Search

Size effect has a significant influence on the accuracy of two key factors of parameters and models in crystal plasticity simulation. This study introduces a parameter identification method that considers the indentation size effect, determining the initial slip resistance of IN625 alloy. Based on the identified parameters and utilizing the integral point traversal method, a grain boundary affected zone (GBAZ), whose strength field related to the distance to the grain boundary (GB) is introduced into the polycrystalline microstructure to represent the hindering effect of GBs on dislocations. This method effectively predicts the Hall-Petch effect and strain hardening behavior of IN625 alloy. The research reveals that dislocation pile-ups primarily concentrate in small grain clusters within the material. In fine-grained microstructures, a large volume fraction of GBs promotes dislocation pile-ups, reducing the mean free path of dislocations, leading to an increase in dislocation multiplication rate, and consequently, enhancing the strain hardening rate. An increase in GBAZ thickness results in a large stress level within the material, accompanied by a decrease in the homogeneity of stress distribution. However, the sensitivity of strain to GBAZ thickness is found to be low. The method proposed in this work holds significant applicative relevance in parameter calibration and prediction the mechanical properties of polycrystalline materials. • A modified method for identifying crystal plasticity parameters was proposed. • There is a strong linear relationship between strength and hardness at the micro-nano scale. • An explicit grain boundary affected zone was introduced into the model. • The Hall-Petch effect and strain hardening behavior of IN625 alloy was predicted. [ABSTRACT FROM AUTHOR]

The hydrogen diffusion and damage characteristics within the microstructure at the crack tip are direct factors determining hydrogen embrittlement (HE) phenomena, yet research in this area from a mesoscale perspective is still insufficient. This study employs a non-local crystal plasticity constitutive model coupled with a hydrogen diffusion model that considers grain boundary (GB) characteristics and incorporates fracture initiation parameter accounting for the HELP + HEDE mechanisms. The research investigates hydrogen diffusion behavior at the crack tip in pure nickel and provide a detailed exploration of the mechanism underlying hydrogen-assisted crack propagation. The results indicate that the non-local model exhibits advantages in simulating the hydrogen diffusion process. Hydrogen induces intragranular cracks to propagate along slip planes with a high dislocation density. High-energy GBs and triple junctions are more susceptible to hydrogen accumulation, and under the influence of the HEDE mechanisms, they represent the primary sites for crack initiation. The entire fracture process involves the continuous coalescence of primary cracks with secondary cracks. Moreover, the HE resistance is better in equiaxed microstructures compared to rolled microstructures, particularly when the crack plane is parallel to the TD direction. • The hydrogen diffusion behavior in the microstructure at the crack tip was studied. • The interaction between hydrostatic stress and strain induces hydrogen-assisted cracking. • High-energy GBs serve as the primary enrichment sites for hydrogen atoms. • The HE resistance of the rolled microstructures is inferior to the equiaxed ones. [ABSTRACT FROM AUTHOR]

Size effect has a significant influence on the accuracy of two key factors of parameters and models in crystal plasticity simulation. This study introduces a parameter identification method that considers the indentation size effect, determining the initial slip resistance of IN625 alloy. Based on the identified parameters and utilizing the integral point traversal method, a grain boundary affected zone (GBAZ), whose strength field related to the distance to the grain boundary (GB) is introduced into the polycrystalline microstructure to represent the hindering effect of GBs on dislocations. This method effectively predicts the Hall-Petch effect and strain hardening behavior of IN625 alloy. The research reveals that dislocation pile-ups primarily concentrate in small grain clusters within the material. In fine-grained microstructures, a large volume fraction of GBs promotes dislocation pile-ups, reducing the mean free path of dislocations, leading to an increase in dislocation multiplication rate, and consequently, enhancing the strain hardening rate. An increase in GBAZ thickness results in a large stress level within the material, accompanied by a decrease in the homogeneity of stress distribution. However, the sensitivity of strain to GBAZ thickness is found to be low. The method proposed in this work holds significant applicative relevance in parameter calibration and prediction the mechanical properties of polycrystalline materials. • A modified method for identifying crystal plasticity parameters was proposed. • There is a strong linear relationship between strength and hardness at the micro-nano scale. • An explicit grain boundary affected zone was introduced into the model. • The Hall-Petch effect and strain hardening behavior of IN625 alloy was predicted. [ABSTRACT FROM AUTHOR]

• A novel hydrogen diffusion model coupled with CPFE framework was proposed. • The GB energy and HS jointly determine the distribution of hydrogen. • Hydrogen diffusion along GB is affected by the concentration within the grains. • Alloys with medium-sized grain microstructures exhibit good hydrogen tolerance. The influence of grain boundaries (GBs) on hydrogen transportation is a crucial factor in understanding the mechanisms of hydrogen embrittlement (HE) in polycrystalline alloys. Crystal plasticity models have the advantages in simulating the effect of grain microstructure on hydrogen diffusion in polycrystals, but they have not yet been coupled with hydrogen diffusion models that can take into account GB characters. In this study, a hydrogen diffusion model that considers the effect of GBs on the transportation of hydrogen was developed to study the local hydrogen diffusion behavior in bi-crystalline and polycrystalline alloys. The simulation results showed the capability of the model in describing the influence of hydrogen on the material deformation. In addition, this study found that the hydrostatic stress determined the hydrogen concentration in the far-GB region, whereas the GB energy played a control role in and near the GB regions. Notably, hydrogen exhibits a preference for localization near high-angle grain boundaries (HAGBs) and triple junctions. In alloys with medium grain size, hydrogen typically had low average concentration with a more uniform distribution. Furthermore, the hydrogen-assisted crack growth mechanism was analyzed as the continuous coalescence of primary and secondary cracks along GBs. This work presents a hydrogen diffusion model that considers GB effects, and the proposed model has advantages in predicting the deformation and fracture of polycrystalline alloys in hydrogen environments. [ABSTRACT FROM AUTHOR]

The strengthening effects of primary α grains in titanium alloys were systematically investigated by integrating micropillar compression tests and crystal plasticity simulations. This study focused on the deformation behavior of dual-phase micropillars consisting of a single primary α grain and a single-crystal β matrix. During compression, these micropillars exhibited two slip modes, i.e., single- and multi-slip features. Slip analysis was performed based on the compressed morphology of the pillars and the Schmid factors. It was found that the first slip step observed in multi-slip pillars was not attributed to the slip system with the largest Schmid factor. To validate the experimental findings, numerical simulations using crystal plasticity models were conducted. The simulation results accurately reproduced the engineering stress-strain responses and allowed for a comparison of the distribution of von Mises stress and cumulative shear strain between the dual-phase and single-β phase pillars. Also, the stress concentration induced by α precipitates affects the stress distribution and leads to heterogeneous deformation within the micropillars, correlating with the observed slip modes. The experimental and numerical results will provide a further understanding of meso-scale heterogeneous deformation behaviors and offer insights into the microstructure-properties relationship in titanium alloys. [Display omitted] • The presence of α grains can alter the slip modes near α/β heterointerfaces. • Slip steps with lower Schmid factors are activated in multi-slip micropillars. • Severe gradients of stress and shear strain are introduced by α precipitates. • Deformation capacity and anisotropy can both affect mechanical responses. [ABSTRACT FROM AUTHOR]

A well-designed microstructure plays a crucial part in achieving favorable properties and optimizing the service performances of titanium alloys, requiring thorough investigations of the microstructure effect on the heterogeneous deformation and strain partition behaviors. The mechanical responses of titanium alloy with lamellar microstructure are analyzed from lamellae features' crystallographic and geometric aspects through crystal plasticity simulations. It is found that the coarser β and finer α lamellae exhibited improved strain accommodation capacity which mainly benefitting from the large amount of plastic slip occurring in the coarse β lamellae of lamellar microstructure. Furthermore, the interlamellar strain partition coefficient evolves dynamically and gradually stabilizes after 5% deformation. Considering the geometric and crystallographic orientations of α phase, angles γ 1 and γ 2 are used to evaluate the strengthening effects of α lamellae precipitating from 6 types of β variants. Simulated results reveal that a more uniform strain partition occurs when cos γ 1 is in the range of 0.8–1.0 and cos γ 2 is lower than 0.3, while a higher deformation resistance occurs when cos γ 1 and cos γ 2 are in the range of 0.2–0.4 and 0.9 to 1.0, respectively. Therefore, finding an appropriate balance by manipulating the microstructural characteristics can simultaneously enhance the plasticity/strength of a titanium alloy. The obtained results will facilitate understanding the interlamellar strain partition behavior of titanium alloys and theoretically guide the microstructure designing for mechanical properties optimization. [Display omitted] • Crystallography and geometrical features of lamellae affect the mechanical responses. • Coarser β and finer α lamellae exhibit better strain accommodation capacity. • Strain partition coefficient evolves dynamically with increasing deformation. • Stress-strain responses are mapped to pilot microstructure designing for desirable properties. [ABSTRACT FROM AUTHOR]

• A strategy to quantify α phase strengthening in titanium alloys is proposed. • The interface-affected zone arising from spherical primary α grains is introduced. • Elastic interaction energy coupling by the semi-coherent interfaces of lamellae. • The orientation and growth direction affect the non-uniform strain in α lamellae. A strategy to quantify the second phase strengthening of α precipitates in titanium alloys is proposed to predict the mechanical performance through crystal plasticity finite element (CPFE) models. Considering the different dominant features of equiaxed and lamellar microstructures, statistical and microstructural factors are introduced to describe the slip resistance variations in the β matrix. The significant contribution of the interfaces is incorporated by introducing the interface-affected zone (IAZ) into crystal plasticity constitutive laws of equiaxed microstructures. In particular, the slip resistance variation is derived accounting for the interfacial energy distribution inside the IAZ. Meanwhile, the arrangement of the α lamellae is more compact and complex than that of spherical α grains in equiaxed microstructures; thus, instead of the IAZ, the interface length density is applied to describe the strengthening effects of the interfaces in lamellar microstructures. The elastic interaction energy induced by the semi-coherent interfaces of lamellae is obtained according to the micro-elastic theory. Using the advantages of the aforementioned improved models, CPFE simulations of the tensile behavior of equiaxed and lamellar microstructures at room temperature are performed, with the results matching well with the experimental data. Moreover, differences regarding the lattice structures and grain orientations lead to non-uniform strain partitioning in equiaxed and lamellar microstructures. Equiaxed α grains that favor prismatic slip tend to bear more plastic deformation than those favoring basal slip. The growth direction of α lamellae affects the deformation ability as well. Consequently, the proposed approach can precisely predict the mechanical properties of dual-phase titanium alloys through statistical values of microstructural features, and can be utilized in the investigations of other metals with similar structural characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]