PHÉNOMÈNES ANÉLASTIQUES LIÉS À LA PRÉSENCE D'AZOTE DANS LES ACIERS INOXYDABLES À 18% DE CHROME ET 10% DE NICKEL

La mise en ordre des atomes d'azote sous l'influence de la contrainte a été étudiée dans les aciers inoxydables de type 18-10. Un maximum d'amortissement interne est observé vers 220°C aux fréquences de l'ordre de l'hertz. La hauteur du maximum détecté est reliée au carré de la concentration en azote de la solution solide. Une analyse détaillée du spectre de frottement intérieur montre que le maximum contient deux pics plus petits avec des énergies d'activation de 92 et 116 kJ/mole. Le pic de basse température semble être en relation avec l'interaction des paires d'atomes d'azote interstitiels. Le pic de haute température est interprété en termes d'intéraction entre atomes d'azote et de chrome.Stress induced ordering of nitrogen atoms in 18-10 stainless steel. A maximum is found in the vicinity of 220°C at frequencies of the order of 1.0 cps. The hight of the maximum is related to the square of nitrogen content. A detailed analysis indicates the maximum contained two smaller peaks with activation energy of 92 and 116 kJ/ mole. The lower temperature peak was probably caused by interaction of the interstitial nitrogen pairs while the second peak was interpreted in terms of interaction of the atomic nitrogen with chromium

INFLUENCE OF THE NITROGEN CONTENT ON THE INTERNAL FRICTION OF Fe-16.6 wt % Cr ALLOYS

Using N2-H2 mixtures, controlled quantities of nitrogen were introduced in pure iron-chromium alloys. The internal friction was measured during heating and cooling on a 1100°C as quenched sample between room temperature and 400°C. A maximum Q-1max was detected as soon as the nitrogen content was in the 130-200.10-4 wt % range. At a frequency ν = 0.9 Hz, the temperature of this maximum Tm was slightly decreased from 270°C to 250°C when the nitrogen content was increasing. A martensitic phase appeared in the 1100°C as quenched alloy for a nitrogen content between 480 and 580.10-4 %. Then an increase of the height of the maximum and a modification of Tm were detected. Below a 580.10-4 wt % nitrogen content, the maximum was broad and a small reversible peak was detected during cooling. Comparing these results with those obtained on similar alloys containing carbon, the behaviour of these two interstitials in ferritic iron-chromium are discussed

INTERNAL FRICTION MEASUREMENTS DURING THE TEMPERING OF THE 1000°C AS QUENCHED Cu-10.1 wt % Al ALLOY

The damping of 1000°C as quenched samples of Cu-10.1 wt % Al was studied either after tempering or during heating between room temperature and 350°C. The room temperature measurements showed a significant decrease between 50°C and 220°C. Up this tempering temperature a maximum was observed at about 280°C depending on the experimental conditions. The vacancy mobility would be the main reason of the internal friction spectrum. Ordering process appeared in the β' martensite leading to a transition state between S.R.O. and L.R.O. However a flat spectrum Q-1(T) was obtained up to 250°C during the heating of an as quenched-sample

Fabrication of Copper-Rich Cu-Al Alloy Using the Wire-Arc Additive Manufacturing Process

An innovative wire-arc additive manufacturing (WAAM) process is used to fabricate Cu-9 at. pct Al on pure copper plates in situ, through separate feeding of pure Cu and Al wires into a molten pool, which is generated by the gas tungsten arc welding (GTAW) process. After overcoming several processing problems, such as opening the deposition molten pool on the extremely high-thermal conductive copper plate and conducting the Al wire into the molten pool with low feed speed, the copper-rich Cu-Al alloy was successfully produced with constant predesigned Al content above the dilution-affected area. Also, in order to homogenize the as-fabricated material and improve the mechanical properties, two further homogenization heat treatments at 1073 K (800 °C) and 1173 K (900 °C) were applied. The material and mechanical properties of as-fabricated and heat-treated samples were compared and analyzed in detail. With increased annealing temperatures, the content of precipitate phases decreased and the samples showed gradual improvements in both strength and ductility with little variation in microstructures. The present research opened a gate for in-situ fabrication of Cu-Al alloy with target chemical composition and full density using the additive manufacturing process