Papers by Keyword: Structure Stability

Abstract: Nimonic 80A Ni-base superalloy can be used for high temperature steam turbine components.There is a critical requirement for turbine blade application that the stress rupture strength for 105 hrs at relevant high temperatures should be higher than 100MPa.On the other hand, it must keep good structure stability and no harmful phase such as-phase and the TCP phase formation at long time high temperature exposure. Therefore, the long time stress rupture tests at temperatures of 600, 650, 680 and 700°C for different stresses have been carried out. The long time structure stability has been also studied in detail. The results show that Nimonic 80A can meet the critical requirement for USC steam turbine blades at 600~700°C. Any detrimental phases have not been found at the long time stress rupture tests. The morphology of grain boundary carbides also has no apparent change. Based on above mentioned results, Nimonic 80A is recommended to be used for USC steam turbine components in the temperature range of 600~650°C.

Abstract: Cubic δ-NbNfilm with (200) texture, hexagonalδ′-NbN films with a mixed (100)+(110) texture and (110) texture have been deposited on Si (100) substrate at-40, -160 and-200Vsubstrate bias, respectively. Vacuum heat treatments were performed to investigate the effects of annealing temperature on structural stability and hardness of δ-NbN and δ′-NbN films. The results show that for δ-NbN film and δ′-NbN films with a strong (110) texture,no phase transition occuredafter heat treatments.But for δ′-NbN films with a mixed (100)+(110) texture, phase transition from δ′-NbN to δ-NbNtook place, which can be ascribed to small lattice mismatch between δ′-NbN (100) and δ-NbN (111) and low phase transition barrier. In addition, the high substrate bias can improve the interface adhesion due to interface mixing resulting from high energy ions bombardment. Even after annealing at 900°C, the hardness for δ′-NbN deposited at-200V still remains 32GPa, which shows a potential application at the field of protect coatings.

Abstract: Geometric structure of Os_n (n=2-10) clusters are optimized by using Density functional theory (DFT) in DMOL3 package. For the ground-state structure, relative stability are analyzed. The results show that: the ground-state structures of the cluster are plane structure when n=2-4, but the ground-state structures are stereostructure when n≥5. There exhibits the odd-even oscillation effect in stability and Os₈ cluster has the highest stability.

Abstract: Mesoporous material SBA-15 was synthesized using P123 and TEMOS as the templates. Lithium in the form of LiOH was loaded over a previously prepared SBA-15. The basic strength of the prepared samples of SBA-15 was found to increase but the mesoporous structure was severely destroyed. The mesoporous structure of the prepared SBA-15 was retained after coating it with 30 wt. % magnesium prior to LiOH loading. The stability of mesoporous structure was strongly influenced by the extent of magnesium coating. It was also noted that this structure was also affected by LiOH loading and significantly destroyed structure when magnesium coating value exceeded 20 %. These samples were thoroughly characterized for their surface area, pore volume, pore size, basic strength, SAXRD patterns and transmission electron microscopic (TEM) analysis.

Abstract: This article summarises results of structure stability investigation of cast Ni-base and Co-base alloys after prolonged high temperature exposure at 900-1100 °C. Cast Ni (Co)-Cr-W-C alloys are resistant to high-temperature corrosion, due to high chromium content. Their heat resistance is caused by presence of carbides, which are stable at very high temperatures. Carbides precipitate in shape of large plate-like particles or carbide eutectics at casting cell boundaries, thus forming carbide skeleton of the alloy. Carbide morphology and temperature stability depends on chemical composition of the alloy, e.g. carbide content, type and content of carbide-forming elements. Microstructure changes were evaluated by stereological analysis and X ray-spectral microanalysis.

Abstract: The Martensite-Bainite (M/B) dual phase structure has excellent combined processing properties which can be applied to the bearing steel. Frequently, the service conditions of rolling mill bearings are so harsh that the organization and performance of the bearing materials may change during the using process. The study of structural stability of martensite-bainite dual phase structure is extremely essential. This paper determined the superiority of Martensite-Bainite (M/B) dual phase structure applied to G55SiMoV by contrasting the properties of single martensite and M/B dual phase structure. temper resistance is discussed by testing the change of organization and performance after temper.The results show that the combination property of the M/B dual phase structure are better than the martensitic structure. The G55SiMoV steel with martensite-bainite dual phase structure has a greater temperature range to ensure the tempering stability.

Abstract: The crystallographic, magnetic and electronic structures of the magnetic shape memory alloys Ni₂XIn (X=Mn, Fe and Co) are systematically investigated by means of the ab initio calculations within the framework of density functional theory. The equilibrium lattice parameters and the bulk modulus of the austenitic phase in Ni₂XIn are systematically calculated. The formation energy of the L2₁ phase of the Ni₂XIn is estimated, and displays a destabilization tendency if Mn atom is substituted by Fe or Co. Furthermore, the magnetic properties of the Ni₂XIn have been investigated, and the essence of the variation in the magnetic properties with the X atomic number has been illustrated from the view of the electronic density of states.

Abstract: A 700 advanced ultra-supercritical (A-USC) power plant technology project was initiated in China in the year of 2011. The highest temperature components in A-USC boiler are superheater and reheater tubes. The fire-side metal temperature can reach 750 (even higher). Based on the very long time service (30-40 years) these important high temperature tubes require 10⁵h long time stress rupture strength higher than 100MPa and the corrosion/oxidation layer loss less than 2mm for 2×10⁵h. The highest temperature components in 700 steam turbine are the buckets of different stages and require very long service time. At this severe condition only superalloys can fulfill these unusual requirements. This paper reviewed Fe-Ni and Ni-base superalloys from the view point of structure stability and long term mechanical properties and corrosion/oxidation resistance for 700 A-USC power plant materials selection.

Abstract: The primary and secondary mirrors of on-axis three mirror anastigmatic (TMA) space camera are connected and supported by its front mirror-body structure, which affects both imaging performance and stability of the camera. In this paper, the carbon fiber reinforced plastics (CFRP) thin-walled cylinder and titanium alloy connecting rod have been used for the front mirror-body opto-mechanical structure of the long-focus on-axis and TMA space camera optical system. The front mirror-body component structure has then been optimized by finite element analysis (FEA) computing. Each performance of the front mirror-body structure has been tested by mechanics and vacuum experiments in order to verify the validity of such structure engineering design.

Abstract: Ti-Al multilaminate composite was prepared by high-power EB-PVD technology, and under vacuum condition, the samples were annealed at different temperatures. The changed microstructure of the samples after annealing was characterized by XRD, SEM and EDS. The experimental results show that, with the increment of temperature, the ordered phases reduce due to the diffusion of Al into Ti, and the breakdown of layered architecture was induced mainly by pore formation, grain growth and the grain boundary grooving.