Assessment of Ferritic ODS Steels Obtained by Laser Additive Manufacturing.

This study aims to assess the potential of Laser Additive Manufacturing (LAM) for the elaboration of Ferritic/Martensitic ODS steels. These materials are usually manufactured by mechanical alloying of powders followed by hot consolidation in a solid state. Two Fe-14Cr-1W ODS powders are considered for this study. The first powder was obtained by mechanical alloying, and the second was through soft mixing of an atomized Fe-14Cr steel powder with yttria nanoparticles. They are representative of the different types of powders that can be used for LAM. The results obtained with the Laser Powder Bed Fusion (LPBF) process are compared to a non-ODS powder and to a conventional ODS material obtained by Hot Isostatic Pressing (HIP). The microstructural and mechanical characterizations show that it is possible to obtain nano-oxides in the material, but their density remains low compared to HIP ODS steels, regardless of the initial powders considered. The ODS obtained by LAM have mechanical properties which remain modest compared to conventional ODS. The current study demonstrated that it is very difficult to obtain F/M ODS grades with the expected characteristics by using LAM processes. Indeed, even if significant progress has been made, the powder melting stage strongly limits, for the moment, the possibility of obtaining fine and dense precipitation of nano-oxides in these steels.

[Stenting in superficial femoral artery and usCRP: Multicentric study SAFE in 255 patients]. / Stenting de l'artère fémorale superficielle et C-Reactive Protein ultrasensible (CRPus) : étude multicentrique SAFE de 255 patients.

OBJECTIVE: To evaluate mid-term primary patency of the femoral artery stenting in correlation with usCRP level and characteristics of the population, morphological aspect of the lesions and interventional techniques. METHODS: Patients were prospectively included in a multicenter study (18 centers in France) after stenting (SMART, Cordis Johnson & Johnson, Issy-les-Moulineaux, France) of the superficial femoral artery (SFA). Inclusion and exclusion criteria were based on recommendations and every day practice of the centers. RESULTS: Thus 255 patients (183 men; mean age: 69 years; range 44-92) were included. Technical success of the SFA stenting was 100% without any complications and primary angiographic success 97%. usCRP level increased significantly (p < 0.05) between before and 24h after SFA stenting. In the subgroup of patients without initial inflammation (n = 157), usCRP increased significantly (p < 0.05) in the group of patient with initial thrombosis and additional intervention (graft, amputation, angioplasty on other arterial bed) in the same procedure compared to the remaining patients. Restenosis rate was 12.4% (26/209 patients) at 7 ± 2 months. Before stenting, usCRP level was not predictive of a restenosis, whereas after stenting, an increase of the 24h usCRP level was significantly higher in the subgroup of patient with an occlusion at mid-term (8 patients; p < 0.05). CONCLUSION: This study demonstrated good patency at 7 months of SFA stenting with nitinol SMART with an increase of the usCRP level 24h after stenting in favour of the presence of an occlusion at mid-term follow-up.

Optical techniques for real-time penetration monitoring for laser welding.

Optical techniques for real-time full-penetration monitoring for Nd:YAG laser welding have been investigated. Coaxial light emission from the keyhole is imaged onto three photodiodes and a camera. We describe the spectral and statistical analyses from photodiode signals, which indicate the presence of a full penetration. Two image processing techniques based on the keyhole shape recognition and the keyhole image intensity profile along the welding path are presented. An intensity ratio parameter is used to determine the extent of opening at the rear of a fully opened keyhole. We show that this parameter clearly interprets a hole in formation or a lack of penetration when welding is performed on workpieces with variable thicknesses at constant laser power.

Closed-loop power and focus control of laser welding for full-penetration monitoring.

We describe a closed-loop control system ensuring full penetration in welding by controlling the focus position and power of a 4-kW Nd:YAG laser. A focus position monitoring system was developed based on the chromatic aberration of the focusing optics. With the laser power control system we can determine the degree of penetration by analyzing the keyhole image intensity profile. We demonstrate performance in bead-on-plate welding of Inconel 718 and titanium. The focus control system maintained a focal position on tilted and nonflat workpieces, and the penetration monitoring technique successfully controlled the laser power to maintain the full-penetration regime in the presence of linear and step changes of thickness. Finally we discuss the performances and the limits of the systems when applied to a realistic complex aerospace component.