The Effect of Manufacturing Defects on the Fatigue Behaviour of Ti-6Al-4V Specimens Fabricated Using Selective Laser Melting

Additive Manufacturing (AM) technologies are considered revolutionary because they could fundamentally change the way products are designed. Selective Laser Melting (SLM) is a metal based AM process with significant and growing potential for the manufacture of aerospace components. Traditionally a material needs to be listed in the Metallic Materials Properties Development and Standardization (MMPDS) handbook if it is to be considered certified. However, this requires a considerable amount of test data to be generated on the materials mechanical properties. Therefore, the MMPDS certification process does not lend itself easily to the certification of AM components as the final component can have similar mechanical properties to wrought alloys combined with the defects associated with traditional casting and welding technologies. These defects can substantially decrease the fatigue life of a fabricated component. The primary purpose of this investigation was to study the fatigue behaviour of as-built Ti-6Al-4V (Ti64) samples. Fatigue tests were performed on the Ti-6Al-4V specimens built using SLM with a variety of layer thicknesses and build (vertical or horizontal) directions. Fractography revealed the presence of a range of manufacturing defects located at or near the surface of the specimens. The experimental results indicated that Lack-of-Fusion (LOF) defects were primarily responsible for fatigue crack initiation. The reduction in fatigue life appeared to be affected by the location, size and shape of the LOF defect.

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Metallic Materials Prepared by Selective Laser Melting: Part Orientation Issue

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.779.165 ◽

2018 ◽

Vol 779 ◽

pp. 165-173

Author(s):

Michaela Fousova ◽

Drahomír Dvorský ◽

Pavel Lejček ◽

Dalibor Vojtěch

Keyword(s):

Mechanical Properties ◽

Stainless Steel ◽

Selective Laser Melting ◽

Metallic Materials ◽

Stainless Steel 316L ◽

Laser Melting ◽

Individual Effects ◽

Oriented Samples ◽

Part Orientation ◽

Melting Part

This paper shows part orientation issue in the process of Selective Laser Melting (SLM) at four examples of metallic materials (Fe, stainless steel 316L, TiAl6V4 alloy and AlSi11Mg alloy). Horizontally and vertically oriented samples differ in their mechanical properties, especially in plasticity. The causes of these differences are related to a thermal history, microstructural features and porosity. Depending on a particular material, individual effects are manifested under different extents.

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Influence of porosity on the fatigue behaviour of additively fabricated TA6V alloys

MATEC Web of Conferences ◽

10.1051/matecconf/201816502008 ◽

2018 ◽

Vol 165 ◽

pp. 02008 ◽

Cited By ~ 7

Author(s):

Viet-Duc Le ◽

Etienne Pessard ◽

Franck Morel ◽

François Edy

Keyword(s):

Fatigue Life ◽

Additive Manufacturing ◽

Fatigue Strength ◽

Pore Size ◽

Selective Laser Melting ◽

Fatigue Loading ◽

Fatigue Behaviour ◽

Laser Melting ◽

Experimental Campaign ◽

Porosity Fraction

This work is focused on the influence of porosity when dealing with the fatigue behaviour of the TA6V alloys fabricated by the selective laser melting (SLM) process. The presence of porosity is one of the major issue facing additive manufacturing (AM) of metallic components subjected to fatigue loading. In order to study the effect of porosity on the fatigue behaviour, a vast experimental campaign has been undertaken. These materials are fabricated by the SLM process with different building directions (horizontal, vertical and diagonal) thanks to which specimen batches with different pore sizes are obtained. It is observed that despite a low porosity fraction (around 0.01%), the influence of pores on the fatigue strength of the materials is pronounced. A mapping approach is presented, which links the applied stress, the pore size and the fatigue life. This approach makes it possible to accurately characterize the effect of the porosity size, and also to construct Kitagawa-Takahashi diagrams from S-N data.

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Microstructural Characterization of the Anisotropy and Cyclic Deformation Behavior of Selective Laser Melted AlSi10Mg Structures

Metals ◽

10.3390/met8100825 ◽

2018 ◽

Vol 8 (10) ◽

pp. 825 ◽

Cited By ~ 9

Author(s):

Mustafa Awd ◽

Felix Stern ◽

Alexander Kampmann ◽

Daniel Kotzem ◽

Jochen Tenkamp ◽

...

Keyword(s):

Electron Microscopy ◽

Mechanical Properties ◽

Scanning Electron Microscopy ◽

Selective Laser Melting ◽

Microstructural Characterization ◽

Fatigue Tests ◽

Laser Melting ◽

Structural Anisotropy ◽

Scanning Electron

The laser-based fusion of metallic powder allows construction of components with arbitrary complexity. In selective laser melting, the rapid cooling of melt pools in the direction of the component building causes significant anisotropy of the microstructure and properties. The objective of this work is to investigate the influence of build anisotropy on the microstructure and mechanical properties in selective laser melted AlSi10Mg. The alloy is comprehensively used in the automotive industry and has been one of the most frequently investigated Al alloys in additive manufacturing. Using specimens produced in three different building orientations with respect to the build platform, the anisotropy of the microstructure and defects will be investigated using scanning electron microscopy and microcomputed tomography. The analysis showed a seven-times higher pore density for the 90°-specimen compared to the 0°-specimen. The scanning electron microscopy revealed the influence of the direction of the cooling gradient on the constitution of the eutectic phase. Mechanical properties are produced in quasi-static and fatigue tests of variable and constant loading amplitudes. Specimens of 0° showed 8% higher tensile strength compared to 90°-specimens, while fracture strain was reduced almost 30% for the 45°-specimen. The correlation between structural anisotropy and mechanical properties illustrates the influence of the building orientation during selective laser melting on foreseen fields of application.

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From the fatigue properties of Ti6Al4V produced by ALM selective laser melting process to the mechanical design of an aeronautical part

MATEC Web of Conferences ◽

10.1051/matecconf/202032103032 ◽

2020 ◽

Vol 321 ◽

pp. 03032

Author(s):

François Edy ◽

Viet-Duc LE ◽

Claudia BIERE ◽

Monica Perez ◽

Etienne Pessard ◽

...

Keyword(s):

Selective Laser Melting ◽

Mechanical Design ◽

Fatigue Behavior ◽

Melting Process ◽

Fatigue Behaviour ◽

Fatigue Tests ◽

Fatigue Properties ◽

Laser Melting ◽

Fatigue Design ◽

Process Strategy

Selective laser melting SLM is investigated through a study of redesign and characterization of an aeronautic part made of titanium Ti6Al4V. The part must ensure an excellent static and fatigue behaviour. The methodology developed hereby follows 3 main steps: First, the influence of laser power, laser speed and hatch distance on the amount/rate of porosity is performed to define optimized process parameters. Then, the influence of building process strategy, i.e. building direction or as-built surface roughness on the static and fatigue behaviour are studied and understood by following a vast experimental campaign. Obtained properties are finally used in a topology optimization study to find the best compromise between part weight and fatigue behavior . 3 prototypes of simulated part are produced and then characterized. Fatigue tests are conducted on the component and confirm the fatigue design proposed. Obtained results are encouraging and illustrate the fatigue design optimization of a complex Additive Manufacturing component.

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Toward Structural Fatigue Analysis of Horizontally-Fabricated NiTi via Selective Laser Melting

Volume 1: Additive Manufacturing; Advanced Materials Manufacturing; Biomanufacturing; Life Cycle Engineering; Manufacturing Equipment and Automation ◽

10.1115/msec2020-8473 ◽

2020 ◽

Author(s):

Parisa Bayati ◽

Ahmadreza Jahadakbar ◽

Keyvan Safaie ◽

Mohammadreza Nematollahi ◽

Hediyeh Dabbaghi ◽

...

Keyword(s):

Shape Memory ◽

Selective Laser Melting ◽

Initial Step ◽

Fatigue Behaviour ◽

Fatigue Tests ◽

Laser Melting ◽

Practical Applications ◽

Structural Fatigue ◽

Dog Bone ◽

Potential Applications

Abstract NiTi (Nitinol) is a shape memory alloy with distinctive properties, such as shape memory, superelasticity, biocompatibility, and low density. All these unique properties make NiTi a great candidate in different applications. However, the conventional fabrication of NiTi encounters many challenges that significantly limits the practical applications of the alloy. As a solution, the Selective Laser Melting (SLM) which is an Additive Manufacturing (AM) technique has been recently used for the fabrication of NiTi parts. Although complex geometries can be fabricated directly from CAD files via SLM, different process parameters significantly affect the parts’ quality and must be optimized for each application. In most of the potential applications, NiTi components undergo cyclic loads and therefore its structural fatigue must be fully studied and considered in the design process. However, due to the nature of the SLM process, the fatigue behaviour of SLM fabricated NiTi is different from the conventional ones. In this work, as an initial step, the fatigue behaviour of the SLM fabricated NiTi in the horizontal direction is studied and the reasons for failure have been discussed. To this end, strain-controlled fatigue tests were performed on NiTi dog-bone samples, and fractography was used to analyze the different defects which could cause the failure or scatter in the results.

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