Abstract
Isotropy in microstructure and mechanical properties remains a challenge for laser powder bed fusion (LPBF) processed materials due to the epitaxial growth and rapid cooling in LPBF. In this study, a high-strength TiB2/Al-Cu composite with random texture was successfully fabricated by laser powder bed fusion (LPBF) using pre-doped TiB2/Al-Cu composite powder. A series of advanced characterisation techniques, including synchrotron X-ray tomography, correlative focussed ion beam–scanning electron microscopy (FIB-SEM), scanning transmission electron microscopy (STEM), and synchrotron in situ X-ray diffraction, were applied to investigate the defects and microstructure of the as-fabricated TiB2/Al-Cu composite across multiple length scales. The study showed ultra-fine grains with an average grain size of about 0.86 μm, and a random texture was formed in the as-fabricated condition due to rapid solidification and the TiB2 particles promoting heterogeneous nucleation. The yield strength and total elongation of the as-fabricated composite were 317 MPa and 10%, respectively. The contributions of fine grains, solid solutions, dislocations, particles, and Guinier–Preston (GP) zones were calculated. Failure was found to be initiated from the largest lack-of-fusion pore, as revealed by in situ synchrotron tomography during tensile loading. In situ synchrotron diffraction was used to characterise the lattice strain evolution during tensile loading, providing important data for the development of crystal-plasticity models.
Highlights
Laser powder bed fusion (LPBF), an additive manufacturing (AM) technique, uses a laser to melt and fuse the powder selectively to form a 3D structure in a layer-by-layer fashion [1,2,3]
We first presented the microstructural characterisation of the as-fabricated T iB2/Al-Cu composite, including porosity, grain structure, TiB2 and Al2Cu phase, as well as nanoprecipitation
The histogram of sphericity within the logarithmic scale is presented in Fig. 1c, showing more than 85% of pores have near spherical morphology ( >0.7), and less than 0.3% of pores have lower sphericity (
Summary
Laser powder bed fusion (LPBF), an additive manufacturing (AM) technique, uses a laser to melt and fuse the powder selectively to form a 3D structure in a layer-by-layer fashion [1,2,3]. Tan et al [35] mixed 2024 Al alloy powders with Ti nanoparticles, and fine-grained 2024 alloy was successfully fabricated by LPBF. The composite produced by mixed powder shows mechanical properties close to that of wrought 2xxx series alloys [17, 29, 36]. Another approach is to pre-dope the Al-alloy with nanoparticles. By utilising the advantage of synchrotron in situ testing and advanced microscopes, our study produced Al-Cu-based powders predoped with TiB2 particles for the LPBF process and investigated the defects, formation of fine grains, distribution of particles, and their behaviours during deformation. The detailed characterisation and in situ tests allowed us to establish the multi-scales architecture of the TiB2/Al-Cu composite, which significantly facilitates the understanding of the structure–properties relationship of the composite
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