자료유형  

 학위논문

Control Number  

0016932527

International Standard Book Number  

9798379677459

Dewey Decimal Classification Number  

600

Main Entry-Personal Name  

Ding, Jie.

Publication, Distribution, etc. (Imprint  

[S.l.] : Purdue University., 2020

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2020

Physical Description  

1 online resource(202 p.)

General Note  

Source: Dissertations Abstracts International, Volume: 84-12, Section: B.

General Note  

Advisor: Zhang, Xinghang.

Dissertation Note  

Thesis (Ph.D.)--Purdue University, 2020.

Restrictions on Access Note  

This item must not be sold to any third party vendors.

Summary, Etc.  

요약Gradient structured (GS) metallic materials have shown unique properties including the synergy of high strength and good ductility, improved fatigue and wear/friction resistance etc. One of the severe surface modification technique, surface mechanical grinding treatment (SMGT), has been proven an effective method for the generation of gradient structures in metallic materials. Most of Ni-based superalloys are precipitation strengthened and with an extraordinary combination of high strength, ductility and resistance to oxidation at high temperatures. The precipitation behaviors of these materials are sensitive to their initial microstructures. This thesis focuses on the microstructure evolution and mechanical behaviors of two types of gradient Ni alloys.GS Hastelloy C-22HS and Inconel 718 (IN718) Ni-based superalloys were fabricated through the SMGT technique. The gradient structures consist of nanograined (NG) or nanolaminate (NL) surface layer and the subsurface layers with deformation twins. In situ compression test results reveal that intergranular back stress may contributes to the high work hardening capability of the GS C-22HS alloy. Mo-rich thick grain boundaries (GBs) formed in the gradient C-22HS samples after heat treatment. In situ micropillar compression studies coupled with molecular dynamics (MD) simulations reveal that the Mo-rich thick GBs are stronger barriers than conventional thin GBs to the transmission of dislocations, leading to significant strengthening. Furthermore, the formation of thick GBs also contributes to the improvement of thermal stability of nanograins in the C-22HS alloys. The gradient microstructures in the IN718 alloy changed the precipitation behavior and thermal stability of nanograins in the alloy. The studies on precipitation behaviors of GS IN718 alloy reveal that η phase formed in the severely deformed surface NG layer after annealing at 700°C. Thermal stability studies show that NG IN718 alloy with grain sizes smaller than the critical value of ~ 40 nm is thermally more stable than their coarse-grained counterpart. The underlying mechanisms of strengthening and improved thermal stability of the gradient Ni-based superalloys are discussed based on transmission electron microscopy studies and MD simulations. This work suggests that tailoring the gradient microstructures may lead to the discovery of metallic materials with novel mechanical and thermodynamic properties.

Subject Added Entry-Topical Term  

Mechanical properties.

Subject Added Entry-Topical Term  

Statistics.

Subject Added Entry-Topical Term  

Grain growth.

Subject Added Entry-Topical Term  

Chemical elements.

Subject Added Entry-Topical Term  

Grain boundaries.

Subject Added Entry-Topical Term  

Nickel alloys.

Subject Added Entry-Topical Term  

Ductility.

Subject Added Entry-Topical Term  

Strain hardening.

Subject Added Entry-Topical Term  

Stainless steel.

Subject Added Entry-Topical Term  

Stress-strain curves.

Subject Added Entry-Topical Term  

Grain size.

Subject Added Entry-Topical Term  

Microstructure.

Subject Added Entry-Topical Term  

Deformation.

Subject Added Entry-Topical Term  

Alloys.

Subject Added Entry-Topical Term  

Shear strain.

Subject Added Entry-Topical Term  

Annealing.

Subject Added Entry-Topical Term  

Materials science.

Subject Added Entry-Topical Term  

Mechanics.

Added Entry-Corporate Name  

Purdue University.

Host Item Entry  

Dissertations Abstracts International. 84-12B.

Host Item Entry  

Dissertation Abstract International

Electronic Location and Access  

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Control Number  

joongbu:642995