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Contribution of Microstructural Constituents on Hot Cracking of MAR-M247 Nickel Based Superalloy

Rakoczy Ł., Grudzień M., Zielińska-Lipiec A.

Archives of Metallurgy and Materials

2018

Vol. 63, iss. 1

181--189

The aim of this study is to investigate influence of selected parameters of gas tungsten arc welding on microstructure of MAR-M247 nickel based superalloy originating from turbine vane. MAR-M247 is a precipitation-strengthened superalloy which is widely used in aerospace engines. The main strengthening phase in this material is ordered L12 intermetallic γ' phase Ni3 (Al, Ti). The surface of alloy was modified by electric arc in order to present microstructural changes in weld and heat affected zone. Investigation of the heat affected zone revealed that constitutional liquation of γ' particles and primary carbides is responsible for the formation of a liquid grain boundary layer which finally contributed to cracking. Scanning electron microscopy indicated high susceptibility to cracking of MAR-M247 alloy which is connected with high content of γ'-formers aluminum and titanium.

Employing various metallography methods at high temperature alloy fatigue tests evaluation

Belan J., Kucharikova L., Vasko A., Chalupova M., Svecova I.

Production Engineering Archives

2016

Vol. 13, No. 4

11--15

Microstructures of superalloys have dramatically changed throughout the years, as modern technology of its casting or forging has become more sophisticated. The first superalloys have polyedric microstructure consisting of gamma solid solution, some fraction of gamma prime and of course grain boundaries. As demands on higher performance of aero jet engine increases, the changes in superalloys micro-structure become more significant. A further step in microstructure evolution was directionally solidified alloys with columnar gamma prime particles. The latest microstructures are mostly monocrystalline, oriented in [001] direction of FCC gamma matrix. All microstructure changes bring necessity of proper preparation and evaluation of microstructure. Except for the already mentioned structures have gamma double prime and various carbides form can be seen. These structural parameters have mainly positive influence on important mechanical properties of superalloys. The paper deals with a microstructural evaluation of both groups of alloys – cast and as well as wrought. Micro-structure evaluation helps to describe mechanism at various loading and failure of progressive superalloys. Such an example where micro-structure evaluation is employed is fractography of failure surfaces after fatigue tests, which are examples of metallography evaluation de-scribed in this paper as a secondary objective.