Porosity regrowth during heat treatment of hot isostatically pressed additively manufactured titanium components

Tammas‐Williams, Samuel; Withers, Philip J.; Todd, Iain; Prangnell, P.B.

doi:10.1016/j.scriptamat.2016.05.002

Cited by 233 publications

(89 citation statements)

References 12 publications

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“…Additive manufacturing processes often produce microstructures with internal pores of various shapes and sizes that are detrimental to fatigue performance . Postprocessing techniques (ie, hot‐isostatic pressing [HIP'ing]) may be employed to close pores, but HIP'ing adds cost, alters the microstructure, relieves engineered residual stresses, and may not close all pores . Consequently, it may be beneficial to provide models to relate the fatigue life reduction from pores to pore size, pore shape, loading, and other fatigue life parameters.…”

Section: Introductionmentioning

confidence: 99%

Application of critical distances to fatigue at pores

Sobotka

Enright

McClung

2019

Fatigue Fract Eng Mat Struct

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This work applies Taylor's theory of critical distance to quantify the effect of defects on fatigue initiation in an additively manufactured metal. We focus on hollow pores that are ideal spherical, prolate, and oblate spheroids isolated in an otherwise homogeneous linear‐elastic material. These conditions support the development of exact solutions using the exterior Eshelby tensor for a pore in a remote, arbitrary stress field. For spheres, this solution process admits simple closed‐form solutions for principal stresses disturbed by the pore. For prolate and oblate spheroids, we present the solutions as graphical curves showing stress variations under uniaxial tension. This report then extends the analysis to determine the effect of defects on a parametric, power‐law stress range vs fatigue life model. By propagating the distributed stress fields through this model, this study demonstrates the effect of pore size, pore shape, stress, and parametric fatigue properties on the life reduction due to porosity. These results suggest several approaches to increasing fatigue lives in porous materials, eg, reducing the pore size, promoting spherical pores, and increasing the microstructural parameter (comparable to the El Haddad parameter). Results presented in this work may be useful to inform trends of fatigue strength and fatigue initiation lives in metallic alloys with limited porosity, eg, additively manufactured materials that have been HIP'ed.

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Section: Introductionmentioning

confidence: 99%

Application of critical distances to fatigue at pores

Sobotka

Enright

McClung

2019

Fatigue Fract Eng Mat Struct

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show abstract

“…Postbuild treatments such as hot isostatic pressing (HIP) have been frequently applied to AM parts and have demonstrated, by some studies, effective in removing the pores from the metal parts . However, other studies have shown that HIP's effectiveness is inconsistent across various AM platforms . HIP's reduced performance in laser AM parts is likely due to the presence of nonsoluble Ar gas in the pores .…”

Section: Introductionmentioning

confidence: 99%

“…2,11,[22][23][24] However, other studies have shown that HIP's effectiveness is inconsistent across various AM platforms. 11,[24][25][26][27] HIP's reduced performance in laser AM parts is likely due to the presence of nonsoluble Ar gas in the pores. 28 Recent high-resolution X-ray CT studies 24,26 indirectly confirmed the existence of pressurized pores in HIP'ed laser AM parts by noting the regrowth of them during the secondary heat treatment (HT).…”

Section: Introductionmentioning

confidence: 99%

“…11,[24][25][26][27] HIP's reduced performance in laser AM parts is likely due to the presence of nonsoluble Ar gas in the pores. 28 Recent high-resolution X-ray CT studies 24,26 indirectly confirmed the existence of pressurized pores in HIP'ed laser AM parts by noting the regrowth of them during the secondary heat treatment (HT). Absent of HIP pressure, elevated temperatures alone may induce morphological changes in the pores.…”

Section: Introductionmentioning

confidence: 99%

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Effect of heat treatments on pore morphology and microstructure of laser additive manufactured parts

Zhang

Meng

Shao

et al. 2019

Mat Design & Process Comms

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The slit‐shaped, lack‐of‐fusion pores (LFPs) persistent in the additively manufactured (AM) metals are detrimental to their fatigue resistance due to the associated stress concentrations at the edges. Postbuild treatments, such as hot isostatic pressing (HIP), are routinely used to eliminate pores resulting in, however, inconsistent improvements in fatigue performance. This work critically examines the effectiveness of HIP to eliminate such pores in AM Ti‐6Al‐4V. In addition, conventional heat treatment (HT) is proposed as a candidate remedial process to alleviate the harmful effects of the LFPs. Specifically, the spheroidization effect of HT on the sharp edges of the LFPs is investigated. Lastly, the effect of HT and HIP on the microstructure is carefully analyzed, safeguarding the beneficial refined microstructure of AM Ti‐6Al‐4V.

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“…Recently, X-ray computed tomography has been widely applied to material science and engineering [9][10][11] and some researchers began to use this technology to analyze the powder-binder separation [12,13], because of its obvious advantages, including 3D and the non-destructive characterization of the spatial structure. In the previous studies, powder-binder separation was analyzed by using gray value distribution in the CT reconstructed data [14,15].…”

Section: Introductionmentioning

confidence: 99%

Analysis of Powder Binder Separation through Multiscale Computed Tomography

Yang¹,

Xu²,

Liu

et al. 2019

Metals

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In this study, X-ray computed tomography was used to analyze powder binder separation in TC4 green bodies. Firstly, for the scanned results of the whole green body, because of the relative low resolution (36 µm), the powder binder separation can only be analyzed by using gray value distribution. Then, local regions (areas near the gate and the central parts) were scanned by using a much higher resolution (2.3 µm). Both of the volume fraction of powder content and gray value distributions indicate that powder particles tend to accumulate in the central parts. Finally, based on the results tested by using submicron resolution (0.8 µm), the effects of the volume and morphology of the powder particles on the powder binder separation were analyzed.

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Porosity regrowth during heat treatment of hot isostatically pressed additively manufactured titanium components

Cited by 233 publications

References 12 publications

Application of critical distances to fatigue at pores

Application of critical distances to fatigue at pores

Effect of heat treatments on pore morphology and microstructure of laser additive manufactured parts

Analysis of Powder Binder Separation through Multiscale Computed Tomography

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