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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

Rakoczy Łukasz, Grudzień-Rakoczy Małgorzata, Rutkowski Bogdan, Cygan Rafał, Hanning Fabian, Cios Grzegorz, Habisch Stefan, Andersson Joel, Mayr Peter, Zielińska-Lipiec Anna

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 2

art. no. e119, 2023

This work presents the influence of microstructural constituents on liquation crack formation in the cast Ni-based superalloy, Rene 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 Rene 108 include γ matrix, γ' precipitates, MC and M23C6 carbides, and M5B3 borides. Based on Gleeble testing, it was found that Rene 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.

The Formation, Properties and Use of Dispersed Iron-Graphite Metallurgical Waste

Dan Leonid, Maslov Vladimir, Trofimova Larysa, Cios Grzegorz

Journal of Casting & Materials Engineering

2022

Vol. 6, no. 4

81--92

Dispersed wastes containing graphite, iron, and its oxides, getting into the air and accumulating in landfills, cause serious harm to human health and the environment. Moreover, even if the issue of the localization of these wastes has been solved successfully, their disposal has not yet been fully organized. In the present study, a systematic analysis of the dispersed iron-graphite waste (IGW) conditions for the formation at metallurgical enterprises, their structure, and their properties were carried out. In this case, special attention is focused on the electrophysical properties: specific saturation magnetization and volume resistivity. The presence of magnetic properties in IGW, combined with low electrical resistivity, makes IGW a promising and inexpensive raw material for obtaining cheap composite materials with radio shielding and radio absorbing properties in the microwave range. As a result of the research, effective ways of improving the magnetic properties of IGW by high-temperature treatment were obtained. The practical result of the research was the development and implementation of a technological scheme of dispersed IGW complex processing, which makes it possible to solve a twofold task – to exclude the ingress of iron-graphite wastes into the environment and to obtain a cheap material for protection against microwave radiation.