two decades. As the fluid temperature decreases (less than 400 ℃), the corresponding thermal energy output decreases to around 40 MWth after a century of fluid circulation. However, exploiting these resources requires that temporal embrittlement of nominally ductile rock achieves bulk permeability values of ~ 10–15–10–14 m2 in a volume of rock with dimensions ~ 0.1 km3, as lower permeabilities result in unreasonably high injection pressures and higher permeabilities accelerate thermal drawdown. After cooling of the reservoir, the model assumes that the rock behaves in a brittle manner, which may lead to decreased fluid pressures due to a lowering of thresholds for failure in a critically stressed crust. However, such an evolution may also increase the risk for short-circuiting of fluid pathways, as in regular EGS systems. Although our theoretical investigation sheds light on the roles of geologic and operational parameters, realizing the potential of the ductile crust as an energy source requires cost-effective deep drilling technology as well as further research describing rock behavior at elevated temperatures and pressures.

DFT simulation to study the physical properties of ternary intermetallic materials ACuSb (A=Ca, Sr, Ba) for solar cell and TBC materials

This study carried out the configurational, bulk, electronic, optical as well as thermodynamic features of ternary materials ACuSb (A = Ca,Sr, Ba) using first-principles DFT-based calculations. The explored lattice constants as well as unit cell volume are very close to hypothetical results which make sure the correctness of the present study. According to the investigated elastic stiffness constants, the studied compounds are mechanically stable as they hold the Born's stability criteria. Utilizing the calculated values of elastic constants the several polycrystalline parameters such as elastic moduli (B, Y, E), machinability index (μm), hardness (HV), Poisson's ratio, Pugh's and isotropic/anisotropic factor of ACuSb (A = Ca,Sr, Ba) have been calculated and discussed in details. Very high machinability indices of these phases ensure their industrial applications. Since the values of Poisson's and Pugh's are ν < 0.26 and B/G < 0.75, therefore the phases ACuSb (A = Ca,Sr, Ba) show brittle manner. The direction-dependent features of these materials are confirmed from the Universal anisotropy factor analysis. Band structure analysis reveals that every compounds exhibit metallic character. Bond population analysis revealed the different covalent and ionic bonding tendencies in these compounds, with apparent differences in the nature of Cu–Sb bonds. Furthermore, the absorption coefficients of BaCuSb ensures its excellent suitability for solar cell applications, as it demonstrated remarkable UV-range absorption capabilities, distinguishing it from the other compounds in this regard. The thermal analysis demonstrated that these compounds exhibit remarkably low thermal conductivity, indicating their appropriate applications in thermal barrier coating (TBC) materials.

Microstructure and Mechanical Properties of the EN AC-AlSi12CuNiMg Alloy and AlSi Composite Reinforced with SiC Particles

There is growing interest in developing more advanced materials, as conventional materials are unable to meet the demands of the automotive, aerospace, and military industries. To meet the needs of these sectors, the use of advanced materials with superior properties, such as metal matrix composites, is essential. This paper discusses the evaluation of microstructural and mechanical properties of conventional eutectic EN AC-AlSi12CuNiMg aluminum alloy (AlSi12) and advanced composite based on EN AC-AlSi12CuNiMg alloy matrix with 10 wt% SiC particle reinforcement (AlSi12/10SiCp). The microstructure of these materials was investigated with the help of metallographic techniques, specifically using a light microscope (LM) and a scanning electron microscope (SEM). The results of the microstructural analysis show that the SiC particles are uniformly distributed in the matrix. The results of the mechanical tests indicate that the tensile properties and hardness of the AlSi12/10SiCp composite are significantly higher than those of the unreinforced eutectic alloy. For AlSi12/10SiCp composite, the tensile strength is 21% higher, the yield strength is 16% higher, the modulus of elasticity is 20% higher, and the hardness is 11% higher than unreinforced matrix alloy. However, the unreinforced AlSi12 alloy has a percentage elongation that is 16% higher than the composite material. This shows that the AlSi12/10SiCp composite has a lower ductility than the unreinforced AlSi12 alloy. The tensile specimens of the tested composite broke apart in a brittle manner with no discernible neck development, in contrast to the matrix specimens, which broke apart in a ductile manner with very little discernible neck formation.

Impact of Acetylation on the Behaviour of Single-Dowel Timber Connections

This paper presents an experimental study where the mechanical behaviour of single-dowel timber connections made of acetylated Scots pine is compared with the behaviour of connections made from untreated Scots pine. The main aim was to evaluate the influence of the acetylation on the connection brittleness and also to compare the experimental results to the design provisions of the current European structural timber code, Eurocode 5 (EC5). The experiments included embedment tests and tests with connections loaded parallel and perpendicular to the grain, and, for the latter tests, applying different end and edge distances. The acetylated wood showed a 2% increase in density and a 31% increase in embedment strength compared to the untreated wood. For tests on connections loaded parallel to the grain, all specimens made from acetylated wood failed in a brittle manner, while the connections made from untreated wood and complying with minimum end distance of the EC5 design provisions failed due to embedment failure followed by splitting involving cracking along the grain. The connections made of acetylated wood showed a 13–15% higher capacity than the corresponding specimens made from untreated wood. Thus, to fully utilize the potential of the increased embedment strength parallel to the grain, it is concluded that reinforcement of the joint, e.g., by self-tapping screws or externally applied sheet reinforcement would be necessary if the minimum end distances of EC5 are applied. The current design provisions for loading perpendicular to the grain overestimated the capacities severely with predicted characteristic values being 20–50% higher than mean values from tests for the recommended minimum edge distances. Finally, it was found that the splitting capacity in loading perpendicular to the grain was 10–18% lower for the specimens made from acetylated wood compared to the untreated wood.

Microstructure, Phase Composition, and Mechanical Properties of Intermetallic Ni-Al-Cr Material Produced by Dual-Wire Electron-Beam Additive Manufacturing

Electron-beam additive manufacturing is one of the most promising methods for creating complex metal parts and structures. Additive manufacturing has already gained wide acceptance in the creation of various constructions from aluminum, copper, titanium, and their alloys as well as different classes of steels and other metallic materials. However, there are still many challenges associated with the additive manufacturing and post-production processing of intermetallic alloys. Thus, it is currently an urgent task for research. In this work, heat-resistant intermetallic alloys based on nickel, aluminum, and chromium were produced by dual-wire electron-beam additive manufacturing using commercial NiCr and Al wires. The microstructure, phase composition, and microhardness of the intermetallic billets are strongly dependent on the ratio of NiCr and Al wires, which have been fed during the additive growth of the material (NiCr:Al = 3:1 and NiCr:Al = 1:3). A metal-matrix composite material (Al3Ni-based intermetallide in Al-based matrix) was fabricated using the NiCr:Al = 1:3 ratio of the wires during the deposition. In tension, it fractures in a brittle manner before the plastic deformation starts, and it possesses a high microhardness of 6–10 GPa with a high dispersion of the value (the mean value is 8.7 GPa). This is associated with the complex phase composition of the material and the high fraction of a brittle Al3Ni intermetallic phase. In the material, obtained with the ratio NiCr:Al = 3:1, the ordered Ni3Al(Cr) and disordered Ni3Cr(Al) intermetallides are the dominating phases. Its microhardness turned out to be lower (4.1 GPa) than that in Al + Al3Ni-based composite, but intermetallic Ni3Al-based alloy demonstrates good mechanical properties in a high-temperature deformation regime (650 MPa, more than 10% elongation at 873 K). Microstructural studies, analysis of phase composition, and tensile mechanical properties of additively produced intermetallic materials show the perspective of dual-wire electron-beam additive manufacturing for producing intermetallic compounds for high-temperature applications.

Corrigendum for: How the Earth’s upper crust deforms in a viscous or brittle manner and how these behaviors interact and evolve over time: the crucial role of pressure solution creep and sealing processes

Corrigendum for: How the Earth’s upper crust deforms in a viscous or brittle manner and how these behaviors interact and evolve over time: the crucial role of pressure solution creep and sealing processes

Crystal property engineering using molecular-supramolecular equivalence: mechanical property alteration in hydrogen bonded systems.

Most crystal engineering strategies exercised until now mainly rely on the alteration of weak non-covalent interactions to design structures and thus properties. Examples of mechanical property alteration for a given structure type are rare with only a few halogen bonded cases. The modular nature of halogen bonds with interaction strength tunability makes the task straightforward to obtain property differentiated crystals. However, the design of such crystals using hydrogen bond interactions has proven to be non-trivial, because of its relatively higher difference in bonding energies, and more importantly, disparate geometries of the functional groups. In the present crystal property engineering exercise, with the support of CSD analysis, we replaced a supramolecular precursor that leads to plastically bendable crystals, with a molecular equivalent, and obtained an equivalent crystal structure. As a result, the new structure, with comparable hydrogen bonding chains, produces elastically bendable single crystals (as opposed to plastically bendable crystals). In addition, the crystals show multidirectional (here two) elastic bending as well as rare elastic twisting. The occurrence of multiple isostructural examples, including a solid solution, with identical properties further demonstrates the general applicability of the proposed model. Crystals cannot display the concerned mechanical property in the absence of the desired structure type and fracture in a brittle manner on application of an external stress. Nanomechanical experiments and energy framework calculations also complement our results. To the best of our knowledge, this is the first example of a rational crystal engineering exercise using solely hydrogen bond interactions to obtain property differentiated crystals. This strategy namely molecular-supramolecular equivalence has been unexplored till now to tune mechanical properties, and hence is useful for crystal property engineering.

Tensile properties and fracture behaviors of electron-beam welded Ti6242 titanium alloy joints

The microstructure, tensile properties and fracture behaviors of electron-beam welded Ti6242 titanium alloy joints were systematically investigated. The as-received alloy exhibited a typical duplex microstructure consisting of equiaxed primary α phase and laminated secondary α phase/β phase. The high cooling rate during welding resulted in substantially microstructure evolution in the fusion zone (FZ) of the joints, leading to the formation of large columnar β grains with embedded acicular α′ martensitic phase platelets. The influences of such microstructure variations on the mechanical properties and fracture behaviors at different temperatures were analyzed and discussed. In principle, the hard-yet-brittle α′ martensitic phase induced significantly strengthening of the FZ. As a result, for the un-notched specimens, the plastic deformation was concentrated to the soft base material with subsequent ductile fracture via micro-void coalescence mechanism. But for the notched specimen, in which the notch located just within the FR, cracks initiated and proceeded along the FR in a brittle manner.

DELAYED CRACKING FAILURE OF A FREEZER BARREL

Freezers were used to produce ice cream, pumped by a screw pump into a barrel. The barrel’s outer surface was operated with NH3 gas at -40 oC and a 12–13 bar pressure. After being in service for 3 years, the unit experienced cracking. The barrel material was Nickel 200, with a base metal average grain size of 48μm. The weld metal has a larger average grain size of 800μm and contains many gas pockets inside and along the grain boundaries, which coalesce one after another, forming micro-cracks that result in intergranular cracking. The weld metal failed in a brittle manner; this embrittlement was attributed to hydrogen atoms ingressing into the weld metal during welding. Atomic hydrogen will diffuse, forming hydrogen gas. Since atomic diffusion takes place over a long period, the occurrence of cracks is well-known as delayed cracking.

First-principles analysis on phase transition, atomic, electronic, and mechanical properties of kaolinite under pressures

Kaolinite is the major clay mineral and dispersed widely in topsoil and subsoil in the world. The structural, electronic, and mechanical properties of kaolinite are closely related to their various applications in architecture, industry, and agriculture. In the present paper, the phase transition, atomic structural, electronic and mechanical properties of kaolinite under pressure range of 0–10 GPa were systematically investigated using the first-principles density functional theory (DFT). The lattice parameters, bonding nature, total and partial density of states, elastic constants, various modulus, and anisotropy for kaolinite were calculated. The transition pressures of kaolinite occurred at 4.93 GPa (kaolinite-I → kaolinite-II) and 8.23 GPa (kaolinite-II → kaolinite-III), respectively, which were well consistent with experimental data. In the range of 0–10 GPa, the lattice parameters, volume, and typical bond lengths of I, II, and III phases of kaolinite were decreased with increasing pressure. Meanwhile, the calculated density of states, charge density distribution, and band structures had little change with increasing pressure, implied that effects of pressure on electronic property of three phases of kaolinite were weak and corresponding structures were stable. Finally, the elastic constants results of I, II, and III phases of kaolinite implied that (001) plane anti-deformation ability was weaker than (100) and (010) planes and shear deformation resistance of (001) was stronger than these of (100) and (010) plane. The results of bulk modulus, shear modulus, and Young's modulus of the three phases of kaolinite indicated that the ability of kaolinite to resist volume deformation and shear failure was enhanced. Various mechanical quantities were evaluated and implied that the kaolinite-I and kaolinite-II was ductile, while the kaolinite-III in the brittle manner. The present theoretical calculations results are helpful to understand the physico-chemical and mechanical properties of natural kaolinite from the microscopic point of view and provided an important theoretical basis for the application of kaolinite in fields of architecture, industry, and agriculture.