The alpha-beta titanium alloys contain both alpha and beta phases at room temperature. The alpha phase is similar to that of unalloyed titanium but is strengthened by alpha stabilizing additions (e.g., aluminum). The beta phase is the high-temperature phase of titanium but is stabilized to room temperature by sufficient quantities of beta stabilizing elements such as vanadium, molybdenum, iron, or chromium. In addition to strengthening of titanium by the alloying additions, alpha-beta alloys may be further strengthened by heat treatment. The alpha-beta alloys have good strength at room temperature and for short times at elevated temperature. They are not noted for long-time creep strength. With the exception of annealed Ti-6Al-4V, these alloys are not recommended for cryogenic applications. The weldability of many of these alloys is poor because of the two-phase microstructure. However, some of them can be welded successfully with special precautions.
5.4.1 Ti-6Al-4V
5.4.1.0
Comments and Properties — Ti-6Al-4V is available in all mill product forms as well as castings and powder metallurgy forms. It can be used in either the annealed or solution treated plus aged (STA) conditions and is weldable. Useful temperature range is from -320 to 750°F. For maximum toughness, Ti-6Al-4V should be used in the annealed or duplex-annealed conditions whereas for maximum strength, the STA condition is used. The full strength potential for this alloy is not available in sections greater than 1 inch.
Manufacturing Considerations — Ti-6Al-4V alloy may be forged above the beta transus temperature using procedures to promote a high toughness material. The material is routinely finished below beta transus temperature for good combinations of fabricability, strength, ductility, and toughness. Elevated temperatures are usually used for form flat-rolled products although extensive forming may be accomplished at room temperature. Flat-rolled products are usually formed and used in the annealed condition although some forming in the STA condition is possible.
This alloy can be spot welded and is being fusion welded extensively in certain applications. Established titanium-welding techniques must be employed and special design considerations may be involved in fusion weldments. Stress-relief annealing after welding is recommended.
Environmental Considerations — Ti-6Al-4V can withstand prolonged exposure to temperatures up to 750°F without loss of ductility. Its toughness in the annealed condition is adequate at temperatures down to -320°F. (A special low interstitial grade may be used down to -423 °F.) Ti-6Al-4V is resistant to hot-salt stress corrosion to about its maximum use temperature depending on exposure time and exposure stress. The material is marginally susceptible to aqueous chloride solution stress corrosion, but is considered to have good resistance to this reaction compared with other commonly used alloys. Under certain conditions, titanium, when in contact with cadmium, silver, mercury, or certain of their compounds, may become embrittled. Refer to MIL-S-5002 and MIL-STD-1568 for restrictions concerning applications with titanium in contact with these metals or their compounds.
Heat Treatment — This alloy is commonly specified in either the annealed condition or in the fully heat-treated condition. Annealing requires 1 hour at 1300°F followed by furnace cooling if maximum ductility is required.
The specified fully heat-treated, or solution-treated and aged condition for sheet is as follows:
Solution treat at 1700°F for 5 to 25 minutes, quench in water.
Age at 975°F for 4 to 6 hours, air cool.
MIL-HDBK-5J
5.4.1.1
Annealed Condition-Elevated temperature curves for annealed Ti-6Al-4V are shown in Figures 5.4.1.1.1 through 5.4.1.1.5. Typical stress-strain curves at several temperatures are shown in Figures 5.4.1.1.6(a) through (c). Typical full-range stress-strain curves at room temperature are shown in Figure 5.4.1.1.6(d). Unnotched and notched fatigue data are shown in Figures 5.4.1.1.8(a) through (g). Fatigue crack-propagation data for plate are shown in Figure 5.4.1.1.9.
5.4.1.2
Solution-Treated and Aged Condition — Elevated temperature curves for solution-treated and aged alloy are shown in Figures 5.4.1.2.1 through 5.4.1.2.4. Typical tensile and compressive stress-strain and tangent-modulus curves are shown in Figures 5.4.1.2.6(a) through (g). Typical full-range stress-strain curves at several temperatures up to 1000 °F are shown in Figure 5.4.1.2.6(h). A nomograph of typical creep properties of solution-treated and aged sheet for the temperature range 600°F through 800°F is shown in Figure 5.4.1.2.7. Fatigue data at room and elevated temperatures are shown in Figures 5.4.1.2.8(a) through (i).
MIL-HDBK-5J
5.4.2 Ti-6Al-6V-2Sn
5.4.2.0
Comments and Properties — Ti-6Al-6V-2Sn alloy is similar to Ti-6Al-4V alloy in many respects but has higher strength and deeper hardenability (i.e., use of thicker sections possible). A variety of mill product forms are available including billet, bar, plate, sheet, strip, and extrusions and these may be used in either the annealed or the solution-treated and aged (STA) conditions. The maximum strength is developed in the STA condition in sections up to about 2 inches in thickness.
Manufacturing Considerations — To ensure optimum mechanical properties in Ti-6Al-6V-2Sn forgings, at least 50 percent reduction should be done at temperatures below the beta transus temperature (i.e., <1735 °F). The Ti-6Al-6V-2Sn is readily formable in the annealed condition. In the sheet or plate forms the alloy is generally used in the annealed condition, although the alloy is capable of heat treatment to higher strength levels with some loss of toughness. When the Ti-6Al-6V-2Sn sheet and plate are hot formed at any temperature over 1000 °F and air cooled, the material should be stabilized by reheating to 1000 °F followed by air cooling. Welding is not usually recommended although limited weld joining operations are possible if the assembly is amenable to post-weld thermal treatments for the restoration of ductility to the weld and heat-affected zones.
Environmental Considerations — While the short-time elevated-temperature properties and stability of Ti-6Al-6V-2Sn alloy are good, creep strength above 650°F and long-term stability at temperatures above 800°F are not. The material ages during prolonged exposures around 800°F and above, particularly when under stress. Oxidation resistance of Ti-6Al-6V-2Sn is satisfactory in short-term exposures to 1000°F. The material is nearly equivalent to the Ti-6Al-4V alloy in terms of hot-salt and aqueous chloride solution stress-corrosion resistance. Under certain conditions, titanium, when in contact with cadmium, silver, mercury, or certain of their compounds, may become embrittled. Refer to MIL-S-5002 and MIL-STD-1568 for restrictions concerning applications with titanium in contact with these metals or their compounds.
Heat Treatment — This alloy is commonly specified in either the annealed condition or the solution-treated and aged condition. The solution-treated and aged condition is as follows:
Solution treat at 1625°F for ½ to 1 hour, quench in water.
Age at 1000 ± 25 °F for 4 to 8 hours, air cool.
Specifications and Properties — Material specifications for Ti-6Al-6V-2Sn are shown in Table 5.4.2.0(a). Room-temperature mechanical properties are shown in Tables 5.4.2.0(b) through (e). The effect of temperature on physical properties is shown in Figure 5.4.2.0.
5.4.2.1
Annealed Condition — Elevated temperature curves for annealed condition are shown in Figures 5.4.2.1.1(a) through 5.4.2.1.3(b). Typical stress-strain and tangent-modulus curves for this condition are shown in Figures 5.4.2.1.6(a) and (b). A typical full range tensile stress-strain curve is shown in Figure 5.4.2.1.6(c). Unnotched and notched fatigue data are presented in Figures 5.4.2.1.8(a) and (b).
5.4.2.2
Solution-Treated and Aged Condition — Elevated temperature curves are shown in Figures 5.4.2.2.1 and 5.4.2.2.2.
MIL-HDBK-5J
31 January 2003
| Specification | Form |
|---|---|
| AMS-T-9046 | Sheet, strip, and plate |
| AMS 4979 | Bar and forging |
| MIL-T-81556, AMS-T-81556 | Extruded bar and shapes |
| AMS 4971 | Bar and forging |
| AMS 4978 | Bar and forging |
| AMS 4918 | Sheet, strip, and plate |
The M P a b
| Specification | AMS-T-9046, Comp. AB-3, and AMS 4918 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Form | Sheet, strip, and plate | ||||||||||
| Condition | Annealed | Solution treated and aged | |||||||||
| Thickness, in. | <0.1875 | 0.1875-0.500 | 0.501-1.000 | 1.001-1.500 | 1.501-2.000 | 2.001-4.000 | ≤0.1875 | 0.1875-1.500 | 1.501-2.500 | 2.501-4.000 | |
| Basis | A | B | S | S | S | S | S | S | S | S | S |
| Mechanical Properties: | |||||||||||
| Ftu, ksi: | |||||||||||
| L | 155 | 160 | 150 | 150 | 150 | 150 | 145 | 170 | 170 | 160 | 150 |
| LT | 155 | 150 | 150 | 150 | 150 | 150 | 145 | 170 | 170 | 160 | 150 |
| Fty, ksi: | |||||||||||
| L | 145a | 152 | 140 | 140 | 140 | 140 | 135 | 160 | 160 | 150 | 140 |
| LT | 145a | 154 | 140 | 140 | 140 | 140 | 135 | 160 | 160 | 150 | 140 |
| Fcy, ksi: | |||||||||||
| L | 139 | 142 | 146 | 148 | 170 | ||||||
| LT | 151 | 147 | 141 | 136 | 170 | ||||||
| Fsu, ksi: | 91 | 93 | 95 | 95 | 101 | ||||||
| Fbru, ksi: | |||||||||||
| (e/D = 1.5) | 236 | 241 | 247 | 250 | 264 | ||||||
| (e/D = 2.0) | 294 | 303 | 312 | 317 | 324 | ||||||
| Fbry, ksi: | |||||||||||
| (e/D = 1.5) | 193 | 196 | 199 | 202 | 237 | ||||||
| (e/D = 2.0) | 215 | 223 | 234 | 240 | 266 | ||||||
| e, percent (S-basis): | |||||||||||
| L | 10b | 10 | 10 | 10 | 10 | 8 | 8 | 8 | 6 | 6 | |
| LT | 8b | 8 | 8 | 8 | 8 | 6 | 6 | 8 | |||
| E, 103 ksi | 16.0 | ||||||||||
| Ec, 103 ksi | 16.4 | ||||||||||
| G, 103 ksi | 6.2 | ||||||||||
| μ | 0.31 | ||||||||||
| Physical Properties: | |||||||||||
| ω, lb/in.3 | 0.164 | ||||||||||
| C, K, and α | See Figure 5.4.2.0 | ||||||||||
MIL-HDBK-5J
5.4.3 Ti-4.5AL-3V-2FE-2Mo
5.4.3.0
Comments and Properties —Ti-4.5Al-3V-2Fe-2Mo alloy is a beta rich alpha-beta titanium composition developed for improved hot formability and fatigue resistance. The alloy consists of fine microstructure and has excellent superplastic formability at temperatures below 1475 °F. This alloy also shows significantly improved cold formability over Ti-6Al-4V. Although this alloy was originally developed for flat product applications in the annealed condition, it has expanded into other areas such as billets, bars, and forgings. This alloy has been reported to possess significantly better hardenability than Ti-6Al-4V.
Manufacturing Considerations – Superplastic forming of Ti-4.5Al-3V-2Fe-2Mo at temperatures between 1380F-1425 °F is recommended. At these forming temperatures the formation of alpha case is not observed and the thickness of oxygen enriched layer is generally less than 0.001”. Diffusion bonding at 1425 °F is possible but slightly higher temperatures than the superplastic forming temperature e.g., 1470 °F are recommended to ensure perfect bonding. Ti-4.5Al-3V-2Fe-2Mo is weldable by standard titanium welding techniques. This alloy shows an increase in hardness in the welded zone but with limited ductility loss. Stress relief annealing after welding is recommended.
Environmental Considerations – Ti-4.5Al-3V-2Fe-2Mo exhibits significantly improved resistance to aqueous chloride solution stress-corrosion cracking over Ti-6Al-4V. The alloy is nearly equivalent to Ti-6Al-4V hot - salt stress corrosion cracking.
Heat Treatment – This alloy is commonly specified in the annealed condition, but is also used in the solution-treated and aged condition.
Annealing : 1325°F for a time commensurate with product thickness.
Annealing requires 1 hour at 1475°F followed by furnace cooling if maximum ductility is required.
The solution treated and aged conditions commonly employed are as follows :
Solution treat at 1500-1580°F for 1/2 –1hour followed by air cooling.
Age at 900-1060°F followed by air cooling.
Specifications and Properties – Some material specifications for Ti-4.5Al-3V-2Fe-2Mo are shown in Table 5.4.3.0(a). Room temperature mechanical properties and physical properties are shown in Table 5.4.3.0(b) through (d).
Table 5.4.3.0(a). Material Specification for
Ti-4.5Al-3V-2Fe-2Mo Titanium Alloy
| Specification | Form |
|---|---|
| AMS 4899 | Sheet, Strip, and Plate |
| AMS 4964 | Bars, Wire, Forgings, and Rings |
5.4.3.1
Anneal Condition – Typical tensile stress-strain and full-range stress-strain curves are shown in Figures 5.4.3.1.6(a) and (b). Compressive stress-strain and tangent modulus curves are shown in Figure 5.4.3.1.6(c). Unnotched and notched fatigue data as well as fatigue crack propagation data are presented in Figures 5.4.3.1.8(a), (b) and 5.4.3.1.9.