Effect of real-time cooling rate on microstructure in Laser Additive Manufacturing

Farshidianfar, Mohammad H.; Khajepour, Amir; Gerlich, A.P.

doi:10.1016/j.jmatprotec.2016.01.017

Cited by 271 publications

(86 citation statements)

References 16 publications

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“…Based on the results of Saeidi et al, the subgrain boundaries are enriched with heavy elements, mainly Mo. The orientation of this substructure is strongly related to the thermal gradient produced by not only the building direction but also by the thermal influence of neighboring laser scans and, thus, partially remelting . The cell size of 0.5 to 1.0 μm is in accordance with the results of other authors …”

Section: Discussionsupporting

confidence: 87%

“…The laser‐based AM process of metals creates a unique and fine‐grained microstructure compared with conventional cast material due to the high cooling rate of the melt pools during the SLM process . Additionally, the grains in the material are growing along the building direction with a strong texture causing different mechanical quasistatic and fatigue properties parallel and perpendicular to the building direction .…”

Section: Introductionmentioning

confidence: 99%

“…5 The laser-based AM process of metals creates a unique and fine-grained microstructure compared with conventional cast material due to the high cooling rate of the melt pools during the SLM process. 6 Additionally, the grains in the material are growing along the building direction with a strong texture causing different mechanical quasistatic and fatigue properties parallel and perpendicular to the building direction. [7][8][9] The process itself is highly dynamic as unstable melt pools are created and further exposed to the high cooling rates and the continuous reheating and recooling when the next layers above the previous one are molten.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Investigation of the anisotropic cyclic damage behavior of selective laser melted AISI 316L stainless steel

Stern

Kleinhorst

Tenkamp

et al. 2019

Fatigue Fract Eng Mat Struct

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The additive manufacturing technique selective laser melting (SLM) is the most common process for metallic powders. The layer‐by‐layer process allows construction of components with high complex designs compared with conventional process routes. However, the orientation of parts related to the build platform and later to different loading conditions should be taken into account as the process‐induced microstructure and defects creating anisotropic mechanical behavior. To evaluate this influence of the building orientation as well as the process‐induced defects, different fatigue tests were performed on the SLM‐processed austenitic steel AISI 316 L (X2CrNiMo17‐12‐2). The distribution of the process‐induced porosity and, thus, the fatigue behavior is strongly related to the building direction, leading to a reduction of fatigue life for the tested 90° specimens of more than 90%.

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Section: Discussionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Investigation of the anisotropic cyclic damage behavior of selective laser melted AISI 316L stainless steel

Stern

Kleinhorst

Tenkamp

et al. 2019

Fatigue Fract Eng Mat Struct

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“…The deposition temperature gradient of laminated materials samples was greater than K465 samples with the same process parameters, which made the microstructure refined. Mohammad H. Farshidianfar has proven that the solidification structure and the geometrical dilution were closely related to the real-time cooling rate [24]. Comparing the dendritic microstructures of the three different forming methods, it is clear that the microstructure of the laminated material with deposition layer numbers ratio 1:1 was the smallest.…”

Section: Methodsmentioning

confidence: 98%

Microstructure and Microhardness of Laser Metal Deposition Shaping K465/Stellite-6 Laminated Material

Wang

Zhao

et al. 2017

Metals

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K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by laser metal deposition shaping to control the cracking behaviour in laser metal deposition of K465 superalloy. The microstructure differences between the K465 superalloy with cracking and the laminated material were discussed. The microstructure and intermetallic phases were analyzed through scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the microstructure of K465/Stellite-6 laminated material samples consisted of continuous dendrites with a similar structure size in different alloy deposition layers, and the second dendrite arm spacing was finer compared with laser metal deposition shaping K465. The intermetallic phases in the different alloy deposition layers varied, and the volume fraction of carbides in K465 deposition layer of the laminated material was higher than only K465 deposition under the fluid flow effect. In addition, the composition and microhardness distribution of laminated materials variation occurred along the deposition direction.Keywords: laser metal deposition shaping; laminated material; microstructure; microhardness BackgroundK465 superalloy, known as a nickel-based alloy, is widely used for gas turbine blades and vanes [1]. K465 superalloy parts are mainly formed by conventional casting, leading to some disadvantages in forming efficiency and mechanical properties. Laser metal deposition shaping (LMDS) is an efficient way for producing components with near-net-shaped, directional solidification, and controlled porosity or chemical composition gradient [2,3], and it also knows direct laser fabrication (DLF), or laser solid form (LSF [12], and CM247LC [13] were prone to cracking. The crack sensitivity of nickel-based superalloy increases with the increasing of aluminum and titanium elements. As a result, the research focus of LMDS K465 superalloy concentrates on controlling the cracks. Based on previous studies, the crack category of laser deposition superalloy may contain solidification cracking, grain boundary liquation cracking and ductility dip cracking [10]. Among them, the liquation cracks are the most serious in nickel-based superalloy with a high content of (Al + Ti), and may originate from the liquation of low melting point eutectic in the previous build layers. Chen et al. [6] have found that liquation cracking in laser deposited 718 alloy was on account of

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“…Apart from distortion, process variables also affect microstructure and mechanical properties. For example, in 316 stainless steel parts made by AM, formation of detrimental δ-ferrite can be avoided and superior mechanical properties can be achieved by selecting low heat inputs [21][22][23]. It is also established that low heat input (100-500 W and 2000 mm/s) suppresses formation of intermetallic compounds and provides good mechanical properties of some nickel base superalloy builds [24,25].…”

mentioning

confidence: 99%

Mitigation of thermal distortion during additive manufacturing

et al. 2017

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Additively manufactured parts are often distorted because of spatially variable heating and cooling. Currently there is no practical way to select process variables based on scientific principles to alleviate distortion. Here we develop a roadmap to mitigate distortion during additive manufacturing using a strain parameter and a well-tested, three-dimensional, numerical heat transfer and fluid flow model. The computed results uncover the effects of both the key process variables such as power, scanning speed, and important non-dimensional parameters such as Marangoni and Fourier numbers and non-dimensional peak temperature on thermal strain. Recommendations are provided to mitigate distortion based on the results.Laser assisted additive manufacturing (AM) process produces 'near net shape' parts from a stream of alloy powders in a layer-by-layer manner for use in medical, aerospace, automotive and other industries [1,2]. The parts undergo repeated spatially variable heating, melting, solidification and cooling during AM [3,4]. Due to the transient heating and cooling, the fabricated parts exhibit thermal distortion [5-10]. Thermal distortion results in dimensional inaccuracy and adversely affects performance of the fabricated parts [11]. Previous work has shown that increase in net heat input [7] and reduction in dwell time [8] between deposition of successive layers can increase thermal distortion. It is also known that the alloy properties, the deposit and substrate dimensions, the laser scanning pathway, the hatch spacing between layers and the heating and cooling conditions significantly affect thermal distortion [9,12,13].The existing AM literature does not provide any guidance for selecting process variables to minimize thermal distortion. A quantitative understanding of the effects of process variables on thermal distortion and a practical means to mitigate this problem based on scientific principles are needed but not generally available.Here, we show for the first time how thermal distortion during AM can be minimized by back of the envelope calculations. The procedure involves evaluation of the effects of common process variables such as laser power and scanning speed on thermal strain. In addition, the non-dimensional parameters that are important for heat transfer and fluid flow phenomena in AM such as Fourier number, Marangoni number and non-dimensional temperature are correlated with thermal strain. Based on these results we provide recommendations to minimize distortion of the additively manufactured parts.We have recently shown that thermal distortion is related to a strain parameter, ε* [5]:where β is the volumetric coefficient of thermal expansion, ΔT is the maximum rise in temperature during the process, E is the elastic modulus and I is the moment of inertia of the substrate, the product, EI, is the flexural rigidity of the structure, t is the characteristic time, H is the heat input per unit length, F is the Fourier number and ρ is the density of the alloy powder. Fourier number is the ratio o...

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Effect of real-time cooling rate on microstructure in Laser Additive Manufacturing

Cited by 271 publications

References 16 publications

Investigation of the anisotropic cyclic damage behavior of selective laser melted AISI 316L stainless steel

Investigation of the anisotropic cyclic damage behavior of selective laser melted AISI 316L stainless steel

Microstructure and Microhardness of Laser Metal Deposition Shaping K465/Stellite-6 Laminated Material

Mitigation of thermal distortion during additive manufacturing

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