Method for rapidly detecting original beta grain size of near-beta titanium alloy

Abstract

This invention relates to the field of metal material testing technology, and particularly to a method for rapidly detecting the original β-grain size of near-β titanium alloys. The method includes the following steps: S1. A low-magnification sheet of a titanium alloy bar or forging is sequentially heated, held at a certain temperature, and cooled to obtain a sample to be tested; S2. The sample to be tested is polished, the surface is polished twice with a mixed acid, rinsed with anhydrous ethanol, and dried to obtain a treated sample; S3. The β-phase grain size on the surface of the treated sample is observed. The heat treatment method used in this invention can ensure that the original β-phase morphology does not change during heat treatment. After surface etching, it allows for direct observation and statistical analysis of the original β-grain size of near-β titanium alloys, which is more convenient for the formulation and optimization of actual titanium alloy production processes.

Description

Technical Field

[0001] This invention relates to the field of metal material testing technology, and in particular to a method for rapidly detecting the original β grain size of near-β titanium alloys. Background Technology

[0002] Near-β titanium alloys are widely used in aerospace, petroleum, and chemical industries due to their good machinability and excellent strength-plasticity balance. Under service conditions, the β phase content of near-β titanium alloys is approximately 50% or more, and the size of the initial β phase significantly affects the properties of near-β titanium alloy products. Generally, the smaller the initial β phase size, the higher the plasticity and the better the uniformity. During hot working, the initial β phase size is mainly reduced through repeated upsetting and drawing in both single-phase and two-phase regions. However, the later stages of forging in titanium alloy billets or forgings typically employ two-phase forging. Due to the complete fragmentation of the α phase at grain boundaries, the morphology of the initial β phase cannot be directly observed visually or through metallographic testing, which poses difficulties for the formulation and optimization of the preparation process. The morphology of the initial β phase can be obtained through backscattered electron diffraction and associated data processing software, but this method suffers from drawbacks such as complex sample preparation and poor statistical accuracy, limiting its widespread application in industrial production. Summary of the Invention

[0003] To address the shortcomings of the aforementioned processes, this invention provides a method for rapidly detecting the original β grain size of near-β titanium alloys. Through specific heat treatment and surface etching, the original β grain size of near-β titanium alloys can be directly observed and statistically analyzed.

[0004] This invention provides a method for rapidly detecting the original β grain size of near-β titanium alloys, the method comprising the following steps:

[0005] S1. The titanium alloy bar or forging billet is sequentially heated, held at a certain temperature, and cooled to obtain the test sample.

[0006] S2. Grind the sample to be tested, polish and etch the surface with mixed acid, rinse with anhydrous ethanol and blow dry to obtain the treated sample;

[0007] S3. Observe the β-phase grain size on the surface of the treated sample.

[0008] In some embodiments, the heating temperature is 2-20°C below the phase transformation temperature of the titanium alloy bar or forging billet.

[0009] Preferably, the heating temperature is 10-20°C below the phase transformation temperature of the titanium alloy bar or forging billet.

[0010] More preferably, the heating temperature is 10-15°C below the phase transformation temperature of the titanium alloy bar or forging billet.

[0011] In some embodiments, the temperature uniformity of the heating device is ≤5°C.

[0012] This invention does not impose any special limitations on the heating equipment; commonly used equipment in the field, including but not limited to resistance furnaces, can be used.

[0013] In some embodiments, the heat preservation time is 1-20 minutes.

[0014] Preferably, the heat preservation time is 5-10 minutes.

[0015] In some embodiments, the roughness Ra of the polishing is not greater than 2.5 μm.

[0016] Preferably, the roughness Ra of the polishing is not greater than 2.0 μm.

[0017] More preferably, the roughness Ra of the polishing is not greater than 1.6 μm.

[0018] In some embodiments, the polishing is performed using nitric acid and hydrofluoric acid.

[0019] In some embodiments, the thickness of the low-magnification film is 20-30 mm.

[0020] The β-phase grain size on the surface of the sample after observation treatment as described in this invention can be observed visually or by using a metallographic microscope after cutting the metallographic sample by wire cutting.

[0021] In this invention, the original β phase hardly recrystallizes or grows during the heat treatment and heat preservation process. When cooled, needle-like α phases with a single orientation are formed inside the original β phase grains. After surface etching, the morphology of the original β phase grains can be displayed because the contrast of the needle-like α phases in different orientations is different, thus enabling intuitive observation and statistics.

[0022] The existing method CN103616268B for inspecting low-magnification structural defects in titanium alloy raw materials also employs a heating-cooling-acid etching-visual inspection process. The difference between this invention and the method lies in the holding temperature and holding time. Actual experiments have shown that if the temperature and holding time of the aforementioned patent are used, most of the β phase will recrystallize, thus failing to preserve the morphology of the original β phase after forging, and consequently, making it impossible to detect the size of the original β phase.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The heat treatment method used in this invention can ensure that the original β phase morphology does not change during heat treatment. After surface etching, it can realize intuitive observation and statistics of the original β grains of near-β titanium alloy, which is more convenient for the formulation and optimization of the actual production process of titanium alloy. Attached Figure Description

[0025] Figure 1 In the diagrams, A, B, and C represent the orientation characteristics of the original β phase in the forged TC18 titanium alloy, Example 1, and Comparative Example 1, respectively.

[0026] Figure 2 In the diagrams, A, B, and C represent the orientation characteristics of the original β phase in the forged Ti55531 titanium alloy, Example 2, and Comparative Example 2, respectively.

[0027] Figure 3 In the diagrams, A, B, and C represent the orientation characteristics of the original β phase in the forged TC27 titanium alloy, Example 3, and Comparative Example 3, respectively. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] This embodiment provides a method for rapidly detecting the original β grain size of near-β titanium alloys, the method comprising the following steps:

[0031] S1. Cut a 20mm thick low-magnification sheet from the cross section of the TC18 titanium alloy bar, heat it to Tβ-10℃ in a resistance furnace (furnace temperature uniformity ≤5℃), hold it for 5min, and then cool it to room temperature (25℃) to obtain the test sample.

[0032] S2. Grind the sample to be tested to Ra 1.6, polish the sample surface with 60% volume fraction nitric acid and 40% volume fraction hydrofluoric acid, and rinse quickly with water after visually visible machining or milling marks are eliminated; continue to etch the sample surface with 13% volume fraction nitric acid, 16% volume fraction hydrofluoric acid and water to produce a clear low magnification structure, rinse with anhydrous ethanol and blow dry to obtain the treated sample.

[0033] S3. Visually observe the β-phase grain size on the surface of the treated sample.

[0034] Example 2

[0035] This embodiment provides a method for rapidly detecting the original β grain size of near-β titanium alloys, the method comprising the following steps:

[0036] S1. Cut a 25mm thick low-magnification sheet from the cross section of Ti55531 titanium alloy bar, heat it to Tβ-15℃ in a resistance furnace (furnace temperature uniformity ≤5℃), hold it for 10min, and cool it to room temperature (25℃) to obtain the sample to be tested.

[0037] S2. Grind the sample to be tested to Ra 1.6, polish the sample surface with 67% volume fraction nitric acid and 33% volume fraction hydrofluoric acid, and rinse quickly with water after visually visible machining or milling marks are eliminated; continue to etch the sample surface with 20% volume fraction nitric acid, 15% volume fraction hydrofluoric acid and water to produce a clear low magnification structure, rinse with anhydrous ethanol and blow dry to obtain the treated sample.

[0038] S3. Visually observe the β-phase grain size on the surface of the treated sample.

[0039] Example 3

[0040] This embodiment provides a method for rapidly detecting the original β grain size of near-β titanium alloys, the method comprising the following steps:

[0041] S1. Cut a 20mm thick low-magnification sheet from the cross section of the TC27 titanium alloy bar, heat it to Tβ-10℃ in a resistance furnace (furnace temperature uniformity ≤5℃), hold it for 5min, and cool it to room temperature (25℃) to obtain the test sample.

[0042] S2. Grind the sample to be tested to Ra 0.8, polish the sample surface with 65% volume fraction nitric acid and 35% volume fraction hydrofluoric acid, and rinse quickly with water after visually visible machining or milling marks are eliminated; continue to etch the sample surface with 20% volume fraction nitric acid, 15% volume fraction hydrofluoric acid and water to produce a clear low magnification structure, rinse with anhydrous ethanol and blow dry to obtain the treated sample.

[0043] S3. Visually observe the β-phase grain size on the surface of the treated sample.

[0044] Comparative Example 1

[0045] This comparative example provides a method for rapidly detecting the original β grain size of near-β titanium alloys. The specific implementation method is the same as in Example 1, except that the heating temperature and holding time are different. The method includes the following steps:

[0046] S1. Cut a 20mm thick low-magnification sheet from the cross section of the TC18 titanium alloy bar, and heat it in a resistance furnace (furnace temperature uniformity ≤5℃) to Tβ-30℃, hold it for 60min, then heat it to Tβ+15℃, hold it for 30min, and cool it to room temperature (25℃) to obtain the sample to be tested.

[0047] S2. Polish the sample surface with 60% nitric acid and 40% hydrofluoric acid. After visually visible machining or milling marks are eliminated, rinse quickly with water. Continue to erode the sample surface with 13% nitric acid, 16% hydrofluoric acid and water. After producing a clear low-magnification structure, rinse with anhydrous ethanol and blow dry to obtain the treated sample.

[0048] S3. Visually inspect the surface of the treated sample.

[0049] Comparative Example 2

[0050] This comparative example provides a method for rapidly detecting the original β grain size of near-β titanium alloys. The specific implementation method is the same as in Example 1, except that the heating temperature and holding time are different. The method includes the following steps:

[0051] S1. Cut a 25mm thick low-magnification sheet from the cross section of the Ti55531 titanium alloy bar, and heat it in a resistance furnace (furnace temperature uniformity ≤5℃) to Tβ-40℃, hold it for 60min, then heat it to Tβ+20℃, hold it for 30min, and cool it to room temperature (25℃) to obtain the sample to be tested.

[0052] S2. Polish the sample surface with 67% nitric acid and 33% hydrofluoric acid. After visually visible machining or milling marks are eliminated, rinse quickly with water. Continue to erode the sample surface with 20% nitric acid, 15% hydrofluoric acid and water. After producing a clear low-magnification structure, rinse with anhydrous ethanol and blow dry to obtain the treated sample.

[0053] S3. Visually inspect the surface of the treated sample.

[0054] Comparative Example 3

[0055] This comparative example provides a method for rapidly detecting the original β grain size of near-β titanium alloys. The specific implementation method is the same as in Example 1, except that the heating temperature and holding time are different. The method includes the following steps:

[0056] S1. Cut a 20mm thick low-magnification sheet from the cross section of the TC27 titanium alloy bar, and heat it in a resistance furnace (furnace temperature uniformity ≤5℃) to Tβ-30℃, hold it for 60min, then heat it to Tβ+15℃, hold it for 30min, and cool it to room temperature (25℃) to obtain the sample to be tested.

[0057] S2. Polish the sample surface with 65% nitric acid and 35% hydrofluoric acid. After visually visible machining or milling marks are eliminated, rinse quickly with water. Continue to erode the sample surface with 20% nitric acid, 15% hydrofluoric acid and water. After producing a clear low-magnification structure, rinse with anhydrous ethanol and blow dry to obtain the treated sample.

[0058] S3. Visually inspect the surface of the treated sample.

[0059] Performance testing

[0060] The orientation characteristics of the original β phase of the heat-treated samples from forged TC18 titanium alloy, Ti55531 titanium alloy, TC27 titanium alloy, Examples 1-3, and Comparative Examples 1-3 were examined using a scanning electron microscope equipped with an EBSD probe. Figure 1 , Figure 2 , Figure 3 As shown, the orientation and size of the β phase after heat treatment in Examples 1-3 are almost identical to those in the forged state, and the morphology remains unchanged. However, the β phase in Comparative Examples 1-3 has undergone complete or partial recrystallization and cannot retain the morphology of the forged state.

[0061] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for rapidly detecting the original β grain size of near-β titanium alloys, characterized in that, The method includes the following steps: S1. The titanium alloy bar or forging billet is sequentially heated, held at a certain temperature, and cooled to obtain the test sample. S2. Grind the sample to be tested, polish and etch the surface with mixed acid, rinse with anhydrous ethanol and blow dry to obtain the treated sample; S3. Observe the β-phase grain size on the surface of the treated sample; The heating temperature is 10-15°C below the phase transformation point temperature of the titanium alloy bar or forging billet. The temperature uniformity of the heating equipment is ≤5℃; The heat preservation time is 5-10 minutes; The roughness Ra of the polishing process is no greater than 1.6 μm.

Images