As an important structural metal developed in the mid-20th century, titanium has advantages such as high strength, low density, high heat resistance, good corrosion resistance, and good toughness. It is mainly used in the aerospace industry. With the rapid development of economy and technology, in recent years, there have been some breakthrough results in the process research of titanium alloys. Titanium alloys have also been widely used in automobile, marine, petrochemical, medical, shipbuilding and other industries.
Current research on the residual stress, corrosion resistance, fatigue life and creep phenomena of titanium alloy TC4 is insufficient. Based on this, this article analyzes the residual stress, corrosion resistance, fatigue life and creep phenomena of titanium alloy TC4, and provides a certain reference for the performance research of titanium alloy TC4.
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1. Residual stress of titanium alloy TC4
During the processing of titanium alloy TC4, continuous heating at high temperatures will cause certain differences in the heating rates of different areas of the forging. The resulting temperature difference causes residual stress in the forging, causing deformation and fracture of the forging. In response to this problem, Lu Xiaogen et al. used segmented heating to reduce the temperature difference in different areas during the heating process, that is, preheating and insulation before heat treatment, and then heat treatment, which improved the temperature uniformity of the forging and then reduced its residual stress, improving Performance and quality of forgings.
During the heat treatment process of steel, quenching can improve the performance of the steel. However, the selection of quenching medium, quenching intensity, and quenching process parameters during the quenching process all have a certain impact on the evolution of the residual stress of the steel. This impact is mainly on the steel. Caused by the inhomogeneity of the heat transfer process between the quenching medium and the quenching medium.
For titanium alloy TC4, the deformation temperature, deformation degree, and deformation rate are factors that affect its residual stress. When the temperature and rate of deformation are greater, the forging itself will dynamically recover and start the dynamic recrystallization of the forging, which is beneficial to improving the forging. The organizational performance will be more beneficial. In the actual production process, appropriately increasing the deformation temperature and deformation rate of forgings and reducing the degree of deformation of forgings can reduce the residual stress generated during the forging process, thereby improving the quality of the product.
When the degree of deformation of the forging is low, the TC4 titanium alloy forging can dynamically recover autonomously, which helps to reduce the residual stress of the forging. When the degree of deformation of the forging increases, the TC4 titanium alloy forging can dynamically recrystallize. At this time, Will increase the residual stress of forgings. Therefore, when selecting the degree of deformation, the degree of deformation of the forging should be reduced as much as possible.
2. Corrosion resistance of titanium alloy TC4
Different heat treatment processes such as annealing, solid solution, and aging can have different effects on the microstructure of titanium alloys, and in turn affect the corrosion resistance of titanium alloys. The phase composition, chemical element composition, and grain size of titanium alloy TC4 can all affect the corrosion resistance of titanium alloy TC4.
As the annealing temperature rises and the annealing time increases, the equiaxed phase size of TC4 titanium alloy increases (the β phase content increases and the α phase content decreases) and the corrosion resistance decreases. Adding elements Cr and Fe to titanium alloy TC4 can lower the martensitic transformation temperature, thereby improving the stability of the β phase and improving the corrosion resistance of titanium alloy TC4. The martensite structure obtained after solution treatment can enhance the corrosion resistance of titanium alloy materials. However, if the solution temperature decreases, not only the martensite structure will be obtained after solution treatment, but also an α-lamellar structure will be obtained. At this time, titanium The corrosion resistance of the alloy will decrease accordingly. Therefore this process is affected by the solution temperature.
The corrosion resistance of titanium alloys is mainly due to the passivation film of titanium alloys. This passivation film has strong protection for titanium alloys. The passivation film is a mixed structure composed of different oxides, but its specific composition The composition and changes require further analysis and research. When in a hydrochloric acid environment, titanium alloy TC4 suffers from pitting corrosion. This phenomenon is mainly affected by the roughness of the surface of TC4 titanium alloy. If an oxide coating is added to the surface of titanium alloy TC4, the corrosion properties of TC4 titanium alloy can also be changed. The corrosion resistance of the oxide coating is mainly affected by factors such as the number of micropores, pore size, film thickness and composition. The addition of graphene mainly changes the composition and structure of the oxide coating, producing SiC and graphene, SiC and graphene can improve the corrosion resistance of the coating.
Seawater temperature, pressure, pH, and dissolved oxygen content will all affect the corrosion resistance of the material. Microorganisms in the ocean are also a complex group. The impact of microbial attachment and metabolism on TC4 titanium alloy materials is also an unknown issue that requires further research. research.
3. Fatigue life of titanium alloy TC4
When the elastic modulus, tensile strength, yield strength and area reduction of TC4 titanium alloy increase, the fatigue life of the forging will also increase, and there is a positive correlation between them. But this is also the result of single factor analysis. In actual production, temperature and external loads will cause residual stress in forgings, and the generated residual stress will be released with changes in the external environment, which will accelerate the end of the fatigue life of forgings. Therefore, it is a research direction to conduct in-depth research on the fatigue life of TC4 titanium alloy and explore its mechanism of action based on various factors including residual stress, mechanical properties, etc.
The coating can significantly improve the fatigue life of titanium alloy TC4. The fatigue life of the coating will be different under different conditions. Defects in the coating will form cracks on the alloy surface and reduce the fatigue life of titanium alloy TC4. For nickel-titanium alloys, the biocompatibility and fatigue performance of nickel-titanium alloys can be improved by studying its chemical composition, surface coating, surface oxidation, improved processing technology, heat treatment methods, etc., or the research on titanium alloys provide certain ideas.
Microscratches measured in microns on the surface of titanium alloys can significantly reduce the fatigue life of the alloy material, reducing it from extremely high cycle fatigue to high cycle fatigue. Compared with the direction and length of the scratches, the fatigue life of titanium alloys is insignificant. Obviously, the depth and width of scratches have a significant impact on the fatigue life of titanium alloy TC4, which also points out the direction for the research on the fatigue life of titanium alloys.
4. Creep properties of titanium alloy TC4
The occurrence of creep will cause deformation and rupture of forgings, affect the normal operation of forgings, and bring safety hazards and profit losses to industrial production, aerospace, road transportation, etc. There are many factors that affect the creep phenomenon of titanium alloys. The creep behavior of titanium alloys is not only related to the external service environment, but also related to the chemical composition of the alloy, the processing technology, and the size and shape of the forgings.
At low stress levels, the creep of titanium alloys becomes larger with the increase of temperature; at higher stress levels, the creep of titanium alloys in the β forging zone becomes larger with the increase of temperature, α The creep of titanium alloy in the +β forging zone is opposite, and the creep of titanium alloy is not highly sensitive to the amount of forging deformation. Under high temperature environment, the structure and properties of TC4 titanium alloy will change, and due to the sensitivity of titanium alloy, forgings need to have better creep resistance.
The ultra-fine grain structure and the composition of the non-equilibrium phase will also affect the creep properties of titanium alloy TC4, making the titanium alloy contrary to the classic creep power law. During the creep process, the alloy undergoes a β-α phase transformation, and the alloy undergoes The redistribution of elements reduces the creep activation energy of the alloy and improves the creep resistance of the alloy.
Under room temperature conditions, external pressure can refine the structure of TC4 titanium alloy, improve the resistance to plastic deformation of the forging, and at the same time reduce the creep amount of the forging and the creep rate of the material. In addition, the increase in hardness can also improve the creep resistance of the material. At different stress levels, the creep residual variables and creep rates of titanium alloy forgings are also different. They increase with the increase of stress level, but their changing trends are the same.
Under higher stress conditions, the recovery process of the material will become very slow or even ineffective compared to the fast deformation speed. The internal stress during the creep process increases rapidly in the initial stage and becomes stable in the stable stage, and the internal stress increases with the increase of external stress.
Different TC4 titanium alloy materials have different chemical compositions of elements. Adding rare earth elements can improve the high-temperature creep properties of titanium alloy materials. Different rare earth elements added have different effects. For example, after adding the rare earth element Ce to the Ti-Al-Sn-Zr-Mo-Nb-Si alloy, the creep resistance of the alloy decreases. Adding rare earth elements to titanium alloys mainly plays a role in three aspects to improve its creep properties, namely, the internal oxidation of rare earth elements reduces the oxygen content of the alloy matrix, resists the precipitation and development of the alpha phase of the alloy, and promotes the uniform precipitation of fine silicides. At present, further research is needed on the influence of Si and Sc on the creep properties of titanium alloys, especially the rare earth element Sc. Therefore, studying the influence and mechanism of rare earth elements on the creep properties of titanium alloys is one of the future research directions.
Supplier
TRUNNANO is a supplier of TC4 titanium alloy with over 12 years experience in nano-building energy conservation and nanotechnology development. It accepts payment via Credit Card, T/T, West Union and Paypal. Trunnano will ship the goods to customers overseas through FedEx, DHL, by air, or by sea. If you are looking for high-quality TC4 titanium alloy materials, please feel free to contact us and send an inquiry.
