Joël Alexis

Elemental fractionation effects in high repetition rate IR femtosecond laser ablation ICP-MS analysis of glasses

An IR-femtosecond laser ablation ICPMS coupling was used to investigate the influence of the high repetition rate on elemental fractionation effects for the analysis of silicate glass SRM NIST 610. First, elemental fractionation inherent to the ICP was minimised by working on wet plasma conditions which had greater tolerance to mass loading and demonstrated a higher robustness compared to dry plasma conditions. Because of the use of a narrow laser beam producing small craters (17 µm in diameter), a special arrangement of pulses was used to perform resulting craters of 100 µm diameter. The ablation strategy developed in this work consisted in a series of concentric circle trajectories ablated at high repetition rates by moving the laser beam rapidly thanks to a scanning beam device. Two scanner speeds (0.25 mm s−1 and 1.5 mm s−1), five laser repetition rates (from 0.1 kHz to 10 kHz) and three fluence values (5 J cm−2, 14 J cm−2, and 25 J cm−2) were investigated in detail. For this purpose, critical elemental ratios (namely 238U/232Th, 208Pb/238U, and 66Zn/65Cu) of aerosols produced by fs-LA of silicate glass were studied to evaluate the impact of the different laser parameters on elemental fractionation. No heating zones or preferential evaporation of elements were found depending on the repetition rate employed. However, particle-size-fractionation was measured during the ablation of the sample surface, and this effect was reduced by using a high repetition rate as well as a high scanner speed which allow the dilution of the large particles coming from the surface layer with finer particles coming to deeper levels. Additionally, the ablation rate induced by the selected ablation strategy had a low influence on fractionation effects due to the high robustness of the ICP plasma and, on the other hand, fractionation indices were not particularly affected by the laser repetition rate although they could be improved by the use of high fluence values. Finally, it could be stressed that no differences on the structure of the aerosol particles collected on membrane filters were found depending on the ablation parameters.

Direct determination of trace elements in powdered samples by in-cell isotope dilution femtosecond laser ablation ICPMS

A method has been developed for the direct and simultaneous multielement determination of Cu, Zn, Sn, and Pb in soil and sediment samples using femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICPMS) in combination with isotope dilution mass spectrometry (IDMS). The in-cell isotope dilution fs-LA-ICPMS method proposed in this work was based on the quasi-simultaneous ablation of the natural abundance sample and the isotopically enriched solid spike, which was performed using a high repetition rate laser and a fast scanning beam device in a combined manner. Both the sample preparation procedure and the total analysis time have been drastically reduced, in comparison with previous approaches, since a unique multielement isotopically enriched solid spike was employed to analyze different powdered samples. Numerous experimental parameters were carefully selected (e.g., carrier gas flow rate, inlet diameter of the ablation cell, sample translation speed, scanner speed, etc.) in order to ensure the complete mixing between the sample and the solid spike aerosols. The proposed in-cell fs-LA-ICP-IDMS method was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials, and the analysis of Cu, Zn, Sn, and Pb yielded good agreement of usually not more than 10% deviation from the certified values and precisions of less than 15% relative standard deviation. Furthermore, the concentrations were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore that in-cell fs-LA-ICP-IDMS opens the possibility for accurate and precise determinations of trace elements in powdered samples reducing the total sample preparation time to less than 5 min. Additionally, scanning electron microscope measurements showed that the aerosol generated by in-cell fs-LA-ICP-IDMS predominantly consisted of linear agglomerates of small particles (in the order of few tens of nanometers) and a few large spherical particles with diameters below 225 nm.

Experimental Study on the Mechanical Effects of the Vibration-Assisted Ball-Burnishing Process

Burnishing processes are effective methods for treating pieces to increase their durability and roughness. Studies reveal that traditional burnishing can be strongly improved with the assistance of external energy sources. A vibrating module was attached to a classical burnishing tool and was tested on aluminum specimens to find the optimal vibration-assisted burnishing parameters. Vibration caused roughness improvements of the specimens and decreased the processing time by fivefold compared to traditional burnishing. At the tested frequency, no significant consequences were found on hardness and residual stresses.

Corrosion Damages Induced by Cyclic Exposure of 2024 Aluminum Alloy in Chloride-Containing Environments

This paper focuses on the influence of cyclic exposure to chloride solutions on corrosion damage morphology developed on AA2024. The influence of the temperature during the air exposure periods was studied. Cyclic corrosion tests led to enhanced global corrosion damage compared to continuous immersion tests with residual mechanical properties of corroded samples significantly lower for cyclic tests. The corrosion morphology depended on the exposure conditions. For cyclic tests with air exposure periods at room temperature (CR tests), the corrosion defects were significantly longer; for a cyclic test with air exposure periodsat -20 °C (CF tests), the propagation of corrosion defects was not promoted; however, the density of corroded grain boundaries was markedly increased. For CR samples, the corrosion damage observed was mainly explained taking into account electrochemical processes occurring at the tip of the defect which could be considered as an occluded zone characterized by a chloride-enriched electrolyte and Hþ reduction as major cathodic reaction. For CF tests, the interaction between the stresses induced by the phase transformation of the medium i.e solidification and the hydrogen enrichment of the substrate could be a possible mechanism explaining the evolution of the global mechanical properties of the corroded samples

Oxidation resistance of ODS alloy PM2000 from 880°C to 1400°C

This letter compares the performances of alloy PM2000 exposed to air at various temperatures from 880°C to 1400°C in terms of oxidation kinetics and alumina scale morphology, crystal structure and composition.

Comparison of Physical-chemical and Mechanical Properties of Chlorapatite and Hydroxyapatite Plasma Sprayed Coatings

Chlorapatite can be considered a potential biomaterial for orthopaedic applications. Its use as plasma-sprayed coating could be of interest considering its thermal properties and particularly its ability to melt without decomposition unlike hydroxyapatite. Chlorapatite (ClA) was synthesized by a high-temperature ion exchange reaction starting from commercial stoichiometric hydroxyapatites (HA). The ClA powder showed similar characteristics as the original industrial HA powder, and was obtained in the monoclinic form. The HA and ClA powders were plasma-sprayed using a low-energy plasma spraying system with identical processing parameters. The coatings were characterized by physical-chemical methods, i.e. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, including distribution mapping of the main phases detected such as amorphous calcium phosphate (ACP), oxyapatite (OA), and HA or ClA. The unexpected formation of oxyapatite in ClA coatings was assigned to a side reaction with contaminating oxygenated species (O2, H2O). ClA coatings exhibited characteristics different from HA, showing a lower content of oxyapatite and amorphous phase. Although their adhesion strength was found to be lower than that of HA coatings, their application could be an interesting alternative, offering, in particular, a larger range of spraying conditions without formation of massive impurities.

Links Between Machining Parameters and Surface Integrity in Drilling Ni-Superalloy

In aerospace industry, the manufacturing of critical parts (high energy components) requires an important validation process to guarantee the quality of the produced parts, and thus their fatigue lifecycle. Globally, this validation consists in freezing the cutting conditions using metallurgical analysis or fatigue trials, and a test on the first article. This process is extremely complex and expensive. In this way establishing the correlation between the cutting conditions and the surface integrity will help us to optimize the manufacture of those parts. In this article, by the means of an experimental method, we define a domain of validation by combining the cutting conditions according to the classic criteria established by AFNOR E66-520 norm (Couple-Tool-Material) and the criteria of surface integrity for the drilling of a Nickel-base superalloy. The experimental device consists in drilling a Ø15.5 mm hole on a 3-axis milling centre instrumented by a 4 components Kistler dynamometer (Fx, Fy, Fz and Mz), a spindle power sensor “Watt-pilote” and three accelerometers placed following the directions X, Y and Z. Scanning Electron Microscopy (SEM) observations, micro-hardness tests and topographic measurements with an optical profilometer, are carried out to characterize the metallurgical state of the holes manufactured. Finally, correlations were respectively made between the cutting conditions, the recorded signals and the metallurgical state of the holes.

Mechanical and Surface Properties of Chemical Vapor Deposited Protective Aluminium Oxide Films on TA6V Alloy

Mechanical, barrier and surface properties of aluminium oxide films were investigated by nanoindentation, microscratch and micro tensile tests, by isothermal oxidation and voltammetry, and by contact angle measurement. The films were grown on TA6V substrates by a low pressure MOCVD process from aluminium tri-isopropoxide. Modelling of local gas flow, gas concentration and deposition rate profiles was performed using the CFD code Fluent on the basis of an apparent kinetic law. Films grown at 350 °C are amorphous AlO(OH), the one at 480 °C is amorphous Al2O3 and the one at 700 °C is nanocrystalline -Al2O3. Scratch tests and micro tensile tests resulted in adhesive failure on the two films grown at low temperature whereas cohesive failure was observed for the high temperature growth. Sample processed at 350 °C presents significantly lower oxidation kinetics in dry air than the bare substrate. Contact angle changes approximately from 100 to 50 degrees for films processed at 350-480 °C and 700 °C, respectively. Concerning the electrochemical behavior in NaCl environment, polarization curves revealed that amorphous alumina coatings improved the corrosion resistance by comparison with the others oxide films. These consolidated results reveal promising combination of properties for the films grown at different temperatures with regard to the targeted applications.

Experimental characterization of the mechanical behavior of two solder alloys for high temperature power electronics applications

An experimental investigation of two potential candidate materials for the diamond die attachment is presented in this framework. These efforts are motivated by the need of developing a power electronic packaging for the diamond chip. The performance of the designed packaging relies particularly on the specific choice of the solder alloys for the die/substrate junction. To implement a high temperature junction, AuGe and AlSi eutectic alloys were chosen as die attachment and characterized experimentally. The choice of the AlSi alloy is motivated by its high melting temperature Tm (577°C), its practical elaboration process and the restrictions of hazardous substances (RoHS) inter alia. The AuGe eutectic solder alloy has a melting temperature (356°C) and it is investigated here for comparison purposes with AlSi. The paper presents experimental results such as SEM observations of failure facies which are obtained from mechanical shear as well as cyclic nano-indentation results for the mechanical hardening/softening evaluation under cyclic loading paths.

Study of the Influence of the Artificial Ageing Temperature on the AA2024 Alloy Microstructure

For the last 30 years, AA2024 aluminum alloy was very used as structural material in the aerospace industry due to its low density and good mechanical strength. The phenomenon of precipitation hardening in aluminum alloys takes place at relatively low temperature and induces the precipitation of intermetallic particles composed of the main alloying elements i.e., copper and magnesium. The fundamental stage of the age-hardening process consists in the acceleration of the decomposition phenomenon of the supersaturated solid solution, resulting in the coarse intermetallic particle precipitation; stage where the mechanical properties reaches the maximum values, but at the cost of a low corrosion resistance. In this paper, the AA2024 alloy microstructure was studied during the over-ageing process. The over-ageing treatment (T7) is supposed to stabilize the microstructure and the mechanical properties to improve the corrosion resistance. The over-ageing treatment consists in a solution treatment at 495±5°C for 1 hour, quenched into cold water and artificial aged. Three different artificial ageing temperatures were studied: 150°C, 175°C and 190°C. The mechanical properties modifications were followed by Vickers macrohardness measurements. The treatment duration for each temperature (36 days for 150°C, 50 hrs for 175°C and 24 hrs for 190°C) was determined by a given macrohardness reduction. To characterize the over-aged AA2024 alloy microstructure, a statistical analysis of the surface fraction and surface density of intermetallic particles was made. The intermetallic particle dimension distribution, depending on the over-ageing temperature, was also observed. To do so, scanning electron microscope observations were carried out and image analyses were performed from backscattered electron images.