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Papers by Yukinori Yamamoto

alloying additions to increase specific performance factors [13]. Herein, both generations of all... more alloying additions to increase specific performance factors [13]. Herein, both generations of alloys are grouped together as "ORNL model" alloys unless directly specified. As will be shown later, FeCrAl alloys as a class of materials can demonstrate a wide range of properties depending on their structure, chemistry, and processing. Through combining the databases produced on the GE and ORNL model alloys, as well as other significant commercial and model alloy systems, we have developed the first edition of a comprehensive handbook on FeCrAl alloys for nuclear power applications. This handbook serves to draw from nearly half a century of scientific research but it is known that more studies are forthcoming. As such, the following serves as only the first edition; it is expected that as FeCrAl alloys become a more mature concept, the handbook will be updated and become more substantial.

Journal of Nuclear Materials, 2021

Materialia, 2021

Abstract Second phase intermetallic particles in an advanced accident-tolerant FeCrAl (Fe-13Cr-5A... more Abstract Second phase intermetallic particles in an advanced accident-tolerant FeCrAl (Fe-13Cr-5Al-2Mo) alloy are formed in the α-Fe matrix during processing. These particles are prominently related to the added Y. Neutron irradiation to ~7 displacements per atom (dpa) with a dose rate of ~8.16 × 10−7 dpa/s at 282 °C resulted in the amorphization of these precipitates which could degrade the mechanical properties of the FeCrAl alloys. Analytical electron microscopy and diffraction analysis combined with structural freedom analysis have been used to investigate the radiation resistance of the second phase particles. Radiation tolerance is closely linked to the particle Fe-Y content and can be tailored using the structure freedom value.

Materials Science Forum, 2007

ABSTRACT

Transactions of the American Nuclear Society, 2016

JOM, 2016

Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt.% are used a... more Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt.% are used at high temperatures in a wide range of industrial applications that demand microstructural stability, corrosion resistance, and creep strength. Although alumina scales offer better corrosion protection at these temperatures, designing cast austenitic alloys that form a stable alumina scale and achieve creep strength comparable to existing cast chromia-forming alloys is challenging. This work outlines the development of cast Fe-Ni-Cr-Al austenitic stainless steels containing about 25 wt.% Ni with good creep strength and the ability to form a protective alumina scale for use at temperatures up to 800-850°C in H 2 O-, Sand nd C-containing environments. Creep properties of the best alloy were comparable to that of HK-type cast chromiaforming alloys along with improved oxidation resistance typical of aluminaforming alloys. Challenges in the design of cast alloys and a potential path to increasing the temperature capability are discussed.

Materials Science and Engineering: A, 2014

Abstract A series of candidate alumina-forming austenitic (AFA) stainless steels designed to eval... more Abstract A series of candidate alumina-forming austenitic (AFA) stainless steels designed to evaluate the effects of variation in Al, C, Cr, Mn, Nb, and Ni content on high-temperature tensile properties, creep, and oxidation/corrosion resistance were studied. The compositions assessed were based on medium Ni (20–25 wt%) and low Ni (12 wt%) AFA variations strengthened primarily by MC and/or M23C6 carbide precipitates, and a high Ni (32 wt%) AFA superalloy variation strengthened primarily by γ′-Ni3Al intermetallic precipitates. Tensile and creep properties were measured at 650 and 750/760 °C, oxidation resistance from 650 to 900 °C in air with water vapor and steam environments, and sulfidation–oxidation resistance in Ar–20%H2–20%H2O–5% H2S at 550 and 650 °C. Optimized composition ranges for different use temperatures ranges based on these evaluations are presented.

Intermetallics, 2005

This paper summarizes our recent work on the development of cast single crystal gamma TiAl alloys... more This paper summarizes our recent work on the development of cast single crystal gamma TiAl alloys (PST) focusing on both lamellar orientation control of PST crystal in process and the thermal stability of the lamellar microstructure in use at elevated temperatures. PST crystals can easily be produced by unidirectional solidification regardless of the kinds of primary solidification phases of bcc b-Ti or hcp a-Ti solid solutions. The lamellar orientation control can be achieved by controlling the orientation of a single crystal existing just underneath the liquid/solid interface. Seeding with Ti-rich PST crystal does not work because of random nucleation of new grains due to the reverse phase transformation of g to a during heating. However, an Al-rich g single crystal with no solid/solid phase transformation up to the melting point is a promising seed when the average composition of the seed and alloys to grow is in the region of a solidification. During exposure at elevated temperatures interface reaction of energetically unstable variant interface takes place, resulting in the coarsening of g plates and eventually leading to the collapse of the lamellar microstructure unless a 2 plates exist. Thus, thermodynamically stable a 2 plates play an important role in pinning the coarsening of g plates across the lamellae, which is responsible for the high thermal stability of the lamellar microstructure.

Ferritic FeCrAl-based alloys show increased oxidation resistance for accident tolerant applicatio... more Ferritic FeCrAl-based alloys show increased oxidation resistance for accident tolerant applications as fuel cladding. This study focuses on investigating the weldability of three model FeCrAl alloys with varying alloy compositions using laser-welding techniques. A detailed study of the mechanical properties of bead-on-plate welds was used to determine the quality of welds as a function of alloy composition. Laser welding resulted in defect free welds devoid of cracking or inclusions. Initial results indicate a reduction in the yield strength of weldments compared to the base material due to distinct changes in the microstructure within the fusion zone. Although a loss of yield strength was observed, there was no significant difference in the magnitude of the tensile property changes with varying Cr or Al content. Also, there was no evidence of embrittlement; the material in the fusion zones demonstrated ductile behavior with high local ductility.

npj Computational Materials, 2020

High-temperature alloy design requires a concurrent consideration of multiple mechanisms at diffe... more High-temperature alloy design requires a concurrent consideration of multiple mechanisms at different length scales. We propose a workflow that couples highly relevant physics into machine learning (ML) to predict properties of complex high-temperature alloys with an example of the 9–12 wt% Cr steels yield strength. We have incorporated synthetic alloy features that capture microstructure and phase transformations into the dataset. Identified high impact features that affect yield strength of 9Cr from correlation analysis agree well with the generally accepted strengthening mechanism. As a part of the verification process, the consistency of sub-datasets has been extensively evaluated with respect to temperature and then refined for the boundary conditions of trained ML models. The predicted yield strength of 9Cr steels using the ML models is in excellent agreement with experiments. The current approach introduces physically meaningful constraints in interrogating the trained ML mod...

Materials Science and Engineering: A, 2018

FeCrAl alloys are under development as possible candidate materials of accident-tolerant fuel cla... more FeCrAl alloys are under development as possible candidate materials of accident-tolerant fuel cladding in light water reactors. In this study, the cracking resistance of FeCrAl alloys was evaluated using half-size Charpy impact tests at temperatures ranging from room temperature to 600°C. Ingot-metallurgy wrought FeCrAl alloys with base alloy compositions of Fe-(10-13)Cr-6Al-2Mo, in weight percent, and commercial powder-metallurgy FeCrAl alloys (Kanthal APMT) were investigated. All studied alloys showed almost zero absorbed impact energy at room temperature with brittle fracture behavior. The as-received APMT alloys exhibited poor impact toughness even at 600°C. The ductile-brittle transition temperatures of the wrought FeCrAl alloys varied from 119 to 318°C. The possible effects of microstructures, residual strain, materials preparation methods, process conditions, and chemical composition on the impact toughness of FeCrAl alloys were investigated by examining the Charpy impact data in combination with microstructural details of the alloys.