Applications Of High-temperature Materials Research Articles

Degradation of Yb–Gd–Ti-Si middle entropy silicides in oxidizing atmosphere

Using arc melting, a novel rare-earth silicide, middle entropy Yb–Gd–Ti-Si, was fabricated for high-temperature material applications. The oxidation behavior of the Yb–Gd–Ti-Si was evaluated through oxidation tests conducted at 1200 °C for 1, 2, 4, and 8 h in air. The oxidation rate at 1200 °C was almost the same, regardless of the addition of Ti. The oxidation rate of Yb–Gd–Ti-Si at lower temperatures (600 °C to 900 °C) was lower than that of Yb–Gd–Si. In addition, detailed microstructural observations indicate that the formation of TiO2 and other oxides in the Yb-Ti–O (Yb–Ti–Si–O) phase suppresses the formation of Yb2O3, causing a drastic oxidation at intermediate temperatures (600 °C to 900 °C). These results indicate that the addition of Ti to Yb–Gd–Si is effective at preventing the preferential oxidation of the grain boundaries at 600 °C to 900 °C, which is commonly observed in metal silicides.

Influence of alloying elements on the mechanical and thermodynamic properties of ZrB2 boride

To strengthen mechanical and thermodynamic properties of high-temperature ceramics is a critical challenge for the application of high-temperature materials. To enhance the mechanical and thermodynamic properties of ZrB2, we apply the first-principles calculations to study the influence of transition metal on mechanical and thermodynamic properties of ZrB2 boride. Seven transition metals are designed. The results show that the transition metal (TM) doped ZrB2 are thermodynamic and dynamical stability. In particular, these alloying elements enhance the bulk modulus of ZrB2 and improve the ductility of ZrB2. The calculated bulk modulus of the W-doped ZrB2 is up to 270 GPa. Naturally, the enhancement of mechanical properties is that the additive transition metal improves the electronic interaction between B and Zr atoms. The introduction of W markedly enhances the localized hybridization of B–B atoms and W–B atoms, which are verified by the change of B–B bond and TM-B bond. In addition, these transition metals enhance the Debye temperature of ZrB2 due to the role of d-state for transition metals. Therefore, we believe that the introduction of W is a useful metal to improve the mechanical and thermodynamic properties of ZrB2.

Dry machining parameter optimization for γ-TiAl with a rhombic insert

The application of high temperature materials is the key to technological advancement in engineering, particularly in the aerospace and automotive industries, where materials are expected to satisfy stringent operating requirements. New heat-resistant, light-weight materials, such as intermetallic gamma titanium aluminides (γ-TiAl) based alloys are attracting attention, and showing a great potential to meet severe operational demands due to their superior properties such as low density, high melting temperature, high specific yield strength, high specific stiffness, and excellent creep resistance. Consequently, γ-TiAl alloys have a great potential for high temperature applications in the aerospace and automotive industries. On the other hand, they are also well known as hard-to-machine materials due to poor ductility at low to intermediate temperatures that result in low fracture toughness and a fast fatigue-crack growth rate. In addition, there is no evidence in the open literature of these materials being subjected to production machining. These disadvantages have hindered their widespread application in industry. In this work, a rhombic turning tool is investigated to explore the machinability of γ-TiAl and to develop a cost-effective environmentally benign machining process. A set of central composite design (CCD) experiments are carried out for optimization of the machining process. The cutting parameters varied are cutting speed, feed rate, and depth of cut. Responses measured included thrust force, feed force, cutting force, specific cutting energy, surface roughness, chip morphology, and surface integrity. From the analysis of experimental data, quadratic models are developed, and 2-D contour and 3-D surface plots are drawn. Results obtained are of significant importance in terms of machinability of γ-TiAl and its application in the manufacturing of diesel engine valves and other tribological engine components subjected to operating temperatures range of 400 ºC to 800 ºC.

MICRO-CRYSTAL STRUCTURE OF 57Fe15Cr25Ni0.32Mn0.96Si AUSTENITE STEEL AFTER 850°C-5H TEMPERATURE-QUENCHING TREATMENTS FOR HIGH TEMPERATURE MATERIAL APPLICATIONS

MICRO-CRYSTAL STRUCTURE OF 57Fe15Cr25Ni0.32Mn0.96Si AUSTENITE STEEL AFTER 850°C-5H TEMPERATURE-QUENCHING TREATMENTS FOR HIGH TEMPERATURE MATERIAL APPLICATIONS. A serial austenite stainless steel, namely A2-type, has been synthesized by using casting technique at temperature more than 1250 °C in the induction furnace that used an electromagnetic inductive-thermal system. The steel is dedicated for structural component material in multi-purpose applications such as in high-temperature operating environments. So, the material must be resistant to mechanical loads, high temperature, corrosion and irradiation. In order to increase the strength of materials, temperature-quenching treatments are required in some cooling media. Mineral element was extracted from crude ores of Indonesian mines and commercial scrap materials, i.e: ferro scrap, ferro chrome, nickel, manganese, and ferro silicon; all of them in granular shape were prepared to alloy the steel. Titanium was not added to this austenite low carbon steel. The OES-chemical composition in %wt of the materials is 57%Fe, 15%Cr, 25%Ni, 0.34%C and less than 0.1% of impurities that comprised of: titanium, phosphor, copper, niobium and sulphur elements in the steel. X-ray diffraction pattern shows that ascast material had an fcc crystal structure with lattice parameter of 3.632 Å. Meanwhile, two of samples, i.e: annealing and oil quench, have strictly similar lattice parameter to that of air (normalizing) quench (3.580 Å). On the other hand, the lattice parameter of water quenched samples has a slightly lower lattice parameter than the ascast lattice , i.e. 3.587 Å. The peak shift of (111) and (200) -plane in the diffraction profile, is very significant, approximately 0.63 degrees between ascast sample and the last two samples. Ascast microstructure reveals that the austenite phase grains look large and describe an undeformed structure, with an average grain size of about 6 mm, while the annealed sample was larger. Air- and oil- quenched sample microstructures showed a fine grain which was very different to water quenched sample microstructure that showed a coarse grain. The viscousity (h) of the quenching medium had an important role in the formation of grain boundary, because the rate of decreasing temperature was heavily influenced by the diffusion of heat from the high to low temperature spaces.

Teaching high-temperature materials chemistry at university (IUPAC Technical Report)

AbstractOver the last four to five decades, high-temperature materials chemistry (HTMC) has become a flourishing area of scientific and applied research, spurred by both a growing demand for new inorganic materials (e.g., oxide and non-oxide modern multifunctional ceramics, intermetallics, and oxidation-resistant alloys) able to withstand extreme thermal and chemical environments and by the recognition that chemical and physical behavior at high temperatures differs from, and cannot be extrapolated from, behavior at temperatures near room temperature. Despite the important role played by HTMC in modern advanced technology and the fundamental differences in behavior encountered at high temperatures, HTMC topics are rarely covered in chemistry and materials science programs at the university level because of a lack of readily accessible resource material - no textbook exists specifically devoted to HTMC topics. IUPAC's Inorganic Chemistry Division sponsored a project to address this gap, resulting in the present report. The report includes an introduction and seven sections covering historical background, chemical behavior of condensed-phase/gas-phase systems at high temperature, basic concepts of materials thermodynamics, experimental techniques, use of thermodynamic data and modeling, vaporization, and decomposition processes, and gas-solid reactions. The ninth section covers more specific topics, primarily concerning applications of high-temperature materials and processes. Each recommended topic is accompanied by a bibliography of helpful references, a short introduction or explanation including the areas of application, and some relevant teaching suggestions. An extensive annotated resource bibliography is an Appendix to the report available as supplementary material.

A Method to Estimate the Inelastic Response in Notched Structures of Anisotropic Materials with Elastic ‐ Perfectly Plastic Behavior

AbstractThe fatigue strength of engineering structures is often limited by notches which arise from constructive features or manufacturing defects. The constitutive behavior in notch regions is then characterized by small plastic zones which are contained in an elastic region.To avoid costly plastic calculations, approximate methods have been developed to estimate the inelastic stress‐strain response at the notch tip. One of the first and best known approximate models is that of Neuber which, over the last 40 years, has received considerable attention particularly in connection with fatigue life prediction. Numerous studies have been conducted to the verification and the generalization of the Neuber approach which respect to multiaxiality, cyclic loading and creep conditions. Recently an extension of the Neuber method to anisotropic materials has been proposed in [1] and applied to directionally solidified and single crystal Nickel based superalloys as they are used in high temperature material applications. In this short notice we modify the approach in [1] for the special case of an elastic ‐ perfectly plastic anisotropic material.

Research and development of ultra-high temperature materials in Japan

Gas turbines for aircraft engine and power generation are typical fields of application of high temperature materials. Nickel-based superalloys are excellent and most useful materials for these applications and have been well developed especially with the outstanding progress of jet engines. In future, from a view point of global environmental problems, there will be strong demands for special materials for high temperature and high efficiency gas turbines for power generation. However, the temperature capability of the superalloys will saturate to some limit because of their melting points which are lower than 1400°C. So-called ultra-high temperature materials, such as intermetallic compounds, refractory metals and alloys, ceramics, and various composite materials are expected to surpass the temperature capability of the superalloys, although these materials have several problems such as difficulty of processing, lack of ductility and toughness or the poor resistance to oxidation and hot-corrosion. In this paper, present and future prospects of R&D of these ultra-high temperature materials have been briefly reviewed.

Platinum-Enriched Superalloys

At the International Conference on the Behaviour of High Temperature Alloys in Aggressive Environments, held in October at Petten in the Netherlands under the sponsorship of Bond voor Materialenkennis, NL, the Commission of the European Communities Joint Research Centre, Petten Establishment, and the U.K. Metals Society, recent developments in the application of high temperature materials were reported. This paper is based upon a presentation made at the conference and describes the concept of using platinum group metals as alloying constituents in new nickel-based superalloys. The alloys developed have considerably enhanced resistance to oxidation and corrosion in aggressive environments at high temperatures, and also exhibit mechanical properties which are equal, and sometimes superior, to their conventional counterparts.