scholarly journals Self-Induced Internal Corrosion Stress Transgranular Cracking in Gradient-Structural Ploycrystalline Materials at High Temperature

Metals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1465
Author(s):  
Xianjun Lei ◽  
Xiaopeng Wang ◽  
Fantao Kong ◽  
Haitao Zhou ◽  
Yuyong Chen
Keyword(s):  
Grain Boundary ◽  
Crack Nucleation ◽  
Internal Stresses ◽  
Transgranular Fracture ◽  
Compositional Gradient ◽  
Internal Corrosion ◽  
Intermetallic Materials ◽  
Grain Boundary Wetting ◽  
And Diffusion ◽  
Structural Intermetallic

Self-induced internal corrosion stress transgranular cracking is investigated theoretically and experimentally linking grain boundary wetting (GBW) and grain boundary diffusion (GBD) to improve the ability to reveal the micro mechanism of crack in compositional gradient-structural intermetallic materials. Theoretical analysis shows that the grain boundary wetting and diffusion induce the diffusion-coupled dynamic internal stresses, and their interaction leads to crack nucleation. The experimental results show a stress concentration zone have been established at the grain boundary interface where the cracks preferentially nucleate and then extend through the inside of the grain to both sides, forming a typical transgranular fracture.

The Effect of Pressure on Grain Boundary Wetting, Segregation and Diffusion

1998 ◽  
Vol 156 ◽  
pp. 163-174 ◽  
Author(s):  
Witold Łojkowski ◽  
Eugen Rabkin ◽  
Boris B. Straumal ◽  
Lasar S. Shvindlerman ◽  
W. Gust
Keyword(s):  
Grain Boundary ◽  
Effect Of Pressure ◽  
Grain Boundary Wetting ◽  
And Diffusion

scholarly journals Microstructure and Magnetic Properties of NdFeB Sintered Magnets Diffusion-Treated with Cu/Al Mixed Dyco Alloy-Powder

2017 ◽  
Vol 62 (2) ◽  
pp. 1263-1266 ◽  
Author(s):  
M.-W. Lee ◽  
K.-H. Bae ◽  
S.-R. Lee ◽  
H.-J. Kim ◽  
T.-S. Jang
Keyword(s):  
Grain Boundary ◽  
Diffusion Path ◽  
Boundary Phase ◽  
Core Shell ◽  
Phase Layer ◽  
Sintered Magnets ◽  
The Core ◽  
Shell Type ◽  
Property Changes ◽  
And Diffusion

AbstractWe investigated the microstructural and magnetic property changes of DyCo, Cu + DyCo, and Al + DyCo diffusion-treated NdFeB sintered magnets. The coercivity of all diffusion treated magnet was increased at 880ºC of 1stpost annealing(PA), by 6.1 kOe in Cu and 7.0 kOe in Al mixed DyCo coated magnets, whereas this increment was found to be relatively low (3.9 kOe) in the magnet coated with DyCo only. The diffusivity and diffusion depth of Dy were increased in those magnets which were treated with Cu or Al mixed DyCo, mainly due to comparatively easy diffusion path provided by Cu and Al because of their solubility with Ndrich grain boundary phase. The formation of Cu/Al-rich grain boundary phase might have enhanced the diffusivity of Dy-atoms. Moreover, relatively a large number of Dy atoms reached into the magnet and mostly segregated at the interface of Nd2Fe14B and grain boundary phases covering Nd2Fe14B grains so that the core-shell type structures were developed. The formation of highly anisotropic (Nd, Dy)2Fe14B phase layer, which acted as the shell in the core-shell type structure so as to prevent the reverse domain movement, was the cause of enhancing the coercivity of diffusion treated NdFeB magnets. Segregation of cobalt in Nd-rich TJP followed by the formation of Co-rich phase was beneficial for the coercivity enhancement, resulting in the stabilization of the metastable c-Nd2O3phase.

Investigating behaviours of hydrogen in a tungsten grain boundary by first principles: from dissolution and diffusion to a trapping mechanism

2010 ◽  
Vol 50 (2) ◽  
pp. 025016 ◽  
Author(s):  
Hong-Bo Zhou ◽  
Yue-Lin Liu ◽  
Shuo Jin ◽  
Ying Zhang ◽  
G.-N. Luo ◽  
...  
Keyword(s):  
Grain Boundary ◽  
First Principles ◽  
Trapping Mechanism ◽  
And Diffusion

Effect of Hexagonal Crystal Structure Anisotropy on the Selective Grain Boundary Mobility during Texture Formation and Secondary Recrystallization in Zn

2005 ◽  
Vol 495-497 ◽  
pp. 1231-1236
Author(s):  
Vera G. Sursaeva
Keyword(s):  
Grain Boundary ◽  
Secondary Recrystallization ◽  
Stress Fields ◽  
Internal Stresses ◽  
Recrystallization Process ◽  
Boundary Mobility ◽  
Texture Formation ◽  
Hexagonal Crystal ◽  
Grain Boundary Mobility ◽  
Grain Boundary Motion

Texture formation during secondary recrystallization depends on the nature of secondary recrystallization process itself. So microstructure evolution and texture development during secondary recrystallization should be discussed concurrently. The main goal of the paper is studying of the effect of internal stresses on grain boundary motion or, more generally, the interaction of grain boundaries with stress fields and the effect of deformation inhomogeniety on grain boundary mobility during secondary recrystallization. Considering transformation from normal grain growth to secondary recrystallization, the attempt was made to characterize the microstructure and to relate it to the processes of nucleation and growth of new rains. The nucleation process is heterogeneous. The data allow us to assume that the nuclei are strain free grains.

Molecular Dynamics Analysis of the Acceleration of Intergranular Cracking of Ni-Base Superalloy Caused by Accumulation of Vacancies and Dislocations Around Grain Boundaries

2020 ◽  
Author(s):  
Ryo Kikuchi ◽  
Shujiro Suzuki ◽  
Ken Suzuki
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Fatigue Loading ◽  
Transgranular Fracture ◽  
Dynamics Analysis ◽  
Intergranular Cracking ◽  
Creep Fatigue ◽  
Schmid Factor

Abstract Ni-based superalloys with excellent high temperature strength have been used in advanced thermal power plants. It was found that grain boundary cracking is caused in the alloy under creep-fatigue loading due to the degradation of the crystallinity of grain boundaries and the grain boundary cracking degrades the lifetime of the alloy drastically. In order to clarify the mechanism of intergranular cracking, in this research, static and dynamic strains were applied to a bicrystal structure of the alloy perpendicularly to the grain boundary using molecular dynamics analysis. In addition, the effect of the accumulation of vacancies in the area with high-density of dislocations on the strength of the bicrystal structure was analysed. It was found that the fracture mode of the bicrystal structure changed from ductile transgranular fracture to brittle intergranular one as strong functions of the combination of Schmid factor of the two grains and the density of defects around the grain boundary. The local heavy plastic deformation occurred around the grain boundary with large difference in Schmid factor between nearby grains and the diffusion of the newly grown dislocations and vacancies was suppressed by the large strain field due to the large mismatch of the crystallographic orientation between the grains. The accumulation of vacancies accelerated the local plastic deformation around the grain boundary. Therefore, the mechanism of the acceleration of intergranular cracking under creep-fatigue loading was successfully clarified by MD analysis.

Thermo-Mechanical Fatigue of Mar-M247: Part 1—Experiments

1990 ◽  
Vol 112 (1) ◽  
pp. 68-79 ◽  
Author(s):  
D. A. Boismier ◽  
Huseyin Sehitoglu
Keyword(s):  
Grain Boundary ◽  
Prediction Model ◽  
Life Prediction ◽  
Crack Nucleation ◽  
Mechanical Tests ◽  
Fatigue Tests ◽  
Boundary Crack ◽  
Mechanical Fatigue ◽  
Nickel Based Superalloy ◽  
Life Prediction Model

Isothermal fatigue tests, out-of-phase and in-phase thermo-mechanical fatigue tests were performed on Mar-M247 nickel-based superalloy. The experiments were conducted in the temperature range 500°C to 871°C. Results indicate that the lives differ with strain-temperature phasing and with strain rate. The results of out-of-phase thermo-mechanical tests correspond well with strain-life data of isothermal tests conducted at the peak temperature (871°C). However, the in-phase thermo-mechanical results differed depending on the strain amplitude. Significant surface and crack tip oxidation and gamma prime depletion has been observed based on metallographic and Auger Spectroscopic analyses. These changes were measured as a function of time. The environment induced changes significantly influenced the fatigue lives in isothermal and out-of-phase thermo-mechanical fatigue cases. In these cases transgranular cracking was observed. Grain boundary crack nucleation and grain boundary crack growth dominated the in-phase thermo-mechanical fatigue cases. Based on these observations the requirements for a life prediction model are outlined. The life prediction model and the predictions are given in Part 2 of this paper.

Sign in / Sign up

Export Citation Format

Share Document