Interior Of Grains Research Articles

Making Al-Cu-Mg alloy tough by Goss-oriented grain refinement

The microstructure evolution and its effect on the strength properties and fatigue performance of the Al-Cu-Mg alloy are investigated by using optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). Results show that the strength-ductility trade-off can be improved and the fatigue crack propagation (FCP) rate of the Al-Cu-Mg alloy can be reduced by refining Goss-oriented grains. Post-fatigue electron back-scatter diffraction revealed that the strain homogenization can make the interior of fine Goss-oriented grain to occur the tiny deformation, which is not easy to transmit damage to adjacent grains. Therefore, refining Goss-oriented grains not only increases the strength but also improves the ductility and promotes crack deflection, reducing the FCP rate.

Microstructures and mechanical properties of a hot-extruded Mg−8Zn−6Al−1Gd (wt%) alloy

Microstructural evolution and mechanical properties of a Mg−8Zn−6Al−1Gd (wt%) alloy were thoroughly investigated in this work. The results indicate that the dominant intermetallic phases in the as-cast sample are ϕ-Al2Mg5Zn2, τ-Mg32(Al,Zn)49, i-Mg44Al15Zn41 and Al2Gd phases and almost free Gd was detected in the former three phases. After extrusion, the sample has a fully recrystallized microstructure with the average grain size being ~1.5 µm, and exhibits a weak rare earth texture. Additionally, fine particles were approximately homogeneously dispersed in the fine-grained structure. Most of them are quasicrystal phase (i-phase) but have no identical orientation relationship with Mg matrix regardless of whether they distribute at grain boundaries or inside grains. Finally, the as-extruded sample exhibits good strength-ductility balance in both tension and compression and simultaneously has a slight reverse tension/compression asymmetry. Microstructural observations indicate that the excellent mechanical performance of the studied alloy is highly related to its fine grains, weak RE texture, and numerous homogeneously distributed fine particles.

Effect of loading path on grain misorientation and geometrically necessary dislocation density in polycrystalline aluminum under reciprocating shear

Solid phase processing (SPP) is a promising alloy fabrication technique to produce fine and homogeneous grain structures for high-performance alloys. However, there is very limited modeling capability to understand and predict the grain refinement during SPP. In this work, the crystal plasticity theory was used to study elastic–plastic deformation in polycrystalline aluminums under large shear deformation. Two approaches, kernel averaged misorientation (KAM) and grain reference orientation deviation (GROD), were used to assess the grain misorientations. The geometrically necessary dislocation (GND) density was computed with the plastic strain rate. The deformation simulations were carried out under two loading conditions to investigate the effect of loading paths on the evolutions of grain misorientation and GND density. The results show that the regions with high misorientation and GND density first appear near grain boundaries. These regions then extend toward interior grains. The loading path affects plastic deformation accumulation and recovery, hence dislocation evolution and misorientation. Both two- and three-dimensional simulations showed that the spatial and temporal evolutions of GROD, KAM, and GND density are closely correlated, which indicates they all can be used as criteria of grain refinement or recrystallization, the essential information for grain refinement simulations.

Grain and grain boundary behaviors and electrical transport properties of TiO<sub>2</sub> nanowires under high pressure

In this work, anatase Titanium dioxide (TiO<sub>2</sub>) nanowires are synthesized by the hydrothermal method, and its grain and grain boundary behaviors and electrical properties are investigated by alternating current (AC) impedance method under high pressure (up to 34.0 GPa). The relationship between the frequency dependence of impedance <i>Z''</i> and pressure indicate that the conduction mechanism of anatase phase TiO<sub>2</sub> nanowires in the test pressure range is electronic conductivity. It should be noted that the characteristic peaks of <i>Z''</i> move toward high frequency region with pressure increasing, demonstrating that the effect of grain interior on impedance becomes apparent. Additionally, the overall variation trends of grain and grain boundary resistance go downward with pressure increasing, and the descent rate of grain boundary is larger than those of grain before and after phase transition. However, in a range of phase transition (8.2–11.2 GPa, from anatase to baddeleyite phase), grain boundary resistance shows a discontinuously change (increases to 11.2 GPa and then decreases). Based on the different variation trends of grain and grain boundary resistance, it becomes obvious that the phase transition from anatase to baddeleyite phase first occurs at the surface of grain, and then extends to the interior of grain gradually. Also, as an intrinsic characteristic, the relaxation frequency is independent of the geometrical parameters. The pressure dependence of activation energy is obtained by fitting the pressure dependence of relaxation frequency. The activation energy of grain and grain boundary decrease with pressure increasing, implying that the contribution of pressure on the conductivity of sample is positive. Furthermore, the space charge potential for the whole test pressure range is positive, which is determined by the relationship between pressure and relaxation frequency. This fact illustrates that the anion defects are easily formed in the space charge region, and the oxygen defects are the main inducement for TiO<sub>2</sub> phase transformation.

Microstructure evolution and mechanical properties of a high-strength Mg-10Gd-3Y–1Zn-0.4Zr alloy fabricated by laser powder bed fusion

A high-strength Mg-10Gd-3Y–1Zn-0.4Zr (GWZ1031K, wt%) alloy was prepared by laser powder bed fusion (LPBF), and the microstructure and mechanical properties of the as built, LPBF-T5, LPBF-T4, and LPBF-T6 states were systematically studied. The as built alloy is composed of fine equiaxed ɑ-Mg grains with an average grain size of 4.1 ± 0.5 µm, reticular β-(Mg,Zn)3(Gd,Y) eutectic phase and flaky Y2O3 oxide phase, and exhibits yield strength (YS) of 310 ± 8 MPa, ultimate tensile strength (UTS) of 347 ± 6 MPa and elongation (EL) of 4.1 ± 0.8%. A simple direct aging heat treatment at 175 ℃ for 64 h after LPBF leads to an ultra-high YS of 365 ± 12 MPa but a low EL of 0.8 ± 0.3% in the LPBF-T5 alloy. The solution heat treatment improves ductility by transforming the hard and brittle eutectic phase into the relatively soft and deformable lamellar long period stacking ordered (LPSO) structure inside grains and X phase at grain boundaries without obvious grain growth. Moreover, the LPBF-T4 alloy solution-treated at 450 ℃ for 12 h exhibits YS of 255 ± 8 MPa, UTS of 328 ± 9 MPa, and EL of 10.3 ± 0.5%. Aging heat treatment after solution introduces numerous prismatic β′ and β1 precipitates, which help to increase tensile strength. The YS, UTS, and EL of the LPBF-T6 alloy are 316 ± 5 MPa, 400 ± 7 MPa, and 2.2 ± 0.3%, respectively. It can be concluded that the LPBF process when combined with specially designed post-processing holds great promise for the manufacturing of high-performance components of the Mg-rare earth alloys with significantly higher YS for various applications.

Effects of Grain Boundary Angles on Initial Deformation of 304 Austenitic Stainless Steel under Nanoindentation: A Molecular Dynamics Simulation

Nitrogen-containing 0Cr19Ni10 (304 NG) austenitic stainless steel plays a significant role in Generation IV reactor pressure vessels. The structure and properties of 304 NG are heavily influenced by the grain boundaries (GBs), especially the initial mechanical response and dislocation evolutions. Hence, in this paper, we carried out molecular dynamics (MD) simulations to investigate the effects of the GB angles on the initial deformation of 304 models under nanoindentation. It is found that the GB angle has great effects on the mechanical properties of 304 NG. With the GB angles changing from 90° to 150°, the values of Young’s modulus and maximum shear stress first decrease and then increase due to decreasing of the interaction among the GBs and the grain interiors (GIs) and the smoother shape of GBs. The hardening region slope decreases rapidly result from the GB angles changing the grain size on the both sides, which fully fits the Hall–Petch relationship. After the dislocations reaching the GBs along the slip system, the dislocation piles-up on the GBs at first, and then GBs serve as a source of dislocation and emit dislocation to free surface with the depth of nanoindentation increasing. This work provides a better understanding on the angle effects of GBs in materials.

Microstructural heredity of Ni-containing cryogenic steel and its effect on the toughness at 77 K

The microstructural heredity of as-rolled lath martensite with different prior austenite grain morphologies during inter-critical quenching has been studied by using a quasi in-situ EBSD technique in a 6.5%Ni-containing cryogenic steel, to reveal the effect of as-rolled microstructure on final microstructure and toughness at 77 K. It is found that the refinement of final microstructure can be achieved by refining the as-rolled lath martensite through both refinement and elongation of prior austenite grains, which is attributed to two aspects of heredity effect. On the one hand, the fine as-rolled martensitic structure in the interiors of prior austenite grains is inherited during inter-critical quenching. On the other hand, the refinement of as-rolled lath martensite promotes the formation of newly oriented grains along the prior austenite grain boundaries to further refine the microstructure. The cryogenic toughness of Ni-containing cryogenic steels is significantly improved through the heredity effect of as-rolled lath martensitic refinement.

Geochemical constraints on the formation of chondrules: Implication from Os and Fe isotopes and HSE abundances in metals from CR chondrites

CR chondrites are suitable for understanding the genetic linkage between metals and chondrules due to the unique characteristics of the coexisting metal phases with chondrules. Metal grains are found in three different locations of CR chondrites; chondrule interior (“interior grain”), chondrule surficial shells (“margin grain”), and the matrix (“isolated grain”). Here we report the abundances of highly siderophile elements (HSEs) and major elements in three types of metals (interior, margin, and isolated grains) from three CR chondrites (NWA 801, NWA 7184, and Dhofar 1432) by using femtosecond LA-ICP-MS (fs LA-ICP-MS) and EPMA. Additionally, we report the isotopic compositions of Os and Fe in the metals by using micro-milling sampling coupled with N-TIMS and MC-ICP-MS. The CR metals have variations in 187Os/188Os and δ57Fe values ranging from 0.1193 to 0.1314 and from −1.05 to +0.25, respectively. HSE abundances, except for Pd and Au, in the three types of metals increase as the abundance of Ir increases. A possible explanation for the variations of HSE abundances within and among grains, 187Os/188Os values within each grain, and δ57Fe values among grains, is the condensation of liquid metal from a gaseous reservoir followed by fractional crystallization. Most of the CR metals have negative δ57Fe values, suggesting that Fe in metal phases might have formed by condensation prior to Fe condensation in silicate phases. The chondrules and three types of metal grains in CR chondrites are believed to have formed contemporaneously in the same region. The existence of large isolated metals in matrix and compound chondrules might be the result of collision and merging of the metal and silicate droplets.

Radiation induced hardening of beryllium during low temperature He implantation

• Helium implantation resulted in significant hardness increase of beryllium. • Dislocation loops and helium bubbles are responsible for hardening. • Low purity grade has higher irradiation induced hardening after 200°C implantation. • Crystallography leads to significant scatter in indentation hardness. • Softer grains exhibited higher irradiation induced hardening. The effect of ion irradiation on evolution of microstructure and hardening of beryllium with different impurity levels was investigated using TEM and nanoindentation. High purity S-65 grade and less-pure S-200-F grade were implanted by helium ions at temperatures of 50°C and 200°C. 11 different energies were used, so as to create a quasi-homogeneous 3 µm irradiated layer with average radiation damage of 0.1 dpa and average He content of 2000 appm. Nanoindentation experiments demonstrated that before irradiation, the S-200-F and S-65 grades have an average hardness of 3.7±0.8 GPa and 3.4±0.8 GPa correspondently. After implantation the hardness of both grades increased by about 60% for the 200°C irradiation and 100% for the 50°C irradiation. The crystallographic analysis of indented grains demonstrated that in the as-received materials the hardness is about 2.5 times higher when the indentation direction is close to the [0001] c-axis of beryllium compared to indentation perpendicular to [0001]. Hardness anisotropy significantly decreased after irradiation: the “soft orientation” was most sensitive to irradiation-induced hardening, with hardness increasing by about 140% after irradiation at 50°C and 100% after irradiation at 200°C, compared to about 15 - 20% for the “hard” orientation at both irradiation temperatures. The higher purity grade had smaller increase of the “soft orientation” hardness: 2.5±0.3 GPa for the S-65 and 2.9±0.2 GPa for the S-200-F. At both temperatures in both grades, under TEM investigation the radiation damage appears as “black dots” which are likely to be small dislocation loops with the number density of ~ 10 22 m −3 . No bubbles were observed by TEM inside grains and at grain boundaries. Analysis of the possible hardening contribution demonstrated that the observed “black dots” could be responsible for up to half of the measured hardening, while the rest of the hardening should originate from helium bubbles with the size below the TEM resolution (at or below 1.5 nm).

Research on homogeneous nucleation and microstructure evolution of aluminium alloy melt.

In this paper, based on the embedded atom method (EAM) potential, molecular dynamics simulations of the solidification process of Al–4 at.%Cu alloy is carried out. The Al–Cu alloy melt is placed at different temperatures for isothermal solidification, and each stage of the entire solidification process is tracked, including homogeneous nucleation, nucleus growth, grain coarsening and microstructure evolution. In the nucleation stage, the transition from high temperature to low temperature manifests a change from spontaneous nucleation mode to divergent nucleation mode. The critical nucleation temperature of the Al–Cu alloy is determined to be about 0.42 Tm (Tm is the melting point of Al–4 at.%Cu) by calculating the nucleation rate and the crystal nucleus density. In the nucleus growth stage, two ways of growing up are observed, that is, a large crystal nucleus will absorb a smaller heterogeneous crystal nucleus, and two very close crystal nuclei will merge. In the microstructure evolution of the isothermally solidified Al–Cu alloy, it is emerged that the interior of all nanocrystalline grains are long-period stacking structure composed of face centred cubic (FCC) and hexagonal close-packed (HCP). These details provide important information for the production of Al–Cu binary alloy nano-polycrystalline products.

Effect of high-energy attrition milling and La2O3 content on the microstructure of Mo-La2O3 composite powders

Mo-La2O3 composites are potential high-temperature materials for future technology devices operating at temperatures above 1300 °C because of their excellent thermal stability, high mechanical properties and good creep resistance. In this study, we focused on the preparation of Mo-matrix/lanthanum oxide (La2O3) composite powders using high-energy attrition milling. The effects of rotational milling speed (350 and 800 rpm) and La2O3 content (2.5 and 10 vol. %) on the microstructural evolution, phase composition, morphology, and distribution of the second phase in the produced composite Mo-La2O3 powders were investigated in details. The results show that the most interesting composite powder was Mo-10 vol.% La2O3 produced using a rotational speed of 800 rpm, which exhibited better distribution, smaller particle size and higher amount of ceramic phase introduced in the interiors of the Mo grains.

Mechanical behavior in the interior and boundary of magnesium aluminate spinel (MgAl2O4) grain under nanoindentation.

The understanding of mechanical behavior in magnesium aluminate spinel (MgAl2O4) at the nanoscale lays a foundation for its material removal mechanism in ultraprecision machining. Nanoindentation tests are carried out in the interior and boundary of spinel grain with different loads. An obvious indentation size effect exhibits in both of these areas. First, the nano-hardness and elastic modulus decrease, followed by stabilization due to an increase of pressure. The measured elastic modulus, hardness, and fracture toughness of the grain interior are 277.7±8.4GPa, 19.79±0.83GPa, and 1.12±0.02MPa⋅m1/2, respectively. Deformation of spinel transits from elastic to plastic at approximately 0.8 mN load, which corresponds to the discontinuous steps of load-displacement curves. By comparing the fracture toughness and the residual indent morphology, the grain boundary exhibits lower brittleness than the grain interior. Radial cracks form on the grain surface as indentation load exceeds 29 mN, whose propagation is influenced by the loading conditions and the grain boundary effect.

The role of crystal orientation and grain boundaries in the cavitation resistance of EN 1.4301 austenitic stainless steel: An EBSD study

Characterization of crystal orientation and grain boundaries is of great interest in the understanding of the mechanisms taking place during the degradation process originated by the exposure of materials to erosive media. In the present study, an austenitic stainless steel previously analyzed by electron backscatter diffraction was exposed to ultrasonic cavitation erosion. Several parameters such as crystal orientation, misorientation, coincidence site lattice, Schmid factor and twin orientation were examined in order to determine their influence on the local susceptibility to early damage induced by cavitation. Crystallographic orientation was found to play a significant role in the deformation mechanisms occurring inside grains. Furthermore, high misorientation between adjacent grains was recognized as a determining factor leading to early damage observed at random grain boundaries, while the difference in Schmid factor was identified to have a significant effect on the cavitation resistance of twin boundaries. Moreover, the effect of the deviation from the ideal orientation predicted for coherent twins was analyzed in connection with cavitation resistance.

Impact of RbF and NaF Postdeposition Treatments on Charge Carrier Transport and Recombination in Ga‐Graded Cu(In,Ga)Se2 Solar Cells

AbstractTwo key strategies for enhancing the efficiency of Cu(In,Ga)Se2 solar cells are the bandgap gradient across the absorber and the incorporation of alkali atoms. The combined incorporation of Na and Rb into the absorber has brought large efficiency gains compared to Na‐containing or alkali‐free layers. Here, transient absorption spectroscopy is employed to study the effect of NaF or combined NaF+RbF postdeposition treatments (PDT) on minority carrier dynamics in different excitation volumes of typical composition‐graded Cu(In,Ga)Se2 solar cells. Electron lifetimes are found to be highly dependent on the film composition and morphology, varying from tens of nanoseconds in the energy notch to only ≈100 ps in the Ga‐rich region near the Mo‐back contact. NaF PDT improves recombination lifetimes by a factor of 2–2.5 in all regions of the absorber, whereas the effectiveness of the RbF PDT is found to decrease for higher Ga‐concentrations. Electron mobility measured in the absorber region with large grains is promoted by both alkali PDTs. The data suggest that NaF PDT passivates shallow defect states (Urbach tail) throughout the Cu(In,Ga)Se2 film (including the interior of large grains), whereas the additional RbF PDT is effective at grain boundary surfaces (predominantly in regions with medium to low Ga‐concentrations).

Cryogenic formability and deformation behavior of 2060 Al–Li alloys with water-quenched and T4 aged temper

In this study, the formability and deformation behavior of new third-generation aluminum-lithium alloys at temperatures ranging from 113 to 298 K were studied by uniaxial tension tests, Erichsen cupping tests, and microstructure observations. The results show that the water quenched 2060 alloy exhibits excellent formability at 113 K with a fracture elongation of 34.1%, and Erichsen cupping value of 10.1 mm that are 33.2% and 40.3% higher than those at 298 K. Homogeneous plastic deformation was obtained at the cryogenic temperature for the water quenched alloy, as was reflected by the following three observations: 1) homogeneous lattice rotation and fewer coarse slip bands occurred in the grains; 2) a large number of substructures (i.e., dislocation cells, subgrains) uniformly distributed in the interior grains; 3) serrated flow caused by the dynamic strain aging disappeared at the cryogenic temperature. The naturally aged 2060 alloy exhibited limited formability improvement. As temperature decreased from 298 K to 113 K, the fracture elongation increased slightly by 11.8% and the Erichsen cupping value decreased by 26.4% for the naturally aged Al–Li alloy. The δ' precipitation phase of the naturally aged Al–Li alloy gave rise to planar slip due to the low misfit with the Al matrix and induced stress concentration at the grain boundaries. Meanwhile, the planar slip resulted in a higher texture and anisotropy at the cryogenic temperature, triggering early fracture and decreasing the ductility.

A unified mechanistic model for Hall–Petch and inverse Hall–Petch relations of nanocrystalline metals based on intragranular dislocation storage

Nanocrystalline (NC) metals often show transition from Hall–Petch (HP) strengthening to inverse HP softening as the average grain size decreases below a critical value. Compared to the HP behavior whose mechanism is well understood as the dislocation pile-up at grain boundaries (GBs), several hypotheses have been proposed to explain the veiled inverse HP behavior and no consensus has been reached yet. In this work, we propose a size-dependent model considering the influence of grain size on the intragranular dislocation storage ability and unify the HP and inverse HP relations for NC metals. The reduction of the intragranular dislocation storage ability with decreasing grain size is revealed as the underlying mechanism of the breakdown of the HP behavior in NC. Prediction of the critical grain size of 26.9nm for the HP-inverse HP transition of NC copper agrees well with experimental results. Numerical results suggest that the harmonized deformation of GB and grain interior (GI) dominates the remarkable ductility enhancement of NC metals in the inverse HP region. Moreover, our results suggest that the formation of dimple structures spanning several grains at fracture surfaces of NC metals is attributed to the coalescence of inter- and intra-granular microcracks and microvoids in clustered grains with Goss texture in local shear bands. As the GB strength increases, NC metals show enhancement in yield strength and delay in occurrence of the inverse HP behavior. Our studies give new insight into the contribution of GB sliding to the plastic behaviors of NC metals, and provide valuable guidance for the rational design of NC metals with high ductility and high strength.

Mechanical properties and microstructural evolution of pressureless sintered ceramics obtained from high-energy ball-milled TiB2–TiC powders

A series of TiB2–TiC composites were successfully fabricated through one-step and two-step pressureless sintering using powders obtained by high-energy ball-milling. Effects of ball-milling time on crystal size and morphology of powders as well as microstructural evolution and mechanical properties of TiB2–TiC composites were investigated. The crystal size of TiB2–TiC powders decreases to 14.7 nm after ball milling for 30 h. Two-step pressureless sintering is beneficial to the densification process without obvious grain coarsening. The core-rim structure of carbides in TiB2–TiC composites is formed by nonuniform diffusion of W atoms from the outside to the interior of TiC grains. The phenomenon of selective solution of WC into TiC grains was carried out through experiments and verification of first-principles DFT calculations. An in-situ TiB2 plate toughened microstructure is developed for TiB2-40 wt %TiC composites two-step sintered at 1500 °C for 4 h and 2000 °C for 1 h with excellent comprehensive performances.

Coexistence of two distinct fatigue failure mechanisms in Super304H welded joint at elevated temperatures

Super304H steel is a promising candidate for boiler tube materials in thermal power plants operating under ultra-supercritical conditions, and the fatigue properties of its welded joint play a key role in the structural reliability of the thermal power plants. Herein, we report that there is a transition in the fatigue failure location (i.e., fatigue failure mechanism) from the base metal at a high strain amplitude (≥~0.4%) to the weld metal at a low strain amplitude (≤~0.3%) at a constant temperature in the operating range of 500–700 °C, and this leads to a significant reduction in the fatigue resistance of the welded joint as compared to that of the base metal. We found that a longer fatigue test time at a low strain amplitude induces a thermal aging effect that promotes different microstructural evolutions in the base metal and weld metal, deepening material inhomogeneity in the welded joint, and thereby triggering strain localization in the weld metal. With increasing fatigue test time (i.e., thermal aging time), Cr23C6 carbides precipitated in the interdendritic region of the weld metal and at the austenitic grain boundary of the base metal, and Nb (C, N) phases precipitated in the interior of austenitic grain in the base metal, which increased local hardness, whereas there was no significant microstructural change in the dendrite core of the weld metal, retaining its initial hardness. The intensified local hardness inhomogeneity caused the softest zone in the welded joint, wherein strain localization occurred, serving as a crack nucleation site and propagation path, to shift from the base metal to the weld metal (dendrite core). This induced a shift in the fatigue failure location from the base metal to the weld metal with decreasing strain amplitude.

In-situ revealing the degradation mechanisms of Pt film over 1000 °C

• The high temperature degradation behaviors of passivated Pt film was studied by in-situ STEM. • The voids formed preferentially at intersections of grain boundaries with Pt-SiN x interface at 1020–1040 °C. • At temperatures above 1040 °C, the voids formed at both the grain boundaries and inside Pt grains. • The growth of voids inside the grains was accelerated by electromigration at high temperature. Degradation of a metallic film under harsh thermal-mechanical-electrical coupling field conditions determines its service temperature and lifetime. In this work, the self-heating degradation behaviors of Pt thin films above 1000 °C were studied in situ by TEM at the nanoscale. The Pt films degraded mainly through void nucleation and growth on the Pt-SiN x interface. Voids preferentially formed at the grain boundary and triple junction intersections with the interface. At temperatures above 1040 °C, the voids nucleated at both the grain boundaries and inside the Pt grains. A stress simulation of the suspended membrane suggests the existence of local tensile stress in the Pt film, which promotes the nucleation of voids at the Pt-SiN x interface. The grain-boundary-dominated mass transportation renders the voids grow preferentially at GBs and triple junctions in a Pt film. Additionally, under the influence of an applied current, the voids that nucleated inside Pt grains grew to a large size and accelerated the degradation of the Pt film.

Twins – A weak link in the magnetic hardening of ThMn12-type permanent magnets

Nd2Fe14B-type materials exhibit the highest energy product around room temperature and hence dominate the high-performance permanent magnet market. Intensive research efforts aim at alternative material systems containing less critical elements with similar or better magnetic properties. Nd- and Sm-based compounds with a ThMn12-type structure exhibit intrinsic properties comparable or even superior to Nd2Fe14B. However, it has not been possible to achieve technically relevant coercivity and remanent magnetization in ThMn12-based bulk sintered magnets. Using SmFe11Ti as a prototypical representative, we demonstrate that one important reason for the poor performance is the formation of twins inside micro-crystalline grains. The nature of the twins in SmFe11Ti was investigated in twinned “single crystals” and both bulk and thin film poly-crystalline samples, using advanced electron microscopy and atom probe tomography as well as simulations and compared with benchmark Nd2Fe14B. Both micro-twins and nano-twins show a twin orientation of 57±2° and an enrichment in Sm, which could affect domain wall motion in this material. Micromagnetic simulations indicate that twins act as nucleation centers, representing the magnetically weakest link in the microstructure. The relation between twin formation energies and geometrical features are briefly discussed using molecular dynamic simulations.