What is the difference between pure titanium and titanium alloy GR5?

Commonly used titanium grades

GR1 (Grade2) industrial pure titanium

GR2 (Grade3) industrial pure titanium

GR7 (Grade11) Ti-0.2Pd

GR10 (Grade12) Ti-0.3Mo-0.8Ni

GR5 (AB-1) Ti-6Al-4V

Industrial pure titanium is divided into three grades: GR1, GR2 and GR3 according to its impurity content. The interstitial impurity elements of these three types of industrial pure titanium gradually increase, so their mechanical strength and hardness also gradually increase, but the plasticity and toughness decrease accordingly.

The industrially pure titanium commonly used in industry is GR2 because of its moderate corrosion resistance and comprehensive mechanical properties. GR3 can be used when higher wear resistance and strength requirements are required. GR1 can be used when better molding performance is required.

GR1, GR2 and GR3 in the national standard correspond to Gr0, Gr1 and Gr2 in the UNS.

GR1 and GR2 have good low-temperature toughness and high low-temperature strength when the iron content ω is 0.095%, the oxygen content ω is 0.08%, the hydrogen content ω is 0.0009%, and the nitrogen content ω is 0.0062%, and can be used as Low temperature structural materials below -253℃.

The difference between GR1 and GR2 is that the latter has higher iron and oxygen content, so the strength of GR2 is higher than GR1.

GR5 represents most low-temperature titanium alloys. Its strength will increase as the temperature decreases, but its plasticity will not change much. It maintains good ductility and toughness at low temperatures of -196-253°C, avoiding the cold brittleness of metal, which makes it an ideal material for cryogenic containers, storage boxes and other equipment.

There are many brands and varieties of titanium alloys, more than 100 types. There are 40-50 types available in industry, and only a dozen are most commonly used. These include various industrial pure titanium and selected titanium alloys of different tastes, such as Ti-6AL-4V, Ti-5AL-2.5Sn, Ti-2AL-1.5Mn, Ti-3AL-2.5V, Ti-6AL- 2Sn-4Zr-2Mo, Ti-6AL-2Sn-4Zr-6Mo, Ti-8AL-1Mo-1V, Ti-13V-11Cr-3AL, Ti-15V-3Cr-3AL-Sn and Ti-10V-2Fe-3AL and Ti-0.20Pd, Ti-0.3Mo-0.8Ni, etc. However, for most countries, the first two important alloys (Ti-6Al-4V; Ti-5Al-2.5Sn) are the most typical and recognized by countries around the world.

Titanium alloys are generally named according to their structures, namely α titanium alloys (including near α titanium alloys), β titanium alloys and (α+β) titanium alloys. In Chinese national standards, TA, TB, and TC are used as prefixes to represent the type of titanium alloy, followed by a number to represent the alloy serial number. For example, TA represents alpha titanium alloy, GR6 titanium alloy is Ti5Al-2.5Sn alloy; TB represents beta titanium. Alloy, TB2 is Ti-5Mo-5V-8Cr-3Al alloy; TC represents α+β alloy, such as GR5 titanium alloy is Ti-6Al-4V alloy.

Alpha titanium alloys mainly contain alpha stable elements. In a stable state at room temperature, they are basically alpha phase titanium alloys, such as industrial pure titanium (GR1, GR2, GR3, GR4) and GR6 (Ti-5Al-5Sn). Alpha titanium alloys are mainly used in the chemical, petrochemical and processing industries. In these industries, the primary consideration is the corrosion resistance and processability of the alloy. Industrial pure titanium (TA0-GR3 four types), GR7 titanium alloy palladium-containing alloy ( GR7 titanium-palladium alloy) and alloys containing small amounts of molybdenum and nickel (GR10 titanium-molybdenum-nickel alloy) are preferred.

Near α titanium alloy, a small amount of β stabilizing elements are added to this type of titanium alloy. In a stable state at room temperature, the annealed structure contains a small amount of β phase or intermetallic compounds, generally not more than 10%, such as GR11 (Ti-8Al-1Mo-1V ), which is a titanium alloy developed in the United States for use at high temperatures, but high aluminum content can cause thermal salt stress corrosion problems; GR15 (Ti-6.5Al-1Mo-1V-2Zr) is a BT20 alloy developed in Russia. GR11 titanium alloy is a similar alloy to GR15 titanium alloy. The latter reduces the aluminum content and increases zirconium, thus maintaining heat resistance and improving hot salt effect stress corrosion. α+ compound alloy GR13 (Ti-2.5CU) is an IMI230 alloy developed in the UK.

α+β titanium alloy contains more β-stabilizing elements and is a titanium alloy composed of α and β phases in a stable state at room temperature. β content is generally 10%-50%. α+β titanium alloy has medium strength and can be strengthened by heat treatment, but its welding performance is poor. Depending on the molybdenum equivalent, this type of alloy can be divided into martensitic and transitional types. Among them, the typical alloy Ti-6Al-4V was developed by the Water City Arsenal in the United States in 1954. It is widely used in the aerospace industry. This alloy product accounts for 55%-65% of titanium alloy production and can be used to produce various large-sized aerospace products. Forgings and parts, Ti-6Al-4V alloy has excellent comprehensive properties, is the most intensively researched, has been used for the longest time, and has the widest range of applications. Therefore, the alloy has maintained strong vitality since its birth half a century ago. The Chinese brand is GR5, the Timet division of the American Titanium Metal Company is Ti-6Al-4V, the American Active Metal Company is RMI6Al4V, the British Titanium Company is IMI318, Russia is BT6, Sumitomo of Japan is ST-Al40, and France is TA6V. Germany is LT31.

Adding elements to titanium alloys are expressed by molybdenum equivalent [Mo1]ep and aluminum equivalent [Al]ep: α and near-α titanium alloy [Mo1]ep is 12-13, [Al]ep is 5-8; α+β titanium Alloy [Mo1] ep is 5-12, [Al] ep is 6-30; β titanium alloy (metastable alloy) [Mo1] ep is 12-25, [Al] ep is 5-8. It is more suitable for designers to classify according to intensity, which can be divided into low intensity, normal intensity, medium intensity, high intensity and maximum intensity.

⑴Industrial pure titanium

Industrial pure titanium is dense metallic titanium with a titanium content of not less than 99% and containing a small amount of iron, oxygen, carbon, nitrogen, hydrogen and other impurities. The impurities that have the most obvious impact on the mechanical properties of pure titanium are oxygen, nitrogen and iron, especially oxygen. The reaction between hydrogen and titanium is reversible. The main impact of hydrogen on titanium's performance is "hydrogen embrittlement". It is usually stipulated that the hydrogen content should not exceed 0.03%-0.05% hydrogen. Although industrial pure titanium has a close-packed hexagonal lattice (α) at room temperature, its axial ratio is small (c/a=1.587) and has good processability. Pure titanium has good formability and welding properties and is not sensitive to heat treatment.

Industrial pure titanium has been included in the ISO5832-2-1999 international standard as a metal material for surgical implants. Materials that meet the long-term implants should have the following basic requirements: corrosion resistance, biocompatibility, superior tensile strength, fatigue resistance and It has good toughness, elastic abrasive tools, wear resistance and a satisfactory price.

⑵ Corrosion-resistant titanium alloy

Corrosion-resistant titanium alloys are suitable for use in highly corrosive media, mainly low-strength alloys. In non-aerospace fields, the advantage of good corrosion resistance is mainly used. Corrosion-resistant titanium alloys improve the corrosion resistance of industrial pure titanium in reducing media (such as hydrochloric acid, sulfuric acid, phosphoric acid, oxalic acid and formic acid). Currently, mature titanium molybdenum, titanium palladium, titanium molybdenum nickel, titanium nickel, titanium tantalum, etc. alloy.

Titanium-molybdenum alloy was the earliest studied (in 1952). It has excellent corrosion resistance in reducing hydrochloric acid. Ti-30Mo alloy is resistant to boiling 5% carbonic acid, boiling 5% sulfuric acid, boiling 10% phosphoric acid, boiling In 10% acetic acid and boiling 50% formic acid, the general maximum corrosion rate is 0.0254-0.0508mm/a. The corrosion rate of pure titanium in 10% sulfuric acid solution at 93.3°C reaches 38.1-50.8mm/a; Ti-30Mo alloy in Corrosion resistance in oxidizing media is poor. Due to the addition of high-density molybdenum-hafnium alloy, the smelting, processing and welding will bring certain air disasters. From titanium-molybdenum alloys, corrosion-resistant titanium alloys such as titanium-molybdenum-niobium, titanium-molybdenum-zirconium, and titanium-molybdenum-palladium are derived.

GR7 titanium-palladium alloy has excellent corrosion resistance in oxidizing media. It also has certain corrosion resistance to reducing media, and can especially improve its resistance to crevice corrosion in media with high chloride ion concentration. GR7 titanium alloy contains 0.2% palladium. In 5% boiling sulfuric acid, GR7 titanium-palladium alloy can reduce the corrosion rate from 48.26mm/a (industrial pure titanium) to 0.508mm/a, and increase the corrosion resistance by about 95 times. The alloy has good processing, forming and welding properties, but contains the precious metal palladium and is costly.

Beta titanium alloy. This type of titanium alloy contains enough beta stable elements. At an appropriate cooling rate, the room temperature structure is all beta phase. It can usually be divided into heat-treatable beta titanium alloy (meta-stable beta titanium alloy) and stable beta titanium. alloy. Heat-treatable beta titanium alloy has very good process plasticity under quenching conditions, can be cold formed into plates, and can obtain room temperature tensile strength of up to 1300-1400MPa through aging treatment.

The nominal composition of GR10 titanium-molybdenum-nickel alloy is Ti-0.3Mo-0.8Ni. It is a Ti-12 alloy researched and developed by the United States in the mid-1970s. It is a titanium alloy resistant to crevice corrosion. The tensile strength of the alloy at 300°C It is twice as high as pure titanium, and its corrosion resistance to reducing media is significantly improved. Crevice corrosion does not occur in chloride at 150-200°C.

The use temperature of titanium-nickel alloy (Ti-2Ni) in high-temperature desalination equipment can reach about 200°C.

Titanium-tantalum alloy (Ti-5Ta) is a nitric acid corrosion-resistant α-type titanium alloy produced by Russia under the 4204 alloy brand and Japan's Kobe Steel under the KS50Ta brand. The alloy has good process performance and welding performance, and the corrosion rate in flowing nitric acid at 100-200°C is less than 0.1mm/a. It has been applied in nitric acid recovery equipment and nuclear fuel reprocessing processes.

⑶Structural titanium alloy

Low-strength titanium alloys classified by strength are mainly used in corrosion-resistant environments, while other titanium alloys are used in structural parts, called structural titanium alloys. Ordinary strength titanium alloys (about 500MPa), mainly including industrial pure titanium, Ti-2Al-1.5Mn (TC1), and Ti-3Al-2.5V (GR18), have been widely used. Due to its good processing and formability properties and weldability, the alloy is used to make various aviation plate parts and hydraulic pipes, as well as bicycle civilian products. The typical alloy of medium-strength titanium alloy (about 900MPa) is Ti-6Al-4V (GR5), which is widely used in the aerospace titanium alloy industry. Plate high-strength titanium alloy has a room temperature tensile strength of more than 1100MPa. It is composed of near-β titanium alloy and metastable β-titanium alloy. It is mainly used to replace high-strength structural steel commonly used in aircraft structures. Its typical alloys are Ti-13V- 11Cr-3Al, Ti-15V-3Cr-3Al-3Sn and Ti-10V-2Fe-3Al alloys, etc.

4. Heat-resistant titanium alloy

Heat-resistant titanium alloy is a titanium alloy suitable for long-term operation at higher temperatures. It has high instantaneous and durable strength over the entire operating temperature range. It has good thermal stability, creep resistance and plasticity at room temperature, and has good fatigue resistance at high temperature. It is mainly used to manufacture discs, blades, air intake casings and aircraft components in compressors. Heat-resistant titanium alloys have been solid solution strengthened α + β type and near α type titanium alloys. α+β type heat-resistant titanium alloys that can work for a long time below 500°C contain more α-stabilizing elements, and the aluminum equivalent is above 6. By adding appropriate beta stabilizing elements, the alloy not only displays high instantaneous strength at high temperatures, but also has sufficient plasticity. Typical alloys include GR5 (Ti-6Al-4V), TC6 (Ti-6Al-2.5Mo-2Cr-0.5 Fe-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 contain a small amount of α-stabilizing elements. The aluminum equivalent is almost all 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°C. Because the nearly α-type alloy has these excellent comprehensive properties, it has become the main system of heat-resistant alloys. Typical alloys are Ti-8Al-1Mo-1V (US Ti-811), Ti6Al-2Zr-1Mo-1V (Russian BT20), Ti-6Al-2Sn-4Zr-2Mo (US Ti-6242) and Ti-5.5Al -3.5Sn-3Zr-1Nb-0.3Mo-0.3Si (UK IMI-829).

5. Low temperature titanium alloy

Low-temperature titanium alloys are α and α+β titanium alloys suitable for use at low temperatures. This type of alloy increases as the temperature decreases, and its toughness rarely decreases as the temperature decreases, so it can be used as low-temperature structural parts. The development trend of low-temperature titanium alloys is to reduce the oxygen content from 0.2% (ordinary grade) to 0.12% to form extremely low gap grade titanium alloy (ELI). Can be used at ultra-low temperatures (<77K). Typical alloys are Ti-5Al-2.5Sn (ELI). Ti-5Al-2.5Sn (ELI is the US military standard MIL-9047) developed in the United States in the early 1960s. China successfully copied the alloy in the late 1970s and called it GR6 titanium alloy, Ti-5Al-2.5Sn (ELI) alloy. Especially suitable for liquid fuel storage containers operating at low temperatures of -255°C. There are many brands and varieties of titanium alloys, more than 100 types. There are 40-50 types available in industry, and only a dozen are most commonly used. These include various industrial pure titanium and selected titanium alloys of different tastes, such as Ti-6AL-4V, Ti-5AL-2.5Sn, Ti-2AL-1.5Mn, Ti-3AL-2.5V, Ti-6AL- 2Sn-4Zr-2Mo, Ti-6AL-2Sn-4Zr-6Mo, Ti-8AL-1Mo-1V, Ti-13V-11Cr-3AL, Ti-15V-3Cr-3AL-Sn and Ti-10V-2Fe-3AL and Ti-0.20Pd, Ti-0.3Mo-0.8Ni, etc. However, for most countries, the first two important alloys (Ti-6Al-4V; Ti-5Al-2.5Sn) are the most typical and recognized by countries around the world.