Titanium and stainless steel define overlapping alloy groups with an amazing range of properties. Titanium is also an elemental metal which is often used in its pure form, having many beneficial and exceptional properties.
This article examines the properties, applications, and selection criteria for titanium and stainless steel. We’ll compare their strength, weight, thermal conductivity, and corrosion resistance across various industries including aerospace, medical, chemical processing, and automotive.
The discussion covers the specific advantages of each material, their limitations, and the factors to consider when choosing between them. From cost considerations to manufacturability, we’ll explore the nuances that inform material selection in high-performance applications.
Quick overview
In many ways, this group of metals and alloys are a central pillar in the more extreme applications of metals – offering exceptional corrosion resistance, heat tolerance, strength and in the case of many Titanium alloys strength to weight ratio advantages.
- Titanium properties: Titanium offers among the best strength-to-weight ratio of all alloys and pure metals. It also possesses exceptional corrosion resistance, resulting in great biocompatibility and chloride ion resilience, in particular. Its combination of particularly low density, high thermal tolerance and tensile/fatigue strength make it invaluable in weight sensitive and high stress applications.
- Titanium applications: The aviation and space sectors make extensive use of the material and its alloys, for the combination of weight reduction, high strength and resilience to corrosion and heat. It serves in prosthetic applications for weight/strength advantages and in implants for low weight and high biocompatibility. Race auto parts, sports gear, chemical plant equipment, and the marine marine sector also benefit from the material, where cost is a lesser factor than performance.
- Stainless steel properties: Stainless steels are a broad group, ranging from basic and low cost materials in the 400 series classification, through higher performing and more corrosion resistant alloys such as 300 series, through to Titanium containing surgical steels and up to various superalloys that can be described as stainless steels.
- Stainless steel applications: Stainless steels cover an extraordinary range of applications from the mundane, such as wood screws, to the extreme such as rocket engine combustion chambers and gas turbine blades. While the great majority of applications that use stainless steel are not candidates for the use of Titanium, at the leading edge of challenges in temperature tolerance, corrosion resistance and strength/toughness, there is considerable overlap in between Titanium (and its alloys) and stainless steels.
These two families of engineering materials have commonality in that Titanium is alloyed with stainless steel (among other metals) and it’s worth noting that the definition of stainless steel can be open to interpretation at the upper performance end, where Nickel-Chrome-Iron alloys in the superalloy range are closely related to stainless steels. The alloys families have common areas in application, but stainless steel has utility far lower down the cost spectrum than does Titanium.
Selection process
Comparing Titanium and stainless steel provides key understanding that can inform the selection of solutions for highly demanding applications. The demand can be exceptional on any one (or more) of a number of axes that differentiate the materials. The effective selection often requires a compromise between conflicting demands, where priorities must be assigned on these demand axes to effectively differentiate the options.
- Weight and strength trade-offs: Comparing their specific strengths can determine which material is optimal for overall performance, with a wide spectrum of durabilities available.
- Corrosion resistance: The corrosion behaviors of Titanium, Titanium alloys, stainless steels and superalloys are a complex spectrum That must be carefully considered case by case in their selection. Typically, a property of stainless steels is self passivation – an isolating oxide film forms on the surface and self heals where damaged. Titanium is a noble metal, and simply doesn’t react rapidly under most conditions.
- Cost considerations: In many applications, cost is a major factor and this typically rules out Titanium and high-Titanium alloys. Where other factors are dominant, the selection process is more open.
- Sector specifics: Industries typically require specific compliances, resultant from specific properties of alloys. The more advanced and regulated the sector, the fewer options can generally be considered.
- Environmental impact: Evaluating recyclability/sustainability can be a significant concern, although typically all metals offer optimum recyclability compared with any alternative option.
- Manufacturability: Ease of fabrication and volume suitability of the manufacturing process is key. While stainless steels and superalloys pose challenges in manufacture, Titanium and high-Titanium alloys are among the most costly and challenging to process.
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Strength and weight
Titanium application
Titanium finds high value application, in particular due to its strength-to-weight ratio and intrinsic corrosion resistance. Titanium is very lightweight and possesses high strength. It lends these properties to alloys it is used in, in proportion to its percentage. Its high cost of utilization and processing are only counterbalanced by higher value applications that demand its particular and outstanding properties.
This is optimal for aerospace applications, like aircraft spacecraft stress parts, where minimizing weight while maximizing structural integrity is paramount. High strength-to-weight ratio helps in medical implants, sporting equipment and military applications.
Stainless Steel application
Stainless steel is as close to a ‘universal’ class of materials as exists. It is applied to the mundane and the exceptional, and entails such a wide range of grades and conditions that it serves in virtually all product sectors.
It is suited to many applications due to its excellent corrosion resistance, high strength, and durability. It withstands harsh environments, making it ideal for use in construction, medical devices, and food processing. Its aesthetic appeal, ease of fabrication, and recyclability also contribute to its widespread use in various industries.
Comparing strength, Titanium and Stainless Steel
Titanium alloys generally exhibit similar tensile strengths to the more extreme stainless steels. The tensile strength of Titanium alloys can range from 345 to 1380 MPa (50,000 to 200,000 psi), depending on the specific alloy and heat treatment.
Aluminum alloys typically lie in the range of 140 to 480 MPa (20,000 to 70,000 psi). This is still a high strength, so a balance between application resilience, weight, total volume of parts and part cost (from material AND processing) will drive the selection.
The strength of Aluminum and Titanium results directly from their alloying and properties:
- Stainless steels display a range of crystalline structures – austenitic (FCC), martensitic (body centered tetragonal BCT), ferritic (BCC), duplex (BCC and FCC in varied proportions) and precipitation hardening (FCC OR BCC), while elemental titanium has a hexagonal close-packed (HCP) crystal structure. Notably many superalloys are also stainless steels, or they belong to grades that are stainless steel adjacent. Atomic structures affect dislocation planes, defining the materials’ ultimate strength, ductility and malleability. Titanium’s HCP structure acts as an aggressive block on the formation of slip planes, directly resulting in high strength and low ductility.
- Restricting grain size by precipitation and heat treatment processes greatly affects properties in stainless steels, also influencing Titanium in the pure form.
- Stainless steel is intrinsically alloyed, where Titanium can be used in the native OR alloyed form. In all cases where alloying is performed, the selection of constituents and processing can massively affect material properties.
- Thermal manipulations such as heat/quench and controlled cooling can be effective in all of the stainless steels, Titanium alloys and even elemental Titanium.
- Titanium possesses high strength at elevated temperatures (up to 550°C), but this can be greatly enhanced by alloying with Aluminum, which can extend the maximum service temperature greatly. The highest temperature performances are achieved by progressive, slow cooling of superalloys with a propagating wave from one end of a casting to the other, resulting in monocrystalline structures that offer exceptional heat tolerance.
Usage and applications
Titanium and its extensive alloy family has uses across most high value industries and some consumer product sectors in which cost concerts are not paramount.
This results from its unique properties, but also from a marketing pressure for novelty that can override cost and processing concerns.
Typical applications are:
- Aerospace: Titanium’s high strength and low density, corrosive environment resilience, and elevated temperature tolerance are highly relevant in this sector. It is used in aerospace frame, actuator and engine components in jet/rocket engines, aircraft/spacecraft and satellites.
- Medical: Titanium and various of its alloys are highly biocompatible, suitable for tissue-involved medical implants – artificial joints, dental implants, and surgical instruments.
- Chemical processing: Its corrosion resistance when exposed to aggressive chemicals make it relevant in chemical processing, heat exchangers, valve components, and reaction chambers.
- Military: Strength and durability make it a preferred choice for military applications, including armored vehicles, aircraft, and naval equipment.
- Sports equipment: Bicycle components, golf clubs and racquets benefit from its high strength to weight ratio. In many cases, the impression benefit is at least as significant as the functional benefit.
- Automotive: Race vehicle exhaust systems and suspension parts are improved by Titaniums corrosion resilience and lightweight strength.
- Oil and Gas: Marine exposed and caustic fluid handling equipment can benefit from being made in Titanium or its alloys.
- Desalination: Titanium offers exceptional chloride ion corrosion resistance, making these materials valuable in salt water handling.
Titanium's non-toxic nature and versatile applications
Titanium is appreciated for its non-toxic and biocompatible character, rendering both the material and its alloy family a good choice for medical applications such as implants, prosthetics, and surgical instruments. Its resistance to corrosion ensures long-term durability within tissue contact, while its lightweight nature reduces the weight burden. Beyond medicine, titanium’s non-toxicity is crucial in food processing, where it’s used in equipment that must avoid contamination: aerospace and marine industries, where its strength-to-weight ratio and corrosion resistance make it valuable for aircraft, spacecraft, and submarines.
Choice of application: Titanium vs stainless steel
Choosing between Stainless steel and Titanium depends on the specific needs of each application – strength/weight ratio, temperature tolerance, corrosion properties, cost etc.
- Stainless steel alloys offer typically lower cost materials with high strength and the possibility of extreme temperature tolerance.
- Titanium offers typically better strength-to-weight ratio, good corrosion resistance and biocompatibility, with capability in aerospace/engine components, medical implants, and moderately aggressive chemical processing applications.
- The critical decision factor in selecting Titanium is typically weight. Titanium is very high cost in both material and manufacturing, so it is only selected when the critical drivers override cost.
Density and weight ratio
Titanium's lower density compared to aluminum
Titanium has a density of approximately 4.5 g/cm³, whereas stainless steels have a significantly higher density range of about 7.5 and 8.1 g/cm³. Despite its higher cost, Titanium is often chosen for applications where its superior strength-to-weight ratio, corrosion resistance, and other properties overwhelm the material and processing cost issues.
Impact of density on weight ratio
Titanium has a high specific strength and it imparts this to many of the alloys it is used in. Titanium Aluminum alloys, particularly gamma Titanium aluminide, offer exceptional specific strength (i.e. high strength with low weight) making these materials suitable as substitutes for considerably higher density superalloys, particularly in weight critical and high temperature applications such as gas turbine blades.
Where component weight is less critical than cost, various high performance stainless steels can offer exceptional service capacity and durable solutions in difficult and aggressive environments.
Advantages and disadvantages of Titanium and its alloys
- High strength-to-weight ratio, making Titanium is as strong as many advanced steels for considerably lower mass, ideal for aerospace and other weight critical applications.
- Titaniums corrosion resistance is excellent, even in harsh environments, making it suitable for chemical processing and marine applications.
- It is non-toxic and well-tolerated by the human body, making it perfect for medical implants and devices where biocompatibility is as important as strength.
- High temperature stability, where higher Titanium alloys maintain their strength and integrity at elevated temperatures, useful in aerospace and industrial applications.
- Titanium is expensive to produce and very hard to process, limiting its use to high-performance and extreme applications.
- Its toughness and hardness make it challenging to form and machine, increasing manufacturing costs.
- Titanium is prone to wear and galling under friction, requiring surface treatments for durability.
Alloy elements and their influence on weight
Titanium alloys include a range of alloying agents:
- Aluminum in Titanium alloys contributes to reduced weight without excessive loss of strength.
- Vanadium enhances the alloy’s mechanical properties.
- Iron is often added to improve weldability.
- Titanium is included in some stainless steel alloys, to improve corrosion resistance.
These alloying elements are carefully balanced to maintain the inherent lightweight characteristic while enhancing its strength, corrosion resistance etc.
Stainless steels are formed from a wide array of metallic and some non metallic constituents, typically containing(in addition to steel:
- Chromium, typically above 10.5 to 30%, delivering self passivation with Chromium dioxide while degrading the ductility.
- Nickel at 8 to 20% which enhances corrosion resistance and restores some ductility.
- Carbon – usually below 1.2% to enhance hardness and strength. At higher levels it typically degrades corrosion resilience.
- Manganese of 2 to 10% which improves hardness, strength and wear resistance and improves smelting quality.
- Also Molybdenum, Silicon, Nitrogen, Phosphorous and Sulphur.
Titanium in stainless steels is unusual but not unknown:
- In type 321 stainless steel, Titanium is added (typically 0.5% to 1%) to stabilize the alloy. Titanium binds with carbon to form Titanium carbides, which prevent the formation of Chromium carbides. This helps maintain the high temperature corrosion resistance of the steel, and improves the material’s weldability.
- Titanium can be added to steels intended for high-temperature applications to improve creep resistance under sustained high temperatures.
- In some specialized applications, titanium can be added to steel to enhance its resistance to specific forms of corrosion.
Alloying titanium with steel is challenging because of titanium’s high affinity for Oxygen and its high melting point. This requires careful control during the alloying process to avoid contamination and ensure the desired properties are achieved.
Thermal conductivity and corrosion resistance
Stainless Steel and Titanium’s poor thermal conductivity
Titanium offers very low thermal conductivity which quickly falls away with rising temperature, where most stainless steels show similarly poor conductivity and a positive coefficient in response to rising temperature.
Titanium's surface properties and corrosion resistance
Titanium offers exceptional corrosion resistance due to the formation of a very robust protective oxide layer on its surface, despite being a fairly reactive metal. This surface also possesses a low coefficient of friction, making it resistant to galling and seizing.
Stainless steel offers similar protection in the formation of Chromium oxide surface coating that is tough and acts as an oxygen barrier.
Importance of corrosion resistance in different applications
Corrosion resistance is vital in both Aluminum and Titanium applications for durability and safety. It extends the lifespan of components, reduces maintenance costs, and ensures structural integrity, especially in aerospace and automotive sectors.
The elevated chemical resilience of Titanium is exploited in chemical processing, medical implants, aerospace and marine applications, delivering functional reliability, biocompatibility and reduced maintenance burden.
Both materials require careful consideration of their particular corrosion vulnerabilities, but Titanium remains unreactive in most environments and at elevated temperatures. Stainless steel is also resilient in many environments, but more commonly suffers from oxide film degradation and scale formation at elevated operating temperatures. Some stainless steel alloys perform better in this regard: ferritic grade 446 is renowned for not scaling at up to 1100° C due to its very high Chromium content (24%).
Cost and price
Titanium's higher cost compared to aluminum
The spot price of elemental Titanium is around US$5.75 per kg. This is very high compared with 304 and 316 stainless steel which generally cost $3.00 per kg. This differential is not simple, as material usage in any application is not weight comparable directly. Less titanium by mass is required for equivalent strength of stainless steel, in most applications.
Selecting between the two materials can be a price driven decision, but more often the performance issues will drive a selection.
Factors to consider when evaluating cost-effectiveness
When evaluating the cost-effectiveness of choosing between aluminum and titanium, several crucial factors should be considered:
- Material costs: Balancing the material purchase cost effect.
- Processing: Take into account processing costs, which can be much greater than raw material costs – and can be X10 for Titanium compared with Aluminum.
- Weight savings: Does Titanium’s weight reduction benefit justify its higher cost.
- Chemical resilience: Does the application need exceptional corrosion endurance?
- Lifetime: Consider long-term maintenance and replacement costs, where titanium’s durability can represent long term value.
- Volume: Large-scale production can impact costs significantly, Aluminum is considerably easier to transition to high volume.
- Industry norms: Ensure compliance with industry standards and safety.
- Environmental impact: Analyze environmental regulations and disposal costs for lifecycle impact.
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Other factors to consider
Linear thermal expansion and its implications
Differentials in linear thermal expansion coefficients are important where dimensional stability with temperature variations is crucial.
- Titanium has a relatively low coefficient of linear thermal expansion, typically around 8.6 x10-6 per °C (or 8.6 μm/m·°C). Some more advanced alloys display ZERO coefficient of thermal expansion in normal operational ranges.
- Stainless steels have a range of higher coefficient of linear thermal expansion, typically around 11-18 x 10-6 per °C (or 11-18 μm/m·°C).
Formation of oxide layers and their effects on material properties
Titanium and Aluminum both form resilient oxide layers, with significant effects on their material properties:
- Titanium: The metal is intrinsically reactive, so when exposed to Oxygen, Titanium possesses a thin, chemically resilient and self-healing protective oxide layer of TiO2. This provides a barrier to most chemical attack and is directly responsible for the biocompatibility of the material and many of its alloys.
- Stainless steel: Stainless steel forms a thin, protective oxide film primarily composed of chromium oxide (Cr₂O₃) when exposed to oxygen. This passive layer is self-repairing and prevents further oxidation, providing corrosion resistance. The film forms spontaneously and rapidly in the presence of Oxygen. The Chromium content in stainless steel, usually at least 10.5%, is crucial for this process.
Overall, these oxide layers enhance the material properties of both alloy families, contributing to their corrosion resistance and durability in diverse applications.
Conclusion
When comparing stainless steel and Titanium, both offer particular advantages in specific applications. Stainless steel stands out for its cost-effectiveness, ease of fabrication, and reliable performance in a wide range of environments. It’s an excellent choice for applications where budget, availability, and general durability are key considerations.
Titanium excels in scenarios that demand superior strength-to-weight ratio, exceptional corrosion resistance, and biocompatibility. Although more expensive and challenging to machine, titanium is invaluable in high-performance industries like aerospace, medical, and marine environments.
Ultimately, the choice between stainless steel and titanium depends on the specific requirements of the application. Whether it’s the affordability and versatility of stainless steel or the lightweight strength and resilience of titanium, understanding the properties of each material ensures optimal performance and longevity in their respective fields.
There is no single deciding factor in this material matchup. Head to head decisions rely entirely on the fine details of the components application considerations in chemical resilience, strength, absolute component weight and cost sensitivity.
As a rule, Titanium wins where weight is the critical factor. It can also win in chemical resilience, although generally that requires a broader comparison with other high stability metals (and non-metal options).
Where cost and/or high volume are the drivers, stainless steel wins every time.
Where high temperature performance is the most critical, options and selection become more complex, as the alloys families of stainless steel and Titanium are wide and divergent in properties.
The history of Titanium in military applications in the former USSR and now Russia is a prime example – close to the source and with a ‘better than anyone’ approach, Titanium is an easier choice to make.
The decision to use Titanium or one of its alloys can often be a market impression driven one – where the apparent value outweighs the tangible costs in sourcing and processing.