Cube Texture Research Articles

Microstructural characterisation and mechanical properties of Ti-5Al-5V-5Mo-3Cr built by wire and arc additive manufacture

ABSTRACT The as-deposited microstructure and mechanical properties of the near-β titanium alloy Ti-5Al-5V-5Mo-3Cr (Ti-5553) produced by wire-arc additive manufacture (WAAM) were investigated, to understand its microstructural evolution under WAAM deposition conditions and to establish correlations between the microstructure features formed and the thermal cycles experienced during deposition. The ‘as-deposited’ Ti-5553 WAAM material exhibited higher tensile strengths than other as-deposited additively manufactured Ti-5553 deposits previously reported in the literature, but had significant anisotropy in elongation, as a consequence of the coarse and columnar β-grain structure that formed on solidification, which exhibited a strong cube texture. The multiple reheating cycles, inherent to the WAAM process, were recorded using a novel ‘harpoon’ thermocouple technique, and the α precipitation evolution was related to the thermal history. Electron probe microanalysis chemical maps revealed significant solute microsegregation during solidification, which influenced the subsequent precipitation due to its effect on the local β-phase stability. As each layer experienced more reheating cycles, the microstructure evolution could be ‘time resolved’ and the α laths were found to precipitate in a specific sequence of nucleation sites, starting at the β-grain boundaries and then inter-dendritically, where there was lower matrix β stability. However, after the reheating peak temperature was insufficiently high to have any further effect, the microstructure consisted of a relatively uniform distribution of α laths.

Analysis of ESAFORM 2021 cup drawing benchmark of an Al alloy, critical factors for accuracy and efficiency of FE simulations

This article details the ESAFORM Benchmark 2021. The deep drawing cup of a 1 mm thick, AA 6016-T4 sheet with a strong cube texture was simulated by 11 teams relying on phenomenological or crystal plasticity approaches, using commercial or self-developed Finite Element (FE) codes, with solid, continuum or classical shell elements and different contact models. The material characterization (tensile tests, biaxial tensile tests, monotonic and reverse shear tests, EBSD measurements) and the cup forming steps were performed with care (redundancy of measurements). The Benchmark organizers identified some constitutive laws but each team could perform its own identification. The methodology to reach material data is systematically described as well as the final data set. The ability of the constitutive law and of the FE model to predict Lankford and yield stress in different directions is verified. Then, the simulation results such as the earing (number and average height and amplitude), the punch force evolution and thickness in the cup wall are evaluated and analysed. The CPU time, the manpower for each step as well as the required tests versus the final prediction accuracy of more than 20 FE simulations are commented. The article aims to guide students and engineers in their choice of a constitutive law (yield locus, hardening law or plasticity approach) and data set used in the identification, without neglecting the other FE features, such as software, explicit or implicit strategy, element type and contact model.

Texture and microstructure characterizations of Fe-3.5wt%Si soft magnetic alloy fabricated via laser powder bed fusion

Manufacturing stable grain-oriented electric steel with fewer procedures remains a challenge due to the formation of detrimental γ-fiber (〈111〉//ND) texture. In this work, Laser Powder Bed Fusion (LPBF) process was employed to obtain a strong λ-fiber (〈100〉//ND) texture in a Fe-3.5wt%Si electrical steel. The texture and microstructure were characterized by Electron Backscatter Diffraction (EBSD), Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDS) and High-Resolution Transmission Electron Microscopy (HRTEM). The EBSD results showed a strong λ-fiber texture on the top plane of Fe-Si alloy. It included {001}〈001〉 Cube texture, {001}〈110〉 rotated cube texture and {100}〈105〉 texture. With the lowest energy density, an area fraction of 16.6% γ-fiber texture was formed on the top plane. Additionally, the formation of amorphous precipitates in additively manufactured Fe-Si alloy was firstly reported. The lattice constant of 2.7975 Å was calculated in the matrix area. The work has shown LPBF can open a new door to manufacture grain-oriented electrical steel for industrial applications. • The Fe-3.5wt%Si alloy was fabricated via laser powder bed fusion. • Amorphous precipitates were observed in additively manufactured Fe-Si alloy. • A strong λ-fiber (〈100〉//BD) texture is obtained on the top plane of the additively manufactured Fe-Si sample. • A strong rotated cube ({100}〈110〉) texture is also obtained on the top plane of the additively manufactured Fe-Si sample.

Recrystallization and grain growth kinetics of IN718 manufactured by laser powder bed fusion

The recrystallization and grain growth behaviour of IN718 alloy additively manufactured by laser powder bed fusion (L-PBF) is presented herein. The effects of three different temperatures (1050, 1150 and 1250 °C) and holding times (15, 45 and 90 min) were investigated. The texture evolution of the samples was recorded via electron backscatter diffraction (EBSD). The as-built sample is composed of bowl-shaped melt pools, a chessboard-like grain pattern and has a cube texture {100}<001>. Recrystallized grains were observed in the samples treated at 1150 °C for 15 min, as well as the samples treated for longer periods and at higher temperatures. Recrystallization was observed to start from high dislocation density regions, including the overlapping melt pools and the borders of the chessboard-like pattern. The initial cube texture transforms into a first-generation cube-twin texture {122}<212> via a twinning-assisted recrystallization mechanism. Then, those recrystallization nuclei sweep through the high defect density matrix; during which almost no new twins are formed. The samples treated at 1250 °C are almost completely recrystallized, which forms a weaker cube texture and a stronger P-orientation {011}<112>. However, the growth of recrystallized grains is very limited due to the presence of non-coherent precipitates.

Texture in cold rolled and high-temperature annealed Cu foils

Thick single crystal Cu foil substrates with specific crystallographic orientations such as {111} and {110} planes parallel to the rolling plane are desired for epitaxial growth of two-dimensional materials such as graphene. In this study, annealing experiments of a 46 μm thick cold-rolled foil were carried out at temperatures in the range of 300-1040 °C. The texture evolution during annealing was followed by electron backscatter diffraction (EBSD) orientation mapping. It was found that the texture evolution may be divided into three stages: at relatively low annealing temperatures, a strong cube texture develops with a small population of grains having relatively larger deviations from the cube orientation; at medium temperatures, these grains with large deviations grow abnormally; and at the highest temperature, annealing twins form in the abnormally growing grains giving rise to new orientations including some with the {111} planes parallel to the rolling plane.

Tailoring the crystallographic texture of pure copper through control of the scanning strategy in Electron Powder Bed Fusion

There has been increasing interest over the past few years to evaluate how additive manufacturing can be used to tailor the microstructure of metallic materials. The objective of this work is to demonstrate through a few illustrative examples the possibility to tailor the crystallographic texture of pure copper processed by Electron Powder Bed Fusion (PBF-EB) by manipulating the molten pool morphology via the scanning strategy. We illustrate schematically how changes in molten pool geometry via modifications of the scanning strategies can affect texture development. Different processing conditions are selected to produce dense samples by PBF-EB while altering the crystallographic texture. The samples produced are examined by optical microscopy and Electron Back-Scattered Diffraction (EBSD) to characterize the molten pool geometry and the inherited microstructure to experimentally validate the pragmatic approach suggested in this work. Manipulations of the scanning strategies are shown to be efficient to produce a strong Cube texture or Goss texture or alternatively, a mixture between the two. A Cube texture is generated by promoting the formation of a melt pool with a flat geometry (its width being much larger than its depth). A Goss texture results from melt pools having a more hemispherical geometry with a large overlap between adjacent tracks. Adjusting the hatch spacing is a good way to achieve a mixture between columnar grains having a Cube texture and others exhibiting a Goss one. The results of this work could be considered as a guideline to tailor the microstructure of other cubic materials processed by PBF-EB.

Effects of inter-layer remelting frequency on the microstructure evolution and mechanical properties of equimolar CoCrFeNiMn high entropy alloys during in-situ powder-bed arc additive manufacturing (PBAAM) process

An equiatomic CoCrFeNiMn High Entropy Alloy (HEA) was in-situ deposited by the powder-bed arc additive manufacturing (PBAAM) process for the first time. Comparative research was conducted on the evolution of phase, crystallographic orientation, dislocation morphology, precipitation, and mechanical performance with the accumulation of inter-layer remelting times. The experimental outcomes manifested that the PBAAMed CoCrFeNiMn HEA consists of a stable solid-solution FCC structure, with decreased lattice parameter but slightly increased (full width at half maximum) FWHM as the accumulation of the inter-layer remelting. The {001}<100> cube texture with a weakened texture intensity was detected with an increment of inter-layer remelting frequency from once to 5 times, yet it was transformed into {011}<100> Goss texture with a further increase to 7 times. Additionally, the mean grain diameter distinctly decreased, while the volume fraction of (low angle grain boundaries) LAGBs and dislocation density remarkably added up as the accumulated inter-layer remelts. Predominant cellular substructure generated in all process conditions and could be easily differentiated by elemental segregation. Both the σ and M23C6 Cr-rich precipitates in nano-scale and submicron MnS precipitate were detected on the grain boundaries of the PBAAMed deposited components, with a rather sparse distribution. Speaking of mechanical performance, the YS, UTS, and hardening rate are generally increased while the UE is gradually decreased as increased inter-layer remelting times. The studied PBAAMed CoCrFeNiMn HEA possesses comparable mechanical performances with the counterparts of laser-deposited and as-cast ones. The strengthening mechanisms of the studied material are predominantly the grain boundary strengthening and dislocation strengthening. This investigation would be a valuable resource in the research field of fabricating HEA alloys with acceptable microstructure and properties using the PBAAM method.

Influence of cold rolling and thermal treatment on microstructure and texture evolution, and tensile behaviour of high strength Al-Co-Sc-Zr alloys

• The chilled suction casting of Al-0.1Co-0.15(Sc, Zr) at% alloy enabled substantial amounts of stable compounds of Al 9 Co 2 , primary Al 3 (Sc 1−x Zr x ) dispersoids, and Al 3 Sc precipitates. • Cold rolling and ageing at 375 °C, offer yield strength of 251 MPa and UTS of 276 MPa with good ductility (19%) was achieved. • Solid solution, precipitation and dispersion hardening, and formation of fine subgrained structure have enhanced the mechanical properties. The present work is an effort to develop a set of newer aluminum alloys with a minor amount of alloying additions such as Co, Sc and Zr to pure Al in order to achieve higher strength along with a reasonable tensile ductility and improved microstructural stability at elevated temperatures. The alloys were melted using vacuum arc melting and were produced in rectangular slabs by suction casting. The slabs were cold rolled at room temperature up to ~80% reduction followed by direct aging at two different temperatures of 375 °C and 450 °C for 24 h. The effects of alloying additions, cold rolling and subsequent thermal aging were investigated by detailed microstructural examination and tensile testing at room temperature. Microstructural analysis revealed that the alloy contained significant volume fraction of second phase particles such as Al 9 Co 2, Al 3 Sc and Al 3 (Sc 1−x Zr x ) and were preferentially distributed in supersaturated equiaxed cells of Al matrix. The existence of Al 3 (Sc 1−x Zr x ) precipitates together with large fraction of Al 9 Co 2 phase led to higher yield strengths of ~180–250 MPa and 17–20% tensile elongation. Electron backscattered diffraction observations showed equiaxed cells extensively deformed columnar grains and subgrain formation within the elongated grains in the rolling direction. The cold rolled plus aged samples exhibited a major fraction of rotated cube texture along with improved microstructural stability after high-temperature aging. This could be related to the existence of fine and stable Al 9 Co 2 phase and Al 3 (Sc 1−x Zr x ) precipitates, which control grain growth and thereby these alloys thermally stable at high temperatures.

Identification of texture characteristics for improved creep behavior of a L-PBF fabricated IN738 alloy through micromechanical simulations

Additive manufacturing (AM) of nickel-based superalloys, due to high temperature gradients during the building process, typically promotes epitaxial growth of columnar grains with strong crystallographic texture in form of a 〈001〉 fibre or a cube texture. Understanding the mutual dependency between AM process parameters, the resulting microstructure and the effective mechanical properties of the material is of great importance to accelerate the development of the manufacturing process. In this work, a multi-scale micromechanical model is employed to gain deeper insight into the influence of various texture characteristics on the creep behavior of an IN738 superalloy. The creep response is characterized using a phenomenological crystal plasticity creep model that considers the characteristic γ–γ′ microstructure and all active deformation mechanisms. The results reveal that the creep strength increases with decreasing texture intensities and reaches its maximum when the 〈001〉 fibre and cube textures are misaligned to the specimen building direction by 45°. The simulations also predict that the uncommon 〈111〉 and 〈110〉 fibres offer significantly higher creep resistance than the typically observed 〈001〉 fibre, which provides a further incentive to investigate AM processing conditions that can produce these unique textures in the material. As the intensities and the alignment of 〈001〉 fibre and cube textures can be attributed to the laser energy density and the scan strategy employed and as the formation of distinct fibre textures depends on the geometry of the resulting melt pool, the laser powder bed fusion process parameters can be optimized to obtain microstructures with features that improve the creep properties.

Mechanical properties and microstructure evolution of an Al–Cu–Li alloy via cross cryorolling

The anisotropy of mechanical properties limits the applications of Al–Cu–Li alloys. In this study, microstructure evolution and mechanical properties of an Al–Cu–Li alloy via room-temperature rolling (RTR), room-temperature cross rolling (RCR), cryorolling (CR) and cross cryorolling (CCR) were investigated. The processing of Al–Cu–Li alloy by CCR gave the highest ultimate tensile strength of 471 MPa and an elongation of 8.4% along rolling direction (RD). The elongation of the CCR alloy along the diagonal direction (DD) was higher than those processed by CR, RCR, and RTR. The in-plane anisotropy (IPA) factor of the ultimate tensile strength (3.26%) of the CCR alloy indicated its relatively low anisotropy of the strength. Kernel average mapping (KAM) showed that the deformation was relatively uniform for the CCR alloy. A prominent local low KAM zone appeared in the alloy processed by RCR and RTR. The alloy in the CCR condition exhibits the highest strain hardening rate, progressively decreasing in a sequence of CR, RCR, and RTR. The refined grains and the texture, including mainly copper texture, little Cube texture, little Goss texture and little S texture, are the main reasons for the excellent mechanical properties and balanced strength-ductility of the CCR alloys.

Influence of Strain Rate Sensitivity on Cube Texture Evolution in Aluminium Alloys

The influence of strain rate sensitivity on development of Cube texture and on the morphology of Cube-oriented grains is often neglected in simulations approaches. Therefore, crystal plasticity simulations and experiments were performed up to 73 pct of thickness reduction for cold rolling on Al 6016. It is found, that low values of strain rate sensitivity promote Cube grains fragmentation and avoid formation of transition bands already at 50 to 55 pct thickness reduction. High values of strain-rate sensitivity cause formation of Cube transition bands leaving thin Cube grains in the microstructure and delay their fragmentation. Other texture components are affected by changes in strain rate sensitivity as well. The Copper volume fraction in the final texture diminishes as the strain rate sensitivity decreases, while Brass and S components of the beta fiber show a moderately higher volume fraction when the strain rate sensitivity increases. The final volume fraction of Goss is highest when the strain rate sensitivity is 10−2 but low if the strain rate sensitivity is 10−3 or raises up to 10−1. Recrystallization texture components (P, Q) are not affected by strain rate sensitivity, while the invGoss fraction decreases for high values of strain rate sensitivity. The results found in cold rolling crystal plasticity simulations were compared with experimentally determined Cube distribution and texture components obtained through thickness for Al6016 rolled at 80 m/min and 600 m/min. Further crystal plasticity simulations were performed to predict the influence of strain rate sensitivity during several hot rolling conditions where activity of non-octahedral slip systems was included in the simulations. During hot rolling, high values of strain rate sensitivity contribute to Cube stabilization and promote formation of Copper texture and delay Brass and S.

Effect of activated slip systems on dynamic recrystallization during rotary swaging of electro-conductive Al-Cu composites

The study focuses on structure investigations of newly designed electro-conductive Al-Cu composites produced via room temperature rotary swaging with constant and altering swaging directions. The swaging route affected the activated slip systems and the development of dynamic recrystallization. Altering the swaging direction supported the activation of {100} <10-1> slip system at the expense of the {111} 〈110〉 one. All the swaged composites featured the tendency to form four dominant ideal texture orientations – deformation textures Cu (90°,35°,45°), B (120°,55°,45°), and Bb (60°,55°,45°), and recrystallization texture Cube (0°,0°,0-90°). However, their volume fractions differed. Samples swaged with altering direction exhibited high fractions of Cube orientation. Dynamic recrystallization dominated over deformation strengthening for the final 10 mm diameter composite swaged with altering directions. This composite also featured the highest presence of recrystallized grains and the smallest average grain size (6.0 µm).

Effect of Molten Pool Spatial Arrangement on Texture Evolution in Pulsed Laser Additive Manufacturing of Inconel 718.

The epitaxial growth of dendrites, which often results in a strong texture, is the most common phenomenon during the laser additive manufacturing process. In this study, the epitaxial growth of dendrites and texture evolution in three directions were studied by changing the z-increment, pulse period, and track offset, respectively. The influence of the molten pool interface on the growth and competition of dendrites is analyzed. Both green grains (<110> // BD) with rotated cube texture in the molten pool overlapping zones and red grains (<100> // BD) with fiber texture in the molten pool center zones coexist for different z-increment samples, forming the typical sandwich texture feature. In a short pulse period, the dendrites can grow directly epitaxially and form the strong fiber texture due to gentle interface and short distance. With the decrease of the track offset, the molten pool morphology changes from flat to narrow and deep. When θ is close to 90°, dendrites grow along the secondary dendrite arms at the overlapping zone, forming V-shape grains. This work also provides a promising method for texture customization for laser additive manufacturing.

Machine-learning convex and texture-dependent macroscopic yield from crystal plasticity simulations

The influence of the microstructure of a polycrystalline material on its macroscopic deformation response is still one of the major problems in materials engineering. For materials characterized by elastic-plastic deformation responses, predictive computational models to characterize crystal-plasticity (CP) have been developed. However, due to their large demand of computational resources, CP simulations cannot be straightforwardly implemented in hierarchical computational models such as FE2. This bottleneck intensifies the need for the development of macroscopic simulation tools that can be directly informed by microstructural quantities. Using a 3D finite element solver for CP, we generate a macroscopic yield function database based on general loading conditions and crystallographic texture. Leveraging the advancement in statistical modeling we describe and apply a machine learning framework for predicting plane stress macroscopic yield as a function of crystallographic texture. The convexity of the data-driven yield function is guaranteed by using partially input convex neural networks as the predictive tool. Furthermore, in order to allow for the predicted yield function to be directly incorporated in time-integration schemes, as needed for the finite element method, the yield surfaces are interpreted as the boundaries of signed distance function level sets. Results generated for an example cube texture are discussed.

Phase constitution and texture distribution in the vortex zone of Co/Cu explosive welded plates

Cobalt has a reputation for its excellent electrical and magnetic properties, and exceptional wear and corrosion resistance, which has many applications in the batteries, electronic industry and semiconductor industry. In this work, the explosive welding technique was successfully performed to join Co/Cu dissimilar metals. To reveal the phase constitution and texture distribution of the vortex zone at Co/Cu joining interface, the electron backscatter diffraction (EBSD) test was carried out. It was concluded that the typical vortex structure composed of fine crystal band, sub-grains and twin structures was formed at the Co/Cu joining interface. In addition, the dynamic recrystallized structure and local internal stress at the vortex was attributed to severe plastic deformation and rapid solidification of liquid metals resulted from high strain state collision. Furthermore, the S, copper, brass and fiber deformation textures and the cube and gross recrystallization textures were confirmed at the vortex zone due to plastic deformation and dynamic recrystallization.

Role of twin boundaries and copper content on the mechanism of recrystallization in Ni-Cu alloys

The evolution of microstructure and texture at the surface of the cold-rolled and annealed Ni-Cu alloys are strongly influenced by the Cu content. Effect of shear deformation leads to strong ND-rotated cube {001}<110> component at the surface along with Bs component and there is a strong correlation of the development of later component from that of the former. The addition of Cu suppresses the strength of {001}<110> component while enhancing the Bs component. The evolution of <110>, <100>, and <111> fibers in decreasing order of intensity are observed in both the cold-rolled and annealed condition. During recrystallization, Cu addition to Ni-Cu alloy enhances the twin density and suppresses the cube texture component. Annealing twin density is maximum for 60Ni-40Cu sample (8856/mm2), and it is approximately three times larger than other samples. Suppression of strong cube component during annealing is attributed to the formation of coherent twin boundaries, Bs component, and unfavorable conditions for oriented growth.

Texture evolution during processing and post-processing of maraging steel fabricated by laser powder bed fusion

In this study, the evolution of solidification texture during LPBF of Ti-free grade 300 maraging steel, and its effect on texture development during subsequent post-fabrication heat treatments was characterized using Electron Backscatter Diffraction (EBSD). It was found that in the as-fabricated state, no texture was observed in the room temperature martensitic phase. However, the reconstructed parent austenite phase displayed a Cube texture with a minor fraction of Rotated Goss texture. During subsequent aging treatments involving two different routes, namely direct aging of the as-fabricated samples, and conventional solution treatment + aging of the as-fabricated samples, significant changes in the texture components of parent austenite were observed, whereas no changes in texture were observed in the room temperature martensitic phase. During direct aging, it was found that with an increase in the aging temperature up to 520 °C, the texture components of the parent austenite changed from Cube/Rotated Goss to Brass, whereas during the conventional solution treatment and aging cycle, interestingly a change in texture component to rotated copper was observed. The transitions in texture components have been discussed using the concepts of recrystallization and twinning in austenite during annealing and/or aging, and strain energy release maximization (SERM) theory. Furthermore, the importance of these preferred orientations on the mechanical properties was quantified using transformation potential diagrams.

Constitutive behavior and microstructural evolution of 2060 Al–Li alloy under high strain rate: Experiment and simulation

Being impacted at higher strain rates, the dislocation density in the metal material increases, which leads to the phenomenon of grain refinement. The refined grains demonstrate the hardening effect of the material processed by high-velocity impacts well. However, the mechanical response and the microstructure evolution of the new material, 2060 Al–Li alloy, under high-velocity impact remain to be unclear. In this study, the mechanical behavior of 2060 Al–Li alloy at high strain rates was investigated by split Hopkinson pressure bar (SHPB), and the influence of higher strain rates on the microstructure evolution of 2060 Al–Li alloy was further revealed by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) experiments. Meanwhile, a coupling constitutive model was proposed to correlate the macro and micro properties of the material and was applied to characterize the mechanical behavior and microstructure evolution of 2060 Al–Li alloy. The experimental results showed that when the strain rate increased from 3189 s−1 to 9053s−1, a significant strain rate hardening phenomenon was exhibited in 2060 Al–Li alloy, which could be ascribed to the significant increase in the dislocation density. Meanwhile, as the strain rate increases, the proportion of low-angle grain boundaries (LAGB) in the material increases, along with the augmented sub-grains. After the impact, the Goss texture {110}<001> became conspicuous, while the Cube texture {100}<001> in the material became gradually eclipsed. When the strain rate is up to 9053s−1, the Goss texture took on orientational dominance. Finally, based on the coupling constitutive model, the dislocation density and grain size of the specimen after impact were predicted, and the calculated results were in good agreement with the experiments.

Effect of deformation mode on hot deformation characteristics and microstructural evolution in Cu-Cr-Zr-Ti alloy

Uniaxial (UC) and plane strain compression (PSC) tests were performed on the Cu-Cr-Zr-Ti alloy specimens to investigate the effect of the deformation mode on the stress-strain response, work hardening behaviour and microstructural evolution in the alloy. These tests were performed at a strain rate of 1 s−1 and in the temperature range of 700–800 °C to impart von Mises equivalent strains of 0.15, 0.45 and 0.69. The alloy showed a regime of constant work hardening rate in the recovery stage before transitioning to the steady state under UC as opposed to PSC in which the alloy exhibited a smooth transition from recovery stage to the steady state stage. The microstructures evolved under UC consisted of randomly oriented equiaxed grains delineated by high angle boundaries (HABs) with high fraction of Σ3 boundaries. On the other hand, under PSC a very strong {001}〈100〉 cube texture evolved with increase in strain. This strong cube texture was ascribed to the evolution of and the increased stability of cube-oriented elongated substructures observed in the deformed matrix. The difference in the work hardening behaviour was thus attributed to the higher evolved Σ3 fraction under UC and the cube-oriented elongated substructures evolved under PSC. The dynamically recrystallized grains fraction calculated from area of grain orientation spread (GOS) map with GOS < 2o was found to be lower in the alloy under PSC owing to the presence of high orientation gradients within the evolved cube-oriented elongated substructures.

Effect of laser intensity profile on the microstructure and texture of Inconel 718 superalloy fabricated by direct energy deposition

Epitaxial growth of dendrites often results in a strong texture, which is a common phenomenon in a laser additive manufacturing process. In this study, pulsed lasers with flat-top and Gaussian intensity profiles were used to modulate the molten pool morphology and the solidification texture with a unidirectional scanning strategy. The melt pool is planar for the flat-top mode and it turns arc-shaped for the Gaussian mode. Long columnar grains are uniformly distributed and a strong fiber texture with a weak cube texture is obtained for the flat-top mode sample due to a uniform heat flux through many deposition layers. In contrast, large grains and fine grains are alternately arranged for Gaussian mode sample. The large grains exhibit a strong rotated cubic texture with a V-pattern in the overlapping area of the melt pool due to side-branching from the curved melt pool boundary; while the fine grains exhibit a weak fiber texture in the center of melt pool with a less restriction of the other two crystallographic axes perpendicular to the build direction. After heat treatment, the intensity of the textures of both samples is reduced. More recrystallized grains with twin boundaries are found under Gaussian mode due to the accumulated residual strain. This work manifests a promising method for texture customization by manipulating the heat flux strategy for laser additive manufacturing.