Fig 5 - uploaded by Gerhard Leichtfried
Content may be subject to copyright.
Electron backscatter diffraction inverse pole figure (EBSD-IPF) grain orientation maps in building direction of the as-built specimens of (a) RAW-2024; (b) RAW-2024 with higher magnification; and (c) ND-2024. The IPF color code for the EBSD-IPF orientation maps is shown in the lower right corner. The calculated {001}, {111} and {110} pole figures and the {001}, {101}, {111} IPFs of the RAW-2024 and ND-2024 specimens are shown in (h) and (i), respectively. The corresponding color scale in (g) indicates the relative intensity of the diffraction peaks. EBSD kernel average misorientation (KAM) maps of (d) RAW-2024, (e) RAW-2024 with higher magnification and (f) ND-2024 were retrieved from the EBSD-IPF orientation maps in (a), (b) and (c). The color scale, representing the misorientation angle values in degrees, is illustrated at the lower right corner (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).
Source publication
The 2024 aluminum alloy (Al-Cu-Mg) is widely used in aerospace; however, due to its solidification-cracking tendency, its processability using laser powder bed fusion (LPBF) remains a critical issue. The addition of 2 wt% CaB6 nanoparticles induces a columnar-to-equiaxed transition (CET), resulting in an immediate improvement in LPBF processability...
Contexts in source publication
Context 1
... EBSD inverse pole figure (IPF) maps show the crystallographic orientation of the α-Al grains, in a cross-section parallel to the building direction of both alloys in the as-built condition (Fig. ...
Context 2
... RAW-2024 specimen has a predominantly elongated columnar grain structure, with a grain width of 5-30 µm and a grain length of 80-150 µm ( Fig. 5a and b). Its corresponding IPF and pole figure (PF) (Fig. 5h) indicate < 001 > fiber-texture parallel to the building direction. Solidification cracks, which are intergranular and extend over the entire length of the columnar grain, are also apparent. In contrast, an equiaxed, crack-free microstructure, with an average grain size of 0.91 ± ...
Context 3
... RAW-2024 specimen has a predominantly elongated columnar grain structure, with a grain width of 5-30 µm and a grain length of 80-150 µm ( Fig. 5a and b). Its corresponding IPF and pole figure (PF) (Fig. 5h) indicate < 001 > fiber-texture parallel to the building direction. Solidification cracks, which are intergranular and extend over the entire length of the columnar grain, are also apparent. In contrast, an equiaxed, crack-free microstructure, with an average grain size of 0.91 ± 0.32 µm is identified for the ND-2024 alloy (Fig. 5c). ...
Context 4
... figure (PF) (Fig. 5h) indicate < 001 > fiber-texture parallel to the building direction. Solidification cracks, which are intergranular and extend over the entire length of the columnar grain, are also apparent. In contrast, an equiaxed, crack-free microstructure, with an average grain size of 0.91 ± 0.32 µm is identified for the ND-2024 alloy (Fig. 5c). The IPF colors are randomly distributed, which indicates a textureless alloy (Fig. 5c). The KAM distribution maps of both alloys are shown in Fig. 5d, e and f. Misorientation values in the vicinity of grain boundaries are ~2°, whereas inside the grain they are ...
Context 5
... Solidification cracks, which are intergranular and extend over the entire length of the columnar grain, are also apparent. In contrast, an equiaxed, crack-free microstructure, with an average grain size of 0.91 ± 0.32 µm is identified for the ND-2024 alloy (Fig. 5c). The IPF colors are randomly distributed, which indicates a textureless alloy (Fig. 5c). The KAM distribution maps of both alloys are shown in Fig. 5d, e and f. Misorientation values in the vicinity of grain boundaries are ~2°, whereas inside the grain they are ...
Context 6
... the entire length of the columnar grain, are also apparent. In contrast, an equiaxed, crack-free microstructure, with an average grain size of 0.91 ± 0.32 µm is identified for the ND-2024 alloy (Fig. 5c). The IPF colors are randomly distributed, which indicates a textureless alloy (Fig. 5c). The KAM distribution maps of both alloys are shown in Fig. 5d, e and f. Misorientation values in the vicinity of grain boundaries are ~2°, whereas inside the grain they are ...
Citations
... Laser powder bed fusion (LPBF), the most widely used additive manufacturing technology for metals and alloys, uses a high-energy laser to fuse powder particles layer by layer [1]. The extremely high cooling rate of up to 10 8 K/s occurring in this process [2] typically induces martensite formation in Ti-6Al-4V, the most commonly used Ti alloy in LPBF [3]. ...
This work studied the microstructure and mechanical properties of Ti-6Al-4V in situ alloyed with 3 wt% Cr by laser powder bed fusion (LPBF). Specimens with a relative density of 99.14 ± 0.11% were produced, showing keyhole and lack of fusion pores. Due to incomplete mixing of the components during melting, chemical inhomogeneities were observed in the solidified material. The addition of Cr promoted thermal supercooling during solidification and induced a reduction in the primary β grain size in the longitudinal direction and a weakening of the otherwise strong ⟨100⟩β texture, both typical issues for Ti-6Al-4V produced by LPBF. The primary β at first transformed martensitically to α’, but by preheating the substrate plate to 500 °C and cyclically reheating the material by melting subsequent layers, in situ martensite decomposition was achieved, resulting in a fine lamellar α + β microstructure. In addition, the B19 phase was detected in the β matrix, presumably caused by Fe impurities in the Cr powder feedstock. Specimens exhibited a hardness of 402 ± 18 HV10, and an excellent ultimate tensile strength of 1450 ± 22 MPa at an elongation at break of 4.5 ± 0.2%.
... Adding ceramic nanoparticles is an effective way to refine the grain structure, eliminating hot cracking in L-PBF-processed aluminum alloys [17,27,28]. Primarily, borides are effective grain refiners, improving the printability of aluminum alloys [29]. ...
... For structural applications in aerospace and automotive applications, other hardenable alloys, such as the 2xxx, 6xxx and 7xxx series, are usually preferred. However, the wide range of solidification temperatures, high solidification shrinkage and thermal contraction of these alloys, and high energy density needed for processing by SLM cause these alloys to present some problems when processed by SLM, such as hot cracking [20][21][22][23][24], pores produced by the unstable processability of these alloys [25] and the partial evaporation of components [26]. A general view of the technology associated with Al alloy additive manufacturing can be seen in other research [13,17,22]. ...
... Dadbakhsh et al. [26] added 6 wt% zinc oxide to 6061 powder to eliminate hot cracks; although this addition drastically reduces the number of cracks, they are not completely eliminated. Conversely, the addition of 2 wt% CaB 6 [24] or 0.7 wt% Ti [29] to 2024 powder eliminates the hot cracks in 2024 SLM-produced pieces. Despite all these efforts to eliminate hot cracks and improve the mechanical properties of these SLM-produced alloys, there are no analyses to date of their effects on improving the fatigue properties of these materials. ...
... This is primarily due to the difficulties associated with the additive manufacturing of these alloys. The high-strength aluminium alloys have a relatively large solidification range, such as 135 K in Al 2024 alloy compared to 40 K in AlSi10Mg [5] and high susceptibility towards solidification cracking during additive manufacturing. The solidification cracking in additively manufactured Al alloys is usually observed along the grain boundaries of the columnar grains formed due to a high thermal gradient [6]. ...
... The current study investigates the addition of the GRA approach for achieving the CET in Al 2024 alloy due to its ability to improve the solidification cracking while simultaneously improving the mechanical properties, such as tensile strength and fracture toughness. The GRA used in the aluminium alloys are primarily of two types: solute atoms such as Sc [7], Zr [6], Ti [8], or composite particles such as TiB 2 [9], CaB 6 [5]. The selection of the right GRA depends on the composition of the aluminium alloys, for example, the Ti-rich particles such as TiH 2 has been successfully used as a grain refining agent for high-strength aluminium 7075 alloy [10]. ...
... In LPBF, AlSi10Mg is by far the most studied alloy due to its neareutectic composition and high castability (effect of Si), allowing to achieve very low porosity values. Notwithstanding this, an increasing number of works in the literature is focusing on other LPBF-processed Al alloys, such as AlSi12Mg [18], AlSi7Mg (A357) [19] and 2024 [20]. ...
... So far, the adaption of inoculation treatment has produced encouraging results in the AM of aluminum (Al) alloys [13][14][15][16][17]. Some of the inoculants (or grain refiners) developed in cast Al alloys, such as TiB 2 and hexaborides (e.g., LaB 6 , CeB 6, and CaB 6 ), have been successfully adopted in AM to refine Al alloys [14,15,[18][19][20]. In addition, new inoculants, such as the L1 2 -Al 3 X (X = Zr, Ti, Sc, Hf, or Ta) formers, have also been developed specifically for the rapid solidification conditions in AM [16,21,22]. ...
The present work aims to boost our understanding of factors governing the grain-refining efficiency of inoculation treatments by comparing the grain-refining efficiencies of two inoculators: Ti nanoparticles and LaB6 nanoparticles, in a 2024 Al alloy during additive manufacturing (AM). Experimental results obtained by scanning electron microscopy show that the LaB6 nanoparticle possessed almost no refining effect on the alloy, with the addition content ranging from 0.5 wt.% to 2 wt.%. Conversely, the Ti nanoparticle resulted in a more pronounced refinement and a fine, fully equiaxed microstructure at 1 wt.% Ti addition. Based on transmission electron microscopy analysis, the higher refining efficiency of Ti inoculation was ascribed to the incorporation of both Ti solute and the in situ-formed L12-Al3Ti nucleation particles. The former significantly increased the overall undercooling ahead of the growing Al grain, which ensured the activation of heterogeneous nucleation on the L12-Al3Ti nanoparticles, leading to grain refinement. This work highlights that despite the addition of nucleation particles, the incorporation of appropriate solutes to generate sufficient undercooling is the prerequisite for the activation of heterogenous nucleation in AM.
... As discussed above, the crystal structure of Al 3 (Sc,Zr) is similar to FCC aluminum. The lattice parameter of FCC aluminum is 4.049 A [61,62], while Al 3 (Sc 1Àx Zr x ) (L1 2 ) is reported to be proportional to x, ranging between 0.4092 nm for x ¼ 0.5 and 0.4103 nm for x ¼ 0 [63]. Hence, these intermetallics act as seeds for the growth of a multitude of aluminum crystals in the FGZ during solidification. ...
Additively manufactured Scalmalloy® using laser powder bed fusion (LPBF) has been showing increasing potential for industrial adoption. Its intended application in space, aerospace, and automotive industries requires extensive testing and characterization to produce parts with repeatable properties and safe operations. In the present paper, a thorough investigation of the association between small-scale (micro/nano-scale) and macro-scale (e.g., tensile) properties and microstructural features has been conducted. The prime novelty is the correlation of the small-scale hardness with the tensile properties, which is studied in both as-built and heat-treated conditions (325 °C/4 h) along parallel and perpendicular build directions of the samples. Advanced microstructural characterization including scanning and transmission electron microscopies (SEM/TEM), as well as electron backscatter diffraction (EBSD), was carried out on each condition to correlate microstructure and mechanical properties. While significant improvement in strength was found from as-built to heat-treated conditions, due to the precipitation of secondary Al3Sc and Al3(Sc, Zr), grain size or texture did not change considerably. The grain size analysis revealed a fine-grained zone (FGZ: mostly between 0.5 and 1 μm) next to the coarse-grained zone (CGZ: mostly between 2 and 15 μm). All samples show texture-free FGZ and textured CGZ with a predominance of crystal directions parallel to the building direction.
... However, the additive manufacturing of high-strength aluminium alloys, such as Al 2024, Al 7075 etc., is highly susceptible to hot cracking. This high susceptibility is usually attributed to the high thermal gradient inherent to additive manufacturing (in the order of 10 5 À 10 7 C/s [4]) and large solidification range of these alloys (135 K in Al 2024 alloy [5]). The high cracking susceptibility in these alloys can be mitigated by modifying the composition of the alloys. ...
The current study investigates the high-temperature deformation behaviour, and microstructural evolution of the laser powder bed fused, Ti modified Al 2024 alloy. The high-temperature performance was evaluated using a hot compression test performed in the temperature range of 200 – 350°C and strain rate range of 0.1 – 10 s-1. The flow behaviour at elevated temperatures at different strain rates can provide us insight into the high temperature application and can also be utilized for optimization of deformation-based post processing technique. The deformation-based post processing method utilizes work hardening to improve the mechanical properties and to reduce the inherent defect of additively manufactured parts, such as pores and lack of fusion. The optimal deformation conditions for these processes can be obtained from the processing map. The flow stress during different deformation conditions (strain, strain rate and temperature) was predicted using different phenomenological models such as Johnson-Cook (JC) model, strain compensated Arrhenius equation, and artificial neural network (ANN). The JC model was observed to be the least suited method in the current investigation, whereas the ANN method was observed to be best suited for predicting flow stress with an average absolute relative error of 0.5% and a correlation coefficient of 0.9998. Different deformation mechanisms such as dynamic recovery (DRV) and dynamic recrystallization (DRX) were investigated for different deformation conditions using empirical models, finite element analysis (FEA) and microstructural characterization using TEM, and EBSD. The primary DRX mechanism in the current study was observed to be continuous dynamic recrystallization or CDRX mechanism.
... The laser powder bed fusion process (LPBF) is one of the most promising metal additive manufacturing techniques that can bring tremendous opportunities for producing complex metallic components. A wide variety of industries, such as defense, aerospace, automotive, biomedical, etc., can derive great value from the unique advantages offered by the LPBF process, such as weight reduction due to design freedom and complexity [1,2]. The high-strength aluminium alloys have been used in a wide variety of applications, such as automotive, aerospace, machinery, defense, construction, etc., due to their lightweight, high strength-to-weight ratio, and high corrosion resistance. ...
... These alloys have a narrow solidification range compared to conventional aluminium alloys, which makes them very suitable for the LPBF process. For example, the AlSi10Mg has a narrow solidification range of 40 K compared to 135 K in Al 2024 alloy [2] and 80 K in Al 6061 alloy [4]. However, the Al -Si alloys have lower mechanical properties such as tensile and fatigue strength compared to the conventional highstrength aluminium alloy [5]. ...
... Both studies reported printing of crack-free and highly dense (density ≥ 99.5%) aluminium alloy. Mair et al. [2] have also explored the effect of 2% CaB 6 nanoparticle on mechanical properties and cracking behaviour of the laser powder bed fused Al 2024 alloy. They observed an ultrafine microstructure with an average grain size of 0.91 μm and a tensile strength of 391 MPa. ...
... For a wider diffusion of beam-based AM in the aeronautic industry, the design and development of high-strength Al alloys with good L-PBF processability is considered as one of the main challenges. Therefore, the addition of grain refiners [71,122,[166][167][168][169][170][171] and modification of alloy composition [172,173] have been used to overcome, or at least reduce, this disadvantage. ...
In aeronautics, additive manufacturing (AM) leads to specific benefits, mainly connected to topological optimization for weight reduction, the decrease in “buy-to-fly” ratio, and the operations of maintenance, repair, and overhaul. Al alloys processed by AM technologies are extensively investigated and play an increasing role in the production of aircraft structural parts. Based on the recent literature and research activity of the authors, this work examines advantages and drawbacks involved in the printing of Al alloys. Defects, microstructure, mechanical properties, development of new alloys, and postprocess treatments are described and critically discussed by focusing the attention on the effects of the specific alloy composition, AM process, and process parameters.
