Etude expérimentale du soudage par laser YAG de l'alliage base nickel Hastelloy X

Le procédé de soudage laser YAG est envisagé pour remplacer le procédé de soudage TIG manuel pour la réalisation de pièces de turboréacteur en alliage nickel-chrome-molybdène Hastelloy X. Cette étude expérimentale a permis de définir un domaine de soudabilité de cet alliage répondant aux critères spécifiques du secteur aéronautique

Characterization of refractory titanium alloys welded by TIG and laser processes

The use of refractory titanium alloys for the components of structure subjected to increasing temperatures is in full expansion in the air transport. Within the framework of European project HORTIA, aiming to develop and design a conduit of refractory titanium alloy helicopter by associating innovative processes and the industrial constraints, this work relates to the implementation and characterization of Ti6242 and Beta-21 S welded sheets by TIG and C02 laser processes. The determination of the mechanical characteristics in connection with the metallurgical transformations relating to the Ti6242/Ti6242, Beta 2IS /Beta 2lS and Ti6242/Beta2lS assembly configurations allowed a rigorous comparison of the processes and studied materials. The influence of the heat treatment 600°C/8h on the relations structures/mechanical properties was also studied in order to envisage the behaviour of the assemblies under the real service use conditions

Adherence of electrodeposited Zn-Ni coatings on EN AW2024 T3 aluminium alloy

The use of hexavalent chromium in surface treatments will be reduced in the future, as it is suspected to be carcinogenic. Electrodeposition of Zn-Ni, which is currently used on steel, represents a non-chromate alternative surface treatment for the corrosion protection of aluminium alloys. Zn-Ni coatings were electrodeposited onto an EN AW2024 T3 aluminium alloy sheet in a laboratory flow cell. To obtain several percentages of Ni in the coatings, solutions with different Ni2+ concentrations were used. The influence of a specific pretreatment to promote adherence, such as zincate immersion (109 g L-1 ZnO, 525 g L-1 NaOH) or phosphoric anodisation (36 wt-%H3PO4, 20°C) prior to electrodeposition was also investigated. The smoothness of the coating, measured on a three-dimensional roughness tester, increased when the percentage of Ni increased. This can be explained by a microstructural refinement observed using SEM and AFM. These microstructural changes are due to the evolution of the crystal structure of the coatings and can be observed by X-ray diffraction. The mechanical properties of the coatings (hardness and Young's modulus) were measured by microindentation and nanoindentation. The adherence of the coatings was tested by a scratch test and a three point bending test dedicated to coatings. The scratch behaviour of the coatings was a function of the percentage of Ni. The scratches observed indicate a ductile fracture for coatings with a low percentage of Ni and a brittle fracture for a high percentage of Ni. Bending tests demonstrated the favourable effect of pretreatments such as zincate immersion or phosphoric anodisation as well as adhesion enhancement as a function of increasing percentage of Ni

Validation of mechanical damage monitoring on aluminium freestanding thin films using electrical measurements

This paper describes a new technique allowing the monitoring of damage in metallic freestanding thin films during micro-tensile test by using electrical characterization. After a presentation of the set-up, results obtained on aluminium thin coatings by using two calculation methods for damage variable are presented and commented

Influence of Yb:YAG laser beam parameters on Haynes 188 weld fusion zone microstructure and mechanical properties

The weldability of 1.2 mm thick Haynes 188 alloy sheets by a disk Yb:YAG laser welding was examined. Butt joints were made, and the influence of parameters such as power, size, and shape of the spot, welding speed, and gas flow has been investigated. Based on an iconographic correlation approach, optimum process parameters were determined. Depending on the distribution of the power density (circular or annular), acceptable welds were obtained. Powers greater than 1700 W, welding speeds higher than 3.8 m mm1, and spot sizes between 160 and 320 lm were needed in the circular (small fiber) configuration. By comparison, the annular (large fiber) configuration required a power as high as 2500 W, and a welding speed less than 3.8 m min�1. The mechanical properties of the welds depended on their shape and microstructure, which in turn depended on the welding conditions. The content of carbides, the proportion of areas consisting of cellular and dendritic substructures, and the size of these substructures were used to explain the welded joint mechanical properties

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Elective cancer surgery in COVID-19-free surgical pathways during the SARS-CoV-2 pandemic: An international, multicenter, comparative cohort study

PURPOSE As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19–free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19–free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19–free surgical pathways. Patients who underwent surgery within COVID-19–free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19–free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score–matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19–free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION Within available resources, dedicated COVID-19–free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Elective Cancer Surgery in COVID-19-Free Surgical Pathways During the SARS-CoV-2 Pandemic: An International, Multicenter, Comparative Cohort Study.

PURPOSE: As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19-free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS: This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19-free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS: Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19-free surgical pathways. Patients who underwent surgery within COVID-19-free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19-free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score-matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19-free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION: Within available resources, dedicated COVID-19-free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Weldability of superalloys Hastelloy X by Yb : YAG laser

International audienceRequirements of aircraft parts welded becoming increasingly severe especially in termsof reproducibility of geometry and metallurgical grade of weld bead; laser welding is a viable method of assembly to meet these new demands by its automation to replace longer term the manual TIG welding process. The purpose of this study is to determine the weldability of Hastelloy X alloy by the butt welding process Nd: YAG laser. To identify influential parameters of the welding process (laser power, feed rate, focal diameter and flow of gas) while streamlining testing, an experimental design was established with the CORICO software that uses the graphic correlation method. The position of the focal point was fixed at -1/3 of the thickness of the sheet. The gas flow rate and the power of the beam seem to have a major role on the mechanical properties and geometry of the weld. The strength of the weld is comparable to that of base metal. However, there is a significant drop in the elongation at break of about 30 %. The first observations of the cross section of the weld by scanning electron microscopy coupled with EBSD analysis show generally a molten zone presenting dendritic large grain compared to the equiaxed grains of the base metals without a heat affected zone