Alloy Design of Ordered Intermetallics

1990 ◽  
Vol 186 ◽  
Author(s):  
E. P. George ◽  
C. T. Liu
Keyword(s):  
Brittle Fracture ◽  
Theoretical Calculations ◽  
Model Alloy ◽  
High Symmetry ◽  
Test Environment ◽  
Ambient Temperatures ◽  
Environmental Embrittlement ◽  
Ordered Alloys ◽  
Intergranular Brittleness ◽  
Alloy Systems

AbstractOrdered intermetallics based on aluminides and silicides constitute a unique class of metallic materials possessing promising high-temperature properties. However, brittle fracture and poor ductility have limited their use as engineering materials in most cases. During the past ten years extensive research has been conducted on ordered intermetallics. As a result, significant progress has been made in identifying various causes of brittle fracture, and their relative importance in different ordered alloys. In some cases this understanding has helped achieve dramatic improvements in ductility. We review here three different classes of brittle fracture in ordered intermetallics and discuss the results in terms of model alloy systems chosen from each class. Ni3A1 and NiAl are discussed as prototypical ordered alloys prone to intrinsic intergranular brittleness. They are used to review our current understanding of intrinsically weak grain boundaries and the mechanisms by which boron is thought to suppress intergranular fracture. Next, FeAl and Fe3A1 are discussed as examples of ordered intermetallics that are susceptible to environmental embrittlement at ambient temperatures. Recent discoveries in these two alloy systems are reviewed with special emphasis on some of the rather interesting but subtle effects of test environment. Finally, A13X type intermetallics (A13 Sc, Al3Ti-base, and Al3 Zr-base alloys) are discussed as examples of ordered alloys that have high symmetry (L12 structure), are relatively soft, yet cleave transgranularly with very little ductility. In all these cases, experimental results are compared with theoretical calculations.

Review of Environmental Effects in Intermetallics

1994 ◽  
Vol 364 ◽  
Author(s):  
E. P. George ◽  
C. T. Liu
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Atomic Hydrogen ◽  
Ambient Air ◽  
Sole Source ◽  
Model Alloy ◽  
Test Environment ◽  
Simultaneous Generation ◽  
Hydrogen Molecules ◽  
Environmental Embrittlement

AbstractThe recent progress made in our understanding of the phenomenology and mechanisms of environmental embrittlement in ordered intermetallics is reviewed by considering two model alloy systems of the L12 and B2 crystal classes (Ni3Al and FeAl). The poor ductility commonly encountered when these alloys are tensile tested in ambient air is due mainly to environmental embrittlement, in the absence of which, both alloys are now known to be quite ductile. Both H2O and H2, at levels found in ordinary ambient air, are found to cause environmental embrittlement, with the former usually more deleterious. In the case of H2O, the micromechanism involves reaction with the intermetallic to form an oxide (or hydroxide) and simultaneous generation of atomic hydrogen which then enters the metal and causes embrittlement. In the case of H2, on the other hand, atomic hydrogen is generated as a result of the dissociation of physisorbed hydrogen molecules on the intermetallic surfaces. Consistent with the proposed embrittlement mechanism, ductility is found to increase with decreasing amounts of H2O (or H2) in the test environment, increasing strain rate, and decreasing (or increasing) temperature. Environmental embrittlement in Ni3Al (and other L12 alloys) occurs predominantly intergranularly, whereas in FeAl (and other B2 alloys) it can also occur transgranularly—presumably because diffusion of hydrogen is fast enough through the bulk in the more open B2 structure but only so along grain boundaries in the L12 structure. Microalloying with B, which segregates strongly to the grain boundaries, can overcome environmental embrittlement in L12 alloys, but not in B2 alloys; in the latter, alloying additions probably have to be added at significantly higher (macroalloy) levels to affect the bulk properties. In neither alloy is environmental embrittlement the sole source of brittleness: depending on the alloy stoichiometry, and grain boundary character, a given grain boundary may be intrinsically weaker (or stronger) than the bulk, thereby influencing overall ductility.

scholarly journals Calculated mixing enthalpies of 11 IIB-IVB and IIB-VB binary alloy systems using a subregular model

2010 ◽  
Vol 46 (2) ◽  
pp. 141-151 ◽  
Author(s):  
Z. Bangwei ◽  
S. Xiaolin ◽  
L. Shuzhi ◽  
Y. Xiaojian ◽  
X. Haowen
Keyword(s):  
Binary Alloy ◽  
First Principles ◽  
Theoretical Calculations ◽  
Points Of View ◽  
Group B ◽  
Miedema Theory ◽  
First Time ◽  
Subregular Model ◽  
Mixing Enthalpies ◽  
Alloy Systems

There have been no theoretical calculations of the mixing enthalpies for group B metal alloy systems using the famous Miedema theory or from first principles. Therefore such systematic calculations for the 11 group IIB?IVB and IIB?VB binary alloy systems are performed for the first time using a subregular model. The results show that the agreement between the calculations and experimental data is pretty good and could be accepted from the theoretical or experimental points of view. It can be concluded from the results that the subregular model can be used for calculating the mixing enthalpies of the group B alloy systems, at least for the IIB?IVB and IIB?VB alloy systems.

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.

scholarly journals Detecting quadrupole: a hidden source of magnetic anisotropy for Manganese alloys

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Jun Okabayashi ◽  
Yoshio Miura ◽  
Yohei Kota ◽  
Kazuya Z. Suzuki ◽  
Akimasa Sakuma ◽  
...  
Keyword(s):  
Magnetic Anisotropy ◽  
Quantum Physics ◽  
Theoretical Calculations ◽  
Magnetic Moments ◽  
Perpendicular Magnetic Anisotropy ◽  
Linear Dichroism ◽  
First Principles Calculation ◽  
X Ray ◽  
Manganese Alloys ◽  
Ordered Alloys

Abstract Mn-based alloys exhibit unique properties in the spintronics materials possessing perpendicular magnetic anisotropy (PMA) beyond the Fe and Co-based alloys. It is desired to figure out the quantum physics of PMA inherent to Mn-based alloys, which have never been reported. Here, the origin of PMA in ferrimagnetic Mn3− δ Ga ordered alloys is investigated to resolve antiparallel-coupled Mn sites using x-ray magnetic circular and linear dichroism (XMCD/XMLD) and a first-principles calculation. We found that the contribution of orbital magnetic moments in PMA is small from XMCD and that the finite quadrupole-like orbital distortion through spin-flipped electron hopping is dominant from XMLD and theoretical calculations. These findings suggest that the spin-flipped orbital quadrupole formations originate from the PMA in Mn3− δ Ga and bring the paradigm shift in the researches of PMA materials using x-ray magnetic spectroscopies.

Structural and Vibrational Properties of Manganese Sulfide

2013 ◽  
Vol 209 ◽  
pp. 186-189
Author(s):  
Brijmohan Y. Thakore ◽  
A.Y. Vahora ◽  
S.G. Khambholja ◽  
A.R. Jani
Keyword(s):  
Bulk Modulus ◽  
Density Functional ◽  
Local Density ◽  
Theoretical Calculations ◽  
Manganese Sulfide ◽  
High Symmetry ◽  
Isothermal Bulk Modulus ◽  
Pressure Derivative ◽  
Density Functional Perturbation Theory ◽  
Quantum Espresso

Structural properties of MnS have been studied using plane wave pseudopotential density functional theory as implemented in Quantum Espresso code. Local density approximation (LDA) along with ultrasoft pseudopotential has been used for total energy calculations. The calculated total energies are fitted to Murnaghan equation of state to calculate equilibrium lattice constant, isothermal bulk modulus and pressure derivative of isothermal bulk modulus for NaCl-type structure of MnS and compared with previous experimental and theoretical calculations and good agreement is achieved with those results. Phonon frequencies have also been derived for B1 phase of MnS along high symmetry directions using the density functional perturbation theory at ambient condition.

scholarly journals The SARS-COV-2 outbreak around the Amazon rainforest: the relevance of the airborne transmission

2020 ◽  
Author(s):  
Edilson Crema
Keyword(s):  
Theoretical Calculations ◽  
Global Analysis ◽  
Decisive Role ◽  
Theoretical Explanation ◽  
Amazon Rainforest ◽  
Striking Difference ◽  
Contamination Rate ◽  
Airborne Transmission ◽  
Ambient Temperatures ◽  
Health Authorities

Background This paper presents a global analysis of the SARS-COV-2 outbreak in Brazil. Amazonian States have a much higher contamination rate than the southern and southeastern States. So far, no explanation has been provided for this striking difference that can shed light on the airborne transmission of the virus. Minimizing airborne transmission, health authorities recommend two meters as a safe distance. However, recent experiments reveal that this can be the main form of contagion. There is a lack of theoretical explanation on how airborne transmission works. Methods To investigate the spread of SARS-COV-2 in different macro environments, we analyzed the daily official data on the evolution of COVID-19 in Brazil. We compared our epidemiologic results obtained in States with very different climatic characteristics, and that had adopted, almost simultaneously, similar social isolation measures. To understand the virus spread, it was necessary to calculate theoretically the movement and behavior in the air of saliva droplets. Findings The transmission of SARS-COV-2 is much faster in the Amazon rainforest region. Our theoretical calculations explain and support the empirical results observed in recent experiments that demonstrate the relevance of aerial transmission of the coronavirus. Interpretation An onset of collective immunity may have been achieved with a contamination rate of about 15% of the Amazonian population. If confirmed, this result will have an essential impact on the management of the pandemic across the planet. The airborne transmission played a decisive role in the striking difference in the evolution of the pandemic among Brazilian regions. Air humidity is the most important climatic factor in viral spreading, while usual ambient temperatures do not have strong influence. There is no safe indoor distance for the coronavirus transmission. So, mask and eye protection are essential.

Plastic Behavior and Deformation Structure of Silicide Single Crystals with Transition Metals at High Temperatures

1993 ◽  
Vol 322 ◽  
Author(s):  
Y. Umakoshi ◽  
T. Nakashima ◽  
T. Nakano ◽  
E. Yanagisawa
Keyword(s):  
Brittle Fracture ◽  
Slip System ◽  
Single Crystals ◽  
Low Temperatures ◽  
Plastic Behavior ◽  
Deformation Structure ◽  
Secondary Slip ◽  
Ambient Temperatures ◽  
Brittle Transition ◽  
Increasing Temperature

AbstractThe mechanical and plastic behaviors of refractory silicide single crystals with Cllb (MoSi2), C40 (CrSi2, TaSi2 and NbSi2), D88 (Ti5Si3) and Cl (CoSi2 and (Co0.9Ni0.1)Si2) structures were investigated. The C40–type silicides were deformed by (0001)<1120> slip. Their yield stress decreased sharply with increasing temperature but NbSi2 and TaSi2 which were deformable even at low temperatures, exhibited anomalous strengthening around 1350°C. Deformation of Ti5Si3 whose ductile-brittle transition occurred around 1300°C was controlled by twins and the brittle fracture occurred on the basal plane. In CoSi2 the {001}<100> slip was only activated at ambient temperatures but addition of Ni activated {110}<110> slip as secondary slip system and improved the ductility. The creep behavior of MoSi2 and CrSi2 single crystals were also investigated and was found to be controlled by the viscous and glide motion of dislocations.

Electronic Properties and Stability of the TiAl3 and MoPt2 Type Ordered Structures in Binary Transition Metal Alloys

1982 ◽  
Vol 21 ◽  
Author(s):  
R. Kuentzler ◽  
R.M. Waterstrat ◽  
P. Turek ◽  
A. Bieber
Keyword(s):  
Transition Metal ◽  
Band Structure ◽  
Specific Heat ◽  
Electronic Properties ◽  
Systematic Study ◽  
Theoretical Calculations ◽  
Metal Alloys ◽  
Ordered Structures ◽  
Transition Metal Alloys ◽  
Ordered Alloys

ABSTRACTIn view of the recent constitution diagrams (for binary transition metal alloys) a systematic study of the electronic properties of all alloys which have either the TiAl3 or MoPt2 type of structure has been undertaken. Specific heat results are reported and briefly discussed in the frame of the theoretical calculations about band structure and stability of ordered alloys.

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