Unalloyed titanium typically contains between 99%-99.5% titanium, with the balance being made up of iron and the interstitial impurity elements hydrogen, nitrogen, carbon, and oxygen. The microstructure of unalloyed titanium consists of grains of alpha phase, with the possibility of small amounts of beta phase. The ‚Äúunalloyed‚Äù grades of titanium are generally less expensive, and are easier to fabricate than alloyed, and generally stronger grades of titanium.
ALPHA AND NEAR-ALPHA ALLOYS
Titanium alloys have a fully alpha structure only if they contain alpha stabilizers such as aluminum, tin, and oxygen. These elements also act as solid solution strengtheners. The typical all-alpha alloy is Ti-5Al-2.5Sn. Near-alpha alloys include Ti-8Al-1Mo-1V, Ti-6Al-2Sn-4Zr- 2Mo.
ALPHA-PLUS BETA (α-β) ALLOYS
These alloys contain both alpha stabilizers and beta stabilizers. These alloys can be heat treated to develop a range of micro-structures. The alpha-beta alloys are moderately heat treatable and weldable. The alpha-beta alloys have greater hardenability and thus can be through-hardened in thicker section by heat treatment. The most important α-β alloy is Ti-6Al-4V. The other α-β alloys include Ti-6Al-6V-2Sn and Ti-6Al-2Sn- 4Zr-6Mo.
Beta alloys contain a balance of beta stabilizers to alpha stabilizers, which is sufficiently high that a fully beta phase microstructure can be retained on cooling. Their generally high strength, high toughness, and improved formability, as compared with alpha-beta alloys, provides an attractive combination of properties. However, processing and material costs are often quite high. Ti-3Al-8V-6Cr-4Zr-4Mo is an example of a commonly utilized beta alloy.
Titanium Grade 1: UNS R50250 (ASTM B265 / ASTM B337 / ASTM B338 / ASTM B348)
Commercially Pure Grade 1 is one of the softest and most ductile grades exhibiting the greatest formability. It has excellent corrosion resistance property and is used in wide variety of applications. This grade material is mainly used in Marine & chemical industries where the parts are subjected to very harsh environments. This material is also used for fabricating anodes for cathodic protection applications.
Titanium Grade 2: UNS R50400 (AMS 4902 /AMS 4941/ AMS 4942 /ASTM B265 /ASTM B337 /ASTM B338 /ASTM B348 )
Commercially Pure Grade 2 is slightly stronger than Grade 1 but equally corrosion resistant against most applications. Grade 2 Extremely high resistance to oxidising or neutral media. Excellent resistance to sea water and solutions polluted by chlorides. Best strength to weight ratio in any corrosion resistant material. This grade is one of the most common Titanium Grades and is used for Heat Exchangers, Condenser Tubing & Bleaching plants in paper industry, offshore oil installation water pipe lines.
Titanium Grade 3: UNS R50550 (AMS 4900 / ASTM B337 / ASTM B338)
This CP3 grade unalloyed grade offers slightly higher mechanicals when compared with Commercially Pure Grade 2 while displaying similar ductility and formability.Generally used where corrosion resistance is a major design factor in chemical production components, marine and airframe applications.
Titanium Grade 4: AMS 4901 / AMS 4921 / ASTM B265 / ASTM B348
The highest strength pure unalloyed Titanium. High oxygen, extra high strength. Grade 4 displays the highest strength of all the unalloyed CP grades. It combines excellent corrosion resistance with good formability and weldability. While mill availability is not a problem, distributor availability is limited and should be a consideration in alloy selection. Mainly used in hydraulic and instrumentation tubing. Generally chosen for its corrosion resistance in a variety of chemical process equipment as well as marine and airframe applications.
Titanium Grade 5: UNS R56400 (AMS 4911 / AMS 4920 / AMS 4928 / ASTM B265)
Ti-6Al-4V is the most commonly used Titanium Grade, its high strength; lightweight and corrosion resistance enables this grade to be used in many applications. The Industries for which this material is generally used are Aerospace, Marine, Medical and Chemical Processing. This non-magnetic alpha-beta alloy is the workhorse alloy of the titanium industry. The alloy is fully heat treatable in section sizes up to 15mm and is used up to approximately 400°C (750°F). Since it is the most commonly used alloy over 70% of all alloy grades melted are a sub-grade of Ti6Al4V, its uses span many aerospace air-frame and engine component uses and also major non-aerospace applications in the marine, offshore and power generation industries in particular.
Bio-compatibility: Excellent, especially when direct contact with tissue or bone is required. Ti-6Al-4V’s poor shear strength makes it undesirable for bone screws or plates. It also has poor surface wear properties and tends to seize when in sliding contact with itself and other metals. Surface treatments such as nitriding and oxidizing can improve the surface wear properties.
Titanium Grade 6: 5Al 2.5Sn UNS R52400 (ASTM B265/ASME SB-265/AMS 4910/AMS 4926)
Titanium 5-2.5 offers high temperature stability, strength, oxidation and creep resistance.
Titanium Grade 7: UNS R52400 (ASME SB-265/ASME SB-348)
Commercially Pure Grade 7 is very similar to Grade 2 but with a Palladium content. This content enables this material to be used in very low Temperatures. Applications are Power Generation and Chemical Processing.
Titanium Grade 8: UNS R56320 (ASTM B265 / AMS 4943 / AMS 4944 / AMS 4945)
Ti-3Al-2.4V has exceptional corrosion resistance and can be used in higher temperatures that Grade 1 through to Grade 4. The grade has many applications in Aerospace, Medical, Marine, Automotive, Transportation and Chemical Processing.