High Temperature Titanium Alloy

High temperature titanium alloy, also known as high temperature titanium alloy. Titanium alloy with higher strength at 400～600℃. According to the organization, it is divided into α+β type and near α type titanium alloy. The typical martensitic α+β titanium alloy has BT9, the composition is Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, the service temperature is 500℃. Most practical alloys are near α alloys, Ti-6242 alloy composition is Ti-6Al-2Sn-4Zr-2Mo, and the operating temperature is 540℃; IMl-834 alloy composition is Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo -0.35Si, the use temperature can reach 600℃. Mainly used in the manufacture of aero-engine compressor discs and rotor blades. The manufacture of compressor discs requires high creep strength, and is suitable for bimodal organization or mesh basket organization. The manufacture of compressor rotor blades requires high fatigue strength at room temperature and high temperature, and isometric organization should be adopted.

High temperature titanium alloy, a titanium alloy for long-term use in high temperature environments. It has high instantaneous and lasting strength in the working temperature range, good creep resistance and good thermal stability. The main product that can work for a long time below 500°C is the high-aluminum equivalent martensite α+β type heat-resistant titanium alloy. They contain more evil. Stabilizing elements, with aluminum equivalents above 6%, are strengthened by solid solution. The phase obtains the corresponding high-temperature durability and creep strength; adding appropriate β-stabilizing elements (such as molybdenum) to improve the instantaneous strength and thermal stability. Typical alloys are: Ti-6Al-2.5Mo-2Cr-0.3Si-0.5Fe, Ti-6.5Al-3.3Mo-1.5Zr-0.25Si and Ti-6Al-2Sn-4Zr-6Mo. Long-term work above 500 ℃ is mainly near α-type heat-resistant titanium alloy. They not only contain a variety of α-stabilizing elements such as aluminum, tin, and zirconium, but also contain a small amount of β isomorphous stabilizing elements such as molybdenum and niobium, and the aluminum equivalent is almost all above 7%. Compared with the martensitic α+β type heat-resistant titanium alloy, the near-α type heat-resistant titanium alloy has higher creep resistance and better resistance to fatigue crack growth and fracture toughness above 500°C. Typical alloys are Ti-6Al-2Sn-4Zr-2Mo, Ti-5.5Al-2.5Sn-3Zr-1Nb-0.3Mo-0.3Si and Ti-6.5Al-2.5Sn-4Zr-1Nb-0.7Mo-0.15Si, etc. . The aluminum equivalent of all heat-resistant alloys is less than 8% per strand to ensure excellent thermal stability. Mainly used to manufacture discs, blades, guides, spacers, air intake receivers and other parts in gas engines

Heat-resistant titanium alloy is a titanium alloy suitable for long-term work at higher temperatures. It has high instantaneous and lasting strength in the entire operating temperature range. It has good plasticity, good creep resistance and good thermal stability at room temperature. It has good fatigue resistance at room temperature and high temperature. It is mainly used to manufacture discs, blades, air intake receivers and aircraft structural parts in compressors. The heat-resistant titanium alloys that have been used include solid solution strengthened α+β type and nearly α type titanium alloys. The α+β type heat-resistant titanium alloys that can work for a long time below 500°C, they all contain more α-stabilizing elements, and the aluminum equivalent is above 6. The addition of appropriate β-stabilizing elements makes the alloy not only display high instantaneous strength at high temperatures, but also have sufficient plasticity. Typical alloys are TC4 (Ti-6Al-4V), TC6 (Ti-6Al-2.5Mo-2Cr-0.5Fe-0.3Si) and TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si). Α-type heat-resistant titanium alloys that work for a long time below 500°C, they all contain a small amount of α-stabilizing elements. Almost all of the aluminum equivalent is above 7, and the alloy has more α phase in the equilibrium state, so these alloys have higher creep resistance and better fatigue resistance and fracture toughness above 500 ℃. Because the near-α alloy has these excellent comprehensive properties, it has become the main system of heat-resistant alloys. Typical alloys are Ti-8Al-1Mo-1V (Ti-811 in the United States), Ti-6Al-2Zr-1Mo-1V (BT-20 in Russia), Ti-6Al-2Sn-4Zr-2Mo (Ti-6242 in the United States) and Ti-5.5Al-3.5Sn-3Zr-1Nb-0.3Mo-0.3Si (UK IMI-829).

The development of heat-resistant alloys with a temperature higher than 500°C is mainly to solve the contradiction between the thermal strength and thermal stability of the alloy. At present, the heat-resistant titanium alloy used in foreign countries at 500～600℃ is the British IMI-834 (Ti-6Al-4.5Sn-4Zr-1Nb-0.5Mo-0.4Si-0.02Fe), and its maximum use temperature can reach 600℃. The US Ti-1100 (Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si-0.02Fe) is under evaluation. The heat-resistant titanium alloy used for the temperature of 600°C is nearly the only titanium alloy developed by Timet in 1988.

It is expected that a new type of heat-resistant titanium alloy with high damage tolerance, Ti3Al and TiAl as matrix intermetallic compounds. Ti3Al alloy has low plasticity at room temperature. Representative alloys are Ti-14Al-21Nb, Ti-14Al-21Nb-3V-2Mo alloy and Ti-24Al-10Nb, Ti-25Al-8Nb-2Mo-2Ta, Ti-25Al-10Nb -3V-1Mo and Ti-22Al-27Nb alloy.

The General Classification Of High Temperature Titanium Alloy

There are many ways to classify titanium alloys. According to the organization structure, it can be divided into α titanium alloy, α+β titanium alloy and β titanium alloy; according to the operating temperature, it can be divided into aircraft structure titanium alloy and engine structure titanium alloy; according to the purpose and characteristics, it can be divided into low-strength titanium alloy, medium High-strength titanium alloys, high-strength titanium alloys, ultra-high-strength titanium alloys, damage-tolerant titanium alloys, low-cost high-performance titanium alloys, etc.

(1) α-type titanium alloy

Industrial pure titanium and Ti are added with α-stabilizing elements such as Al or neutral elements Sn, Zr, etc., and the annealed microstructure is a single α-phase alloy called only type alloy. This type of alloy is dissolved in the α phase by adding α stabilizing elements to ensure the thermal strength and structural stability of the alloy. Such alloys generally cannot be strengthened by heat treatment. They have medium and low strength, good notch toughness and high temperature creep properties, as well as high plasticity, weldability and thermal stability, but they have poor processing properties.

Such alloys include industrial pure titanium (such as TA1, TA2, TA3, etc.) and Ti-AI, Ti-Al-Sn, Ti-Zr, Ti-Sn-Zr and other series such as TA6 (Ti-5Al), TA7 (Ti- 5Al-2.5Sn), TA16 (Ti-2Al-2.5Zr), TA19 (Ti-6Al-2Sn-42r-2Mo-0.1Si), etc. The alloy grades are represented by TA, such as TA1～TA28.

(2) Near α type titanium alloy

Add a small amount of β-stabilizing elements (≤2%) or Mo equivalent ≤2%, such as Mn, Mo, V, Nb, Cr, etc., to the instrument alloy, so that the balance microstructure of the alloy is mainly α phase , There is still a small amount of β phase (≤15%). This type of alloy has the advantages of only type alloys, and at the same time improves the processing performance due to the β phase. It can achieve a certain strengthening effect through heat treatment, and maintains better thermal strength, structural stability and good comprehensive performance at high temperatures. At present, most of the heat-strength titanium alloys belong to this category, such as IMI-834, Ti-1100, BT36, Ti-6242S and so on. In addition, because this type of alloy is not prone to plastic-brittle transition, it has good low-temperature properties and can be used at extremely low temperatures, such as Ti-5Al-2.5Sn.

The grades of this type of alloy are usually represented by TA. Such as TA12 (Ti-5.5Al-4Sn-2Zr-1Nb-1Mo-0.25Si), TA15 (Ti-6.5Al-2Zr-1Mo-1V) and so on. Some are also expressed by TC, such as TC1 (Ti-2AI-1.5Mn), TC2 (Ti-4AI-1.5Mn) and so on.

(3) α+β titanium alloy

When titanium contains a stable element and 2% to 8% B stable element V, Mo, Cr, Nb, Fe, etc. (or Mo equivalent is 2% to 10%), the equilibrium structure is generally only The main phase contains 10%-30% β phase. This type of alloy is α+β alloy, usually called two-phase titanium alloy. When the content of β phase in the alloy is 30% to 50%, it is also called β-rich alloy. The increase in the content of β phase in the alloy not only improves the processing performance of the alloy, but also increases the effect of heat treatment strengthening. Therefore, this type of titanium alloy has higher high temperature tensile strength and room temperature tensile plasticity, and better room temperature low cycle fatigue Strength and other properties, but also has a wide organizational variability, the performance can be adjusted by heat treatment, so that it can be used in low temperature environment (such as Ti-6Al-4V ELI), can also be used in the medium temperature range, such as Ti- 6Al-4V and Ti-6Al-2Sn-4Zr-6Mo are currently the most widely used titanium alloys of this type. The grades of α+β alloys are generally expressed by TC, such as TC4 (Ti-6Al-4V), TC4 ELI (Ti-6Al-4V ELI), TC4-DT (Ti-6Al-4V βELI), TC11 (Ti-6.5 A1 -3.SMo -1.52r -0.3Si), TC21 (Ti-6Al-2Zr-2Sn-3Mo-1Cr-2Nb-0.1Si), TC17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr), etc.

(4) β-type titanium alloy

The main elements added to this type of titanium alloy are Mo, V, Cr, etc. Beta titanium alloys have higher strength and excellent stamping properties, which can be further strengthened by quenching and aging. In the aging state, the structure of the alloy is β-phase dispersed and distributed fine α-phase particles.

The typical alloy grade is TB2, and its composition is Ti-5Mo-5V-8Cr-3Al, which is suitable for the manufacture of compressor blades, shafts, wheels and other heavy-duty parts.

Working conditions and composition

High-temperature titanium alloys are mainly used in the manufacture of aero-engine compressor parts, such as discs, blades, guides, spacers, air intake casings and other parts. These parts require materials to be high under high temperature working conditions (300～600℃). The specific strength, high temperature creep resistance, fatigue strength, endurance strength and organizational stability. With the increase of the thrust-to-weight ratio of aero engines, the increase in the outlet temperature of the high-pressure compressor causes the working temperature of the high-temperature titanium alloy blades and discs to continue to rise. After decades of development, the maximum working temperature of solid solution strengthened high-temperature titanium alloy has been increased from 350°C to 600°C.

The United States successfully developed the world’s first titanium alloy Ti-64 (Ti-6Al-4V) in the early 1950s, with a service temperature of 300~350℃, and then various countries have successively developed those with a service temperature of about 400℃. IMI-550, BT31 and other alloys; IMI-679, IMI-685, Ti-6246, Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) and other alloys whose use temperature is above 450℃; use temperature up to 550～600 ℃ IMI-829, IMI-834, Ti-6242S, Ti-1100, BT18Y, BT36 and other alloys. Among them, the most widely used titanium alloy grades are Ti-64 and Ti-6242. There are more than 70 new types of titanium alloys developed in my country. The 600℃ high temperature titanium alloys under development mainly include Ti-60, Ti-600 and other alloys. However, various performance indicators for long-term use in a 600℃ environment have yet to be verified.

The Application Of High Temperature Titanium Alloy

Titanium and titanium alloys are light, high-strength, and corrosion-resistant structural materials. They are used in aviation, aerospace, ships, weapons, chemicals, petrochemicals, metallurgy, electric power, light industry, salt making, construction, marine engineering, medicine, sporting goods and It has been widely used in daily life appliances and other fields.

Aero-engine is one of the earliest and most promising fields of titanium alloy application. As early as the 1870s, the amount of titanium alloy in Russian aero-engines reached 50% of the metal parts products. In recent years, it is worth noting that the amount of titanium alloy in military aircraft engine products has shown a downward trend, on the contrary, the amount of titanium alloy in large-scale civil engines has shown an upward trend.

This increasing trend is mainly due to the wider application of gas turbine engines in large passenger aircraft, the accumulation of experience in the production and application of titanium alloys, and the improvement in the performance and reliability of titanium alloys. At present, turbofan engines used in large passenger aircraft and transport aircraft are the most advanced. The application of titanium alloy in the new gas turbine fan engine, only from the point of view of weight reduction, its benefits are very obvious. In recent years, the production of such engines has increased significantly, and has shown a trend of further increase.

Compared with the new combustion turbofan engine, the amount of titanium alloy used in military engines has shown a downward trend. The main reason for the relative decrease in the amount of titanium used in military engines can be explained as small production batches or military aircraft. The desired engine is a supersonic engine-turbojet engine, so the amount of titanium used is relatively small.

Titanium alloys are mainly used in the manufacture of engine fans and compressor discs, blades and isolation devices, as well as engine intake casings, air collectors and other parts. Heat-resistant titanium alloys can generally work at a temperature of 500-550°C, even at 600°C, while structural titanium alloys can only work at 300-350°C.

Structural titanium alloys have better specific strength, plasticity and fracture resistance than heat-resistant titanium alloys. Therefore, structural titanium alloys are particularly suitable for the manufacture of blisks and blades of large-size turbofans.
A variety of materials and data indicate that the use of titanium alloys instead of steel materials for aircraft engines can reduce the weight of the engine structure by 30% to 40%. The economy of weight reduction mainly depends on the amount and design of the structural titanium alloy.