冷加工對鎳基合金600於模擬BWR水質之動態應變時效影響研究

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研究生：	黃郁婷 Huang, Yu-Ting
論文名稱：	冷加工對鎳基合金600於模擬BWR水質之動態應變時效影響研究 Effect of cold work on the DSA behavior of Inconel 600 alloy in simulated BWR coolant environments
指導教授：	喻冀平 Yu, Ge-Ping 黃嘉宏 Huang, Jia-Hong
口試委員:	黃俊源 Huang, Jiunn-Yuan 王星豪 Wang, Shing-Hoa
學位類別：	碩士 Master
系所名稱：	原子科學院 - 工程與系統科學系 Department of Engineering and System Science
論文出版年：	2013
畢業學年度：	101
語文別：	英文
論文頁數：	86
中文關鍵詞：	動態應變時效、冷加工、慢速率拉伸試驗、英高鎳600 、藍脆
外文關鍵詞：	Dynamic strain aging, Cold work, Slow strain rate tensile test, Inconel 600, Blue brittleness
相關次數：	點閱：2 下載：0
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本研究探討不同冷加工量之Inconel 600鎳基合金於高溫溶氧水環路中的動態應變時效(Dynamic Strain Aging，簡稱DSA)現象，與DSA對材料機械性質之影響，並利用於應力-應變曲線中呈現的鋸齒流(Serrated Flow)兩種特徵，分別是應力增加量(Stress increment, △σ)和時效時間(Aging time, △t)討論溫度及冷加工量對DSA現象的影響。藉由慢速率拉伸試驗獲得於固定應變速率10-6/s下，不同試驗溫度 (200、250、275及300℃) 之溶氧水環路的應力-應變曲線。拉伸試棒則以在常溫下輥軋(Rolling)方式將合金板材冷加工至10%、20%、30% CW後再以機械加工而成，且一律採用垂直輥軋之方向(Transverse direction)進行試驗。本實驗選擇的試驗環境主要是為了模擬沸水式反應器(BWR)之高溫高壓溶氧水環路，以取得冷加工Inconel 600鎳基合金組件於該水環境下發生劣化的可能性與發生機制之相關訊息。
機械性質方面，隨冷加工量愈低，差排增生能力上升，但強度仍受加工硬化制約。於200℃出現伸長率最小值，但截面縮減率最大值，且應變硬化指數最小值，有提早頸縮現象，此即為DSA典型特徵─藍脆現象。此外，△σ和△t的研究結果指出，30% CW於200℃時，△σ和△t隨應變量增加有顯著地上升，即顯示出鎳基合金600於小幅變形量下溶質原子與差排間的交互作用最為劇烈。因此，30% CW鎳基合金600於200℃之溶氧水環路下塑性變形時所出現的DSA現象將最不利於鎳基合金 600的機械性質。

The slow strain rate tensile (SSRT) tests were conducted on the cold-rolled Inconel 600 alloy with different amounts of cold work (CW), 10%, 20% and 30% respectively at a nominal strain rate 1×10-6/sec in simulated BWR coolant environment. The dynamic strain aging (DSA) behavior at 200, 250, 275 and 300℃ was studied by two characteristics of serrations, stress increment (△σ) and aging time (△t), except for the observation of mechanical properties. Serrated flow was observed in all stress-strain curves which was one of the DSA manifestations. For the SSRT tests at 200℃, except the curve for the 10% CW Alloy 600 showed a combination of A-, B- and C- type serrations, type A+B serrations were observed for the as-received, 20% CW and 30% CW Alloy 600. Type B serrations were observed for those tested at the temperatures range of 250℃-300℃.
At 200℃, the cold-rolled Alloy 600 showed a minimum elongation, but a maximum the reduction of area, and a minimum strain hardening exponent. These results showed the “blue brittleness” feature and could be accounted for by the localized deformation induced by DSA effect. Moreover, the stress increment (△σ) and aging time (△t) significantly increased with increasing strain for the 30% CW Alloy 600 tested at 200℃, it could be concluded that the interactions between solute atoms and dislocations in oxygenated water environment exacerbated the mechanical properties most.

Table of Contents
Table of Contents ............................................................................................................ iv
List of Tables .................................................................................................................... vi
List of Figures ................................................................................................................. vii
Chapter 1 Introduction .................................................................................................. 1
Chapter 2 Literature Review
1 Nickel-base Inconel 600 alloy ....................................................................... 3
1.1 Effects of alloying elements ................................................................... 3
1.2 Types of carbides ................................................................................... 4
1.3 Strengthening mechanism ...................................................................... 5
2 Dynamic strain aging (DSA) ......................................................................... 7
2.1 General aspects ...................................................................................... 7
2.2 Types of serrations ................................................................................. 7
2.3 Models of DSA .................................................................................... 11
2.4 DSA in nickel-base alloys .................................................................... 14
3 Suzuki segregation ....................................................................................... 17
Chapter 3 Experimental Procedures
1 Specimen Preparation .................................................................................. 20
2 Microstructure analysis ................................................................................ 22
3 Hardness (Vickers) test ................................................................................ 23
4 Residual stress determination ...................................................................... 24
4.1 XRD sin2ψ method ............................................................................... 24
4.2 Through-hole-drilling method ............................................................. 26
5 Slow strain rate tensile (SSRT) test ............................................................. 29
v
Chapter 4 Results
1 Microstructural observations ....................................................................... 32
2 Vickers hardness (HV) ................................................................................. 42
3 Residual stress determination ...................................................................... 45
4 Serrated flow in the stress-strain (σ-ɛ) curves .............................................. 48
5 Mechanical properties in the DSA temperature range ................................. 51
6 Fractography ................................................................................................ 54
Chapter 5 Discussion
1 Microstructural characterization .................................................................. 58
1.1 As-received Alloy 600 ......................................................................... 58
1.2 Cold-rolled Alloy 600 .......................................................................... 58
2 Hardness distribution of cold-rolled Alloy 600 ........................................... 61
3 Residual stress in T-L-S directions .............................................................. 62
4 Effect of DSA on mechanical properties of Alloy 600 ................................ 63
5 Characteristics of serrated flow ................................................................... 64
6 Effect of the amount of cold work on DSA behavior .................................. 68
7 Effect of temperature on DSA behavior ...................................................... 73
Chapter 6 Conclusions ................................................................................................. 78
                                

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