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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]

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 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]

The microscopic deformation behavior is always been of significant interest in revealing the mechanism of the dwell fatigue effect. This study systematically characterized the deformation system activation in Ti–6Al–3Nb–2Zr–1Mo (Ti6321) alloy using in situ tensile and quasi-in situ dwell fatigue tests. The critical resolved shear stresses of the basal and prismatic slip systems in the Ti6321alloy were first calculated using the slip trace analysis method. The study demonstrated that, under dwell fatigue, basal and prismatic slips consist of major microscopic deformation modes. Most of the slip deformation occurred rapidly during the early stage of dwell fatigue and was independent of the dwell loading. The basal slip was found to be the predominant slip mode regardless of the dwell conditions. The results suggested that the elastic anisotropy of the hexagonal-closed-packed (HCP) structure could lead to heterogeneous microscopic stress, thus activating more basal slip activities. Such activities were found to participate in the crack initiation through two unique cracking modes: basal plane crack and (0001) twist boundary crack. [Display omitted] • The critical resolved shear stress was quantitatively evaluated through in situ tensile tests. • Dwell fatigue deformation modes were revealed by the crystallographic characteristics. • Basal slip deformation was proved to be the predominant slip mode and highly participated in the crack initiation. [ABSTRACT FROM AUTHOR]