Effect of Preoxidation and Grain Size on Ductility of a Boron-Doped Ni3Al at Elevated Temperatures

1988 ◽  
Vol 133 ◽  
Author(s):  
M. Takeyama ◽  
C. T. Liu
Keyword(s):  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Short Circuit ◽  
Tensile Tests ◽  
Oxide Formation ◽  
Fine Grained ◽  
Oxygen Penetration ◽  
Grain Sizes ◽  
Boron Doped ◽  
The Difference

ABSTRACTThe ductility of preoxidized Ni3Al (Ni-23Al-0.5Hf-0.2B, at.%) specimens with various grain sizes (17∼193 μm) was evaluated by means of tensile tests at 600 and 760°C in vacuum. It was found that the preoxidation does not affect the ductility of the finest-grained material at either temperature, whereas it causes severe embrittlement in the largest-grained material, especially at 760°C. A continuous, thin Al-rich oxide layer, which forms on the fine-grained samples, protects the underlying alloy from oxygen penetration, preventing any loss of ductility, whereas the nickel-rich oxide which forms on the large-grained samples allows oxygen to penetrate along grain boundaries, causing severe embrittlement. The grain boundaries act as short-circuit paths for rapid diffusion of aluminum atoms from the bulk to the surfaces, and this is responsible for the difference in oxidation behavior between fine- and large-grained materials. The embrittlement of large-grained samples can be eliminated through control of oxide formation on Ni3Al surfaces.

Molecular Dynamics Based Observations of Grain Boundaries and Lattice Defects Functions in Fine Grained Metal

2010 ◽  
Vol 654-656 ◽  
pp. 1582-1585 ◽  
Author(s):  
Toshihiro Kameda ◽  
Bao Rong Zhang
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundaries ◽  
Deformation Process ◽  
Crystal Defects ◽  
View Point ◽  
Dislocation Source ◽  
Fine Grained ◽  
Grain Sizes ◽  
Polycrystalline Metals ◽  
Source And Sink

In order to study the characteristics of fine grained polycrystalline metals, it is important to recognize the function of grain boundaries (GB), crystal defects such as dislocation and/or nanoscale voids, since the fraction of GB increases as grain sizes decreases, the deformation process of these metals could be different from those in larger size grains. In this study, we first evaluate the hypothesis that GB behaves as dislocation source and sink during the deformation of fine grained metal, then compare the behavior between GB and a tiny defect from the view point of dislocation source and sink phenomena. Since continuous dislocation supplies could be considered as the key issue to improve the toughness of fine grained metals, this concept could be helpful to design next generation polycrystalline metals.

Electroplated Cu Recrystallization in Damascene Structures at Elevated Temperatures

1999 ◽  
Vol 564 ◽  
Author(s):  
Qing-Tang Jiang ◽  
Michael E. Thomas ◽  
Gennadi Bersuker ◽  
Brendan Foran ◽  
Robert Mikkola ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Grain Size ◽  
Film Thickness ◽  
Grain Growth ◽  
Elevated Temperatures ◽  
Retardation Effect ◽  
Cu Films ◽  
Grain Sizes ◽  
Geometrical Constraints ◽  
The Difference

AbstractTransformations in electroplated Cu films from a fine to course grain crystal structure (average grain sizes went from ∼0.1 µm to several microns) were observed to strongly depend on film thickness and geometry. Thinner films underwent much slower transformations than thicker ones. A model is proposed which explains the difference in transformation rates in terms of the physical constraint experienced by the film since grain growth in thinner films is limited by film thickness. Geometrical constraints imposed by trench and via structures appear to have an even greater retardation effect on the grain growth. Experimental observations indicate that it takes much longer for Cu in damascene structures to go through grain size transformations than blanket films.

Miniaturized Disk-Bend Testing of Ni3 Al: Effect of Stoichiometry and Boron Content

1990 ◽  
Vol 213 ◽  
Author(s):  
H. Li ◽  
A. J. Ardell
Keyword(s):  
Grain Boundaries ◽  
Boron Content ◽  
Maximum Load ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Al Alloy ◽  
Independent Evidence ◽  
Al Content ◽  
Boron Segregation ◽  
Boron Doped

ABSTRACTThe results of miniaturized disk-bend tests on samples of Ni 3Al of different stoichiometry and boron content are presented. The yield strengths and ductilities of alloys containing 24, 25 or 26 %Al. either boron-free or doped with 0.3 or 0.35 %B, were measured. Specimens 3 mm in diameter and approximately 200 μm thick were tested, some of these having been cut from the grip sections of previously tested tensile bars. The yield strengths were in excellent agreement with the results obtained from the uniaxial tensile tests. The load-displacement curves for the brittle alloys (all but the boron-doped 24 %Al alloy) exhibited a maximum load corresponding to crack initiation. The shapes of the deformed specimens confirmed the assumption that they deform as if they were clamped even though they are not. The fracture surfaces of the brittle alloys are consistent with intergranular failure. Nevertheless, the ductility of the alloys increases with decreasing Al content and decreasing grain size, even for the boron-free alloys which are all brittle. The fracture stress of the boron-doped 26 %Al alloy is about 30% greater than that of the boron-free alloy. It is argued that this is most likely a consequence of the depletion of aluminum at grain boundaries, coupled with boron segregation. Independent evidence suggests that this should increase the cohesive strength of grain boundaries in the boron-doped 26 %Al alloy.

Sulfur Effects on High-Temperature Creep and Fracture Behavior of 25Cr35Ni-Nb Alloys

2013 ◽  
Author(s):  
Tao Chen ◽  
Xuedong Chen ◽  
Juan Ye ◽  
Xiyun Hao
Keyword(s):  
Elevated Temperature ◽  
Grain Boundaries ◽  
Fracture Behavior ◽  
Elevated Temperatures ◽  
Rupture Life ◽  
Local Stress ◽  
Tensile Tests ◽  
Creep Rupture ◽  
Scanning Electron Micrographs ◽  
Nucleation Sites

Centrifugal cast 25Cr35Ni-Nb alloy furnace tubes with different contents of S are selected to investigate effects of S addition on creep and fracture behavior. Rupture tests in air at 1100 °C and 17 MPa and slow rate tensile tests at 850 °C showed that the presence of S decreased the creep rupture life and elevated temperature ductility of 25Cr35Ni-Nb alloy obviously. Scanning electron micrographs (SEM) of the fracture and energy dispersive X-ray spectroscopy (EDS) analysis results indicated that S was the important element to control creep rupture life and elevated temperature ductility. S segregated to grain boundaries at elevated temperatures, blocky fine sulfide particles with smooth surface distribute on the grain boundaries. The presence of sulfides became effective nucleation sites for intergranular creep cavities. Micro cracks occurred by linking up cavities at elevated temperatures due to local stress concentration. Eventually, early failure happened.

Effect of grain shape on environmental embrittlement in Ni3Al tested at elevated temperatures

1989 ◽  
Vol 4 (2) ◽  
pp. 294-299 ◽  
Author(s):  
C. T. Liu ◽  
B. F. Oliver
Keyword(s):  
Grain Boundaries ◽  
Normal Stress ◽  
Elevated Temperatures ◽  
Grain Shape ◽  
Environmental Embrittlement ◽  
Boron Doped

This paper describes the effect of grain shape on environmental embrittlement in boron-doped Ni3Al (24 at. % Al). The alloy showed severe embrittlement when tested at 600 and 760 °C in air. The embrittlement can be alleviated by control of grain shape, and the material with a columnar-grained structure produced by directional levitation zone remelting shows good tensile ductilities when tested in oxidizing environments. The columnar-grained structure with vertical grain boundaries minimizes the normal stress and consequently suppresses nucleation and propagation of cracks along the boundaries.

Transient creep in fine-grained polycrystalline Al2O3 with Lu3+ ion segregation at the grain boundaries

2001 ◽  
Vol 16 (3) ◽  
pp. 716-720 ◽  
Author(s):  
Hidehiro Yoshida ◽  
Yuichi Ikuhara ◽  
Taketo Sakuma
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Testing Temperature ◽  
Grain Boundary Sliding ◽  
Transient Creep ◽  
Transient Time ◽  
Fine Grained ◽  
Boundary Sliding ◽  
The Difference ◽  
Good Agreement

The creep deformation in fine-grained polycrystalline Al2O3 is highly suppressed by the addition of 0.1 mol% LuO1.5. The transient creep behavior in Lu-doped Al2O3 was examined at the testing temperature of 1250–1350 °C, and the data were analyzed in terms of the effect of stress and temperature on the extent of transient time and strain. The experimental data on the transient creep in Lu-doped Al2O3 showed good agreement with the prediction from a time function of the transient and the steady-state creep associated with grain boundary sliding as well as an undoped one. The difference in the transient creep between Lu-doped and undoped Al2O3 can also be explained by the retardation of grain boundary diffusion due to the Lu3+ ions segregation in the grain boundaries.

Boron and Hydrogen in NI3AL: Part II. Mechanical Testing of Bicrystals

1993 ◽  
Vol 319 ◽  
Author(s):  
Patricia E. Johnson ◽  
W. Gourdin ◽  
A. Gonis ◽  
N. Kioussis ◽  
M. Vaudin
Keyword(s):  
Water Vapor ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Tensile Tests ◽  
Stress And Strain ◽  
Boron Segregation ◽  
Environmental Embrittlement ◽  
Boron Doped ◽  
Low Symmetry ◽  
Strength And Ductility

AbstractTo provide a sensitive measurement of the effect of boron segregation on the strength and ductility of Ni3A1 grain boundaries, bicrystal tensile tests were performed on small specimens of boron doped Ni76A124 cut from extremely large-grained boules. Five specimens with the same “random” or low-symmetry grain boundary (disorientations measured by means of backscattered Kikuchi patterns) and two specimens with a second random grain boundary were tested in quenched and slow-cooled conditions. Duplicate tests performed in a low (7 ppm) water-vapor environment showed that the fracture mode and the stress and strain at fracture are altered by environmental embrittlement at individual, partially strengthened grain boundaries.

Submicron/nano Grained Stainless Steel with Superior Mechanical Properties

2005 ◽  
Vol 903 ◽  
Author(s):  
Shreyas Rajasekhara ◽  
M. C. Somani ◽  
M. Koljonen ◽  
L. P. Karjalainen ◽  
A. Kyröläinen ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Yield Strength ◽  
Austenitic Stainless Steels ◽  
Tensile Tests ◽  
Total Elongation ◽  
Fine Grained ◽  
Grain Sizes ◽  
Transmission Electron ◽  
Superior Mechanical Properties ◽  
Cold Rolled

AbstractMetastable austenitic stainless steels may transform to martensite when subjected to cold rolling. Upon subsequent annealing the martensite reverts back to ultra-fine grained austenite. Based on this concept, nano/submicron austenitic grains have been produced in a 63% cold rolled commercial AISI 301LN subjected to annealing treatments at 600°C, 800°C and 1000°C for 1, 10 and 100 seconds.Transmission Electron Microscopy (TEM) observations show the formation of equiaxed austenitic grains as small as ∼ 200nm in samples annealed at 800°C, and a dramatic increase in grain size as the annealing temperature and duration is increased. Additional tensile tests indicate that samples annealed at 800°C for 1 second exhibit a yield strength of ∼ 740 MPa and an total elongation of ∼ 45%. This combination of strength and ductility is excellent exceeding those of conventionally annealed steels (σy=350 MPa; Ductility ∼ 40%) or cold-rolled steels (σy=650 MPa; Ductility ∼ 30%).Finally, a correlation between the observed grain sizes and mechanical properties, in particular the yield strength, is obtained. Preliminary analysis indicates that the Hall-Petch equation can satisfactorily relate the observed yield strength with corresponding grain sizes.

Sulfur Effects on High-Temperature Creep and Fracture Behavior of 25Cr35Ni–Nb Alloys

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Tao Chen ◽  
Xuedong Chen ◽  
Juan Ye
Keyword(s):  
Elevated Temperature ◽  
Grain Boundaries ◽  
Fracture Behavior ◽  
Elevated Temperatures ◽  
Rupture Life ◽  
Local Stress ◽  
Tensile Tests ◽  
Creep Rupture ◽  
Scanning Electron Micrographs ◽  
Nucleation Sites

Centrifugal cast 25Cr35Ni–Nb alloy furnace tubes with different contents of S are selected to investigate effects of S addition on creep and fracture behavior. Rupture tests in air at 1100 °C and 17 MPa and slow rate tensile tests at 850 °C showed that the presence of S decreased the creep rupture life and elevated temperature ductility of 25Cr35Ni–Nb alloy obviously. Scanning electron micrographs (SEM) of the fracture and energy dispersive X-ray spectroscopy (EDS) analysis results indicated that S was the important element to control creep rupture life and elevated temperature ductility. S segregated to grain boundaries at elevated temperatures, and blocky fine sulfide particles with smooth surface distribute on the grain boundaries. The presence of sulfides became effective nucleation sites for intergranular creep cavities. Micro cracks occurred by linking up cavities at elevated temperatures due to local stress concentration. Eventually, early failure happened.

Constrained minimal-interface structures in polycrystalline copper with extremely fine grains

Science ◽  
2020 ◽  
Vol 370 (6518) ◽  
pp. 831-836
Author(s):  
X. Y. Li ◽  
Z. H. Jin ◽  
X. Zhou ◽  
K. Lu
Keyword(s):  
Grain Boundaries ◽  
Pure Copper ◽  
Three Dimensional ◽  
Fine Grained ◽  
Grain Sizes ◽  
Equilibrium Melting Point ◽  
Polycrystalline Solids ◽  
Dynamics Simulations ◽  
Amorphous States ◽  
Interface Structures

Metals usually exist in the form of polycrystalline solids, which are thermodynamically unstable because of the presence of disordered grain boundaries. Grain boundaries tend to be eliminated through coarsening when heated or by transforming into metastable amorphous states when the grains are small enough. Through experiments and molecular dynamics simulations, we discovered a different type of metastable state for extremely fine-grained polycrystalline pure copper. After we reduced grain sizes to a few nanometers with straining, the grain boundaries in the polycrystals evolved into three-dimensional minimal-interface structures constrained by twin boundary networks. This polycrystalline structure that underlies what we call a Schwarz crystal is stable against grain coarsening, even when close to the equilibrium melting point. The polycrystalline samples also exhibit a strength in the vicinity of the theoretical value.

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