Papers by Keyword: Hastelloy X

Abstract: The present research work has an aim to modify microstructure and oxidation behavior of Hastelloy X, a solid solution nickel base alloy, by both aluminium and titanium additions by mean of arc melting process. The Hastelloy X was added both Al and Ti (50:50) for 2% 4% and 6% by weight and casted by vacuum arc melting furnace. Then all received specimens were performed heat treatment, which consist of solutioning treatment at 1175°C for 4 hours and aging temperatures for 760°C, 800°C and 845°C for 24 hours. From the obtained results, it was found that the amount of both Al and Ti additions as well as precipitation aging temperature provided significant effect on both final microstructure and oxidation behaviors at 900°C and 1000°C. Widmanstatten type of microstructure was found in many case. Intermetallic phase formation of molybdenum and chromium was also found in all cases by element mapping. This phase should be γ’-phase. Both aluminium and titanium additions could not provide beneficial effect on oxidation resistance tests at temperature of 900°C and 1000°C. However, with 4%wt. of both aluminium and titanium addition, it resulted in slightly increasing of oxidation resistance at temperature of 1000°C

Abstract: Hastelloy X is a commercially available nickel-chromium-molybdenum superalloy with a good oxidation resistance, a good mechanical properties at high temperature and a significant formability; sine qua criteria for the choice of materials for the production of chambers turbojet combustion which is part of this study [1]. Arc welding technique is commonly used for the manufacturing of parts but the aeronautical requirements becoming increasingly severe especially in terms of reproducibility of geometry and metallurgical grade fillet weld. Laser welding is a viable method of assembly to meet these new demands by its automation to replace longer term the manual TIG welding. The high power CO₂ laser is extensively used for practical applications such as cutting and welding laser welding. The CO₂ laser is very used in the industry with regard to Yb:YAG laser which until now was not rather powerful but this changes. The aim of this study was to evaluate the effect of Yb:YAG laser beam parameters on the microstructure and mechanical properties of the laser beam welded superalloys Hastelloy X to define a field of weldability. The implementation of an experimental design approach is required due to the multitude of input parameters and the complexity of the phenomena involved [2-3].

Abstract: The nickel base alloy, grade Hastelloy X was modified by Aluminum and Titanium additions by means of vacuum arc melting process in order to improve microstructural characteristics and oxidation resistance. The arc melted Hastelloy X was added Aluminum and Titanium each for 2%, 4% and 6% by weight. Then all specimens were performed with heat treatment, which consists of solutioning treatment at 1125°C for 24 hours and precipitation aging at temperatures of 760°C, 800°C and 845°C for 24 hours. Both aluminum and titanium additions resulted in network intermetalic phase formation, namely, σ-phase, throughout the matrix. Furthermore, the addition of both elements provided the better oxidation resistance for the alloys.

Abstract: In this paper, the thermal oxidation behavior, adhesion and tribological properties of TiAlON films coated on hastelloyX substrate, typically used for fuel nozzle in gas turbine engine application, have been studied. The uncoated and coated samples were heated to different temperatures, i.e. 950, 1050 and 1150 °C in the controlled atmosphere. The surface appearance, microstructure, chemical composition and adhesion of films were investigated. The thermal oxidations were observed in all testing conditions showing thicker oxide film at higher temperature. However, spalling of oxide scales was found in hastelloyX and TiAlON coated at 1150°C suggesting the maximum working temperature of < 1150 °C. The critical loads corresponding to the full delamination of the thermal oxidation coated specimens were found to be higher than the non-thermal oxidation specimens. The effect of thermal oxidation on damage patterns during scratch tests, i.e. less chipping and cracking for thermal oxidation specimen, were also observed. The tribological properties were also investigated under different load under room temperature and 600 and 1000°C. The results suggested significant improvement in wear resistance of coated sample especially at low load at all temperatures.

Abstract: In this paper, the thermal oxidation behavior of TiAlCrSiN and AlCrTiN films coated on hastelloyX substrate, typically used for fuel nozzle in gas turbine engine application, have been studied. The thermal oxidation behavior at 950, 1050 and 1150 °C in controlled atmosphere were investigated. The surface appearance, microstructure, chemical composition and adhesion of films were investigated. The thermal oxidations were observed in all testing conditions showing oxide films at the surface with thicker oxide film at higher temperature. However, spalling of oxide scales was found in both coated and uncoated specimens at 1150°C suggesting the maximum working temperature of < 1150 °C for turbine engine applications. The critical loads corresponding to the full delamination of the thermal oxidation coated specimens were found to be higher than the non-thermal oxidation specimens. The effect of thermal oxidation on damage patterns during scratch tests, i.e. less chipping and cracking for thermal oxidation specimen, were also observed.

Abstract: Sulfur is the main element which caused Nickel-based alloy embrittlement. In this study, the sulfur in Hastelloy X superalloy was determinated with Auger Electron Spectroscopy (AES) for samples quenched from 1180 °C and aged at 500 °C for different time. Experiments results confirmed the non-equilibrium segregation characteristics of sulfur. The results showed that a segregation peak of sulfur is at about 20 min during ageing. This peak was satisfactorily elucidated by the theory of non-equilibrium grain-boundary segregation. By theoretical calculation, the critical time constant of impurities sulfur atom in the Hastelloy X δs= 357. At the same time, the result provides a theoretical basis for sulfur segregation mechanism.

Abstract: Cracks induced by metal fatigue and structural aging effect can’t be fixed by traditional Gas Tungsten Arc Welding (GTAW), consequently cause the increasing of defect ratio. Although some cracks might be acceptable and qualified to field service standard subject to the military regulation, however, in certain areas, e.g. brazing and coating areas, the results are not ideal especially the HAZ and residual stress. In this study, Nd-YAG Laser welding and traditional GTAW processes were performed on Hastelloy X superalloy for comparison. Post-welding residual stress distribution was measured by X-ray diffraction method. Macro- and microstructure were observed by metallurgical OM and SEM in comparison to the hardness testing. Tensile test results show that traditional welding technology has better ultimate tensile strength and ductility. For the Nd:YAG laser welding, residual stress is limited to 3mm of the both sides of weld and drops drastically, while higher amplitude and widely spread in the GTAW welding. It is proposed that combining both methods, the repairing process can be optimized to reduce the defect ratio and save repairing time.

Abstract: To design HTGR components for up to 1000oC, their creep curves are necessary during a design process. In this study, the full creep curves were modeled by the nonlinear least square fitting method using the Kachanov-Rabotnov (K-R) creep model. A series of creep data was obtained experimentally under various stress levels for Hastelloy-X at 950oC, and the data was used to model the creep curves. The K-R model gave a poor description of modeling creep curves, but the modified K-R one, which has another variable, K in the K-R model, was in better agreement than the K-R one. It was found that the λ parameter in the K-R model was constant regardless of the stress variations. The λ value was about 3.9 for the K-R model and about 5.8 for the modified one.

Abstract: The creep properties for the Hastelloy-X alloy which is one of candidate alloys for a high temperature gas-cooled reactor are presented. The creep data was obtained with different stresses at 950oC, and a number of the creep data was collected through literature surveys. All of the creep data were combined together to obtain the creep constants and to predict a long-term creep life. In the Norton’s creep law and the Monkman-Grant relationship, the creep constants, A, n, m, and m’ were obtained. Creep master curves based on the Larson-Miller parameter were presented for the standard deviations of 1σ, 2σ and 3σ. Creep life at each temperature was predicted for a longer-time rupture above 105 hours. Failure probability was also estimated by a statistical process of all the creep rupture data.

Abstract: To suppress interdiffusion between the coating and alloy substrate in addition to ensuring slow oxide growth at very high temperatures advanced coatings were developed, and they were classified into four groups, (1) the diffusion barrier coating with a duplex layer structure, an inner σ−(Re-Cr-Ni) phase as a diffusion barrier and outer Ni aluminides as an aluminum reservoir formed on a Ni based superalloy, Hastelloy X, and Nb-based alloy. (2) the up-hill diffusion coating with a duplex layer structure, an inner TiAl2 + L12 and an outer β-NiAl formed on TiAl intermetallic and Ti-based heat resistant alloys by the Ni-plating followed by high Al-activity pack cementation. (3) the chemical barrier coating with a duplex layer structure, an inner* γ + β + Laves three phases mixture as a chemical diffusion barrier and an outer Al-rich γ-TiAl as an Al reservoir formed by the two step Cr / Al pack process. (4) the self-formed coating with the duplex structure, an inner α-Cr layer as a diffusion barrier and an outer β-NiAl as an Al-reservoir on Ni-(20
50)at% Cr alloy changed from the δ-Ni2Al3 coating during oxidation at high temperature. The oxidation properties of the coated alloys were investigated at temperatures between 1173 and 1573K in air for up to 1,000 hrs (10,000 hrs for the up-hill diffusion coating). In the diffusion barrier coating the Re-Cr-Ni alloy layer was stable, existing between the Ni-based superalloy (or Hastelloy X) and Ni aluminides containing 12
50at%Al when oxidized at 1423K for up to 1800ks. It was found that the Re-Cr-Ni alloy layer acts as a diffusion barrier for both the inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate. In the chemical barrier coating both the TiAl2 outermost and Al-rich γ-TiAl outer layers maintained high Al contents, forming a protective Al2O3 scale, and it seems that the inner, γ, β, Laves three phase mixture layer suppresses mutual diffusion between the alloy substrate and the outer/outermost layers.