High-temperature Structural Stability Research Articles

High temperature structure stability of GH4169 superalloy

The long-term thermal stability of GH4169 superalloy has been studied as a function of heat treatment and thermal exposure. The GH4169 superalloy was subjected to long-term unstressed heat treatment at 650°C, from 200 to 1000h. The microstructure, tension and stress rupture properties of the samples before and after long-term thermal exposure were characterized. The coarsening of strengthing phase γ′ and γ″ was observed after exposing at 650°C. Coarsening of two different precipitates proceeds by Oswald ripening controlled by volume diffusion of solute atoms in the alloy. The tension strength at room-temperature and 650°C decreases slowly and the stress rapture life decreases remarkably with the increase of thermal exposure time. The decreasing of volume fraction and increasing of mean distance for the precipitates appears to be the main factor in the degradation of the mechanical properties.

STRUCTURAL AND BIOPHYSICAL PROPERTIES OF ARTERIAL CALCIUM DEPOSITION

Co20Cr20Cu20Fe20Ni20 (at.%) (Al-0) and Al33.35Co13.33Cr13.33Cu13.33Fe13.33Ni13.33 (at.%) (Al-2.5) high-entropy alloy films with thicknesses less than 500 nm were successfully fabricated by sputter technique using alloy targets. Their microstructures are characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectrometer, transmission electron microscopy and nanoindentation techniques. It is found that compositions for both films are uniformly in depth. The both as-deposited films are composed of nanometer-sized grains with serious lattice distortion. The as-deposited Al-2.5 film, having a hardness of 15.4 GPa and reduced Young’s modulus of 203.8 GPa, exhibits a body-centered cubic structure and remains stable up to 873 K for 20 min whereas the as-deposited Al-0 film, having a hardness of 6.3 GPa and reduced Young’s modulus of 87.9 GPa, exhibits a face-centered cubic structure and remains up to 773 K for 20 min. It seems that due to high temperature structure stability and high hardness, the Al-2.5 film could be used as a potential coating material on high-temperature Ni-based alloys.

650°C Long-Term Structure Stability Study on 18Cr10NiNb Heat-Resistant Steel

The Nb-contained austenitic heat-resistant steel 18Cr10NiNb(TP347H) has been widely used as super-heater and re-heater tube material for modern ultra-super-critical (USC) power plants in the world. High temperature structure stability is considered to be one of the most important factors for long-term service. Long-term aging at 650 °C for this steel was conducted till 10,000 hours. Effect of aging time on microstructure was studied by means of SEM and TEM. Tensile tests were carried out after aging at 650 °C for different times. Experimental results show that MX phase and M23C6 carbides are major strengthening precipitates in this steel. With increasing of aging time, fine nano-size MX particles precipitate in grains and its size keeps about 50 nm till 10,000 h at 650 °C. Carbide M23C6 mainly precipitates at grain boundaries but coarsens quickly. Investigation results show that MX phase plays the most important strengthening effect in grains. The amount of MX phase increases with increasing of Nb and C contents. The effects of Nb and C contents on mole fractions of MX phase in 18Cr10NiNb steel have been calculated by using Thermo-Calc software.

Processing and mechanical properties of three-dimensional network alumina ceramic/alloy steel composites

A new style Ni-containing alumina ceramic based network skeleton with excellent high-temperature structural stability was designed and prepared by die-molding and sintering. Subsequently, three-dimensional network alumina/steel metal matrix composites (MMCs) were produced successfully by pressureless infiltration of steel melt into the network skeletons at 1600 °C in vacuum. The obtained MMCs were observed by SEM, EDS and XRD, respectively. Finally, bending strength and fretting wear behavior of the MMCs were investigated.

650°C Long-Term Structure Stability Study on 18Cr-9Ni-3CuNbN Heat-Resistant Steel

The Cu-containing austenitic heat-resistant steel 18Cr-9Ni-3CuNbN has been widely used as superheater and reheater tube material for modern ultra-super-critical (USC) power plants in the world. High temperature structure stability is considered to be an important factor for long-term service. Long-term aging at 650°C for this steel was conducted from 100 to 10,000hours. Effect of aging time on microstructure was studied by means of SEM, TEM and 3DAP (three dimensional atom probe). Micro-hardness tests were carried out after aging at 650°C for different times to be considered as a representative of strength. Experimental results show that Cu-rich phase, MX and M23C6 are major strengthening precipitates in this steel. With on increasing of aging time, fine nano-size Cu-rich phase particles precipitate in the grains and its size is in the range of several nanometers to 35nm till 10,000h at 650°C. The fraction of MX also increases with aging time and its average size is about 100nm till 10,000h. Carbide M23C6 mainly precipitates at grain boundaries and coarsens quickly. Investigation results show that the most important strengthening effect for 18Cr-9Ni-3CuNbN steel is contributed by Cu-rich phase and MX in the grains and M23C6 carbide at the grain boundaries.

Miniaturization and Geometry Optimization of a Polymer-Based Rectilinear Ion Trap

The fabrication, operation, and characterization of a polymer-based rectilinear ion trap mass analyzer is discussed. A novel, fast prototyping technique, stereolithography (SLA)-based fabrication, traditionally reserved for end use production parts and to fabricate master molds for rubber products, is applied here as a tool to create precise, arbitrary geometries. Taking full advantage of the SLA methodology, an open corner, polymer-based ion trap has been fabricated and tested. The use of a custom resin, Nanoform 15120 (DSM Somos, New Castle, DE), has resulted in a polymer with high heat deflection temperature and greater structural stability at higher temperatures and lower capacitance. The mass analyzer was mounted in a polymer holder and tested in a custom vacuum system using modified LCQ Duo (Thermo Fisher Corp.) electronics. The resolution, mass/charge range, and MS/MS capabilities were examined using electrospray ionization as well as atmospheric pressure chemical ionization. In the course of this study, three traps of different sizes were fabricated, beginning with a "full size" device measuring 10 x 8 x 50 mm. The next two traps were scaled down by linear factors of a half and a third. SLA is shown to allow fabrication of light, small rectilinear ion traps, which are less expensive and have the same performance as traditional machined devices of the same size. In addition, smaller traps can be built just as easily, and they show unit mass resolution to mass 300, tandem mass spectrometry capabilities, and low power consumption.

High Temperature Structure Stability Study on Nb-Containing Nickel-Base Superalloys

High temperature structure stability of 2 important Nb-containing Ni-base superalloys Inconel 718 (Ni-19Cr-18Fe-3Mo-5Nb-1Ti-0.5Al) and Inconel 740 (Ni-25Cr-20Co-0.5Mo-2Nb -1.8Ti-0.8Al) have been studied on the relationship of microstructure to mechanical properties via SEM, TEM, SAD, XRD and quantitative determination of precipitated phases by micro-chemical analysis. The longest exposure times are 50,000hrs at 650°C for Alloy 718 and 4,000hrs at 704°C, 725°C and 760°C for Alloy 740. The structure instabilities for these 2 Alloys are: 1) strengthening phases γ″/γ′ coarsening; 2) meta-stable strengthening phases change to stable phase, such as γ″→ δ-Ni3Nb for Alloy 718 and γ′→ η-Ni3Ti for Alloy 740; 3) embrittling phases formation, such as α-Cr and σ-phase formation in Alloy 718 and high Si-containing G-phase formation in Alloy 740. On the base of understanding phase changes at high temperature exposures the structure stability of Inconel 718 and Inconel 740 has been improved both by minor adjustment of alloys chemistry. The modifications of Alloy 718 and Alloy 740 are to be developed in the near future.

Metastable phase evolution in Al2O3dispersed nanocrystalline NiCr alloys

The high temperature structural stability of nanograined NiCr alloys reinforced with nanoscale yttria and alumina dispersoids, fabricated by electron beam physical vapor deposition (EBPVD), was examined. The yttria particles coarsened very little and also inhibited grain growth in the matrix successfully, whereas the alumina dispersoids coarsened rapidly and were not as effective in restricting matrix grain growth. A hierarchy of phase transformations took place in the Al2O3particles present as nano dispersoids in a nanograined NiCr matrix, on annealing. Coarsening of the alumina particles was accompanied by these phase transitions. The phase evolution is attributed to differences in free energies between the metastable and stable phases and a kinetic hierarchy in nucleation, brought about by structural and hence interfacial energy considerations.

High-temperature structure stability and mechanical properties of novel 718 superalloy

Phase transformation from γ″ (bct) to δ (orthorhombic) at 650 °C or elevated temperature is the main obstacle preventing the conventional In 718 alloy from elevated temperature applications. A kind of novel 718 alloy, which offers 30 °C temperature advantage over conventional In 718, was designed and fabricated by adjustment of chemical composition which included the increasing in content of Al + Ti, the ratio of Al/Ti and the level of P and B. Microstructure of the novel 718 alloy at as-heat treated condition was studied. Variety and morphology of the strengthening phase were evaluated by SEM, TEM and SAED observations. High-temperature structure stability and mechanical properties of the novel 718 alloy were examined after long-term exposure at 680 °C. Results indicate that the strengthening phases in novel 718 alloy are spherical morphology γ′-phase and sandwich γ′ + γ″-phases. The unique structure makes this novel 718 alloy have excellent high-temperature structure stability and mechanical properties compared to the conventional In 718.

Differential role of nanoscaled oxide dispersoids (Y2O3 vs Al2O3) in the high-temperature structural stability of NiCr alloys

The effect of nanoscaled dispersoids in contributing to the high-temperature stability of nanograined NiCr alloys has been studied. Nanoscale yttria dispersoids were far more effective in contributing to the retention of a fine-grained microstructure in NiCr alloys (via the electron beam-physical vapor deposition (EB-PVD) route) as compared to the alumina particles. The fine yttria particles (<20 nm) shared a common orientation relationship with the matrix and exerted a Zener pinning force to inhibit rapid grain growth at elevated temperatures. Coarsening of yttria took place by diffusion of the metallic species through the NiCr matrix and was marginal compared to the alumina particles, which underwent a hierarchy of phase transformations (γ(spinel)→δ→α) as an outcome of coarsening. Phase selection at the nanoscale has been examined on the basis of free energies of formation of the metastable vs stable phases at the respective size ranges. The main factor responsible for the differential role of coarsening between the two types of dispersoids has been attributed to their relative free energies of formation, at these elevated temperatures.

Estudo do nitreto de alumínio para aplicações termo-mecânicas

O nitreto de alumínio é muito utilizado como material semicondutor em dispositivos óptico-eletrônicos na qual sua alta condutividade térmica permite uma boa dissipação de calor. Por outro lado, devido à alta resistência mecânica e boa estabilidade estrutural à alta temperatura, tem sido crescente o seu estudo para aplicações termo-mecânica levando em considerações os avanços tecnológicos no processamento e caracterização destes materiais. Neste trabalho serão apresentados os resultados dos estudos de prensagem a quente do nitreto de alumínio aditivado com 5%, 10% e 20% de uma mistura contendo Al2O3 + Y2O3. A massa específica foi determinada de acordo com a norma ASTM C20-87, as fases presentes por difração de raios X e as análises microestruturais por microscopia eletrônica de varredura. A microdureza e tenacidade à fratura foram avaliadas pelo método de indentação Vickers. Os resultados promissores alcançados de densificação, próximos à densidade teórica, e propriedades mecânicas, mostraram a viabilidade da utilização do AlN em aplicações estruturais.

High-temperature phase stability and tribological properties of laser clad Mo 2Ni 3Si/NiSi metal silicide coatings

Mo 2Ni 3Si/NiSi wear-resistant metal silicide composite coatings consisting of Mo 2Ni 3Si primary dendrite and interdendritic Mo 2Ni 3Si/NiSi eutectic were fabricated on substrate of an austenitic stainless steel AISI321 by laser cladding using Ni–Mo–Si elemental powder blends. The high-temperature structural stability of the coating was evaluated by aging at 800 °C for 1–50 h. High-temperature sliding wear resistance of the as-laser clad and aged coatings was evaluated at 600 °C. Results indicate that the Mo 2Ni 3Si/NiSi metal silicides coating has excellent high temperature phase stability. No phase transformation except the dissolution of the eutectic Mo 2Ni 3Si and the corresponding growth of the Mo 2Ni 3Si primary dendrite and no elemental diffusion from the coating into the substrate were detected after aging the coating at 800 °C for 50 h. Aging of the coating at 800 °C leads to gradual dissolution of the interdendritic eutectic Mo 2Ni 3Si and subsequent formation of a dual-phase structure with equiaxed Mo 2Ni 3Si primary grains distributed in the NiSi single-phase matrix. Because of the strong covalent-dominated atomic bonds and high volume fraction of the ternary metal silicide Mo 2Ni 3Si, both the original and the aged Mo 2Ni 3Si/NiSi coating has excellent wear resistance under pin-on-disc high-temperature sliding wear test conditions, although hardness of the aged coating is slightly lower than that of the as-clad coating.

UDIMET 720

Abstract Udimet 720 is a nickel-base alloy used in turbine blade and disk applications requiring high-temperature strength and structural stability. This datasheet provides information on composition microstructure as well as fracture toughness and creep. It also includes information on high temperature performance and corrosion resistance as well as heat treating. Filing Code: Ni-620. Producer or source: Special Metals Corporation.

Crystallization and high-temperature structural stability of titanium oxide nanotube arrays

The stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments. The tubes crystallized in the anatase phase at a temperature of about 280 °C irrespective of the ambient. Anatase crystallites formed inside the tube walls and transformed completely to rutile at about 620 °C in dry environments and 570 °C in humid argon. No discernible changes in the dimensions of the tubes were found when the heat treatment was performed in oxygen. However, variations of 10% and 20% in average inner diameter and wall thickness, respectively, were observed when annealing in a dry argon atmosphere at 580 °C for 3 h. Pore shrinkage was even more pronounced in humid argon environments. In all cases the nanotube architecture was found to be stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotube array.

A New Design Methodology for High Temperature Structural Components Made of Continuous Fibre Ceramic Composites Exhibiting Thermally Induced Anisotropic Damage

Continuous Fibre Ceramic (Matrix) Composites (CFCCs) have found during the last decade numerous of industrial applications in a variety of technological areas, where structural components are subjected to high temperature combined with significant mechanical loading. The present work deals with the application of an innovative design methodology for the development of an industrial gas turbine combustor chamber made of oxide/oxide composite materials. Oxide/oxide composites offer high-temperature structural stability without the need of any kind of oxidation protection and thus permit the increase of working temperature of the gas turbine, increasing the efficiency of the system and decreasing NOx emissions. Since, oxide/oxide composites degrade their structural properties as a function of the operating temperature (for temperature higher than 1000°C) and the exposure time, an incremental approach has been introduced as a structural design methodology for the combustion chamber, where each increment represents a thermal exposure stage. The data set required for the application of the present design approach, was obtained through an extensive material characterization program based on the measurement of the anisotropic properties of oxide/oxide composites using ultrasonic techniques.

Development of a nucleation inhibitive coated mold for the rapid solidification of superalloy melt

The development of a glass-lined mold from gels in the ternary system of SiO 2–ZrO 2–B 2O 3 by adopting the shell molding technique and sol–gel processing has been investigated. The crystallization characteristics of ZrO 2 particles and the high temperature structure stability of Si–Zr–B coating were demonstrated. The inhibitive effect of B 2O 3 on crystallization in the Si–Zr–B coating was explained. Finally, the result that DD3 single crystal superalloy can obtain high undercooling and realize rapid solidification in it establishes that the Si–Zr–B coated mold has an ideal non-catalytic nucleation inhibition for superalloy melt.

Solidification of superalloy in a SiO 2–ZrO 2–B 2O 3 coating mould

The preparation of glass-lined coating mould from gels in the ternary system of SiO 2–ZrO 2–B 2O 3 has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO 2 as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO 2 matrix. While the inhibitive effect of B 2O 3 on crystallization of the SiO 2–ZrO 2–B 2O 3 coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO 2–ZrO 2–B 2O 3 coating mould has an ideal nucleation inhibition for superalloy.

Crystallization of gels in the SiO2-ZrO2-B2O3 system

The preparation of glasses from gels in the ternary system of SiO2-ZrO2-B2O3 has been investigated. The crystallization character of ZrO2 particles and high-temperature structure stability in the SiO2-ZrO2-B2O3 gels were analyzed. The effect of B2O3 as the inhibitor of crystallization was illustrated. Finally, the result that the purified DD3 single crystal superalloy melt can retain high undercooling in the SiO2-ZrO2-B2O3 coating mold indicates that the coating has an ideal non-catalytic nucleation property.

High-temperature structural stability of MoSi2-based nanolayer composites

A systematic study of the high-temperature structural stability is reported for the following three nanolayered composites: (1) MoSi2–MoSi2Nx, (2) Mo–MoSi2Nx, and (3) Mo–MoSi2Nx–MoSi2, where x∼3–4. The alternating layers with layer thickness varying from 1 to 50 nm were synthesized by sputtering techniques. The structural evolution in these composites has been studied by cross-sectional transmission electron microscopy as a function of annealing temperature. As-deposited Mo layers exhibit nanocrystalline structure, while the other types of layers are amorphous in structure. With increasing annealing temperature, MoSi2 crystallizes to form a metastable C40 phase at ∼500 °C and then transforms to the stable C11b phase at ∼900 °C, while MoSi2Nx remains amorphous up to temperature as high as 1000 °C. No difference in crystallization behavior was observed for the constituents in either single phase or multilayered form. One way to improve the toughness of MoSi2 is through the addition of a ductile phase, e.g., Mo. However, the Mo and MoSi2 layers react and the layer structure deteriorates. Previous study has shown that the compound, MoSi2Nx, stays amorphous at 1000 °C. This suggests that it could function either as a stable second-phase reinforcement or as a diffusion barrier between Mo and MoSi2. The MoSi2–MoSi2Nx, Mo–MoSi2Nx, and Mo–MoSi2–MoSi2Nx nanolayers are found to remain stable up to 900 °C (highest temperature tested).

High temperature structural stability of chemically vapor-deposited silicon carbide filaments

The structural stability of SCS-6 filament was investigated in the temperature interval 1000–1600 °C by differential scanning calorimetry (DSC) and in situ X-ray diffraction techniques. It was found that this filament is composed mostly of the cubic β polytype of SiC and of graphite, and that these phases are stable in the temperature interval studied. The lattice parameter for β-SiC was determined between room temperature and 1600°C, and the calculated average linear thermal expansion of the lattice in this temperature interval (5.24 × 10−6 °C−1 is in agreement with macroscopic thermal expansion measurements on single filaments. Thermal events observed by DSC occur at 1380 °C on heating and at 1300°C on cooling, and are suggested as being related to the melting and solidification, respectively, of excess silicon. These results are analysed in relation to the anomalous thermal expansion behavior exhibited by this filament.