Comparative study of the microstructure between a laser beam melted 17-4PH stainless steel and its conventional counterpart

The aim of this work was to compare the microstructures of 17-4PH martensitic stainless steels (MSSs) obtained by conventional manufacturing (CM), and additive manufacturing (AM) using laser beam melting (LBM) process. Both materials were studied after the same H900 heat treatment. Significant differences in microstructure were observed between the two MSSs, with a higher austenite content for the AM-H900 sample, as compared to the CM-H900 sample. Transmission electron microscopy (TEM) analyses allowed to identify both retained and reversed austenite in the AM-H900 sample, but most part of the austenite detected was found to be reversed austenite. The high amount of reversed austenite in the AM-H900 sample was attributed to a heterogeneous distribution in austenite-stabilising elements in the solution heat treated AM sample, leading to a decrease in Ms value and subsequent increase in the driving force for the martensite to austenite transformation during the ageing at 480 °C. Moreover, TEM analyses highlighted thinner martensite laths for the AM-H900 steel as compared to the CM-H900 one. This was interpreted as an increase in both nucleation sites and growth rate for reversed austenite. Despite those differences in microstructure, the AM-H900 and CM-H900 samples showed similar tensile behaviour, with similar UTS and Rp0.2 values, but a decrease in the strain to fracture was observed for the AM-H900 sample, probably related to the pores and/or to intergranular carbides

Behavioral and biological risks of women seeking HIV test in an anonymous testing center

Due to the high prevalence and morbidity sexually transmitted diseases are highly relevant to public health, especially for women. OBJECTIVES: To determine and compare the behavioral and biological risks associated with human immunodeficiency virus acquisition. METHODS: A group of 253 women who voluntarily sought anonymous testing were interviewed to find out their behavioral risk. Biological risk was identified by means of gynecological exam, colposcopy as well as blood and cervicovaginal sampling for serological and microbiological exams. Using known traditional risk factors, a table of scores classified the subjects into high, low and absent for behavioral and biological risks. Frequency and percentage of each risk was tabulated and the correlation between risks was obtained by calculating the Kappa statistic. RESULTS: 79.8% of subjects were found to have behavioral risks, and 79.1% biological risks. It was also found that 66.7% of the women (169) with high behavioral risk also had high biological vulnerability. However, 31 out of 51 women without any behavioral risk had biological vulnerability 12.2 %. The Kappa statistic demonstrated low agreement between the latter risks [K = 0.05 95% CI (-0.06 to 0.17)]. CONCLUSION: Women who seek care in centers for anonymous testing have high biological risk, which is neither proportional nor concurrent to behavioral risk. The low concordance found between these risks suggests the need for routine gynecological investigation (clinical and microbiological) for all women.36036

Influences mécaniques et métallurgiques de procédés haute température sur un alliage d\u27aluminium 6061-T6

Le travail de thèse présenté dans ce mémoire s\u27inscrit dans le cadre des actions de qualification anticipée du caisson du RJH (Réacteur Jules Horowitz). Le caisson est une enceinte sous pression fabriquée en alliage d\u27aluminium 6061-T6. Il s\u27agit d\u27un alliage à durcissement structural dont les propriétés mécaniques sont étroitement liées à l\u27état de précipitation dans le matériau. Des essais de traction ont permis de mesurer l\u27évolution des propriétés mécaniques du matériau ayant subi des chargements thermiques représentatifs d\u27une opération de soudage par faisceaux d\u27électrons (soudage FE). Des essais ont été menés à température ambiante et à chaud. Des observations métallurgiques par Diffusion de Neutrons au Petits Angles (DNPA) et par Microscopie Electronique en Transmission (MET) donnent par la suite la taille et la fraction volumique des précipités. Les résultats de ces campagnes d\u27essais permettent de comprendre l\u27évolution des propriétés mécaniques. Ces expérimentations ont ensuite été utilisées pour mettre en place un modèle métallurgique permettant de calculer les caractéristiques de l\u27état de précipitation. Ce modèle étant couplé à un modèle de durcissement structural, il calcule la limite d\u27élasticité du matériau pour divers chargements thermiques. Un modèle mécanique phénoménologique a également été développé afin de modéliser le comportement d\u27une structure soumise à un chargement thermique

Influences mécaniques et métallurgiques de procédés haute température sur un alliage d'aluminium 6061-T6

Le travail de thèse présenté dans ce mémoire s'inscrit dans le cadre des actions de qualification anticipée du caisson du RJH (Réacteur Jules Horowitz). Le caisson est une enceinte sous pression fabriquée en alliage d'aluminium 6061-T6. Il s'agit d'un alliage à durcissement structural dont les propriétés mécaniques sont étroitement liées à l'état de précipitation dans le matériau. Des essais de traction ont permis de mesurer l'évolution des propriétés mécaniques du matériau ayant subi des chargements thermiques représentatifs d'une opération de soudage par faisceaux d'électrons (soudage FE). Des essais ont été menés à température ambiante et à chaud. Des observations métallurgiques par Diffusion de Neutrons au Petits Angles (DNPA) et par Microscopie Electronique en Transmission (MET) donnent par la suite la taille et la fraction volumique des précipités. Les résultats de ces campagnes d'essais permettent de comprendre l'évolution des propriétés mécaniques. Ces expérimentations ont ensuite été utilisées pour mettre en place un modèle métallurgique permettant de calculer les caractéristiques de l'état de précipitation. Ce modèle étant couplé à un modèle de durcissement structural, il calcule la limite d'élasticité du matériau pour divers chargements thermiques. Un modèle mécanique phénoménologique a également été développé afin de modéliser le comportement d'une structure soumise à un chargement thermique.The thesis work is part of the actions of early qualification of a pressure vessel in the RJH (Jules Horowitz Reactor). This vessel is made of aluminium alloy 6061-T6. this is an age hardening allow whose mechanical properties are closely related to the precipitation state in the material. Tensile tests were used to measure the evolution of the mechanical properties of the material previously subjected to thermal loading representative of an electron beam welding operation (EB welding). Tests were conducted at room temperature and at high temperature. Then metallurgical observations by small Angle Neutron Scattering (SANS) and by Transmission Electron Microscopy (TEM) gave the size and the volume fraction of precipitates. The results of these campaigns improved our understanding of the mechanical properties and evolution with thermal history. Furthermore, these experiments were used to develop a metallurgical model to forecast the characteristics of the precipitation state. A model was linked to a hardening model for the calculation of the yield strength of the material after various thermal loading. A phenomenological mechanical model was also developed to represent the behaviour of a structure subjected to thermal loading.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Susceptibility to Pitting and Environmentally Assisted Cracking of 17-4PH Martensitic Stainless Steel Produced by Laser Beam Melting

Materials produced by additive manufacturing (AM) often have different microstructures from those obtained using conventional metallurgy (CM), which can have significant impacts on the materials’ durability, and in particular, resistance to corrosion. In this study, we were concerned with the susceptibility to pitting and environmentally assisted cracking (EAC) of 17-4PH martensitic stainless steel (MSS). We focused on the evolution from pitting to EAC, and the behaviour of MSS produced by AM was compared with that of its CM counterpart. Potentiodynamic polarisation tests were combined with chronoamperometry measurements performed without and with mechanical loading to study both stable and metastable pitting and the influence of stress on these processes. EAC tests were carried out and combined with observations of fracture surfaces. MSS produced by AM was more resistant to pit initiation due to fewer and finer NbC particles. However, the propagation kinetics of stable pits were higher for this MSS due to a higher amount of reversed austenite. The stress was found to stabilise the metastable pits and to accelerate the propagation of stable pits, which resulted in an increased susceptibility to EAC of the MSS produced by AM. These results clearly highlighted the fact that the reversed austenite amount has to be perfectly controlled in AM processes

Modélisation du développement des microstructures en procédé laser sur lit de poudre – Application au superalliage IN718

International audienc

Modelling of microstructures development in laser powder bed fusion process – Application to IN718 superalloy

International audienc

Modélisation des microstructures obtenues en fabrication additive par fusion laser sur lit de poudre d’un alliage base Nickel

International audienc

Influence of hydrogen on the stress-relaxation properties of 17-4PH martensitic stainless steel manufactured by laser powder bed fusion

To evaluate the interactions between hydrogen and the mechanical behavior of additively manufactured (AM) 17-4PH martensitic stainless steel (MSS), stress-relaxation tests were performed for both non-charged and hydrogen-charged samples. Similar tests were performed for the conventional 17-4PH MSS counterpart (CM). The results clearly indicated significant differences in the relaxation properties between the CM and AM MSSs in the H900 state, which were attributed to the higher reversed austenite amount in the AM MSS than that in the CM MSS. In particular, the influence of hydrogen on the dislocation mobility in the austenite was clearly shown