In-situ residual stress reduction, martensitic decomposition and mechanical properties enhancement through high temperature powder bed pre-heating of Selective Laser Melted Ti6Al4V

Ali, Haider; Ma, Le; Ghadbeigi, Hassan; Mumtaz, Kamran

doi:10.1016/j.msea.2017.04.033

Cited by 278 publications

(150 citation statements)

References 23 publications

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“…This recognises the varying influence that build platform temperature and thermal stresses have on the microstructure formation. This finding was further supported by the work of Ali et al [18], in an investigation of the effects of powder bed preheating, which highlighted the significant influence of the powder bed temperature on the SLM Ti-6Al-4V microstructure formation. In particular, preheating the powder bed at different temperatures resulted in slowing the cooling rate, promoting α decomposition into α and growing β between α laths.…”

Section: Introductionsupporting

confidence: 66%

“…However, it is possible to reduce the residual stresses in situ, namely during the fabrication process. For example, a residual stresses' reduction scheme has been recently proposed by Ali et al [18], whereby it was demonstrated that reduction can be achieved by increasing the preheat temperature of the powder bed (reducing effectively the thermal gradient). Furthermore, it was shown with heat transfer numerical simulations that employing optimised scanning strategies can reduce the build-up of residual stresses [37].…”

Section: Residual Stressesmentioning

confidence: 99%

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A Review of the As-Built SLM Ti-6Al-4V Mechanical Properties towards Achieving Fatigue Resistant Designs

Agius

Kourousis

Wallbrink

2018

Metals

157

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Ti-6Al-4V has been widely used in both the biomedical and aerospace industry, due to its high strength, corrosion resistance, high fracture toughness and light weight. Additive manufacturing (AM) is an attractive method of Ti-6Al-4V parts' fabrication, as it provides a low waste alternative for complex geometries. With continued progress being made in SLM technology, the influence of build layers, grain boundaries and defects can be combined to improve further the design process and allow the fabrication of components with improved static and fatigue strength in critical loading directions. To initiate this possibility, the mechanical properties, including monotonic, low and high cycle fatigue and fracture mechanical behaviour, of machined as-built SLM Ti-6Al-4V, have been critically reviewed in order to inform the research community. The corresponding crystallographic phases, defects and layer orientations have been analysed to determine the influence of these features on the mechanical behaviour. This review paper intends to enhance our understanding of how these features can be manipulated and utilised to improve the fatigue resistance of components fabricated from Ti-6Al-4V using the SLM technology.

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Section: Introductionsupporting

confidence: 66%

Section: Residual Stressesmentioning

confidence: 99%

A Review of the As-Built SLM Ti-6Al-4V Mechanical Properties towards Achieving Fatigue Resistant Designs

Agius

Kourousis

Wallbrink

2018

Metals

157

View full text Add to dashboard Cite

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“…Melt pools in location 3 appear to be relatively shallow and have an average depth of 51.1 ± 18.3 µm. The significant difference in temperature between the building platform and the melted powder causes a large temperature gradient and high cooling rates at the beginning of the 3D printing process [28,29]. Rapid cooling towards the bottom of the specimen causes melted powder to solidify and cool quickly.…”

Section: Microstructure Of the As-printed Inconel 718mentioning

confidence: 99%

Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases

Seede

Mostafa

Braïlovski

et al. 2018

JMMP

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Abstract:In this work, the microstructure, texture, phases, and microhardness of 45 • printed (with respect to the build direction) homogenized, and hot isostatically pressed (HIP) cylindrical IN718 specimens are investigated. Phase morphology, grain size, microhardness, and crystallographic texture at the bottom of each specimen differ from those of the top due to changes in cooling rate. High cooling rates during the printing process generated a columnar grain structure parallel to the building direction in the as-printed condition with a texture transition from (001) orientation at the bottom of the specimen to (111) orientation towards the specimen top based on EBSD analysis. A mixed columnar and equiaxed grain structure associated with about a 15% reduction in texture is achieved after homogenization treatment. HIP treatment caused significant grain coarsening, and engendered equiaxed grains with an average diameter of 154.8 µm. These treatments promoted the growth of δ-phase (Ni 3 Nb) and MC-type brittle (Ti, Nb)C carbides at grain boundaries. Laves phase (Fe 2 Nb) was also observed in the as-printed and homogenized specimens. Ostwald ripening of (Ti, Nb)C carbides caused excessive grain growth at the bottom of the HIPed IN718 specimens, while smaller grains were observed at their top. Microhardness in the as-fabricated specimens was 236.9 HV and increased in the homogenized specimens by 19.3% to 282.6 HV due to more even distribution of secondary precipitates, and the nucleation of smaller grains. A 36.1% reduction in microhardness to 180.5 HV was found in the HIPed condition due to γ phase dissolution and differences in grain morphology.

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“…By increasing the bed pre-heat temperature, the temperature gradient reduces between the melt-pool and the solidified material leading to a reduction in residual stress build up [18]. The bed temperature used within this study is lower than the solidification temperature of the newly formed alloy (380 °C and 577 °C, respectively).…”

Section: Residual Stress Measurementmentioning

confidence: 99%

Customised Alloy Blends for In-Situ Al339 Alloy Formation Using Anchorless Selective Laser Melting

et al. 2017

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Abstract:The additive manufacturing process Selective Laser Melting (SLM) can generate large thermal gradients during the processing of metallic powder; this can in turn lead to increased residual stress formation within a component. Metal anchors or support structures are required to be built during the process and forcibly hold SLM components to a substrate plate and minimise geometric distortion/warpage due to the process induced thermal residual stress. The requirement for support structures can limit the geometric freedom of the SLM process and increase post-processing operations. A novel method known as Anchorless Selective Laser Melting (ASLM) maintains processed material within a stress relieved state throughout the duration of a build. As a result, metal components formed using ASLM do not develop signification residual stresses within the process, thus, the conventional support structures or anchors used are not required to prevent geometric distortion. ASLM locally melts two or more compositionally distinct powdered materials that alloy under the action of the laser, forming into various combinations of hypo/hyper eutectic alloys with a new reduced solidification temperature. This new alloy is maintained in a semi-solid or stress reduced state for a prolonged period during the build with the assistance of elevated powder bed pre-heating. In this paper, custom blends of alloys are designed, manufactured and processed using ASLM. The purpose of this work is to create an Al339 alloy from compositionally distinct powder blends. The in-situ alloying of this material and ASLM processing conditions allowed components to be built in a stress-relieved state, enabling the manufacture of overhanging and unsupported features.

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In-situ residual stress reduction, martensitic decomposition and mechanical properties enhancement through high temperature powder bed pre-heating of Selective Laser Melted Ti6Al4V

Cited by 278 publications

References 23 publications

A Review of the As-Built SLM Ti-6Al-4V Mechanical Properties towards Achieving Fatigue Resistant Designs

A Review of the As-Built SLM Ti-6Al-4V Mechanical Properties towards Achieving Fatigue Resistant Designs

Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases

Customised Alloy Blends for In-Situ Al339 Alloy Formation Using Anchorless Selective Laser Melting

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