August 2025 Volume 7

MATERIALS

Technical Considerations Titanium and Titanium Alloy forgings, as compared to other structural materials, are characterized by high relative strength in the wide temperature range and excellent corrosion resistance in many chemically aggressive environments (see Figure 7).

Titanium Alloys • Alpha, Alpha + Beta and Beta Alloys • Alpha phase/alloys are HCP ( hexagonally close packed ) crystal structure • Beta phase/alloys are BCC ( body centered cubic ) crystal structure • Alpha/Beta alloys are a mixture of alpha and beta phases • Alpha/Beta and Beta alloys can be heat treated for strengthening Premium Quality Melting The production of titanium from reduction of ore through melting was discussed previously. However, for flight applications, a premium quality (PQ) level is required. PQ materials typically are produced via triple vacuum arc re-melt (3XVAR) or hearth melt VAR (HMVAR) processes, but more recently, the Skull plus VAR (SVAR) process has been introduced. Hard-alpha rates have continued to decline over the last decade primarily for the HMVAR process.

Figure 7: Other Engineering Properties – Ti vs Other Such properties create many possibilities of improvements of technological processes, tooling and products in various industries. The high strength-to-weight ratio, low modulus, and good elevated temperature properties (600°-1000°F) make it an excellent choice for aircraft structural and engine components (see Figure 8). Therefore, this technical discussion will focus on flight applications and the most popular alloy (Ti 6Al – 4V).

Figure 9: Premium Quality Melting and Inspection Points [15] The JETQC (Jet Engine Titanium Quality Committee) was formed under the auspices of the FAA (Federal Avion Administration) in 1990 following the United Airlines DC10 crash at Sioux City. The origin of the accident was traced back to the presence of a melt-related inclusion in the fan disk of the tail mounted engine that cracked, ultimately leading to the separate of the disk and the subsequent crash landing. The primary purpose of addressing the quality of premium / rotor quality titanium alloy production. Titanium suppliers provide melt-related inclusion data. JETQC focuses on hard-alpha and HDI inclusion rates in premium quality (PQ) Titanium alloy products for critical rotating aircraft engine applications [15]. The JETQC* (Jet Engine Titanium Quality Committee) Basics • Tracks & monitors PQ Ti alloy mill product and components • Members: • ATI, Arconic-RTI, PCC-TIMET, VSMPO • GE, Honeywell, MTU, PW (US & CAN), RR (UK & US), Safran, Williams • FAA Note that there is a similar committee, JENQC (Jet Engine Nickel Quality Committee) for Nickel Alloys mill products and components. This will be discussed in a future article.

Figure 8: Comparison of Specific Strengths - Ti vs. Other A summary of commerically pure (CP) titanium and titanium alloys (with Al, V, Mo, Sn, Zr) with key characteristics and structures includes: Commercially Pure (CP) Titanium • Grades 1-4 that vary in strength and ductility • Fe and Interstitial content ( O, N and H ) determine strength/ ductility • Higher interstitial content results in higher strength and lower ductility • CP Titanium is not heat treatable

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