Horological Meandering

Having been a titanium freak for some decades now, I took note of Cookies' report on a new G-P watch where he commented on the grade of titanium G-P used - implying Grade 5 was better than Grade 2.

I have materials handbooks, reference guides, and piles of titanium items around the house. After some research, I'm not sure I can agree that one grade is better than another when used in a watch case. So in case you are similarly undecided about which grade is YOUR FAVORITE titanium material, read on...

TITANIUM BACKGROUND

Titanium was first purified into its metallic forms in the early 1900s and is not particularly rare -- in fact, it is the fourth most abundant metal on Earth. Titanium is the ninth most abundant element, making up about 0.6% of the Earth's crust. It occurs in nature only in chemical combination, usually with oxygen and iron. Mineral sources for titanium are rutile, ilmenite, and leucoxene (derived from ilmenite). Rutile is 93% to 96% titanium oxide (TiO2), ilmenite is between 44% and 70% TiO2, and leucoxene concentrates may contain up to 90% TiO2. 

Titanium is difficult to purify, partially due to its extremely high melting temperature. Refinement requires huge amounts of (normally expensive) electrical energy, and can cost about 5x the price of aluminum refining.

In the late 1940 US production was a few hundred pounds a year. No other country was producing titanium commerically at that time. Large-scale production began around 1950 when almost 60 tons were available! Seventy years later, the total world production is about a quarter million tons a year.

Elemental titanium is a silver-grey non-magnetic metal with a density almost half that of steel. It falls into the “light metal” category as does aluminum. Modern titanium comes either as elemental titanium or in various titanium alloys, all made to increase both the strength and corrosion resistance of the base titanium. These alloys have the necessary strength to work as aerospace, structural, biomedical, and high-temperature materials, while elemental titanium is usually reserved as an alloying agent for other metals.

Titanium (compared to steel) is more prone to increased ductile behavior before fracturing .. meaning that it stretches almost half its length before fracturing. This is one reason why titanium is so difficult to machine, as it pulls and deforms instead of chipping or cutting. Steel comes in many varieties but generally has a low elongation at break, making it harder and more prone to brittle fracture under tension.

Hardness is a comparative value that describes a material’s response to scratching, etching, denting, or deformation along its surface. It is measured using indenter machines. For high-strength metals, the Brinell hardness test is often specified. Even though the Brinell hardness of steel varies greatly with heat treatment and alloy composition, it is usually harder than titanium. This is not to say that titanium deforms easily when scratched or indented; on the contrary, the titanium dioxide layer that forms on the surface is exceptionally hard and resists most penetration forces. They are both resistant materials that work great when exposed to rough environments, barring any additional chemical effects.

Titanium is difficult to weld, machine, or form, but can be heat-treated to increase its strength. It has the unique advantage of being biocompatible, meaning titanium inside the body will remain inert, making it indispensable for medical implant technology. It has an excellent strength-to-weight ratio, and is resistant to corrosion thanks to the layer of oxide formed on its surface in the presence of air or water. It also resists cavitation and erosion, which predisposes it towards high-stress applications such as aircraft and military technologies. Titanium is vital for projects where weight is minimized but strength is maximized, and its great corrosion resistance and biocompatibility lend it to some unique industries not covered by more traditional metals.

Only about 5% of the world's annual production of titanium minerals goes to make titanium metal. The other 95% of such production is used primarily to make white TiO2 pigment. Because of its whiteness, high refractive index, and resulting light- scattering ability, TiO2 is the predominant white pigment for paints, paper, plastics, rubber, and various other materials.

The United States has become highly dependent on imports of the minerals used to make titanium and TiO2, which primarily come from Australia and Canada. A major problem affecting the titanium metal industry is the wide fluctuations on demand caused by changes in requirements for both military and commercial aircraft programs. Titanium sponge producers have repeatedly increased capacity in response to anticipated demand and have then been left with excess capacity when these programs were canceled or cut back. The most recent example of such a fluctuation was the historic peak in demand and price reached in 1980-81 and the subsequent collapse in 1982-84. The sharp rise and fall of demand and prices were believed to be aggravated by overestimation of aircraft orders that did not materialize or were later canceled.

Commercially Pure Titanium Grades:

• Grade 1
• Grade 2
• Grade 3
• Grade 4

Titanium Alloys:

• Grade 5 (6Al-4V)
• Grade 23 (6AL-4V ELI)
• Grade 7
• Grade 11
• Grade 12
• Ti 5Al-2.5Sn

Titanium Grades and Alloys: Properties and Applications

PURE TITANIUM

Grade 1

Grade 1 titanium is the first of four commercially pure titanium grades. It is the softest and most ductile of these grades. It possesses the greatest formability, excellent corrosion resistance and high impact toughness. Because of all these qualities, Grade 1 is the material of choice for any application where ease of formability is required and is commonly available as titanium plate and tubing. These include:

• Chemical processing
• Chlorate manufacturing
• Dimensional stable anodes
• Desalination
• Architecture
• Medical industry
• Marine industry
• Automotive parts
• Airframe structure

Grade 2

Grade 2 titanium is called the “workhorse” of the commercially pure titanium industry, thanks to its varied usability and wide availability. It shares many of the same qualities as Grade 1 titanium, but it is slightly stronger. Both are equally corrosion resistant. This grade possesses good weldability, strength, ductility and formability. This makes Grade 2 titanium bar and sheet are the prime choice for many fields of applications:

• Architecture
• Power generation
• Medical industry
• Hydro-carbon processing
• Marine industry
• Exhaust pipe shrouds
• Airframe skin
• Desalination
• Chemical processing
• Chlorate manufacturing

Grade 3 

This grade is least used of the commercially pure titanium grades, but that does not make it any less valuable. Grade 3 is stronger than Grades 1 and 2, similar in ductility and only slightly less formable - but it possesses higher mechanical strength and major corrosion resistance. Users include:

• Aerospace structures
• Chemical processing
• Medical industry
• Marine industry

Grade 4

The strongest of the four grades of commercially pure titanium. It is also known for its excellent corrosion resistance, good formability and weldability. Though it is normally used in the following industrial applications, Grade 4 has recently found a niche as a medical grade titanium. It is needed in applications in which high strength is required:

• Airframe components
• Cryogenic vessels
• Heat exchangers
• CPI equipment
• Condensor tubing
• Surgical hardware
• Pickling baskets

TITANIUM ALLOYS

Grade 5 6Al-4V 

Known as the “workhorse” of the titanium alloys, Ti 6Al-4V, or Grade 5 titanium, is the most commonly used of all titanium alloys. It accounts for 50 percent of total global titanium usage. Its usability lies in its many benefits. Ti 6Al-4V may be heat treated to increase its strength. It can be used in welded construction at service temperatures of up to 600° F. This alloy offers its high strength at a light weight, useful formability and high corrosion resistance. Ti 6AI-4V’s usability makes it the best alloy for use in several industries, like the aerospace, medical, marine and chemical processing industries. It can be used in the creation of such things as:

• Aircraft turbines
• Engine components
• Aircraft structural components
• Aerospace fasteners
• High-performance automatic parts
• Marine applications
• Sports equipment

Grade 7

Grade 7 is mechanically and physically equivalent to Grade 2, except with the addition of the interstitial element palladium, making it an alloy. Grade 7 possesses excellent weldability and fabricality, and is the most corrosion resistance of all titanium alloys. In fact, it is most resistant to corrosion in reducing acids. Grade 7 is used in chemical processes and production equipment components.

Grade 11

Grade 11 is very similar to Grade 1, except for the addition of a tiny bit of palladium to enhance corrosion resistance, making it an alloy. This corrosion resistance is useful to protect against crevice erosion and reducing acid in chloride environments. Other useful properties include optimum ductility, cold formability, useful strength, impact toughness and excellent weldability. This alloy can be used in the same titanium applications as Grade 1, especially where corrosion is a concern such as:

• Chemical processing
• Chlorate manufacturing
• Desalination
• Marine applications

Grade 12

Grade 12 titanium holds an “excellent” rating for its high quality weldability. It is a highly durable alloy that provides a lot of strength at high temperatures. Grade 12 titanium possesses characteristics similar to 300 series stainless steels. This alloy can be hot or cold formed using press brake forming, hydropress forming, stretch forming or drop hammer method. Its ability to be formed in a variety of ways makes it useful in many applications. This alloy’s high corrosion resistance also makes it invaluable where crevice corrosion is a concern. Grade 12 can be used in the following industries and applications:

Shell and heat exchangers

Hydrometallurgical applications

Elevated temperature chemical manufacturing

Marine and airfare components

Grade 23 6AL-4V ELI

Grade 23 Surgical Titanium 6AL-4V ELI is a higher purity version of Ti 6Al-4V. It can be made into coils, strands, wires or flat wires. It’s the choice for any sort of situation where a combination of high strength, light weight, good corrosion resistance and high toughness are required. It has a superior damage tolerance to other alloys. Grade 23 is the ultimate dental and medical titanium grade. It can be used in biomedical applications such as implantable components due to its biocompatibility, good fatigue strength and low modulus. It can also be used in detailed surgical procedures, as:

• Orthopedic pins and screws
• Orthopedic cables
• Ligature clips
• Surgical staples
• Springs
• Orthodontic appliances
• In joint replacements
• Cryogenic vessels
• Bone fixation devices

Ti 5Al-2.5Sn

Ti 5Al-2.5Sn is a non-heat treatable alloy that can achieve good weldability with stability. It also possesses high temperature stability, high strength, good corrosion resistance and good creep resistance. Creep refers to the phenomenon of plastic strain over long periods of time, which happens at high temperatures. Ti 5Al-2.5Sn is mostly used in aircraft and airframe applications, as well as cryogenic applications.

  login to reply