Effect Of Building Direction Research Articles

Effects of Build Direction and Heat Treatment on the Defect Characterization and Fatigue Properties of Laser Powder Bed Fusion Ti6Al4V

Laser powder bed fusion (LPBF) is one of the high-precision additive manufacturing techniques for producing complex 3D components. It is well known that defects appear in additive-manufactured parts, and they deeply affect the fatigue properties; even heat treatment is performed after printing. In order to meet the safe-life design requirements of additive-manufactured aircraft structures, the effects of build direction and heat treatment on defects and fatigue properties need to be quantified. Hence, Ti6Al4V alloy samples with different build directions were designed and printed by LPBF. X-ray computed tomography was used to quantitatively analyze the defect size, the sphericity, and the defect orientation. And their effects on fatigue properties were studied. An extended effective defect size and a defect-based fatigue anisotropy evaluation process are proposed to qualify the effects of the defect size, sphericity, and defect orientation. It is shown that the build direction can affect the porosity distribution and maximum defect size, while the annealing treatment can cause the coalescence of small defects and higher porosity. The defect orientation exhibited a fluctuating trend of 0°–90°–0°–90°–0° as the volume increased. The elongated lack of fusion defects related to the build direction was the main crack source and could lead to fatigue anisotropy of LPBF Ti6Al4V.

Influence of Post-processing and Build Direction on the Wear Behaviour of Laser Powder Bed Fused Maraging Steel

Abstract Present study investigates the effect of post processing (heat treatment: solutionising at 850°C for 2 hr with aging at 490°C for 3 hr and cryogenic treatment at -196°C for 24 hr) and the effect of build direction (along the build direction (BD) and perpendicular to the build direction (PBD)) on the wear behavior of maraging steel fabricated by Laser powder bed fusion (LPBF). The results are also compared with conventional hot-forged samples. The pin on disc equipment was used to conduct the wear experiments with an EN31 steel disk as the counter body. Heat treatment decreased the wear rate of LPBF material by 54.78% and 83.84% in BD and PBD, respectively. This is due to the restriction of grain expansion by the Ni-based precipitants in age hardening treatment. The cryogenic treatment further decreased the wear rate of LPBF material by 87.84% and 90.9% in BD and PBD, respectively. This significant reduction can be attributed to the change of phase to martensite, as confirmed through microstructure and X-ray diffraction (XRD) analysis. Moreover, hot forged material also obtained a reduced wear rate after heat and cryogenic treatments. The highest wear resistance was found with the LPBF cryo-treated BD sample due to increased hardness from 388 HV to 640 HV. The worn surface of test samples was examined by using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), 3D profilometer, and XRD analysis. Oxidation wear, adhesive wear, and abrasive wear are the predominant wear mechanisms identified using SEM.

Surface Texture and Microstructural Characterization of Thin-Walled Ti6Al4V Part Processed Using Laser Powder Bed Fusion Technique: Effect of Build Direction

Abstract Objective: The current research investigates the surface texture and microstructural characterization of thin-walled Ti6Al4V along the build direction processed using laser powder bed fusion (LPBF) technology using an intra-comparison approach. Methodology: The two-dimensional and three-dimensional surface morphology and multi-scale surface roughness analysis of all Ti6Al4V samples were performed using an opto-digital microscope (with extended focus imaging coupled with high dynamic range imaging). Moreover, the scanning electron microscope, microhardness tester, and X-ray diffraction techniques were used to analyze the microstructural and microhardness values. Findings: (1) The lath thickness was relatively thicker in the LPBF-processed Ti6Al4V sample’s microstructure at central locations than in the top and bottom locations. (2) The areal surface roughness (Sa), Rk, and Sk values were relatively lower for the middle region than for the bottom and top regions of the thin-walled part, implying nonuniform surface topography along the build direction. (3) The middle region had a higher surface texture and texture amplitude symmetry periodicity than the top and bottom regions along the build direction. Value: Overall, the established methodology employed on the thin-walled Ti6Al4V part processed using LPBF technology enables the selection criteria of a suitable surface finishing process to achieve isotropic finish for practical industrial applications.

Effect of build direction on tension–tension low cycle fatigue behavior of polyamide 12 parts printed by Multi Jet fusion

The effects of build direction on the tensile properties, tension–tension low cycle fatigue behavior, and failure mechanism of polyamide 12 parts fabricated by Multi Jet Fusion have been investigated by addressing the roles of formed voids, sintering interfaces, and geometrical imperfections. Results indicate that the Young’s modulus of bulk material with vertical build direction is higher than that of bulk material with horizontal build direction due to the carbon black enhanced sintering interfaces. The tensile strength of the printed bulk material with horizontal and vertical build directions is comparable. It is found that the anisotropic tension–tension low cycle fatigue behavior for the bulk material is significant, while that for the re-entrant lattice structure is weak. The anisotropic fatigue strength of bulk material is derived from the anisotropic distribution of internal voids and sintering interfaces. The fatigue behavior of the re-entrant lattice structure is determined by the geometrical imperfections. The coalescence of the large voids or clusters of voids contributes to the crack initiation and propagation processes that lead to the failure of the bulk material. While the failure of re-entrant lattice structure is mainly determined by the intersection of strut junction rather than the void defect. This result provides the fatigue data that can be used for the structural design with Multi Jet Fusion polyamide 12 as well as reveals the effects of voids, sintering interfaces, and geometrical imperfections on the fatigue behavior of the printed parts.

Anisotropic tensile and fatigue properties of laser powder bed fusion Ti6Al4V under high temperature

Laser powder bed fusion (LPBF) Ti6Al4V has a great potential to be applied in high temperature vehicle structure. The columnar grains of the LPBF components grow along the build derection. Duo to the specific microstructures, the tensile and fatigue properties of LPBF components are anisotropic. So, the study on high temperature mechanical properties of LPBF Ti6Al4V need to be intestigated further. In this paper, high temperature tensile and fatigue samples were designed and manufactured by LPBF. Tensile tests were carried out at 350 °C, 450 °C and 550 °C. The effects of build direction and temperature on high temperature tensile properties were analyzed and compared. The fatigue tests were carried out at 450 °C, and the strain amplitude was in the range of ±1.5 %. The effects of build direction on the hysteresis loops and the fatigue fracture surfaces of fatigue samples were studied. The results showed that the build direction can affect the kinematic hardening significantly, but it has little effect on isotropic hardening.

Fatigue life affected by various defects of a selective laser-manufactured Titanium alloy

Manufacturing defects introduced by selective laser melting of powder beds typically lead to lower fatigue strength and a larger scatter in fatigue life compared to conventional manufacturing methods. In this paper, the effect of build direction on the low cycle fatigue performance of laser powder bed fused Ti6Al4V alloy was studied. Tests under room temperature were conducted and fractographies were examined to identify the crack initiation source. Results show that fatigue cracks in all samples initiated from sub-surface pores. The roundness of pores was proved to have an influence on fatigue life. Therefore, pores were assumed as existing cracks and its roundness was used to modify a fracture mechanic-based life prediction model.

Effect of build direction on the microstructure evolution and their mechanical properties using GTAW based wire arc additive manufacturing

In recent years, welding-based wire-arc additive manufacturing has been enthusiastically accepted to fabricate different parts of structural materials. In this study, a gas tungsten arc welding-based wire-arc additive manufacturing setup was developed, and a low-carbon alloy steel ER 70S-6 filler wire was used to fabricate a geometry. To analyze the mechanical properties of the printed alloy, room temperature tensile test, hardness and Charpy toughness tests are produced. The microstructure reveals a mostly homogeneous ferrite phase as a matrix and a small amount of pearlite phase at grain boundaries, except for the last build surface. The grain size was found to be doubled from middle build to last build surfaces. The tensile test results show isotropic tensile properties in both directions. The observed morphological features of the fractured surfaces in both directions were found to be in good agreement with their tensile test results, confirming a higher ductility across the build samples. Large scatter was observed in the hardness tests concerning the building direction.

Effects of build direction on thermal exposure and creep performance of SLM Ti6Al4V titanium alloy

With the development of typical additive manufacturing SLM, SLM Ti6Al4V has the potential to be used in high temperature vehicle structure. Mechanical properties after thermal exposure and creep performance of SLM Ti6Al4V and its build direction effects need to be studied in detail. In this paper, tensile and creep samples with 0°, 45° and 90° three build directions were designed and manufactured by SLM. Tensile tests were performed after 500 ℃ and 600 ℃ thermal exposure; And creep tests were carried out at 450 ℃ for all samples. The tensile properties after thermal exposure and the creep behaviors were studied and compared. The same size forged Ti6Al4V samples were manufactured and tested. It was shown that the yield strength (YS) and the ultimate tensile strength (UTS) of forged samples increased 24.23% and 16.70% after 500 ℃ exposure; while YS and UTS decreased after 600 ℃ exposure. The build direction had a significantly effect on the tensile ductility of SLM Ti6Al4V after thermal exposure. After 500 ℃ exposure, the tensile property of 90° sample was the best. Although the strength of 90° sample was slightly lower than that of 0° sample and 45° sample, the elongation was about 36.7% higher than that of 0° sample and 45° sample. After 600 ℃ exposure, 90° sample had both the highest strength and the elongation. Compared with forged samples, the SLM samples had longer creep ruptured time but lower ductility. For the SLM samples, 45° samples had best creep properties, while the properties of 0° samples were the worst. Fracture surfaces, failure modes and effects of build directions were investigated. Based on the features of SLM microstructures, two improved constitutive models were proposed and can be used to predict the anisotropic behavior of SLM material.

Effect of build direction on creep properties of TiAl4822 alloy additively manufactured by electron beam melting

Effect of build direction on creep properties of TiAl4822 alloy additively manufactured by electron beam melting

Effect of build direction and surface finish on wear behavior of AlSi10Mg alloy casted by laser powder bed fusion

In this research the Al10SiMg alloy were printed with different build direction (horizontal, vertical and inclined) using laser powder bed fusion (LPBF) method. The primary aim of this present study was to investigate the effect of build direction and surface finish condition on wear behavior of laser powder bed fusion printed AlSi10Mg alloy. The significance of printing direction and surface finish was revealed via wear behavior using pin-on-disc. According to the results the horizontally casted alloy shows lesser surface roughness. Subsequently the rough finished AlSi10Mg alloy on to the abrasive surface produced less wear loss. The fine finished alloy produced higher wear loss due to adhesion and erosion wear loss mechanism. Overall the horizontally casted cum rough finished AlSi10Mg alloy showed better wear resistance than other print direction and surface finish condition. The optical microscope and scanning electron microscope worn surface morphology confirmed the scar formation on fine finished AlSi10Mg alloy. These wear resistance improved AlSi10Mg alloy could be used as building material in aircraft and automobile applications where light weight and high wear resistance properties are required.

Effect of Building Direction on Anisotropy of Mechanical Properties of Gh4169 Alloy Fabricated by Laser Powder Bed Fusion

Effect of Building Direction on Anisotropy of Mechanical Properties of Gh4169 Alloy Fabricated by Laser Powder Bed Fusion

The effect of build direction and geometric optimization in laser powder bed fusion of Inconel 718 structures with internal channels

A laser powder bed fusion (LPBF) strategy was developed for manufacturing small channels with high dimensional accuracy in Inconel 718 structures. Particular attention was paid to surface characteristics such as equivalent diameter and shape factor. The inherent surface quality of external surfaces was optimized by a systematic variation of the LPBF contour parameters as well as the channel cross-section. The mean arithmetic roughness Sa was analysed for upskin, vertical and downskin surfaces with respect to the build platform. Simultaneously, the effect of the build direction on the quality of internal free-shaped surfaces was investigated on channels with diameters from 500 to 1000 µm and build orientations from the horizontal (0°) to vertical (90°). A significant improvement in dimensional accuracy was achieved by using an optimized droplet-shaped cross-section that is scaled as a function with the build inclination. An angular analysis of the surface roughness in different regions of the channels confirms that this modified cross-section reduces the fraction of channel regions that show a particularly high surface roughness due to inward melting. In combination with an optimized contour processing strategy, the modified channel resulted in the best properties for inclinations below 45°. The shape factor increased from 0.4 to almost 0.9, i.e., close to the ideally round shape.

The effect of build direction and heat treatment on atmospheric stress corrosion cracking of laser powder bed fusion 316L austenitic stainless steel

Austenitic stainless steels are susceptible to stress corrosion cracking (SCC) when exposed to chloride ions and tensile stresses. For laser powder bed fusion (LPBF) components, high residual tensile stresses exist from the large thermal gradients during solidification. While post fabrication heat treatments can relieve residual stresses, their effectiveness in improving SCC resistance of LPBF material is undetermined. The effects of different heat treatments (i.e. temperature and cooling method) and build orientations on SCC susceptibility of LPBF 316L were explored. Samples were exposed to MgCl 2 and maintained at 75 °C and 70% RH for the test duration. Cracks were highly branched and propagated perpendicularly to build direction even in the presence of an applied perpendicular 60 MPa stress. Vertical as-built specimens exhibited higher cracking densities than horizontal ones, due to higher surface residual stresses. SCC and corrosion favoured one side for horizontal specimens while the distribution was random for vertical specimens. After 750 °C (2 h, furnace cooled) heat treatment, SCC susceptibility reduced for vertical 316L but increased for horizontal 316L. This was attributed to competing effects: reduction in residual surface tensile stresses (beneficial) and loss of non-equilibrium microstructure (detrimental). Encapsulation to prevent oxidation during heat treatment negatively impacted SCC resistance of LPBF 316L, likely due to changes to surface oxide condition. No SCC was observed after 900 °C (0.5 h) heat treatments within the test duration, however, pitting corrosion persisted.

Effect of build direction on microstructure and mechanical properties of TiAl4822 alloy additively manufactured by electron beam melting

Effect of build direction on microstructure and mechanical properties of TiAl4822 alloy additively manufactured by electron beam melting

Effects of Build Direction on the Mechanical Properties of a Martensitic Stainless Steel Fabricated by Selective Laser Melting.

Mechanical properties and microstructure are investigated for a martensitic stainless steel (AISI 420) fabricated by selective laser melting (SLM) in three build directions. The tensile specimens built by SLM are classified into three groups. Group A is horizontally built in the thickness direction, Group B is horizontally built in the width direction, and Group C is vertically built in the length direction. The loading direction in tensile test is parallel to the build direction of Group C, but perpendicular to that of Groups A and B. Experimental results indicate build direction has significant effects on the residual stress, hardness, and tensile properties of SLM builds. Microstructural analyses indicate the as-fabricated SLM AISI 420 builds exhibit elongated cells and acicular structures which are composed of martensite and retained austenite phases growing along the build direction. Such anisotropy in the microstructure leads to anisotropic mechanical properties as Group C specimens (length direction) exhibit greater yield stress, ultimate tensile stress, and elongation than the specimens of Groups A (thickness direction) and B (width direction). The residual compressive stress in the gauge section also contributes to the superior tensile properties of Group C (length direction), as compared to Groups A (thickness direction) and B (width direction), which exhibit residual tensile stress in the gauge section.

Effects of build direction on tensile and creep properties of 316L stainless steel produced by selective laser melting

AbstractThe influence of build direction on the mechanical properties of SS316L produced by selective laser melting was investigated. The tensile tests were performed at room temperature for vertical and horizontal specimens. Large crater‐like voids were found, which are believed to be responsible for the reduced strength and premature failure of the vertical specimens, whereas the nano‐sized dimples were detected on the fracture surface of the horizontal specimens. Creep tests were also conducted at 650°C in the applied stress range of 149 to 226 MPa in vertical and horizontal directions. The vertical direction specimen showed better creep resistance. The micro‐cracks were delayed compared with the horizontal case. Optical micrographs of the tip of the creep rupture specimens along the cross‐sectional area were observed. The micro‐cracks located at grain boundaries. The grain shapes orientated in the applied stress direction for the vertical specimens, and perpendicular to the applied stress direction for the horizontal specimens.

Effect of Build Direction on Fatigue Performance of L-PBF 316L Stainless Steel

The microstructure and fatigue and tensile properties of 316L stainless steel fabricated via laser powder bed fusion (L-PBF) were investigated. Two 316L stainless steel specimens with different loading directions which are either perpendicular to or parallel to building direction were prepared by L-PBF process. The results of X-ray diffraction tomography showed that there was no significant difference in morphology and size/distribution of the defects in the HB and VB samples. Since long axis of columnar grains is generally parallel to the build direction, the fatigue crack encounters more grain boundaries in VB samples under cyclic loading, which led to enhanced fatigue resistance of VB samples compared with HB sample. In contrast to HB sample, the VB sample has a higher fatigue strength due to a higher resistance to localized plastic deformation under cyclic loading. The differences in fatigue properties of L-PBF 316L SS with different build directions were predominantly controlled by solidification microstructures.

Effect of build direction on the mechanical properties of Cu-10Sn parts by laser powder bed fusion

Effect of build direction on the mechanical properties of Cu-10Sn parts by laser powder bed fusion

Osteoblast compatibility of 3D printed Co–Cr–Mo alloys with different building direction

Three-dimensional (3D) metal printing is an attractive technique for fabricating biomedical devices. The microstructures and mechanical properties of the fabricated 3D metal printed products show anisotropy because the grains grow along the z-axis direction. However, the effects of different printing directions on the cytocompatibility of the products are unknown. In the present study, cobalt–chromium–molybdenum (Co–Cr–Mo) alloy cylinders were fabricated along the z-axis (vertical) and x-axis (horizontal), respectively, and the effect of build direction on the cytocompatibility was evaluated. The build direction of 3D printed Co–Cr–Mo alloy changed grain anisotropy; however, there was no statistical difference in grain size. The wettability, protein adsorption, cell attachment, and cell proliferation on the disks of vertical and horizontal products were similar to those on cast alloy; they were significantly lower than those of commercially pure titanium and tissue culture polystyrene. The build direction of 3D printed Co–Cr–Mo alloy does not affect osteoblast compatibility.

Effects of build direction and heat treatment on creep properties of Ni-base superalloy built up by additive manufacturing

The effects of build direction and heat treatment on the creep properties of Ni-base superalloy fabricated by additive manufacturing were examined at 650°C. The creep rupture lives and ductilities of materials produced by additive manufacturing were lower than those of conventionally wrought material. The horizontal-direction specimen exhibited inferior creep life and worse ductility than the vertical-direction specimen because of the direction of the interdendritic δ-phase precipitates, which were arrayed perpendicular to the stress axis in the former specimen. The morphology and a row of interdendritic δ-phase with incoherent interfaces were found to affect the materials' creep life and ductility.