Determination of Ruthenium in Heat-Resistant Nickel Alloys by Atomic Emission Spectrometry with Inductively Coupled Plasma

Abstract

UDC 543.423 A technique for measuring 0.5-6.5 mass% ruthenium in heat-resistant nickel alloys using atomic emission spectrometry with inductively coupled plasma was developed. The measurement precision (repeatability and reproducibility) was determined. Introduction. One of the most important applications of heat-resistant nickel (Ni) alloys (HNA) is the preparation from them of aviation gas-turbine engine blades and disks. The gas temperature at the turbine intake has risen during the last 50 years of aviation development from 1200 K in second-generation engines to 1800-1950 K in fi fth-generation engines (1-3). HNA are complicated doped compounds with a heterophase structure, the principal components of which are disperse (<0.5 μm) particles of the γ'-phase based on the ordered intermetallic compound Ni3Al and a complicated doped nickel γ-solid solution. Furthermore, topologically densely packed (TDP) phases that reduce the stability of the alloy phases can form in HNA under certain crystallization and heat-treatment conditions (4). As a result, the operational properties of the alloys degrade. Rhenium (Re) (up to 5-6 mass%) was previously added to the alloy in order to stabilize the phase composition and to reduce the probability of segregating TDP phases. Doping of fi fth-generation HNA with ruthenium (Ru) was also proposed recently (5-11). This made the alloys even more heat-resistant and produced several defi nite advantages over Re. It had almost half the density, was less prone to TDP phase formation, and practically did not sweat during crystallization. Simple, rapid, and robust analytical methods that enable Ru to be determined in alloys from 0.5 to 6.5 mass% are needed in order to monitor the Ru content in HNA during their fabrication and production. Several techniques and standards for methods of determining Ru in Pt-Ru alloys are known (12-14). However, robust, modern, and attested techniques for determining Ru in HNA at a content of 0.5-6.5% are not available in Russia. The goal of the present work was to develop a technique for measuring the Ru mass fraction (0.5-6.5 mass%) in HNA using atomic emission spectrometry with inductively coupled plasma (ICP-AES). The technical and experimental principles for using the ICP-AES method are well known (15-17). Experimental. A Varian 730-ES ICP-AES spectrometer equipped with a horizontally positioned high-temperature (up to 10,000°C) induction burner (longitudinal view) operated by a high-frequency (40 mHz) plasma system; a purged echelle polychromator (spectral range 176-785 nm) with full computer control of the plasma view point; plasma gas fl ows; and web-integrated ICP-Expert TM II software was used for the measurements. Samples of the last generations of nickel alloys with Ru content in them according to TU (technical specifi cations) and HNA ZhS 1 (containing all components except Ru) for preparing a control solution were selected for developing the measurement technique and establishing the metrological characteristics of the measured HNA Ru mass-fraction. Measurements were made using Ru emission line λ = 343.674 nm, which was free of interferences from other elements. A series of aqueous calibration solutions based on a standard sample (SS) of Ru solution (High-Purity Standards, USA) with Ru concentration 1000 mg/dm 3 were prepared in order to study the emission signal intensity as a function of solution Ru