Self-assembly of alkylphosphonic acids on stainless steel was investigated under different conditions. Four different alkylphosphonic acids exhibiting alkyl chain of various size were synthesized and studied: butylphosphonic acid (C4P), octylphosphonic acid (C8P), decylphosphonic acid (C10P), and hexadecylphosphonic acid (C16P). Electrochemistry experiments were extensively carried out in order to determine electrochemical surface blocking of adsorbed layers in function of grafting time. In term of surface blocking, an 8h modification time was optimal for all alkylphosphonic acids. Longer immersion times lead to degradation of adsorbed layers. For the first time, grafting of C16P was studied under high frequency ultrasound irradiation. Interestingly, grafting process is highly accelerated under sonication and well-covering C16P modified substrates are obtained after 1h of immersion under ultrasound irradiation. This would allow to elaborate high-quality alkylphosphonic acids modified samples within much shorter times. Water contact angles measurements and X-ray Photoelectrons Spectroscopy (XPS) confirmed presence of adsorbed alkylphosphonic acids on stainless steel surface. A very tight link between electrochemical blocking, surface hydrophobicity and species chemical grafting was established.
Self-assembling of undecanthiol (C11SH) on polycrystalline gold was investigated under two different conditions. The kinetics of C11SH grafting was studied without and under high frequency ultrasound irradiation. Two electrochemical experiments were extensively carried out in order to determine electrochemical surface blocking of adsorbed layers as a function of grafting time: chronoamperometry in-situ monitoring and cyclic voltammetry. Interestingly, the grafting process is highly accelerated under sonication, and C11SH modified substrates of good quality are obtained after 3h' immersion under ultrasound irradiation. This would allow elaboration of high-quality alkanethiol modified samples within much shorter times. Water contact angle measurements and X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of adsorbed undecanthiol on the gold surface. A very close link between electrochemical blocking, surface hydrophobicity and species chemical grafting was established.
If the technological progresses of additive manufacturing have enabled to achieve outstanding components with complex geometries, without adversely affecting their core mechanical and structural properties, their degraded surface state remains a critical issue which constitutes a key obstacle for its broad deployment. Indeed, surfaces of parts elaborated by this technic are characterized by a high roughness (Ra up to 40 µm), a strong texture (directly linked to the process and the manufacturing parameters) and to the presence of potentially detachable unmelted particles. Evaluating and developing relevant finishing post-treatments is the aim of the AFTER-ALM project (AFTER-Additive Layer Manufacturing) managed by the IRT M2P (Metz, France) which brings together industrial partners with major OEM such as Airbus, Safran, Liebherr, Collins Aerospace, Stelia, NavalGroup and ArianeGroup. The project also concerns companies specialized in additive manufacturing production (LISI Aerospace, WeAreAerospace, Spartacus 3D, Add-up, Volum-e), surface treatment applicators (Galvanoplast, Chrome Dur Industriel, DEC SA, Satys, GIT), technological partners (Micronics, ABC Swisstech, Beckmann Institute, IREPA laser, R&D Nano, INVENTEC, AQUARESE) and academics ones (UTINAM, CIRIMAT, ENISE).The work presented here focuses on development of an electrofinishing process dedicated to 316 L stainless steel developed by SLM. A study, performed at laboratory scale, allowed to characterize the electrochemical behavior of raw substrates (produced according to different laser scan strategies) was the opportunity to define the bests operating conditions for the levelling (electrolyte composition, temperature, electrical parameters U/I, treatment duration...) with acceptable dissolution rates (around 5 µm/min). The transposition to a pilot unit for the treatment of decametric sizes workpieces (flat or more complex specimens with variable grooves, tubes) requires a precise recalibration. Difficulties are essentially due to the high roughness of the SLM substrates (Ra ⋍30 µm, Rz ⋍ 200 µm), but also to issues related to the process scale-up such as current lines distribution which induces an inhomogeneous dissolution. It is possible to obtain very good results in roughness decrease, but to the detriment of the dimensional characteristics.To meet the dual objective of roughness reduction combined with respect for the geometrical integrity, the use of pulsed potentials has been shown to be highly effective. Tested at laboratory scale and then extended to the pilot scale, a 90% decrease of the roughness was measured while preserving as much as possible the geometries of all samples. These good performances were explained by differences in the mechanisms involved with constant or pulsed potential, as highlighted by transient curves study (figure 1) and spectral power density processing of roughness data. Figure 1
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