Formation of phase during glow-discharge nitriding of tantalum alloys with tungsten

Abstract

Many methods are used to harden tantalum (solid-solution hardening, plastic deformation, grain ordering, dispersion hardening, and introduction of hardening dispersion phases in the form of particles, filaments, whiskers, fibers, etc.). The influence of conditions of glow-discharge nitriding of tantalum and the alloy Ta-10% W on the microhardness and phase composition of the diffusion layer is discussed.N itriding is a comparatively new method of hardening tantalum and its alloys [ 1, 2]. The use of a glow discharge makes it possible to substantially extend the technological capabilities of nitriding. Ion-beam nitriding has a number of advantages over ordinary gas nitriding [3]. Its main advantages are a high saturation rate and a possibility of controlling the structure and phase composition of the layers obtained so as to ensure that the parts treated have the necessary ensemble of service characteristics. The published data on ion-beam nitriding of tantalum and its alloys are limited. Accordingly, the sequence of phase formation and the effect of substitutional alloying elements on nitrogen diffusion in tantalum remain open questions.We studied high-purity TVCh tantalum and the commercial tantalum-tungsten alloy TV-10 (Ta-10% W). Ion-beam nitriding was carried out an experimental setup in purified nitrogen in the temperature range 700-1000°C and a saturatingmedium pressure of 0.4-20 GPa for 0.5-5 h.The structure and phase composition of the nitrided alloys were studied by metallographic, electron-microscopic, massspectrometric, and microdurometric methods.The microstructure of the nitrided layers was studied under a NEOPHOT 21 metallographic microscope. Thin foils cur from various parts of a layer were examined in a JEM-100B electron microscope. The nitrogen distribution in the surface layer was evaluated by secondary-ion-mass spectrometry on an a-DIDA instrument. The phase composition of the diffused layers was determined by layer-by-layer x-ray structural analysis. The x-ray photographs were taken in copper and iron characteristic Kc~ radiation on a DRON 2 diffractometer with monochromatization by the ionization method. On the basis of the x-ray structural data we also determined the thickness of the nitride zone. The microhardness of the nitrided alloys was measured on a PMT-3 instrument under a load of 0.5 N.The nitride zone of the nitrided layer, as a rule, is very small and after nitriding even at high nitrogen pressures in the working chamber of the apparatus is not more than 3-5 ~m thick and so is not always detected metallographically. The nitride zone is visible in microsections of samples nitrided for a long time only after saturation at nitrogen pressures higher than 15 GPa.The microstructure of the base of the alloys (core), corresponding to the annealed state, remains virtually unchanged after nitriding in the given range of temperatures and pressures. Because it is so thin the inner nitride layer is not revealed after treatment at the indicated nitrogen pressures.The phases formed in the nitride...

Direct Alpha Ta Formation on TaN by Resputtering for Low Resistive Diffusion Barriers

“…It has been shown that the resulting phase of the TaN compound in sequence with increasing N 2 ratio follows a mixture of beta-Ta and alpha Ta, alpha Ta bcc-TaN x and fcc TaN. [12][13][14][15] Figure 6 demonstrates that the bilayer resistivity after 8 nm resputtering decreases sharply starting from the N 2 /Ar ratio of about 10% and reaches the minimum when the ratio is over 23%. This suggests that the presence of enough nitrogen Intensity (arb.)…”