High Toughness Alumina/Aluminate: The Role Of Hetero-Interfaces

1995 ◽  
Vol 409 ◽  
Author(s):  
M. E. Brito ◽  
M. Yasuoka ◽  
S. Kanzaki
Keyword(s):  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Auger Electron ◽  
High Strength ◽  
Interfacial Debonding ◽  
Amorphous Phases ◽  
High Toughness ◽  
Interface Structures

AbstractSilica doped alumina/aluminate materials present a combination of high strength and high toughness not achieved before in other alumina systems, except for transformation toughened alumina. We have associated the increase in toughness to crack bridging by anisotropically grown alumina grains with concurrent interfacial debonding of these grains. A HREM study of grain boundaries and hetero-interface structures in this material shows the absence of amorphous phases at grain boundaries. Local Auger electron analysis of fractured surfaces revealed the coexistence of Si and La at the grain facets exposed by the noticeable intergranular fracture mode of this material. It is concluded that a certain and important degree of boundaries weakness is related to both, presence of Si at the interfaces and existence of alumina/aluminate hetero-interfaces.

scholarly journals Research on the Re-Deformation Characteristics of Hot Stamping of Boron Steel Parts with Tailored Properties

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1136 ◽  
Author(s):  
Ling Kong ◽  
Yan Peng ◽  
Caiyi Liu
Keyword(s):  
Grain Boundaries ◽  
Initial Phase ◽  
Hot Stamping ◽  
High Strength ◽  
Boron Steel ◽  
Deformation Characteristics ◽  
Maximum Strain ◽  
Soft Zone ◽  
Local Misorientation

Traditional hot-stamping products have super-high strength, but their plasticity is usually low and their integrated mechanical properties are not excellent. Functionally graded property structures, a relatively novel configuration with a higher material utilization rate, have increasingly captured the attention of researchers. Hot stamping parts with tailored properties display the characteristics of local high strength and high plasticity, which can make up for the limitations of conventional hot stamping and optimize the crash safety performance of vehicles. This new idea provides a means of personalized control in the hot-stamping process. In this paper, a new strategy of local induction heating and press hardening was used for the hot stamping of boron steel parts with tailored properties, of which the microstructure from the hard zone to the soft zone shows a gradient distribution consisting of a martensite phase, multiphase and initial phase, with the hardness ranging from 550 HV to 180 HV. The re-deformation characteristics of hot stamping parts with tailored properties have been studied through the uniaxial tensile test, in cooperation with digital image correlation (DIC) and electron backscattered diffraction (EBSD) techniques. The experiments show that there are easily observable strain distribution characteristics in the re-deformation of hot stamping parts with tailored properties. In the process of tensile deformation, the initial phase zone takes the role of deformation and energy absorption, with the maximum strain before necking reaching 0.32. The local misorientation of this zone was high, and a large number of low angle grain boundaries were formed, while the proportion of small angle grain boundaries increased from 13.5% to 63.3%, and the average grain size decreased from 8.15 μm to 3.43 μm. Meanwhile, the martensite zone takes on the role of anti-collision protection, with a maximum strain of only 0.006, and its local misorientation is mostly unchanged. The re-deformation experimental results show that the hot stamping of boron steel parts with tailored properties meets the functional requirements of a hard zone for anti-collision and a soft zone for energy absorption, suitable for automobile safety parts.

scholarly journals Critical assessment of hydrogen effects on the slip transmission across grain boundaries in α -Fe

2016 ◽  
Vol 472 (2185) ◽  
pp. 20150617 ◽  
Author(s):  
I. Adlakha ◽  
K. N. Solanki
Keyword(s):  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Energy Barrier ◽  
Strain Energy ◽  
Strengthening Mechanism ◽  
Dislocation Motion ◽  
Dislocation Network ◽  
Mode Transition ◽  
Slip Transmission

Grain boundaries (GBs) play a fundamental role in the strengthening mechanism of crystalline structures by acting as an impediment to dislocation motion. However, the presence of an aggressive environment such as hydrogen increases the susceptibility to intergranular fracture. Further, there is a lack of systematic investigations exploring the role of hydrogen on the dislocation–grain-boundary (DGB) interactions. Thus, in this work, the effect of hydrogen on the interactions between a screw dislocation and 〈111〉 tilt GBs in α -Fe were examined. Our simulations reveal that the outcome of the DGB interaction strongly depends on the underlying GB dislocation network. Further, there exists a strong correlation between the GB energy and the energy barrier for slip transmission. In other words, GBs with lower interfacial energy demonstrate a higher barrier for slip transmission. The introduction of hydrogen along the GB causes the energy barrier for slip transmission to increase consistently for all of the GBs examined. The energy balance for a crack initiation in the presence of hydrogen was examined with the help of our observations and previous findings. It was found that the presence of hydrogen increases the strain energy stored within the GB which could lead to a transgranular-to-intergranular fracture mode transition.

Study of Bonding of Grain Boundaries in Steels Using EELS

2005 ◽  
Vol 475-479 ◽  
pp. 4063-4066
Author(s):  
X. Zhang ◽  
Lina Zhang ◽  
Jun Jie Qi ◽  
Yue Ma
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Fracture Property ◽  
Transgranular Fracture ◽  
The Difference ◽  
Relationship Of ◽  
The Relationship

A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.

Mechanical Properties, Fracture Behavior, and Grainboundary Chemistry of B-Doped Nial

1990 ◽  
Vol 186 ◽  
Author(s):  
E. P. George ◽  
C. T. Liu ◽  
J. J. Liao
Keyword(s):  
Yield Strength ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Fracture Behavior ◽  
Boron Concentration ◽  
Tensile Ductility ◽  
Transgranular Cleavage ◽  
Boron Doped ◽  
Fracture Ductility

AbstractThis paper summarizes the results of our work aimed at overcoming the intrinsic grainboundary weakness of NiAI by microalloying with boron. In previous work we have shown that 300 wppm boron is very effective in suppressing intergranular fracture in NiAI [1]. It does this by segregating strongly to the grain boundaries and strengthening them. Despite this dramatic effect on the fracture mode, however, boron is unable to improve ductility because it is a potent solid solution strengthener, more than doubling the yield strength relative to that of undoped NiA1. The present work attempts to decrease this deleterious hardening effect by lowering the bulk concentration of boron in NiA1. Our results show that if the boron concentration in the bulk is lowered to 30 wppm, the yield strength of boron-doped NiA1 is only about 30% higher than that of undoped NiAI. In addition, there is enough boron at the grain boundaries of this alloy to suppress intergranular fracture. Under these conditions, boron-doped NiAI has a tensile ductility of 2%, which is essentially identical to that of undoped NiA1. This result, namely that the strengthening of grain boundaries by boron does not by itself improve ductility, indicates that although grain boundaries might well be the weakest links in NiAI, cleavage planes are not much stronger. In other words, even though boron additions serve to strengthen the grain boundaries and suppress intergranular fracture, ductility is not improved, because the next brittle fracture mode, namely transgranular cleavage, takes over before significant plastic deformation can occur.

Brittle fracture and grain boundary chemistry of microalloyed NiAl

1990 ◽  
Vol 5 (4) ◽  
pp. 754-762 ◽  
Author(s):  
E. P. George ◽  
C. T. Liu
Keyword(s):  
Solid Solution ◽  
Yield Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Tensile Ductility ◽  
Hard Sphere Model ◽  
Strengthening Effect ◽  
Boundary Chemistry

The room-temperature tensile properties, fracture mode, and grain boundary chemistry of undoped stoichiometric NiAl, as well as NiAl doped with boron, carbon, and beryllium, have been investigated, Pure, stoichiometric NiAl fractures with limited tensile ductility in a predominantly intergranular manner. Auger analyses revealed that the grain boundaries in NiAl are extremely clean and free of any segregated impurities, indicating that they are intrinsically brittle. Boron, when added to stoichiometric NiAl at a bulk level of 300 wt. ppm, segregates to the grain boundaries and suppresses intergranular fracture. However, there is no attendant improvement in tensile ductility because boron is an extremely potent solid solution strengthener in NiAl, more than doubling its yield strength. As a result, any potential benefit of improving grain boundary strength is more than offset by the increase in yield strength. Unlike boron, both carbon (300 ppm) and beryllium (500 ppm) are ineffective in suppressing intergranular fracture in NiAl, and Auger analyses of the C-doped alloy revealed that carbon did not affect the fracture mode because it did not segregate to the grain boundaries. Although neither beryllium nor carbon suppressed grain boundary fracture, their effects on the tensile ductility of NiAl were quite different: the ductility of the Be-doped alloy was higher than that of the B-doped alloy because beryllium, unlike boron, has a rather modest strengthening effect in NiAl, whereas the C-doped alloy was brittle like the B-doped alloy, because carbon is a potent solid solution strengthener, just like boron. These observations were rationalized by considering a hard-sphere model for interstitial and substitutional sites in NiAl. It was concluded that boron and carbon occupy interstitial sites, whereas beryllium dissolves substitutionally. In all the alloys that were investigated, the Ni and Al contents of the grain boundaries were not significantly different from the bulk levels, and no evidence was found for B–Ni cosegregation.

Segregation of Calcium to Magnesium Oxide Grain Boundaries

2004 ◽  
Vol 467-470 ◽  
pp. 789-794 ◽  
Author(s):  
F. Papillon ◽  
P. Wynblatt ◽  
Gregory S. Rohrer
Keyword(s):  
Fracture Surface ◽  
Grain Boundary ◽  
Auger Electron Spectroscopy ◽  
Grain Boundaries ◽  
Magnesium Oxide ◽  
Intergranular Fracture ◽  
Electron Spectroscopy ◽  
Auger Electron ◽  
Strong Anisotropy ◽  
Two Sides

Grain boundary (GB) segregation has been measured in Ca-doped MgO by examining intergranular fracture surfaces with Auger electron spectroscopy. The measurements reveal several interesting features. The composition of any given GB on the fracture surface is almost uniform, except for small variations due to deviations from planarity. There is a strong anisotropy of GB composition, which can amount to as much as a factor of six between low and high segregation GB's. Finally, although the compositions of opposite sides of a GB fracture are uniform, there are sometimes significant differences between the two sides, in agreement with a recently formulated model of GB composition as a function of GB character.

scholarly journals The Role of Grain Boundary Precipitates during Intergranular Fracture in 6xxx Series Aluminium Alloys

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 894
Author(s):  
Inga G. Ringdalen ◽  
Ingvild J. T. Jensen ◽  
Calin D. Marioara ◽  
Jesper Friis
Keyword(s):  
Tensile Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Aluminium Alloys ◽  
Density Functional ◽  
Tensile Tests ◽  
Free Zone ◽  
Transmission Electron

During ageing, 6xxx aluminium alloys will develop a microstructure characterised by needle-shaped Mg/Si-rich precipitates in the bulk, precipitate-free zones along the grain boundaries and larger Mg/Si-rich precipitates on the grain boundary. Depending on, among other things, the size of the precipitate-free zone, these alloys are prone to intergranular fracture. The role of the grain boundary precipitates during the initiation and propagation of the intergranular fracture is still not fully understood. Transmission Electron Microscopy has been used to characterise the grain boundaries and grain boundary precipitates. The precipitates were found to be of the β′ type surrounded by a layer of U2 structure. The atomic details of relevant interfaces of Al-β′ were characterised for further investigation. Density Functional Theory simulations were performed on the bulk precipitate structures and on the interfaces obtained experimentally. The decohesion energy of these interfaces was calculated and compared to bulk values. In addition, simulated tensile tests were performed in order to find values for the tensile strength σt. The dependence of the interfacial energy and tensile strength of β′ grain boundary precipitates were found to depend on the orientation and type of interface in addition to the amount of defects on the interface.

Elucidation of block boundaries as the dissolution channels in hydrated cement

1978 ◽  
Vol 36 (1) ◽  
pp. 484-485
Author(s):  
N.V. Belov ◽  
U.I. Papiashwili ◽  
B.E. Yudovich
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Benzoyl Peroxide ◽  
Phase Contrast ◽  
Active Role ◽  
Point Of View ◽  
Hardened Cement ◽  
Hydrated Cement ◽  
Hardened Cement Paste

It has been almost universally adopted that dissolution of solids proceeds with development of uniform, continuous frontiers of reaction.However this point of view is doubtful / 1 /. E.g. we have proved the active role of the block (grain) boundaries in the main phases of cement, these boundaries being the areas of hydrate phases' nucleation / 2 /. It has brought to the supposition that the dissolution frontier of cement particles in water is discrete. It seems also probable that the dissolution proceeds through the channels, which serve both for the liquid phase movement and for the drainage of the incongruant solution products. These channels can be appeared along the block boundaries.In order to demonsrate it, we have offered the method of phase-contrast impregnation of the hardened cement paste with the solution of methyl metacrylahe and benzoyl peroxide. The viscosity of this solution is equal to that of water.

Carbide precipitation and chromium depletion on coherent twin boundaries in deformed 304 stainless steels

1992 ◽  
Vol 50 (2) ◽  
pp. 1216-1217
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
Interfacial Free Energy ◽  
Carbide Precipitation ◽  
Twin Boundaries ◽  
Invariant Structure ◽  
Heat Treated ◽  
Constant Structure ◽  
Cr Depletion

Coherent annealing-twin boundaries are constant structure and energy interfaces with an average interfacial free energy of ∼19mJ/m2 versus ∼210 and ∼835mJ/m2 for incoherent twins and “regular” grain boundaries respectively in 304 stainless steels (SS). Due to their low energy, coherent twins form carbides about a factor of 100 slower than grain boundaries, and limited work has also shown differences in Cr-depletion (sensitization) between twin versus grain boundaries. Plastic deformation, may, however, alter the kinetics and thermodynamics of twin-sensitization which is not well understood. The objective of this work was to understand the mechanisms of carbide precipitation and Cr-depletion on coherent twin boundaries in deformed SS. The research is directed toward using this invariant structure and energy interface to understand and model the role of interfacial characteristics on deformation-induced sensitization in SS. Carbides and Cr-depletion were examined on a 20%-strain, 0.051%C-304SS, heat treated to 625°C-4.5h, as described elsewhere.

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