자료유형  

 학위논문

Control Number  

0016935426

International Standard Book Number  

9798380735599

Dewey Decimal Classification Number  

621

Main Entry-Personal Name  

Gao, Mingze.

Publication, Distribution, etc. (Imprint  

[S.l.] : The Pennsylvania State University., 2023

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2023

Physical Description  

1 online resource(191 p.)

General Note  

Source: Dissertations Abstracts International, Volume: 85-05, Section: B.

General Note  

Advisor: Debroy, Tarasankar;Palmer, Todd A.

Dissertation Note  

Thesis (Ph.D.)--The Pennsylvania State University, 2023.

Restrictions on Access Note  

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

Summary, Etc.  

요약High power laser welding, with powers on the order of 10 kW, represents an attractive pathway for improving productivity in the single pass joining of thick section structures. During high power laser welding of Inconel 740H, a candidate material for the steam pipes in advanced ultra supercritical power plants, defects were observed, including keyhole collapse porosity, liquation cracking in the heat affected zone, and solidification cracking in the fusion zone, which displayed variations with processing conditions. Although liquation cracks and keyhole porosity were observed for all these high power laser welding conditions due to the high heat input and keyhole instability, horizontal solidification cracks across the fusion zones were observed at depths of around 70% to 80% of the weld depths, while the same material does not display similar solidification cracking during arc welding and low power laser welding conditions. A similar crack was not observed in another nickel alloy, Inconel 690, under the same welding conditions.To capture the complex interactions between alloy composition and processing conditions leading to the appearance of these cracks, well-tested heat transfer and fluid flow and thermomechanical models were integrated to calculate temperature histories, solidification conditions, and the resulting stresses and strain rates across the solidifying mushy zone. The coupling of these powerful models provided a means for evaluating horizontal solidification cracking susceptibility and predicting crack locations by identifying the simultaneous appearance of critical strain rate and tensile stress levels across different processing conditions and alloys.Since alloy composition is usually fixed within a specified range, the prevention of these defects requires tight control of the processing conditions. Wobble head laser welding, as an emerging tool in high power laser welding, was employed, which provides new opportunities to alter process conditions and produce defect free welds. Due to the additional transverse and backward motions with the laser beam oscillation, the laser energy density distribution across the weldment was altered, leading to variations in weld pool dimensions, solidification conditions, and stress state across the welds. The application of beam oscillation led to shorter, wider, and shallower weld pools. Due to these changes in weld profiles, the solidification rate was reduced while the temperature gradient was increased compared with the linear welds. These changes in the process conditions also impacted the stress state, which provide opportunities to prevent solidification cracking during high power laser welding process.

Subject Added Entry-Topical Term  

Heat transfer.

Subject Added Entry-Topical Term  

Solidification.

Subject Added Entry-Topical Term  

Single crystals.

Subject Added Entry-Topical Term  

Lasers.

Subject Added Entry-Topical Term  

Grain boundaries.

Subject Added Entry-Topical Term  

Nickel alloys.

Subject Added Entry-Topical Term  

Aluminum alloys.

Subject Added Entry-Topical Term  

Pressure distribution.

Subject Added Entry-Topical Term  

Energy.

Subject Added Entry-Topical Term  

Cracks.

Subject Added Entry-Topical Term  

Alloys.

Subject Added Entry-Topical Term  

Geometry.

Subject Added Entry-Topical Term  

Morphology.

Subject Added Entry-Topical Term  

Solids.

Subject Added Entry-Topical Term  

Materials science.

Index Term-Uncontrolled  

Laser welding

Index Term-Uncontrolled  

Keyhole porosity

Index Term-Uncontrolled  

Nickel alloy

Index Term-Uncontrolled  

Alloy composition

Added Entry-Corporate Name  

The Pennsylvania State University.

Host Item Entry  

Dissertations Abstracts International. 85-05B.

Host Item Entry  

Dissertation Abstract International

Electronic Location and Access  

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Control Number  

joongbu:639791