Composition of TC17 Titanium Alloy
TC17, known internationally as Ti-5Al-2Sn-2Zr-4Mo-4Cr, contains 4.5 to 5.5 percent aluminum, 1.6 to 2.4 percent tin, 1.6 to 2.4 percent zirconium, 3.5 to 4.5 percent molybdenum and 3.5 to 4.5 percent chromium. Aluminum and tin strengthen the alpha phase, while molybdenum and chromium stabilize the beta phase and give the alloy deep hardenability. The balanced beta stabilizer content allows thick forgings to develop uniform strength through the cross section.
Mechanical Properties
In the annealed or beta processed condition, TC17 provides a minimum tensile strength of about 1120 MPa with good ductility and fracture toughness. The alloy retains useful strength up to approximately 400 degrees Celsius, and its fatigue strength supports the cyclic loads of rotating engine parts. The combination of high strength, toughness and hardenability distinguishes TC17 from lower-strength alpha-beta alloys such as TC4.
Heat Treatment Behavior
TC17 responds to solution treatment and aging, where the beta solution treatment followed by aging precipitates a fine alpha phase that raises strength. Because of its high beta stabilizer content, the alloy can be cooled slowly after solution treatment without losing hardenability, which makes it suitable for large forgings. The heat treatment schedule is selected to balance strength against fracture toughness for the specific component.
Forging and Processing
Large TC17 components are produced by multiple forging steps in the alpha-beta and beta phase fields, with careful control of deformation temperature to develop the desired microstructure. The alloy is more difficult to forge than TC4 because of its higher flow stress, and forging equipment must have sufficient capacity. After forging, components are solution treated, aged, machined and inspected by ultrasonic methods.
Applications in Jet Engines
TC17 is used for fan and compressor disks, shafts and large structural forgings in aircraft engines, where thick sections must carry high centrifugal loads at moderate temperature. The alloy also appears in landing gear components and other airframe parts requiring high strength with deep section hardenability. Its combination of properties makes it a standard material in high-thrust engine programs.
Selection Compared with Other Alloys
Compared with TC4, TC17 offers higher strength and better hardenability in thick sections at the cost of more difficult processing. Compared with high-temperature alloys such as Ti-6Al-2Sn-4Zr-2Mo, TC17 has a lower service temperature limit but higher strength at room temperature. Engine designers select the alloy that matches the stress, temperature and section thickness of each part.
Frequently Asked Questions
Q: What is the composition of TC17 titanium alloy?
A: TC17 contains 4.5 to 5.5 percent aluminum, 1.6 to 2.4 percent tin and zirconium, and 3.5 to 4.5 percent molybdenum and chromium.
Q: What is the strength of TC17?
A: TC17 provides a minimum tensile strength of about 1120 MPa in the heat treated condition with good fracture toughness.
Q: Where is TC17 titanium alloy used?
A: TC17 is used for jet engine compressor and fan disks, shafts and large structural forgings requiring high strength in thick sections.
Q: Why does TC17 contain so much beta stabilizer?
A: Molybdenum and chromium give TC17 deep hardenability, allowing thick forgings to be strengthened uniformly by heat treatment.
Q: How does TC17 differ from TC4?
A: TC17 offers higher strength and better hardenability in thick sections than TC4, but it is harder to forge and process.
