Interphase Stresses Research Articles

Deformation behavior and fracture mechanisms of 430 ferritic stainless steel after dual-phase zone annealing via quasi in-situ tensile testing

This study systematically investigated the deformation behavior and fracture mechanisms of AISI 430 ferritic stainless steel (FSS) following dual-phase zone annealing with varying martensite contents, using quasi in-situ tensile testing. In 430 FSS with a low martensite volume fraction, significant deformation occurred through dislocation slip in the ferrite phase, involving the activation of multiple slip systems and dislocation transmission at grain boundaries. In contrast, in sample with high martensite fraction, dislocation slip within the ferrite was restricted, leading to an overall decrease in plasticity. During the tensile process, ferrite grains exhibited different responses under external stress. Additionally, strain concentration mainly occurred at ferrite-martensite phase boundaries and at interfaces between large and small grains. As deformation progressed, strain distribution gradually homogenized in the low martensite fraction sample. However, in the high martensite fraction sample, fracture occurred before strain distribution could become uniform. Weak bonding at ferrite-martensite phase boundaries renders these interfaces critical sites for crack initiation. The combined effects of dislocation accumulation and strain incompatibility lead to the initiation and propagation of cracks, ultimately causing material failure. Optimizing the dual-phase zone annealing processes enables ferrite grains to achieve moderate and uniform sizes while maintaining the continuous distribution of ferrite and the discontinuous distribution of martensite. This microstructural control can effectively reduce interphase stress concentration, enhance the coordinated deformation capabilities of ferrite, and thereby significantly improve the overall performance of 430 FSS.

Understanding the High-Temperature Deformation Behaviors in Additively Manufactured Al6061+TiC Composites via In Situ Neutron Diffraction

Aluminum matrix composites (AMCs) are designed to enhance the performance of conventional aluminum alloys for engineering applications at both room and elevated temperatures. However, the dynamic phase-specific deformation behavior and load-sharing mechanisms of AMCs at elevated temperatures have not been extensively studied and remain unclear. Here, in situ neutron diffraction experiments are employed to reveal the phase-specific structure evolution of additively manufactured Al6061+TiC composites under compressive loading at 250 °C. It is found that the addition of a small amount of nano-size TiC significantly alters the deformation behavior and increases the strength at 250 °C in comparison to the as-printed Al6061. Unlike the two-stage behavior observed in Al6061, the Al6061+TiC composites exhibit three stages during compression triggered by changes in the interphase stress states. Further analysis of Bragg peak intensity and broadening reveals that the presence of TiC alters the dislocation activity during deformation at 250 °C by influencing dislocation slip planes and promoting dislocation accumulation. These findings provide direct experimental observations of the phase-specific dynamic process in AMCs under deformation at an elevated temperature. The revealed mechanisms provide insights for the future design and optimization of high-performance AMCs.

Quantifying the solid electrolyte interphase stress induced capacity fading of lithium-ion batteries via a multiscale mechanical-electrochemical coupling model

Quantifying the solid electrolyte interphase stress induced capacity fading of lithium-ion batteries via a multiscale mechanical-electrochemical coupling model

Multi-stage load partitioning in additively manufactured Al6061+TiC nanocomposite characterized by in-situ neutron diffraction

Metal matrix composites (MMCs), combining metal matrix and ceramic particles, exhibit high mechanical strength and stiffness compared to conventional metallic materials. During fusion-based additive manufacturing (AM), MMCs undergo a rapid heating and cooling thermal history, which affects the interfacial bonding, thermal misfit stress and mechanical load transfer behavior between the metal matrix and particles, thus impacting the bulk mechanical performance. Here, we investigate the deformation dynamics and phase-specific load transfer in fusion-based AMed Al6061 +TiC MMCs through in-situ neutron diffraction. By calculating the phase-specific lattice strains, a multi-stage load transfer and deformation behavior during uniaxial compression is revealed: (1) elastic deformation in Stage I for both phases; (2) sudden stress rebalance between two phases in Stage II, evidenced by a sudden decrease in Al lattice strain and increase in TiC; (3) active load carrying by both phases in Stage III, with both phases experiencing an increase in lattice strains. The deformation mechanism of each stage is deducted by correlating the evolutions of the interphase stresses and peaks’ broadening and intensity of the Al matrix. The local plastic deformation of the Al matrix near the phase interface is triggered and leads to stress rebalancing in Stage II. The global plastic deformation subsequently propagates throughout the Al matrix in Stage III, and the composite is further hardened through both dislocation multiplication and load transfer. The findings offer valuable insights into deformation and load-sharing behavior in AMed MMCs.

Evolution of interphase stress over a crack propagation plane as a function of stress relief heat treatments in a PBF‐LB/M AlSi10Mg alloy

AbstractIn this study, we compare the residual stress state in a laser powder bed fusion (PBF‐LB/M) AlSi10Mg alloy in the as‐built (AB) condition with that after two different heat treatments (265 °C for 1 h, HT1; and 300 °C for 2 h, HT2). The bulk residual stress (RS) is determined using synchrotron X‐ray diffraction (SXRD), and near‐surface profiles are determined using laboratory energy‐dispersive X‐ray diffraction (EDXRD). The EDXRD results do not reveal any notable difference between the conditions at a depth of 350 μm, suggesting that the machining process yields a comparable residual stress state in the near‐surface regions. On the other hand, the SXRD results show that HT1 is more effective in relieving the bulk RS. It is observed that HT1 reduces the RS state in both the aluminium matrix and the silicon network. In addtion, HT2 does not have a significant impact on relaxing the RS as‐built state of the matrix, although it does induce a reduction in the RS magnitudes of the Si phase. It is concluded that the heat treatment stress relieving is effective as long as the Si‐network is not disaggregated.

Deformation behavior of nickel-based superalloys with bimodal γ′ size distribution studied by in-situ neutron diffraction combined with EVPSC modeling

Nickel-based superalloys with multimodal γ′ size distribution microstructure have been designed to employ in extreme environments due to their excellent mechanical performance. Whilst the effect of γ′ size on deformation mechanism has been studied before, little has been done to assess the deformation sequence and contribution to the load partition for different types of γ′ precipitates. In order to address this gap, this study focused on bimodal superalloys of GH4738 (containing the secondary and tertiary γ′ precipitates) and GH4720Li (containing the primary and tertiary γ′ precipitates) alloys. In-situ neutron diffraction assisted by a 2-site elastic-viscoplastic self-consistent (EVPSC) model was employed to elucidate the deformation mechanisms. The effects of different types of γ′ precipitates on the partitioning of interphase stress and the underlying mechanisms have been revealed. The findings indicated that bimodal superalloys exhibited distinct deformation behaviours compared to unimodal ones. Notably, premature load partitioning was observed in the microplasticity stage, attributable to Orowan looping for secondary γ′ precipitates or the emission of dislocations from the straight interface of primary γ′ precipitates. In the macroplasticity stage, considerable dislocations shear three types of γ′ precipitates, especially for the tertiary γ′ precipitates, which results in the decrease in the increment rate of interphase stress. These findings could contribute to a better understanding of deformation mechanisms in superalloys with multimodal γ′ size distributions and shine a spotlight on material design to modulate intergranular and interphase stresses.

Cross-linking gradient model in disperse systems

The article presents the research results of the disperse systems cross-linking process containing solid and liquid phase bases on the continuum mechanics apparatus use within the incompressible fluid model framework. The system formation schemes of interfacial layers in fine clearances between solid particles with wall-adjacent zones formation, in which conditions of liquid and solid phase interphase contact are provided, and the cores with constant interphase pressure are considered. The authors have obtained expressions for the values of wedging pressure depending on the thickness of the interfacial layers overlapping area, which determine the interfacial contacts strengthening degree. The dependences given in the paper are a theoretical basis for a new approach to modelling surface phenomena from the position of continuum mechanics equilibrium. The facilitating mechanism of the wedging pressure long-range action outside the interfacial layers system area is given. The authors present the modelling results of a single liquid-solid interphase layer bounded, on the one side, by a solid surface and, on the other side, by a volume liquid phase and the results of modelling the effects of structuring disperse systems based on the liquid interphase layer study formed in the clearance between solid surfaces. Under certain conditions in such systems the effect of structuring, leading to a sharp increase in the strength properties of disperse-filled composite materials, which is the basis of modern nanotechnology concepts, is manifested. The dualism of the liquid phase, consisting in the ability to exhibit the properties of both liquid and solid body, is shown. It is proved that the main disperse systems structure formation factor is the formation of interphase stresses powerful gradients at the thickness of interphase layers.

Analytical and parametric analysis of interface stress behaviour in nanoclay/polymer composite

Nowadays, nanoclay-reinforced polymers are one of the most widely used nanocomposites due to their high aspect ratio, higher contact area and their unique properties. These composites are used in a number of industrial applications, such as construction (building sections and structural panels), automotive (gas tanks, bumpers, interior and exterior panels), chemical processes (catalysts), pharmaceutical (as carriers of drugs and penetrants), aerospace (flame retardant panels and high performance components), food packaging and textiles, etc. Their interphase properties are essential for determining their proper design and safety application when applying large mechanical loads on them. In this work, a parametric analysis is performed to investigate how the change in the interphase properties influences the interphase shear stress (ISS) and interphase peel stress (IPS) in a nanoclay/polymer nanocomposite structure, subjected to axial load. The two-dimensional (2D) stress-function method is applied, which results in obtaining an analytical solution for ISS and IPS. The implemented parametric analysis shows how varying of the interphase mechanical properties (Young's modulus and Poisson's ratio) and their geometric properties (thickness and length) influence the value of the model interphase stresses. It was found, that increasing the value of Young modulus of the interphase does not change significantly the value of the model ISS, as well as the value of IPS, in the considered nanoclay/polymer structure. On the other hand, increasing the value of the interphase layer thickness becomes important for the value of ISS and IPS after 25nm. It turned out, that the interphase layer length is the most appreciable parameter, influencing both the model ISS and IPS. The obtained results could be useful for the proper design and safety application of similar nanoclay/polymer composites in industry.

The HRTEM characterization of electropolishing-induced ζ-hydride in the α-Zr/δ-hydride interface in Zircaloy-4

In the research, we report the ζ-hydride as the intermediate phase precipitates in the α-Zr/δ-hydride interface in electropolished Zircaloy-4 TEM lamella. High-resolution transmission electron microscopy confirms the intermediate phase in the α-δ interface as ζ-hydride with orientation relationship of (0002)ζ//(0002)α and [11 2¯ 0]ζ//[11 2¯0]α with α-Zr, (0002)ζ//(1¯ 1 1¯)δ and [11 2¯ 0]ζ//[011]δ with δ-hydride. It is proposed that the formation of ζ-hydride as the intermediate phase in the α-δ interface which could reduce the local interphase stress.

Определение когерентности интерфейса твердорастворной и интерметаллидной фазыв монокристаллических литейных сплавах на основе интерметаллида Ni3Al рентгенодифрактометрическим методом

The paper considers splitting of the solid solution gamma phase diffraction peaks in the nickel heat-resistant alloys, including alloys based on the Ni3Al intermetallic compound with the heterophase structure. It is shown that the effect of splitting the solid solution gamma phase diffraction peaks is missing in the alloys based on the Ni3Al intermetallic compound with heterophase structure, in contrast to the nickel heat-resistant alloys. It was established that splitting of the solid solution gamma phase diffraction peaks in the diffraction pattern was caused by tetragonal distortion of the gamma phase crystal lattice (solid solution) exposed to the interphase stresses. Only under condition of the interphase boundary coherence exposed to the interfacial stresses the tetragonal distortion of the gamma phase crystal lattice (solid solution) appeared. Therefore, a conclusion could be made based on the absence of splitting the gamma phase diffraction peaks that the interphase boundary (interface) coherence was missing in alloys based on the Ni3Al intermetallic compound with the heterophase structure.

In-situ analysis of the elastic-plastic characteristics of high strength dual-phase steel

Modeling the elastic behavior of dual-phase steels is complex due to the strain dependency of Young's modulus and high elastic nonlinearity. Since it is assumed that reasons for this are to be found in microstructural behavior, microscopic in-situ analysis are necessary, but due to the overlap of the martensite and ferrite peaks, the evaluation of diffraction profiles is highly complex. Within this work, CR590Y980T (DP1000) is investigated in a continuous cyclic tensile and tension-compression test under synchrotron radiation at High Energy Material Science beamline P07 in Petra III, DESY. On basis of additional EBSD measurements, an evaluation approach is shown to analyze the dual-phase diffraction profiles in such a way that martensite and ferrite can be separated for three lattice planes. The origin of the specific elastic-plastic behavior of dual-phase steels in terms of onset of yielding, anelasticity or early re-yielding is analyzed on the basis of lattice strains and interphase stresses. For this, the time-synchronously measured micro data is correlated with the macro stress-strain relationship and thermoelastic effect. The results help to better understand strain-dependent elastic-plastic behavior of DP steels on a micro level and provide great potential to improve characterization and modeling in terms of springback prediction.

In-situ synchrotron-based high energy X-ray diffraction study of the deformation mechanism of δ-hydrides in a commercially pure titanium

We used by in-situ high energy X-ray diffraction to investigate the deformation behavior of Grade 2 commercially pure titanium that was hydrogen charged to form hydrides. The results showed that the peak broadening in the diffraction patterns are due to the high internal and interphase stresses generated within and around hydrides due to the volume expansion induced by the phase transformation. The hydrides exhibit a typical high strength but brittle secondary phase behavior, which undertakes more elastic strain than matrix and is the location where cracks are first generated. Interestingly, the δ-hydrides sustain larger strains than the matrix, especially after the matrix yields. This study on the deformation mechanism of hydrides in pure titanium provides insight into the hydride deformation behavior and hydrogen embrittlement in both titanium and zirconium.

Nanoindentation measurement of core–skin interphase viscoelastic properties in a sandwich glass composite

Debonding at the core–skin interphase region is one of the primary failure modes in core sandwich composites under shear loads. As a result, the ability to characterize the mechanical properties at the interphase region between the composite skin and core is critical for design analysis. This work intends to use nanoindentation to characterize the viscoelastic properties at the interphase region, which can potentially have mechanical properties changing from the composite skin to the core. A sandwich composite using a polyvinyl chloride foam core covered with glass fiber/resin composite skins was prepared by vacuum-assisted resin transfer molding. Nanoindentation at an array of sites was made by a Berkovich nanoindenter tip. The recorded nanoindentation load and depth as a function of time were analyzed using viscoelastic analysis. Results are reported for the shear creep compliance and Young’s relaxation modulus at various locations of the interphase region. The change of viscoelastic properties from higher values close to the fiber composite skin region to the smaller values close to the foam core was captured. The Young’s modulus at a given strain rate, which is also equal to the time-averaged Young’s modulus across the interphase region was obtained. The interphase Young’s modulus at a loading rate of 1 mN s−1 was determined to change from 1.4 GPa close to composite skin to 0.8 GPa close to the core. This work demonstrated the feasibility and effectiveness of nanoindentation-based interphase characterizations to be used as an input for the interphase stress distribution calculations, which can eventually enrich the design process of such sandwich composites.

The interdependence of microstructure, strength and fracture toughness in a novel β titanium alloy Ti–5Al–4Zr–8Mo–7V

In order to study the correlation between microstructure, strength and fracture toughness (KIC) and optimize the strength-KIC combination, BASCA (β annealing slow cooling plus aging) and STA (α/β solution treatment plus aging) heat treatment followed by near β forging is conducted to obtain a variety of multiscale lamella structure and Bi-modal structure. The results show that multiscale lamella structure exhibits good strength-toughness combination. The fracture toughness is ~52 MPa⋅m0.5 at the strength level of ~1460 MPa. By decreasing the tensile strength to ~1260 MPa, the fracture toughness increases to ~64 MPa⋅m0.5. In both lamella structure and Bi-modal structure, fracture toughness increases with decreasing yield strength which is attributed to a lager plastic zone at crack tip of lower strength. A linear relationship between yield strength and KIC gives a good fit in multiscale lamella structure. This suggests that continuum property (e.g. strength and ductility) governs KIC in the same microstructure type. Comparing different microstructure type, multiscale lamella structure exhibited higher KIC than Bi-modal structure at similar strength level. This is mainly attributed to the effect of back stress during deformation. A lower α/β interphase stress (back stress) and homogeneous strain distribution are exhibited in lamella structure which retards the crack propagation and increases the KIC. Meanwhile, coarse α lamella in multiscale lamella structure promotes the crack deflection. This crack shielding decreases the effective stress intensity (Keff) at crack tip and increase fracture toughness accordingly. Our study indicates that forming multiscale lamella α phase by BASCA treatment is an effective approach to overcome the mutually exclusive properties of strength and fracture toughness in high strength β titanium alloys. Multiscale lamella structure improves KIC by both intrinsic toughening (a more homogeneous strain distribution) and extrinsic toughening (improved crack propagation resistance).

Two-stage interface enhancement of aramid fiber composites: Establishment of hierarchical interphase with waterborne polyurethane sizing and oxazolidone-containing epoxy matrix

Hydroxy-terminated waterborne polyurethane (WPU) and oxazolidone-containing epoxy (OXEP) matrix were designed to realize two-stage interface enhancement of WPU sized aramid fiber/oxazolidone-containing epoxy (WAF/OXEP) composite, and the interfacial properties and interphase reinforcing mechanism were investigated. Compared with commercial aramid fiber (CAF), the surface roughness and energy of WAF were increased, and the fracture toughness and elongation at break of OXEP matrix were improved relative to those of general epoxy (GEP) matrix. In contrast to CAF/GEP and CAF/OXEP composites, the flexible interphase with high bonding capability from WPU sizing was constructed in WAF/GEP composite, which released interphase stress through deformation and improved interfacial adhesion. The hierarchical interphase encompassing inner modulus intermediate layer and outer flexible layer was established in WAF/OXEP composite, which could prevent crack propagation onto fiber surface and induce crack deflection through the enhancement of modulus and deformability of hierarchical interphase.

Analysis of thermal and mechanical properties of annealed surface modified nanodiamond/epoxy nanocomposites

In this paper, the effects of the annealed Nanodiamonds (NDs) on the bulk mechanical and thermal property of NDs/epoxy nanocomposites were investigated. The properties of the annealed NDs were confirmed through x-ray diffraction, Fourier transforms infrared spectroscopy, Raman spectroscopy, and Thermogravimetric analysis methods. In this study, the (NDs)/epoxy nanocomposites were prepared by using an ultrasonically dispersing method with different wt% of NDs such as 0.1, 0.3, and 0.5 in the epoxy matrix. The formation of strong chemical bonding on the annealed surface-modified NDs and epoxy resin, due to presence of the functional groups leads to the formation of an efficient interphase stress transfer. High-resolution transmission electron microscope (HRTEM) studies confirmed cluster free uniform dispersion of NDs in epoxy matrix, which lead to the enhancement of the tensile strength by 133%, tensile modulus by 20%, and storage modulus by 12% corresponding to the loading of 0.3 wt% of NDs in epoxy matrix. Thus, the nanocomposites developed in this method can be used in the high-end structural applications as well as improved thermal stability and viscoelastic behavior.

Development of high-coercivity state in high-energy and high-temperature Sm-Co-Fe-Cu-Zr magnets upon step cooling

The work compares the peculiarities of the high-coercivity state formation in the Sm-Co-Fe-Cu-Zr high-temperature and high-energy permanent magnets (HTPM and HEPM) in the course of the heat treatment with the stepwise decreasing temperature from 830 to 400 °C. Two types of magnets with varying Fe concentration, i.e., Sm(Co0.88-xFexCu0.09Zr0.03)7 with x = 0–0.12 (the HTPMs) and Sm(Co0.91-xFexCu0.06 Zr0.03)7.5 with x = 0.24–0.33 (the HEPMs) were studied at different temperatures of heat treatment for phase formation by x-ray diffraction followed by magnetic property measurements. Microstructure characterization was performed using transmission electron microscopy, whereas the three-dimensional elemental distribution at near-atomic scale was obtained using atom probe tomography. In HEPMs, the main increase in coercivity and relaxation of stresses accompanied by intensive enrichment of the 1:5 phase in Cu are observed at high temperatures (Т ≈ 700 °C). In HTPMs, the coercivity monotonously increases in the entire temperature range of the slow cooling from 700 to 400 °C at a rate of 0.5 °C/s. At the temperature close to the Curie temperature (∼550 °C) of the Sm(Co,Cu)5-type phase, the anomaly of the coercivity increment has been observed. The interphase stresses grow and the elemental redistribution appears to be accelerated simultaneously. The non-uniform Cu distribution in the 1:5 phase can be described by the formation of Cu-rich interlayers at the interface of the Sm(Co,Cu)5 and Sm2(Co,Fe)17-type phases.

Evolution of phase stresses in Al/SiCp composite during thermal cycling and compression test studied using diffraction and self-consistent models

In this work, the evolutions of stresses in both phases of the Al/SiCp composite subjected to thermal cycling during in situ compression test were measured using Time of Flight neutron diffraction. It was confirmed that inter-phase stresses in the studied composite can be caused by differences in the coefficient of thermal expansion for the reinforcement and matrix, leading to a different variation of phase volumes during sample heating or cooling. The results of the diffraction experiment during thermal cycling were well predicted by the Thermo-Mechanical Self-Consistent model. The experimental study of elastic-plastic deformation was carried out in situ on a unique diffractometer EPSILON-MDS (JINR in Dubna, Russia) with nine detector banks measuring interplanar spacings simultaneously in 9 orientations of scattering vector. For the first time, the performed analysis of experimental data allowed to study the evolution of full stress tensor in both phases of the composite and to consider the decomposition of this tensor into deviatoric and hydrostatic components. It was found that the novel Developed Thermo-Mechanical Self-Consistent model correctly predicted stress evolution during compressive loading, taking into account the relaxation of thermal origin hydrostatic stresses. The comparison of this model with experimental data at the macroscopic level and the level of phases showed that strengthening of the Al/SiCp composite is caused by stress transfer from the plastically deformed Al2124 matrix to the elastic SiCp reinforcement, while thermal stresses relaxation does not significantly affect the overall composite properties.

Lattice and phase strain evolution during tensile loading of an intermetallic, multi-phase γ-TiAl based alloy

Intermetallic γ-TiAl based alloys are promising materials for lightweight high-temperature applications, but their limited room temperature ductility poses an obstacle to the exploitation of their full potential. Especially in the case of multi-phase TiAl alloys, such as the β-stabilised TNM alloy of a nominal chemical composition of Ti-43.5Al-4Nb-1Mo-0.1 B (in at.%), an understanding of deformation and load partitioning mechanisms is required that works at all scales and encompasses all phases, including e.g. βo. In the present work, in situ high-energy X-ray diffraction measurements were conducted on a recent TNM sheet to study the load-bearing mechanisms and their sequential order upon tensile loading for the first time on the level of individual lattice planes and phases. Four specific stages of deformation were revealed. The direction-dependent analysis of the diffraction elastic moduli offered insights into the anisotropy of the individual phases and the initiation of intergranular and interphase stresses in the elastic regime. Plastic deformation was found to commence in the γ phase at applied stress levels of roughly 670–690 MPa. Load partitioning between differently oriented grains of the γ phase was observed, followed by a load transfer onto the α2 and βo phase. Further tensile loading entailed the onset of plasticity within favourably oriented α2 grains. The globular βo phase was found to deform elastically until failure. Differently oriented specimens of the weakly textured TNM sheet showed that the macroscopic mechanical properties can be assumed nearly isotropic.

Peculiar Kinetics of Coercivity of Sintered Sm(Co0.78Fe0.10Cu0.10Zr0.02)7 Magnet Upon Slow Cooling

The origin of coercivity of the sintered Sm(Co0.78Fe0.10Cu0.10Zr0.02)7 magnets has been studied in the course of step annealing by X-ray diffraction and magnetic measurements. The Cu redistribution in the Sm(Co,Cu)5 boundary phase of the cellular structure modifies the domain-wall energy and increases the coercivity upon step cooling. Interphase stresses are considered to be the main reason for copper redistribution upon slow cooling. It is shown that the coercivity abruptly increases in the course of annealing at a temperature of 500 °C, which is close to the Curie temperature of the Sm(Co,Cu)5 phase. The effect may be caused by an increase in the interphase stresses at the boundary of the coherent 1:5 and 2:17 phases in the course of the annealing at the temperature close to the Curie temperature of the 1:5 phase. The accelerated Cu diffusion into the boundary compensates these stresses. The new scheme of the Cu redistribution over the cell-boundary phase is suggested. Contrary to the known schemes, it assumes that Cu is localized in the 1:5 phase near the interface between the phases, rather than in the center of the 1:5 phase.