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Abstract Heterogeneous plastic deformation behavior of < hkl > oriented individual grains-family with respect to the tensile direction in austenitic steels was studied using electron back scatter diffraction (EBSD) and neutron diffraction (ND) measurements. The kernel averaged misorientation value determined by EBSD for a plastically deformed specimen was different in grain to grain, suggesting different dislocation densities. Such insights obtained from the surface observations with EBSD were quantitatively evaluated as bulk-averaged data using ND. The convolutional multiple whole profile fitting (CMWP) for ND profiles has revealed different dislocation densities in < hkl > oriented grains-families, showing good coincidence with the EBSD results in trend. [ABSTRACT FROM AUTHOR]

The plastic deformation of the AlSi10Mg alloy manufactured via laser powder bed fusion (LPBF) is incompatible at the microscale, which causes residual strains/stresses and dislocation pile-ups at the Al/Si interfaces and grain boundaries. Hence, it is of fundamental significance to clarify these microscopic properties during plastic deformation. Here, in-situ neutron diffraction is employed to explore the residual strains, stresses, and dislocation density in the LPBF AlSi10Mg during loading-unloading-reloading deformation. It is found that the maximum residual stresses of the Al and Si phases in the loading direction reach up to about −115 (compressive) and 832 (tensile) MPa, respectively. A notable dislocation annihilation phenomenon is observed in the Al matrix: the dislocation density decreases significantly during unloading stages, and the amplitude of this reduction increases after experiencing a larger plastic deformation. At the macroscale, this dislocation annihilation phenomenon is associated with the reverse strain after unloading. At the microscale, the annihilation phenomenon is driven by the compressive residual stress in the Al matrix. Meanwhile, the annihilation of screw dislocations during unloading stages contributes to the reduction in total dislocation density. Unlabelled Image • In-situ neutron diffraction of additively manufactured AlSi10Mg during loading-unloading-reloading was conducted. • The residual stresses of Al and Si in the loading direction and their evolutions are quantified. • A notable dislocation annihilation phenomenon during unloading stages is detected and quantified. • Average fraction of edge dislocations increases, and that of screw ones decreases as the plastic deformation proceeds. [ABSTRACT FROM AUTHOR]

In situ neutron diffraction experiments have been performed under loading in cast-wrought (CW) and additively manufactured (AM) equiatomic CoCrNi medium-entropy alloys. The diffraction line profile analysis correlated the faulting-embedded crystal structure to the dislocation density, stacking/twin fault probability, and stacking fault energy as a function of strain. The results showed the initial dislocation density of 1.8 × 1013 m −2 in CW and 1.3 × 1014 m −2 in AM. It significantly increased up to 1.3 × 1015 m −2 in CW and 1.7 × 1015 m −2 in AM near fracture. The dislocation density contributed to the flow stress of 470 MPa in CW and 600 MPa in AM, respectively. Meanwhile, the twin fault probability of CW (2.7%) was about two times higher than AM (1.3%) and the stacking fault probability showed the similar tendency. The twinning provided strengthening of 360 MPa in CW and 180 MPa in AM. Such a favorable strengthening via deformation twinning in CW and dislocation slip in AM was attributed to the stacking fault energy. It was estimated as 18.6 mJ/m2 in CW and 37.5 mJ/m2 in AM by the strain field of dislocations incorporated model. Dense dislocations, deformation twinning, and atomic-scale stacking structure were examined by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). [Display omitted] [ABSTRACT FROM AUTHOR]

The present study investigated the tensile deformation behavior of quenched and tempered martensite steels at various austenitization and tempering temperatures using in situ neutron diffraction experiments. Phase lattice strains in the bcc and cementite (θ) phases and dislocation structures in the bcc phase were analyzed. The phase lattice strain in bcc (ε p h a s e b c c) became almost stagnant after yielding as the tempering temperature increased. The phase lattice strain in θ increased linearly with an increase in the flow stress, independent of the austenitization and tempering temperatures. The stress partitioning between bcc and θ was confirmed after the yielding of bcc, which contributed to the work hardening. The phase stresses of bcc and θ and their stress partitioning improve the mechanical properties of martensite steels, which can be summarized by the systematic changes in phase lattice strain and dislocation properties due to the austenitization and tempering temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

• In-situ neutron diffraction of additively manufactured AlSi3.5Mg2.5 samples after annealing and aging. • The dislocation densities in both annealed and aged samples during tensile loading were measured. • The dislocation density is much lower in the annealed sample than in the aged one. • The dislocation storage rate is much lower in the annealed sample than in the aged one upon loading. • The dislocation annihilation rate is higher in the annealed sample than in the aged one upon loading. The ductility of the Al alloys produced by additive manufacturing (AM) has become a critical property, as the AM Al alloys are increasingly used in the automotive industry. However, the ductility of as-built AM Al alloys is relatively low, even with optimized AM conditions. The post-annealing treatment provides an efficient way to improve ductility. Previous investigation has shown that the annealed AM AlSi3.5Mg2.5 alloy possesses superior ductility. However, the plastic deformation micro-mechanisms of the annealed AM AlSi3.5Mg2.5 alloy remain unclear. In this study, in-situ neutron diffraction was employed to explore the annealed AM AlSi3.5Mg2.5 alloy. The evolutions of phase stresses, dislocation density, and crystallite size in the annealed AM AlSi3.5Mg2.5 alloy during tensile deformation were analyzed. The experimental investigation reveals that the dislocation density in the Al matrix of the annealed AM AlSi3.5Mg2.5 alloy increases slowly in the early plastic deformation stage, and it reaches a saturated level upon the following uniform deformation. The crystallite size decreases quickly in the early deformation stage, and then it decreases slowly. The Kocks-Mecking model and the Voce model can capture the strain hardening behavior well. The determined physical constitutive equations can be applied in continuum mechanical computer simulations. [ABSTRACT FROM AUTHOR]

To better understand and predict the mechanical properties of additive manufacturing (AM) Al–Si–Mg alloys, developing a physically-based constitutive model is crucial. Among different models, the dislocation-density-based Kocks-Mecking (K-M) constitutive model has been widely used. Unfortunately, two challenges arise when the K-M model is used for the multiphase Al alloys. Firstly, an accurate K-M model demands the separation of phase stresses. Secondly, a thorough analysis of the K-M model involves the measurement of dislocation density during deformation. In-situ neutron diffraction, a powerful method to measure the phase stress and dislocation density in bulk polycrystalline materials under loading, is employed to investigate the AM AlSi3.5Mg1.5 and AlSi3.5Mg2.5 (wt.%) alloys. Based on the present results and reported data of AlSi10Mg, a multiscale constitutive model is developed for different AM Al–Si–Mg alloys. At the microscale, the evolution of dislocation density in the Al matrix with plastic strain can be well predicted by the K-M model. Meanwhile, the developments of the average stresses in different phases with plastic strain can be well captured by the Voce model. The measured microscopic k 2 / n c values agree with the theoretical value two of the K-M model quite well. Here, n c is the characteristic factor of the microscale Voce model, while k 2 is the coefficient associated with the dynamic recovery process in the microscale K-M model. At the macroscale, the mechanical behavior can also be well reproduced by the K-M model and the Voce model. However, the macroscopic K 2 / N c ratio is far away from two, where N c and K 2 are the characteristic factor and coefficient of the macroscale Voce model and K-M model, respectively. • In-situ neutron diffraction of additive manufactured AlSi3.5Mg1.5 and AlSi3.5Mg2.5 has been conducted. • Crystal-orientation-dependent lattice strains, average phase stresses, and dislocation densities have been measured. • A multiscale Kocks-Mecking model has been developed based on the experimental data. • At the microscale, the determined k 2 / n c ratio agrees with the theoretical value two of the Kocks-Mecking model quite well. • At the macroscale, the determined K 2 / N c ratio is far away from two. [ABSTRACT FROM AUTHOR]