Elongation Anisotropy Research Articles

Effect of laser remelting processing on microstructure and mechanical properties of 17-4 PH stainless steel during laser direct metal deposition

Abstract Laser direct metal deposition (DMD) is an efficient and flexible additive manufacturing technique which has broad application prospects, but it is also limited due to defects and mechanical anisotropy. Laser remelting (LR) is a process that after each layer is deposited, re-scan the deposition layer with the same slice data but without powder deliver, and it is often used during selective laser melting. Herein, LR process has been applied during the DMD process of a 17-4 PH steel to enhance the densification level and relieve the mechanical anisotropy. It is found that the thermal history, porosity and microstructural evolution are dependent on the LR energy density. Moreover, the roughness of top surface of the deposited layer and intralayer porosity decrease with increase of the laser remelting energy density. While for interlayer defects, there is an optimal LR energy density corresponding to the lowest interlayer porosity. Furthermore, LR process can enhance the holding time at high temperature, even sometimes heat the sample above Ac1, resulting in change in contents of austenite and carbide. In addition, LR process greatly dilutes the pre-solidified texture. It was also proved that the flat defects in-plane to the interlayer and the anisotropy of the crystallographic orientations are extremely harmful for the mechanical isotropy of the DMDed samples. Finally, sample manufactured with laser remelting at 15.0 J/mm2 has the lowest porosity and most random crystallographic orientations resulting in near isotropous tensile strength, but the contribution of laser remelting to eliminate anisotropy in elongation is limited because of the interlayer defects.

Mechanical properties of steel gun barrel processed by cold radial forging with stepped mandrel under different forgingratios

Mechanical properties of 30SiMn2MoVA steel gun barrel processed by cold radial forging with stepped mandrel under the different forging ratios were investigated in the present work. This work mainly reported the axial and circumferential mechanical properties of forged gun barrel before and after annealing. The axial and circumferential mechanical properties were measured by tensile test and bulging test, respectively. The results suggested that the strength was enhanced and elongation was decreased by forging which was caused by cold work hardening. After annealing, the anisotropy of elongation was observed. The circumferential elongation was weaker than the axial. With the increasing of forging ratios, strength anisotropy was exacerbated gradually. The circumferential strength was inferior to the axial. Besides, there were axial penetrating cracks in the failure state of circumferential bulging test specimens. Through the electron microscopic examination, the axial micro cracks and wrinkles in the inner wall of the forged tubes were observed. It showed that the cold radial forging with stepped mandrel may result in the defect in the inner surface of the gun barrel which should be paid attention.

Effect of boron on the microstructure and mechanical properties of Ti-6Al-4V produced by laser directed energy deposition after heat treatment

The nearly rapid solidification and high-temperature thermal cycles associated with laser directed energy deposition of titanium alloys using laser solid forming (LSF) lead to the formation of coarse prior β columnar grains and continuous coarse-grain-boundary α (αGB) phases, which result in anisotropic properties and poor ductility. The influence mechanisms of trace B (up to 0.3 wt. %) on the solidification, solid state transformation, and tensile properties of LSFed Ti-6Al-4V after solution and aging treatment were studied using thermodynamic calculations. With an increase in B content, the size of prior β grains decreased owing to the growth-restricting effect it caused during the solidification and the Zener pinning caused by TiB during reheat cycles and heat treatments. The continuous coarse αGB phases were almost eliminated owing to the discontinuous distribution of TiB between the dendrites, and the length and aspect ratio of intragranular α phases were gradually reduced. Moreover, both ultimate tensile strength and yield strength increased, fracture elongation decreased, strength anisotropy decreased, and elongation anisotropy initially increased and then decreased significantly. The findings in this study will promote the development of new Ti alloys befitting additive manufacturing technology.

Microstructure and Elongation Anisotropy of Cold Rolled and Solution Treated A356 Alloy Strips Fabricated via High-Speed Twin-Roll Casting

Microstructure and Elongation Anisotropy of Cold Rolled and Solution Treated A356 Alloy Strips Fabricated via High-Speed Twin-Roll Casting

Effect of impurity reduction on dynamic recrystallization, texture evolution and mechanical anisotropy of rolled AZ31 alloy

Dynamic recrystallization, texture evolution and mechanical anisotropy of rolled AZ31 alloys with varying impurity content were systematically investigated in the present work. The results suggested that, after rolling reduction of 20% and 50%, reducing impurity content led to an increase in the volume fraction of dynamic recrystallized (DRXed) grains. For the AZ31 alloys with rolling reduction of 50%, the texture was weakened and the mechanical anisotropy was improved with decreasing impurity content. The ultimate tensile strength anisotropy (UA), yield strength anisotropy (YA) and elongation anisotropy (EA) decreased significantly from 21.4%, 48.1% and 91.3% to 5.2%, 14.3% and 42.2%, respectively. The planar anisotropy Δr also decreased from 0.0969 to 0.0523. The improved anisotropy was attributed to the weakened basal texture, fine grain size and homogeneous microstructure caused by accelerated DRX process.

Influence of trace boron addition on microstructure, tensile properties and their anisotropy of Ti6Al4V fabricated by laser directed energy deposition

The mechanical anisotropy of laser directed energy deposition (L-DED) titanium alloys using laser solid forming (LSF) is significantly deteriorated owing to the coarse prior β columnar grains and continuous grain boundary α-laths (αGB). The influence mechanisms of trace boron (up to 0.25 wt%) on the microstructure, tensile properties and anisotropy of Ti6Al4V manufactured by LSF were investigated. The sizes of β grains and α phases both decreased with increasing boron content. Compared with the Ti6Al4V deposit, when the addition of boron was 0.08 wt%, the average width of β grains was reduced by about one order of magnitude owing to the growth restricting effect caused by boron and Zener pinning by TiB. Besides, the average length and aspect ratio of α-laths were reduced by 43% and 33%, respectively, owing to the refinement of β grains and the heterogeneous nucleation of α phases on TiB particles. With an increase in boron content, the strength anisotropy gradually decreased for the disappearance of αGB, the elongation anisotropy initially increased and then significantly decreased for the poor deformation compatibility between the TiB and the matrix. A better combination of strength and elongation could be obtained with the addition of 0.08 wt% boron to Ti6Al4V.

Study of Anisotropic Material Behavior for Inconel 625 Alloy at Elevated Temperatures

Abstract Deformation behaviour of materials can be precisely analysed by determining anisotropic behaviour and mechanical properties. Hot tensile deformation behaviour of Inconel 625 alloy has been examined from Room Temperature to 600°C with strain rates ranging from 0.1 s-1 to 0.0001s-1 at an interval of 200 0C. At eclectic variety of temperature’s and strain rate various material properties such as yield stress, tensile strength, % total elongation and strain hardening exponent have been carried out and evaluated. Additionally, anisotropic material properties of Inconel 625 alloy mainly; Lankford coefficient (R), normal anisotropy (RN), planer anisotropy (∆R), in-plane anisotropy (AIP) and anisotropic index (δ) have been studied. Influence of temperature and strain rate showed substantial disparity in material properties. From the experimental observation, yield stress, ultimate tensile stress decreases and % elongation increases with increasing the temperature. In-plane anisotropy value is the highest at room temperature, and replicates large variation of tensile yield strengths in three orientation. Presence of low values of anisotropic index δ indicates very less elongation anisotropy with rise in deformation temperature for Inconel 625 alloys.

Anisotropy of the Microstructure and Tensile Properties in Ti-5Al-5Mo-5V-1Cr-1Fe near β Titanium Alloy during Hot Rolling and Heat Treatment

Ti-55511 billet with the acicular α initial microstructure was hot rolled (HR sample) and then heat treated (HR+HT sample) at 750 °C. The effects of HR and HT on the anisotropy of microstructure, texture, and tensile properties were investigated. The tensile results show that there are obvious anisotropic tensile properties between RD and TD. The anisotropic elongation of HR sample is related to the morphology of α phase. After HR, the acicular α is parallel to RD. As for RD specimen, the transgranular propagation of microcrack passing through the acicular α phase leads to the ductile fracture, thus showing the higher ductility than TD specimen. While the intergranular propagation of microcrack passing by the equiaxed α phase in TD specimen causes the brittle fracture. The anisotropic strength of HR sample depends on the relationship among texture type of α phase, slip system, and loading direction. The maximum texture intensity at TD leads to the easy activation of basal slip system in RD and that of prismatic slip system in TD, and then causes the lower strength of RD specimen than TD specimen. After HT, the decreased anisotropy of elongation and strength can be attributed to the increased α size and the decreased texture intensity of α phase. These results demonstrate that anisotropic tensile properties mainly depend on the morphology and texture of α phase.

Microstructure and Elongation Anisotropy of Cold Rolled and Solution Treated A356 Alloy Strips Fabricated via High-Speed Twin-Roll Casting

Microstructure and Elongation Anisotropy of Cold Rolled and Solution Treated A356 Alloy Strips Fabricated via High-Speed Twin-Roll Casting

Effect of heat treatment on the inherent anisotropy of cold sprayed copper deposits

In the present investigation, the effect of post-spray heat treatment (PSHT) on the microstructural and mechanical anisotropies of cold spray (CS) Cu deposits was investigated. The electron back-scattered diffraction and nanoindentation techniques were employed to characterize the microstructure and micromechanical properties in the cross-sectional (v-face) and parallel direction (p-face) to the surface following PSHT. Tensile tests were performed at various loading angles to identify the effect of PSHT on the in-plane tensile anisotropic behavior. It is revealed that microstructural anisotropy exists in both the as-sprayed and annealed CS deposits. And PSHT can effectively reduce the micromechanical anisotropy between the v-face and p-face. Tensile results show that the strong anisotropy of in-plane tensile strength can be moderated with PSHT. However, its effect on elongation anisotropy is quite limited, and the anisotropy is greatly increased at 700 °C. The existence of parallel multiple passes during CS remains the main factor hampering the further modification of the inherent in-plane tensile anisotropy especially elongation anisotropy.

Effect of travel speed and stress relief on thin Ti-6Al-4V laser wire deposits

The effect of two travel speeds on thin Ti-6Al-4V buildups produced by Laser Wire Deposition (LWD) has been investigated. A travel speed set at 1.4 mm/s promoted recrystallization of columnar prior β grains into horizontal prior β grains. It was associated with lower strength hardly meeting minimum wrought requirements as set by the AMS4911. On the other hand, it was shown that by increasing the travel speed to 7.2 mm/s, sufficiently high cooling rates are occurring creating a fine α + β basket weave structure, while no recrystallization of the prior β grains has been observed. Tensile properties were improved with strength consistently exceeding minimum wrought requirements. An additional stress relief cycle preserved the effect of deposition parameters on material properties. A strong anisotropy in elongation was associated with the slower travel speed where higher values were derived along the Z direction. While the faster travel speed exhibited isotropic properties. Strengthening of the deposits has been observed following a stress relief cycle.

Effect of travel speed and sub-β transus post deposition heat treatments on thin Ti-6Al-4V laser wire deposits

Annealing or HIP below the β transus temperature was found to coarsen the as-built developed microstructure while preserving the developed macro morphology of Laser Wire Deposition (LWD) buildups. Following these thermal cycles, a general decrease in strength along with an increase in elongation have been observed. However, no trends in the tensile results could be extracted due to the scattering of the results. An additional aging cycle substantially stabilized the developed results. Samples processed at 1.4 mm/s exhibited low strength hardly meeting any of the ASTM and AMS minimum requirements and a strong anisotropy in elongation with lower values when tested along the Z direction. Samples processed at 7.2 mm/s exhibited good strength meeting the minimum wrought requirements as set by AMS4911 while elongation showed an isotropic behavior. Hardness has been found to be mostly independent of the experienced sub-β transus post deposition heat treatment. Moreover, the grain boundary strengthening mechanism with regards to the α platelets thicknesses was found to be travel speed dependent.

Effects of asymmetric feeder on microstructure and mechanical properties of high strength Al-Zn-Mg alloy by hot extrusion

The asymmetric feeder die extrusion was introduced on high strength Al-Zn-Mg alloy. The hot extrusion experiments were carried out using flat die without feeder, with symmetric and asymmetric feeders. The grain morphology, second particle distribution and microtexture were examined, and the tensile tests were performed along 0°, 45°, and 90° with extrusion direction. Moreover, the numerical simulation was performed to have a better understanding on the experimental findings. The results show that the utilization of feeder chamber results in the increase of effective strain and slight decrease of strain rate. The microstructure of all extruded plates consists of elongated grains and small amount of fine grains. The asymmetry feeder is favorable for the dynamic recovery process. Although the fraction of dynamic recrystallization is low in all cases, it is slightly higher in the plate extruded without feeder. The main texture components of the extruded plates are {110}〈111〉 Y, {001}〈100〉 Cube, and {110}〈112〉 Brass. The fraction of above mentioned texture varies significantly by the utilization of symmetric and asymmetric feeders. The elongation is greatly enhanced in the plates extruded by feeder die. Importantly, the anisotropy of elongation is obviously reduced in the plate extruded using the asymmetric feeder.

Characterization of the anisotropic necking in duplex stainless steels with lamellar microstructures

Duplex stainless steels are characterized by oriented microstructures, in which its constituent phases, ferrite (α) and austenite (γ) form layered or fibrous phase arrangements depending on forming operations (e.g. rolling). These microstructures have the potential to induce anisotropy in the macroscopic mechanical properties of the material. A very interesting phenomenon related to this microstructurally-induced anisotropy is the subject of investigation in the present work: a sample submitted to tensile testing, which presents a regular initial geometry (either circular or square transverse sections), exhibits an anisotropic necking zone after fracture (with the transverse section becoming, respectively, elliptical and rectangular). The phenomenon is most surprising since the region of the specimen which remains homogeneously strained (that is, outside the necking zone) remains regular. This result suggest that this anisotropy develops due to the cavitation damage orientation in the necking zone. Present results confirm that the lamellar microstructure, typical of these steels, is responsible for the observed anisotropy. Observation of fracture surfaces clearly demonstrate that cavities align according to the underlying microstructure and a model is introduced to explain the observed anisotropy in elongation observed in samples extracted parallel or perpendicular to the rolling direction in rolled plates.

Microstructure and texture evolution in Cu–Ni–Si–Mg alloy processed by secondary cold rolling

In this work,experiments were conducted to evaluate the evolution of microstructure and texture in a commercial Cu–2.77Ni–0.65Si–0.18Mg (wt.%) alloy during processing by secondary cold rolling at room temperature. The influence of rolling reduction was investigated by electron backscatter diffraction. The results show that with the increase of secondary rolling reduction after formation of the solid solution, both the strength and elongation anisotropy of the Cu–Ni–Si–Mg alloy show an initial decrease followed by an increase. The anisotropy is weakest when the alloy is in its intermediate reduction state. Detailed measurements demonstrate that the anisotropy was largely affected by Brass and S texture. The shear bands contribute to second phase precipitation and lead to a decrease in the anisotropy degree. In addition, the Brass texture gradually increased by intense microscopic shear band formation.

Quantitative relationship between anisotropic strain to failure and grain morphology in additively manufactured Ti-6Al-4V

The aim of this study was to identify processing-microstructure-mechanical property links in additively manufactured Ti-6Al-4V. First, the microstructure and mechanical properties of Ti-6Al-4V produced via two laser powder bed fusion (LPBF) additive manufacturing (AM) methods, one using a pulsed laser (P-LPBF) and the other a continuous-wave laser (CW-LPBF), were investigated and compared. Second, existing data from the literature were integrated with the present data in order to identify a general quantitative relationship between anisotropic ductility and grain morphology in additively manufactured Ti-6Al-4V. This revealed that an exponential relationship exists between the anisotropic grain morphology and anisotropic elongation to failure in Ti-6Al-4V. In particular, this relationship shows that a prior-β grain aspect ratio (grain height to grain width) exceeding 6 results in significant anisotropy in elongation. Namely, the columnar grains dominate the fracture mechanics by furnishing significant damage accumulation paths for tension in the longitudinal direction, resulting in higher ductility in the build direction than that in the longitudinal direction. With respect to processing, it was shown that as-built CW-LPBF samples had nearly equiaxed grains while those made by P-LPBF had elongated columnar grains. This resulted in greater yield strength, ultimate tensile strength, and ductility in the CW-LPBF samples compared to P-LPBF samples.

Texture, Microstructure and Mechanical Properties of 6111 Aluminum Alloy Subject to Rolling Deformation

The mechanical properties, texture and microstructural evolution of a 6111 aluminum alloy during hot rolling and cold rolling deformation were systematically investigated in this article. The results show that cold rolling and hot rolling have significant effects on the tensile behaviors of the alloy. The shear texture and recrystallization texture mainly formed during the hot rolling deformation process, while the rolling texture mainly formed during the cold rolling deformation. The grain refinement mechanisms depend significantly on the rolling process. Movement of shear zone and recrystallization are the main grain refinement mechanisms during the hot rolling process, while dislocations tangling is the main grain refinement mechanism during the cold rolling process. The recrystallization textures and shear textures affect the anisotropy in elongation but the rolling textures affect significantly the anisotropy in yield strength.

Plastic anisotropy and deformation behavior of extruded Mg-Y sheets at elevated temperatures

The plastic anisotropy in terms of tensile mechanical property, Lankford coefficient (r), and microstructure evolution of as-extruded Mg-1Y (wt%) and Mg-5Y (wt%) sheets along the extrusion direction (ED), transverse direction (TD), and diagonal direction (DD) were investigated in detail at temperatures between 25℃ (RT) and 300℃. The sheets exhibited anisotropic deformation behavior at lower temperatures, and nearly isotropic for Mg-5Y at 300℃ in these three directions. For both sheets, the ultimate tensile strength anisotropy (UA) and elongation anisotropy (EA) was not sensitive to the temperature, while the yield strength anisotropy (YA) decreased significantly from 49.1% (Mg-1Y) and 40.2% (Mg-5Y) at RT to 7.2% and 2.7% at 300℃, respectively. The r values of Mg-1Y in all directions first increased from 0.66-1.4 (RT) to 0.81–1.98 (200℃) then decreased to 0.67–1.56 (300℃), while those of Mg-5Y decreased from 1.04-2.05 (RT) to 1.18–1.35 (300℃) with increasing temperature. Few twins were observed in Mg-5Y after tension at RT while large amounts of twins occurred in Mg-1Y. The huge reduction of twins and the weakened basal texture are believed to increase the r value from 0.66 (Mg-1Y) to 1.04 (Mg-5Y) at RT. At 300℃, dynamic recrystallized (DRX) grains appeared in Mg-1Y while only a few DRX grains showed up in the vicinity of grain boundaries in Mg-5Y, which may be closely related to grain boundary segregation of the yttrium atoms.

Comparison of annealing on microstructure and anisotropy of magnesium alloy AZ31 sheets processed by three different routes

Cold rolling and annealing treatment were applied to magnesium alloy AZ31 sheets fabricated by three processing routes: extrusion-rolling (EX), hot-rolling (HR) and twin-roll casting (TRC) in the present work to investigate the effect of annealing treatment on the microstructure evolution and mechanical anisotropy. The results showed that processing routes had a significant influence on the microstructure evolution and mechanical properties under same cold rolling and annealing conditions. The TRC sheet exhibited slight grain coarsening even when annealed up to 450°C, while the grain growth was obviously observed in HR sheet with increasing annealing temperature. The tensile tests at room temperature indicated that the mechanical anisotropy of EX sheet was insensitive to temperature, but sharply decreased in HR sheet at elevated temperature. The fracture elongation anisotropy of all three sheets decreased with increasing annealing temperature, especially in the TRC sheet.

Influence of Y and Nd on microstructure, texture and anisotropy of Mg–5Li–1Al alloy

Mg–5Li–1Al–0.5Nd/0.5Y alloys were prepared using a vacuum induction melting furnace. The microstructure and phase composition were investigated by optical microscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties of alloys were measured with tensile tester. The addition of rare earth element results in the formation of an Al–RE compound, such as Al2Nd and Al2Y, and it has a refining effect on the microstructure of the alloy. Dynamic recrystallization that happens during the rolling refines the grains of the alloy obviously. The addition of rare earth element activates the non-basal slip system, changes stacking fault energy of magnesium alloy, and weakens the basal texture because of PSN (particle stimulated nucleation) mechanism. The addition of Nd/Y enhances the strength anisotropy of the alloy, while it weakens the elongation anisotropy of the alloy.