Rotated Cube Texture Research Articles

Formation mechanism of edge crack during hot rolling process of high-grade non-oriented electrical steel

Edge crack formed during the hot rolling process significantly affected the quality of high-grade non-oriented electrical steel (NOES), posing substantial challenges to production. This study investigated the formation mechanism of serrated edge cracks in hot rolled strip, characterized by unusually coarse strip-like grains with typical thicknesses ranging from 0.5 to 0.8 mm and lengths ranging from 10 to 15 mm. These coarse strip-like grains evolved from abnormal columnar grains at the edges of reheating slab. During the continuous casting process, the bulge phenomenon occurred easily in high-grade NOES slabs, due to its lower yield strength at high temperatures. This bulge induced high internal stress at the slab edge, leading to abnormal growth of the columnar grains during the slab reheating process at high temperature. The orientation of coarse grains gradually changed to a rotated cube texture ({100}<011>) throughout the hot rolling process. These grains with rotated cube texture exhibited fewer slip systems and lower deformation storage energy, which is not conducive to the plastic deformation in thickness direction. Consequently, coarse grains at the slab edge deformed along TD direction and overflowed towards the lower surface of hot rolled strip, resulting in the original edge boundary enveloped by the overflowed metal to generate crack source. Finally, the serrated edge crack was formed from crack source under tensile stress during finish hot rolling.

Crystallographic texture evolution during friction stir processing of AA7075 alloy

This study investigates the effects of heat input on the crystallographic texture evolution during friction stir processing of AA7075 alloys. Three different heat input levels were applied to develop friction stir-modified regions. Electron backscattered diffraction (EBSD) was utilized to measure the micro-texture in the as-received base metal and friction stir processed (FSPed) stir zones. In particular, inverse pole figure (IPF) maps, pole figures, and orientation distribution functions were employed to compare the micro-textures of different processed regions. The results indicate that as the heat input decreases, the average microhardness of the nugget zone declines, accompanied by an increase in the size of recrystallized grains. The base metal AA7075 exhibits a predominantly rotated cube texture ({001} <110>). After friction stir processing, the stir zone transitions to a rotated cube texture with decreased intensities and the presence of copper texture ({112} <111>). Notably, as the heat input increases, the rotated cube texture transforms into a copper texture.

Microstructure evolution and mechanical properties of new Co-free maraging steel produced by wire arc additive manufacturing

In this work, P-MIG is used as additive process, a new low-cost Co-free maraging steel wire is used as raw material to additive manufacturing block component, and the microstructure and mechanical properties of the component is investigated. The microstructure of the component is composed of martensite and austenite, and the closer to the bottom, the more serious the elemental segregation and the more austenite content. From the top to the bottom the high-angle grain boundaries increase and the grain size decrease, the difference of the heat dissipation condition and the thermal cycle are the reasons for this phenomenon. The texture of austenite is mainly Cube texture, and the texture of martensite is Rotated Cube texture and Goss texture. The tensile strength of XD, YD, ZD three directions is 1172 ± 15 MPa, 1021 ± 7 MPa, 1139 ± 16 MPa, respectively, impact toughness is 64.7 ± 1.6 J/cm2, 51.1 ± 5.6 J/cm2, 51.4 ± 3.1 J/cm2, respectively, TRIP effect occurs in the process of tensile, the main mode of fracture in tensile and impact is toughness fracture. The microhardness decreases gradually from bottom to top, which is due to the short-lived aging strengthening by thermal cycle, the change of grain size and GND density. The results of the work reveal the successful application of the new low-cost Co-free maraging steel wire in WAAM and provide an important reference for the adjustment of additive process, subsequent heat treatment and the adjustment of wire composition.

Hot Processing Maps and Texture Evolution during Hot Compression of CF170 Maraging Stainless Steel

In this work, the hot processing maps of CF170 maraging stainless steel were generated by using flow stress data obtained from an isothermal compression experiment on the Gleeble-3800 hot compression simulator. The microstructure corresponding to the stable regions in the hot processing map was observed with an optical microscope. The results showed that the steel is susceptible to deformation temperature, strain, and strain rate, and the optimal hot working parameter is a strain rate range of 0.01∼0.1 s−1 and a temperature range of 1350∼1373 K when the strain is 0.6. In addition, the texture evolution of prior austenite during hot compression was investigated based on reconstructing a parent grain by Electron Back-Scattered Diffraction. The results showed that twinning-induced dynamic recrystallization is another mechanism except for strain-induced dynamic recrystallization at a higher strain rate. Further, the deformed microstructure with a Cube texture (1 0 0) 〈0 1 0〉 will preferentially nucleate, and the increase in temperature makes the Cube texture (1 0 0) 〈0 1 0〉 change to the rotated Cube texture (1 0 0) 〈1 1 0〉, and the increase of strain rate inhibits the growth of recrystallized grains and weakens texture.

Texture evolution prediction of 2219 aluminum alloy sheet under hydro-bulging using cross-scale numerical modeling

A simultaneous prediction of macroscopic deformation and microstructure evolution is critical for understanding the deformation mechanism of components. In this work, the hydro-bulging process of 2219 aluminum alloy sheet was investigated using cross-scale numerical modeling, in which the macroscopic finite element method (FEM) and crystal plasticity finite element method (CPFEM) were combined. The calculated texture evolution exhibits good agreement with the experimental results, and the stress error between the two scales is generally small. The effects of different strain states on texture evolution and slip mode are further discussed. As the strain ratio η increases, the volume fractions of the initial Rotated Copper texture component and γ-Fiber texture component decrease significantly, which tend to be stabilized at P texture component. The initial Rotated Cube texture component is inclined to rotate towards the Cube texture component, while the volume fraction of this orientation is relatively stable. The lower strain ratio can considerably enhance the activity of more equivalent slip systems, promoting a more uniform strain distribution over grains. The difficulty of grain deformation changes as the lattice rotates. The grain with easy-to-deform orientation can gradually rotate to a stable orientation during plastic deformation, which has a lower Schmid factor.

Microstructure and texture characteristics of laser-clad Ti6Al4V/NiCr-Cr3C2 composite coating

• The recrystallization grains of β-Ti are coarse equiaxed after laser cladding. • GND density of β-Ti near by the Ti 2 C is slightly higher than other places. • Weak textures exist in β-Ti/Ti 2 C/CeO 2 composite coating. • CeO 2 as the heterogeneous nucleation core grows in the same direction with Ti 2 C. • The grains of matrix β-Ti and Ti 2 C had a special orientation relationship. Microstructure and texture characteristics of laser-clad Ti 2 C/CeO 2 /β-Ti composite coatings are investigated. The matrix β-Ti belong to equiaxed recrystallization grains with high-angle grain boundaries (HAGB). The well-developed Ti 2 C dendrites can grow through the multiple β-Ti grains. In addition, the matrix β-Ti grains near Ti 2 C have higher geometrically necessary dislocation (GND) density than that far away from Ti 2 C and within Ti 2 C. Furthermore, the relatively weak texture {1 1 1} 〈1 1 0〉 and {0 0 1} 〈1 0 0〉 exists in matrix β-Ti, and similar rotated cube texture {0 0 1} 〈1 1 0〉 forms in both Ti 2 C and CeO 2 . Besides, the special orientation relationships, 100 β - Ti / / 100 Ti 2 C and 100 β - Ti / / 100 Ti 2 C , are found between Ti 2 C and β-Ti.

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.

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.

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.

A crystal plasticity investigation on the influence of orientation relationships on texture evolution during rolling in fcc/bcc two phase materials

In two phase materials like duplex stainless steels that contain both the phases in nearly equal proportions, the crystallographic texture in the phases is related by special orientation relationship (OR). Most of the studies related to ORs are focused on characterising the type of ORs due to phase transformations and recrystallisation. However, very little is known about the stability of ORs and their role in the texture evolution during deformation. In this work, we present a detailed study on the role of ORs in the texture evolution during rolling in fcc/bcc two phase materials. Three different ORs; Bain, Kurdjumov–Sachs, Nishiyama–Wassermann and two different parent phases; fcc and bcc are considered. Using three-dimensional representative volume element (RVE) based crystal plasticity fast Fourier simulations, we report that the final textures depend strongly on the initial parent phase textures and the existence of an OR, and is independent of the type of the OR. A copper type texture is observed in the fcc phase, when the parent phase is bcc with cube texture. However, a brass type texture is observed when the parent phase is bcc with rotated cube texture. A detailed investigation using a series of bicrystal studies further revealed that even within an OR, the type of Bain variant plays a vital role in the overall texture evolution. It is also observed that there is no marked impact of the initial CRSS ratios and strain hardening on final textures of both the parent and child phases.

The beneficial effect of rolling on the fracture toughness and R-curve behavior of pure tungsten

Selected microstructural states of pure tungsten sheets with thicknesses of 1, 0.5, 0.2 and 0.1 mm were tested at room-temperature (RT) and 200 °C regarding their fracture properties with focus on the occurrence of an R-curve (crack growth resistance curve) behavior. Through thermomechanical rolling and the resulting increase of deformation a pronounced refinement of microstructure and strengthening of the rotated cube texture was induced with decreasing sheet thickness. The fracture experiments exhibited large variations of the fracture behavior depending on the testing temperature, material thickness and microstructure: While at RT, the 1 mm material did not exhibit R-curve behavior, it was found at 200 °C irrespective of the sample thickness. With decreasing sample thickness and grain-size the RT fracture-behavior changed and showed the onset of an extended R-curve behavior for the 0.5 mm followed by an increasing extent of this characteristic for the thinner material states. The change of the fracture behavior at RT is associated with a transition of the failure behavior from transcrystalline fracture for the thicker samples to a mixture of transcrystalline with delamination fracture to uniform delamination failure for the thinnest material. These observations suggest a continuous shift of the ductile to brittle transition temperature from 200 °C to RT and even below RT with decreasing sample thickness. The fracture toughness in terms of the maximum stress intensity, Kmax, increased at RT from approximately 20 MPam1/2 for the 1 mm samples to values up to 60 MPam1/2 for the thinnest material states, whereas at 200 °C this increase was less pronounced.

Thermal stability of thin rolled potassium-doped tungsten sheets during annealing at temperatures up to 1400 °C

Microstructural changes will occur in tungsten when used as plasma-facing material in future fusion reactors due to the high operation temperatures. Potassium doping has proven to delay such undesired changes in drawn tungsten wires. The same strategy is adapted to thin cold-rolled tungsten sheets containing 80 ppm potassium. Their thermal stability is characterized by isochronal annealing for two hours as well as isothermal annealing at selected temperatures for longer times. Mechanical degradation is quantified by micro hardness testing; microstructure and texture evolution are investigated using scanning electron microscopy and electron backscatter diffraction. During annealing for two hours at temperatures between 800 °C and 1400 °C, the potassium-doped tungsten sheets undergo recovery. The strong rotated cube texture present in the as-rolled condition intensifies enormously during annealing for two hours, but does not change significantly during further annealing. Isothermal annealing at temperatures between 1300 °C and 1400 °C causes significant loss in hardness during the first two hours, but only smaller changes further on, indicating that solely extended recovery is occurring. No evidence for primary recrystallization is found as recrystallization is retarded by a combination of high angle boundaries being absent due to the strong texture and their immobilization by potassium bubbles. The recovery kinetics is quantified based on Kuhlmann’s recovery model and compared with observations on differently rolled thin plates of pure tungsten. Despite different amounts of recoverable hardness, the recovery parameters resolved for potassium-doped tungsten fit nicely to the master curve for recovery obtained earlier on pure tungsten plates confirming that recovery is indeed the dominating restauration mechanism and that doping with 80 ppm potassium does not alter the recovery mechanism fundamentally.

The evolution of abnormally coarse grain structures in beta-annealed Ti-6Al%-4V% rolled plates, observed by in-situ investigation

The factors controlling the evolution of abnormally coarse grain (ACG) structures during standard β annealing of titanium-6Al%-4V% (Ti64) hot-rolled plates, have been investigated in more detail than previously, using both ex-situ through-thickness large area, and in-situ EBSD micro-texture observation. Starting with a typical, through thickness, α+β deformation texture distribution that gives rise to ACGs at the plate mid-section, each stage of the annealing process has been sequentially characterised and phenomenologically linked to the spatial texture evolution that occurs during transient heating through the α→β phase transformation and the subsequent isothermal hold at the β-annealing temperature. It was found that during the ramp heating phase, the rotated cube texture component greatly expands from just below the β transus by broad front strain induced boundary migration (BF-SIBM), driven by a disparity in stored energy with neighbouring texture bands from the α and γ fibres. This subsequently sets up the necessary conditions for unstable coarsening of surviving grain clusters with predominately near α fibre orientations during the super-transus hold, in a process with similar characteristics to discontinuous recrystallisation. Humphreys’ mean field model of the stability of cellular microstructures, effectively explains the process by which these grain clusters, which have a lower misorientation range relative to the rotated cube component matrix, have a higher probability of entering a discontinuous growth regime, compared to other components from the α and γ fibres. Furthermore, the conditions that give rise to the development of ACG structures could be linked to the high strain rate and temperature experienced at the central mid-thickness of rolled plates.

Microstructural Evolutions of 2N Grade Pure Al and 4N Grade High-Purity Al during Friction Stir Welding.

The grain refinement mechanisms along the material flow path in pure and high-purity Al were examined, using the marker insert and tool stop action methods, during the rapid cooling friction stir welding using liquid CO2. In pure Al subjected to a low welding temperature of 0.56Tm (Tm: melting point), the resultant microstructure consisted of a mixture of equiaxed and elongated grains, including the subgrains. Discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and geometric dynamic recrystallization are the potential mechanisms of grain refinement. Increasing the welding temperature and Al purity encouraged dynamic recovery, including dislocation annihilation and rearrangement into subgrains, leading to the acceleration of CDRX and inhibition of DDRX. Both C- and B/-type shear textures were developed in microstructures consisting of equiaxed and elongated grains. In addition, DDRX via high-angle boundary bulging resulted in the development of the 45° rotated cube texture. The B/ shear texture was strengthened for the fine microstructure, where equiaxed recrystallized grains were fully developed through CDRX. In these cases, the texture is closely related to grain structure development.

An exploration of microstructural in-homogeneity in the 6082 Al alloy processed through room temperature multi-axial forging

In the current work, open die multi-axial forging (MAF) of 6082 Al alloy was performed at room temperature. The resulting microstructure and mechanical properties were found to have a gradient from the periphery towards the center. The resulting inhomogeneity was quantified with the help of electron backscattered diffraction, X-ray diffraction analysis, hardness and tensile strength measurement. The recrystallized grains were found after the partition of inverse pole figure (IPF) maps by using the criteria (Grain orientation spread<1°& boundary misorientation angle>15°). The sub-grains were found by partition of the IPF-maps by using the criteria (Grain orientation spread>2° & 2° < Grain rotation angle<15°). The high driving force (dislocation density) available at center of the MAF sample was responsible for the increase in sub-grains size up-to micrometer regime as well as increase in the volume fraction of recrystallized grains. The presence of a strong deformation texture (Goss ({110} 〈001〉)) and the recrystallized texture (Rotated Cube texture ({001} 〈110〉)) were observed, as we proceed towards the center of the MAF sample.

Effects of Oxide Inclusions on Texture of 1235 Al-Alloy after Deformation

Texture characteristics of compressed 1235 Al-alloy treated by different purification methods are studied by electron backscattered diffraction. The effects of oxide inclusions on texture components of material are studied as well. The main textures in hot-compressed 1235 Al-alloy are Cube texture, R texture, Gross texture, Brass texture, and Rotated cube texture. The lower the content of oxide inclusions in the material, the smaller the total relative ratio of textures. The total relative ratio of textures goes to the smallest by 1.8 % in high-efficient purified 1235 Al-alloy by oxide inclusion content of 0.051 %. The purification results have obvious effects on types and percentage of texture in the deformed alloy. With the decreasing content of oxide inclusion, the ratio of deformation texture decreases and recrystallization texture increases. Brass texture is gradually replaced by Goss texture in the deformation textures. R texture is the main texture in recrystallization textures. Therefore, reducing the content of oxide inclusions is effective for improving the hot deformation properties of 1235 Al-alloy.

Strong rotated cube textures in thin cold-rolled potassium-doped tungsten sheets during annealing up to 1300 °C

Due to the high operation temperatures, microstructural changes will occur in tungsten when used as plasma-facing material in future fusion reactors. In drawn tungsten wires, potassium doping has proven to prevent such undesired changes effectively. This strategy has been adapted to thin cold-rolled tungsten sheets containing 80 ppm potassium. Their texture evolution during annealing is investigated using electron backscatter diffraction. In the as-rolled condition, a strong cube texture is present with a volume fraction of 67.0 % deviating maximal 15° from the rotated cube orientation. This texture intensifies strongly during isochronal annealing for 2 h at temperatures between 1000 °C and 1300 °C; the higher the temperature, the higher the rotated cube fraction. The volume fraction of 94.8 % obtained after 2 h at 1300 °C does not change significantly during further annealing. These are remarkably strong textures for a body-centered cubic metal compared e.g. to commonly reported high volume fractions of 30 % for Goss orientations in silicon steels. Reliable quantification of such strong texture components requires analysis of orientations individually.

Friction surfacing of AISI 904L super austenitic stainless steel coatings: Microstructure and properties

Microstructure, texture, pitting corrosion resistance and hardness of surfaces and cross-sections of the friction-surfaced (FSed) super austenitic stainless steel 904L coatings fabricated at various spindle speeds were investigated. The microstructure of the coatings was governed by both dynamic recovery (DRV) and continuous dynamic recrystallization (cDRX) owing to the high stacking fault energy (SFE) of 904L. The grain orientations in DRV were in A 2 ⁎ shear texture component, while the rotated cube textures were related to the cDRXed grains. Immersion tests of the FSed coatings in 3.07 mol/L Cl − solution showed that the corrosion pits were slightly preferred to generate at the {111} DRVed grains on the coating surfaces, since these grains were likely to have a higher elastic strain during FS. Compared with AISI 304, the pitting potential of the FSed coatings in 3.5 wt% NaCl solution was significantly shifted to nobler direction and also insensitive to spindle speed owing to the high SFE of 904L. However, the passive films of the FSed coatings were thinner and more difficult to reform, as evidenced by slightly larger average pit diameters and lower protection potentials owing to the high residual stress caused by FS. • Microstructures of FSed 904L coatings were governed by DRV in A 2 ⁎ shear component and cDRX in rotated cube textures. • Increment of spindle speed tended to enhance cDRX but suppress DRV at the same time. • The FSed coatings could maintain excellent pitting corrosion resistance of as-received 904L. • Due to high SFE of 904L, elastic strain in {111} grains was reduced. • Crystallographic effect on pitting cororsion resistance of the coatings was weakened. • Increase in misorientation density induced by cDRX led to hardness improvement and ductility reduction for the coatings

The Influence of Normalization Temperatures on Different Texture Components and Magnetic Properties of Nonoriented Electrical Steels

The effects of normalization on different texture components and magnetic properties in G50W600 nonoriented electrical steel are studied by electron backscatter diffraction (EBSD). The results show that normalization can coarsen surface {110}‐oriented grains and recrystallized rotated cube or {114}&lt;481&gt;‐oriented grains in the center. Moreover, the highest texture intensity change from original rotated cube texture to the {114}&lt;481&gt; texture with the increase of normalization temperature. Just after the completion of recrystallization in final sheets corresponding to hot‐rolled samples, {111}&lt;112&gt; is the main texture component, while that in final sheets corresponding to normalized samples is {114}&lt;481&gt;. The final sheets normalized at 920 and 980 °C have a higher iron loss and higher magnetic induction than the final sheets corresponding to hot‐rolled samples, which is caused by the fact that normalized samples show finer final grain size, higher volume faction of {100} and {110}, and lower volume fraction of γ‐fiber than hot‐rolled samples. With the increasing of annealing temperature and time, the magnetic induction and iron loss of normalized samples decrease. Furthermore, the final sheets normalized at 940 °C have the best magnetic properties. During final high temperature annealing, the non γ‐fiber oriented grains show a higher growth ability than γ‐fiber oriented grains.

The brittle-to-ductile transition in cold-rolled tungsten sheets: On the loss of room-temperature ductility after annealing and the phenomenon of 45° embrittlement

The high brittle-to-ductile transition (BDT) temperature of conventionally produced tungsten (W), challenges the design of W-based structural components. Recent studies have demonstrated the potential of cold rolling to produce W sheets, which are ductile at room temperature and exhibit a BDT temperature of 208 K. In order to assess the thermal stability of these materials, we conducted isothermal heat treatments (at 1300 K, for annealing durations between 0.1 h and 210 h) combined with studies on the evolution of mechanical properties and microstructure of a severely deformed undoped W sheet. With this work, we demonstrate the need for a stabilized microstructure before utilization of cold-rolled W in high-temperature applications can take place successfully. After annealing at 1300 K for 6 h, the material properties changed remarkably: The BDT temperature increases from 208 K to 473 K and the sharp BDT of the as-rolled condition transforms into a wide transition regime spanning over more than 200 K. This means in fact, an endangered structural integrity at room temperature. We also address the so-called phenomenon of 45° embrittlement of W sheets. Here we show that cleavage fracture in strongly textured W sheets always takes place with an inclination angle of 45° to the rolling direction, independent of the studied material condition, whether as-rolled or annealed. An in-depth study of the microstructure indicates a correlation between an increased BDT temperature caused by annealing and microstructural coarsening presumably by extended recovery. We conclude that 45° embrittlement needs to be comprehended as a combined effect of an increased spacing between grain boundaries along the crack front, leading to an increased BDT, and a high orientation density of the rotated cube component or texture components close to that, which determine the preferred crack propagation of 45° to the rolling direction.