CN-115938510-B - Theoretical design method for improving chromizing rate of alloy, alloy and preparation method thereof

CN115938510BCN 115938510 BCN115938510 BCN 115938510BCN-115938510-B

Abstract

The invention discloses a theoretical design method for improving alloy chromizing rate by adding rare earth elements and application thereof. The theoretical design method comprises classifying rare earth elements according to characteristic differences, selecting specified elements, constructing phase diagram thermodynamic data of a Cr-C-X-RE system based on a phase diagram calculation method, calculating at least to obtain a balance state phase diagram and a Gibbs free energy curve of a liquid phase, a face-centered cubic phase and a first carbide phase, realizing primary screening, calculating to obtain the change conditions of diffusion energy barriers and diffusion coefficients of Cr elements and C elements before and after RE action through a first sex principle, simulating the influence rule of the rare earth elements on the stability of an oxide film on the surface of a substrate through molecular dynamics, and confirming the rare earth elements according to the change conditions and the influence rule. The integrated calculation material engineering comprehensive design thought is used for screening reasonable rare earth elements, so that the aim of advanced theoretical design can be fulfilled, and the effects of saving time and cost are achieved.

Inventors

CHANG KEKE
XU KAI
WANG LIPING
PU JIBIN
LOU MING
HU XIAOFEI
CHEN LEILEI

Assignees

中国科学院宁波材料技术与工程研究所

Dates

Publication Date: 20260505
Application Date: 20221117

Claims (10)

1. A theoretical design method for improving alloy chromizing rate by adding rare earth elements is characterized by comprising the following steps: 1) Classifying the rare earth elements according to the characteristic difference of the rare earth elements, and selecting the appointed elements in each class; 2) Constructing phase diagram thermodynamic data of a Cr-C-X-RE system based on a phase diagram calculation method, wherein X is a main element of a base material of an alloy, RE is the specified element, and at least calculating to obtain a balance state phase diagram and Gibbs free energy curves of a liquid phase, a face-centered cubic phase and a first carbide phase, so as to realize primary screening of rare earth elements; 3) Constructing a first structural model of a body-centered cubic phase, a second carbide phase and a selected compound phase which possibly occur in the chromizing process of the alloy, and calculating to obtain the conditions of diffusion energy barriers and diffusion coefficients of Cr element and C element before and after the RE action through a first sexual principle; 4) Constructing a second structural model consisting of a matrix of the alloy including a face-centered cube and an oxide film on the surface of the matrix, and simulating the rule of influence of rare earth elements on the stability of the oxide film on the surface of the substrate through molecular dynamics; 5) And (3) confirming the required rare earth element according to the change condition detected in the step (3) and the influence rule detected in the step (4).
2. The theoretical design method of claim 1, wherein in step 1), the characteristics of the rare earth element include atomic radius, melting point, and steady state structure; and/or criteria for classifying rare earth elements include atomic radius variation, bimodal effect, 4f electron number, and standard state crystal structure.
3. The theoretical design method of claim 2, wherein the rules for classifying and selecting the specified elements using the criteria include classifying elements that produce a bimodal effect based on 1) standard state crystal structure as close-packed hexagonal structure or non-close-packed hexagonal structure, 2) atomic radius mutation caused by half-filling or full-filling of the 4f electron layer, and then randomly specifying one rare earth element in each class.
4. The theoretical design method of claim 1, wherein step (2) specifically comprises calculating the equilibrium phase diagram and the gibbs free energy curves of the liquid phase, the face-centered cubic phase and the first carbide phase by using a phase diagram calculation method, and obtaining the correlation and the energy competition relationship between the liquid phase, the face-centered cubic phase and the first carbide phase along with the temperature change according to at least the phase diagram calculation result, and performing primary screening on the rare earth element to realize primary screening on the rare earth element.
5. The theoretical design method of claim 4, wherein the phase diagram calculation method specifically comprises: obtaining a thermodynamic database of a Cr-C-X-RE system, and calculating a phase diagram through phase diagram calculation software to obtain a phase relation, a zero variable reaction temperature and a liquidus change condition caused by the change of the types and the contents of the rare earth elements, wherein X represents a main element of an alloy, and RE represents the specified element; and calculating Gibbs free energy curves of the liquid phase, the face-centered cubic phase and the first carbide phase according to the phase relation, the zero-variable reaction temperature and the liquidus line change condition.
6. The theoretical design method of claim 1, wherein in step 3), the second carbide phase comprises a Cr 7 C 3 phase and the selected compound phase comprises a σ phase.
7. The theoretical design method of claim 6, wherein step 3) specifically comprises: Constructing a first structural model of a body-centered cubic phase, a Cr 7 C 3 phase and a sigma phase, and calculating to obtain a simulation result; Obtaining at least the relation between the root mean square displacement of Cr element and time according to the simulation result; And calculating the change condition according to the relation between the root mean square displacement and time.
8. The theoretical design method of claim 1, wherein step 4) specifically comprises: Constructing a multi-layer model comprising a face-centered cubic substrate, an oxide film on the surface of the face-centered cubic substrate, and a primary screening element on the surface of the substrate as the second structural model; And simulating the activation process of the oxide film through molecular dynamics to obtain the effect result of the rare earth element on the stability of the oxide film.
9. A method of preparing an alloy having improved chromizing rate comprising: Designing a material system doped with rare earth elements by adopting the theoretical design method of any one of claims 1-8, preparing the alloy according to the designed material system, and performing surface chromizing.
10. An alloy prepared by the method of claim 9.

Description

Theoretical design method for improving chromizing rate of alloy, alloy and preparation method thereof Technical Field The invention relates to the technical field of material research methods, in particular to a theoretical design method for improving alloy chromizing rate, an alloy and a preparation method thereof. Background In general, failure of an alloy is due to the surface. The surface strengthening technology can change the components, the organization and the structure of the alloy surface to a certain extent, prolong the service life and reduce the cost. Surface chromizing is one of the common methods for strengthening alloy surfaces, and can improve the hardness, strength, corrosion resistance, high temperature resistance and other properties of the base material. The chromium element not only has larger solid solubility with iron, titanium, nickel and the like, but also can form continuous solid solution, and is more easily combined with trace carbon in a matrix to form a surface carbide layer. The carbide layer not only can improve the strength and hardness of the base material to a certain extent, but also can further realize the surface strengthening of the alloy by combining with the subsequent nitriding treatment. The catalytic permeation and modification of rare earth elements in chromizing process are widely accepted in industry. The atomic radius of rare earth element is often larger than that of other alloy element atoms (about 40% larger than that of iron), and the matrix of the base material is distorted after infiltration, so that interstitial atoms are enriched in a distorted region and become nucleation cores of carbide and nitride, and a compound layer is formed. The atomic radius, melting point, steady-state structure and the like of different rare earth elements are different, so that the promotion effect in the chromizing process is also different. The chromizing rate can be improved by adding rare earth elements, but the process is closely related to the screening of rare earth element types and the design of corresponding technological parameters, but no strict and reliable design screening thought is formed in the prior art, so that the defects of long time, high cost and the like exist in the process of screening the rare earth elements. Disclosure of Invention Aiming at the defects of the prior art, the invention aims to provide a theoretical design method for improving the chromizing rate of an alloy, the alloy and a preparation method thereof. In order to achieve the purpose of the invention, the technical scheme adopted by the invention comprises the following steps: in a first aspect, the present invention provides a theoretical design method for increasing chromizing rate of an alloy by adding a rare earth element, comprising: 1) Classifying the rare earth elements according to the characteristic difference of the rare earth elements, and selecting the appointed elements in each class; 2) Constructing phase diagram thermodynamic data of a Cr-C-X-RE system based on a phase diagram calculation method, wherein X is a main element of a base material of an alloy, RE is the specified element, and at least calculating to obtain a balance state phase diagram and Gibbs free energy curves of a liquid phase, a face-centered cubic phase and a first carbide phase, so as to realize primary screening of rare earth elements; 3) Constructing a first structural model of a body-centered cubic phase, a second carbide phase and a selected compound phase which possibly occur in the chromizing process of the alloy, and calculating to obtain the conditions of diffusion energy barriers and diffusion coefficients of Cr element and C element before and after the RE action through a first sexual principle; 4) Constructing a second structural model consisting of a matrix of the alloy including a face-centered cube and an oxide film on the surface of the matrix, and simulating the rule of influence of rare earth elements on the stability of the oxide film on the surface of the substrate through molecular dynamics; 5) And (3) confirming the required rare earth element according to the change condition detected in the step (3) and the influence rule detected in the step (4). In a second aspect, the present invention also provides a method for preparing an alloy for increasing chromizing rate, comprising: the method is adopted to design a material system of the alloy doped with rare earth elements, and then the alloy is prepared according to the designed material system and the surface chromizing is carried out. In a third aspect, the present invention also provides an alloy prepared by the above preparation method. Based on the technical scheme, compared with the prior art, the invention has the beneficial effects that: The theoretical design method for improving the chromizing rate of the alloy by adding the rare earth elements comprises the steps of classifying the added elements according to cha