Titanium alloys and products manufactured therefrom

Abstract

The present invention discloses titanium alloys and products made therefrom. The present invention relates to non-ferrous metallurgy, namely the development of a low-alloyed titanium alloy characterized by high temperature strength and thermal stability, which can be used to manufacture products for long-term use at high temperatures, namely parts of the exhaust system of automobile engines. The titanium alloy contains aluminum, molybdenum, silicon, oxygen, nitrogen, iron and hydrogen, and the alloying elements, calculated in wt%, are: 1.5~3.0 Aluminum, 0.1-0.5 molybdenum, Silicone 0.1 to 0.6 Iron up to 0.2, Oxygen up to 0.15, Up to 0.1 carbon, Nitrogen up to 0.03, and 0.015 maximum hydrogen; and The balance includes titanium and unavoidable impurities. In one embodiment, the titanium alloy further contains 0.5 to 1.5 wt % copper, and a product is manufactured from the titanium alloy. The technical result of embodiments of the present invention is the production of titanium alloys that feature a combination of high mechanical and performance properties, including higher levels of creep resistance, and have cold forming capabilities.

Description

Technical Field

[0001] The present invention relates to non-ferrous metallurgy, i.e., to the development of low-alloyed titanium alloys characterized by high-temperature strength and thermal stability, and can be used for the production of products for long-term use at high temperatures, i.e., parts of the exhaust system of automobile engines.

Background Art

[0002] In various commercial applications, such as engines and exhaust systems, titanium alloys are used in the manufacture of parts such as intake and exhaust valves, housings, turbine impellers, pipes and tanks. In many of these applications, engine parts, especially exhaust systems, made of low-alloyed titanium alloys may have an operating temperature of 500 - 800 °C. Therefore, performance characteristics of the alloy such as high-temperature strength and oxidation resistance are prioritized. Also, since the parts are mainly manufactured by cold forming of metal rolling sheets and bending of welded pipes, the materials used should exhibit sufficient processing ductility.

[0003] As engine designers improve the efficiency of engines, characteristics such as boost pressure, compression ratio and operating temperature improve. To increase the levels of these characteristics, in the combustion chamber and exhaust system, materials that resist distortion (creep) at operating temperatures and pressures higher than those currently achievable with conventional low-alloyed titanium alloys are required. Creep, which is the sensitivity of a solid material to slow displacement or residual strain under load, occurs when a metal is subjected to a constant tensile stress at high temperature. High creep resistance allows the material to be used for a long time without deformation of shape and dimensions, but it is important to maintain the level of the characteristics of the raw materials.

[0004] Thus, in addition to being inexpensive, materials with an optimal combination of high mechanical and performance characteristics are required.

[0005] High-strength, oxidation-resistant titanium alloys are known, primarily composed of (calculated in wt%) 0.2 to less than 0.5% iron, 0.02 to less than 0.12% oxygen, 0.15 to 0.6% silicon, and the remainder being titanium and unavoidable impurities. These alloys further contain at least one element selected from the group consisting of Al, Nb, V, Mo, Sn, Zr, Ni, Cr, and Ta, in a total content of less than 1.5% (U.S. Patent No. 7,767,040, published August 3, 2010, IPC C22C14 / 00).

[0006] This alloy exhibits high plasticity but has low resistance to high-temperature oxidation.

[0007] Low-alloy titanium alloys are known to exhibit excellent resistance to high-temperature oxidation and corrosion. These alloys are used as materials for exhaust systems in automobiles or motorcycles, and prototypes contain (calculated in wt%) 0.30-1.50% Al, 0.10-1.0% Si, and 0.1-0.5% Nb (U.S. Patent No. 7,166367, published January 23, 2007, IPC B32B15 / 01, C22C14 / 00, F01N7 / 16).

[0008] This alloy exhibits high strength and plasticity at both room temperature and high temperatures, but its resistance to high-temperature creep is insufficient. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention aims to develop a low-alloy titanium alloy that can be used to manufacture a variety of products, including those used in automobile engine components and exhaust systems. [Means for solving the problem]

[0010] The technical result of the embodiments of the present invention is to produce a titanium alloy that has cold-formability and is characterized by a combination of high mechanical properties and performance properties, including a higher level of creep resistance.

[0011] The technical results show a titanium alloy containing aluminum, molybdenum, silicon, oxygen, nitrogen, iron, and hydrogen, with the alloy composition calculated in wt%. 1.5~3.0 aluminum, 0.1-0.5 molybdenum, Silicone with a thickness of 0.1 to 0.6 mm, Up to 0.2 iron, Maximum 0.15 oxygen, Up to 0.1 carbon, Up to 0.03 units of nitrogen, and It contains a maximum of 0.015 units of hydrogen, and This is achieved by a titanium alloy containing titanium and inevitable impurities (Titanium and inevitable impurities - balance) in the remainder. In one embodiment, the titanium alloy further contains 0.5 to 1.5 wt% copper, and the product is manufactured from this titanium alloy. [Brief explanation of the drawing]

[0012] [Figure 1] The tensile properties of the alloy under (annealed) delivery conditions are shown in the comparative graph in Figure 1. [Figure 2] The results of evaluating oxidation resistance compared to the prototype alloy are shown in Figure 2, which is a graph of the increase in alloy weight as a function of the square root of oxidation time at 560°C. [Figure 3] The results of evaluating oxidation resistance compared to the prototype alloy are shown in Figure 3, which is a graph of the increase in alloy weight as a function of the square root of oxidation time at 800°C. [Figure 4] The results of the creep resistance of the claimed alloy compared to the prototype alloy are shown in the graph in Figure 4. [Modes for carrying out the invention]

[0013] Alloying elements are introduced into the alloy composition from a variety of stabilizers, including α-stabilizers such as aluminum, oxygen, carbon, and nitrogen, and β-stabilizers such as molybdenum, iron, and silicon. In one embodiment of the present invention, copper as a β-stabilizer is introduced into the alloy.

[0014] Aluminum improves high-temperature strength and creep resistance, and reduces scale formation at high temperatures. The aluminum content in the alloy is set to 1.5-3.0 wt%. To maintain optimal ductility, the maximum aluminum content in the alloy is limited to 3.0 wt%.

[0015] When the oxygen, nitrogen, and carbon content is within the specified limits, it not only improves strength but also raises the temperature of titanium's allotropic transformation, ensuring the maintenance of high levels of strength and ductility. Higher concentrations of oxygen, carbon, and nitrogen reduce the alloy's ductility and impact strength.

[0016] Regarding the group of β-stabilizers (Mo, Fe, Si, Cu) The addition of 0.1-0.5 wt% molybdenum to the alloy promotes improved strength due to the appearance of a β phase layer in the structure, functions as an interphase boundary, suppresses dislocation movement during deformation, and prevents the growth of α particles at high temperatures. However, when the molybdenum content exceeds 0.5 wt%, the high-temperature strength decreases because the β transition temperature of the alloy decreases and the amount of β phase in the structure increases.

[0017] The presence of silicon in an alloy within a titanium solid solution improves creep resistance. The silicon content in the alloy is set to 0.1-0.6 wt%. Within this range, silicon forms intermetallic compounds containing titanium silicide (Ti3Si). When the required amount of silicide is formed in the alloy, it improves high-temperature strength and creep resistance, and prevents the growth of α-particles at high temperatures. Furthermore, silicon significantly improves the oxidation resistance of the alloy up to a concentration of 0.6 wt%. At higher concentrations, ductility and formability decrease.

[0018] The alloy may further be alloyed with copper. Copper is a eutectoid-forming element, has a high solubility in the titanium α-phase, and exhibits the effect of solid solution strengthening. The formation of Ti2Cu intermetallic particles that limit the movement of boundaries at high temperatures helps improve the high-temperature strength of the alloy. However, an excessive number of Ti2Cu phase particles reduces the ductility of the alloy at room temperature. Therefore, the copper content in the proposed alloy is set at a maximum of 1.5 wt%.

[0019] The maximum hydrogen content in the alloy, which is limited to 0.015 wt%, helps avoid embrittlement of the alloy due to the potential formation of titanium hydride.

[0020] The composition of elements, which is introduced into the alloy at a predetermined ratio and is characterized solely by imparting a favorable effect on the oxidation resistance of titanium, helps achieve an additive effect of obtaining a high creep resistance value of the alloy while ensuring strength and plasticity with sufficient oxidation resistance compared to conventional low-alloyed titanium alloys.

[0021] The industrial applicability of the present invention is demonstrated by exemplary embodiments.

[0022] According to an industrial process using the vacuum arc remelting method, the compositions of two ingots weighing 2100 kg were melted to measure the properties of the proposed alloy. The chemical compositions No. 1 and No. 2 of the alloy are shown in Table 1.

[0023]

Table 1

[0024] A coil with a thickness of 0.9 mm was produced by hot working an ingot through forging and rolling. Samples were taken under the extrusion conditions, and the mechanical properties of the alloy were evaluated. Tensile tests were performed at temperatures of 20°C, 500°C, and 700°C to analyze the mechanical properties, and the Erichsen deep drawing cup test was performed to evaluate the criteria for material formability. The tensile property values ​​of the alloy under (annealed) extrusion conditions are shown in Table 2, and a comparison graph is shown in Figure 1.

[0025] [Table 2]

[0026] To simulate the material performance of the product in operation, samples of both compositions were isothermal annealed in static experimental air at temperatures of 560°C and 800°C, with holding times of 100 hours and 200 hours, respectively. The results were then measured in mg / cm². 2 The oxidation resistance was evaluated by calculating the weight increase of the sample represented by [formula]. The results of evaluating the oxidation resistance compared to the prototype alloy are shown in the graphs of the increase in alloy weight as a percentage of the square root of the oxidation time at 560°C and 800°C, respectively, in Figures 2 and 3.

[0027] Furthermore, creep resistance, expressed as a function of relative strain at a stress of 30 MPa, was measured for alloy samples under the specified discharge conditions at 500°C for 100 hours. The results of the claimed alloy's creep resistance compared to the prototype alloy are shown in the graph in Figure 4.

[0028] Analysis of test results and evaluation data revealed that the proposed alloy exhibits a superior combination of mechanical and performance properties, including high-temperature creep resistance, compared to conventional low-alloy alloys. The evaluation results of the oxidation resistance of alloy samples after long-term isothermal annealing demonstrate the durability of the material.

Claims

1. A titanium alloy containing aluminum, molybdenum, silicon, iron, oxygen, carbon, nitrogen, and hydrogen, wherein the alloy composition, when calculated in wt%, is: 1.5 to 3.0 aluminum, 0.1 to 0.5 molybdenum, Silicone of 0.1 to 0.6 Up to 0.2 iron, Maximum 0.15 oxygen, Up to 0.1 carbon, Up to 0.03 units of nitrogen, and It contains a maximum of 0.015 units of hydrogen, and Titanium alloy, consisting of the remainder being titanium and unavoidable impurities.

2. The alloy according to claim 1, further containing 0.5 to 1.5 wt% of copper.

3. A titanium alloy product characterized by being manufactured from the alloy described in claim 1 or 2.

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