Stage Of Solidification Research Articles

Unveiling deformation microstructure during cyclic straining of 316 L stainless steel at 873 K

Cyclic plastic deformation behaviour of 316L steel with an average grain size ∼ 30 μm was investigated at high temperature (873K) under completely reversed straining at ±0.5% strain amplitude with a constant total strain rate of 3 × 10−3S−1. Maximum true tensile stress initially increased due to cyclic hardening until 100 cycles, then stress saturation occurred and finally failed at 1250 cycles. Deformation microstructure varied significantly with imposed fatigue cycles. Occurrence of planar glide and isolated dislocation walls were observed in the initial hardening stage, while dislocation walls accompanied by connected equiaxed dislocation cells were predominant in the saturation stage. The deformation microstructure at failure stage mainly composed of elongated dislocation cells and diffusive dislocation walls. Dislocation densities estimated by X-ray diffraction were ∼ 1013m-2.

A Comparison Study of High-Temperature Low-Cycle Fatigue Behaviour and Deformation Mechanisms Between Incoloy 800H and Its Weldments

The high-temperature low-cycle fatigue (LCF) behaviour of Incoloy 800H and its weldments with Haynes 230 and Inconel 82 filler metals, which were fabricated with the gas tungsten arc welding (GTAW) technique, was investigated and compared at 760 °C. The results revealed that the Incoloy 800H weldments showed lower fatigue lifetimes compared to the base metal. However, the weldments with the Haynes 230 filler metal demonstrated an improved fatigue life at the low strain amplitude compared to both Incoloy 800H and the weldment with the Inconel 82 filler metal. The Incoloy 800H base metal showed pronounced initial cyclic hardening with hardening factors increasing with strain amplitudes. In contrast, the weldments with Haynes 230 and Inconel 82 filler metals displayed short initial cyclic hardening and saturation stages, followed by long continuous cyclic softening. The fractography and microstructure after LCF the tests were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Transgranular fracture with multiple crack initiations was the predominant failure mode on the fracture surfaces of both Incoloy 800 base metal and the weldments. TEM examination revealed that planar dislocation slips at the low strain amplitude evolved to wavy slips, eventually forming a cell structure at high strain amplitudes in the Incoloy 800H material as the strain amplitudes increased. However, the weld metal exhibited a planar slip mode deformation mechanism regardless of cyclic strain amplitude in the weldment specimens. The differing cyclic hardening and softening behaviours between Incoloy 800H and its weldments are attributed to the higher strength of the weldment specimens compared to the base metal. In the Incoloy 800H base material specimens, the reverse strains during LCF created wavy dislocation structures, which could not fully recover due to the non-reversible nature of the microstructure. As a result, cells or subgrains formed within the microstructure once created. In contrast, the higher strength of the weld metal in the weldment specimens significantly suppressed the formation of wavy dislocation structures, and deformation primarily manifested as planar arrays of dislocations.

In situ X-ray imaging and quantitative analysis of balling during laser powder bed fusion of 316L at high layer thickness

Balling is the main surface defect in additive manufacturing, leading to surface roughness and uneven powder deposition. Through the in-situ X-ray imaging technology, the melting process of high layer thickness 316L powder under different process parameters was investigated in real time in this work. We systematically elaborate the complex formation mechanism of balling at high layer thickness, and the key mechanism underlies the splatter’s coalescence during the flight and solidification stages. The frequent spatters coalescence dominates the large-size balling. The spatter coalescence event was roughly quantified, and the coalescence rate ranges from 42.42 % to 73.04 %. The swing of the irregular balls and jumping of the regular small balls were observed, and the solidification time ranges from 10 ms to 20 ms. Moreover, the detailed morphological parameters including the contact angle and counts of the spatter were clarified, and the algebraic equations about the contact angle and the volumetric energy density were established. This study provides a systematical understanding of the balling phenomenon during laser powder bed fusion of 316L at high layer thickness.

Investigation on solidification crack susceptibility for weld metals of GH3539 alloy with Trans-Varestraint test

In this work, the welding solidification crack susceptibility of GH3539 alloy was investigated under different strains using a trans-varestraint test. The results indicate that the saturation strain of GH3539 alloy reaches a bending strain of 1 %. High-angle grain boundaries in the weld metal are fragile areas where welding solidification cracks are formed due to element segregation and stress concentration, which are essential factors causing crack initiation and propagation. Furthermore, the surface residual stress of the crack tip was calculated by two-dimensional synchronous micro X-ray diffraction analysis of the partial Debye ring, which was deduced as the major factor for the cracking. The element Si in the alloy tends to segregate at grain boundaries, forming low-melting liquid films with elements such as Mo, Cr, and Mn during the final solidification stage. These liquid films reduce the interfacial bonding strength at the grain boundaries. The failure of the liquid films to accommodate local stress, resulting in subsequent interface separation, serves as the other catalyst for initiating solidification cracks in welding.

Evaluation of Wellbore Stability by Small Parameter Perturbation Nonlinear Elastoplastic Model

Abstract Wellbore instability is a frequent occurrence during drilling and a popular research topic among petroleum workers. Most of the previous studies simplified the hardening stage and ignored or classified it into the elastic stage. Engineering practice shows that the total stress–strain process of rock can more truly reflect the bearing and deformation characteristics of rock. This study establishes a total stress–strain constitutive model by combining the perturbation index equation with the linear elastic equation. Additionally, the physical model of rock around the well is presented using the total deformation theory for the plastic zone. The stress field of the rock surrounding the well is analyzed based on the physical model of the rock surrounding the well, taking into account the influence of rock strength and geostress state. The relationship between rock strength, geostress state, drilling fluid density, and plastic radius is given. The calculation method of drilling fluid density limit is also given. The practical application demonstrates that the stability of a borehole wall can be evaluated by analyzing the size and direction of the plastic radius, as well as the distribution of radial, tangential, and shear stress for various combinations of stress states and rock strengths. The maximum shear stress is always found in the softening zone, which is also the region where wellbore instability is most likely to happen. Therefore, the area within the softening radius is regarded as an unstable area, and the softening radius can be used to determine the range of wellbore instability.

Role of Ti-6Al-4V addition in modulating crack sensitivity, solidification microstructure and mechanical properties of laser powder bed fused γ-TiAl alloys

Solidification cracking is still the primary challenge for laser powder bed fusion (LPBF) without high-temperature preheating of γ-TiAl alloys. Circumventing the peritectic reaction and promoting β-solidification by adding the β-stablizing elements have been proved to be an effective way to suppressing the crack formation. In this work, we attempted a more economic method to realize β-solidification via the addition of Ti-6Al-4V (TC4) pre-alloyed powder. The results showed that the TC4 addition successfully changed the solidification path from L→L+β→L+α→α→α+γ→α2+γ to L→L+β→β→α+β→α2+β/B2. As a result, the solidified microstructure was mainly comprised of primary α2 phase and small amount of retained β/B2 (8.5 %) phase distributed along the molten pool boundary. What's more important was that the TC4 addition led to a 44.6 % decrease in crack density. Contributions to low hot cracking sensitivity were found to mainly origin from the relatively lower cooling rate, higher fraction of low-angle grain boundaries (LAGBs) and smaller dendrite coalescence undercooling induced by the TC4 addition. Besides, the smaller temperature interval (10.63K) in the final solidification stage (0.90<fs < 0.94) for the TC4/TiAl alloy was also conducive to facilitate the liquid feeding and dendrite coalescence.

Effect of Loading Direction on Tensile-Compressive Mechanical Behaviors of Mg-5Zn-2Gd-0.2Zr Alloy with Heterogeneous Grains

The tension-compression yield asymmetry caused by the strengthening of Mg-Zn-Gd-Zr alloy due to extrusion deformation is an important issue that must be addressed in its application. In this study, the effects of loading direction on the tensile and compressive mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy were systematically investigated. As the loading angle (the angle between the loading direction and the extrusion direction) increases from 0° to 30°, 45°, 60° and 90°, the tensile yield strength decreases more significantly than the compressive yield strength. Consequently, the tension-compression yield asymmetry is gradually improved. Additionally, the ultimate compressive strength decreases more markedly than the ultimate tensile strength with the increment of the loading angle. In tensile tests conducted at 0°, 30° and 45°, two distinct stages of decreasing strain hardening rates are typically observed. For the 60° and 90° tensile tests, one unusual ascending stage of strain hardening rate is observed. For all compressive tests, three stages of strain hardening are consistently noted; however, the increment in strain hardening rate caused by {10–12} extension twinning decreases with the increasing loading angle. A model combining loading angle and Schmid factor distribution was established. The calculated results indicate that the dominant deformation modes during the yielding process also vary significantly with the loading conditions. This clarification highlights the differences in yield strength variations between tension and compression. Finally, an analysis of the plane trace and crack propagation direction near the fracture surface reveals the fracture mechanisms associated with tensile and compressive tests at different loading directions. This study promotes understanding of the mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy under different loading directions, and helps to thoroughly elucidate the anisotropic effects of texture on the mechanical properties of magnesium alloys.

An investigation on effect of tramp elements and solidification processing on homogenization kinetics of AA 7xxx series aluminum alloys

AA 7068 Aluminum alloy is produced via conventional solidification (CS) and controlled diffusion solidification (CDS) processing and homogenized at 450 °C for 6 and 12 h. Optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive x-ray spectroscope (EDS) were used to examine the as-cast and homogenized samples. It was found that although the CS sample is more chemically homogenized in the as-solidified state, the CDS sample exhibits a higher homogenization rate during the treatment. The calculated phase diagram (CALPHAD) methodology was employed to study the effect of silicon and iron on the solidification path and homogenization of the alloy. Silicon consumes magnesium atoms on the surface of the α-Al phase to form the Mg2Si phase. Therefore, the magnesium concentration on the α-Al phase required for the formation of the σ phase must be increased. Calculations shows that all the Mg atoms at this stage are completely supplied from the bulk of the αAl phase. It can be hypothesized that during the last stage of solidification, a solid/liquid diffusion couple can be created between the primary αAl and the remaining liquid for several minutes (4 min at a cooling rate of 0.2 oC/s). As a result of the activation of this couple, the Mg atoms diffuse from the α-Al bulk to its surface, and vacancies diffuse from the surface to the bulk, forming a line of Kirkendall voids. With CDS processing, the surface of the primary phase is less Mg-concentrated than that in the CS process and this significantly reduces the formation of the Mg2Si phase. Conversely, the vacancy and Mg concentration of the αAl phase in CDS is higher than that of CS and this lets other alloying elements other than Mg diffuse to the primary phase, decreasing the homogenization time. The presence of Si in the alloy leads to the formation of the Mg2Si phase, which significantly reduces the final Mg concentration in the α-Al phase after full homogenization. In the pure alloy, the Mg concentration is 2.42 wt%, while in the FeSi-containing alloy, it is reduced to 1.58 wt% due to solid solution and dispersion strengthening mechanisms. Through CDS processing, the negative impact of Si can be reduced by disrupting the mechanism of Mg2Si formation.

An innovative strategy for improving ductility of seawater sea-sand engineered cementitious composites beam reinforced with GFRP bar

Seawater sea-sand engineered cementitious composites (SS-ECC) members with glass fiber reinforced polymer (GFRP) bars have inferior ductility due to the brittle nature of GFRP bars. In the current research, an enlarged head anchorage system (EHAS) was recommended to improve the ductility of GFRP bars reinforced SS-ECC beams. To explore the bond characteristics between SS-ECC and GFRP bars with EHAS, a total of 39 specimens were tested by pull-out loading. The influences of enlarged head shape, stirrup spacing and SS-ECC's strength grade on the bond characteristics were experimentally investigated. GFRP longitudinal bars in specimens with EHAS presented rupture failure rather than anchorage failure. EHAS could effectively realize the slip hardening of GFRP bars in low strength SS-ECC, and ensure the reliable bond of GFRP bars in high strength SS-ECC. Additionally, the failure mechanism of specimens under pull-out loading was explored by finite element analysis (FEA). The pull-out resistance was mainly provided by EHAS in force transition stage and slip hardening stage. The influences of fiber reinforced polymer (FRP) bar type on the bond performance were investigated by FEA. EHAS could realize the slip-hardening behaviors of aramid, basalt and carbon FRP bars in normal strength SS-ECC. More importantly, to verify the effectiveness of the proposed ductility enhancement strategy, SS-ECC beams reinforced with GFRP bars were tested by four-point bending. These beams with different enlarged head shapes possessed excellent ductility and strong ultimate deformation capacity. It was recommended that low strength SS-ECC and GFRP bars with EHAS were jointly utilized to enhance the ductile performance of the beams.

Compensating for Concrete Shrinkage with High-Calcium Fly Ash

Shrinkage of concrete during hardening is a serious problem in attempts to maintain the integrity of concrete structures. One of the methods of combating shrinkage is compensating for it using an expansive agent. The purpose of this work is to develop and study an expanding agent to concrete, including high-calcium fly ash and calcium nitrate as an expansion activator. The content of Ca(NO3)2 can be used to regulate the degree of expansion of the additive itself during hydration and, accordingly, to control shrinkage, thus obtaining shrinkage-free or expanding concrete. Shrinkage–expansion deformations of concrete can also be regulated by the amount of expanding additive replacing part of the cement. With the Ca(NO3)2 content of fly ash being 10% or more, concrete experiences expansion in the initial stages of hardening. The transition of deformation through 0 to the shrinkage region occurs depending on the composition and content of the additive after 8–15 days of hardening. It has been established that replacing cement with pure fly ash with a curing period of 90 days or more has virtually no effect on the strength of concrete, either in bending or in compression. The use of an expanding additive containing 5–15% Ca(NO3)2 reduces the strength of concrete by an average of 9%, despite the fact that calcium nitrate is a hardening accelerator.

Effect of hot-wire method on microstructure and mechanical properties of wire arc additive repaired superalloy

This study shows that the hot wire is an effective way to reduce the amount of undesirable Laves phase during the repair of 718Plus components, which are detrimental to the mechanical properties. The complex relationship between microstructure and hotwire was studied in detail. Five damaged components were repaired by depositing the melted 718Plus wire onto the wrought substrate using directed energy deposition-arc (DED-arc). A finite element model was used to provide clues for the thermal process analysis. The hot-wire method enhanced the cooling rate of the molten pool and suppressed the remelting behaviour of secondary dendritic arms (SDA) in the reheated zone. The resultant microstructure contained refined dendrites with more obvious SDA, which allows the production of tiny reticular Nb-rich liquid spots between dendrites during final solidification stage. These spots beyond a threshold of Nb could cause eutectic reaction, leading to the morphologic transformation from long-stripped to granular Laves phase and a lower volume fraction. Moreover, the hot-wire method hindered the dynamic precipitation of γ' phase due to the shortened precipitation time, which was responsible for the inferior mechanical properties. The heat-treatment re-optimized the precipitation of γ' phase and further dissolved Laves phase to release more Nb for γ' phase, which leads to the improvement of strength about 10 %.

Crystallization behavior of BOF slag during the cooling process towards leaching for CO2 sequestration

This work addresses the crystallization behavior and microstructure feature of the molten basic oxygen furnace (BOF) slag during a slow cooling process. The aim is to provide a reference for the modification of BOF slag for subsequent leaching of Ca as part of CO2 sequestration. Integrated analysis of XRD, SEM-EDS, and thermodynamic calculations suggest a crystallization behavior of BOF slag during the cooling process. RO phases ((Mg, Fe, Mn) O) was the equilibrium phase at a high temperature of around 1600 °C, followed at lower temperatures by the formation of Ca3SiO5 (C3S) and α-Ca2SiO4 (α-C2S). The Ca2Fe2O5 (C2F) phase forms during the latter stages of melt solidification. On the basis of the combined analysis of the leaching test results and crystallographic analysis, a future direction of modification of BOF slag is suggested that enriches Ca into the C2S and hinders the formation of C2F. However, inhibiting the generation of C2F by adjusting the cooling process alone is difficult since its crystallization rate is fast. The phase of C2F was observed in XRD and SEM even if the BOF slag was quenched from 1600 °C. Furthermore, the chemical characterization and morphological evolution of the crystalline phase of molten BOF slag during the slow cooling process was observed.

Study of Mechanical Properties of Different Hydrate Reservoirs

Based on the triaxial shear tests of mud sediments in the South China Sea, mud chalk-type sediments in the South China Sea, and sandy sediments in the Nankai Trough, Japan, at different hydrate saturation and enclosing pressures, the stress-strain relationships of hydrate-bearing clays, mud chalk-type soils, and sandy soils were analyzed. The test results show that:(1)The stress-strain curves of the South China Sea clay sediments show three stages of elasticity, plastic deformation and strain hardening, which are significantly different from those of the hydrate-free clays; the stress-strain relationships of the hydrate-containing clays before and after hydrate decomposition are significantly different, and the undrained strength of the clays decreases by up to 50% after hydrate decomposition compared with that before hydrate decomposition; the above results indicate that the presence of hydrate enhances the linkage or cementation between the clay particles. The above results indicate that the presence of hydrate enhances the linkage or cementation between the clay particles.(2)For the mechanical properties of the hydrate specimens of the muddy chalky sand type in the South China Sea, the hydrate endowment, effective stresses and pore pressures all have some influence on the strength and deformation properties. The inclusion of hydrate in the pore space enhances the shear expansion characteristics of the sediments. For the effect of effective stress on the mechanical properties of hydrate sediments, the increase of effective peritectic pressure reduces the strain softening properties of hydrate sediments. The destructive strength of the sediments increases with the increase of effective confining pressure.(3)For the hydrate specimens in the Nankai Trough of Japan under the same effective circumferential pressure conditions, with the increase of hydrate saturation, the stress-strain law of the sediments showed a tendency to transform from strain hardening to strain softening, and the morphology of sandy sediment axial strain-lateral strain curves was controlled by the factors of hydrate saturation, and the absolute value of the slope of the curves expressed the rule of change of the tangent Poisson's ratio.

Advanced modeling of higher-order kinematic hardening in strain gradient crystal plasticity based on discrete dislocation dynamics

An extensive study of size effects on the small-scale behavior of crystalline materials is carried out through discrete dislocation dynamics (DDD) simulations, intended to enrich strain gradient crystal plasticity (SGCP) theories. These simulations include cyclic shearing and tension-compression tests on two-dimensional (2D) constrained crystalline plates, with single- and double-slip systems. The results show significant material strengthening and pronounced kinematic hardening effects. DDD modeling allows for a detailed examination of the physical origin of the strengthening. The stress–strain responses show a two-stage behavior, starting with a micro-plasticity regime with a steep hardening slope leading to strengthening, and followed by a well-established hardening stage. The scaling exponent between the apparent (higher-order) yield stress and the geometrical size h varies depending on the test type. Scaling relationships of h−0.2 and h−0.3 are obtained for respectively constrained shearing and constrained tension-compression, aligning with some experimental observations. Notably, the DDD simulations reveal the occurrence of the uncommon type III (KIII) kinematic hardening of Asaro in both single- and double-slip cases, emphasizing the relevance of this hardening type in the realm of small-scale plasticity. Inspired by insights from DDD, two advanced SGCP models incorporating alternative descriptions of higher-order kinematic hardening mechanisms are proposed. The first model uses a Prager-type higher-order kinematic hardening formulation, and the second employs a Chaboche-type (multi-kinematic) formulation. Comparison of these models with DDD simulation results underscores their ability to effectively capture the observed strengthening and hardening effects. The multi-kinematic model, through the use of quadratic and non-quadratic higher-order potentials, shows a notably better qualitative congruence with DDD findings. This represents a significant step towards accurate modeling of small-scale material behaviors. However, it is noted that the proposed models still have limitations, especially in matching the DDD scaling exponents, with both models producing h−1 scaling relationships (i.e., Orowan relationship for precipitate size effects). This indicates the need for further improvements in gradient-enhanced theories in order to guarantee their suitability for practical engineering applications.

ASSESSMENT OF THE INFLUENCE OF INORGANIC PIGMENTS ON THE TECHNOLOGICAL PROPERTIES OF DECORATIVE CEMENTS

The article presents the results of research on the influence of inorganic pigments on the technological properties of decorative cements. It has been established that regardless of the color of the pigment, with an increase in its quantity in the system, we get a more saturated and bright color of cement stone, but at the same time there is a negative effect of pigments and technological and physical and mechanical properties of artificial stone. The research was conducted on cement systems based on white Portland cement without additives and on cement systems based on white Portland cement modified with polycarboxylate superplasticizer. An increase in the amount of pigment, regardless of its color, leads to an increase in the water consumption of the cement system, however, when a superplasticizer is introduced, the effect of the pigment is not so significant. At the same time, the introduction of a superplasticizer reduces the water consumption of white cement without the introduction of pigments by an average of 37-40%. In addition, it was established that the introduction of pigments affects the hardening time of cement systems. At the same time, pigments, depending on their color and dosage, have different effects on both the start and end of aging. With an increase in the pigment content in a cement system without a plasticizer, the time of the onset of hardening increases, and the introduction of a permanent pigment has the greatest effect on the end of hardening of such a system. The introduction of pigments into plasticized cement systems increases both the start and end time of hardening. As the number of pigments of all colors increases, the strength of the samples decreases. At the same time, the red pigment leads to the greatest decline in strength at all stages of hardening. The decrease in strength can be explained by the increased water consumption, and, as a result, the increased porosity of pigmented samples compared to samples without the introduction of pigments. Further research aimed at finding additives that will reduce the negative impact of inorganic pigments on the processes of hydration and hardening of the cement system, and therefore on the durability of the obtained artificial stone, will be relevant. At the same time, it is important to preserve the intensity of the color and the absence of sediment formation.

Microstructural refinement in a high elastic modulus Al-18Si-8Ni casting alloy

A new Al-Si-based casting alloy with high elastic modulus in the range of 90‐100 GPa and low density, less than 3 g/cm3, was developed by alloy design and microstructural refinement approaches. The addition of 8 wt.% Ni to a hypereutectic Al-18Si alloy introduces large volume fractions (∼40 vol.%) of hard primary Si and primary Al3Ni phases. Coarse primary Si and primary Al3Ni formed in the early stage of solidification, however, can interfere with the melt flow, reducing the castability, and also were deleterious to elongation. By the assessments of the crystallographic misfit between a nucleant substrate and a nucleated solid, we discovered key inoculants, AlP and TiB2, which can successfully refine such coarse and brittle primary phases, Si and Al3Ni, respectively. More importantly, along with the improved elastic modulus, the combined addition of AlP and TiB2 results in a significant increase in the elongation up to 1% with an advantageous yield strength of over 230 MPa. The important role of an inoculant, particularly TiB2 in nucleating the Al3Ni phase is also discussed based on the theoretical lattice misfit calculations and experimental characterization, further confirming their orientation relationship between the Al3Ni and the TiB2 as (110)[11¯0]Al3Ni∥ (0001)[12¯10]TiB2.

Progressive failure analysis of woven and non‐woven CFRP composite/steel bolted joints

AbstractDue to recent advancements in textile fabrication, woven fabric reinforcements are used in composite structures as an alternative to traditional unidirectional fiber reinforcing layups. In this paper, experimental work was performed to study the behavior of multiple bolt‐lapped joints under uniaxial tension. Different bolt numbers, composite layups, and fabric configurations were studied. Single‐ and double‐lap configurations were used to investigate the effect of secondary stresses. It was found that the P‐δ curves of lapped joints exhibit four primary stages: a linear elastic stage, followed by a nonlinear hardening stage, then linear hardening leading up to the peak, and finally a softening stage. For double‐lapped non‐woven joints, the curves encompass only the first three stages; however, for woven composites, the last stage is very small. In addition, among the laminates, the non‐woven laminate sustains the highest normalized failure load, except in the staggered case, where the quasi‐isotropic woven laminate exhibits higher strength. Conversely, the bidirectional woven laminate demonstrates the lowest loads and the highest deformation.Highlights A study compared bolted joint performance of woven and uni‐based composites. Lapped joints with different bolt arrangements were experimentally studied. P‐δ curves showed elastic, nonlinear, linear hardening, and softening stages. Woven laminates showed higher displacements compared to non‐woven laminates. Secondary bending induced additional stress with less impact on woven samples. Bearing failure predominated, with variations in extent of bearing damage.

Optimizing hot tearing susceptibility of Al-5.5Zn-2.4 Mg-1.3Cu alloys by grain refinement, increasing mold and casting temperature

The Al-Zn-Mg-Cu alloy is widely used in automotive lightweighting and other applications due to its excellent mechanical properties. However, when this alloy is cast using metal molds, it exhibits high hot tearing susceptibility (HTS), increasing the risk of use. Volumetric shrinkage due to density differences during the transition from liquid to solid metal produces shrinkage stresses. At the same time, lacks feeding of the remaining liquid phase in the late solidification stage can also lead to hot tearing. The purpose of this paper is to present a device for quantitatively determining and optimizing HTS. The relationship between solidification shrinkage displacement and stress was tested in a quantitative way using a Self-designed T-tester equipped with stress and displacement sensors. The test results show that the reduction of grain size shifts the solidification shrinkage of the alloy and reduces the solidification shrinkage stress, which avoids hot tearing caused by higher solidification shrinkage stress and local stress inhomogeneity. Secondly, the grain size reduction increases the number of feeding channels in the solidification vulnerable stage, and more liquid phase is available for crack healing. In addition, the influence of casting process parameters on the HTS was studied.

The influence of selected grain size fractions of coal fly ash on properties of clay-cement mortars used for the flood levees construction

This study examines the influence of different grain size fractions of coal fly ash on the properties of clay-cement mortars used in flood levee construction. Dry aerodynamic separation and mesh sieving were used to obtain ultrafine, fine, and medium fractions of high-calcium and silica fly ash. The experimental results reveal that the rheological properties of fresh mortars are significantly influenced by these fractions. High-calcium fly ash mortars exhibit high reactivity and rapid increase in viscosity, with finer fractions showing the highest reactivity. Silica ashes show increased reactivity in the later stages of suspension hardening. Their spherical shape contributes to reducing internal friction during flow in initial technological operations. Furthermore, the compressive strength of hardened mortars improves as the particle size decreases for both ashes, resulting in a dense and uniform microstructure. The separation and fractionation of fly ashes contribute to the obtaining of fractions that influence the parameters of clay-cement suspension application on different scales. The results show the potential benefits of ash separation, which can bring advantages in terms of economic viability, engineering performance, and ecological sustainability.

Nucleation and growth behavior of primary Al11Ce3 intermetallic compounds during solidification in a hypereutectic Al–Ce alloy

In this study, the nucleation and growth mechanisms of Al11Ce3 intermetallic compounds (IMCs) in a hypereutectic Al–Ce alloy during solidification were investigated through synchrotron radiation X-ray real-time imaging. The results showed that Al11Ce3 IMCs nucleate and grow from the melt as the primary phase at the initial stage of solidification. Growth preferred orientations were observed in two opposite directions, resulting in an I-shaped growth pattern. Based on the minimum energy criterion, the morphology of Al11Ce3 IMCs displayed either hollow cubic tubes or grooves. The nucleation and growth rates of Al11Ce3 IMCs gradually decreased over time, owing to the variations in the Ce concentration in the melt and the undercooling. The nucleation and growth characteristics of Al11Ce3 IMCs can provide the theoretical basis for optimization on the performance of Al–Ce alloys.