Quantified Relation between Grain Boundary Angle and Interfacial Stability of PWA1484 Superalloy during Thermal Exposure

2019 ◽  
Vol 51 (1) ◽  
pp. 380-389
Author(s):  
Qinjia Wang ◽  
Jinxia Song ◽  
Dinggang Wang ◽  
Chengbo Xiao ◽  
Xidong Hui
Keyword(s):  
Grain Boundary ◽  
Thermal Exposure ◽  
Interfacial Stability

MC Carbide Decomposition during Thermal Exposure of Polycrystalline Ni-Base Superalloys

2007 ◽  
Vol 124-126 ◽  
pp. 1505-1508 ◽  
Author(s):  
Baig Gyu Choi ◽  
In Soo Kim ◽  
Doo Hyun Kim ◽  
Chang Yong Jo
Keyword(s):  
Grain Boundary ◽  
Casting Process ◽  
Thermal Exposure ◽  
Exposure Temperature ◽  
Type Carbide

MC decompositions during thermal exposure have been investigated in three conventional cast Ni-base superalloys, GTD111, IN738LC, and CM247LC. MC decomposition in GTD111 and IN738LC depends on exposure temperature. While MC decomposed into M23C6 at 982°C, η formed from MC after exposure at 927°C and 871°C. Ta and Ti separated from MC during thermal exposure made η phase to form instead of γ'. The decomposition of the MC in CM247LC depends on their morphology and position. Segregation during casting process affected the morphology and composition of MC type carbide in this alloy. Acicular M6C was found near scriptal MC in the dendrite. Blocky MC near γ-γ' eutectic decomposed into M23C6. Both M23C6 and M6C can be found on grain boundary after thermal exposure in CM247LC.

A nanoindentation study on grain-boundary contributions to strengthening and aging degradation mechanisms in advanced 12 Cr ferritic steel

2007 ◽  
Vol 22 (1) ◽  
pp. 175-185 ◽  
Author(s):  
Jae-il Jang ◽  
Sanghoon Shim ◽  
Shin-ichi Komazaki ◽  
Tetsuya Honda
Keyword(s):  
Grain Boundary ◽  
Ferritic Steel ◽  
Microstructural Analysis ◽  
Thermal Exposure ◽  
Strengthening Effect ◽  
Degradation Mechanisms ◽  
Block Boundary ◽  
Softening Behavior ◽  
Matrix Strength ◽  
Virgin Sample

Nanoindentation experiments and microstructural analysis were performed on advanced 12% Cr ferritic steel having extremely fine and complex martensitic microstructures, to answer unsolved questions on the contributions of grain boundaries to strengthening and aging degradation mechanisms in both as-tempered and thermally aged steels. Interesting features of the experimental results led us to suggest that among several high angle boundaries, block boundary is most effective in enhancing the macroscopic strength in as-tempered virgin sample, and that a decrease in matrix strength rather than reduction in grain-boundary strengthening effect is primarily responsible for the macroscopic softening behavior observed during thermal exposure.

Precipitation and evolution of grain boundary boride in a nickel-based superalloy during thermal exposure

2017 ◽  
Vol 128 ◽  
pp. 109-114 ◽  
Author(s):  
Beining Du ◽  
Liyuan Sheng ◽  
Chuanyong Cui ◽  
Jinxia Yang ◽  
Xiaofeng Sun
Keyword(s):  
Grain Boundary ◽  
Thermal Exposure ◽  
Nickel Based Superalloy

Effect of Minor Elements on the Grain Boundary Strengthening of a Single Crystal Superalloy RR2072

2007 ◽  
Vol 124-126 ◽  
pp. 1405-1408
Author(s):  
D.H. Kim ◽  
Y.S. Yoo ◽  
Chang Yong Jo ◽  
C.N. Jones
Keyword(s):  
Grain Boundary ◽  
Single Crystal ◽  
Rupture Life ◽  
Stress Rupture ◽  
Thermal Exposure ◽  
Single Crystal Superalloy ◽  
M23c6 Carbide ◽  
Carbide Formation ◽  
Minor Elements ◽  
Grain Boundary Strengthening

Effect of carbon and boron on the grain boundary strengthening of a second generation single crystal superalloy RR2072 was investigated. Single crystal and bicrystal specimen with three kinds of tilt type misorientation angle were grown by Bridgman technique. Creep and stress rupture tests were conducted at 950oC and 1050oC. Rupture life of single crystal of the alloy modified with carbon and boron was comparable to that of the RR2072 which is free from boron and carbon. TCP phase precipitation such as sigma was suppressed in the modified alloy during thermal exposure and creep deformation. Rupture life of the modified alloy bicrystal was superior to that of the RR2072 bicrystal. M23C6 carbide formation and suppression of γ′ band growth is thought to be the role of minor elements for the grain boundary strengthening of a nickel base single crystal superalloy RR2072.

Long-Term Thermal Stability of Alloy 825 as a High-Level Nuclear Waste Container Material

1995 ◽  
Vol 412 ◽  
Author(s):  
D. S. Dunn ◽  
Y.-M. Pan ◽  
G. A. Cragnolino ◽  
N. Sridhar
Keyword(s):  
Grain Boundary ◽  
Nuclear Waste ◽  
Elevated Temperatures ◽  
Thermal Exposure ◽  
Boundary Region ◽  
Waste Container ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Welding Processes ◽  
Container Material

AbstractThe thermal exposure of Fe-Cr-Ni-Mo materials to certain temperature regimes often results in the formation of grain boundary carbides and the associated depletion of alloying elements. This phenomenon, termed sensitization, is frequently the result of welding processes or in service exposure to elevated temperatures. In this investigation, alloy 825, a candidate high-level nuclear waste (HLW) container material, was thermally exposed to temperatures in the range of 550 to 800 °C for periods of up to 1,000 hr. Sensitization of the material was evaluated by corrosion tests and grain boundary analyses using an analytical electron microscope. The sensitized microstructure was found to contain M23C6-type carbides as well as a Cr-depleted region in the vicinity of the grain boundaries. The degree of sensitization was correlated to the extent of Cr depletion in the grain boundary region.

Effect of Hafnium on the Microstructure and Creep Property of a Hot Corrosion Resistant Superalloy

2015 ◽  
Vol 816 ◽  
pp. 641-647 ◽  
Author(s):  
Jie Shan Hou ◽  
Jian Ting Guo ◽  
Chao Yuan ◽  
Yong An Guo ◽  
Gu Song Li ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Creep Property ◽  
Thermal Exposure ◽  
Boundary Phase ◽  
Primary Carbide ◽  
Bayesian Neural Network ◽  
Creep Life ◽  
Σ Phase

The effects of the selective addition of Hafnium (Hf) on the grain boundary, phase, carbides and creep properties of experimented nickel superalloy after standard heat treatment and long-term exposure were investigated. Predicted by the Bayesian neural network, the creep life is prolonged with Hf content of 0-0.6 mass%, which is more effective at low stresses. The decrease of creep life of Hf free alloy after long term exposure was pronounced. Comparative study showed that the mainly small, coherent, blocky and closely spaced MC(2)and M23C6carbides precipitated on the grain boundaries in the 0.4wt% Hf contained alloy, and that relatively larger, incoherent MC(1)carbides precipitated on the grain boundaries in the Hf free alloy. During long term thermal exposure, fine discrete M23C6carbides decomposed from primary carbide, inducing a layer along the grain boundary, and the coarsening of grain boundary in Hf free alloy is more pronounced. At high stresses, the Hf-free alloy exhibited a stronger tendency of rafting than the 0.4Hf alloy, while the tendency of appearance of rafting was very similar at low stresses. However, Hf can render the alloy prone to the formation of σ phase, according to D-electrons method. Thus, the Hf content needs to be controlled to a suitable level.

Degeneration of Primary MC Carbide in a Cast Ni-Base Superalloy

2007 ◽  
Vol 546-549 ◽  
pp. 1301-1304 ◽  
Author(s):  
X.Z. Qin ◽  
Jian Ting Guo ◽  
C. Yuan ◽  
Jie Shan Hou ◽  
Heng Qiang Ye
Keyword(s):  
Grain Boundary ◽  
Thermal Exposure ◽  
Diffusion Controlled ◽  
Base Superalloy

During long-term thermal exposure, the degeneration of primary MC carbide is a diffusion-controlled process. With the element exchange between the primary MC carbide and the γ matrix, three MC degeneration reactions, that is, γ + MC → γ' + M23C6 (Reaction I), MC + γ →η+ M23C6 (Reaction II) and MC + γ →η+ M6C (Reaction III), sequentially operates. Of them Reaction III has never been reported in the previous references and is kinetically most difficulty. It is also shown that the grain boundary MC decomposes much more rapidly than the grain interior MC and that Reaction III is not as often seen at the grain boundary as in the grain interior.

Stability of Microstructure and Mechanical Properties of GH984G Alloy during Long-Term Thermal Exposure

2013 ◽  
Vol 747-748 ◽  
pp. 647-653 ◽  
Author(s):  
Ting Ting Wang ◽  
Chang Shuai Wang ◽  
Jian Ting Guo ◽  
Lan Zhang Zhou
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Power Plants ◽  
Low Cost ◽  
Thermal Exposure ◽  
Tensile Tests ◽  
Experimental Results ◽  
Σ Phase ◽  
Microstructure And Mechanical Properties

A low cost Ni-Fe-based wrought superalloy for 700 advance ultra-supercritical coal-fired power plants was developed. The stability of microstructure and mechanical properties of this alloy during long-term thermal exposure was investigated by SEM,TEM and tensile tests. The experimental results showed that the major precipitates in the alloy were spherical γ, MC and discrete M23C6 distributing along grain boundary after the long-term exposure at 700 and 750 and no harmful phases, such as σ phase and η phase, were found. However, after exposure at 800 up to 3000 h, small amount of lath-like η phase precipitated at grain boundary by consuming the surrounding γ. The η phase exhibited a fixed orientation relationship with the γ matrix. During thermal exposure γ coarsened with increasing the exposure time and exposure temperature. In addition, all major phases and their stability temperature ranges were calculated by JMatPro and these results were confirmed by the experimental results. The 700 tensile tests revealed that the alloy after exposure at 700 and 750 for 3000 h exhibited excellent ductility and strength. Therefore, the GH984G alloy possessed excellent stability of microstructure and mechanical properties between 700 and 750 up to 3000 h, and it is a promising material for 700 advance ultra-supercritical coal-fired power plants.

Dependence of Intergranular Fracture on Boundary Topography and Cohesion

1973 ◽  
Vol 31 ◽  
pp. 150-151
Author(s):  
J. E. Doherty ◽  
A. F. Giamei ◽  
B. H. Kear ◽  
C. W. Steinke
Keyword(s):  
Grain Boundary ◽  
Room Temperature ◽  
Nickel Base Superalloy ◽  
Boundary Shear ◽  
Room Temperature Ductility ◽  
Solid Solution Matrix ◽  
Nickel Base ◽  
Solution Matrix ◽  
Different Levels ◽  
Base Superalloy

Recently we have been investigating a class of nickel-base superalloys which possess substantial room temperature ductility. This improvement in ductility is directly related to improvements in grain boundary strength due to increased boundary cohesion through control of detrimental impurities and improved boundary shear strength by controlled grain boundary micros true tures.For these investigations an experimental nickel-base superalloy was doped with different levels of sulphur impurity. The micros tructure after a heat treatment of 1360°C for 2 hr, 1200°C for 16 hr consists of coherent precipitates of γ’ Ni3(Al,X) in a nickel solid solution matrix.

Two Investigations into Grain Boundary Structure

1977 ◽  
Vol 35 ◽  
pp. 688-691
Author(s):  
P. Humble
Keyword(s):  
Grain Boundary ◽  
Dark Field ◽  
Boundary Structure ◽  
Boundary Dislocation ◽  
Bright Field ◽  
Intrinsic Structure ◽  
Weak Beam ◽  
Grain Boundary Structure ◽  
Independent Information ◽  
Diffraction Patterns

There has been sustained interest over the last few years into both the intrinsic (primary and secondary) structure of grain boundaries and the extrinsic structure e.g. the interaction of matrix dislocations with the boundary. Most of the investigations carried out by electron microscopy have involved only the use of information contained in the transmitted image (bright field, dark field, weak beam etc.). Whilst these imaging modes are appropriate to the cases of relatively coarse intrinsic or extrinsic grain boundary dislocation structures, it is apparent that in principle (and indeed in practice, e.g. (1)-(3)) the diffraction patterns from the boundary can give extra independent information about the fine scale periodic intrinsic structure of the boundary.In this paper I shall describe one investigation into each type of structure using the appropriate method of obtaining the necessary information which has been carried out recently at Tribophysics.

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