Additive manufacturing of Ti-Ni bimetallic structures

A Afrouzian, CJ Groden, DP Field, S Bose, A Bandyopadhyay

Materials & Design 215, 110461

Bimetallic structures of nickel (Ni) and commercially pure titanium (CP Ti) were manufactured in three different configurations via directed energy deposition (DED)-based metal additive manufacturing (AM). To understand whether the bulk properties of these three composites are dominated by phase formation at the interface, their directional dependence on mechanical properties was tested. X-ray diffraction (XRD) pattern confirmed the intermetallic NiTi phase formation at the interface. Microstructural gradient observed at the heat-affected zone (HAZ) areas. The longitudinal samples showed about 12% elongation, while the same was 36% for the transverse samples. During compressive deformation, strain hardening from dislocation accumulation was observed in the CP Ti and transverse samples, but longitudinal samples demonstrated failures similar to a brittle fracture at the interface. Transverse samples also showed shear band formation indicative of ductile failures. Our results demonstrate that AM can design innovative bimetallic structures with unique directional mechanical properties.

Modeling of porosity and grain size effects on mechanical behavior of additively manufactured structures

M Hamid, MS Saleh, A Afrouzian, R Panat, HM Zbib

Additive Manufacturing 38, 101833

Additive manufacturing (AM) methods such as Aerosol Jet (AJ) printing allow the fabrication of structures via sintering of micro and/or nanoparticles, leading to microstructures that consist of various combinations of pore and grain sizes. It has been reported that AJ printed and sintered silver micropillars show an unusual behavior of high stiffness and high strain-to-failure for structures with high porosity and vice versa (Saleh et al. 2018 [1]). This behavior, however, is accompanied by the stiffer structures having smaller grain sizes and softer structures having larger grain sizes. To explain the physics of this behavior where a trade-off between hardening caused by size effects (grain refinement and gradients) and softening caused by porosity is expected to play a critical role, a multi-scale modeling approach is proposed in this paper. The model formulation consists of a continuum dislocation dynamics (CDD) framework, coupled with continuum plasticity and finite element analysis. The dislocation dynamics formulation is introduced into a user material subroutine and coupled with a finite element commercial solver, in this case, LS-DYNA, to solve the model in three-dimensional scale with the same size as the AM micropillars. The results from the model capture the general trends observed in compression tests of AM micropillars. In particular, it is shown that the grain size and dislocation density have a disproportionately higher influence over the mechanical deformation of metallic structures when compared to the porosity. These results show that the behavior of AM structures in the plastic regime is dominated by grain size effects rather than porosity. Some limitations of the model and possible future refinements are discussed. The paper provides an important analytical framework to model the mechanical behavior of AM structures with internal porosity in the plastic regime.

Progressive failure analysis of fiber-reinforced laminated composites containing a hole

H Bakhshan, A Afrouzian, H Ahmadi, M Taghavimehr

International Journal of Damage Mechanics 27 (7), 963-978

The present work aims to obtain failure loads for open-hole unidirectional composite plates under tensile loading. For this purpose, a user-defined material model in the finite element analysis package, ABAQUS, was developed to predict the failure load of the open-hole composite laminates using progressive failure analysis. Hashin and modified Yamanda-Sun’s failure criteria with complete and Camanho’s material degradation model are studied. In order to achieve the most accurate predictions, the influence of failure criteria and property degradation rules are investigated and failure loads and failure modes of the composites are compared with the same experimental test results from the literature. A good agreement between experimental results and numerical predictions was observed.

Effect of nano-particles on the tensile, flexural and perforation properties of the glass/epoxy composites

A Afrouzian, H Movahhedi Aleni, GH Liaghat, H Ahmadi

Journal of reinforced plastics and composites 36 (12), 900-916

The objective of this study is to characterize the damage in glass fiber reinforced composite laminated reinforced with nanosilica particles subjected to tensile, flexural, and transverse loadings. Tensile, three-point bending, quasi-static indentation test, and ballistic impact tests were used in order to obtain the perforation response, flexural and tensile behavior of the composites and nanocomposites. Experimental test series was carried out to determine the tensile and flexural strength and stiffness, impact energy absorption, and failure mechanisms of composites in the presence of nanoparticle. Hand lay-up method has been used to manufacture nanocomposites constituted of 12 layers of 2D woven glass fibers with 40% fiber volume fraction. The composites were reinforced by adding organically modified nano-silica in a 0%, 0.5%, 1%, and 3% ratio in weight with respect to the matrix. Results revealed that in 0.5 wt.% nanoparticles, energy absorption and tensile strength are maximum, but flexural strength has the highest value in 3 wt.%. Furthermore, the highest energy absorption, elastic energy, and energy absorption at maximum force in quasi-static penetration occur in 0.5% nanosilica content. In the case of ballistic tests, effect of nanosilica is more tangible than in quasi-static indentation. Nanocomposite at 0.5% nanosilica recorded higher ballistic limit and energy absorption in comparison with other composites and nanocomposites. SEM images showed that fracture surfaces in 0.5 wt.% nanocomposites are rough and engender more crack tips in comparison with other specimens, which contributes to higher energy absorption in static and dynamic tests.

Biotribocorrosion of 3D-printed silica-coated Ti6Al4V for load-bearing implants

A Afrouzian, JD Avila, A Bandyopadhyay

Journal of Materials Research 36 (19), 3974-3984

Laser-based 3D printing was utilized to deposit a silica (SiO2) coating on the surface of Ti6Al4V (Ti64) alloy for implementation onto articulating surfaces of load-bearing implants. The surface laser melting (SLM) technique was implemented in 1- and 2-laser passes (1LP and 2LP) after SiO2 deposition to understand the influence of remelting on the coating’s hardness and tribological performance. It was observed that compositional and microstructural features increased the cross-sectional hardness. Wear rate was observed to decrease from 2.9 × 10–4 mm3/Nm in the Ti64 to 5.2 × 10–6 mm3/Nm, 3.8 × 10–6 mm3/Nm and 2.1 × 10–7 mm3/Nm for the as-processed or zero laser pass (0LP), 1LP, and 2LP, respectively. Coated samples displayed a positive shift in open-circuit potential (OCP) during linear wear by displaying a 368 mV, 85 mV, and 613 mV increase compared to Ti64 for 0LP, 1LP, and 2LP, respectively. Our results displayed promising tribological performance of SiO2-coated Ti64 for articulating surfaces of load-bearing implants.

Martian regolith–Ti6Al4V composites via additive manufacturing

A Afrouzian, KD Traxel, A Bandyopadhyay

International Journal of Applied Ceramic Technology

In order to investigate the in-space in situ resource utilization, directed energy deposition (DED)-based additive manufacturing (AM) has been utilized to process Martian regolith—Ti6Al4V (Ti64) composites. Here we investigated the processability of depositing 5, 10, and 100 wt% of Martian regolith premixed with Ti6Al4V using laser-based DED, analyzing the printed structure via X-ray diffraction, Vicker's microhardness, scanning electron microscopic imaging, and wear characteristics utilizing an abrasive water jet cutter to simulate abrasive environments on the Martian surface. The results indicate that the surface roughness and hardness of the composites increase with respect to the Martian regolith’ weight percentage due to in situ ceramic reinforcement. For instance, i5-wt% addition of Martian regolith increased the Vicker's microhardness from 366 ± 6 HV0.2 for as-printed Ti64 to 730 ± 27 HV0.2 while maintaining similar abrasive wear performance as Ti6Al4V. The results point toward laser-based AM for fabricating Ti64—Martian regolith composites with comparable properties. The study also reveals promising results in limiting the mass burden for future space missions, resulting in cheaper and easier launches.