Research Papers

Mechanical Anisotropy and Strain Rate Dependency Behavior of Ti6Al4V Produced Using E-Beam Additive Fabrication

[+] Author and Article Information
Leila Ladani

Mechanical Engineering Department,
University of Connecticut,
Storrs, CT 06269
e-mail: lladani@engr.uconn.edu

Jafar Razmi

Mechanical Engineering Department,
University of Connecticut,
Storrs, CT 06269
e-mail: razmi@engr.uconn.edu

Soud Farhan Choudhury

Mechanical Engineering Department,
University of Connecticut,
Storrs, CT 06269
e-mail: soud.choudhury@uconn.edu

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 8, 2013; final manuscript received May 19, 2014; published online June 5, 2014. Assoc. Editor: Ashraf Bastawros.

J. Eng. Mater. Technol 136(3), 031006 (Jun 05, 2014) (7 pages) Paper No: MATS-13-1186; doi: 10.1115/1.4027729 History: Received October 08, 2013; Revised May 19, 2014

Anisotropic mechanical behavior is an inherent characteristic of parts produced using additive manufacturing (AM) techniques in which parts are built layer by layer. It is expected that in-plane and out-of-plane properties be different in these parts. E-beam fabrication is not an exception to this. It is, however, desirable to keep this degree of anisotropy to a minimum level and be able to produce parts with comparable mechanical strength in both in-plane and out-of-plane directions. In this manuscript, this degree of anisotropy is investigated for Ti6Al4V parts produced using this technique through tensile testing of parts built in different orientations. Mechanical characteristics such as Young's modulus, yield strength (YS), ultimate tensile strength (UTS), and ductility are evaluated. The strain rate effect on mechanical behavior, namely, strength and ductility, is also investigated by testing the material at a range of strain rates from 10−2 to 10−4 s−1. Local mechanical properties were extracted using nanoindentation technique and compared against global values (average values obtained by tensile tests). Although the properties obtained in this experiment were comparable with literature findings, test results showed that in-plane properties, elastic modulus, YS, and UTS are significantly higher than out-of-plane properties. This could be an indication of defects in between layers or imperfect bonding of the layers. Strong positive strain rate sensitivity was observed in out-of-plane direction. The strain rate sensitivity evaluation did not show strain rate dependency for in-plane directions. Local mechanical properties obtained through nanoindentation confirmed the findings of tensile test and also showed variation of properties caused by geometry.

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Fig. 1

Dog-bone samples fabricated using the Arcam machine in three different orientations with respect to the build table. The schematic of the gage cross sections is also provided.

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Fig. 2

(a) Top view of the flat-built sample and (b) side view of the side-built sample

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Fig. 3

True stress–strain curves extracted through tensile testing

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Fig. 4

Comparison of stress–strain data for different build orientations

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Fig. 5

Comparison of (a) yield strength, (b) ultimate tensile strength, and (c) elastic modulus in different build orientation with literature values

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Fig. 6

Comparison of UTS in different strain rates in different sample build directions

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Fig. 7

Comparison of yield strength at different strain rates in different build orientations

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Fig. 8

SEM images of fracture surfaces of (a) flat build, (b) side build, and (c) top build specimens

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Fig. 9

Location of indentation point on (a) side-built, (b) top-built, (c) flat-built samples, and (d) indentation matrix and direction of movement of the tip

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Fig. 10

Hardness obtained through nanoindentation for side build samples

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Fig. 11

Hardness obtained through nanoindentation for flat-built samples

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Fig. 12

Hardness obtained through nanoindentation for top-built location on the grip section of samples

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Fig. 13

Average value of hardness obtained for different build orientation in comparison to literature

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Fig. 14

Average value of elastic modulus obtained for different build orientations




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