Table 1: Titanium Alloying elements and their properties
| Element | Effect |
| Aluminum |
|
| Molybednum |
|
| Carbon |
|
| Chromium |
|
| Cobalt |
|
| Copper |
|
| Gallium |
|
| Germanium |
|
| Hydrogen |
|
| Iron |
|
| Manganese |
|
| Molybdenum |
|
| Nickel |
|
| Niobium |
|
| Nitrogen |
|
| Oxygen |
|
| Palladium |
|
| Silicon |
|
| Tantalum |
|
| Tin |
|
| Vanadium |
|
| Zirconium |
|
Titanium Alloys
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
The combination of high strength-to-weight ratio, excellent mechanical properties, and corrosion resistance makes titanium the best material choice for many critical applications. The high cost of titanium alloy components may limit their use to applications for which lower-cost alloys, such as aluminium and stainless steels. Titanium is rather difficult to fabricate because of its susceptibility to oxygen, nitrogen, and hydrogen impurities which cause the titanium to become more brittle. Elevated temperature processing must be used under special conditions in order to avoid diffusion of these gasses into the titanium. Most alloys of titanium can be formed by conventional means such as rolling, forging and casting.
. Grades 1, 2, 3, 4, 7, 11, and 12 and considered 'unalloyed' titanium and have similar mechanical properties. Grades 1 through 4 allow increasing levels of impurities. Grades 7 and 11 have 0.2% palladium added to improve titanium's already excellent corrosion resistance. Grade 12 features 0.8% Ni and 0.3% Mo to improve the corrosion resistance at a lower cost than Pd. Titanium alloys generally feature higher strength than unalloyed titanium.
for most applications titanium is alloyed with small amounts of Aluminum and Vanadium, typically 6% and 4% respectively, by weight. This mixture has mechanical propertiesa which varies dramatically with temperature, allowing it to undergo precipitation hardening. This process is carried out after the alloy has been worked into its final shape but before it is put to use, allowing much easier fabrication of a high-strength product.
Commercially pure titanium with minor alloy contents include various titanium-palladium grades and alloy Ti-0,3Mo-0,8Ni (ASTM grade 12 or UNS R533400). The alloy contents allow improvements in corrosion resistance and/or strength
Alloy Ti-0,3Mo-0,8Ni (UNS R533400, or ASTM grade 12) has applications similar to those for unalloyed titanium but has better strength and corrosion resistance. However, the corrosion resistance of this alloy is not as good as the titanium-palladium alloys. The ASTM grade 12 alloy is particularly resistant to crevice corrosion in hot brines.
The most widely used titanium alloy is the Ti-6Al-4V alpha-beta alloy. This alloy is well understood and is also very tolerant on variations in fabrication operations, despite its relatively poor room-temperature shaping and forming characteristics compared to steel and aluminium. Alloy Ti-6Al-4V, which has limited section size hardenability, is most commonly used in the annealed condition.
Other titanium alloys are designed for particular application areas. For example:
- Alloys Ti-5Al-2Sn-2Zr-4Mo-4Cr (commonly called Ti-17) and Ti-6Al-2Sn-4Zr-6Mo for high strength in heavy sections at elevated temperatures. Compressor discs, heavy section forgings for gas turbine engine components. High tensile strength and good fracture toughness.
- Alloys Ti-6242S, IMI 829, and Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) for creep resistance
- Alloys Ti-6Al-2Nb-ITa-Imo and Ti-6Al-4V-ELI are designed both to resist stress corrosion in aqueous salt solutions and for high fracture toughness
- Alloy Ti-5Al-2,5Sn is designed for weldability, and the ELI grade is used extensively for cryogenic applications
- Alloys Ti-6Al-6V-2Sn, Ti-6Al-4V and Ti-10V-2Fe-3Al for high strength at low-to-moderate temperatures. Used to form near net shape forgings for high strength components, primarily aircraft components.
Wrought Titanium
Commercially produced titanium products are made in net shape mill wrought forms such as plate, tubing, sheet, wire, extrusions. Additionally, Titanium is often formed to net shape though forging and welded or brazed assemblies. The relatively high cost is often the result of the intristic raw material cost of metal, fabricating costs and the metal removal costs incurred in obtaining the desired final shape.
Titanium Casting
Titanium can also be cast, which must be done in a vacuum furnace because of titanium's reactive nature. Generally, Titanium castings are hot isostatically pressed to close porosity that would affect strength. Precision casting is fairly well developed developed and widely used in the aircraft industry to produce titanium net shape parts.
As aircraft engine manufactures seek to use cast titanium at higher operating
temperatures, Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-2Sn-4Zr-6Mo are being specified
more frequently. Other advanced high-temperature titanium alloys for service up
to 595oC, such as Ti-1100 and IMI-834 are being developed as
castings. The alloys mentioned above exhibit the same degree of
elevated-temperature superiority, as do their wrought counterparts over the more
commonly
used Ti-6Al-4V.
Titanium Casting
Several new titanium net shape technologies are on the horizon including powder metallurgy (P/M), superplastic forming (SPF). It is used to make lightweight alloys for aircraft, replacement hip joints and chemical plants. bone pins and other things requiring light weight metals or metals that resist corrosion or high temperatures.
Titanium Alloys
Table 1: Titanium Alloys Composition
| designation | UNS | ASTM | DIN | Aerospace American AMS |
Aerospace American MIL-T 9046-9047 |
Remarks |
| GR-1 | 1 | 3.7025 | CP4 | |||
| GR-2 | 2 | 3.7035 | 4902,4941 4942,4951 |
CP3 | Commercially pure titanium, used primarily for corrosion resistance. Strength increases with Grade Number. | |
| GR-3 | 3 | 3.7055 | 4900 | CP2 | ||
| GR-4 | 4 | 3.7065 | 4901 | CP1 CP-70 | ||
| GR-7 | 7.11 | Industrial alloys with superior corrosion resistance. | ||||
| GR-12 | 12 | |||||
| GR-5 | 5 | 3.7165 | 4911, 4928 |
AB1/AB2 | Popular alloys of medium strength for airframe and engines. | |
| Ti-4Al-4 Mo-2.5Sn (550) | ||||||
| Ti-10Fe-2V-3Al (10-2-3) | > | 4983 | Beta alloys having excellent fabricability and high strength developed by heat treatment. | |||
| Ti-15V-3Al-3 Cr-3Sn (15-3) | 4916 | |||||
| Ti-6Al-2Sn 4Zr-2Mo (6-2-4-3) | 4975 4976 |
AB4 | Alloys developed for aero engine use | |||
| T-6Al-2Sn-4Zr 6Mo(6-2-4-6) | 4981 | |||||
| Ti-5Al-2Sn-2Zr-4Mo-4Cr | R58650 |
Table 3: ZAMAK series alloy composition
| Designation | 10-2-3 | 6-4 | ZP5 | ZP7 | |
| UNS Alloy Number | T? | T? | T? | T? | |
| ASTM Number | ? | ? | ? | ? | |
| Alloy Symbol | Ti10Fe2V3Al | Ti6Al4V | ZnAl4Cu1 | ||
| Aluminum % | Max. | 3.4 2.6 |
5.5 6.75 |
4.3 3.5 |
4.3 3.5 |
| Min. | |||||
| Vanadium % | Max. | 11.0 9.0 |
0.25 N/A |
1.25 0.75 |
0.25 N/A |
| Min. | Iron % | Max. | 2.2 1.6 |
0.30 -- |
0.080 0.030 |
0.020 0.005 |
| Min. | Nickel % | Max. | N/A | N/A | N/A | 0.005 0.020 |
| Min. | |||||
| Nirogen (N) | Max (%) | 0.05 | ? | 0.10 | 0.075 |
| Oxygen (O) | Max (%) | 0.13 | ? | 0.005 | 0.003 |
| Hydrogne (H) | Max (%) | 0.015 | 0.0125 | 0.004 | 0.002 |
| Tin (Sn) | Max (%) | -- | -- | 0.003 | 0.001 |
Physical properties of Titanium alloys
Table 6: Titanium Alloy Physical Properties
| #3 | #5 | #7 | #2 | ZA-8 | ZA-12 | ZA-27 | |
| Ultimate Tensile Strength: psi x 103 (MPa) | 41 (283) | 48 (328) | 41 (283) | 52 (359) | 54 (374) | 58 (400) | 61 (421) |
| Yield Strength - 0.2% Offset: psi x 103 (MPa) | 32 (221) | 39 (269) | 32 (221) | 41 (283) | 42 (290) | 46 (317) | 55 (379) |
| Elongation: % in 2" | 10 | 7 | 13 | 7 | 6-10 | 4-7 | 1-3 |
| Shear Strength: psi x 103 (MPa) | 31 (214) | 38 (262) | 31 (214) | 46 (317) | 40 (275) | 43 (296) | 47 (325) |
| Hardness: Brinell | 82 | 91 | 80 | 100 | 95-110 | 95-115 | 105-125 |
| Poisson's Ratio | 0.27 | 0.27 | 0.27 | 0.27 | 0.29 | 0.30 | 0.32 |