Abstract
In this study, an investigation was conducted to examine two types of Ni-based alloys upon long-term heat treatment and compare their grains, surface corrosion layers and microhardness values. The working environment of the tested samples was a temperature of 1000 °C for 5000 h. Two samples, respectively, contained low (~8 wt.%) and high (~16 wt.%) contents of Mo, and the low-Mo-content sample contained Nb (~4 wt.%) and other elements. The grains, precipitates, corrosion layers and microhardness values of the samples before and after heat treatment were determined by scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy, X-ray diffraction analysis and Vickers hardness tests. The results revealed that the grain was surprisingly stable in the sample with the higher Mo content; after heat treatment, the grain size was ~35 μm, which was similar to the grain size before heat treatment. Moreover, for the sample with the higher Mo content, the microhardness was found to be higher, especially after long-term high-temperature treatment, which is of great significance for the long service life of materials.
Highlights
Ni-based alloys have attracted increasing attention as new candidates for hightemperature materials due to their high hardness, low density, good corrosion resistance and good dimensional stability [1]
The practical performances of polycrystalline materials are strongly affected by the formedThe microstructure inside, which is of mostly dominated bymaterials grain growth practical performances polycrystalline are behaviors
High temperatures will cause the growth of crystals, which many research institutes find formed microstructure inside, which is mostly dominated by grain growth be undesirable [8]
Summary
Ni-based alloys have attracted increasing attention as new candidates for hightemperature materials due to their high hardness, low density, good corrosion resistance and good dimensional stability [1]. The addition of molybdenum (Mo) to Ni-based alloys is of great importance due to its wide range of applications, especially under long-term high-temperature heat treatment [2]. Among the different alloys containing molybdenum, Ni-Mo alloys are of great interest due to their high corrosion resistance and low overpotential for hydrogen evolution reaction [3]. The effects of the addition of niobium (Nb) on the microstructures of Ni–based alloys were systematically investigated by Wei et al [5]. In an Ni–based alloy with the addition of Nb, needle-like
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