RESUMO
This study characterizes the mechanical performance of the AlSi10Mg alloy produced by powder bed fusion-laser beam (PBF-LB) subjected to two combined cycles consisting of multilayer coating deposition (electroless nickel (Ni-P) + diamond-like carbon (DLC)) and heat treatment. In particular, the DLC deposition phase replaces the artificial aging step in the T5 and T6 heat treatments, obtaining the following post-production cycles: (i) Ni-P + DLC deposition and (ii) rapid solution (SHTR) (10 min at 510 °C) before Ni-P + DLC deposition. Microstructural characterization shows no appreciable modifications in the morphology and dimensions of the hard Si-rich phase of the eutectic network and secondary spheroidal Si phase. However, overaging phenomena induced by DLC coating deposition and differences in elastic-plastic properties between the multilayer coating and the PBF-LB AlSi10Mg substrate lead to a reduction in tensile strength by up to 31% and a significant decrease in ductility by up to 58%. In contrast, higher resistance to crack opening thanks to improved surface hardness and residual compressive stresses of the coating and reduced defect sensitivity of the substrate increase the fatigue resistance by 54% in T5-coated alloy and 24% in T6R-coated alloy. Moreover, the coating remains well adherent to the substrate during fatigue testing, not becoming a source of fatigue cracks.
RESUMO
Additive processes like Laser Beam Powder Bed Fusion (PBF-LB) result in a distinctive microstructure characterized by metastability, supersaturation, and finesse. Post-process heat treatments modify microstructural features and tune mechanical behavior. However, the exposition at high temperatures can induce changes in the microstructure. Therefore, the present work focuses on the analyses of the tensile response at room and high (200 °C) temperature of the A357 (AlSi7Mg0.6) alloy processed by PBF-LB and subjected to tailored T5 (direct aging) and T6R (rapid solution treatment, quenching, and aging) treatments. Along with the effect of microstructural features in the as-built T5 and T6R alloy, the role of typical process-related defects is also considered. In this view, the structural integrity of the alloy is evaluated by a deep analysis of the work-hardening behavior, and quality indexes have been compared. Results show that T5 increases tensile strength at room temperature without compromising ductility. T6R homogenizes the microstructure and enhances the structural integrity by reducing the detrimental effect of defects, resulting in the best trade-off between strength and ductility. At 200 °C, tensile properties are comparable, but if resilience and toughness moduli are considered, as-built and T5 alloys show the best overall mechanical performance.
RESUMO
Few systematic studies on the correlation between alloy microstructure and mechanical failure of the AlSi10Mg alloy produced by laser-based powder bed fusion (L-PBF) are available in the literature. This work investigates the fracture mechanisms of the L-PBF AlSi10Mg alloy in as-built (AB) condition and after three different heat treatments (T5 (4 h at 160 °C), standard T6 (T6B) (1 h at 540 °C followed by 4 h at 160 °C), and rapid T6 (T6R) (10 min at 510 °C followed by 6 h at 160 °C)). In-situ tensile tests were conducted with scanning electron microscopy combined with electron backscattering diffraction. In all samples the crack nucleation was at defects. In AB and T5, the interconnected Si network fostered damage at low strain due to the formation of voids and the fragmentation of the Si phase. T6 heat treatment (T6B and T6R) formed a discrete globular Si morphology with less stress concentration, which delayed the void nucleation and growth in the Al matrix. The analysis empirically confirmed the higher ductility of the T6 microstructure than that of the AB and T5, highlighting the positive effects on the mechanical performance of the more homogeneous distribution of finer Si particles in T6R.
RESUMO
The electric resistance welding procedure is used to join a titanium bar with specific implant abutments in order to produce a framework directly in the oral cavity of the patient. This investigation studied the effects of the welding process on microstructure and hardness properties of commercially pure (CP2 and CP4) Ti components. Different welding powers and cooling procedures were applied to bars and abutments, normally used to produce the framework, in order to simulate the clinical intraoral welding procedure. The analyses highlighted that the joining process did not induce appreciable changes in the geometry of the abutments. However, because of unavoidable microstructural modifications in the welded zones, the hardness decreased to values lower than those of the unwelded CP2 and CP4 Ti grades, irrespective of the welding environments and parameters.