In situ microstructure analysis of Inconel 625 during laser powder bed fusion

AbstractLaser powder bed fusion is an additive manufacturing process that employs highly focused laser radiation for selective melting of a metal powder bed. This process entails a complex heat flow and thermal management that results in characteristic, often highly textured microstructures, which lead to mechanical anisotropy. In this study, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during LPBF. The nickel-base alloy Inconel 625 was used for in situ experiments using a custom LPBF system designed for these investigations. The diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation. A combination of high laser power and scanning speed results in a strong preferred crystallographic orientation, while low laser power and scanning speed showed no clear texture. The observation of a constant gauge volume revealed solid-state texture changes without remelting. They were related to in situ recrystallization processes caused by the repeated laser scanning. After recrystallization, the formation and growth of segregations were deduced from an increasing diffraction peak asymmetry and confirmed by ex situ scanning transmission electron microscopy. Graphical Abstract

Download Full-text

Linking In Situ Melt Pool Monitoring to Melt Pool Size Distributions and Internal Flaws in Laser Powder Bed Fusion

Metals ◽

10.3390/met11111856 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1856

Author(s):

Claudia Schwerz ◽

Lars Nyborg

Keyword(s):

Near Infrared ◽

In Situ Monitoring ◽

Ex Situ ◽

Process Conditions ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Melt Pool ◽

Melt Pool Size

In situ monitoring of the melt pools in laser powder bed fusion (LPBF) has enabled the elucidation of process phenomena. There has been an increasing interest in also using melt pool monitoring to identify process anomalies and control the quality of the manufactured parts. However, a better understanding of the variability of melt pools and the relation to the incidence of internal flaws are necessary to achieve this goal. This study aims to link distributions of melt pool dimensions to internal flaws and signal characteristics obtained from melt pool monitoring. A process mapping approach is employed in the manufacturing of Hastelloy X, comprising a vast portion of the process space. Ex situ measurements of melt pool dimensions and analysis of internal flaws are correlated to the signal obtained through in situ melt pool monitoring in the visible and near-infrared spectra. It is found that the variability in melt pool dimensions is related to the presence of internal flaws, but scatter in melt pool dimensions is not detectable by the monitoring system employed in this study. The signal intensities are proportional to melt pool dimensions, and the signal is increasingly dynamic following process conditions that increase the generation of spatter.

Download Full-text

On the in situ elimination of pores during laser powder bed fusion of a titanium alloy

10.21203/rs.3.rs-386269/v1 ◽

2021 ◽

Author(s):

ling zhang ◽

Wenhe Liao ◽

Tingting Liu ◽

Huiliang Wei ◽

Changchun Zhang

Keyword(s):

Titanium Alloy ◽

Real Time ◽

Laser Power ◽

Layer By Layer ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Printing Quality ◽

High Laser

Abstract The printing quality of the laser powder bed fusion (LPBF) components largely depends on the presence of various defects such as massive porosity. Thus, the efficient elimination of pores is an important factor to the production of a sound LPBF product. In this work, the efficacy of two in situ laser remelting approaches on the elimination of pores during LPBF of a titanium alloy Ti-6.5Al-3.5Mo-l.5Zr-0.3Si (TC11) were assessed using both experimental and computational methods. These two remelting methods are the surface remelting, and the layer-by-layer printing and remelting. A multi-track and multi-layer phenomenological model was established to compute the evolution of pores with the temperature and velocity fields. The results showed that surface remelting with a high laser power such as 180 W laser can effectively eliminate pores within three deposited layers. However, such a remelting cannot reach defects in deeper regions. Alternatively, the layer-by-layer remelting with a laser power of 180 W can effectively eliminate the pores formed in the previous layer in real time. The results obtained from this work can provide useful guidance for the in situ control of printing defects supported by the real time monitoring, feedback and operation systems of the intelligent LPBF equipment.

Download Full-text

Laser Powder Bed Fusion Produced Ti-6Al-4V: Influence of High-Energy Process Parameters on In-Situ Martensite Decomposition, Stress Relief and Prior Beta Grain Texture

SSRN Electronic Journal ◽

10.2139/ssrn.3978454 ◽

2021 ◽

Author(s):

Gerrit Matthys Ter Haar ◽

Thorsten Hermann Becker

Keyword(s):

Process Parameters ◽

Stress Relief ◽

High Energy ◽

Grain Texture ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Energy Process ◽

High Energy Process

Download Full-text

In Situ Alloying of a Modified Inconel 625 via Laser Powder Bed Fusion: Microstructure and Mechanical Properties

Metals ◽

10.3390/met11060988 ◽

2021 ◽

Vol 11 (6) ◽

pp. 988

Author(s):

Giulio Marchese ◽

Margherita Beretta ◽

Alberta Aversa ◽

Sara Biamino

Keyword(s):

Mechanical Properties ◽

Base Alloy ◽

Heat Treatments ◽

Inconel 625 ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Melt Pool ◽

Composition Modification

This study investigates the in situ alloying of a Ni-based superalloy processed by means of laser powder bed fusion (LPBF). For this purpose, Inconel 625 powder is mixed with 1 wt.% of Ti6Al4V powder. The modified alloy is characterized by densification levels similar to the base alloy, with relative density superior to 99.8%. The material exhibits Ti-rich segregations along the melt pool contours. Moreover, Ti tends to be entrapped in the interdendritic areas during solidification in the as-built state. After heat treatments, the modified Inconel 625 version presents greater hardness and tensile strengths than the base alloy in the same heat-treated conditions. For the solution annealed state, this is mainly attributed to the elimination of the segregations into the interdendritic structures, thus triggering solute strengthening. Finally, for the aged state, the further increment of mechanical properties can be attributed to a more intense formation of phases than the base alloy, due to elevated precipitation strengthening ability under heat treatments. It is interesting to note how slight chemical composition modification can directly develop new alloys by the LPBF process.

Download Full-text

In-Situ XRD Study of Phase Transformation Kinetics in a Co-Cr-W-Alloy Manufactured by Laser Powder-Bed Fusion

Crystals ◽

10.3390/cryst11020176 ◽

2021 ◽

Vol 11 (2) ◽

pp. 176

Author(s):

Patrick Hegele ◽

Jonas von Kobylinski ◽

Leonhard Hitzler ◽

Christian Krempaszky ◽

Ewald Werner

Keyword(s):

Residual Stresses ◽

Sample Surface ◽

Treatment Temperature ◽

Ex Situ ◽

Patient Specific ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Corrosion Properties ◽

Powder Bed

The additive manufacturing process of laser powder-bed fusion (L-PBF) is an increasingly popular approach for patient-specific production of dental frameworks made from Co-Cr alloys. Macroscopically, frameworks produced in this way exhibit high anisotropy especially in Young’s modulus, and are missing standardized requirements. Microscopically, pronounced texture and high residual stresses are characteristic. To reduce resulting detrimental effects, the as-built (AB) parts are heat treated. Dependent on the treatment temperature, effects like the transformation of the γ-phase matrix in the AB condition to ϵ-phase, precipitation, stress relief, and grain growth were observed. While the existence of these processes was established in the past, little is known about their kinetics. To fill this gap, these effects were studied with in-situ X-ray diffraction (XRD) methods in isothermal heat treatments (HTs) at four different sample surface temperatures TS reaching from 650∘C to 900∘C. Furthermore, room temperature ex situ XRD and SEM/EDS measurements completed the analysis. An evaluation of the datasets, with single peak fitting and QXRD methods, yielded the following results. In the HTs below a certain threshold, a γ-to-ϵ transformation was observed in the sample bulk and close to the sample surface. In the latter case, evidence for a partially strain-induced transformation related to oxide formation was present. Above this threshold and possibly slightly below, σ- and Laves-phase precipitated. Additionally, peak profile evolutions hinted at a drop of inter- and intragranular stresses within the first 30 to 60 min. Therefore, an HT of about 30 to 60 min slightly above the threshold is proposed as optimal for reducing residual stresses while retaining a predominantly single-phased microstructure, possibly superior in corrosion properties and likewise in bio-compatibility.

Download Full-text

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

Materials ◽

10.3390/ma14010165 ◽

2020 ◽

Vol 14 (1) ◽

pp. 165

Author(s):

Junfeng Li ◽

Yunxiao Wu ◽

Bokang Zhou ◽

Zhengying Wei

Keyword(s):

Relative Density ◽

Laser Power ◽

Grain Morphology ◽

Scanning Speed ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

High Laser ◽

Columnar Grains ◽

Hatch Spacing

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.

Download Full-text

Process–Structure–Property Relationships of Copper Parts Manufactured by Laser Powder Bed Fusion

Materials ◽

10.3390/ma14112945 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2945

Author(s):

Mohamed Abdelhafiz ◽

Kassim S. Al-Rubaie ◽

Ali Emadi ◽

Mohamed A. Elbestawi

Keyword(s):

Laser Power ◽

Scanning Speed ◽

Powder Bed Fusion ◽

Structure Property ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

X Ray ◽

Structure Property Relationships ◽

Process Structure ◽

Hatch Spacing

The process–structure–property relationships of copper laser powder bed fusion (L-PBF)-produced parts made of high purity copper powder (99.9 wt %) are examined in this work. A nominal laser beam diameter of 100 μm with a continuous wavelength of 1080 nm was employed. A wide range of process parameters was considered in this study, including five levels of laser power in the range of 200 to 370 W, nine levels of scanning speed from 200 to 700 mm/s, six levels of hatch spacing from 50 to 150 μm, and two layer thickness values of 30 μm and 40 μm. The influence of preheating was also investigated. A maximum relative density of 96% was obtained at a laser power of 370 W, scanning speed of 500 mm/s, and hatch spacing of 100 μm. The results illustrated the significant influence of some parameters such as laser power and hatch spacing on the part quality. In addition, surface integrity was evaluated by surface roughness measurements, where the optimum Ra was measured at 8 μm ± 0.5 μm. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were performed on the as-built samples to assess the impact of impurities on the L-PBF part characteristics. The highest electrical conductivity recorded for the optimum density-low contaminated coils was 81% IACS.

Download Full-text