3D Printing Of Metallic Structures From A Green Ink

A green metallic ink is developed for 3D printing of metallic structures featuring high mechanical and electrical performances. The metallic ink consists of steel micro powders and a water-based chitosan/acetic acid polymer solution which replaces the previously used toxic polylactic acid (PLA)/dichloromethane (DCM) polymer solution. The optimized ink is printed at room temperature to build a metal/polymer hybrid structure. While printing, a fan is used to blow air over the ink filament upon extrusion to accelerate the solvent evaporation and shorten the solidification time, which significantly reduces the sagging and deformation. After a drying period at ambient conditions, the as-printed structure is then thermally treated using a furnace. The polymer binder is decomposed and the metal powders are sintered, resulting in a strong metallic structure. Melted copper is infiltrated into the sintered structure to achieve a fully dense metal/metal hybrid structure. The sintered structure exhibits high stiffness (205 GPa), electrical conductivity (9 × 105 S/m) and low filament porosity (7%)

Copper precipitation at engine operating temperatures in powder-forged connecting rods manufactured with Fe–Cu–C alloys

The effect of copper precipitation on the mechanical properties of Fe–Cu–C alloys prepared for Powder Metallurgy and used to manufacture connecting rods for the automotive industry through powder forging was evaluated at engine operating temperatures, ranging between 100 °C and 150 °C. Tensile tests were conducted at room temperature as well as at 120 °C and 150 °C on specimens machined from connecting rods. The test results clearly indicated an improvement in the strength of Fe–Cu–C alloys at 120 °C and 150 °C. Scanning and transmission electron microscopies were employed to investigate the strengthening mechanism causing the improvement. The microscopy investigations pointed to stress-induced second phase precipitation strengthening in super-saturated Fe–Cu–C alloys even at these relatively low temperature levels as copious Cu nano precipitates were observed in the specimens submitted to tensile testing at 120 °C and components submitted to engine dynamometer testing. Clear evidence of interactions between dislocations and copper precipitates was found in both tensile specimens and components

Environment-friendly and reusable ink for 3D printing of metallic structures

ABSTRACT: There is an increasing need for 3D printing of metallic structures in a green and cost-effective way. Here, an environment-friendly and reusable metallic ink was developed for an economical metal 3D printing method. The metallic ink is composed of steel micro powders, a biodegradable polymer: chitosan, acetic acid and deionized water. The metal 3D printing method consists of: (i) 3D printing of metallic structures using the metallic ink at room temperature, (ii) thermal treatments on the as-printed structures that decompose the polymer binder and sinter the steel powders, and (iii) an optional step: infiltrating melted copper into the sintered structures to achieve fully dense metal/metal hybrid structures. We demonstrate that any incorrectly built as-printed structures and scrap materials can be recycled and reused for 3D printing by dissolving them again in acetic acid. The fabricated structures after copper infiltration feature a low filament porosity of 1.0% which enables high properties such as an electrical conductivity of 1.3 × 106 S/m and a Young's modulus of 160 GPa. The metallic ink can be used for the 3D printing of high performance metallic structures while demonstrating a low environmental impact and a very effective utilization of metallic materials

Synthesis and characterization of (Al,Si)₃(Zr,Ti)-D0₂₂/D0₂₃ intermetallics: Understanding the stability of silicon substitution

ABSTRACT: (Al,Si)₃(Zr,Ti)-D0₂₂/D0₂₃ are phases that may form in aerospace and automotive aluminium alloys. The substitution of Zr/Ti in these solid solutions is widely reported in the literature; however, it remains relatively unexplored for Si. In this work, in situ precipitation of (Al,Si)₃(Zr,Ti)-D0₂₂/D0₂₃ intermetallics was performed using Al-Si-Zr-Ti alloys. The precipitation, sedimentation and concentration of numerous intermetallic particles were accomplished by filtrating the residual molten aluminium using a temperature/pressure-controlled vessel adapted with a PoDFA filter. A combination of SEM, TEM, XRD and EMP analysis allowed the identification of (Al,Si)₃(Zr,Ti)-D0₂₂/D0₂₃ intermetallics concentrated within α-FCC matrices of non-Si-doped (sample S2) and Si-doped (samples S4 and S6) alloys. EDS analysis confirmed that Zr and Ti substitute each other in the D0₂₂ and D0₂₃ phases, whereas Si substitutes in Al sites. Acceptance of Si inside the D0₂₃ phase was not expected according to FTlite (FactSage) and TCAL7 (Thermo-Calc) databases. Additionally, Si was found to enhance the formation of (Al,Si)₃(Zr,Ti)-D0₂₂ intermetallics with high Zr-content, contrary to FactSage 7.3 predictions. TEM results showed intermetallic/FCC crystal coherency for samples S2 and S6, implying that these intermetallics acted as nucleation sites for the Al-phase due to their small lattice mismatch. Furthermore, Si site occupancy was calculated for both (Al,Si)Ti-D0₂₂ and (Al,Si)₃Zr-D0₂₃ phases via DFT, showing that sites 2b and 4e are the most favorable for Si occupation, respectively. Finally, a thermodynamic model is derived to describe Si substitution upon solidification. Experimental and numerical examinations indicate that Si substitution preferentially occurs in the D0₂₂ intermetallics compared to the D0₂₃ phase