Table 1: Titanium Alloying elements and their properties

Element Effect
Aluminum
  • primary alloying constituent
  • promotes precipitation hardening
  • alpha phase stabilizer.
Molybednum
  • Lower cost corrosion inhibitor that palladium
  • beta phase stabilizer
Carbon
  • forms carbides to improve tensile strength
  • alpha phase stabilizer
Chromium
  • beta phase stabilizer
Cobalt
  • beta phase stabilizer
Copper
  • beta phase stabilizer
Gallium
  • alpha phase stabilizer
Germanium
  • alpha phase stabilizer
Hydrogen
  • increases brittleness
Iron
  • beta phase stabilizer
Manganese
  • beta phase stabilizer
Molybdenum
  • high temperature stability for castings
  • beta phase stabilizer
Nickel
  • Improves corrosion resistance
  • beta phase stabilizer
Niobium
  • replaces vanadium for biomedical devices
  • beta phase stabilizer
Nitrogen
  • increases brittleness
  • alpha phase stabilizer
Oxygen
  • increases brittleness
  • alpha phase stabilizer
Palladium
  • improves corrosion resistance
  • beta phase stabilizer
Silicon
  • beta phase stabilizer
Tantalum
  • beta phase stabilizer
Tin
  • high temperature stability for castings
  • biologically neutral
  • improves toughness in cryogenic applications
Vanadium
  • primary alloying constituent
  • promotes precipitation hardening
  • increases tensile strength
  • decreases elongation
  • reduces impact resistance
  • not used in biomedical alloys due to toxicity issues
  • beta phase stabilizer
Zirconium
  • high temperature stability for castings
  • biologically neutral

 

Titanium Alloys

Titanium has the following advantages:

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:

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