Density control method for titanium alloy powder metallurgy product

Abstract

The invention belongs to the technical field of titanium alloy powder metallurgy, and provides a titanium alloy powder metallurgy product compactness control method which specifically comprises the following steps: S1, powder preparation and grading optimization; s2, die forming; s3, multi-stage vacuum sintering is conducted, specifically, a directly-pressed compact is sintered, the sintering process is conducted under high vacuum, and the following three-stage sintering curve is executed; and S4, cooling. The problem of insufficient mechanical properties of the titanium alloy is effectively solved, and a technical basis is provided for popularization and application of the titanium alloy and light weight of special vehicles.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy powder metallurgy technology, and particularly relates to a method for controlling the density of titanium alloy powder metallurgy products. Background Technology

[0002] With the increasing demand for lightweight special vehicles, the weight control of structural components is becoming increasingly stringent. Titanium alloys, as lightweight metals with strength comparable to steel but only 60% of its density, are ideal materials for weight reduction. Powder metallurgy is a low-cost near-net-shape forming technology with advantages such as short process, low cost, and high material utilization. Its principle involves reacting titanium with hydrogen at high temperatures to form brittle titanium hydride, which is then mechanically crushed and finally dehydrogenated under vacuum to obtain titanium powder. However, titanium alloy powder metallurgy products generally face a technical challenge: insufficient final density. Low density (usually below 95%) leads to a significant decrease in the mechanical properties of parts (especially fatigue performance and toughness), making it difficult to meet the requirements of high-end equipment such as special vehicles. The factors affecting density are complex and permeate the entire manufacturing process. ① Powder raw materials: The particle size distribution, morphology, and oxygen content of powder directly affect the filling density and sintering activity.

[0003] ② Forming process: Forming density is the basis for sintering densification. Uneven pressing will lead to deformation and uneven density after sintering.

[0004] ③ Sintering process: Sintering temperature, time, atmosphere, and heating / cooling regime are the driving forces for atomic diffusion and densification. Improper processes can lead to residual pores or abnormal grain growth.

[0005] Currently, optimization is typically achieved through single-step methods, such as increasing sintering temperature or using finer powders. However, these methods have limitations. Increasing the sintering temperature can lead to grain coarsening, impairing performance; using ultra-fine powders is costly and can introduce high oxygen content. Therefore, a systematic solution is urgently needed to achieve precise and repeatable control over the density of titanium alloy powder metallurgy products without sacrificing other properties. Summary of the Invention

[0006] The technical problem to be solved by this invention is: how to achieve precise and repeatable control over the density of titanium alloy powder metallurgy products.

[0007] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows: A method for controlling the density of titanium alloy powder metallurgy products specifically includes the following steps: S1. Powder preparation and gradation optimization Spherical titanium alloy powder and irregularly shaped hydrogenated dehydrogenated titanium alloy powder are provided, and the two powders are mixed in a certain way; S2, Compression molding The mixed powder is loaded into a mold and pressed into shape under a unit pressure of 400~600MPa to obtain a compact with a green density of not less than 60% of the theoretical density. S3, Multi-stage vacuum sintering The directly pressed compact is sintered under high vacuum, and the following three-stage sintering curves are executed: First stage, low temperature degassing: heat up to 800~1000℃ at a rate of 3~5℃ / min and hold for 60~120 minutes; The second stage, medium-temperature activation: slowly increase the temperature to 90% to 95% of the sintering temperature at a rate of 1 to 2℃ / min, and hold for 30 to 60 minutes; The third stage, high-temperature final sintering: rapidly increase to the final sintering temperature at a rate of 2~3℃ / min, the final sintering temperature being 10~30℃ below the β phase transformation point of the titanium alloy, and hold at that temperature for 120~240 minutes. S4, Cooling After cooling to below 300°C in the furnace, high-purity argon gas is introduced to break the vacuum before the furnace is removed.

[0008] Furthermore, in step S1, the median particle size of the spherical powder is 25~45μm, and the median particle size of the hydrogenation dehydrogenation powder is 15~30μm.

[0009] Furthermore, spherical titanium alloy powder and irregularly shaped hydrogenated dehydrogenated titanium alloy powder are mixed at a mass ratio of (70~90)%:(30~10)%.

[0010] This invention offers the following advantages: it establishes a systematic control method for improving the density of titanium alloy powder metallurgy products. This method first optimizes the powder gradation by mixing spherical and irregularly hydrogenated / dehydrogenated titanium alloy powders in a specific ratio to increase the initial filling density. Subsequently, a suitable forming process is used to prepare green blanks. Finally, a three-stage vacuum sintering process, including low-temperature degassing, medium-temperature activation, and high-temperature final sintering, synergistically promotes the densification process. This invention breaks through the limitations of traditional single-stage optimization, providing a complete process solution capable of stably producing high-performance titanium alloy parts with a relative density ≥99.0%, effectively solving the problem of insufficient mechanical properties and providing a technical foundation for the widespread application of titanium alloys and the lightweighting of special vehicles. Detailed Implementation

[0011] To better understand the purpose, structure, and function of this invention, the invention will now be described in further detail.

[0012] This embodiment provides a systematic method for controlling the density of titanium alloy powder metallurgy products. This method optimizes the entire process parameters from powder proportioning and forming to sintering, resulting in a synergistic effect that ultimately yields titanium alloy structural parts with relatively high density. The specific scheme is as follows: Powder preparation and gradation optimization were performed to provide spherical titanium alloy powder and irregularly shaped hydrogenated dehydrogenated titanium alloy powder. The two powders were mixed at a mass ratio of (70–90)%:(30–10)%. The median particle size of the spherical powder was 25–45 μm, and the median particle size of the hydrogenated dehydrogenated powder was 15–30 μm. This bimodal gradation system utilizes the small-sized hydrogenated dehydrogenated powder to fill the voids between the large-sized spherical powder, thereby significantly improving the tap density of the mixed powder.

[0013] (2) Molding: The mixed powder is loaded into a mold and pressed into shape. The unit pressure is 400~600MPa to obtain a green compact with a density not less than 60% of the theoretical density.

[0014] (3) Multi-stage vacuum sintering, in which the directly pressed compact is sintered, the sintering process is carried out in a high vacuum (≤10 ~ 3 The sintering process was carried out at Pa) and the following three-stage sintering curves were executed: First stage (low-temperature degassing): Heat to 800-1000℃ at a rate of 3-5℃ / min and hold for 60-120 minutes. This stage aims to thoroughly remove adsorbed gases and residual hydrocarbons from the surface and interior of the billet, and prevent the formation of closed pores.

[0015] The second stage (intermediate-temperature activation): The temperature is slowly increased to 90%–95% of the sintering temperature (approximately 1150–1250°C for Ti₆Al₄V) at a rate of 1–2°C / min, and held for 30–60 minutes. This stage provides sufficient energy to induce vigorous atomic diffusion and rapid growth of the grain necks, preparing for final densification while inhibiting excessively rapid grain growth.

[0016] The third stage (high-temperature final sintering): The temperature is rapidly increased to the final sintering temperature at a rate of 2~3℃ / min. This final sintering temperature is 10~30℃ below the β phase transformation point (Tβ) of the titanium alloy (approximately 1200~1260℃ for Ti~6Al~4V), and held at this temperature for 120~240 minutes. In this stage, the porosity is finally eliminated and densified through volume diffusion and grain boundary diffusion mechanisms.

[0017] (4) Cooling: After the furnace is cooled to below 300°C, high-purity argon gas can be introduced to break the vacuum and remove the furnace.

[0018] This embodiment organically combines three elements: "optimizing powder gradation to improve initial filling density", "innovating forming process to ensure compact uniformity", and "precisely designing multi-stage sintering curves to promote efficient pore discharge", forming a closed-loop control method and its process parameters, which is the key point of this technical solution.

[0019] This invention does not optimize a single parameter in isolation, but rather starts from the design of the powder system and extends throughout the entire forming and sintering process to form a complete and synergistic technical solution that solves the systemic problem of density control.

[0020] Through innovative dual-particle-size and dual-morphology powder gradation, the initial filling density is significantly improved, laying a solid foundation for sintering densification. Combined with a unique multi-stage sintering curve, porosity can be effectively eliminated, ultimately enabling the relative density of the product to stably reach over 99.0%, and even up to 99.5%.

[0021] Although embodiments of the present invention have been described, those skilled in the art will be able to make various modifications and improvements without departing from the principles of the present invention, and these modifications and improvements should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for controlling the density of titanium alloy powder metallurgy products, characterized in that, Specifically, the steps include the following: S1. Powder preparation and gradation optimization Spherical titanium alloy powder and irregularly shaped hydrogenated dehydrogenated titanium alloy powder are provided, and the two powders are mixed in a certain way; S2, Compression molding The mixed powder is loaded into a mold and pressed into shape under a unit pressure of 400~600MPa to obtain a compact with a green density of not less than 60% of the theoretical density. S3, Multi-stage vacuum sintering The directly pressed compact is sintered under high vacuum, and the following three-stage sintering curves are executed: First stage, low temperature degassing: heat up to 800~1000℃ at a rate of 3~5℃ / min and hold for 60~120 minutes; The second stage, medium-temperature activation: slowly increase the temperature to 90% to 95% of the sintering temperature at a rate of 1 to 2℃ / min, and hold for 30 to 60 minutes; The third stage, high-temperature final sintering: rapidly increase to the final sintering temperature at a rate of 2~3℃ / min, the final sintering temperature being 10~30℃ below the β phase transformation point of the titanium alloy, and hold at that temperature for 120~240 minutes. S4, Cooling After cooling to below 300°C in the furnace, high-purity argon gas is introduced to break the vacuum before the furnace is removed.

2. The method for controlling the density of titanium alloy powder metallurgy products according to claim 1, characterized in that, In step S1, the median particle size of the spherical powder is 25~45μm, and the median particle size of the hydrogenation dehydrogenation powder is 15~30μm.

3. The method for controlling the density of titanium alloy powder metallurgy products according to claim 1, characterized in that, Spherical titanium alloy powder and irregular hydrogenated dehydrogenated titanium alloy powder are mixed at a mass ratio of (70~90)%: (30~10)%.