TC4 (Ti-6Al-4V, ASTM Gr. 5) is one of the most widely used titanium alloys in the global aerospace industry, playing a central role in aircraft structural components and oil & gas downhole tools due to its high specific strength and excellent fatigue performance. TC4 ELI (ASTM Gr. 23), with strictly controlled interstitial elements, maintains high strength while significantly improving fracture toughness and damage tolerance, making it the key material for orthopedic implants and high-damage-tolerance aerospace parts. This guide provides procurement and engineering professionals with a systematic analysis of typical applications, selection criteria, and purchasing considerations for both titanium grades across aerospace, medical, and oil & gas sectors.
Two grades, one system, different safety margins.
TC4 and TC4 ELI belong to the same Ti-6Al-4V alloy family with nearly identical nominal compositions: approximately 6% aluminum, 4% vanadium, and the balance titanium. The performance differences between them stem entirely from the control of interstitial element content—primarily oxygen and iron.
The maximum oxygen content for TC4 is 0.20%, and the maximum iron content is 0.40%. This level of interstitial elements provides high strength while maintaining good ductility and formability. TC4 ELI reduces oxygen to below 0.13% and tightens iron to within 0.25%. This control of interstitial elements typically improves fracture toughness and damage tolerance while retaining high strength levels.
From an engineering perspective: TC4 prioritizes "maximum load capacity," while TC4 ELI emphasizes "remaining service life under damage." Within the same alloy family, these two variants define distinct safety margins. For procurement and engineering teams, selecting the correct grade hinges on accurately prioritizing strength, toughness, and damage tolerance requirements based on operating conditions.
Quick Reference: Core Differences Between TC4 and TC4 ELI：
Comparison Criteria | TC4 (Gr. 5) | TC4 ELI (Gr.23) |
Key Benefits | High Intensity | High damage tolerance |
Maximum Oxygen Content | ≤ 0.20% | ≤ 0.13% |
Typical Use Cases | Aerospace structural components, oil & gas tools | Implants and damage-tolerant critical components |
Relative Cost | Lower | High |
Material Selection Priority | Capacity | Safety Margin |
Aviation sector: TC4's volume market, TC4 ELI's quality market
TC4: The Classic Choice for Aerospace Structural Components
TC4 is one of the most widely used titanium alloys in the global aerospace industry. From fuselage frames and wing connection joints to engine mounts, landing gear components, and thousands of titanium fasteners, parts machined from TC4 titanium bars are found throughout the load-bearing areas of modern aircraft.
Selection Logic: Aerospace structural components demand extreme weight reduction. TC4 has a density of approximately 4.5g/cm g/cm³ and a tensile strength of ≥895 MPa, offering specific strength far superior to high-strength steel and aluminum alloys. Additionally, it maintains reliable mechanical properties across a wide temperature range, typically from 300°C to 350°C depending on operating conditions, covering the full spectrum from high-altitude cruising to ground storage.
Typical Aircraft Components:
Fuselage frame forgings and connection fittings
Wing-to-fuselage fittings – must comply with applicable aerospace material standards
Engine mount and bracket
Aerospace Fasteners – Extensively machined from TC4 titanium rods; aerospace fasteners must be manufactured using material specifications that align with component design requirements.
Procurement Requirements: TC4 titanium bars for aviation applications typically must comply with AMS 4928 (bar stock) or customer-specific specifications. Materials shall be supplied in the annealed or solution-treated and aged condition, accompanied by complete heat treatment records, mechanical property reports, and ultrasonic inspection reports. Nadcap-certified heat treatment and NDT are commonly required across many aviation supply chains.
TC4 ELI: The Upgrade Choice for Damage-Tolerance-Critical Components
When aerospace components demand higher resistance to crack growth and improved damage tolerance, TC4 ELI becomes the preferred design material over standard TC4. For such parts, once a fatigue crack initiates, extended inspection intervals are required to ensure the crack does not reach critical size before detection.
Typical Use Cases:
Fuselage structures and fittings designed for damage tolerance
High-strength fasteners for critical components (partial applications)
Structural components for low-temperature environments (e.g., high-altitude UAV airframes)
Selection logic: TC4 ELI is not used to "fully replace TC4" in aviation; rather, ELI is selected when damage tolerance is a critical design requirement. Both grades coexist within the aviation supply chain, and procurement must strictly follow the standard number specified on the part drawing.
TC4 ELI's home turf in the medical field
If the aerospace market is shared between TC4 and TC4 ELI, then medical implants are the exclusive domain of TC4 ELI.
Why must implants use ELI?
Orthopedic implants—including plates, spinal rod systems, femoral stems, and femoral knee components—are subjected to millions of cycles of loading in the human body. Any minor defect or crack within the material can propagate under cyclic stress, potentially leading to implant fracture. Such failure requires revision surgery for patients and triggers product recalls and regulatory risks for manufacturers.
TC4 ELI's "extra-low interstitial" (ELI) grade directly addresses this critical concern: lower oxygen content reduces interstitial solid-solution strengthening, thereby improving ductility, fracture toughness, and damage tolerance; reduced iron content minimizes heterogeneous nucleation sites. In corrosion-fatigue environments containing body fluids, the advantages of ELI are even more pronounced.
Typical Medical Components:
Pedicle screws and connecting rods for spinal fixation — direct machining from TC4 ELI bar stock
Hip stems and femoral knee components — Machining of TC4 ELI forged bars
T-plates and bone screws — Machined from TC4 ELI bar or sheet
Dental Implant Abutment — Small-Diameter TC4 ELI Bar
Regulations and Standards: TC4 ELI titanium bars for medical implants must comply with ASTM F136 (Ti-6Al-4V ELI forged material for surgical implants) or ISO 5832-3. While these standards are largely equivalent in chemical composition and mechanical properties, EU CE registration typically cites ISO standards, whereas US FDA registration typically cites ASTM standards. Material suppliers must provide complete heat lot traceability documentation, EN 10204 3.1 or 3.2 material certificates, and a declaration of compliance with implant regulations.
Important Notice: Not all TC4 ELI materials meeting the ASTM F136 chemical composition requirements are suitable for direct use in implant manufacturing. Medical device manufacturers must also verify material biocompatibility, complete cleaning and passivation process validation, and ensure the entire manufacturing process complies with ISO 13485 quality management system standards and implant regulations. The ultimate compliance responsibility for medical devices lies with the device manufacturer.
Oil & Gas: TC4's Downhole Advantages
Balancing acidic environments with high-intensity demands
Downhole oil and gas tools—including drill collars, MWD housings, packer mandrels, and downhole safety valve components—face complex extreme conditions: high internal and external pressure, sour media containing hydrogen sulfide, cyclic stresses from wellbore bending and vibration, and downhole temperatures ranging from 150°C to 200°C.
TC4 demonstrates unique comprehensive advantages in these applications: higher specific strength than most corrosion-resistant alloys and superior corrosion resistance compared to high-strength steels. Titanium alloys can be evaluated for service in certain acidic environments per NACE MR0175/ISO 15156, but applicability must be confirmed based on specific hydrogen sulfide partial pressure, temperature, pH, and chloride ion concentration.
Typical Oil & Gas Components:
MWD and LWD housings – high specific strength reduces tool string weight
Packer mandrel and setting tool — designed for high pressure and axial loads
Downhole safety valve spring and seat — requiring high fatigue resistance and corrosion resistance
Oil and Gas Well Tubing Connections – Leveraging Titanium's Reliability in Highly Corrosive Environments
About ELI in Oil & Gas: TC4 is the standard for downhole tools. TC4 ELI appears only occasionally in specialized applications requiring higher fracture toughness, but it is far less common than in medical fields. Oil and gas buyers prioritize NACE MR0175 environmental compliance and high-temperature mechanical properties over the interstitial element control associated with ELI grades.
Comparison of Chemical Composition and Mechanical Properties for Two Material Grades
The following data represents typical reference values for annealed bars. Actual performance requirements may vary depending on the product standard and heat treatment condition.
Project | TC4 (Gr. 5) | TC4 ELI (Gr.23) |
Aluminum (Al) | 5.50 - 6.75 | 5.50 - 6.50 |
Vanadium (V) | 3.50 - 4.50 | 3.50 - 4.50 |
Iron (Fe) ≤ | 0.40 | 0.25 |
Oxygen (O) ≤ | 0.20 | 0.13 |
Tensile Strength (MPa) ≥ | 895 | 860 |
Yield Strength (MPa) ≥ | 828 | 795 |
Elongation (%) ≥ | 10 | 10 |
Typical Product Standards | ASTM B348, AMS 4928 | ASTM B348, ASTM F136, AMS 4930 |
App Decision Quick Reference：
Use Cases | Recommended Grades | Why Choose Us | Procurement Priorities |
Aerospace Structural Components | TC4 (Gr. 5) | High-intensity, AMS-compliant | AMS certification, non-destructive testing, heat treatment records |
Damage-tolerant aviation parts | TC4 ELI (Gr.23) | High fracture toughness and high fatigue crack growth resistance | Damage Tolerance Performance Data, AMS Standards |
Orthopedic Implants | TC4 ELI (Gr.23/F136) | Regulatory requirements, high damage tolerance | ASTM F136 certification, heat lot traceability, and biocompatibility |
Downhole Oil & Gas Tools | TC4 (Gr. 5) | High-strength, corrosion-resistant | NACE Environmental Suitability Assessment, High-Temperature Mechanical Properties |
Industrial Fasteners | TC4 (Gr. 5) | High specific strength, corrosion-resistant | Compliance, Dimensional Accuracy |
Frequently Asked Questions
Q1: Can TC4 and TC4 ELI be used interchangeably?
Not recommended. TC4 has slightly higher strength, while TC4 ELI offers superior fracture toughness and damage tolerance. Due to fundamental safety differences in aviation damage-tolerant components and medical implants, procurement must strictly adhere to drawings and standards.
Q2: Should I choose TC4 or TC4 ELI for aerospace fasteners?
Most aerospace fasteners use TC4. TC4 ELI is selected only when design specifications explicitly require it, typically for damage tolerance designs. Fastener procurement must adhere to the material standards specified on the part drawing.
Q3: Must medical implants use ELI?
For load-bearing orthopedic implants, ASTM F136 (ELI grade) is the industry standard. Some non-load-bearing implants may use commercially pure titanium. Final material selection must be determined by the device design specifications and applicable regulations. The device manufacturer bears full responsibility for the compliance of the final product.
Q4: What precautions should be taken when using TC4 in acidic oil and gas environments?
Titanium alloys may be evaluated per NACE MR0175/ISO 15156 under certain acidic service conditions, but suitability must be confirmed based on specific hydrogen sulfide partial pressure, temperature, pH, and chloride concentration. When purchasing, provide suppliers with complete operating parameters and explicitly state NACE compliance requirements in the procurement documents.
Q5: Can you supply TC4 and TC4 ELI titanium bars? What is the lead time?
We supply TC4 and TC4 ELI titanium bars per ASTM B348, ASTM F136, AMS standards, and customer technical requirements. Available in hot-rolled or forged forms, with custom cutting to size as specified. Standard sizes are stocked for quick delivery; lead times for custom sizes depend on dimensions and quantity. Please specify if you require material certificates for aerospace (AMS) or medical (ASTM F136) grades when requesting a quote.
Conclusion
TC4 and TC4 ELI represent two optimization paths within the Ti-6Al-4V alloy system: strength versus toughness. TC4 maximizes load-bearing capacity per unit weight, while TC4 ELI prioritizes safety in the presence of defects. The choice between them hinges on whether strength or damage tolerance takes precedence under service conditions. Understanding this logic is more valuable than memorizing performance tables.
For technical selection guidance, material certification samples, or pricing for TC4 and TC4 ELI titanium rods, please send us your requirements. We'll provide tailored material solutions and quotes based on your application and specifications.
[Send your specifications to receive a TC4/TC4 ELI titanium rod technical solution and quote]
(Yucheng Haitai Industry | TA2 / TC4 / TC4 ELI Titanium Rods |yuchenghaicompany.com）
English Version
TC4 vs. TC4 ELI Titanium Bar: Selecting Grade 5 and Grade 23 for Aerospace, Medical, and Oil & Gas Applications
TC4 (Ti-6Al-4V, ASTM Grade 5 is widely regarded as one of the most critical titanium alloys for global aerospace applications. With its high specific strength and excellent fatigue resistance, it plays a central role in aerospace structural components and oil & gas downhole tools. TC4 ELI (ASTM Grade 23) offers enhanced fracture toughness and damage tolerance, primarily achieved through stricter control of interstitial elements—especially oxygen, nitrogen, and carbon—and by limiting iron content. This makes it the material of choice for load-bearing orthopedic implants and fracture-critical aerospace parts. Designed for procurement and engineering professionals, this guide systematically covers typical applications, material selection criteria, and procurement considerations for these two titanium bar grades across the aerospace, medical, and oil & gas sectors.
Two grades, one system, different safety margins.
TC4 and TC4 ELI belong to the same Ti-6Al-4V alloy family with nearly identical nominal compositions: approximately 6% aluminum, 4% vanadium, and the balance titanium. Their performance differences stem entirely from the control of interstitial element content—primarily oxygen and iron.
TC4 has a maximum oxygen content of 0.20% and a maximum iron content of 0.40%. The level of interstitial elements in this grade provides high strength while maintaining good ductility and machinability. TC4 ELI reduces the oxygen content to below 0.13% and limits iron content to 0.25%. This tighter control of interstitial elements typically improves fracture toughness and damage tolerance while retaining high strength levels.
From an engineering perspective: TC4 emphasizes maximum load-bearing capacity, while TC4 ELI focuses on service life under damage. Together, they offer distinct safety margins within the same alloy family. For procurement and engineering teams, selecting the correct grade depends on accurately prioritizing strength, toughness, and damage tolerance based on service conditions.
Quick Reference: Core Differences Between TC4 and TC4 ELI：
Comparison Criteria | TC4 (Gr. 5) | TC4 ELI (Gr.23) |
Key Benefits | High Intensity | High damage tolerance |
Maximum Oxygen Content | ≤ 0.20% | ≤ 0.13% |
Typical Use Cases | Aerospace structural components, oil & gas tools | Implants and damage-tolerant critical components |
Relative Cost | Lower | High |
Material Selection Priority | Capacity | Safety Margin |
Aviation sector: TC4's volume market, TC4 ELI's quality market
TC4: The Classic Choice for Aerospace Structural Components
TC4 is one of the most widely used titanium alloys in the global aerospace industry. From fuselage frames and wing connection joints to engine mounts, landing gear components, and thousands of titanium fasteners, parts machined from TC4 titanium bars are found throughout the load-bearing structures of modern aircraft.
Material Selection Logic: Aircraft structural components demand extreme weight reduction. TC4 has a density of approximately 4.5g/cm³ and a tensile strength of ≥895 MPa, offering specific strength far superior to high-strength steel and aluminum alloys. It also maintains reliable mechanical properties across a wide temperature range, typically from 300°C to 350°C depending on service conditions, covering the full spectrum from high-altitude cruising to ground storage.
Typical Aircraft Components:
Fuselage frame forgings and connection fittings
Wing-to-fuselage fittings – Must comply with applicable aviation material standards
Engine mount and bracket
Aerospace Fasteners – Extensively Machined from TC4 Titanium Rods. Aerospace fasteners must be manufactured using applicable aerospace material specifications as defined by component design requirements.
Procurement Requirements: TC4 titanium bars for aviation applications typically must comply with AMS 4928 (bar stock) or customer-specific specifications. Materials shall be supplied in the annealed or solution-treated and aged condition, accompanied by complete heat treatment records, mechanical property reports, and ultrasonic inspection reports. Nadcap-certified heat treatment and NDT are commonly required across many aviation supply chains.
TC4 ELI: The Upgrade Choice for Damage-Tolerance-Critical Components
When aerospace components demand higher resistance to crack growth and improved damage tolerance, TC4 ELI becomes the preferred design material over standard TC4. For such parts, once a fatigue crack initiates, extended inspection intervals are required to ensure the crack does not reach critical size before detection.
Typical Use Cases:
Fuselage structures and fittings designed for damage tolerance
High-strength fasteners for critical components (partial applications)
Structural components for low-temperature environments (e.g., high-altitude UAV airframes)
Selection logic: TC4 ELI is not used to "fully replace TC4" in aviation; rather, ELI is selected when damage tolerance is a critical design requirement. Both grades coexist within the aviation supply chain, and procurement must strictly follow the standard number specified on the part drawing.
TC4 ELI's home turf in the medical field
If the aerospace market is shared between TC4 and TC4 ELI, then medical implants are the exclusive domain of TC4 ELI.
Why must implants use ELI?
Orthopedic implants—including plates, spinal rod systems, femoral stems, and femoral knee components—are subjected to millions of cycles of loading in the human body. Any minor defect or crack within the material can propagate under cyclic stress, potentially leading to implant fracture. Such failure requires revision surgery for patients and triggers product recalls and regulatory risks for manufacturers.
TC4 ELI's "extra-low interstitial" (ELI) grade directly addresses this critical concern: lower oxygen content reduces interstitial solid-solution strengthening, thereby improving ductility, fracture toughness, and damage tolerance; reduced iron content minimizes heterogeneous nucleation sites. In corrosion-fatigue environments containing body fluids, the advantages of ELI are even more pronounced.
Typical Medical Components:
Pedicle screws and connecting rods for spinal fixation — direct machining from TC4 ELI bar stock
Hip stems and femoral knee components — Machining of TC4 ELI forged bars
T-plates and bone screws — Machined from TC4 ELI bar or sheet
Dental Implant Abutment — Small-Diameter TC4 ELI Bar
Regulations and Standards: TC4 ELI titanium bars for medical implants must comply with ASTM F136 (Surgical Implant Grade Ti-6Al-4V ELI Forgings) or ISO 5832-3. Although these standards are largely equivalent in terms of chemical composition and mechanical properties, the EU CE registration typically cites ISO standards, while US FDA registration usually references ASTM standards. Material suppliers must provide complete heat lot traceability documentation, EN 10204 3.1 or 3.2 material certificates, and a compliance statement meeting implant regulatory requirements.
Important Notice: Not all TC4 ELI materials meeting the ASTM F136 chemical composition requirements are suitable for direct use in implant manufacturing. Medical device manufacturers must also verify material biocompatibility, complete cleaning and passivation process validation, and ensure the entire manufacturing process complies with ISO 13485 quality management system standards and implant regulations. The ultimate compliance responsibility for medical devices lies with the device manufacturer.
Oil & Gas: TC4's Downhole Advantages
Balancing acidic environments with high-intensity demands
Downhole oil and gas tools—including drill collars, MWD housings, packer mandrels, and downhole safety valve components—face complex extreme conditions: high internal and external pressure, sour media containing hydrogen sulfide, cyclic stresses from wellbore bending and vibration, and downhole temperatures ranging from 150°C to 200°C.
TC4 offers unique advantages in these applications: higher specific strength than most corrosion-resistant alloys and better corrosion resistance than high-strength steels. Titanium alloys can be evaluated under certain acidic service conditions per NACE MR0175/ISO 15156, but suitability must be confirmed based on hydrogen sulfide partial pressure, temperature, pH, and chloride concentration.
Typical Oil & Gas Components:
MWD and LWD housings – high specific strength reduces tool string weight
Packer mandrel and setting tool — designed for high pressure and axial loads
Downhole safety valve spring and seat — requiring high fatigue resistance and corrosion resistance
Oil and Gas Well Tubing Connections – Leveraging Titanium's Reliability in Highly Corrosive Environments
ELI in Oil & Gas: Grade TC4 is the mainstream choice for downhole tools. TC4 ELI appears only occasionally in specialized tools requiring higher fracture toughness, but it is far less common than in medical applications. Oil and gas buyers prioritize NACE MR0175 environmental compliance and high-temperature mechanical properties over ELI-level interstitial element control.
Comparison of Chemical Composition and Mechanical Properties for Two Material Grades
The following data represents typical reference values for annealed bars. Actual performance requirements may vary depending on the product standard and heat treatment condition.
Project | TC4 (Gr. 5) | TC4 ELI (Gr.23) |
Aluminum (Al) | 5.50 - 6.75 | 5.50 - 6.50 |
Vanadium (V) | 3.50 - 4.50 | 3.50 - 4.50 |
Iron (Fe) ≤ | 0.40 | 0.25 |
Oxygen (O) ≤ | 0.20 | 0.13 |
Tensile Strength (MPa) ≥ | 895 | 860 |
Yield Strength (MPa) ≥ | 828 | 795 |
Elongation (%) ≥ | 10 | 10 |
Typical Product Standards | ASTM B348, AMS 4928 | ASTM B348, ASTM F136, AMS 4930 |
App Decision Quick Reference：
Use Cases | Recommended Grades | Why Choose Us | Procurement Priorities |
Aerospace Structural Components | TC4 (Gr. 5) | High-intensity, AMS-compliant | AMS certification, non-destructive testing, heat treatment records |
Damage-tolerant aviation parts | TC4 ELI (Gr.23) | High fracture toughness and high fatigue crack growth resistance | Damage Tolerance Performance Data, AMS Standards |
Orthopedic Implants | TC4 ELI (Gr.23/F136) | Regulatory requirements, high damage tolerance | ASTM F136 certification, heat lot traceability, and biocompatibility |
Downhole Oil & Gas Tools | TC4 (Gr. 5) | High-strength, corrosion-resistant | NACE Environmental Suitability Assessment, High-Temperature Mechanical Properties |
Industrial Fasteners | TC4 (Gr. 5) | High specific strength, corrosion-resistant | Compliance, Dimensional Accuracy |
Frequently Asked Questions
Q1: Can TC4 and TC4 ELI be used interchangeably?
Not recommended. TC4 has slightly higher strength, while TC4 ELI offers superior fracture toughness and damage tolerance. There are fundamental safety differences between the two for aerospace damage-tolerant components and medical implants. Procurement must strictly adhere to drawings and specifications.
Q2: Should I choose TC4 or TC4 ELI for aerospace fasteners?
Most aerospace fasteners use TC4. TC4 ELI is selected only when design specifications explicitly require it (typically for damage tolerance designs). Fastener procurement must comply with the material standards specified on the part drawing.
Q3: Must medical implants use ELI?
For load-bearing orthopedic implants, ASTM F136 (ELI grade) is the industry standard. Some non-load-bearing implants may use commercially pure titanium. Final material selection shall be determined by device design specifications and applicable regulations. Device manufacturers bear full responsibility for the compliance of the final product.
Q4: What precautions should be taken when using TC4 in acidic oil and gas environments?
Titanium alloys may be evaluated under certain acidic service conditions per NACE MR0175/ISO 15156, but suitability must be confirmed based on specific hydrogen sulfide partial pressure, temperature, pH, and chloride concentration. When purchasing, provide suppliers with complete operating parameters and explicitly state NACE compliance requirements in the procurement documents.
Q5: Do you supply TC4 and TC4 ELI titanium bars? What is the lead time?
We supply TC4 and TC4 ELI titanium bars per ASTM B348, ASTM F136, AMS standards, and customer technical requirements. Available in hot-rolled or forged forms, with custom cutting to size. Standard sizes are ready from stock; lead times for custom sizes depend on dimensions and quantity. Please specify if you require material certificates for aerospace (AMS) or medical (ASTM F136) standards when requesting a quote.
Conclusion
TC4 and TC4 ELI represent two optimization directions in the Ti-6Al-4V alloy system: strength versus toughness. TC4 maximizes load-bearing capacity per unit weight, while TC4 ELI prioritizes safety in the presence of defects. Choosing between them depends on whether strength or damage tolerance is the priority under operating conditions. Understanding this logic is more valuable than memorizing performance tables.
For technical selection guidance, material certificate samples, or pricing for TC4 and TC4 ELI titanium rods, please send us your requirements. We will provide tailored material solutions and quotes based on your application needs and specifications.
[Send your specifications to receive a technical proposal and quote for TC4/TC4 ELI titanium rods]
(Yucheng Haitai Industry | TA2 / TC4 / TC4 ELI Titanium Bar |yuchenghaicompany.com）