The nickel-base cast alloy IN 100 is used for turbine blades for service in the temperature range above 800deg C. On account of the high proportion of the γ'-precipitation hardening phase of more than 50% IN 100 belongs the top group of high-temperature nickel-base superalloys. It is reported on investigations with IN 100 in order to better understand the casting-specific, large property variations and to define and to optimize the creep characteristics and the creep to rupture properties through variation of the γ'-precipitation hardening phase. It is explained how cast initial state, heat-treatment, microstructure, and the creep to rupture strength are linked with each other. (orig.)
Pillhoefer, H.; Track, W.; Wege, R.
Creep values of the nickel-based cast alloys IN 100 and IN 713C were determined at the Institute for Materials of the Darmstadt Technical College on behalf of the FVV Working Party on 'Long Term Creep' and these were evaluated with the aim of: Producing documentation of structural changes, documentation of changes of the ..gamma.. separation phase depending on temperature, stress and time. Clearing up the stress to which ..gamma.. separation particles remain stable; from this one can judge how sensible it is to produce a defined hardened structure in IN 100 by heat treatment. Formulating subjects and tasks for an FVV Research Project 'Creep equations'. (orig./IHOE).
The influence of γ\\' size on critical resolved shear stress in alloy IN100 at 650. °C has been examined by considering dislocation/precipitate interactions involving particle shearing and Orowan by-passing mechanisms. To achieve this, heat treatment procedures were carried out on smooth specimens to produce materials with variations in secondary and tertiary γ\\' size, while maintaining their respective volume fractions. These specimens were subjected to strain-controlled fully reversed cyclic loading at 650. °C. Thin foils extracted from these specimens, post-testing, were examined by transmission electron microscopy to identify the nature of the precipitate/dislocation interactions during plastic deformation. Results indicated the presence of shearing and Orowan by-passing mechanisms. These observations have been used as a basis to calculate the critical resolved shear stress as a sum of components contributed by solid solution and by γ\\' particles being sheared and looped. In this analysis, a critical particle size defining the shearing/looping transition has been determined and this has been used to calculate the relative volume fraction and size of particles contributing to the critical resolved shear stress. These analytical results have been compared with those experimentally obtained at 650. °C using smooth specimens with different precipitate sizes. © 2013 Elsevier B.V.
Highlights: • Micro-LAAM was proposed to deposit crack-sensitive Ni-base alloy IN100. • Crack-free deposition of IN100 was achieved using micro-LAAM. • Fine γ′ phase was formed with the γ′/γ approximately 60–40%. • Different types of carbides were observed at grain boundaries and in the grains. • Excellent tensile properties of the deposited IN100 were obtained. - Abstract: Layer by layer fabrication using micro-laser aided additive manufacturing (micro-LAAM) was successfully implemented on nickel-base superalloy IN100. It is known that IN100, a type of superalloy having high titanium and aluminum contents, has poor weldability due to weld liquation cracking in the heat-affected zone (HAZ) and strain age cracking. In this study, micro-LAAM process was optimized through a set of designed experiments to eliminate crack formation and reduce porosity. It was found that the crack-free deposition can be achieved owing to the fact that micro-LAAM process used in this study had very low heat input. Three distinct sizes of γ′ precipitates were observed on the post heat-treated samples. The volume fractions of γ to γ′ phases were found to be approximately 60–40%. Microstructure and chemical analysis results showed that γ′ phase was embedded within γ-Ni matrix while various carbides (MC, M23C6 and M6C) were observed as precipitates at grain boundaries or within grains. Electron backscatter diffraction (EBSD) was used to compare grain morphologies and size distribution of three distinctly different regions on each layer. The achieved ultimate tensile strength and yield strength are much better than the minimum requirements specified in aerospace material specification 5397 for cast IN100