Keyou Mao

Profile Information
Name
Dr. Keyou Mao
Institution
Oak Ridge National Laboratory
Position
Postdoctoral Research Associate
h-Index
4
ORCID
0000-0002-2909-813
Biography

Keyou Mao is interested in nuclear fuels and materials using microscopy characterization and miniature mechanical testing. 

Expertise
Accident Tolerant Fuel, Additive Manufacturing, Advanced Alloys, Phase Transformation
Publications:
"Comparative Thermal Aging Effects on PM-HIP and Forged Inconel 690" Keyou Mao, David Gandy, Janelle Wharry, JOM Vol. 70 2018 2218-2223 Link
"Effect of laser welding on deformation mechanisms in irradiated austenitic stainless steel" Janelle Wharry, Keyou Mao, Cheng Sun, Xiang Liu, Haozheng Qu, Aaron French, Paula Freyer, Frank Garner, Lin Shao, Journal of Nuclear Materials Vol. 528 2020 151878 Link
Deformation mechanism of a laser weld on neutron irradiated AISI 304L stainless steel was studied by in-situ microcompression test at room temperature. The deformation-induced austenite-to-martensite phase transformation occurs in {101}-oriented grains in the irradiated base metal, while deformation twinning prevails in {101}-oriented grains in the weld heat affected zone (HAZ). A high number density of irradiation-induced voids in the base metal provides sufficient nucleation sites for the austenite-to-martensite phase transformation under compression at room temperature. A deformation map is established to predict critical twinning stress for face-centered-cubic (fcc) metals and alloys. Our results show that irradiation-induced voids can tailor the deformation mechanisms of austenitic stainless steel.
"Effects of corrosion-inhibiting surface treatments on irradiated microstructure development in Ni-base alloy 718" Keyou Mao, Vijay Vasudevan, Janelle Wharry, Journal of Nuclear Materials Vol. 512 2018 276-287 Link
"Grain orientation dependence of nanoindentation and deformation-induced martensitic phase transformation in neutron irradiated AISI 304L stainless steel" Keyou Mao, Cheng Sun, Yina Huang, Ching-Heng Shiau, Frank Garner, Paula Freyer, Janelle Wharry, Materialia Vol. 5 2019 100208 Link
"Laser weld-induced formation of amorphous Mn-Si precipitate in 304 stainless steel" Janelle Wharry, Keyou Mao, Yaqiao Wu, Cheng Sun, Emmanuel Perez, Materialia Vol. 3 2018 174-177
"Microstructure-property relationships across AISI 304/308L stainless steel laser weldments" Janelle Wharry, Keyou Mao, Vikas Tomar, Yaqiao Wu, Materials Science & Engineering A Vol. 721 2018 234-243
"Role of cavities on deformation-induced martensitic transformation pathways in a laser-welded, neutron irradiated austenitic stainless steel" Janelle Wharry, Keyou Mao, Cheng Sun, Ching-Heng Shiau, Kayla Yano, Paula Freyer, Anter EL-AZAB, Frank Garner, Aaron French, Lin Shao, Scripta Materialia Vol. 178 2020 1-6 Link
The role of cavities on deformation-induced martensitic phase transformations is studied in a laser-welded and neutron irradiated austenitic stainless steel. Orientation dependent nanoindentation experiments are performed in the base metal and the weld heat affected zone (HAZ) at room temperature. Transmission electron microscopy study of deformed microstructures indicates indentation-induced α’-martensite forms in the base metal, whereas α’- and ε-martensite arise in the HAZ. The different pathway of martensite phase transformation is attributed to the laser weld-induced annealing of cavities. Our results suggest that deformation-induced martensitic phase transformation of austenitic stainless steel is correlated to neutron irradiated cavity structures.
"Thermal Aging and the Hall–Petch Relationship of PM-HIP and Wrought Alloy 625" Janelle Wharry, Keyou Mao, David Gandy, Elizabeth Getto, JOM Vol. 71 2019 2837 Link
Powder metallurgy with hot isostatic pressing (PM-HIP) is an advanced alloy processing method capable of fabricating complex nuclear reactor components near-net shape, reducing the need for machining and welding. For heat exchangers and steam generators, thermal aging of PM-HIP materials must be comparable or superior to conventional castings or forgings. This study compares thermal aging effects in PM-HIP and wrought alloy 625. Isothermal aging is carried out over 400–800°C for 100 h. Both PM-HIP and wrought materials have equiaxed grains with a uniform orientation distribution. The PM-HIP material has finer grains than the wrought material at all aging conditions. Both PM-HIP and wrought materials have a comparable hardness and modulus measured by nanoindentation. Hardness remains unchanged with aging except the wrought material aged at 800°C, which exhibits softening. Overall, PM-HIP alloy 625 responds comparably to wrought alloy 625 and is superior at 800°C. Results are used to calculate a Hall–Petch coefficient.
Presentations:
"Effect of residual stress mitigation surface treatment techniques on the irradiation tolerance of Ni-base alloys" Keyou Mao, Vijay Vasudevan, Janelle Wharry, FONTEVRAUD 9 September 17-20, (2018)
"Microstructural and mechanical integrity of laser weldment of neutron irradiated AISI 304 SS" Keyou Mao, Paula Freyer, Frank Garner, Janelle Wharry, TMS 2018 March 11-15, (2018)
"Microstructural and micromechanical characterization of laser weld repairs on neutron irradiated 304 stainless steel" Keyou Mao, Paula Freyer, Cheng Sun, Frank Garner, Janelle Wharry, NUMAT 2018 October 15-18, (2018)
"Microstructure evolution of laser weld repairs of 304SS at high dose ion irradiation" Keyou Mao, Paula Freyer, Jonathan Tatman, Frank Gift, Frank Garner, Janelle Wharry, Poster - FONTEVRAUD 9 September 17-20, (2018)
NSUF Articles:
RTE 1st Call Awards Announced - Projects total approximately $1.4 million These projects will continue to advance the understanding of irradiation effects in nuclear fuels and materials in support of the mission of the DOE-NE. Friday, February 8, 2019 - Calls and Awards
From the Users Group: Vote for Your New Executive Committee - Election closes 10/31 The goal of the Users Group is to provide a formal and clear channel from the NSUF users to the NSUF program office as well as advocate for the experimental activities at NSUF, and the Executive Committee helps facilitate this. Wednesday, October 9, 2019 - Users Group, Newsletter
New Users Organization Executive Committee Members Announced - Their term will begin in January 2020 The Users Organization Executive Committee will work to advance NSUF user concerns and priorities. Tuesday, November 26, 2019 - Newsletter, Users Group