Papers by Keyword: High Temperature Alloy

Abstract: The primary coolant of High-Temperature Gas-cooled Reactor (HTGR) is expected to contain impurities that can make corrosion to structural metallic materials at elevated temperatures. According to the chemical thermodynamics and kinetics, the carbon activity of helium can be calculated, and it is indicated that a high “CH₄/H₂O” ratio may lead to severe carburizing of the alloys. On this basis, corrosion tests were conducted on the three heat-resistance alloys Inconel 617, Hastelloy X, and Incoloy 800H at 950°C using helium environment with impurities, and mainly the effect of carburization was investigated. The corrosion samples were observed by Scanning Electron Microscopy (SEM) with Energy Disperse Spectroscopy (EDS), Electron Probe Microanalyzer (EPMA), and Carbon-sulfur Analyzer. These all alloys showed the oxidation and carburizing behavior, in which the carburized depth of Hastelloy X was shallow due to the dense oxide scale.

Abstract: The served harsh environment of advanced aircraft engine puts forward higher requirements for high temperature titanium alloy performance. The optimized heat treatment technology provides effective theoretical basis for improving the microstructure and properties of high temperature titanium alloys. In this paper, we study the influence of different heat treatment systems on microstructure and mechanical properties of high temperature alloy with equiaxed structure, in order to obtain the corresponding relationship between the process and the microstructure performance of the alloy and the optimal heat treatment process. Analysis the effect of solution treatment on the primary α phase quantitatively by optical microscope and Image-Pro-Plus 6.0 software based on the forged high temperature titanium alloy in α+β phase region. Observe the precipitation of α2 phase and silicide by TEM, optimize the aging process according to hardness test. The results show that the content of primary a phase decrease from 63.3% at 920°C to 15.3% at 990°C with the increase of solution temperature. When the temperature rises to 980~990°C, the structure changes from equiaxed structure to α+β duplex microstructure. And change into lamellar structure when the solution temperature raise to 1010°C. The secondary α phase precipitates more fully when the aging temperature increases. And with increasing aging time, the trend of α2 phase growth become more significantly. The optimum heat treatment system obtained in this experimental is 990°C/1h/AC+700°C/5h/AC, and the α phase is about 15.3%. Hence, the excellent microstructure and properties match has been obtained.

Abstract: High temperature alloy is the key hot end parts' material, which is often used in the modern aircraft, spacecraft and the rocket engines, as well as naval vessels and industry gas turbine. And it's also used in the nuclear reactor, chemical equipment, coal conversion technologies etc. as the very important high temperature structural materials. High temperature alloy of turning processing is the technical difficulties in mechanical cutting work, this paper introduces the high temperature alloy turning processing features, turning processing tool, cutting parameters, the choice of the cutting fluid and machining notice proceedings, etc.

Abstract: The Al-Cu-Mg alloys currently used at elevated temperature for aerospace applications, such as 2618 and 2219, were developed in the 1950s. Since then, not only have property requirements evolved significantly with the widespread introduction of damage tolerant design, but also the understanding and modelling capacity of the alloys' property-composition-processing relationships have developed beyond recognition. Moreover there is a renewed need for higher strength/toughness, higher temperature solutions in many aircraft's hot areas.A kinetic model has been developed to predict the strengthening capability and the thermal stability of hardening phases. It is based on a homogeneous nucleation, growth and coarsening model applied to S' (Al₂CuMg) and θ' (Al₂Cu); the yield strength is then calculated from the precipitates' size distribution. It suggests two areas of interest in the Al-Cu-Mg diagram.Three targeted compositions were then explored inside and outside the areas of interest and their thermal stability assessed up to 250°C. Different behaviours were observed and are explained by the strengthening potential and the coarsening resistance of S' and θ'. The two interesting areas for thermally stability are confirmed. An area of poorer thermal stability was also identified, associated with a high Cu content in solid solution which accelerates precipitate coarsening kinetics.

Abstract: Problems to evacuate chips will arise from manufacturing deep holes, especially for small diameters. Such problems induce frequent tool breakage and poor surface quality. The vibratory drilling enables the chip to be split into small elements thanks to the axial vibrations of the drill, self-maintained by the cutting energy. This research aims to improve breaking chip concerning high temperature alloy by vibraiont drilling as well as to establish a drilling technology. The development of breaking chip technology was presented. By the aid of the self-made vibrating drilling table, the axial vibration drilling was experimented on high temperature alloy with different parameter of vibration drilling. The breaking chip effect of vibration cutting was studied, and the axial drilling force and torque of vibration drilling were analyzed. The relation of each parameter and its effect on machining process was theoretically discussed. The experiment results show that vibration drilling is in favor of breaking chip, making the volume of chip small, and removing chips fluently, and the change of drilling force is relatively steady with some drilling parameters.

Abstract: Discovery of new high temperature alloys is a multidimensional problem which encompasses the intrinsic thermodynamic stability and their thermo-chemical and thermo-mechanical response to the combustion environment. Even when considering only the transition metals in combination with stable oxide formers, the number of ternary combinations exceeds 104. Hence, the traditional Edisonian process is not a practical approach to develop new alloy systems. Using formation enthalpy as a guide to compound stability, we propose a hierarchical scheme for identifying potential alloy systems which involves sifting through large regions of phase space with increasingly more accurate analysis. The coarsest sieve is a semi-empirical method based on the Miedema model extended to ternary systems. The next stage is ab initio simulations for a more accurate assessment and the basis for selecting system to investigate experimentally. We describe the implementation of this approach through the discovering of ternary additions that improve the oxidation stability -NiAl alloy.

Abstract: The junction line entering is the common flaw that has often arisen in the resistance welding, especially within the resistance seam welding for the high-temperature alloys. It decreases the effective nugget diameter and reduces the tensile-shear strength of welding joint. Stress concentration can be easily created in the junction line entering under moving loading, which induces crack formation and thus seriously affects the welding quality. Owing to the plenty of factors effect on the junction line entering as well as big difficulties for experiment and the high failure rates，junction line entering has the great significance for the stability of welding quality to study its forming and protective measure. The junction line entering for the high-temperature alloy GH163 was studied through the seam welding as follows: surface conditions, welding variables, and agitation force. Some reasonable solutions for entering were provided.

Abstract: High-temperature alloy GH536 is a difficult-to-cut material. The paper finished milling experiment of GH536 with cemented carbide tool based on orthogonal test, obtained regulations between milling force and feed speed, cutting depth and spindle speed. Results indicate that the milling force increases with feed speed and cutting depth, decreases with spindle speed. Exponential formulas of milling force were obtained by SPSS, variance analysis showed it agreed well with experimental data.

Abstract: In the present work, we have developed two ferritic stainless steels, Fe + 20%Cr + 0.8%Mn + 0.2%Ti + 0.5%Y2O3 and Fe + 17%Cr + 0.1%C + 1%Si + 1%Mn + 0.5%Y2O3 for oxide fuel cell (SOFC) interconnects. Nano-sized Y2O3 particles were dispersed in the metallic matrix by high-energy ball-milling. The alloys exhibited excellent electrical conductivity and thermal expansion coefficient suitable for SOFC applications. The finely dispersed nano-sized yttria is thought to be attributed to high conductivity.

Abstract: Average ternary interdiffusion coefficients in Ni3Al with Ir additions have been determined using solid-to-solid diffusion couples annealed at 1200°C for 5 hours. Disc shaped alloy specimens were prepared by the vacuum arc melting at compositions of Ni-24Al, Ni-25Al, Ni-26Al, Ni-23.5Al-1Ir, Ni-24.5Al-1Ir, Ni-23Al-2Ir, Ni-23Al-2Ir, Ni-24Al-2Ir, Ni-23Al-3Ir (at.%). Surfaces of alloys were polished down to 1200 grit and diffusion couples were assembled in Si3N4 jig for initial bonding heat treatment at 1200°C for 0.5 hours. Additional diffusion anneal was carried out at 1200°C for 4.5 hours outside of Si3N4 jig so that diffusion couples can be water quenched. Concentration profiles of individual components were measured by electron probe microanalysis using pure standard of Ni, Al and Ir. Interdiffusion flux of individual component was determined directly from the experimental concentration profiles, and the moments of interdiffusion flux were examined to calculate the average ternary interdiffusion coefficients, D˜ ij k either with Al or Ni as dependent component. Calculated interdiffusion coefficients suggest that Ir-alloyed Al2O3-forming oxidation resistant coatings would be beneficial to reduce the interdiffusion flux of Ni from superalloy substrates to the coating, and reduce the interdiffusion flux of Al from the coating to the superalloy substrate.