PROJECT OBJECJ1VES

Numerous experimental investigations have been carried out to understand the thermo-

mechanical properties of the high chromium creep resistant alloys, especially the creep behavior

for the Fossil Energy (FE)power plant application. However, the results corning from the "same

condition" and "same alloy" from different groups are considered scatter. Systematic

investigation, especially physics based models of creep behavior is greatly needed for the base

alloys and weldment.

.g~idance on ~~()~~:~~illlprovethe5reep,:~~~i~l~ec,e,of Gr\91 alloys; ""'"~c,.","/,',',""""""",,,,.,,,," ,_,."",'",._,'

The long-term. goal of the proposed program is to develop a model for creep and fatigue

resistant alloys with different elemental systems, compositions, and processing parameters of

, weldment and heat treatment. In addition, new creep and fatigue resistant alloys are to be

designed based on the predictions from the model.

The specific project objectives are as follows: 1.) Predict the phase stability and

microstructure of Gr.91 base alloy and weldment with the computational thermodynamics and

kinetics (CALPHAD) approach; 2.) Carry out welding, heat treatment, and creep test for the

Gr.91 alloy; 3.) Develop a model which has excellent match with the experimental data from the

current work and also from the previous existing work; 4.) Predict how to improve the long-

term creep resistance for the Gr.91 family alloys.

INTRODUC110N

The typical commercial FE power plants has strict requirement for the expected lifetime

of the structural alloys used, which varies from 40 to 70 years. The main concern of the

structural alloys is the thermomechanical properties including the long-term creep resistance

and also the fatigue resistance because of the cyclic operation 3.4. In addition, special attention

needs to be paid to the Heat-Affected Zone (HAZ) due to welding of structural alloys where

premature failure is typically observed 5,6.

Meanwhile, the advanced technologies FE power plant operates at temperature and

pressure/stress conditions that exceed current commercial FE power plants. This will added

even stricter requirement on the creep and fatigue resistance for the choice of structural alloys.

It is well known that the most critical failure mechanism for the high Cr creep strength

enhanced ferritic alloy is not in the base alloy or weld metal 5,6. The typical creep cracking

happens in HAZ, especially toward the outer edge of the visible HAZ, i.e. the Fine Grain HAZ

(FGHAZ) and Intercritical HAZ (ICHAZ) region 7. Such cracking is called the type IV creep

cracking as shown in Figure 1. It has been identified that the premature cracking is related to

the formation and coarsening of the several precipitates including M23C6,MX, Laves phases, and

Z phase (depends on the composition of ferritic alloys) 8-10. For example it is claimed that the

fine M23C6phase has the strengthen effect in the early life of the steels but it will coarsen quickly

and therefore should not be treated as strengthen

phase in the long-term operations; the fine MX

phase (NbC or VN) is beneficial to the steel, which Base Alloy

has very low coarsening rate and is able to pin

grain boundaries and dislocationst-. However, Figure 1. Type IV creep cracking in FGHAZ and ICHAZ.

comprehensive investigation is needed to link the composition, process, precipitates stability,

microstructure, and creep resistance. As a commonly used alloy in ,the FE power plants, Gr.91 has

drawn a lot of interests from industry and R&D and will be investigated in the current work.

PI'S PREVIOUS SUCCESS STORY ON CREEP RESISTANT ALLOYS

The PI had worked on the Mg alloy development using the ICME approach. The overall

goal was to use the ICME approach to develop a prediction method to improve the creep

resistance of Mg alloys. It was a project in collaboration with Dr. Alan Luo (was in General

Motors and now a professor in OSU).Dr. Luo had carried out the experimental investigation on

the creep mechanism of the Mg alloys 12·17.The poor creep

resistance was identified due to the discontinuous

precipitation of the y-Al12Mg17phase on the grain boundary.

To improve creep resistance in magnesium alloys 18, it was

proposed to suppress the formation of y-Al12Mg17phase and

form high melting temperature secondary phase particles at

grain boundaries to pin grain boundary sliding. The addition

of calcium to Mg-Al based alloys was reported to improve the

1000

900

800

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400

300

0.2 0.4 0.6 0.8AI Mole Fraction. Mg

Figure 2. The latest AI-Mg binarythermodynamic database developed by thePI 1,2. Y phase is the main reason for thepoor creep resistance due to its low melting .temperature and weak bonds.

creep resistance in 1960 19 and draw a lot of interests.

The PI developed the Mg-Al-Ca thermodynamic database with the CALPHAD approach

and predicted the stability of various phases including the y phase, C14, CIS, C36 Laves phases

for the Mg-Al-Ca alloys as shown in Figure 3. The poor creep resistance of Mg-Al alloys can be

easily explained because the detrimental y phase is very stable. The beneficial effect of the

addition of Ca can be clearly shown in Figure 3 as the detrimental y phase was suppressed and

the beneficial Laves phases were formed. It has good. agreement with the experimental

observation (GM-B(2%Ca) and GM-C (3%Ca)by Dr. Luo) on the creep resistance improvement.

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Figure 3. The PI's equilibrium cooling and Scheil simulation for the Mg-4.5%AI, Mg-4.5%AI-1.0%Ca, and Mg-4.5%AI-1.9%Ca, in which the real condition will be. between these two conditions. It shows with the addition of Ca, y (the bad phase)becomes less stable, while the Laves phase (the good phases) will be the secondary phase form on the grain boundar/D.

.' .

In addition, besides the computational effort, the PI has carried out the experimental

investigation on the GM-B and GM-C alloy. The SEM/EDSanalysis clearly shows the existence

of (Mg,Al)2Caphase (later verified as C36 Laves phase) in the as-cast sample. But it changed to

CIS Laves phase after heat treatment. The experimental observation has excellent agreement

with the modeling prediction on the phase stability and the microstructure change and verified

the reliability of the prediction from the Mg-Al-Ca thermodynamic database. More details can

be found in the PI's publications 20,21.

Figure 4. SEMIEDS analysis carried by the PIon the grain boundary phase from as cast GM-C sample ((Mg,AlhCa C36Laves phase on the left) and from heat treated sample (A12Ca CIS Laves phase on the right). It shows excellent agreement withthe prediction from the Mg-AI-Ca database 22.

The above work demonstrates the idea that the fundamental investigation based on the

ICME approach will provide guidance on the alloy design to improve the creep resistance,

which inspires the current proposed work on the creep resistance of steels.

lvlERIT REVIEW CRITERION DISCUSSION

Inspired by the previous successful effort on the creep

resistance of Mg alloys, we are proposing to improve the creep

resistance of Gr.91 alloys with the following the ICME approach

outlined in Figure 5.

In the current work, existing experimental data from

other groups such as welding, Post-Welding Heat Treatment

(PWHT), and creep tests will be used as the input to provide the

necessary phase stability and microstructure information for the

-thermodynamic and kinetic simulations. The thermodynamic

simulations will mainly focusing on the phase stability of

precipitates, while the kinetic simulations will mainly focus onFigure 5. Sketch of the ICME approachto develop the model for the creep

the microstructure changes such ~s the precipitates dissolution resistance property of Gr.91 alloy.

and coarsening. The thermodynamic and kinetic simulations will be used to correlate with the

previous experimental data from other groups. It will also be used to determine the processing

parameters for our current experimental investigations including the experimental setup for the

welding, PWHT, and creep tests. The characterization results from SEM, FIB/TEM,and XRD

will provide the feedback and refine the thermodynamic and kinetic simulations. Iterations may

be needed until the agreement is satisfactory. With the comprehensive understanding of the

precipitation phase stability and the microstructures from the modeling prediction and the

experimental investigation, we will build the link among Composition - Processing Parameters

.- Phase Stability <Microstructure - Creep Resistance for the Gr.91 alloy.

MRC 1- Scientific and Technical Merit1) The degree to which development of the proposed technology can be expected to

contribute to a developmental breakthrough for the challenges described in the topic area.

The Funding Opportunity Announcement (FOA) specifically seeks a physics based

description of creep behavior. In addition, the model needs to have best fit to wide range of data

for a specific alloy and identify the experimental error and systematic variability from different

groups. This proposed project is to address these requests in the FOA. The manner in which

these areas will be addressed, and lead to the development breakthrough, will be described in

the following subsections:

A. A general fundamental creep resistance model for Gr.91 alloy and BEYOND

Most R&D effort on the new materials design focuses on the property and performance of

the materials. However, as shown in Figure 6, the core of the materials design is the

fundamental thermodynamics and kinetics, which will determine the property and performance of

the materials. Phenomenological 'models focusing only on

the property and performa~ce are not able to find out the

reason for the conflicting creep test results for the "same

alloys" from different groups.

It is well known that the creep resistance is

greatly linked with the precipitates stability and the

microstructure changes, both of which are determined by

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thermodynamics and kinetics. The current work will build a fundamental creep resistance model

focusing the the fundamental thermodynamics and kinetics, which will build the link among

Composition - Processing Parameters - Phase Stability - Microstructure - Creep Resistance

for the Gr.91 alloy and clarify the factors affecting the conflicting creep test results from

different groups. In addition, the creep and fatigue failure is not a problem just for Gr.91 alloy.

The general approach to be established in the current work can be easily applied to other alloys.

B. Prediction on the stability of metastable phase and intermediate phases

Thermodynamic calculations were typically carried out to understand the stable phases

under equilibrium condition. However, the metastable and intermediate phases have been

observed in the long-term operation of high Cr ferritic alloys. These experimentally observed

phases are critical to the long-term creep resistance. In the current work, the comprehensive

thermodynamic and kinetic combined simulation will be carried out to understand the

stabilities, dissolution, and coarsening of stable, metastable, and intermediate phases.

C. Comprehensive Investigation based on the ICME approach

In the current proposed work, we are proposing to use the ICME approach to develop

an integrated model for the prediction of the thermo-mechanical property prediction. The ICME

approach has be proposed years ago and is widely used in the alloys design, which is especially

useful in the multicomponent systems. However, the main challenge is how to link the

fundamental thermodynamics and kinetics to the property and performance the industry interested.

The PI has experience in the investigation of creep resistance of Mg alloys 1,20-29 with the

ICME approach and will use the similar approach (Figure 5) in the current work for Gr.91 alloys

to overcome the challenge mention above. In addition, our own experimental investigation will

be carried out even though there are already extensive experimental investigations on Gr.91

alloy because:

1.) We will have controls and records all the details of our own alloy composition,

processing parameters, and the characterization results. This will greatly reduce the possibility

of the discrepancy due to the different choice of composition, processing parameters and clarify

the common observed scatters with the "same alloy" from different groups.

2.) Instead just the standard procedure such as welding, tempering, and creep test. We

can change the parameters (parameter study) to verify the prediction from the modeling. It will

improve the reliability of the modeling prediction.

2) The thoroughness and relevance of the scientific, engineering, and technical information

and data provided to support readiness of the proposed technology.

A: The ICME approach has been widely accepted in the investigation of

multicomponent alloys 30. For example, the recent huge successes for new alloys design with

the ICME approach are 1.) The new Ford F:-150 truck with the new high strength military grade

aluminum alloy frame and the new Ford EcoBoost engine, which greatly reduced the truck

weight and improved the fuel efficiency, 2.)The LS-karat Gold cases for the Apple watch.

B: The PI had used the ICME approach to successfully explain and predict the creep

resistance mechanism of Mg alloys. Similar work will be carried out for the Gr.91 alloy.

C: Numerous experimental data are available for the Gr.91 alloy (we will carry out our

own experiments as well), which will provide the input for the thermodynamic and kinetic

simulations. They will also be used to compare with the simulation results.

0: The thermodynamic and kinetic databases are ready because of the advance of the

CALPHAD approach in the last forty years 31. We will use the thermodynamic database

(TCFE8) and mobility database (MOBFE3),both of which are customized mainly for the Fe-

based alloys and cover all the elements and phases for the Gr.91 alloy. They should be reliable

to make the prediction of the precipitates phase stability and the microstructure change, such as

the dissolution and coarsening of the precipitates.

3) The degree to which the proposed work is based on sound scientific and engineering

principles.

The above sections include a thorough background of the scientific and engineering

principles. The next subsection (#2 in MRC2) describes how the approach will lead to a

significant advancement in the fundamental model development to solve the data scattering

problem for the creep behavior of Gr.91 alloys.

MRC 2- Technical Approach and Understanding1) The likelihood that the overall approach will result in successful achievement of the

objectives and deliuerables described in the applicable topic area, including the extent to which

the proposed Statement of Project Objectives is organized, logical and complete, with

appropriate technical decision points.

The supporting background and current state of the technology is discussed in the

Introduction and MRC 1, which supports the likelihood of success. The feasibility of achieving

the stated objectives is supported by the background and previous supporting work by the PI

(in the Readiness Section in MRC 1). The specifics ofthe work plan and milestones are located

within the SOPO following MRC 3. The risk challenges, mitigation strategies, and decision

points have been added into the appropriate section within the Project Management Plan.

2) The extent to which the proposed approach satisfies the requirements, goals and objectives

of the applicable topic area.

DOE-NETL solicitation indicates that an improved model is needed for the high

performance structural alloys for existing and advanced technology FE power plant. The main

requirement for the structural alloys is the creep behavior during the operation condition. It is

requested that the investigation needs to address the following criteria: 1.) A specific high Cr

alloy need to be specified; 2.) The scatter of the previous existing models and experimental data

need to be addressed; 3.)A physics based model is needed.

The list below describes how this work will satisfy each criterion: 1.) The most

promising Gr.91 alloy is picked, which belongs to the high Cr ferritic alloys; 2.) We will have

controls of our own samples, processing parameters, and experiments/characterization results.

All the data generated will be used to compare with the existing data from other groups. It will

greatly address the data scattering problem; 3.) Systematic fundamental investigation will be

carried out for the Gr. 91 structural alloys. the link among the composition, process, precipitates

stability, microstructure, and creep resistance will be established, which will greatly address and

the data scattering problem and guarantee the prediction reliability of our model.

3) Adequacy and completeness of the PMP in establishing the technical scope, budget, and

schedule baselines, in identifying key milestones and decision points, in controlling project

performance relative to these baselines and decision points, and in defining the actions that

will be taken when these baselines must be revised.

The required information is located within the PMP section.

4) Adequacy and completeness of the identification of, and mitigation strategies for, project

risks, including technical, organizational, cost share support and other risks affecting the

potential for success.

The required information is located within the PMP section.

MRC 3- Technical Capabilities, Facilities, and Equipment1) Ability and commitment of key personnel and subcontractors to support successful

completion of the project including: scientific mastery of the described technology, pertinent

systems operations and analysis experience, project management experience, and

demonstrated R&D experience and capabilities relevant to the proposed work.

The PI has 15 years' experience in ICME based on computational thermodynamics and

kinetics, with a portfolio of over 22 publications in the field's leading peer-reviewed journals.

The PI's doctoral work focused on the development of creep resistant Mg-alloy for

automobile industry. With the ICME approach, the PI has successfully clarified the alloying

effect to the creep resistance of commercial Mg alloys. All these contributions pave the way to

design new Mg alloys with high creep resistance, and thus reduce the time and cost for new Mg

alloy development. During his eight-year career in Saint Gobain, the PI was the senior internal

technical consultant in charge of the application of ICME approach in various industrial

applications, including structural materials (SiC, B4C,Ab03, Si3N4,etc.) and function materials

for Solid Oxide Fuel Cell (SOFC)and Oxygen Transport membrane (OTM) applications. During

that time, the PI was cognizant of an array of real-world challenges facing R&D in industry. The

PI recently moved from industrial R&D to academia because of his passion to promote the idea

of the urgency of the needs of the ICME approach on the discovery of new materials.

Dr. Wei Zhang (OSU) will work as the subcontract of the current work. He has more

than 15 years experience of the experiments and modeling of welding.

2) 171C extent of prior corporate experience in managing projects of similar type, size, and

complexity, and in successfully completing similar R&D projects.

Dr. Zhong has been the PI for more than 10 projects in Saint-Gobain. Most of the

contributions were published internally with more than twenty technical memos. Although

most of the works were confidential, the investigation on the long-term degradation of SOFC

that the PI was in charge of was published with the approval from Saint-Gobain 32,33.

The PI has received the funding from the American Chemical Society (ACS) Petroleum

Research Funds (PRF) in 2014. Within two years after funded, the PI had four conference papers

accepted 34-37,four journal papers 38-41 and one book chapter 42published/accepted.

3) The project organization, showing responsibilities and lines of authority (both technical

and administrative, including participating organizations and key subcontractors) is

clearly described and optimized to assure successful project execution.

This project uses a scientist-manager approach in management, for which no funds are

specifically requested. The overall project will be managed by Dr. Yu Zhong. He will lead the

computational thermodynamics and kinetics, PWHT, and characterization work at FlU. Dr. Wei

Zhang (OSU) will work as the subcontractor and focus on the welding experiments and creep

test. Dr. Zhong will organize the teleconference monthly. Quarterly reviews of ongoing work

will be conducted. Evaluation of the work in the research team will be performed by comparing

the work timeline of the team member against tasks for which he/she has responsibility.

Activities in the project will be documented in quarterly reports. Task schedules will be

evaluated at the times of the quarterly reports and annual progress report, and revision of the

task schedules will be made if needed. At the end of the project, a final technical report will be

prepared.

4) I11e appropriateness and availability of facilities, equipment, and their relevance to

technology development and/or commercial applications as applicable.

The Complete list of detail equipment and facilities can be found in the Appendix.

A: The thermodynamic and kinetic simulations (Task 3) will be carried out with Thermo-

Calc and Oictra 43, sister programs developed by the KTH Royal Institute of Technology. For

over 40 years, Thermo-Calc and Oictra has been at the forefront of scientific software and

databases for calculations involving computational thermodynamics and kinetics 31,44.

B: The experimental investigation of Subtask 4.2 and Task 6 will be performed at the

Center for the Study of Matter at Extreme Conditions (CeSMEC)45 and the Advanced Materials

Engineering Research Institute (AMERI) 46 at FlU. CeSMEC's X-ray powder diffraction

laboratory has a Bruker GAOO/08 X-Ray system, which allows for in situ XRO analysis for

temperatures up to 3000K. AMERI's process development laboratory has metal processing, arc

melting, and thermal processing (e.g., air, vacuum, hydrogen, controlled atmosphere furnaces).

Its analytical instrumentation laboratory contains a field-emission scanning electron microscope

(FESEM), a 200-keV transmission electron microscope (TEM), an atomic force microscope

(AFM),X-ray diffraction, and thermal testing (e.g., DSC, TGA, DMA, flush diffusion).

c: Subtask 4.1 and Task 5 will be carried out in OSu. OSU has the only ABET

(Accreditation Board for Engineering and Technology) accredited undergraduate Welding

Engineering Program in North America, and also offers advanced degrees (M.S.and Ph.D.). It is

the home to Manufacturing and Materials Joining Innovation Center (Ma2JIQ, a U.S. National

Science Foundation sponsored center for industry-university research collaboration. It is

recognized worldwide arid its welding engineering graduates are highly valued by industry.

The two facilities specifically related to the current project are: automated, robotic gas metal arc

welding (GMAW) and gas tungsten arc welding (GTAW) systems and thermal-mechanical

testing systems.

RELEVANCEAlVD OUTCOMES/IMPACTSDOE-NETL solicitation indicates that an improved model is needed for the high

performance structural alloys for existing and advanced technology FE power plant. The main

requirement for the structural alloys is the creep behavior during the operation condition. It is

requested that the investigation needs to address the following criteria: 1.) A specific high Cr

alloy need to be specified; 2.) The scatter of the previous existing models and experimental data

need to be addressed; 3.) A physics based model is needed.

The list below describes how this work will satisfy each criterion: 1.) The most

promising Gr.91 alloy is picked, which belongs to the high Cr ferritic alloys; 2.) We will have

controls of our own samples, processing parameters, and experiments/characterization results.

All the data generated will be used to compare with the existing data from other groups. It will

greatly address the data scattering problem; 3.) Systematic fundamental investigation will be

carried out for the Gr. 91 structural alloys. the link among the composition, process, precipitates

stability, microstructure, and creep resistance will be established, which will greatly address and

the data scattering problem and guarantee the prediction reliability of our model.

Besides the specific alloy and problem to be solved, we are developing a approach to

link among Composition - Processing Parameters - Phase Stability - Microstructure - Creep

Resistance. Our current investigation will be helpful to the following two areas:

.1. There are a lot of alloying elements and candidate alloys to be considered for the

structural alloys of the advanced technologies FE plants. Our ICME approach be applied to the

other candidate alloys and design brand new candidate alloys.

2. The challenge on thermo-mechanical properties is not just for the structural alloys for

the FEplants. There are a lot of other applications, such as the nuclear reactors.

The specific outcomes of the current project will be as follows: 1.)

Thermodynamic/kinetic predictions for Gr.91 base alloy and the weldment including HAZ will

be accomplished; 2.) Various characterization techniques will be adopt in the experimental

investigation for the Gr.91 base alloy and the welded alloys including HAZ; 3.) A fundamental

model with the computational and experimental integrated effort on the creep resistance

prediction for Gr.91 will be developed; 4.) 1 Ph.D. students will be complete his/her dissertation

research; 5.) a minimum of 3 peer-reviewed publications will be published from this work.

ROLES OF PARTICIPANTS

Dr. Yu Zhong (FlU, Mechanical and Materials Engineering) will act as the PI of the

program (both technical and administrative). He has more than 15 years experience on the new

materials design with the ICME approach and will be responsible for the project management

and planning (Task 1), literature review (Task 2), thermodynamic and kinetic simulations (Task

3), PWHT (Subtask 4.2), Characterization (Task 6), and Model development (Task 7). Dr. Wei

Zhang (OSU,Materials Science and Engineering) will act as the subcontractor of the project.Dr.i

Wei Zhang has over 15 years experience on welding modeling and experiments. He will be in

charge of the welding experiments (Subtask 4.1) and cre:p tests (Subtask 5).

A1ULTIPLE PRINCIPAL INVESTIGATORS

Dr. Yu Zhong (FlU, MME) will act as PI of the program. He will also serve as the main

contact with Dr. Wei Zhang (the subcontractor) and will assume fiscal and administrative

management, including maintaining communication among the team and key personnel

through monthly meeting. All potential publications and presentation will be submitted the

DOE-NETLfor review and approval before the submission or presentation.

STATEMENT OF PROJECT OBJECTIVES (SOPO)

Title: HBCU/OMI AOI [1]:The Fundamental Creep Behavior Model of Gr.91 Alloy by ICME

Approach

A. Objectives

Numerous experimental investigations have been carried out to understand the thermo-

mechanical properties of the high chromium creep resistant alloys, especially the creep behavior

for the Fossil Energy (FE)power plant application. However, the results coming from the "same

condition" and "same alloy" from different groups are considered scatter. Systematic

investigation, especially physics based models of creep behavior is greatly needed for the base

alloys and weldment.

:guid~nfe Qn~o\tt()~I!iprQxe t4~~!eep. r~sistanc~ of_G'r.91alloys; ..

The long-term goal of the proposed program is to develop a model for creep and fatigue

resistant alloys with different elemental systems, compositions, and processing parameters of

weldment and heat treatment. In addition, new creep and fatigue resistant alloys are to be

designed based on the predictions from the model.

B. Scope Of Work

The specific project objectives are as follows: 1.) Predict the phase stability and

microstructure of Gr.91 base alloy and weldment with the computational thermodynamics and

kinetics (CALPHAD) approach; 2.) Carry out welding, heat treatment, and creep test for the

Gr.91 alloy; 3.) Develop a model which has excellent match with the experimental data from the

current work and also from the previous existing work; 4.) Predict how to improve the long-

term creep resistance for the Gr.91 family alloys.

C. Tasks To Be Performed

PHASE I

Task 1. Project Management and Planning (QI-Q12)

This task shall include all work elements required to maintain and revise the Project

Management Plan, and to manage and report on activities in accordance with the plan. It shall

also include the necessary activities to ensure coordination and planning of the project with

DOE/NETL and other project participants.

Task 2. Literature Review of Existing Data (QI-Q2)

There are extensive experimental data and modeling effort on the welding, PWHT, and

creep tests of Gr.91 alloys. We will collect them as the input for the thermodynamic simulation

(Subtask3.1) and kinetic simulations (Subtask3.2). We will mainly focusing on the phase

stability, microstructure, and the corresponding creep test results. For example, we will check

what the stable, metastable, and intermediate phases are at each process and operation step. We

will also check how the precipitates particle size changes. All the reliable experimental data will

~e put together and compare with our own experimental data achieved from Task 4, Task 5,

and Task 6. They will also be used in comparison with the simulations results from Task 3.

Task 3. Thermodynamic/kinetic simulations (Q2-Q6)

Similar to our success on the design of the creep resistant Mg alloys 1,20-29,

computational thermodynamics and kinetics (CALPHAD) approach will be adopted In the

current work to simulate the thermodynamic stabilities and the microstructure changes. The

simulation will be carried out for the Gr.91 base alloy, the weldment, and also the most

important creep premature cracking area, i.e. FGHAZ and ICHAZ. The dissolution and

coarsening of the precipitate phases in the welding, PWHT, creep tests, and the long-term

operation will be simulated. It will be used to compare with the characterization results from

welding PWHT, and creep tests (Task 2 and Task 6).

Subtask 3.1 Thermodynamic Simulations for the Gr.91 Alloys (01-04): The PI will use

Thermo-Calc to simulate on the phase stabilities for the Gr.91 alloy with the TCFE8

thermodynamic database. The simulation will include the thermodynamic phase

transformation of the Gr.91 during welding, how the FGHAZ and ICHAZ will be affected by

the temperature change during welding, PWHT, and the real operation condition. It will mainly

focus on the precipitate phases including M23C6,MX, and other metastable and intermediate

phases. Other necessary thermodynamic information such as the ACI temperature will be

predicted to provide the guidance on parameters for the tempering. In addition, the driving

force between intermediate non-equilibrium states will be predicted which is critical to the

kinetic simulations (Subtask 3.2).

Subtask 3.2 Kinetic Simulations (02-06): The PI will use the Dictra software on the kinetic

simulation with the TCFE8thermodynamic database and the MOBFE3mobility database. It will

be used to simulate the effect of welding, PWHT, creep test, and the real operation condition to

the phase stability and microstructure changes for HAZ including the phase transformation,

solidification, secondary phase nucleation, dissolution, and coarsening of the precipitate phases

including stable, metastable, and intermediate phases. Task 2 and Task 6 will give the input on

the phases and particle sizes at the initial conditions for the kinetic simulation. Meanwhile, the

will also be used to compare with the kinetic simulation results. Iteration may be needed until

the agreement is satisfactory.

Task 4. Welding and Post-Weld Heat Treatment (PWHT) (Q3 - Q7)

The purpose of this task is to generate welded and PWHT samples for microstructure

characterization and creep testing. Dr. Wei Zhang (OSU) will acquire Gr.91 steel plates from a

certified vendor. The welded and PWHT plates will be sectioned for microstructure

characterization at FlU (Task 6).

Subtask 4.1 Welding (03-06): Following the industry standard welding procedure

specified in ASME Boiler and Pressure Vessel (B&PV)code, up to 20 steel plates will be welded

in a butt joint configuration. Pre-heating and inter-pass temperatures will be carefully

controlled via embedded thermocouples. Some of the samples will be sent for characterizations

in Task 6 to see the phase stability and microstructure after welding, some of the sample will be

sent directly to do the creep tests in Task 5 to see the creep behavior of steels without PWHT,

some will be sent to do the post-welding tempering in Subtask 4.2.

Subtask 4.2 Post-Weld Heat Treatment (PWHT) (04-07): PWHT including the post-

welding tempering will be conducted in accordance to the standard temperature-time in the

B&PVcode as well as other temperature-times specified by FlU based on the overall prediction

from the thermodynamic and kinetic simulations (Task 3). For example, the maximum

tempering temperature is determined by the ACI temperature from the Subtask 3.1. The

tempering time will be determined by the existing literature data (Task 2) and also the kinetic

simulation from sub task 3.2. The tempering experiments will be carried out in the FlU furnaces.

Some of the samples will be sent for characterization in Task 6 to understand the phase stability

and the microstructure before the creep test. Some of the sample will be used for the creep tests

in Task 5.

Task 5. Creep testing (Q5-QIO)

Cross-weld samples will be machined from the welded plates, which are subject to

different PWHT in Sub task 4.2. Up to ten samples will be tested at different temperatures and

stresses in a lever-arm creep testing machine to see the microstructure changes at different

testing temperature and stress conditions. The creep test temperature will between 600-670°C,

stress will between lOO-150mPa, and the maximum creep test running time is two weeks. The

detail creep test temperature and stress matrix will be designed based on the thermodynamic

and kinetic simulation predictions from Task 3. The number of hours to creep rupture will be

recorded. The samples reaches the maximum test running time will also be collected. All the

tested samples will be sectioned for microstructure characterization at FlU in Task 6.

Task 6. Characterization (Q4-Qll)

The detail characterization analysis will be carried out in FlU including the SEM, XRD,

and FIB-TEM analysis. The characterization will use, .the samples from before welding, post

welding, post tempering, and post creep test. The characterization will include the Gr.91 base

alloy, the welding area, and specifically in the FGHAZ and ICHAZ for the microstructure

including grain size, the precipitate phases stability and particle size, especially the MZ3C6,MX

and other possible precipitate phases. It will provide the feedback to the subtask 3.1 and

subta;k 3.2 for further simulations.

Task 7. Model development and BEYOND (Q8-Q12)

Experimental information from Task 4, Task 5, and Task 6 will be integrated with the

thermodynamic and kinetic simulations from Task 3. A model will be developed to link the

composition -- phase stability - microstructure - creep resistance. It will be used to compare the

existing experimental data (Task 2), and also provide recommendation on experimental setup. It

will provide the guidance on how to improve the creep resistance of Gr.91 alloys and beyond.

subtask 7.1 Model Verification: All the characterization results from our current

investigation (Task 6) and which from the literature (Task 2) will be compiled together. They

will be used to compare with the prediction from Task 3. Detail analysis will be carried out on

any major discrepancies. The initial conditions of Subtask 3.2 will be modified; iterations may

be needed until the agreement is satisfactory. We will then compare our prediction of phase

stability and microstructure changes with the creep test results to understand the role of

precipitates on the creep resistance. With that, we build the link between the precipitates and

the creep resistance.

Sub task 7.2 Predictions on the Effect of Processing Parameters: The prediction from Subtask

7.1 will give the prediction on the effect of processing parameters to the creep resistance of

Gr.91 alloys. We will run one more test (welding, PWHT, and creep test) based on our modeling

prediction and then compare with the creep behavior observed as the final verification of

reliability of our model.

Subtask 7.3Predictions on the Effect ofAlloying Elements: The role of each alloying elements

in Gr.91 alloys can be predicted with the model developed. In addition, we will explore how to

further improve the creep resistance with alloying elements. Based on the literature review,

some good elements such as boron were considered. We can make prediction of the creep

behavior with the new alloying elements added. It will give the direction how to improve the

creep resistance of Gr.91 family alloys.

D. Deliverables

All the deliveries are listed in Table 1

Number' " Task '''''':\c 'c,: "" ,,'"'\,:/': !,''':'''''",r:';, Description -: ",?" +::' ","';",

01 Task J Quarterly financial and technical reports to DOE (Nov., Feb., May., Aug. starting from 20J 6)02 Taskl Annual progress report to DOE (Aug. 2017; Aug. 2018)03 Task 2 Experimental data from available literature (Feb. 2017)04 Subtask 3, 1 Thermodynamic simulation on precipitate phase stability (Aug. 2017)05 Subtask 3.2 Kinetic simulation on the microstructure changes (Feb. 2018)06 Subtask 4,1 Welding for up to 20 samples (Feb. 2018)07 Subtask 4,2 PWHT (May 2018)08 Task 5 Creep test for up to 10 samples (Feb. 2019)09 Task 6 Characterization results with samples from weld (May, 2018), PWHT (Aug. 2018), and creep tests (May 2019)010 Subtask 7,J Model verification (Jan. 2019)011 Subtask 7.2 Prediction on the Effect of Processing Parameters (Apr. 2019)012 Subtask 7.3 Prediction on the Effect of Alloying Elements (Jul. 2019)013 Task I Final technical report to DOE (Jut. 2019)

Table 1.The schedules of Deliveries (01 to 013)

Appendix:

Appendix A: Facilities and Other Resources

Appendix B:Equipment

Appendix C: References