No abstract

No abstract

Austenitic steels are important core-internal materials for light-water reactors (LWRs). Life extension of LWRs requires steels with enhanced irradiation tolerance and higher strength. Studies have shown that grain boundaries (GBs) act as sinks for radiation-induced defects [1]; hence, a new generation of radiation tolerant materials may be developed by decreasing grain size and thereby increasing GB volume fraction. The present study involves pre-irradiation characterization of nanocrystalline and ultrafine-grained austenitic steels prepared using two different techniques of severe plastic deformation. The steel samples will then be neutron irradiated at the Advanced Test Reactor located at Idaho National Laboratory.The austenitic steel samples were processed using two techniques: high-pressure torsion (HPT) and equal channel angular pressing (ECAP) [2]. The processing conditions were: 316 steel processed using ECAP Bc route for 6 passes at 380 ºC, 304 steel processed using ECAP Bc route for 6 passes at 450 ºC, and 304 and 316 steels processed using HPT for 10 turns at 300 ºC under 6 GPa pressure. From transmission electron microscopy (TEM) results, HPT 316 has smaller average grain size (~91 nm) than the HPT 304 (~130 nm), and the ECAP 316 has smaller grain size (~170 nm) than the ECAP 304 (~200 nm). Both the HPT and the ECAP samples have significantly increased Vickers micro-hardness compared with the coarse-grained (CG) samples (~175 HV for CG steels, ~350 HV for ECAP 316, ~300 HV for ECAP 304, and ~550 HV for the HPT steels).X-ray diffraction (XRD) was used to study the phase compositions. CG 316 has only austenite phase, and there is not any phase transformation in the material after processing by ECAP or HPT. The phase stability of 316 steel may be due to the higher Ni content than that in 304 steel. CG 304 sample possesses ~30% martensite and ~70% austenite. ECAP 304 sample exhibited a phase transition to pure austenite. The martensite content in HPT 304 is increased compared to that in CG 304. The micro-strain and accordingly dislocation density in the samples were estimated using the Williamson-Hall method.

Critical aspects of innovative design in engineering disciplines like infrastructure, transportation, and medical applications require the joining of dissimilar materials. This study investigates the literature on solid-state bonding techniques, with a particular focus on diffusion bonding, as an effective method for establishing engineering bonds. Welding and brazing, while widely used, may pose challenges when joining materials with large differences in melting temperature and can lead to mechanical property degradation. In contrast, diffusion bonding offers a lower temperature process that relies on solid-state interactions to develop bond strength. The joining of tungsten and steel, especially for fusion reactors, presents a unique challenge due to the significant disparity in melting temperatures and the propensity to form brittle intermetallics. Here, diffusion characteristics of tungsten–steel interfaces are examined and the influence of bonding parameters on mechanical properties are investigated. Additionally, CALPHAD modeling is employed to explore joining parameters, thermal stability, and diffusion kinetics. The insights from this research can be extended to join numerous dissimilar materials for specific applications such as aerospace, automobile industry, power plants, etc., enabling advanced and robust design with high efficiency.