| 1. |
- Matysiak, Hubert, et al.
(författare)
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Microstructure of Haynes® 282® Superalloy after Vacuum Induction Melting and Investment Casting of Thin-Walled Components
- 2013
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 6:11, s. 5016-5037
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to characterize the microstructure of the as-cast Haynes® 282® alloy. Observations and analyses were carried out using techniques such as X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray spectroscopy (EDS), wave length dispersive X-ray spectroscopy (WDS), auger electron spectroscopy (AES) and electron energy-loss spectrometry (EELS). The phases identified in the as-cast alloy include: γ (gamma matrix), γʹ (matrix strengthening phase), (TiMoCr)C (primary carbide), TiN (primary nitride), σ (sigma-TCP phase), (TiMo)2SC (carbosulphide) and a lamellar constituent consisting of molybdenum and chromium rich secondary carbide phase together with γ phase. Within the dendrites the γʹ appears mostly in the form of spherical, nanometric precipitates (74 nm), while coarser (113 nm) cubic γʹ precipitates are present in the interdendritic areas. Volume fraction content of the γʹ precipitates in the dendrites and interdendritic areas are 9.6% and 8.5%, respectively. Primary nitrides metallic nitrides (MN), are homogeneously dispersed in the as-cast microstructure, while primary carbides metallic carbides (MC), preferentially precipitate in interdendritic areas. Such preference is also observed in the case of globular σ phase. Lamellar constituents characterized as secondary carbides/γ phases were together with (TiMo)2SC phase always observed adjacent to σ phase precipitates. Crystallographic relations were established in-between the MC, σ, secondary carbides and γ/γʹ matrix.
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| 2. |
- Rakoczy, Lukasz, et al.
(författare)
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Investigation of the y´ Precipitates Dissolution in a Ni-Based Superalloy During Stress-Free Short-Term Annealing at High Homologous Temperatures
- 2021
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Ingår i: Metallurgical and Materials Transactions. A. - : SPRINGER. - 1073-5623 .- 1543-1940. ; 52:11, s. 4767-4784
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Tidskriftsartikel (refereegranskat)abstract
- The equiaxed Ni-based superalloy Rene 108 was subjected to short-term annealing at five temperatures between 900 degrees C and 1100 degrees C. The phase composition, phase lattice parameters, microstructure, stereological parameters, and chemical composition of y´ precipitates were investigated by thermodynamic simulations, X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Analysis of the y and y´ lattice parameters using the Nelson-Riley extrapolation function showed that the misfit parameter for temperatures 900 degrees C to 1050 degrees C is positive (decreasing from 0.32 to 0.11 pct). At 1100 degrees C, the parameter becomes negative, delta = - 0.18 pct. During the short-term annealing, gamma ‘ precipitates dissolution occurred progressing more rapidly with increasing temperatures. The surface fraction of y´ precipitates decreased with increasing temperature from 0.52 to 0.34. The dissolution of gamma ‘ precipitates did not only proceed through uninterrupted thinning of each individual precipitate, but also included more complex mechanisms, including splitting. Based on transmission electron microscopy, it was shown that after y´ precipitates dissolution, the matrix close to the y/y interface is strongly enriched in Co and Cr and depleted in Al.
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| 3. |
- Rakoczy, Łukasz, et al.
(författare)
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Microstructure evolution of the Gleeble-simulated heat-affected zone of Ni-based superalloy
- 2019
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Ingår i: Power Transmissions 2019 Proceedings. ; 3
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Konferensbidrag (refereegranskat)abstract
- The formation of liquation cracking in a simulated heat affected zone of René108 is reported. The stress controlled thermo-mechanical experiments were carried out on a Gleeble®3800 testing system. The base alloy was lost-wax cast and then solution treated and aged. Light and scanning electron microscopy of this material revealed high volume fraction of γ' precipitates in the dendrite arms and residual eutectic γ/γ' islands in the interdendritic areas. As a result of short-term exposure to high homologous temperature, the volume fraction of γ' phase was significantly decreased due to the dissolution of precipitates in the surrounding matrix. The thin non-equilibrium liquid film, formed locally along grain boundaries, was a key-factor favoring initiation of cracks and their spreading during the Gleeble testing. The liquid appeared as a result of constitutional liquation, mainly of the γ' precipitates.
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| 4. |
- Rakoczy, Łukasz, et al.
(författare)
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The role of the strengthening phases on the HAZ liquation cracking in a cast Ni-based superalloy used in industrial gas turbines
- 2023
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Ingår i: Archives of Civil and Mechanical Engineering. - : Springer. - 1644-9665. ; 23:2
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Tidskriftsartikel (refereegranskat)abstract
- This work presents the influence of microstructural constituents on liquation crack formation in the cast Ni-based superalloy, René 108. The investigation was divided into three parts: characterisation of the material's microstructure in pre-weld condition, hot ductility studies and analysis of liquation cracking induced by the gas tungsten arc welding process. Using advanced electron microscopy techniques it is shown that the base material in pre-weld condition is characterised by a complex microstructure. The phases identified in René 108 include γ matrix, γ' precipitates, MC and M23C6 carbides, and M5B3 borides. Based on Gleeble testing, it was found that René 108 is characterised by high strength at elevated temperatures with a maximum of 1107 MPa at 975 °C. As a result of constitutional liquation, the superalloy’s strength and ductility were significantly reduced. The nil strength temperature was equal to 1292 °C, while the nil ductility temperature was 1225 °C. The low ductility recovery rate (32.1), ratio of ductility recovery (36.2) and hot cracking factor (Rf = 0.05) values confirmed the low weldability of Renѐ 108. In the heat-affected zone (HAZ) induced by welding, constitutional liquation of mainly γ' precipitates, with a contribution of M23C6 carbides and M5B3 borides, was observed. The thin non-equilibrium liquid film, which formed along high-angle grain boundaries, led to crack initiation and their further propagation during cooling. The eutectic γ–γ' re-solidification products are visible on the crack edges.
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