Abstract
The hot ductility behavior of Ni–16Mo–7Cr alloys (named GH3535) exposed at 700°C for different durations has been investigated by means of tensile test. It was found that the alloy exhibited a constant low ductility within the first 10h exposure, and then showed an increasing ductility with the exposure time until 1000h. After that, the ductility of the alloy decreased gradually with the increasing exposure time up to 10000h. Detailed microstructural investigations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) have shown that the change in the ductility of the alloy with the exposure time could be attributed to the precipitation of M12C carbide at the grain boundary. Such precipitates with size of 200nm, which are formed during the thermal exposure within 1000h, can significantly restrain the grain boundary sliding and crack initiation, resulting in the high ductility of the alloy. Further exposure will cause the coarsening of the carbides, making them as the source of grain boundary cracks, hence decreases the ductility of the alloy.
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