Titanium alloyByUsanee thanawutsakunchai 5310751234Sasichai jaithum5310751424

Titanium alloy

• are metallic materials which contain a mixture of titanium and other chemical elements

• Such alloys have very high tensile strength and toughness (even at extreme temperatures), light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures.

why are titanium alloy choice used that can be justified and use for high performance? such as aerospace, chemical processing and prosthetic devices.

• Because Titanium alloys are selected for applications requiring high strength, low weight, high operating temperature or high corrosion resistance. Specific strength is high compared with steel. Densities are approximately 55% those of steel and 60% greater than aluminum alloys. The properties and cost of titanium alloys make them the choice in applications

The combination of high strength-to-weight ratio, excellent mechanical properties, and corrosion resistance makes titanium the best material choice for many critical applications.

Today:•titanium alloys are used for demanding

applications such as static and rotating gas turbine engine components.

• Some of the most critical and highly-stressed civilian and military airframe parts are made of these alloys.

The use of titanium has expanded in recent years

•include applications in nuclear power plants

•food processing plants• oil refinery heat exchangers• marine components and medical

protheses.

 The wrought product forms of titanium and titanium-base

alloys, which include forgings and typical mill products, constitute more than 70% of the market in titanium and titanium alloy production.

The wrought products are the most readily available product form of titanium-base materials, although cast and powder metallurgy (P/M) products are also available for applications that require complex shapes or the use of P/M techniques to obtain microstructures not achievable by conventional ingot metallurgy.

 

• Powder metallurgy of titanium has not gained wide acceptance and is restricted to space and missile applications.

• The primary reasons for using titanium-base products are its outstanding corrosion resistance of titanium and its useful combination of low density (4.5 g/cm3) and high strength.

• The strengths vary from 480 MPa for some grades of commercial titanium to about 1100 MPa for structural titanium alloy products and over 1725 MPa for special forms such as wires and springs.

 •Another important characteristic of titanium-

base materials is the reversible transformation of the crystal structure from alpha (a, hexagonal close-packed) structure to beta (b, body-centered cubic) structure when the temperatures exceed certain level.

• This allotropic behavior, which depends on the type and amount of alloy contents, allows complex variations in microstructure and more diverse strengthening opportunities than those of other nonferrous alloys such as copper or aluminum.

Titanium has the following advantages:

•Good strength •Resistance to erosion and erosion-

corrosion •Very thin, conductive oxide surface film •Hard, smooth surface that limits adhesion

of foreign materials •Surface promotes dropwise condensation

Titanium has the following disadvantages:•Expensive to cast•Expensive material ;processes for forming

and joining titanium are complex and expensive.

•Expensive extraction method

Limitations of titanium alloys•Each of these forma of corrosion will be

explained. Although they are not common limitations to titanium alloy performance, galvanic corrosion and etc. ,that are included in the interest of completeness.

Titanium Alloys are generally classified into five main categories:

-Commercially Pure Alloys-Alpha alloys -Near-alpha alloys-Alpha & Beta Alloys-Beta Alloys

Commercially Pure Alloys:

•There are five grades of what is known as commercially pure or unalloyed titanium, ASTM Grades 1 through 4, and 7. Each grade has a different amount of impurity content, with Grade 1 being the most pure. Tensile strengths vary from 172 MPa for Grade 1 to 483 MPa for Grade 4.

Alpha alloys: • which contain neutral alloying elements (such as tin)

and/ or alpha stabilisers (such as aluminium or oxygen) only.

• These are not heat treatable. • Titanium alpha alloys are alloys that typically contain

aluminum and tin, though they can also contain molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon.

• Alpha alloys do not generally respond to heat treatment, but they are weldable and are commonly used for cryogenic applications, airplane parts, and chemical processing equipment.

Near-alpha alloys:• contain small amount of ductile beta-

phase. Besides alpha-phase stabilisers, near-alpha alloys are alloyed with 1-2% of beta phase stabilizers such as molybdenum, silicon or vanadium.

Alpha & Beta Alloys:• which are metastable and generally include

some combination of both alpha and beta stabilisers, and which can be heat treated.

•  Alpha-beta alloys can be strengthened by heat treatment and aging, and therefore can undergo manufacturing while the material is still ductile, then undergo heat treatment to strengthen the material, which is a big advantage.

• The alloys are used in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware, and prosthetic devices.

Beta Alloys:• which are metastable and which contain sufficient beta

stabilisers (such as molybdenum, silicon and vanadium) to allow them to maintain the beta phase when quenched, and which can also be solution treated and aged to improve strength. 

• The smallest group of titanium alloys, beta alloys have good hardenability, good cold formability when they are solution-treated, and high strength when they are aged. Beta alloys are slightly more dense than other titanium alloys, having densities ranging from 4840 to 5060 kg/m3.

• They are the least creep resistant alloys, they are weldable, and can have yield strengths up to 1345 MPa. They are used for heavier duty purposes on aircraft.

http://metallurgyfordummies.com/titanium-and-its-alloys/phase-diagram-ti-al/

The ASTM defines a number of alloy standards with a numbering scheme for easy reference.

• Grade 1-4 are unalloyed and considered commercially pure or “CP”. Generally the tensile and yield strength goes up with grade number for these “pure” grades. The difference in their physical properties is primarily due to the quantity of interstitial elements. They are used for corrosion resistance applications where cost and ease of fabrication and welding are important.

• Grade 5, also known as Ti6Al4V, Ti-6Al-4V or Ti 6-4, is the most commonly used alloy. It has a chemical composition of 6% aluminium, 4% vanadium, 0.25% (maximum) iron, 0.2% (maximum) oxygen, and the remainder titanium. Grade 5 is used extensively in Aerospace, Medical, Marine, and Chemical Processing. It is used for connecting rods in ICEs.

• Grade 6 contains 5% aluminium and 2.5% tin. It is also known as Ti-5Al-2.5Sn. This alloy is used in airframes and jet engines due to its good weldability, stability and strength at elevated temperatures.

• Grade 7 contains 0.12 to 0.25% palladium. This grade is similar to Grade 2. The small quantity of palladium added gives it enhanced crevice corrosion resistance at low temperatures and high pH.

• Grade 7H contains 0.12 to 0.25% palladium. This grade has enhanced corrosion resistance.

• added palladium gives it increased corrosion resistance.

• Grade 9 contains 3.0% aluminium and 2.5% vanadium. This grade is a compromise between the ease of welding and manufacturing of the “pure” grades and the high strength of Grade 5. It is commonly used in aircraft tubing for hydraulics and in athletic equipment.

• Grade 11 contains 0.12 to 0.25% palladium. This grade has enhanced corrosion resistance.

• Grade 12 contains 0.3% molybdenum and 0.8% nickel.

• Grade 19 contains 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, and 4% molybdenum.

• Grade 20 contains 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, 4% molybdenum and 0.04% to 0.08% palladium.

• Grade 21 contains 15% molybdenum, 3% aluminium, 2.7% niobium, and 0.25% silicon.

• Grade 23 contains 6% aluminium, 4% vanadium, 0.13% (maximum) Oxygen. Improved ductility and fracture toughness with some reduction in strength.

• Grade 24 contains 6% aluminium, 4% vanadium and 0.04% to 0.08% palladium.

• Grade 25 contains 6% aluminium, 4% vanadium and 0.3% to 0.8% nickel and 0.04% to 0.08% palladium.

• Grades 26, 26H, and 27 all contain 0.08 to 0.14% ruthenium.

• Grade 28 contains 3% aluminium, 2.5% vanadium and 0.08 to 0.14% ruthenium.

• Grade 29 contains 6% aluminium, 4% vanadium and 0.08 to 0.14% ruthenium.

• Grades 30 and 31 contain 0.3% cobalt and 0.05% palladium.

• Grade 32 contains 5% aluminium, 1% tin, 1% zirconium, 1% vanadium, and 0.8% molybdenum.

• Grades 33 and 34 contain 0.4% nickel, 0.015% palladium, 0.025% ruthenium, and 0.15% chromium .

• Grade 35 contains 4.5% aluminium, 2% molybdenum, 1.6% vanadium, 0.5% iron, and 0.3% silicon.

• Grade 36 contains 45% niobium.

• Grade 37 contains 1.5% aluminium.

• Grade 38 contains 4% aluminium, 2.5% vanadium, and 1.5% iron. This grade was developed in the 1990s for use as an armor plating. The iron reduces the amount of Vanadium needed as a beta stabilizer. Its mechanical properties are very similar to Grade 5, but has good cold workability similar to grade 9.