The Role of Phase Stability in Ductile, Ordered B2 Intermetallics

2006 ◽  
Vol 980 ◽  
Author(s):  
James R. Morris ◽  
Yiying Ye ◽  
Maja Krcmar ◽  
Chong Long Fu
Keyword(s):  
Phase Stability ◽  
First Principles ◽  
Tensile Ductility ◽  
Stacking Faults ◽  
Low Energy ◽  
First Principles Calculations ◽  
Phase Competition ◽  
Transformation Pathway ◽  
Shape Memory Materials

AbstractWe discuss the underlying atomistic mechanism for experimentally observed large tensile ductility in various strongly ordered B2 intermetallic compounds. First-principles calculations demonstrate that all of the compounds exhibit little energy differences between the B2, B27 and B33 phases. These calculations relate observations of ductility in YAg, YCu and ZrCo to shape-memory materials including NiTi. One transformation pathway between the B2 and B33 phases establishes a connection between this phase competition, and stacking faults on the {011}B2 plane. The low energy of such a stacking fault will lead to splitting of the b=<100> dislocations into b/2 partials, observed in ZrCo, TiCo, and in the B19' phase of NiTi. Calculations demonstrate that this pathway is competitive with the traditional pathway for NiTi.

An effective and efficient approach to p-type AlN by Be2:O codoping from first-principles calculations

2016 ◽  
Vol 30 (20) ◽  
pp. 1650257
Author(s):  
Meng Zhao ◽  
Wenjun Wang ◽  
Jun Wang ◽  
Junwei Yang ◽  
Weijie Hu ◽  
...  
Keyword(s):  
First Principles ◽  
Ionization Energy ◽  
Hole Concentration ◽  
Valence Band Maximum ◽  
First Principles Calculations ◽  
Mutual Compensation ◽  
Efficient Approach ◽  
P Type ◽  
Codoping Method

Various Be:O-codoped AlN crystals have been investigated via first-principles calculations to evaluate the role of the different combinations in effectively and efficiently inducing p-type carriers. It is found that the O atom is favored to bond with two Be atoms. The formed Be2:O complexes decrease the acceptor ionization energy to 0.11 eV, which is 0.16 eV lower than that of an isolated Be in AlN, implying that the hole concentration could probably be increased by 2–3 orders of magnitude. The electronic structure of Be2:O-codoped AlN shows that the lower ionization energy can be attributed to the interaction between Be and O. The Be–O complexes, despite failing to induce p-type carriers for the mutual compensation of Be and O, introduce new occupied states on the valence-band maximum (VBM) and hence the energy needed for the transition of electrons to the acceptor level is reduced. Thus, the Be2:O codoping method is expected to be an effective and efficient approach to realizing p-type AlN.

Computational and Experimental Insights into the Role of Acidic Molecules on the Corrosion Behavior on 7A46 Aluminum Alloy

2021 ◽  
Vol 21 (4) ◽  
pp. 2221-2233
Author(s):  
Yaru Liu ◽  
Qinglin Pan ◽  
Xiangdong Wang ◽  
Ye Ji ◽  
Qicheng Liu ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Aluminum Alloy ◽  
Corrosion Behavior ◽  
First Principles ◽  
First Principles Calculations ◽  
Corrosive Media ◽  
Corrosion Depth ◽  
Corrosion Mechanisms ◽  
Nanoscale Level

The corrosion mechanisms for different corrosive media on the aged 7A46 aluminum alloy were systematically investigated at nanoscale level. The combination of empirical intergranular and exfoliation corrosion behavior was employed, and coupled with first-principles calculations. Results revealed that the dispersed distribution of matrix precipitates (MPs) leads to the enhancement of the corrosion resistance pre-ageing (PA) followed by double-ageing (PA-DA) alloy. The deepest corrosion depth of PA-DA alloy was in hydrochloric acid, and the calculation result demonstrates that the passivation effect in combination with the accumulation of corrosion products in nitric acid protect the PA-DA alloy from further corrosion.

scholarly journals Phase Stability and Magnetic Properties of Mn3Z (Z = Al, Ga, In, Tl, Ge, Sn, Pb) Heusler Alloys

2019 ◽  
Vol 9 (5) ◽  
pp. 964 ◽  
Author(s):  
Haopeng Zhang ◽  
Wenbin Liu ◽  
Tingting Lin ◽  
Wenhong Wang ◽  
Guodong Liu
Keyword(s):  
Magnetic Properties ◽  
Structural Stability ◽  
Phase Stability ◽  
First Principles ◽  
Magnetic Moments ◽  
Heusler Alloys ◽  
Atomic Radius ◽  
Tetragonal Distortion ◽  
Stable Phase ◽  
First Principles Calculations

The structural stability and magnetic properties of the cubic and tetragonal phases of Mn3Z (Z = Ga, In, Tl, Ge, Sn, Pb) Heusler alloys are studied by using first-principles calculations. It is found that with the increasing of the atomic radius of Z atom, the more stable phase varies from the cubic to the tetragonal structure. With increasing tetragonal distortion, the magnetic moments of Mn (A/C and B) atoms change in a regular way, which can be traced back to the change of the relative distance and the covalent hybridization between the atoms.

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