Fine Columnar Grains Research Articles

The Effect of Solution Aging on the Microstructure and Mechanical Properties of a Laser Powder Bed Fusion-Formed WC-Reinforced 18Ni300 Composite

The addition of WC particles has the potential to improve the properties of 18Ni300 alloy, but the effect of heat treatment on the microstructure and mechanical properties of 18Ni300 matrix composites needs to be further investigated. In this work, WC-reinforced 18Ni300 composites were fabricated using laser powder bed fusion (LPBF). The composites were made into solutions at 846 °C for 51 min, followed by aging at 388 °C for 300 min. The microstructural evolution and compressive properties of the composites before and after heat treatment were systematically studied. The results indicate that the microstructures of the composites consist of heterogeneous cellular and fine columnar grains. As the WC content increases, the primary phase in the LPBF-formed samples gradually shifts from α-Fe martensite to γ-Fe austenite. After heat treatment, the primary phase transforms to α-Fe with only a small residual amount of γ-Fe. The microstructure becomes more uniform, featuring a significant reduction in grain size. Many precipitated phases can be found in the intergranular, accompanied by an increase in the thickness of diffusion layers. The WC content in the composite material is positively correlated with its hardness and compressive strength. As the WC reinforcement content increases from 5% to 20%, the yield strength and compressive strength of the LPBF-formed composites increase to 1042.5 MPa and 2900.7 MPa, respectively, while the compressive elongation decreases from 64% to 43%. After heat treatment, the yield strength of the composites significantly increases to 2356.8 MPa, with a slight increase in the compressive strength to 2939.7 MPa. However, the elongation decreases from 32.5% to 22%.

Evolution of cracks in laser powder bed fused AA2024 and its processing parameter dependence

Hot cracking is one of the most hideous issues in the fabrication of high-strength aluminum alloys via laser powder bed fusion (LPBF). This study investigated the evolution of hot cracking in LPBFed AA2024 and explored its processing parameter dependence. Results showed that most cracks distribute along continuous eutectic phases residing at grain boundaries. At the last stage of solidification, the eutectic composition with low melting point exists as a liquid film, which can be easily ruptured under stress caused by thermal contraction. This leads to the formation of cracks along grain boundaries. This cracking process is also related to the misorientation angle of grains, where higher angle results in more stable liquid films. Furthermore, increasing the laser power transforms the grain structure from fine columnar grains to coarse columnar grains, which eventually transform to a mixture of columnar and equiaxed grains. This grain structure transition results in the decrease followed by increase of critical stress for the rupture of liquid film. On the other hand, decreasing the scanning speed increases the eutectic phase content, which could enhance the permeability of mushy zone and thus reduce the cracking susceptibility. These findings could provide guidance for the fabrication of crack-free high-strength aluminum alloys via LPBF.

Microstructure characteristics and failure mechanisms of hybrid manufacturing of FGH96 and IC10 bimetal component using laser directed energy deposition

Hybrid manufacturing technology combines the cost advantage of traditional manufacturing with the flexibility benefit of additive manufacturing, thus providing an effective solution for creating gradient components. In this work, we deposit IC10 alloy powders on the FGH96 hot isostatic pressing substrates to prepare nickel-based gradient materials. A detailed analysis of the microstructural evolution in different regions is provided. The influence of thermal cycles on the heat-affected zone (HAZ) causes the γ′ phase to transform from a multimodal structure formed by hot isostatic pressing to a uniform spherical shape. The grain morphology changes from the ultrafine equiaxed grains of the substrate to fine equiaxed grains in the HAZ, then transforms into fine columnar grains in the gradient region, and finally changes to coarse columnar grains in the deposited zone. Moreover, the influence of grain orientation on the ability of epitaxial growth is investigated, and a grain orientation-dependent growth model is developed to predict the growth direction of columnar grains in the deposited layer. Such a non-uniform microstructure results in mechanical performance, including hardness and tensile strength, with distinctive heterogeneity along the building direction. The hybrid manufactured sample with higher yield strength than the pure alloys was primarily influenced by factors such as grain sizes, the sizes and distributions of the γ′ phases, as well as dislocation densities. However, due to the liquation crack in HAZ, the tensile elongation of the hybrid manufactured sample is lower than the pure alloy.

MICROSTRUCTURAL EVOLUTION AND ANTI-CORROSION CHARACTERISTICS OF AS-CAST AND LPBF PRINTED INCONEL PLATES IN SEAWATER ENVIRONMENT

Inconel 718 (IN 718) belongs to the category of nickel-based superalloys with outstanding mechanical characteristics such as high strength, better corrosion resistance, greater hardness, fatigue and wear resistance. This alloy is mostly implemented in manufacturing the components of aeroengines, nuclear reactors, space shuttles, pressurized boilers and so on. In most cases, the parts made from this alloy work in severe aggressive environments. A prolonged exposure of this alloy in such environments will pave the way for corrosion phenomenon which will minimize the service life of the components. It is reported that the parts made via additive manufacturing will exhibit better mechanical characteristics than the casted and forged parts. This work is aimed to investigate the anti-corrosion characteristics of both as-cast and LPBF printed IN 718 samples at various time intervals in the seawater environment. By means of FESEM micrographs, the microstructural evolution in both as-cast and LPBF printed IN 718 samples was analyzed. The anti-corrosion characteristics of both samples were investigated in the environment containing 3.5 wt.% NaCl (seawater) in terms of EIS and potentiodynamic polarization curves along with the corroded morphology. The results showed that the LPBF printed IN 718 samples exhibit fine cellular and columnar grains decorated with the NbC precipitates along their boundaries, whereas the casted samples have larger and coarser grains with uneven segregation of NbC precipitates. From the Tafel and EIS (Nyquist and Bode) plots, the LPBF IN 718 sample showed greater corrosion resistance in terms of current density and polarization resistance values. In particular, the 15 h LPBF sample has a strong, compact passive film formed on it. This compact passive film paved the way for this sample to exhibit lower current density (3.03 × 10[Formula: see text] A/cm2) and higher polarization resistance (3678 Ω · cm2) when compared with the LPBF and cast samples at other intervals.

Effect of laser energy density on surface morphology, microstructure and mechanical behaviour of direct metal laser melted 17-4 PH stainless steel

Abstract The surface and microstructural characteristics of 3D printed parts play a significant role under mechanical loading. The authors have explored the effect of laser energy densities on the surface morphology, microstructure and mechanical behaviour of 17-4 precipitation hardened stainless steel fabricated under the direct metal laser melting technique. The considered processing parameters were laser energy density and its technical parameters: laser power, layer thickness, hatch spacing and scanning speed. The mechanical and metallurgical properties of the as-printed samples appeared better than the wrought counterpart due to the higher densification level (99.74 %) induced by the rotating scanning strategy. X‐ray diffraction revealed the presence of both the martensitic α phase and austenitic γ phase in the as-printed sample. There is no significant anisotropy in the mechanical behaviour as the build direction has a random texture with a fine columnar grain structure. The high laser energy density with low layer thickness results in an excellent surface finish. The tensile strength (1180 MPa) and the elongation for the as-printed sample (45.0 %) were considerably more significant than that for the wrought sample (1160 MPa and 26.0 %), which is attributed to the combination of low and high-angle boundaries, as confirmed by the electron backscatter diffraction results.

Deformation effect of melt pool boundaries on the mechanical property anisotropy in the SLM AlSi10Mg

The effect of microstructure characteristic on the anisotropy of mechanical properties has been studied for a selective laser melt (SLM) AlSi10Mg material. The cell structure and fine grains at the melt pool boundaries (MPBs) are gradually eliminated by different heat treatment processes. Althought the cell structure of MPB has been eliminated, it is found that the mechanical properties of the transverse specimen and longitudinal specimen are still different due to the heterogeneity of grain. In the process of plastic deformation, when the tensile direction perpendicular to the MPB, the deformation incompatibility between fine grains and columnar grains lead to the excessive stress concentration and rapid fracture along the zone boundary. The change of loading direction can alleviate strain localization and improve the uniform deformation ability of the sample. The heterostructure of SLM AlSi10Mg is related to the remelting and resolidification of MPBs. The results provide guidance for the design of SLM AlSi10Mg material with better mechanical properties.

Effect of line energy on microstructures and mechanical properties of Co-Cr-Mo alloy single-track fabricated by DED method

The additive material built-up by the directed energy deposition (DED) method is affected by the melting and solidification reaction with the substrate material. This work investigated the effect of line energy on microstructures and mechanical properties of Co-Cr-Mo alloy single-track fabricated by the DED method. The line energy is a function of scanning speed and laser power, which are the main process parameters for the DED method. The Co-Cr-Mo alloy single-track with low line energy has a columnar grain microstructure with a strong (0 0 1)γ texture parallel to the build direction. As the line energy increased, the single-tracks had mixed microstructure, including fine columnar grains and coarse equiaxed grains with random texture. In addition, the secondary dendrite arm spacing of the single-track depends on the line energy due to the rapid cooling rate. The ε-Co phase in Co-Cr-Mo alloy single-track increased with increasing line energy throughout the isothermal γ → ε martensitic transformation. The effect of the ε-Co phase on the mechanical properties of the Co-Cr-Mo alloy single-track is insignificant. The diffusion of alloying elements from the substrate material throughout the fusion zone occurred and influenced the mechanical properties of the Co-Cr-Mo alloy single-track. The elastic modulus and nano hardness decreased with increasing line energy because of the diffusion of alloying elements from the substrate material.

Additive manufacturing of Ti-6Al-4V alloy by micro-laser metal wire deposition with pulsed wave emission: processability and microstructure formation

In this work, the micro-laser metal wire deposition (μLMWD) with ms-pulsed wave emission and low duty cycles was utilized to build the Ti-6Al-4V thin walls. The work first investigated the influence of the process parameters on single track stability and geometry. With the developed processing conditions thin walls with multiple layers were produced. The μLMWD produced thin walls were characterized by fine grain size expected to be due to the columnar to equiaxed transition (CET) in the produced wall. Fine columnar grains formed in the bottom region of wall due to the restriction of melt pool size and large cooling speed, while equiaxed grain formation and further refinement were achieved in the middle region, attributed to the intermittent stirring force that broke dendritic arms and increased nucleation events before solid–liquid interface. From the bottom to top region microstructures transferred from acicular α′ to short α lamella constituting basketweave structure, and the periodic heating and cooling generating by pulsed laser reduced the acicular α′ at higher cooling rate and decreased α size. The forming of equiaxed grain and fine grain and microstructure increased the wall microhardness.

Anisotropy optimization of HDDR magnetic powders by precursor alloy annealing

The anisotropy of hydrogenation–disproportionation–desorption–recombination (HDDR) method to form Nd2Fe14B powders was effectively improved by annealing the strip casting (SC) alloy precursors at 1080 °C. According to the analysis of the evolution of microstructure, the excellent anisotropy was attributed to the nearly consistent orientation of the nanoscale Nd2Fe14B grains in the HDDR magnetic powders, which perfectly inherited that of the coarse grains in the treated SC alloy flakes. In contrast, for the untreated specimen, more nanoscale clusters of different orientations were generated after smashing and HDDR treatment of fine columnar Nd2Fe14B grains with different orientations in the original SC alloy, severely affecting the anisotropy of the magnetic powders. This study provides new insights into the development of high-anisotropy and high-performance Nd-Fe-B magnets.

Finite element analysis and experimental investigation of moving heat source model for GMAW deposited mild steel weld bead

An investigation has been done to identify the heat source model suitable for numerical modeling of the Gas Metal arc Welding (GMAW) welding process. In the present investigation, a numerical model was constructed to simulate the GMAW welding process through transient thermal analysis for different thermal heat source models for weld deposition of Mild steel considering semi-cylindrical weld bead geometry. The Gaussian heat source with radial coordinate system and double ellipsoidal thermal heat source have been considered to develop a Finite Element Analysis (FEA) model. Validation of numerical analysis results has been confirmed through experimental investigation. Numerical modeling confirms the utilization of both heat sources, i.e. Gaussian and Double ellipsoidal for the prediction of the weld bead deposition profile. However, the numerical modeling developed using a double ellipsoidal heat source has more resembles experimental investigation due to the utilization of bead profile data. However, the Gaussian heat source is found to be suitable in the case of the unavailability of experimental data. The experimental studies show a variation in the weld bead geometry, along its welding direction due to multiple environmental factors. The microstructural investigation also shows the development of a fine columnar grain structure at the welding bead & weld penetration zone, and the grain structure became coarser at the Heat Affected Zone (HAZ).

Effect of High Laser Energy Density on Selective Laser Melted 316L Stainless Steel: Analysis on Metallurgical and Mechanical Properties and Comparison with Wrought 316L Stainless Steel.

The austenitic 316L stainless steel (SS) is used extensively for marine applications as well as in construction, processing, and petrochemical industries due to its outstanding corrosion resistance properties. This study investigates the density, microhardness, and microstructural development of 316L SS samples fabricated by selective laser melting (SLM) under high laser energy densities. The selective laser melted (SLMed) specimens were fabricated under high laser energy densities (500, 400, and 333.33 J/mm3) and their metallurgical and mechanical properties were compared with the wrought specimen. SLMed 316L SS showed excellent printability, thereby enabling the fabrication of parts near full density. The porosity content present in the SLMed specimens was determined by both the image analysis method and Archimedes method. SLMed 316L specimens fabricated by the SLM process allowed observation of a microhardness of 253 HV1.0 and achieved relative density up to 98.022%. Microstructural analysis using optical microscopy and phase composition analysis by X-ray diffraction (XRD) has been performed. Residual stresses were observed using the XRD method, and compressive stress (-68.9 MPa) was noticed in the as-printed specimen along the surface of the build direction. The microstructure of the as-built SLMed specimens consisted of a single-phase face-centered cubic solid solution with fine cellular and columnar grains along the build direction. The SLMed specimens seemed to yield better results than the wrought counterpart. IRB approval and Clinical Trial Registration Number are not applicable for this current work.

The effect of post-processing heat treatment on the microstructure, residual stress and mechanical properties of selective laser melted 316L stainless steel

Additively manufactured 316L austenitic stainless steel typically displays a hierarchical microstructure consisting of fine columnar grains, cellular dislocation tangles and nano-inclusions, which provides a combination of exceptional strength and ductility. However, the rapidly solidified microstructure often contains significant residual stress and various post-processing heat treatments are generally used to relieve the residual stress and to alter the microstructure and properties. In this work, a 316L austenitic stainless steel additively manufactured by a laser-based powder bed fusion process (selective laser melting, SLM) was for the first time subjected to various heat treatments to systematically study the evolution of residual stress, microstructure and mechanical properties. Significant compressive residual stress was revealed in the core volume of the as-built condition, whilst moderate to full stress relief of 24%, 65% and ~90% was achieved upon 2 h post-processing annealing at 400 and 650 °C and solution annealing at 1100 °C for 5 min, respectively. The extent of stress-relieving is closely associated with the evolution of substructure (i.e., dislocation tangles), which also affects the yield strength. Marked alteration from the as-built metastable microstructure was seen except for the low-temperature treatment at 400 °C. This includes the precipitation of embrittling σ phase or its precursors at 650–800 °C which results in a reduction in ductility. Unlike conventional wrought 316L, no carbide formation was seen in the treatment temperature regime. Recrystallization of columnar grains and coarsening of nano-inclusions took place over time upon solution annealing at 1100 °C, causing softening and unexpected reductions in ductility. This work led to the establishment of heat treatment-property relationships and corresponding microstructural changes, which are of great significance for the component design and structural application of SLM 316L.

Tensile strain induced texture evolution in a Ni–Mo alloy with extremely fine nanotwinned columnar grains

In the present paper, plastic deformation in an electrodeposited nanotwinned columnar grained Ni–Mo film with an extremely fine columnar grain size of 8 ± 1.7 nm and a twin thickness of 1.3 ± 0.5 nm was investigated via uniaxial micro-tensile tests at room temperature. We found significant detwinning and an evident texture evolution from a randomly-oriented in-plane fiber texture to a highly-oriented out-of-plane texture in the alloy upon tensile straining when tensile direction was oriented in parallel to the twinning plane. Interface energy minimization characterized by the substitution of high angle grain boundaries by low angle grain boundaries and incoherent twin boundaries constitutes the driving force of the texture evolution. Tensile plastic deformation can be attributed to the activity of threading dislocations, which not only contributes to a high yield strength of 2.11 GPa, but also results in in-plane lattice rotation with noticeable deformability.

Residual stresses and heat treatments of Inconel 718 parts manufactured via metal laser beam powder bed fusion: an overview

Additive manufacturing (AM) is a unique manufacturing process that disrupted completely the way which components are made, since this process is capable of producing complex parts layer after layer. As a matter of fact, one of its distinct technologies is metal laser beam powder bed fusion (mLB-PBF), also known as selective laser melting (SLM) or direct metal laser sintering (DMLS), which creates metallic parts with the aid of a high-energy laser beam. One of the most employed superalloys in this technology is the Inconel 718 (IN718), a precipitation-hardened alloy that is used in the marine, nuclear power plants, gas turbines, and aerospace field due to its capacity of retaining good mechanical properties at high temperatures. The research novelty of this review manuscript is the compilation of all kinds of information from the last 15 years of investigation about IN718 parts produced via mLB-PBF, namely, information related to distinct heat treatments and the influence they have in increasing mechanical properties of the manufactured components, as well as reducing residual stresses (RS) and part porosity. Throughout the review, it can be seen that the expected microstructure in the as-built state is characterized by fine columnar grains and a saturated γ matrix with the presence of the Laves phase and carbides. However, distinct heat treatments can be employed which lead to the dissolution of the undesired phases (Laves and carbides), the precipitation of the strengthening phases (γ’ and γ”), and the porosity decrease. Furthermore, it was also shown that heat treatments as well as optimized process parameters can be held accountable for lowering the RS of the IN718 manufactured parts. Nevertheless, there are still some problems to overcome, namely, the mechanical properties variability when subjecting IN718 powder to different process parameters. Moreover, the RS evolution under different heat treatments needs to be further investigated.

Laser powder bed fusion of a superelastic Cu-Al-Mn shape memory alloy

Dense and crack-free specimens of the shape memory alloy Cu71.6Al17Mn11.4 (at.%) were produced via laser powder bed fusion across a wide range of process parameters. The microstructure, viz. grain size, can be directly tailored within the process and with it the transformation temperatures (TTs) shifted to higher values by raising the energy input. The microstructure, and the superelastic behavior of additively manufactured samples were assessed by a detailed comparison with induction melted material. The precipitation of the α phase, which inhibit the martensitic transformation, were not observed in the additively manufactured samples owing to the high intrinsic cooling rates during the fabrication process. Fine columnar grains with a strong [001]-texture along the building direction lead to an enhanced yield strength compared to the coarse-grained cast samples. A maximum recoverable strain of 2.86% was observed after 5% compressive loading. The first results of our approach imply that laser powder bed fusion is a promising technique to directly produce individually designed Cu-Al-Mn shape memory parts with a pronounced superelasticity at room temperature.

Critical factor triggering grain boundary cracking in non-weldable superalloy Alloy713ELC fabricated with selective electron beam melting

Grain boundary cracking in non-weldable superalloy fabricated with selective electron beam melting is affected by the interaction of multiple factors including mechanical and compositional effects. In this study, we construct process maps in a wide range high-dimensional parameter space for the non-weldable superalloy Alloy713ELC through employing a machine learning approach, and we could fabricate many cracked and crack-free samples under the optimized conditions by excluding the extrinsic effect of process defects on cracking. Comparing between cracked and crack-free samples reveals that the samples with fine columnar grains can be cracked while those with coarse columnar grains can be crack-free, and that the cracking propensity in the optimized samples within a process window with scan speed ≤ 800 mm/s can be ranked by using a quasi-total plastic strain index (QTPSI), which is calculated via thermo-mechanical analysis. The total plastic strain level is a critical cracking factor and a larger scan speed tends to elevate the total plastic strain level, exhibiting a larger deviation beyond the QTPSI. Besides, the non-weldability in Alloy713ELC significantly attributes to its thermal expansion effect, which correlates to the large Al content. This thermal expansion effect combined with the liquation effect and the strain-age cracking effect reveals the intrinsic cause of non-weldability in Alloy713ELC.

Microstructure and interfacial metallurgical bonding of 1Cr17Ni2/carbon steel extreme high-speed laser cladding coating.

The extreme high-speed laser cladding (EHLA) was employed to fabricate a 1Cr17Ni2 coating. The solidification behavior, phase transformation, and interfacial metallurgical bonding of the coating were systematically investigated. The results showed that the major phase transformation during solidification was liquid to γ-Fe. The large temperature gradient of melting pool and slow grow rate of γ-Fe grain contributed to the fine columnar prior austenite grain (PAG) in coating. The largest thermal conductivity of [0 0 1] crystal direction determined the preferential [0 0 1] orientation of PAG perpendicular to the liquid-solid interface. A thin γ-Fe layer (approximately 5 μm) was observed between coating and substrate. The Bain relationship between interfacial γ-Fe layer and substrate and the K-S relationship between interfacial γ-Fe layer and coating contributed to the reliable metallurgical bonding between coating and substrate. The shear test revealed the high shear strength (approximately 92% of that of substrate) and weaker plastic deformation ability of the interface.Graphical abstract The interfacial γ-Fe layer effectively combined the coating and substrate via K-S and Bain crystallographic relationship.

Laser Powder Bed Fusion of Pure Tungsten: Effects of Process Parameters on Morphology, Densification, Microstructure

Tungsten has been widely used in many industrial fields due to its excellent properties. However, owing to its characteristics of inherent brittleness at room temperature and high melting point, it is difficult to prepare tungsten parts with high complexity via traditional methods. In the present work, tungsten samples were prepared by laser powder bed fusion. The influence of each process parameter including laser power, scanning speed, and hatch spacing on the surface morphology, densification, and microstructure of tungsten samples was systematically investigated. The results showed that the use of the appropriate parameters, especially high laser power, can effectively improve the surface quality and obtain a dense surface. The tungsten samples with a relative density of 98.31% were obtained with optimized parameter combinations: a laser power of 300 W, scanning speed of 400 mm/s, and hatch spacing of 0.08 mm. Compared with scanning speed and hatch spacing, the laser power had a more obvious influence on the relative density. Additionally, for the grain morphology by microstructure inspection, elongated curved grains gradually transformed into fine straight columnar grains as the scanning speed increased. The hatch spacing would change the grain morphology slightly but had no significant effect on the grain size.

Experimental evaluation of direct current magnetron sputtered and high-power impulse magnetron sputtered Cr coatings on SiC for light water reactor applications

Two types of physical vapor deposition Cr coatings were deposited on chemical vapor deposited SiC coupons using conventional direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) to mitigate the corrosion of SiC, an advanced fuel and structural material in light water nuclear reactor cores. Coating microstructure was characterized using scanning electron microscopy and scanning transmission election microscopy. X-ray diffraction analysis was conducted for phase identification and qualitative analysis of residual stresses. The mechanical integrity of the coatings was evaluated using scratch testing, micro-indentation, and nano-indentation tests. The microstructure of the DCMS coating consisted of fine columnar grains with nanoscale intercolumnar channels, while the HiPIMS microstructure was denser and free of any columnar defects. The DCMS coating showed a small tensile residual stress, while the HiPIMS coating was under compressive stress. Both types of coatings showed good mechanical integrity in terms of ductility and adhesion to the substrate. Corrosion performance of the coatings was assessed with a 30-day high temperature water autoclave test. Both types of coatings formed a protective Cr2O3 surface layer 20-30 nm thick during the autoclave test. In the DCMS coating, the columnar defects provided permeation pathways for water penetration resulting in oxide formation in the intercolumnar regions in the interior of the coating. Overall, both types of Cr coatings offer promise for the mitigation of hydrothermal corrosion of SiC in light water reactor operating environments.

Wire-arc additive manufacturing of AZ31 magnesium alloy fabricated by cold metal transfer heat source: Processing, microstructure, and mechanical behavior

The modified cold metal transfer (CMT) heat sources by adjusting the characteristic processing parameters were conducted in wire-arc additive manufacturing (WAAM) of AZ31 magnesium alloy for thin-wall component. The processing, microstructure, and mechanical behaviour were investigated. The CMT characteristic deposited a wide and shallow weld bead coupled with good wettability and low equivalent heat input was selected for CMT-WAAM process. The microstructure of thin-wall component showed obvious layer characteristics, which consisted of the deposited layers with fine columnar dendrite grains and the HAZ interlayers with coarse equiaxed grains and some pores. The thin-wall component exhibited anisotropic tensile properties with lower yield strength, higher elongation, and higher ultimate tensile strength in the deposition direction than in the build direction. CMT-WAAM component of AZ31 magnesium alloy has an accepted mechanical property compared with the as-forged and as-cast components. To improve the component strength, minimizing the softening effect of the HAZ interlayers by preventing grain coarsening and suppressing porosity is essential.