Fatigue performance of laser powder bed fusion hydride-dehydride Ti-6Al-4V powder

Journal Article · Tue Aug 30 00:00:00 EDT 2022 · Additive Manufacturing

DOI:https://doi.org/10.1016/j.addma.2022.103117· OSTI ID:1893598

Asherloo, Mohammadreza ^[1]; Wu, Ziheng ^[2]; Heim, Mike ^[3]; Nelson, Dave ^[3]; Paliwal, Muktesh ^[4]; Rollett, Anthony D. ^[5]; Mostafaei, Amir ^[1]

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1. Illinois Institute of Technology, Chicago, IL (United States)
2. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
3. Nel Pretech Corporation, Tinley Park, IL (United States)
4. Kymera International - Reading Alloys, Robesonia, PA (United States)
5. Carnegie Mellon University, Pittsburgh, PA (United States)

We report hydride-dehydride (HDH) Ti-6Al-4V alloy with particle size distribution of 50–120 µm is laser powder bed fusion (L-PBF) processed using optimum processing parameters and a near-fully dense structure with a density of 99.9 % is achieved. Microstructural observations and phase analyses indicate formation of columnar β grains with acicular α/α' phases in as-built condition. The roughness of the as-fabricated samples is significant with an average roughness of R_a = 15.71 ± 3.96 µm and a root mean square roughness of R_rms = 108.4 ± 24.9 µm, however, both values are reduced to R_a = 0.19 ± 0.04 µm and R_rms = 4.9 ± 0.6 µm after mechanical grinding. Mechanical tests are carried out on as-fabricated specimens followed by stress relief treatment. All samples are tested to failure in fatigue, under fully-reversed tension-compression conditions of R = –1. The as-built samples failed from the surface with crack initiation mainly at micro-notches, whereas after mechanically grinding, crack initiation changed to subsurface defects such as pores. Minimizing surface roughness by mechanically grinding eliminates surface micro-notches which improves fatigue strength in the high cycle fatigue region. Fatigue notch factor calculations showed that the effect of surface roughness was significantly lower when HDH powder is used compared to standard spherical powder. X-ray diffraction analysis revealed an in-plane compressive stress, micro-strain and grain refinement on the surface of the mechanically ground samples. Fractography observations (macroscale) revealed a fully brittle fracture in the first stage of crack growth with a transition to a dominantly ductile fracture in the third stage of crack growth. On the other hand, at the micro scale, even the brittle fracture regions showed evidence of ductile fracture within the α' martensite laths.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); Illinois Institute of Technology; National Science Foundation (NSF)
• Grant/Contract Number: AC52-07NA27344; DMR-2050916
• OSTI ID: 1893598
• Report Number(s): LLNL-JRNL-834850; LLNL-JRNL-836489; 1053643
• Journal Information: Additive Manufacturing, Vol. 59, Issue N/A; ISSN 2214-8604
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
additive manufacturing
non-spherical powder
surface roughness
fractography
micro-computed tomography