The very high temperature gas-cooled reactor (VHTR) design aims for hydrogen production and electric power generation is one of the most promising Generation-IV reactor types. The plant size, reactor thermal power, and core configuration will ensure passive decay heat removal without fuel damage or radioactive material releases during accidents. The conceptual designs may have outlet temperatures up to 950°C and will incorporate a gas-to-gas intermediate heat exchanger (IHX) with a design service life of 60 years. Its major components are the reactor internals, reactor pressure vessel (RPV), piping, hot gas duct (HGD), and intermediate heat exchangers (IHX). The key components of the VHTR system are the HGD and the IHX, which is the material must satisfied the characteristics of high temperature condition for a long period of running time.
The fatigue deformation is expected to be an important damage mode for the IHX as a result of power transients and temperature gradient induced thermal strain during operation as well as startups and shut downs, each of which produces cyclic loading. The effects of temperature and microstructures on fatigue properties of Alloy 617 base metal (BM) have been subjected of numerous studies. However, they did not investigate the fatigue behavior of the WJ. It is important to characterize the fatigue properties of WJ over a strain amplitudes and temperature for ensuring the reliability of welded structures. In this investigation, the Low Cycle Fatigue (LCF) tests were fully reversed (R=-1) with a triangular waveform and were conducted in air for total strain ranges, i.e. 0.6, 09, 1.2, 1.5% according to ASTM E-606. The detailed investigation and the following results is related to the influence of total strain level, temperature, and the material properties, which are concerned with the comparative study of LCF life and the cyclic response behavior of Alloy 617 BM and WJ. Furthermore, the Fracture behavior of Alloy 617 BM and WJ by GTAW process were examined via scanning electron microscope (SEM) and optical microscope (OM).