Classification, Characteristics and Applications of Titanium Alloys

Titanium is one of the strongest metals. Due to its corrosion resistance, it is widely used. Many manufacturers use pure titanium with other alloy elements. However, this metal is the least understood. People are not aware of the classification, characteristics, and applications of titanium alloys.

 

Despite being an excellent material, titanium remains enigmatic. The primary reason behind this is its rarity and high price. The manufacturers do not use it in routine manufacturing processes. However, this material has excellent features and uses.

 

One of the standout features of titanium is its strength and low weight. Therefore, its usage is standard in the aerospace industry. Manufacturers also use their alloys to achieve desired properties. Let’s explore the breadth of this remarkable metal in detail.

 

Overview of Titanium and its Alloys

Titanium is a very lightweight and unique metal. It is the ninth largest material present in our earth’s crust. However, the metal’s popularity is due to its robustness and rust resistance. Parts made with this material can withstand salty and moist conditions.

 

It is vital to note that titanium is not a new metal. It first came into existence in 1791. The British mineralogist William Gregor was the first person to work on it. The discovery of titanium is associated with the work of William Gregor. Titanium was found, but its quantity was meager.

 

Unlike magnesium or aluminum, titanium is not abundant. The alloys of titanium were not immediately known. A titanium alloy named Ti-6Al-4V was produced in the 1940s. This indicates how long it took to find alloys after discovering pure titanium. Nonetheless, it was a significant discovery that excited many manufacturers.

 

As I said, titanium has many valuable features that make it stand out. Those features include strength, low weight, and rust protection. Therefore, manufacturers aggressively use titanium in aerospace and automobiles. In fact, due to rust protection, its usage in the marine industry is also common. Titanium alloys have become a hot commodity in different sectors.

 

Characteristics of Titanium Alloys

Titanium’s performance is determined by its impurity content. Pure titanium is different from impure titanium. Impurities can be carbon, nitrogen, hydrogen, or oxygen. Similarly, the features of titanium alloys will also vary. 

 

The purest titanium iodide contains no more than 0.1% dao. However, its strength and plasticity are low. The 99.5% industrial pure titanium has the following characteristics: 

 

• Density ρ=4.5g/cubic centimeter
• The melting point is 1725℃
• Thermal conductivity λ=15.24W/(mK)
• Tensile strength σb=539MPa
• Elongation δ=25%, hardness HB195
• Section Shrinkage ψ=25%
• Elastic modulus E=1.078×105MPa

 

These characteristics are only valid for pure titanium. Each property will deviate if you make an alloy by adding another element. Manufacturers use those alloys to get desired properties for their work. Let’s dive deeper and discuss the prominent features of titanium. 

 

1- High Strength

 

The density of titanium alloy is about 4.51 g/cm³, which is only 60% of steel. The density of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of structural steel alloys. 

 

These alloys have a higher strength-to-density ratio than other structural materials. So, they can produce parts with high unit strength, good rigidity, and lightweight. The aircraft’s engine components, skeleton, and landing gear all use titanium alloys.

 

2- High Thermal Intensity

 

The service temperature is several hundred degrees higher than that of aluminum alloy. It can still maintain the required strength at medium temperatures. It can work for a long time at a temperature of 450～500℃. 

 

The specific strength of aluminum alloy decreases significantly at 150 degrees Celsius. The working temperature during machining of titanium alloy can reach 500℃, which is very high. It is higher than aluminum alloy, whose temperature remains below 200℃.

 

3- Good Corrosion Resistance

Titanium alloy works in a moist atmosphere and seawater medium. Its corrosion resistance is far better than that of stainless steel. It is particularly resistant to pitting, acid, and stress corrosion. This is not the end, as titanium offers resistance to other elements. Those include alkali, chlorides, chlorine, organic substances, nitric acid, and sulfuric acid. Its corrosion resistance is matchless, which helps titanium win the spotlight.

 

4-  Good Low-Temperature Performance

 

Titanium alloys can maintain their mechanical properties at low and ultra-low temperatures. Alloys like TA7 have deficient interstitial elements. They can keep some plasticity even at -253 degrees Celsius. Because of this, titanium alloy is an essential material for low-temperature structures.

 

5- High Chemical Activity

 

Titanium has high chemical activity in all conditions. It produces chemical solid reactions with O, N, H, CO, CO2, water vapor, and ammonia. When the carbon content is more than 0.2%, it forms hard TiC in the titanium alloy. Reacting with N forms a hard TiN surface layer at high temperatures.

 

When the temperature is above 600℃, titanium absorbs oxygen to form a hardened layer. The increase in hydrogen content will also create an embrittlement layer. The gas-absorbing process can harden a surface layer to 0.1-0.15 mm deep. Its hardness increases by 20-30%. Titanium has a high chemical affinity and adheres to the friction surface.

 

6- Low Thermal Conductivity

 

The thermal conductivity of Titanium λ=15.24 W/(m·K) is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum. Titanium alloys have conductivity about 50% lower than titanium. The elastic modulus of titanium alloy is about 1/2 of that of steel, so it has poor rigidity and is easy to deform.

 

It is not suitable for making slender rods and thin-walled parts. The spring-back of the processed surface during cutting is very large. The question is: how much? It is about 2 to 3 times greater than that of stainless steel. This causes severe friction, adhesion, and adhesive wear on the tool’s flank.

 

Classification of Titanium Alloys

 

There are generally different grades of titanium alloys. However, all the alloys fall under three categories: alpha, beta, and alpha-beta alloys. If the alloy element is oxygen or aluminum, then titanium alloy will be an alpha alloy. 

 

If the alloy element is vanadium and molybdenum, the titanium alloy will be a beta category. The alpha-beta alloys are in the middle between alpha and beta alloys. Each of these categories has different properties. Here is the Table showing their prominent differences:

 

Alpha (α) Alloys	Beta (β) Alloys	Alpha-Beta Alloys
Titanium with elements like aluminum and oxygen.	Alloy elements like vanadium, molybdenum, chromium.	It is intermediate between alpha & beta.
Non-heat treatable, excellent corrosion resistance.	Heat treatable, excellent formability.	Heat treatable and Balanced properties.
Excellent weldability & High-temperature resistance.	Good weldability, temperature resistance is lower than alpha.	Moderate to high-temperature resistance.

 

These alloys further divide and subdivide. You will see many different grades of each titanium alloy. All of these grades are common across many industries. However, I have noticed that the aerospace and auto sectors highly depend on them. The reason is their lightweight and robust nature.

 

Comparison Table of Commonly Used Titanium and Titanium Alloy Grades in Various Countries

Numbering	China GB/T	International standard ISO	USA ASTM	Russia TOCT	France NF	Germany DIN	Japan JIS
1	TA1	Grade1	GradeF1	BT1-00	T40	Ti1	Level 1
2	TA2	Grade2	GradeF2	BT1-0	T40	Ti3	Level 2
3	TA3	Grade4A/4B	GradeF3	BT1-0	T40	Ti4	Level 2
4	TA4	Grade3	GradeF4	BT1-0	T40	Ti4	Level 3
5	TC4	TiAl6v4	GradeF5	BT6	TA6V	TiAl6V4	YATB640
6	TC11	–	–	BT9	–	–	–

 

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Material Name	Chinese standard	USA standard
Titanium and titanium alloy sheet	GB/T3621	ASTM B265
Titanium and titanium alloy bars	GB/T2965	ASTM B348
Titanium and titanium alloy tube	GB/T3624	ASTM B337
Titanium and titanium alloy tubes for heat exchangers and condensers	GB/T3625	ASTM B338
Titanium and titanium alloy strips and foils	GB/T3622	ASTM B265
Titanium and titanium alloy cakes and rings	GB/T16598	ASTM B381
Titanium and titanium alloy wire	GB/T3623	ASTM B863
Titanium and titanium alloy processed materials for surgical implants	GB/13810	ASTM F67
		ASTM F136

 

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Commonly Used Titanium Alloy Grades and Chemical Composition（GB/T 3620.1-2007）

 

Alloy grade

Chemical composition group

Main ingredients/%

Ti

Al

Sn

Mo

V

Cr

Fe

Mn

Zr

Pd

Chinese standard

USA standard

Russia standard

Japan Standard

TA1ELI

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA1

GR1

BT1-0

TP270

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA1-1

GR1

BT1-00

Industrial pure titanium

≤0.20

–

–

–

–

–

–

–

–

TA2ELI

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA2

GR2

TP340

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA3ELI

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA3

GR3

TP450

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA4ELI

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TA4

GR4

TP550

Industrial pure titanium

–

–

–

–

–

–

–

–

–

TC4ELI

Ti-6Al-4VELI

5.5～6.5

–

–

3.5～4.4

–

–

–

–

–

TC4

GR5

BT6

TAP6400

Ti-6Al-4V

5.5～6.75

–

–

3.5～4.5

–

–

–

–

–

TA9

GR7

TP340Pb

Ti-0.2Pd

–

–

–

–

–

–

–

–

0.12～0.25

TA9-1

GR11

Ti-0.3Pd

–

–

–

–

–

–

–

–

0.12～0.26

TA18

GR9

OT4-B

TAP3250

Ti-3Al-2.5V

2.0～3.5

–

–

1.5～3.0

–

–

–

–

–

TA10

GR12

Ti-0.3Mo-0.8Ni

–

–

0.2～0.4

–

–

–

–

–

–

 

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Main ingredients/%					Impurities, not more than/%
Ni	Cu	Nb	Si	B	Fe	C	N	H	O	Other elements
										single	total
–	–	–	–	–	0.1	0.03	0.012	0.008	0.1	0.05	0.2
–	–	–	–	–	0.2	0.08	0.03	0.015	0.18	0.1	0.4
–	–	–	≤0.08	–	0.15	0.05	0.03	0.003	0.12	–	0.1
–	–	–	–	–	0.2	0.05	0.03	0.008	0.1	0.05	0.2
–	–	–	–	–	0.3	0.08	0.03	0.015	0.25	0.1	0.4
–	–	–	–	–	0.25	0.05	0.04	0.008	0.18	0.05	0.2
–	–	–	–	–	0.3	0.08	0.05	0.015	0.35	0.1	0.4
–	–	–	–	–	0.3	0.05	0.05	0.008	0.25	0.05	0.2
–	–	–	–	–	0.5	0.08	0.05	0.015	0.4	0.1	0.4
–	–	–	–	–	0.25	0.08	0.03	0.012	0.13	0.1	0.3
–	–	–	–	–	0.3	0.08	0.05	0.015	0.2	0.1	0.4
–	–	–	–	–	0.3	0.08	0.03	0.015	0.25	0.1	0.4
–	–	–	–	–	0.2	0.08	0.03	0.015	0.18	0.1	0.4
–	–	–	–	–	0.25	0.08	0.05	0.015	0.12	0.1	0.3
0.6～0.9	–	–	–	–	0.3	0.08	0.03	0.015	0.25	0.1	0.4

Application of Titanium Alloys

 

There are tons of titanium applications. This metal is substantial and corrosion-resistant. It offers many valuable perks that manufacturers cannot avoid using. For example, its light weight makes it suitable for aerospace industries. On the flip side, its rust resistance makes it stand out in the marine industry. Let’s dive down and discuss different uses of titanium alloys.

 

1- Aerospace Industry

 

In the aerospace industry, engineers aim to improve aerodynamics. So they use a lightweight material. But these materials are not very durable. In such cases, titanium comes in handy. It is lightweight, strong, and durable, making the aircraft aerodynamically perfect.

 

Manufacturers use it to make many aircraft components. The examples include airframes, landing gear, and wing structures. Many engine components also use different titanium alloys. Blades, disks, castings, etc., highly rely on this material. These parts can also bear high temperatures, which makes them stand out.

 

2- Medical Industry

 

While discussing characteristics, I mentioned that titanium is not harmful to humans. Even if it remains inside the human body, it does not cause toxicity. So, manufacturers make dental implants using titanium alloy. This material’s ability to integrate with living tissue makes it stand out. Many other medical instruments use titanium alloys.

 

Have you ever seen those dental implants and other surgical tools? Their shapes and designs are very complex. Moreover, titanium itself is rugged and robust. In this case, the custom CNC service of titanium comes into play. The CNC machining of titanium ensures the production of complex surgical tools with 100% precision.

 

3- Automotive Industry

 

Titanium is very robust and resistant to high temperatures. Moreover, it is low-weight and density. This makes it an ideal option to be used in the automobile industry. The exhausts of vehicles are made with titanium alloys. 

 

The exhaust system remains at extremely high temperatures. Titanium withstands high temperatures and does not deteriorate. This makes it ideal for use in engine components. Moreover, its lightweight improves vehicle fuel consumption.

 

4- Marine Industry

 

As I said earlier, titanium has excellent rust protection capability. It won’t get rusty quickly, even if used in harsh conditions. This feature makes titanium an excellent choice for the marine industry. Ship hulls, propellers, etc., remain in salty seawater. So, using titanium to make these components will prevent them from rusting for a long time. 

 

5- Military Defense Industry

 

Titanium is expensive, so it is not used in armor or weapons. However, manufacturers also use this material to make military vehicles. Those vehicles should be resistant to explosive devices for better safety. Also, military vehicles operate on rough roads. So, titanium alloys make them durable and long-lasting. Moreover, engineers prefer using titanium in military fighter jets.

 

Conclusion

Titanium metal and its alloys are not commonly used. Their higher prices make them suitable only for high-end products. However, their top-notch characteristics make them unique from the other metals. Just like magnesium, titanium is lightweight but very strong and durable. This guide explains all the characteristics of titanium. After reading their applications, you’ll know why many industries love titanium alloys.