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.

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.

Effect of Aluminum Concentration And Boron Dopant on Environmental Embriitlement In Feal Aluminides

1990 ◽  
Vol 213 ◽  
Author(s):  
C. T. Liu ◽  
E. P. George
Keyword(s):  
Aluminum Alloys ◽  
Grain Boundaries ◽  
Aluminum Concentration ◽  
Al Alloy ◽  
Test Environment ◽  
Environmental Embrittlement ◽  
Boron Doped ◽  
Weak Boundaries ◽  
Boron Dopant ◽  
Strong Segregation

ABSTRACTThe room-temperature tensile properties of FeAl aluminides were determined as functionsof aluminum concentration (35 to 43 at. % Al), test environment, and surface (oil) coating. The two lower aluminum alloys containing 35 and 36.5% Al are prone to severe environmental embrittlement, while the two higher aluminum alloys with 40 and 43% Al are much less sensitive to change in test environment and surface coating. The reason for the different behavior is that the grain boundaries are intrinsically weak in the higher aluminum alloys, and these weak boundaries dominate the low ductility and brittle fracture behavior of the 40 and 43% Al alloys. When boron is added to the 40% Al alloy as a grain-boundary strengthener, the environmental effect becomes prominent. In this case, the tensile ductility of the boron-doped alloy, just like that of the lower aluminum alloys, can be dramatically improved by control of test environment (e.g. dry oxygen vs air). Strong segregation of boron to the grain boundaries, with a segregation factor of 43, was revealed by Auger analyses.

The Microchemistry Studies of Ductile Ll2 Ni-Based Intermetallics

1994 ◽  
Vol 364 ◽  
Author(s):  
Naoya Masahashi
Keyword(s):  
Electron Microscopy ◽  
Auger Electron ◽  
Boron Content ◽  
Atom Probe ◽  
Probe Field ◽  
Composition Fluctuation ◽  
Boron Segregation ◽  
Boron Doped ◽  
Field Ion Microscope ◽  
Stoichiometric Alloy

AbstractAuger electron microscopy (AES) analysis of boron doped Ni3Al have shown boron segregation at grain boundary (GB). Boron segregation was enhanced with increasing bulk boron content independent of stoichiometry, suggesting that hypo-stoichiometric alloy is intrinsically ductile even without boron. A slight Ni cosegregation is confirmed using atom probe field ion microscope (APFIM). In Ni3(Si,Ti), no distinct composition fluctuation was identified between matrix and GB vicinity. These results suggest that atomic bonding atmosphere modification from covalent to metallic in the vicinity of GB is one of factors to modify ductility for Ll2-type intermetallics.

An Atom Probe Field Ion Microscope Investigation Of The Role Of Boron In Precipitates And At Grain Boundaries In NiAl

1991 ◽  
Vol 238 ◽  
Author(s):  
Raman Jayaram ◽  
M. K. Miller
Keyword(s):  
Grain Boundaries ◽  
Atom Probe ◽  
Probe Field ◽  
Analytical Technique ◽  
Boron Segregation ◽  
Boron Doped ◽  
Nial Alloy ◽  
The Matrix ◽  
Boride Phases

ABSTRACTThe high resolution analytical technique of Atom Probe Field Ion Microscopy (APFTM) haseen used to characterize grain boundaries and the matrix of a stoichiometric NiAl alloy doped with 0.04 (100 wppm) and 0.12 at. % (300 wppm) boron. Field ion images revealed boron segregation to the grain boundaries. Atom probe elemental analysis of the grain boundaries measured a boron coverage of up to 30% of a monolayer. Extensive atom probe analyses also revealed a fine dispersion of nanoscale boride precipitates in the matrix. The boron segregation to the grain boundaries was found to correlate with the observed suppression of intergranular fracture. However, the decrease in ductility of boron-doped NiAl is attributed in part to the precipitation hardening effect of the boride phases.

TEM Observations of Dislocation Emission at Grain Boundaries in Response to Uniaxial (Tensile) Straining

1981 ◽  
Vol 39 ◽  
pp. 296-297
Author(s):  
L.E. Murr
Keyword(s):  
Grain Boundaries ◽  
Tensile Deformation ◽  
Tensile Tests ◽  
Convincing Evidence ◽  
304 Stainless Steel ◽  
Uniaxial Tensile ◽  
Dislocation Emission ◽  
Quantitative Studies ◽  
Transmission Electron

Although it now seems to be generally recognized that grain boundaries and other interfaces are sources for dislocations, there are only scant few observations which tend to show convincing evidence for this. Murr earlier suggested that dislocation pile-ups in deformed metals and alloys (especially of low stacking-fault free energy) were primarily dislocation emission profiles, and more recent quantitative studies tend to unambiguously confirm this for uniaxial tensile deformation. Some of these features are illustrated in Fig. 1(a) and (b) which show a systematic increase in the number of dislocation profiles associated with grain boundary ledges at increasing tensile strains; observed in a Hitachi H.U. 200 F transmission electron microscope.The results shown in Fig. 1(a) and (b) were obtained as part of a systematic study of dislocation emission following the straining of 304 stainless steel sheet samples in separate, conventional tensile tests. Consequently these observations, while qualitatively and even quantitatively convincing, lack the force of direct, in-situ observations.

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.

Local Electronic Structure and Cohesion of Grain Boundaries in Ni3Al

1994 ◽  
Vol 364 ◽  
Author(s):  
D. A. Muller ◽  
S. Subramanian ◽  
S. L. Sass ◽  
J. Silcox ◽  
P. E. Batson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Cohesive Energy ◽  
Bulk Material ◽  
Large Angle ◽  
Spatially Resolved ◽  
Boron Segregation ◽  
Environmental Embrittlement ◽  
Boron Doped ◽  
Local Electronic Structure

AbstractOne of the fundamental questions concerning Ni3Al is why doping with boron improves the room temperature ductility of the polycrystalline material. Boron is thought to prevent environmental embrittlement and increase the cohesive strength of grain boundaries since it changes the fracture mode from intergranular to transgranular. This change in cohesive energy must be reflected in the bonding changes at the grain boundary which can be probed using spatially resolved electron energy loss spectroscopy (EELS). We have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24 using EELS, EDX and ADF imaging in a UHV STEM. Ni-enrichment is seen in a 0.5–1 nm wide region at large angle grain boundaries, both in the absence and presence of B. EELS shows that B segregation can vary along the interface. The Ni L2, 3 core edge fine structure which is sensitive to the filling of the Ni d-band, shows only the boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. These results demonstrate that boron segregation increases the cohesive energy and hence improves the fracture resistance of the grain boundary, by making the bonding at boundaries similar to that in the bulk. The measured changes in d band filling may also affect the local solubility of hydrogen.

An Explanation for the Environmental Sensitivity of Ni3Al

1998 ◽  
Vol 552 ◽  
Author(s):  
D. B. Lillig ◽  
D. Legzdina ◽  
I. M. Robertson ◽  
H. K. Birnbaum
Keyword(s):  
Mass Spectrometry ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Secondary Ion Mass Spectrometry ◽  
Environmental Sensitivity ◽  
Boron Segregation ◽  
Boron Doped ◽  
Distribution Of Elements ◽  
Free Material ◽  
Secondary Ion

ABSTRACTSecondary Ion Mass Spectrometry has been used to study the distribution of elements in and near grain boundaries in boron-free and boron-doped Ni76Al24 alloys with and without ∼220 wt. ppm of deuterium. In boron-free alloys, sulfur was distributed about the grain boundaries in both deuterium- free and deuterium-charged samples. The distribution of deuterium followed that of sulfur and was segregated to grain boundaries. In the boron-doped material, sulfur was not found at most grain boundaries in the uncharged material, but was in the charged material. No deuterium was found at the grain boundaries in the boron-doped material. It is proposed that in the boron-free material it is the synergistic effect of sulfur and hydrogen that is responsible for the environmental sensitivity of this alloy. In boron-doped material, boron segregation to the grain boundary prevents sulfur, and to some extent hydrogen, segregating to the grain boundary.

Atomic and Electronic Structure of Boron-Doped Diamond Grain Boundaries Studied by Arhvtem and ab-Initio Calculation

2003 ◽  
Vol 764 ◽  
Author(s):  
Hiroyuki Togawa ◽  
Hideki Ichinose
Keyword(s):  
Ab Initio ◽  
Grain Boundaries ◽  
Ab Initio Calculation ◽  
Structure Model ◽  
Boron Doped Diamond ◽  
Boron Doped ◽  
Transmission Electron ◽  
Diamond Grain ◽  
Electron Energy Loss ◽  
Atomic And Electronic Structure

AbstractAtomic resolution high-voltage transmission electron microscopy and electron energy loss spectroscopy were performed on grain boundaries of boron-doped diamond, cooperated with the ab-initio calculation. Segregated boron in the {112}∑3 boundary was caught by the EELS spectra. The change in atomic structure of the segregated boundary was successfully observed from the image by ARHVTEM. Based on the ARHVTEM image, a segregted structure model was proposed.

scholarly journals Texture Selection Mechanisms during Recrystallization and Grain Growth of a Magnesium-Erbium-Zinc Alloy

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 171
Author(s):  
Fatim-Zahra Mouhib ◽  
Fengyang Sheng ◽  
Ramandeep Mandia ◽  
Risheng Pei ◽  
Sandra Korte-Kerzel ◽  
...  
Keyword(s):  
Grain Growth ◽  
Ternary Alloy ◽  
Solute Drag ◽  
Tensile Tests ◽  
Electron Back Scatter Diffraction ◽  
Zinc Alloy ◽  
Uniaxial Tensile ◽  
Microstructural Stability ◽  
Solid Solution Strengthening ◽  
Zener Drag

Binary and ternary Mg-1%Er/Mg-1%Er-1%Zn alloys were rolled and subsequently subjected to various heat treatments to study texture selection during recrystallization and following grain growth. The results revealed favorable texture alterations in both alloys and the formation of a unique ±40° transvers direction (TD) recrystallization texture in the ternary alloy. While the binary alloy underwent a continuous alteration of its texture and grain size throughout recrystallization and grain growth, the ternary alloy showed a rapid rolling (RD) to transvers direction (TD) texture transition occurring during early stages of recrystallization. Targeted electron back scatter diffraction (EBSD) analysis of the recrystallized fraction unraveled a selective growth behavior of recrystallization nuclei with TD tilted orientations that is likely attributed to solute drag effect on the mobility of specific grain boundaries. Mg-1%Er-1%Zn additionally exhibited a stunning microstructural stability during grain growth annealing. This was attributed to a fine dispersion of dense nanosized particles in the matrix that impeded grain growth by Zener drag. The mechanical properties of both alloys were determined by uniaxial tensile tests combined with EBSD assisted slip trace analysis at 5% tensile strain to investigate non-basal slip behavior. Owing to synergic alloying effects on solid solution strengthening and slip activation, as well as precipitation hardening, the ternary Mg-1%Er-1%Zn alloy demonstrated a remarkable enhancement in the yield strength, strain hardening capability, and failure ductility, compared with the Mg-1%Er alloy.

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