High-energy Grain Research Articles

Evolution mechanism of interfacial multi-layer intermetallic compounds and failure behavior in the Al–Au wire bonding

Evolution mechanism of interfacial multi-layer intermetallic compounds (IMCs) and their impact on failure behavior in Al–Au wire bonding after thermal storage and thermal cycle process are investigated. Microstructural analysis shows that multi-layer IMCs form between the Al wire and barrier layer. After thermal storage and thermal cycle process, the Au8Al3 layer transforms into AuAl2, and Au pad transforms to a thicker layer containing Au2Al and AuAl. Thermodynamic analysis indicates that Au8Al3, Au2Al, AuAl, and AuAl2 have increasing stability. Small-size, equiaxed AuAl2 grains form due to high stored energy, while large-size, columnar Au2Al and AuAl grains result from slower reaction rate and limited recrystallization. The stack-like formation of AuAl2 grains is attributed to the balance between driving force and interfacial energy resistance. During thermal storage, thicker IMC layers cause cracking between IMC layers and Au pad, and micro voids form near the IMC layers/barrier layer interface due to Kirkendall effect. Thermal stress results show that plastic deformation of the Al layer slightly affects the thermal stress in other layers during the thermal cycle process. The cyclic stress at the interface with initial cracks ranges from −157 MPa to 114 MPa, facilitating crack propagation. Additionally, micro void grows under cyclic thermal input, weakening interface adhesion. Therefore, bond strength decreases and frequency of bonding lift-off with cracking along the IMC layers/barrier layer interface increases after thermal storage and thermal cycle process. These results provide the guidance for regulating the interfacial IMCs and predicting the thermal stress in Al–Au wire bonding.

Evolution and mechanism of recrystallization microstructure and texture in GH3536 superalloy foil and their influence on strength performance

To achieve isotropic strength in GH3536 foil, this study investigated the influence mechanism of initial recrystallization microstructure and texture characteristics of GH3536 superalloy foil with different cold-rolled reduction rates (referring to the reduction rate in thickness) on annealing recrystallization microstructure, including secondary recrystallization microstructure, and texture. This was studied by controlling the cold-rolled reduction rate and annealing temperature, in conjunction with microstructure and texture analysis. Meanwhile, this study clarified the dependency of strength performance on recrystallization microstructure and texture. The results of this study indicate that the Coincidence Site Lattice (CSL) grain boundaries and High Energy (HE) grain boundaries did not show significant superiorities, and were not the primary reasons for the formation of Brass ({011}<211>) and Goss ({011}<100>) textures, as well as secondary recrystallization. Instead, by controlling the cold-rolled reduction rate, the initial recrystallization stage formed a significant quantity and size superiority of α-fiber texture ({110}∥ND) in each grain size range. This led to preferential growth, and even abnormal growth of Brass and Goss grains in subsequent high-temperature annealing processes. The control of the α-deformation fiber texture was identified as the driving factor behind the formation of the initial recrystallization texture due to the cold rolling reduction rate. Cold-rolled processes with a deformation amount greater than 40 % yielded a quantity superiority of α-fiber texture shear bands and an appropriate stored energy advantage. This facilitated the nucleation and effective growth of more α grains, while suppressing the random growth of grains with γ-fiber texture ({111}∥ND). Ultimately, a quantity and size superiority was achieved in the initial recrystallization stage. The tensile strength of GH3536 foil was controlled by grain size and texture. By controlling the deformation amount to approximately 30 %, GH3536 foil was successfully produced with no pronounced orientation texture and isotropic strength.

Effects of normalizing process on microstructure, texture, and precipitates of Sn bearing oriented silicon steel

Low temperature heating process of the slab has become the mainstream process for producing high quality oriented silicon steel due to its environmental protection, low cost, and high yield. For this process, the number of inhibitors is less and the size is large, resulting in insufficient inhibition, coarsen grains during primary recrystallization, and insufficient driving force for secondary recrystallization, which reduces the magnetic properties of the product. These shortcomings can be improved by optimizing the inhibitors and normalizing processes. The effects of normalizing processes on the microstructure, texture, and precipitations of low-temperature oriented silicon steel containing Sn were studied by OM, SEM, TEM, and EBSD with Fe–3%Si hot-rolled plate as initial material. The experimental results show that the sample has the best performance in terms of microstructure, texture, and precipitations with the two-stage boiling water cooling normalizing process that the heating temperature is 1150 °C, and the normalizing intermediate temperature is 850 °C. With the above parameters, the microstructure is inhomogeneous along thickness. There are more {111}<112> textures, which are favorable to the growth of Goss texture. The proportion of high energy grain boundary reached 54.2%. The precipitates are significantly refined, which enhances the ability to inhibit primary recrystallization. The sub-surface thickness of the hot rolled plate increases from 40.6% to 62.1% with increasing Sn content from 0.01% to 0.11%. The degree of tin segregation at grain boundary increases with the increase of normalizing temperature and the decrease of medium soaking temperature.

Synergistic effects of laser powder bed fusion and annealing on the texture-selective recrystallization of magnetostrictive Fe-Ga-NbC alloys for biomedical applications

IntroductionMagnetostrictive Fe-Ga alloys have garnered extensive attention owing to their excellent magnetic properties and acceptable biocompatibility. Nevertheless, the polycrystalline Fe-Ga alloys currently available tend to display random texture orientations, which constrain their magnetostrictive performance. ObjectivesTo regulate the texture orientation of Fe-Ga-NbC alloys and thereby enhancing magnetostriction. MethodsIn this study, a processing route comprising laser powder bed fusion (LPBF) followed by secondary recrystallization annealing (800, 1000, and 1200 °C, respectively) was developed to prepare Fe-Ga-NbC alloys. ResultsThe results showed that the LPBF-ed (Fe81Ga19)99(NbC)1 alloys exhibited a high content of high energy grain boundaries (HEGBs) due to the repeated melting and solidification. In subsequent annealing process, the migration of HEGBs induced the rearrangement and recrystallization of grains, during which NbC was found to locate at the grain boundaries and influence the migration path of HEGBs via selective pinning, thereby resulting in a strong Goss texture. With the rise in annealing temperature, the content of Goss texture gradually increased from the initial 3.9 % to 71.3 % at 1200 °C, leading to enhanced magnetostriction, lower saturation magnetization and coercivity. Furthermore, in alternating magnetic fields, the alloys annealed at 1200 °C also exhibited higher magnetostriction than the LPBF-ed alloys. And a noteworthy grain coarsening was also observed after annealing, accompanied by a discernible inclination of magnetic domains towards strip domains. Additional, cell tests demonstrated that the prepared alloys had satisfactory biocompatibility and the ability to promote osteogenic differentiation. ConclusionThese findings indicated that the LPBF-ed and annealed Fe-Ga-NbC alloys might be a promising alternative as magnetostrictive-driven materials for biomedical applications.

Electrochemical behavior and microstructural characterization of nano-SiC particles reinforced aluminum matrix composites prepared via friction stir processing

The present work aims to elucidate the mechanism of microstructural evolution in different regions of nano-SiC particles reinforced aluminum matrix composites prepared by friction stir processing (FSP) on its electrochemical behavior. Electron backscatter diffraction technique (EBSD) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution of stir zone (SZ), advancing side thermomechanically affected zone (AS-TMAZ), retreating side thermomechanically affected zone (RS-TMAZ) and base metal (BM). The electrochemical behaviors of the above zones were investigated using electrochemical tests. A homogeneous and fine microstructure is formed in SZ, not only the nano-SiC is homogeneously distributed within the grains with an average grain size of 3.5 μm, but also the recrystallized grains account for the highest percentage of 85 %. The potentiodynamic polarization curve indicates that the corrosion current densities of the BM, RS-TMAZ, AS-TMAZ and SZ are 0.89, 0.39, 0.85 and 0.36 μA/cm2, respectively, while the polarization impedances are 33.40, 51.42, 48.72 and 73.79 kΩ cm2, respectively. Combining the Nyquist and Bode plots analysis, the optimal electrochemical corrosion resistance is in SZ. The fine and homogeneous recrystallized grains in SZ significantly improve its electrochemical corrosion resistance. This is mainly ascribed to the increase in crystal defects as a result of the increase in grain boundaries, elevating the electron scattering. Simultaneously, the increase in high-energy state grain boundaries is beneficial to the rapid formation of a thicker passivation film.

Chromium partitioning induced evolution of texture, grain boundary constitution, and corrosion behavior of Cu[sbnd]Cr coatings electrodeposited at different temperatures

The corrosion behavior of CuCr coating electrodeposited at three different temperatures (15 °C, 30 °C, 45 °C) was examined. Cr is partitioned in the grain boundaries and as a solute in the Cu matrix. The formation of Cr-oxide at the grain boundaries enhanced the corrosion resistance of the coatings, whereas the presence of Cr as solute significantly altered the matrix micro-texture. The 15 °C deposited coating exhibited the lowest corrosion rate due to higher Cr solute, smaller grain size, (111) surface texture, and a higher fraction of coincidence site lattices. The 45 °C deposited coating exhibited the highest corrosion rate due to lower Cr solute, higher energy (110) surface texture, and higher fraction of high energy grain boundaries.

The origin of {113}&lt;361&gt; grains and their impact on secondary recrystallization in producing ultra-thin grain-oriented electrical steel

Abstract Ultra-thin grain-oriented electrical steel with a thickness of 80 µm is produced by one-step-rolling with industrial grain-oriented electrical steel. The research employs electron back-scattering texture analysis technique to investigate the evolution of deformation and recrystallization textures in this specific steel. Emphasis is placed on examining the origin of {113}&lt;361&gt; grains and their consequential impact on secondary recrystallization. It is revealed that primary, secondary, and tertiary recrystallization phases are integral during the annealing process. The origin of surface {113}&lt;361&gt; grains were result of initial deviated Goss grains with specific shear deformation behavior in cold rolled ultra-thin strips. Additionally, the influence of these grains on texture evolution is predominantly evident during secondary recrystallization. These grains potentially undergo abnormal growth in secondary recrystallization, exploiting high-energy grain boundaries among Goss grains. This phenomenon consequently leads to the diminution of the sharp Goss texture formed during primary recrystallization. Given the magnetic properties and predominant applications of ultra-thin grain-oriented electrical steel in medium-frequency fields, it is recommended to prepare ultra-thin grain-oriented steel during primary recrystallization phase.

Anisotropic diffusion in symmetric tilt grain boundaries in bcc iron: A DFT study

Diffusion analysis at the atomic scale in three orthogonal directions for both low- and high-energy symmetric tilt grain boundaries (GBs) in bcc iron is presented. Using DFT, we report (i) the energetically preferable configurations of point defects in the GBs (112) and (210) as well as in surrounding atomic layers; (ii) the activation barriers for vacancy and self-interstitial hopping in the GB plane and from the GBs to a nearest atomic layer; (iii) the attempt frequencies in each diffusion direction. The obtained values are refined by taking into account the temperature dependence of magnetization. It has been shown that interstitial and combined interstitial-vacancy mechanisms agree with the experimental data on self-diffusion in bcc iron. The temperature dependencies of the diffusion coefficient are obtained as Arrhenius law taking into account transition between ferro- and paramagnetic states. They provide insight into transport processes at relatively low temperatures which can be important for practical applications.

Deformation behaviour, microstructure evolution and dynamic recrystallization mechanism of AZ31 magnesium alloy under co-extruded by Mg-Al composite billet

Conventional methods for hot extrusion of magnesium (Mg) alloy sheets have limitations for microstructure improvement and mechanical property enhancement. Co-extrusion of Mg alloy with an Al alloy core provides an opportunity for refining the grain size and improving basal texture. This study introduces a novel severe plastic deformation (SPD) method, Direct Extrusion-Continuous Shear (DE-CS), utilizing 6063 Al alloy as the core to fabricate innovative Mg/Al clad composite sheets. Monolithic Mg sheets (non-co-extruded condition) are extruded under identical conditions for comparison. By evaluating the microstructure and mechanical properties of AZ31 Mg alloy under co-extrusion and non-co-extrusion conditions, the positive effect of Mg-Al composite billet co-extrusion on AZ31 Mg alloy is established. The grain refinement effect in co-extruded samples is superior, enhancing plasticity without significant reduction in tensile strength. The microstructure evolution and dynamic recrystallization (DRX) behaviour of AZ31 Mg alloy during co-extrusion were analyzed comprehensively. The results indicate that, in the initial stages of deformation, various variants of {10−12} extension twins (ETs) play a crucial role in refining the original grains, forming initial [10−10]//ED fiber texture components alongside other non-basal components. Upon entering the shear deformation (SD) zone, deformed twins disappear, and small dynamically recrystallized (DRXed) grains emerge along boundaries of coarse deformation grains and within the grains. Strong shear deformations and compressive stress from transverse direction (TD) induce intensified prismatic <a> and pyramidal <c+a> slip, promoting continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). CDRX predominantly affects elongated deformed grains, forming an [10−10]//ED fiber texture through high-energy grain boundary segmentation. Subsequently, compatible stress increases due to the activity of non-basal slip dislocation and the reduction in grain boundary (GB) size. DDRX emerges as the dominant mechanism, generating randomized [10−10]//ED fiber and non-fiber textures within parent grains and at boundaries.

96 Impacts of Postweaning Dry Matter Intake Classification on Beef Heifer Performance and Cyclicity

Abstract The objective was to evaluate the relationship of postweaning dry matter intake (DMI) classifications on performance and cyclicity in fall-born beef heifers. Heifers were classified based on DMI as either low (LoDMI; &amp;lt; -0.5 SD from mean), average (AvgDMI; ± 0.5 SD from mean), or high (HiDMI; &amp;gt; +0.5 SD from mean). Hifers (n = 147), either Angus or Hereford sired by commercial dams, were utilized in the analysis. Heifers were early weaned at 82 ± 7 days of age. Following weaning, heifers were managed in partially covered, drylot pens and fed a high-energy grain diet. At postweaning intake evaluation initiation (day 1), heifers were 170 ± 22 kg and 156 ± 7 days of age. Heifer DMI was determined over 56 days using GrowSafe system, and weights were collected every 14 days. Following the postweaning intake evaluation, heifers rotationally grazed endophyte-infected tall fescue paddocks. During the 166-day grazing period, heifers were weighed and assigned a hair shedding score monthly. Heifers returned to drylot pens on day 223 for a prebreeding feed efficiency evaluation on a high-forage diet. Foot scores were assigned on day 1 and 237. Heat detection patches were used to determine percentage of heifers cycling before synchronization. Cyclicity data were analyzed using GLIMMIX and all other response variables were analyzed using the MIXED procedure of SAS 9.4. By design, postweaning DMI differed (P &amp;lt; 0.01) between treatments (5.5, 6.2, and 6.9 kg/d for LoDMI, AvgDMI, and HiDMI, respectively). Average daily gain (ADG) differed (P &amp;lt; 0.01) during the postweaning evaluation period, with LoDMI being least, AvgDMI intermediate, and HiDMI greatest. On days 1 and 56, body weights (BW) differed (P &amp;lt; 0.01); LoDMI were lightest, AvgDMI were intermediate, and HiDMI were heaviest. However, gain to feed during the postweaning evaluation period was not different (P = 0.33) by DMI classification. During the grazing period, BW differed (P &amp;lt; 0.01) on days 84 and 141; HiDMI were heavier than LoDMI and AvgDMI. On day 113, BW differed (P &amp;lt; 0.01); LoDMI were lightest, AvgDMI were intermediate, and HiDMI were heaviest. However, ADG and final grazing BW did not differ (P ≤ 0.12) during the grazing period by DMI classification. Hair shredding score was greater (P ≤ 0.04) for LoDMI than HiDMI on days 56, 84, and 113. Foot scores differed (P = 0.02) on day 1; LoDMI was less than AvgDMI and HiDMI. However, they only tended (P = 0.08) to be different on day 237. Percent cycling prior to synchronization did not differ (P = 0.25) by classification. In summary, LoDMI heifers performed poorer during postweaning evaluation than HiDMI heifers. However, grazing performance and cyclicity was similar among DMI classifications.

PSI-A-5 Effects of Birth Body Weight Classification on Heifer Growth, Dry Matter Intake, Feed Efficiency, and Grazing Performance

Abstract The objective was to evaluate the effect of birth body weight (BBW) classification on post-weaning growth, dry matter intake (DMI), feed efficiency, and grazing performance of fall-born crossbred heifers. Heifers were classified based on BBW as either light (LtBBW, &amp;lt; -0.5 SD from mean), average (AvgBBW, ± 0.5 SD from mean), or heavy (HvyBBW, &amp;gt; +0.5 SD from mean). Angus and Hereford-sired heifers (n = 153) from commercial Angus dams were utilized in the analysis. Heifers were early weaned at 82 ± 7 days of age. Post-weaning management strategy consisted of calves being kept in partially covered drylot pens and fed a high-energy grain diet (35% dried distillers grains with solubles, 30% whole shelled corn, 30% ground fescue hay, and 5% supplement) in GrowSafe bunks. During the post-weaning evaluation (initiated on day 1), heifer (168 ± 23 kg and 156 ± 7 days of age) DMI was collected for 56 days and body weights (BW) were collected every 14 days. Following the intake evaluation, heifers rotated daily for 166 days though 33 paddocks of 2.4 ± 0.5 hectares each and were weighed every 28 days. Data were analyzed using the MIXED procedure of SAS 9.4. As designed, birth body weight differed (P &amp;lt; 0.01) between classifications (27, 32, and 37 kg for LtBBW, AveBBW, and HvyBBW, respectively). Heifers classified as LtBBW were born earlier (P = 0.02) than AvgBBW and HvyBBW. Heifer BBW classification affected (P &amp;lt; 0.01) weaning weights; heifers classified as LtBBW and AvgBBW had lighter weaning weights than HvyBBW heifers. Birth weight category affected (P &amp;lt; 0.01) BW on days 1, 28, and 56. On day 1, heifers classified as LtBBW were the lightest, AvgBBW were intermediate, and HvyBBW were the heaviest; however, on days 28 and 56, heifers classified as LtBBW were lighter than AvgBBW and HvyBBW. Heifers classified as LtBBW and AvgBBW had less (P &amp;lt; 0.01) DMI and average daily gain (ADG) than HvyBBW during the post-weaning evaluation period. Gain to feed during post-weaning evaluation period was not affected (P = 0.94) by heifer BBW classification. Birth weight category affected (P &amp;lt; 0.01) BW during the grazing season on days 28, 56, 84, 113, 141, 168, 196, and 223. On days 84, 96, and 223, heifers classified as LtBBW were lighter than AvgBBW and HvyBBW; however, on days 113, 141, and 168, LtBBW were lightest, AvgBBW were intermediate, and HvyBBW were the heaviest. During the grazing period, ADG did not differ (P = 0.72) between BBW classifications. In conclusion heavy birth weight heifers had greater post-weaning DMI and ADG when fed a high grain diet; however, grazing ADG did not differ. Heavy birth weight heifers were heavier throughout the duration of the experiment.

Evolution of Microstructure and Texture in Grain-Oriented 6.5% Si Steel Processed by Rolling with Intrinsic Inhibitors and Additional Inhibitors.

A grain-oriented steel containing 6.5% Si, characterized by a notable Goss texture, was effectively manufactured through the rolling technique, incorporating both intrinsic inhibitors and additional inhibitors. This investigation focuses on tracking the development of texture and magnetic properties during the manufacturing process and delineates the mechanism underlying secondary recrystallization. The empirical findings clearly demonstrated the significant influence of nitriding duration and quantity on the secondary recrystallization process. In instances where additional nitrogen is absent, the intrinsic inhibitors alone do not lead to secondary recrystallization. However, when the nitriding duration is 90 s and the nitriding amount is 185 ppm, a complete secondary recrystallization structure with a strong Goss texture enables the finished products have excellent magnetic properties. The preferential growth of Goss grains is mainly governed by the enhanced mobility of high-energy (HE) grain boundaries. With the increase in annealing temperature, the occurrence of 20°-45° HE grain boundaries with Goss grains becomes more progressively frequent. At the secondary recrystallization temperature of 1000 °C, the frequency of 20°-45° HE grain boundaries with Goss grains reaches 62.7%, providing favorable conditions for the abnormal growth of Goss grains. This results in a secondary recrystallization structure predominantly characterized by a strong Goss texture. In light of these observations, the present study provides fundamental theoretical insights and serves as a valuable procedural guideline for the industrial manufacturing of 6.5% Si grain-oriented electrical steels.

Preparing Ni–Mo coatings for high-temperature Na2S3 molten salt on aluminium

Pure aluminum was susceptible to corrosion as a casing material for sodium-sulfur batteries. In this context, the effects of different electrodeposition parameters on the sulfur anticorrosion of Ni–Mo alloy coatings on pure aluminum substrate were investigated through an orthogonal test. The corrosion process of aluminum with Ni–Mo composite coatings in Na2S3 molten salt at 350 °C was investigated by static immersion test. The results demonstrated that the optimum parameters for achieving high corrosion resistance coating were Na2MoO4·2H2O concentration of 10 g/dm3, current density of 5 A/dm2, pH value of 9 and temperature of 45 °C. The sodium molybdate content played a crucial role in determining the corrosion resistance of the coating. The grain size of the coating decreased and the Mo content increased accordingly as the sodium molybdate content increased. While the presence of Mo element exhibited inhibitory effects on corrosion, an increase in high-energy grain boundaries resulting from grain refinement had an adverse impact. Consequently, in the single-factor experiment with varying Na2MoO4·2H2O contents, when maintaining the sodium molybdate content of 10 g/dm3, the minimum corrosion rate was 0.02632 mm/y after corrosion in Na2S3 molten salt at 350 °C for 72 h. Additionally, it was found that NiS2 as a corrosion product could effectively inhibit further development of corrosion.

Dynamic competition between coarsening mechanisms of Ti2Cu phase during thermal cycling

The dynamic competition between the coarsening mechanisms activates various coarsening behavior of the precipitate in multi-phase metallic materials, leading to different mechanical performances of alloys. In this work, the morphological evolution and coarsening kinetic of Ti2Cu phase in Ti–14Cu alloy were investigated comprehensively during thermal cycling at 200–600 °C. Our results suggest that the coarsening kinetic showed a gradual transition from the Lifshitz-Slyozov-Wagner (LSW) mechanism to the trans-interface diffusion-controlled (TIDC) mechanism. Ti2Cu phases precipitated at the triple junctions of α-Ti matrix by discontinuous precipitation under the control of LSW mechanism at lower temperatures (200–400 °C), and grew into lamellae along the high-energy grain boundaries. While the low-angle grain boundaries within Ti2Cu phase accelerated solute atom diffusion during the coarsening governed by TIDC mechanism at higher temperatures (400–600 °C), which leads to the boundary splitting of lamellae. In addition, it was also found that the blocky Ti2Cu phase improved the yield strength of the alloy as its high solid solution strengthening. This work provides a clear understanding for the coarsening of Ti2Cu phase, it could provide theoretical evidence for the hot working process design to improve the damage tolerance of Ti–Cu alloys.

Visualizing oxygen transport pathways during intergranular oxidation in Ni-Cr

The transport paths of O during intergranular oxidation in binary Ni-Cr were investigated. To isolate the selective oxidation of Cr, oxidation was performed with a CO/CO2 gas mixture in which the oxygen partial pressure was kept under the NiO dissociation pressure. A combination of electron microscopy and atom probe tomography (APT) was used to study the nanometer-scale details of the passivation and penetrative intergranular oxidation processes at high-energy grain boundaries. Oxygen transport towards the terminating oxidation front is elucidated with dedicated usage of oxygen tracer exchange experiments. Secondary ion mass spectroscopy and APT support classical theories of internal oxidation, revealing preferred transport paths at the oxide/alloy interface with sub-nanometer resolution.

Development of a Gilbert-type delta in the kame environment: An example from NE Poland

Pleistocene kame deltas are known mainly from glaciomarginal environments, whereas there are fewer examples of deltas where kames formed within decaying ice sheets. In this article, we describe deposits of a Gilbert-type delta formed inside a glacial system. The delta succession was identified in the upper part of the hill, a glacial landform developed within the southern sector of the Scandinavian ice sheet in NE Poland during the Warthian glaciation. The landform is interpreted as a kame, the sediments of which were accumulated in an elongated ice crevasse oriented perpendicularly to the front of the ice sheet. The kame was formed in several stages. In the main stage of development, the crevasse was filled with a lake into which the delta prograded. The lake subsequently underwent a few phases of shallowing, and even an episode of complete drainage.The main delta unit was identified in the outcrop. It is composed of a delta slope and prodelta sediments. A partly preserved older deltaic unit of the initial phase of delta sedimentation also was found. The steep (22–42°) slope of the delta is dominated by gravel and sand. The gravels were deposited from high-energy grain flows and grain falls. Sands were deposited mainly from traction currents during periods when the delta-supplying system was less active. Aggradation of the prodelta was mainly due to sand deposition from traction underflows. Deposition from turbidity currents occurred sporadically there. We explain this unusual situation by the fact that the gravelly sediments feeding the delta slope were relatively well-sorted and contained only small admixtures of fine sand and silt. The sediment sorting process took place in a system of englacial or supraglacial conduits, where the gravels were depleted of fine-grained particles. The development of the Gilbert-type delta was possible because the glacial lake, at least 6–8 m deep, periodically maintained a relatively constant water level, which allowed the delta to prograde. This process required the existence of a steady outflow of water from the lake, which was then an open hydrological system. In the final stage of kame formation, when the lake was completely drained, gravel accumulated from shallow sheet flows.

Strategy for suppressing abnormal grain growth of ZK60 Mg alloy during solution by pre-compression: A quasi-in-situ study

Abnormal grain growth (AGG) easily takes place in Mg alloys during high-temperature solutions, resulting in deterioration of mechanical properties. Hence, the compression prior to solution (pre-compression) was conducted to suppress AGG, and the microstructure evolution as well as suppressing mechanisms was investigated based on quasi-in-situ analysis. After compression along the transverse direction, <11–20>//ED grains preferentially nucleated and rapidly grew up, and the initial <10–10>//ED texture was weakened. Two grain growth modes of heat-induced and strain-induced grain boundary migrations were found. The former was attributed to the high interfacial energy of grain boundaries with large curvature. The latter consumed the adjacent grains with high storage energy, forming abnormal grains with irregular shapes. The compression with a reduction > 6% could obviously suppress AGG. The suppressing effects were mainly attributed to weakening the size advantage of <11–20>//ED grains, increasing nucleation, reducing grain boundary character distribution, and redistributing storage energy distribution. After 12% compression along the transverse direction, 30° misorientation of <11–20>//ED grains and high energy grain boundaries were reduced. The {10–12} tensile twins and {10–15} high index twins induced by compression increased the nucleation of static recrystallization. Beside, compression introduces high-density dislocations, which also contributed to suppressing AGG behavior during solution.

Phase-Field Crystal Studies on Grain Boundary Migration, Dislocation Behaviors, and Topological Transition under Tension of Square Polycrystals

In this paper, the tensile deformation behaviors of polycrystals after relaxation were studied using the phase-field-crystal (PFC) method. Here, the free energy density map characterized the 2D energy distribution of atomic configuration effectively. The application of the Read–Shockley equation distinguished high-energy grain boundary (HEGB) and low-energy grain boundary (LEGB) in large-angle grain boundary (LAGB), and they demonstrated different migration behaviors at the early and later stages. The behaviors of small-angle grain boundary (SAGB), including its migration and grains’ rotation, were also studied. Two different mechanisms of dislocation emission and absorption were explored, which demonstrates the possibility of dislocation elevating interfacial energy. The simulated results on the topological transition of grain boundaries prompted us to propose the thinking about the applications of the Neumann–Mullins law and Euler formula.

Role of inhibitor behavior in abnormal growth of Goss grain in grain-oriented silicon steel: experiments and modeling

The role of inhibitor behavior in abnormal growth of Goss grains during secondary recrystallization was studied in combination with experimental observation and phase-field model simulation in grain-oriented silicon steel. The frequency advantages of both HE (high energy) and CSL (coincidence site lattice) grain boundaries around Goss grains over the matrix were identified, with frequency advantages of ∼15% and ∼2% respectively. The HE grain boundary was supposed to play a more important role in abnormal grain growth over CSL grain boundary in this study. The boundary character distribution was necessary but not sufficient for the abnormal growth of Goss grains. Appropriate inhibitor behavior was a prerequisite for secondary recrystallization. The initial content and stability of inhibitor played a key role in stabilizing the matrix, which guaranteed beneficial fine grains around Goss grains. While if the inhibitor force rapidly declined, matrix grains might grow obviously, resulting in coarsened grain colonies with Cube, {112}<110>, {111}<112>, {411}<148>and {210}<001> orientation, which further hindered the abnormal growth of Goss grains. The candidate Goss grains with different misorientations competed with each other during secondary recrystallization and the exact Goss grain exhibited an obvious growth advantage. Only with an appropriate pinning force and grain boundary character, perfect secondary recrystallization can be achieved. The present findings can provide guidance to understand and precise control of abnormal grain growth phenomenon.

Nitride precipitation and formation in IN617 superalloy during creep

Precipitation behaviors of four types of nitrides (including π phase (Cr3.25Ni1.75N), AlN, Cr2N and TiN) were investigated in IN617 after creep rupture at 1000 °C/16 MPa. Nitride formation mechanisms were discussed based on their relative stabilities, crystallographic characteristics, and orientation relationships with the matrix. The influences of nitrides on creep rupture behaviors were discussed. The results indicated that the π phase, which was predicted unstable at 1000 °C by thermodynamical calculations, only precipitated at high-energy grain boundaries and phase boundaries. Thermodynamically stable AlN, Cr2N and TiN could be formed at relatively low-energy sites, such as inside the matrix, at dislocations and twining boundaries. Particularly, AlN and Cr2N are polar crystals and have hcp structures, much different from the fcc matrix. They precipitated from the habit planes with low atomic misfits and grew into a needle shape to reduce the strain energy. Fcc TiN was easy to nucleate and had good coherence with the matrix, so it could either precipitate from the regions with high-density dislocations in a needle shape, or directly from the matrix in spherical or dendritic shapes to minimize the interfacial energy and strain energy. Among those nitrides, the π phase and AlN formed coarse intergranular networks and were difficult to deform and release stress, dominantly responsible for the brittle rupture mode.