Non-destructive characterization of internal surfaces in Laser Powder Bed Fused Inconel 718 channels prior and after post-treatment

The effect of surface finishing treatments for inner surfaces of additvely manufactured Inconel 718 specimens were analyzed using X-ray computed tomography (CT). The tube-shaped specimens were built by Laser Powder Bed Fusion (LPBF) at different build orientations and the inner surface characteristics such as roundness, equivalent diameter, 3D curvature distribution and distance to nominal surface as radial roughness for internal channels, both in the primary as built condition and after the subsequent treatment, were evaluated

Non-destructive characterization of internal surfaces in LPBF Inconel 718 channel

The presented non-destructive computed tomography analysis method provides a comprehensive quantitative characterization of internal surfaces before and after treatment and optimizes etching methods

Micromechanical behavior of annealed Ti-6Al-4V produced by Laser Powder Bed Fusion

the micromechanical behavior of an annealed ti-6al-4V material produced by laser Powder Bed Fusion was characterized by means of in-situ synchrotron X-ray diffraction during a tensile test. the lattice strain evolution was obtained parallel and transversal to the loading direction. the elastic constants were determined and compared with the conventionally manufactured alloy. in the plastic regime, a lower plastic anisotropy exhibited by the lattice planes was observed along the load axis (parallel to the building direction) than in the transverse direction. also, the load transfer from α to β phase was observed, increasing global ductility of the material. The material seems to accumulate a significant amount of intergranular strain in the transverse direction

Influence of manufacturing parameters on microstructure and subsurface residual stress in SLM Ti-6Al-4V

Using non-optimum combination manufacturing parameters in selective laser melting (SLM) may lead to reduction of quality of component: defects generation, distortion of geometry and even cracking. Usually, the optimization of parameters is performed at first with the goal to minimize porosity values, which are easy to measure. However, not only low porosity but also a stable microstructure and low residual stresses will help to achieve the desired mechanical behavior of the material and, thus, the component. In present work, we investigated cuboid-shaped Ti-6Al-4V samples produced with different manufacturing parameters. Residual stresses in subsurface region were investigated by synchrotron X-ray diffraction, which allows to penetrate around 100 µm into the surface and therefore to overcome the problem of high roughness of SLM components without additional sample preparation and resulting artifacts. Only tensile stresses were found along the building direction that can play critical role especially during cyclic loading. The pore shape and spatial distribution obtained by computed tomography varied for samples produced with the same Ev. Importantly, by adjusting specific process parameters it was possible to decrease residual stresses while at the same time obtaining a uniform α+β Ti microstructure and relatively low porosity

Exploring the Correlation between Subsurface Residual Stresses and Manufacturing Parameters in Laser Powder Bed Fused Ti-6Al-4V

Subsurface residual stresses (RS) were investigated in Ti-6Al-4V cuboid samples by means of X-ray synchrotron diffraction. The samples were manufactured by laser powder bed fusion (LPBF) applying different processing parameters, not commonly considered in open literature, in order to assess their influence on RS state. While investigating the effect of process parameters used for the calculation of volumetric energy density (such as laser velocity, laser power and hatch distance), we observed that an increase of energy density led to a decrease of RS, although not to the same extent for every parameter variation. Additionally, the effect of support structure, sample roughness and LPBF machine effects potentially coming from Ar flow were studied. We observed no influence of support structure on subsurface RS while the orientation with respect to Ar flow showed to have an impact on RS. We conclude recommending monitoring such parameters to improve part reliability and reproducibility

Subsurface Residual Stress Analysis in Ti-6Al-4V Additive Manufactured Parts by Synchrotron X-ray Diffraction

Synchrotron X-ray diffraction is a powerful non-destructive technique for the analysis of the material stress-state. High cooling rates and heterogeneous temperature distributions during additive manufacturing lead to high residual stresses. These high residual stresses play a crucial role in the ability to achieve complex geometries with accuracy and avoid distortion of parts during manufacturing. Furthermore, residual stresses are critical for the mechanical performance of parts in terms of durability and safety. In the present study, Ti-6Al-4V bridge-like specimens were manufactured additively by selective laser melting (SLM) under different laser scanning speed conditions in order to compare the effect of process energy density on the residual stress state. Subsurface residual stress analysis was conducted by means of synchrotron X-ray diffraction in energy dispersive mode for three conditions: as-built on base plate, released from base plate, and after heat treatment on the base plate. The quantitative residual stress characterization shows a correlation with the qualitative bridge curvature method. Computed tomography (CT) was carried out to ensure that no stress relief took place owing to the presence of porosity. CT allows obtaining spatial and size pores distribution which helps in optimization of the SLM process. High tensile residual stresses were found at the lateral surface for samples in the as-built conditions. We observed that higher laser energy density during fabrication leads to lower residual stresses. Samples in released condition showed redistribution of the stresses due to distortion