CN-122016424-A - Method for quantitatively describing morphology features of beta spots in TC17 titanium alloy cast ingot

Abstract

The invention relates to a method for quantitatively describing the morphology features of beta spots in TC17 titanium alloy ingots, and belongs to the technical field of metal material detection. The method comprises the following steps of sample preparation and treatment, image analysis and feature extraction, and calculation of fractal dimension. The fractal dimension is innovatively introduced to quantitatively characterize the beta spot defect in the solidification structure of the TC17 titanium alloy ingot. Compared with the traditional qualitative or semi-quantitative method, the fractal dimension can reflect the complex morphological characteristics of the beta spot more carefully and comprehensively, and effectively overcomes the quantitative statistical analysis difficulty of the beta spot caused by the characteristics of a large quantity, emission, irregular shape and the like. Through quantitative analysis of fractal dimension on the morphology of the beta spots, the invention obviously reduces the dependence on artificial experience judgment, reduces errors generated by subjective identification, and realizes the refinement and objectification comparison of the morphology features among different beta spots.

Inventors

• YIN XUCHEN
• DENG HAO
• LUO HENGJUN
• WANG ZHOUTIAN
• LI SONGLIN
• DENG KEN

Assignees

• 中国第二重型机械集团德阳万航模锻有限责任公司
• 太原理工大学

Dates

Publication Date

20260512

Application Date

20260123

Claims (10)

1. 1. The method for quantitatively describing the morphology features of the beta spots in the TC17 titanium alloy cast ingot is characterized by comprising the following steps of: A. sample preparation and treatment, namely cutting a sample from a TC17 titanium alloy cast ingot to be detected, carrying out heat treatment and surface processing on the sample, exposing the solidification structure and beta-plaque morphology of the sample through chemical etching, and obtaining a macroscopic morphology image of the sample; B. Identifying and extracting the morphological parameters of the beta spots from the macro morphology image, wherein the morphological parameters comprise the perimeter P and the area A of each beta spot; C. And calculating a fractal dimension D based on the perimeter P and the area A of each beta spot, and calculating the fractal dimension D of the morphology of the beta spot by utilizing a fractal geometric algorithm, wherein the calculation meets the requirement that the goodness of fit R2 is more than or equal to 0.9, and the fractal dimension D is used as an index for quantitatively representing the complexity degree of the morphology of the beta spot.
2. 2. The method of quantitatively characterizing beta spot morphology in a TC17 titanium alloy ingot of claim 1 wherein said heat treating in step a comprises: the first stage of heat treatment, namely heating the sample to 20-50 ℃ above the alpha+beta/beta transformation point of the titanium alloy, preserving heat for 1-3 hours, and cooling to room temperature; And (2) a second section of heat treatment, namely heating the sample subjected to the first section of heat treatment to a temperature of 25-15 ℃ below the alpha+beta/beta transformation point of the titanium alloy, preserving heat for 0.5-1.5 h, and cooling.
3. 3. The method of quantitatively characterizing beta spot morphology in a TC17 titanium alloy ingot of claim 1 wherein the cooling rate in the first stage heat treatment is 1.5 ℃ per minute or less.
4. 4. The method of quantitatively characterizing beta spot morphology in a TC17 titanium alloy ingot of claim 1 wherein said cooling in the second stage heat treatment is water cooled.
5. 5. The method for quantitatively describing the morphology features of the beta spots in the TC17 titanium alloy cast ingot according to claim 1 or 2, wherein the corrosive agent adopted by the chemical etching is a mixed solution of hydrofluoric acid, concentrated nitric acid and water, the volume ratio of the corrosive agent is hydrofluoric acid, the concentrated nitric acid is water=1:3:40-100, preferably, the method further comprises washing the sample after the chemical etching, and photographing by a high-definition digital camera to obtain the macro morphology image, and the mass fraction of the concentrated nitric acid is preferably 65% -68%.
6. 6. The method for quantitatively describing the morphology of the beta spots in the TC17 titanium alloy cast ingot according to claim 5, wherein the chemical etching time is 1-5 hours.
7. 7. The method of claim 1 or 2, wherein the surface is processed in step a to remove an oxide layer and an oxygen permeable layer from the detection surface of the sample to meet the detection criteria of a low-power sample.
8. 8. The method of claim 1 or 2, wherein the image analysis and feature extraction of step B comprises: b1 Selecting a specific area for analysis according to the obtained macro morphology image, wherein the specific area comprises typical beta-spot morphology and solidification structure, the number of grains in the specific area is not less than 10, and the number of beta-spots is not less than 15; b2 Identifying the beta spot in the specific area through image processing of the beta spot morphology and the solidification structure in the specific area, and clearing morphology information of the beta spot; Preferably in step b 2) the image processing is implemented in combination with computer recognition techniques.
9. 9. The method of quantitatively characterizing β spot morphology in TC17 titanium alloy ingots according to claim 1 or 2, wherein the fractal dimension calculation of C step comprises: c1 Natural logarithms lnP and lnA of the perimeter P and the area A of each beta spot are taken respectively; c2 Linear fitting lnP and lnA with lnA on the abscissa and lnP on the ordinate to obtain a fitted straight line lnP =s lnA+b; C3 Using formula d=2 according to the slope S of the fitted line S, calculating to obtain the fractal dimension D of the beta spot morphology.
10. 10. The method of claim 8, wherein if the goodness of fit R2 is less than 0.9 in step C, repeating steps B through C to properly expand or contract the specific region to increase the degree of self-similarity of the β -spot morphology in the region until the goodness of fit R2 is greater than or equal to 0.9.

Description

Method for quantitatively describing morphology features of beta spots in TC17 titanium alloy cast ingot Technical Field The invention relates to a method for quantitatively describing the morphology features of beta spots in TC17 titanium alloy ingots, and belongs to the technical field of metal material detection. Background Near beta titanium alloy TC17 (Ti-5 Al-2Sn-2Zr-4Mo-4 Cr) is widely applied to key rotating parts (such as a compressor disc, a drum barrel and the like) of an aeroengine due to excellent high strength, fracture toughness and hardenability. The performance and safety of these components is highly dependent on the quality of the raw material ingot. Beta spot is a typical detrimental metallurgical defect in near-beta titanium alloy ingots, and is essentially due to segregation of alloying elements (especially beta stabilization elements such as Cr, mo and the like) during solidification, which results in a significant reduction of the beta transus point in a local area. During subsequent hot working (e.g., forging) and heat treatment, these segregation regions tend to form coarse beta grain structures (i.e., beta spots), severely compromising the fatigue, fracture toughness, and mechanical uniformity of the material. At present, the detection and evaluation of the appearance of the beta spot defect in the bar and the forge piece mainly depend on the traditional low-power inspection method, such as GB/T5168-2020 and GJB/T1538A-2008 and other standards. However, the detection of the beta spots in the cast ingot has no unified standard, and the existing conventional method has remarkable limitations in the aspect of accurate quantitative statistical analysis of the morphological characteristics of the existing conventional method due to the large difference of the morphology of the beta spots in the cast ingot and the characteristics of a large quantity, distribution, irregular shape and the like, firstly, the existing evaluation is independent of qualitative or semi-quantitative observation, is difficult to carefully and comprehensively capture the complex morphological characteristics of the beta spots, cannot provide unified quantization parameters, secondly, the subjectivity is strong, errors are easy to introduce, visual inspection and experience judgment are excessive, the objectivity and the reliability of an analysis result are insufficient, the refined comparison among different beta spots are difficult to realize, thirdly, quantitative relation cannot be established with a known solidification model, and the deep understanding of the beta spot formation rule and the verification of a segregation theoretical model are restricted. Patent CN113624793a discloses a method for determining whether a near-beta titanium alloy has a beta spot defect. Firstly establishing a relation between the content of a primary alpha phase in a standard sample and the heat treatment temperature, then observing a sample to be detected, further calculating an actual beta phase transformation point by detecting chemical components of a suspected region with larger size if the content of the primary alpha phase is lower than 5%, correcting a theoretical value of the content of the alpha phase by a formula, and finally judging whether the target region is a beta spot according to whether the corrected content of the alpha phase is lower than 5%. The method is characterized in that misjudgment caused by normal fluctuation of micro-area components is avoided through component correction, and the judgment is based on chemical components and phase change behaviors in nature, rather than the geometric morphology of defects. CN113624793a, although able to determine the presence or absence of β -spots, is completely unable to describe any quantitative description of the morphological features (e.g. complexity, sharpness, distribution uniformity) of existing β -spots. While topographical features are likely to be directly related to the severity of defects, inheritance to part hazards. Lacking quantitative indicators of morphology, finer grading, evaluation and process tracing of defects are difficult. Fractal theory, on the other hand, has been attempted in the field of material science as a powerful mathematical tool describing complex, irregular morphologies in nature to quantify tissue morphology. For example, patent CN104197858a discloses a method for quantitatively characterizing the morphology of the solidification structure of a continuous cast slab of a variety of steels. According to the method, the continuous casting billet section is subjected to hot pickling to reveal a solidification structure, and then fractal dimensions of different areas such as a chilling layer, a columnar crystal area, an equiaxed crystal area and the like are calculated by a box counting method or a perimeter area method, so that the complexity degree of the crystal grain morphology is quantified, and the correlation with the inte