Titanium Alloy Properties

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Titanium Alloy Properties

مُساهمة من طرف Admin في الأحد نوفمبر 07, 2010 12:19 am

Introduction


Titanium does not occur free in Nature. However, when combined with other elements, it is quite abundant, occurring in small amounts in most of the volcanic, sedimentary and metamorphic rocks.

Its more important minerals are ilmenite, rutile, arizonite (iron titanate), brookite, anatase, leucochene (titanium dioxide), perovskite (calcium titanate), and others. The first two have commercial importance, and can be found in deposits spread all over the world. There are important rutile and ilmenite deposits in Australia, Argentina, USA, Central Africa, Brazil, Canada, Egypt, India and Norway. The largest well-known deposits of rutile are located in Australia.

Titanium and its alloys are relatively new engineering metals since they have been in use only since about 1952. They are extremely attractive materials for engineers because they have a high strength to weight ratio, high elevated temperature properties to about 550oC, and excellent corrosion resistance particularly in oxidising acids and chloride media. This metal is being increasingly used for marine applications. Its resistance to seawater attack combined with its mechanical properties make it a prime choice for equipment operating within the sea or transferring seawater.

Titanium is not an 'exotic' metal, it is the fourth most abundant structural metal in the earth's crust, and the ninth industrial metal. This metal has become the prime selection for a wide range of critical and demanding applications.

Pure Titanium


Titanium is a light metal having a density of about 4540 kg/m3. This compares to steel at 7900 kg/m3 and Aluminium at 2710kg/m3. Titanium has a melting point of about 1668oC which is higher than iron at1560oC. Titanium has a Modulus of Elasticity of 110 x 109 Pa. compared to steel at 210 x 109 Pa. Therefore Titanium has a significantly high deflection under the same load than steel. Pure Titanium can be cold rolled to 90% reduction in thickness at room temperatures without cracking.

There are a number of grades of commercially pure (unalloyed) titanium as identified in ASTM B265 (Gr,1,2,3,4,7,11,and 12) (see table below for Gr 1 to 4)). Each grade has a different amount of impurity content (Grade 1 have lowest impurities). Grade 1 to 4 are classified as pure even though grade 4 is much stronger and less ductile than grade 1. Grade 4 contains higher levels of oxygen which is classified ( for pure titanium ) as an alloying element. Oxygen and Nitrogen and Carbon are all interstitial alloys (they insert themselves in the crystal intertices of the crystals and prevent relative sliding). They therefore increase the hardness and reduce the ductility. Oxygen is the main element controlling the strength of unalloyed titanium.

Titanium Alloys


Titanium Alloys are generally divided into three groups (Alpha, Alpha-Beta and Beta). The Alpha group contain most importantly aluminum and tin. They can also contain molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon. Alpha alloys are not suitable for heat treatment. Alpha alloys are used for aircraft parts and cryogenic equipment.

The Alpha-Beta group can be strengthened by heat treatment. The alloys are used in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware.

The Beta Alloys have good hardenability. Beta alloys are slightly more dense than other titanium alloys, having densities ranging from 4800 to 5050 kg/m3. They are the least creep resistant alloys, they are weldable, and can have yield strengths up to 1345 x 106 Pa.(Solution treated and age hardened) Beta alloys are the smallest group. They are used for heavier duty purposes on aircraft.




Information Tables


The tables below are based on USA ASTM Grades which seem to be the most popular. I also have information on CEN (European grades). These are not as popular and I have not included them at this stage. This information is not detailed and I will attempt to improve its quality over time. Please use the links below for better information.




ASTM B265 Notes
Grade 1 Unalloyed Titanium..Main use in heat exchangers, Airframes, Chemical: desalination and marine parts: Plate-type heat exchangers: cold spun or pressed parts : Platinised anodes: High formability
Grade 2 Unalloyed Titanium. Airframes, aircraft engines: marine chemical parts: heat exchangers: condenser and evaporator tubing. Good combination of strength, formability, ductility and weldability.
Grade 3 Unalloyed Titanium. Chemical, marine, airframe and aircraft engine parts which require formability strength, weldability and corrosion resistance.
Grade 4 The highest strength pure unalloyed Titanium: Chemical, marine, airframe and aircraft engine parts: surgical implants: high speed fans: gas compressors: Used in hydraulic and instrumentation tubing: good formability and corrosion resistance combined with high strength.
Grade 5 Titanium alloy. 6% aluminium, 4% vanadium.:Popular alpha-beta, medium strength alloy : Main uses - airframe and turbine engine parts (blades, discs, wheels, spacer rings)' ordnance equipment: pressure vessels: rocket motor cases. Also used for surgical appliances, implants, pressure vessels & airframes.
Grade 6 --
Grade 7 Unalloyed Titanium plus 0.12% to 0.25% palladium. Medium strength:Comments: Industrial alloy with superior corrosion resistance. standard oxygen. Good corrosion resistance in reducing and oxidising environments.
Grade 9 Titanium Alpha-Beta phase alloy including 3% aluminium and 2.5% vanadium. High strength and corrosion resistance. Aerospace, petrochemical, hydraulic & instrumentation tubing, sports and subsea applications, pressure vessels, honeycomb foil: Normally used in cold-worked stress-relieved condition. Weldable
Grade 11 Unalloyed Titanium plus 0.12% to 0.25% palladium. Low oxygen. Low strength. Especially suitable for deep drawing. Permissible hydrogen content depends on form. Pd additions increase corrosion resistance to certain media. Corrosion resistance: Very good Weldability:
Grade 12 Titanium alloy including 0.3% molybdenum, 0.8% nickel. High strength. Good Heat and Wear resistance. Used for shell and heat exchangers, hydrometallurgical applications. industry. Good corrosion resistance: Highly weldable.
Grade 13 Titanium alloy including 0.5% nickel and 0.05% ruthenium. Low oxygen.
Grade 14 Titanium alloy including 0.5% nickel and 0.05% ruthenium. Standard oxygen.
Grade 15 Titanium alloy including 0.5% nickel and 0.05% ruthenium. Medium oxygen.
Grade 16 Unalloyed Titanium plus 0.04% to 0.08% palladium. Standard oxygen, medium strength. Used in chemical industries (improved corrosion resistance).
Grade 17 Unalloyed Titanium plus 0.04% to 0.08% palladium. Low oxygen, low strength.
Grade 18 Titanium alloy including 3% aluminium, 2.5% vanadium plus 0.04% to 0.8% palladium.
Grade 19 Titanium alloy including 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, 4% molybdenum.
Grade 20 Titanium alloy including 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, 4% molybdenum plus 0.04% to 0.08% palladium.
Grade 21 Titanium alloy including 15% molybdenum, 3% aluminium, 2.7% niobium, 0.25% silicon.
Grade 23 Titanium alloy including 6% aluminium, 4% vanadium, extra low interstitial, ELI.
Grade 24 Titanium alloy including 6% aluminium, 4% vanadium plus 0.04% to 0.08% palladium.
Grade 25 Titanium alloy including 6% aluminium, 4% vanadium plus 0.3% to 0.6% nickel, 0.04% to 0.08% palladium.
Grade 26 Unalloyed Titanium plus 0.08% to 0.14% ruthenium. Standard oxygen, medium strength. Competitive alternative to grade 7.
Grade 27 Unalloyed Titanium plus 0.08% to 0.14% ruthenium. Low oxygen, low strength.
Grade 28 Titanium alloy including 3% aluminium, 2.5% vanadium, plus 0.08% to 0.14% ruthenium. High strength with enhanced corrosion alternative to Grade 9.


Some detailed information

ASTM B265 Fe max O max N max C max H max Pd Al V Mo Ni Elong'n Rp 0.2 Rm
No wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% % MPa MPa
Grade 1 0.2 0.18 0.03 0.1 0.015 24 170—310 240
Grade 2 0.3 0.25 0.03 0.1 0.015 20 275—450 345—480
Grade 3 0.25 0.3 0.05 0.1 0.015 18 360—480 480—700
Grade 4 0.5 0.4 0.05 0.1 0.015 15 500—530 600—680
Grade 5 0.4 0.2 0.05 0.1 0.015 5.5-6.7 10 800—1100 890—1400
Grade 6 0.1 16 780—820 820—860
Grade 7 0.3 0.25 0.03 0.1 0.015 0,12-0,25 20 275—450** 345
Grade 9 0.25 0.15 0.02 0.05 0.015 2,5—3,05 15 550 650
Grade 11 0.2 0.18 0.03 0.1 0.015 0.12—0.25 24 170-310** 240
Grade 12 0.3 0.25 0.03 0.1 0.015 0.3 0.8 25 414—460 499—600
Grade 13 0.5
Grade 14 0.5
Grade 15 0.5
Grade 16 0.04—0.08 27 345 485
Grade 17 0.18 0.04—0.08 35 206 345
Grade 18 0.04—0.08 3 2.5 4
Grade 19 3 8 4
Grade 20 0.04—0.08 3 8 4
Grade 21 3 15 15—8 880—1250

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