CN107330250A - Mg in a kind of aluminium alloy2The characterizing method of Si phase atom stackings - Google Patents

Abstract

The invention discloses Mg in a kind of aluminium alloy₂The characterizing method of Si phases atom stacking on forming core substrate, this method comprises the following steps：Set up the three-dimensional super cell's model of forming core substrate；The interface that the less substrate of mismatch is combined with Newly born phase is gone out according to mismatch theoretical calculation, corresponding substrate crystal face and newborn alternate all Adsorption Models that may be present is built；Energy of adsorption under different Adsorption Models is calculated according to formula, atom stacking of the Newly born phase atom on forming core substrate is characterized.The interaction that the present invention is probed between forming core substrate and Newly born phase atom from atom angle, discloses atom way of stacking of the Newly born phase in early growth period.

Description

A Characterization Method for Mg2Si Phase Atom Stacking in Aluminum Alloy

Technical field:

The invention relates to the technical field of characterization of atomic stacking of new phases on nucleation substrates, in particular to a characterization method of atomic stacking of Mg ₂ Si phases in aluminum alloys on nucleation substrates.

Background technique:

Aluminum alloys are widely used in many engineering fields. Pure aluminum itself has the disadvantages of low strength, low hardness, and low melting point. At present, the most important method to improve the performance of aluminum alloys is alloy strengthening. Reasonable control of the content of Mg and Si elements in aluminum alloys, so that Mg ₂ Si precipitates in the form of primary phases during solidification, can effectively play the role of particle reinforcement and significantly improve the mechanical properties of aluminum alloys. However, in the Al-Mg ₂ Si alloy obtained by melting and casting, the primary Mg ₂ Si is generally relatively coarse and easy to split the matrix, which is not conducive to the improvement of the alloy performance. Some researchers calculated the mismatch degree based on the Bramfitt two-dimensional lattice mismatch model, and proposed that AlP, Al ₄ Sr and Mg ₃ Sb ₂ can serve as good nucleation substrates for Mg ₂ Si, increasing the nucleation particles of Mg ₂ Si, Effectively refine Mg ₂ Si grains, thereby improving the performance of aluminum alloys.

In the study of grain refinement, instruments such as scanning electron microscope (SEM) and transmission electron microscope (TEM) are often used to study grain size and phase structure to reveal the mechanism of grain refinement, but the refinement and deterioration cannot be determined by experimental means. The mechanism is more fundamentally studied. At present, some scholars are gradually revealing the heterogeneous nucleation mechanism through the first principles. Most of these methods are based on the calculation of the lattice mismatch degree to construct the interface model between the nucleation substrate and the nascent phase with a small mismatch degree. The electronic structure, bonding characteristics and binding strength of the interface are calculated, and the mechanism of the nucleation substrate on the nascent phase is explained from the perspective of atoms and electrons. However, no research has revealed the stacking and growth methods of the new phase on the substrate in the initial growth stage before the new phase forms an interface with the substrate.

Invention content:

The object of the present invention is to provide a method for characterizing the interaction between the nucleation substrate in the aluminum alloy and the Mg and Si atoms in the nascent phase Mg ₂ Si in view of the shortcomings of the above prior art. In the early stage of the present invention, with the help of the density functional theory based on first principles, according to the calculation of the lattice mismatch degree, the interface model of the substrate with a small mismatch degree and the nascent phase is constructed, and then the substrate with a better combination with the nascent phase is selected. At the initial stage of heterogeneous nucleation, to study the atomic stacking and growth mode of the new phase on the substrate crystal plane, and to establish the adsorption model between the substrate and the new phase atoms, it can effectively solve the problem that traditional experimental methods cannot The problems at the atomic size level are explored, and the grain refinement mechanism is explored from the root.

A method for characterizing Mg ₂ Si phase atomic stacking in aluminum alloy, characterized in that it comprises the following steps:

Step 1. Establish the three-dimensional supercell atomic model of the nucleation substrate, whose size is N×N×N, wherein the atomic model lattice constant=unit cell lattice constant×supercell dimension, and the unit cell lattice constant is The lattice constant when the unit cell energy of the nucleation substrate is the lowest, and the supercell dimension is the minimum dimension that meets the calculation accuracy requirements;

Step 2. According to the theory of lattice mismatch degree, calculate the crystal plane of the interface between the substrate and the nascent phase when the misfit degree is small, and establish a crystal plane model; there are two stacking modes for the substrate crystal plane and the nascent phase crystal plane: 1) Each atomic layer contains only the same kind of atoms, that is, there are different termination surfaces; 2) Different kinds of atoms appear in each atomic layer at the same time;

When there are two different kinds of atoms in both the substrate and the nascent phase, the two atoms in the substrate are denoted as A and B, and the two atoms in the nascent phase are denoted as I and II respectively. There are 4 situations:

1) Each atomic layer of the substrate crystal plane contains only the same type of atoms A or B, and each atomic layer of the nascent phase crystal plane also contains only the same type of atoms I or II;

2) Each atomic layer of the substrate crystal plane contains only the same kind of atoms A or B, and two kinds of atoms I and II appear in each atomic layer of the nascent phase;

3) Two kinds of atoms A and B appear simultaneously in each atomic layer of the substrate crystal plane, and each atomic layer of the nascent phase crystal plane only contains the same kind of atoms I or II;

4) Two kinds of atoms A and B appear simultaneously in each atomic layer of the substrate crystal plane, and two kinds of atoms I and II appear simultaneously in each atomic layer of the nascent phase;

Step 3. According to the four situations of the combination of the substrate and the nascent phase interface listed in step 2, an adsorption model for adsorbing nascent phase atoms on the substrate crystal plane is established. The adsorption models for various combinations are as follows:

1) Each atomic layer of the substrate crystal plane contains only the same type of atoms A or B, and each atomic layer of the new phase crystal plane also contains only the same type of atoms I or II:

a. The crystal plane of the substrate is terminated by an A atom, and an I atom in the nascent phase is adsorbed on an A atom;

b. The crystal plane of the substrate is terminated by an A atom, and an atom II in the nascent phase is adsorbed on an A atom;

c. The crystal plane of the substrate is terminated by a B atom, and an I atom in the nascent phase is adsorbed on a B atom;

d. The crystal plane of the substrate is terminated by a B atom, and an II atom in the nascent phase is adsorbed on a B atom;

2) Each atomic layer of the substrate crystal plane only contains the same kind of atoms A or B, and two kinds of atoms I and II appear in each atomic layer of the nascent phase:

e. The crystal plane of the substrate is terminated by A atoms, and one atom of I and II in the nascent phase is simultaneously adsorbed on top of the two A atoms;

f. The crystal plane of the substrate is terminated by B atoms, and one atom of I and II in the nascent phase is simultaneously adsorbed on top of the two B atoms;

3) Two kinds of atoms A and B appear simultaneously in each atomic layer of the substrate crystal plane, and each atomic layer of the nascent phase crystal plane only contains the same kind of atoms I or II:

g. Adsorb an I atom in the nascent phase on the A atom of the substrate crystal plane;

h. An atom II in the nascent phase is adsorbed on the A atom of the substrate crystal plane;

i. Adsorb an I atom in the nascent phase on the B atom of the substrate crystal plane;

j. One atom II in the nascent phase is adsorbed on the B atom of the substrate crystal plane;

4) Two kinds of atoms A and B appear simultaneously in each atomic layer of the substrate crystal plane, and two kinds of atoms I and II appear simultaneously in each atomic layer of the nascent phase:

k. The A and B atoms on the crystal surface of the substrate correspond to one atom of I and II in the adsorbed nascent phase, respectively;

l. The A and B atoms on the crystal surface of the substrate correspond to one atom of II and I in the adsorbed nascent phase, respectively;

m. The two A atoms on the crystal plane of the substrate correspond to the I and II atoms in the adsorbed nascent phase, respectively;

n. The two B atoms on the crystal plane of the substrate correspond to the I and II atoms in the adsorbed nascent phase, respectively;

Step 4. Calculate the adsorption energy of each adsorption model in step 3 according to formula (1):

Ε _ads = Ε ₀ + Ε ₁ - Ε _T (1)

In the formula (1), _Εads represents the adsorption energy, _Ε0 represents the total energy of the system when the substrate does not have adatoms, _Ε1 represents the total energy of the adsorbed atoms, and Ε _T represents the total energy of the system after the adatoms;

Step 5. The greater the adsorption energy, the easier it is for atoms to be adsorbed on the substrate crystal surface. By comparing the adsorption energy of the above adsorption models, the stacking mode of the new phase atoms on the substrate can be determined. Now the stacking The way is represented as follows:

(1) When different atoms are adsorbed on the crystal plane of the same substrate, the atom with the larger adsorption energy is preferentially adsorbed, that is, the atom or the atomic layer is preferentially stacked on the substrate;

(2) The same kind of atoms are adsorbed on different substrate crystal planes, and the greater the adsorption energy, the easier it is for the atoms to preferentially stack on the substrate crystal plane or termination plane;

(3) The crystal plane of the same substrate adsorbs the same atom, but when the corresponding positions of the atoms between the substrate and the nascent phase are different, the atoms are preferentially stacked in the way with the largest adsorption energy;

(4) When different atoms are adsorbed on different substrate crystal planes, the interface between the substrate and the nascent phase corresponding to the model with higher adsorption energy is easier to form.

All possible adsorption models described in Step 3 are established based on the interfaces with smaller mismatch degrees calculated in Step 2.

Compared with the prior art, the outstanding advantages of the present invention are:

1. The adsorption model between the nucleation substrate and the new phase is constructed according to the first principles, and the adsorption energy of the interaction between the nucleation substrate and the new phase atoms obtained can further explain the calculation based on the mismatch degree. The atomic stacking method of the interface model can truly reflect the combination of the new phase with the nucleation substrate and the change of the internal microstructure of the material at the early stage of growth, and explore the mechanism of refinement and modification from the atomic scale, thereby revealing the structure-determined properties the essential cause of

2. Make up for the shortcomings of traditional experimental methods that can only do qualitative analysis, and effective theoretical calculations can be used for quantitative analysis, so as to improve the refinement of metamorphic theory and be convincing;

3. This method does not specifically calculate the complex interaction between substrate atoms and nascent phase atoms, but expresses the interaction between them in the form of adsorption energy, which is simple and reliable.

4. Wide application range, not only can characterize the stacking behavior of Mg ₂ Si on the nucleation substrate, but also analyze the stacking of other nascent phase atoms on the substrate.

Description of drawings

Fig. 1(a) is a top view of the adsorption of Mg and Si atoms on the termination surface of AlP(100)Al;

Figure 1(b) is the front view of the adsorption of Mg and Si atoms on the termination surface of AlP(100)Al;

Figure 2(a) is a top view of the AlP(100)P termination surface adsorbing Mg and Si atoms;

Figure 2(b) is the front view of the adsorption of Mg and Si atoms on the termination surface of AlP(100)P.

detailed description:

Below by using AlP as the nucleation substrate of Mg ₂ Si as example, set up AlP adsorption Mg, Si atom adsorption model, tell about the detailed process of the present invention, it should be explained that: the following examples are only to illustrate the present invention and not limit the present invention Describe the technical solution. All technical solutions and their improvements that do not deviate from the spirit and scope of the present invention shall be included in the scope of the claims of the present invention.

The present invention describes a method for characterizing atomic stacking of the Mg ₂ Si phase on the nucleation substrate in an aluminum alloy. We use the previously calculated interface AlP(100)||Mg ₂ Si( 211) as an example to specifically describe the method, including the following steps:

Step 1. Establish a three-dimensional supercell atomic model of the nucleation substrate AlP, whose size is 2×2×2, wherein the atomic model lattice constant=unit cell lattice constant×supercell dimension, and the unit cell lattice The constant is the lattice constant when the unit cell energy of the nucleation substrate is the lowest, and the dimension of the supercell meets the requirements of calculation accuracy;

Step 2. Establish the (100) crystal plane of the substrate AlP supercell in step 1. Each atomic layer of this crystal plane contains only one kind of atom, Al atom or P atom, so there are two terminations of Al termination and P termination On the Mg ₂ Si (211) crystal plane, two kinds of atoms Mg and Si appear in each atomic layer at the same time, then the interface binding mode belongs to the situation 2) in the above 4, and two kinds of adsorption models e and f can be constructed, namely Construct the adsorption model of the AlP(100) surface for the adsorption of Mg and Si atoms on the Al termination surface and the adsorption of Mg and Si atoms on the P termination surface;

Step 3: The adsorption energy of Mg and Si atoms adsorbed on the Al termination surface of the AlP (100) surface is Ε _ads1 , and the adsorption energy of Mg and Si atoms adsorbed on the P termination surface is Ε _ads2 . The adsorption energy of the adsorption model:

Ε _ads = Ε ₀ + Ε ₁ - Ε _T (1)

In the formula (1), _Εads represents the adsorption energy, _Ε0 represents the total energy of the system when the substrate does not have adatoms, _Ε1 represents the total energy of the adsorbed atoms, and _ΕT represents the total energy of the system after the adatoms. The calculated energy values and adsorption energies are shown in Table 1:

Table 1 Adsorption energies of AlP(100) surface with different termination surfaces

Step 4: Compare the adsorption energies obtained in step 3, that is, the larger the adsorption energy is, the easier the atoms are to be adsorbed, and the easier it is for Mg and Si atoms to stack. Therefore, the new phase Mg can be obtained by comparing the adsorption energies. ₂ Atom stacking method preferentially grown on AlP(100) during Si(211) plane growth. It can be seen from Table 1 that Ε _ads1 < Ε _ads2 , that is, the adsorption energy of Mg and Si atoms when adsorbed on the P-terminated surface is greater than that when adsorbed on the Al-terminated surface, indicating that the Mg ₂ Si (211) surface and AlP ( When the 100) plane is combined, Mg and Si atoms are used to terminate the plane stacking on the AlP(100) plane P.

Claims (2)

1. Mg in a kind of aluminium alloy₂The characterizing method of Si phase atom stackings, it is characterised in that comprise the following steps：

Step 1: setting up three-dimensional super cell's atom model of forming core substrate, its size is N × N × N, wherein atom model lattice Constant=unit cells constant × super cell's dimension, lattice when unit cells constant is forming core substrate unit cell minimum energy is normal Number, super cell's dimension is the dimension minimum value for meeting computational accuracy requirement；

Step 2: according to lattice misfit topology degree, calculate mismatch it is smaller when the substrate and crystal face at Newly born phase formation interface, build Vertical crystal face model；There are two kinds of way of stacking with Newly born phase crystal face in substrate crystal face：1) only comprising same in each atomic layer Atom, that is, have different terminal surfaces；2) occurs atom not of the same race simultaneously in each atomic layer；

It is designated as respectively two in A, B, Newly born phase when substrate has two kinds of atoms in two kinds of different atomic time, substrate with Newly born phase Plant atom and be designated as I, II respectively, substrate has following 4 kinds of situations when occurring interface cohesion with Newly born phase：

1) only include and also only included in same atom A or B, each atomic layer of Newly born phase crystal face in each atomic layer of substrate crystal face Same atom I or II；

2) only included in each atomic layer of substrate crystal face and occur two kinds in same atom A or B, each atomic layer of Newly born phase simultaneously Atom I and II；

3) occur simultaneously in each atomic layer of substrate crystal face in two kinds of atom As and B, each atomic layer of Newly born phase crystal face only comprising same A kind of atom I or II；

4) occur occurring two kinds in two kinds of atom As and B, each atomic layer of Newly born phase simultaneously in each atomic layer of substrate crystal face simultaneously Atom I and II；

Step 3: according to 4 kinds of situations of substrate listed in step 2 and Newly born phase interface cohesion, setting up the absorption of substrate crystal face The Adsorption Model of Newly born phase atom, the Adsorption Model in the case of various combinations is as follows：

1) only include and also only included in same atom A or B, each atomic layer of Newly born phase crystal face in each atomic layer of substrate crystal face Same atom I or II：

A. substrate crystal face is terminated with A atoms, and I atom in Newly born phase is adsorbed on an A atom；

B. substrate crystal face is terminated with A atoms, and II atom in Newly born phase is adsorbed on an A atom；

C. substrate crystal face is terminated with B atoms, and I atom in Newly born phase is adsorbed on a B atom；

D. substrate crystal face is terminated with B atoms, and II atom in Newly born phase is adsorbed on a B atom；

2) only included in each atomic layer of substrate crystal face and occur two kinds in same atom A or B, each atomic layer of Newly born phase simultaneously Atom I and II：

E. substrate crystal face is terminated with A atoms, I, II atom each one in adsorbing Newly born phase simultaneously in the top of two A atoms respectively It is individual；

F. substrate crystal face is terminated with B atoms, I, II atom each one in adsorbing Newly born phase simultaneously in the top of two B atoms respectively It is individual；

3) occur simultaneously in each atomic layer of substrate crystal face in two kinds of atom As and B, each atomic layer of Newly born phase crystal face only comprising same A kind of atom I or II：

G. I atom in Newly born phase is adsorbed on the A atoms of substrate crystal face；

H. II atom in Newly born phase is adsorbed on the A atoms of substrate crystal face；

I. I atom in Newly born phase is adsorbed on the B atoms of substrate crystal face；

J. II atom in Newly born phase is adsorbed on the B atoms of substrate crystal face；

4) occur occurring two kinds in two kinds of atom As and B, each atomic layer of Newly born phase simultaneously in each atomic layer of substrate crystal face simultaneously Atom I and II：

K. each one of I, II atom in absorption Newly born phase is corresponded on substrate crystal face A and B atom respectively；

L. each one of II, I atom in absorption Newly born phase is corresponded on substrate crystal face A and B atom respectively；

M. each one of I, II atom in absorption Newly born phase is corresponded on two A atoms of substrate crystal face respectively；

N. each one of I, II atom in absorption Newly born phase is corresponded on two B atoms of substrate crystal face respectively；

Step 4: according to the energy of adsorption of each Adsorption Model in formula (1) calculation procedure three：

Ε_ads=Ε₀+Ε₁-Ε_T (1)

In formula (1), Ε_adsRepresent energy of adsorption, Ε₀Represent the gross energy of system when substrate does not have an adatom, Ε₁Represent to inhale The gross energy of attached atom, Ε_TRepresent the gross energy of system after adatom；

Step 5: energy of adsorption is bigger, atom is more easily attracted on substrate crystal face, is adsorbed by comparing each Adsorption Model of the above The way of stacking, is now characterized as below by the size of energy, it may be determined that way of stacking of the Newly born phase atom on substrate：

(1) substrate crystal face of the same race adsorbs the different atomic time, and the big atoms absorption of energy of adsorption, i.e. atom or the atomic layer exists Preferential stacking on substrate；

(2) various substrates crystal face adsorbs atom of the same race, and energy of adsorption is bigger, show the atom it is easier it is preferential in the substrate crystal face or Stacking on terminal surface；

(3) substrate crystal face of the same race adsorbs atom of the same race, when simply substrate answers position different with newborn alternate atom pair, atoms By the big mode stacking of energy of adsorption；

(4) various substrates crystal face adsorbs different atomic time, the corresponding substrate of the larger model of energy of adsorption and newborn alternate boundary Face is easier to be formed.

2. according to Mg in a kind of aluminium alloy described in claim 1₂The characterizing method of Si phase atom stackings, it is characterised in that：Step All Adsorption Models that may be present described in three are set up according to the less interface of the mismatch calculated in step 2.