AWS G2.4-G2.4M:2014 pdf download.Guide for the Fusion Welding of Titanium and Titanium Alloys
3. Terms and Definitions
AWS A3.0M/A3.0, Standard Welding Terms and Definitions, Including Terms for Adhesive Bonding, Brazing, Soldering,Thermal Cutting, and Thermal Spraying, provides the basis for terms and definitions used herein. However, the follow-ing terms and definitions are included below to accommodate usage specific to this document.
For the purposes of this document, the following terms and definitions apply:
alpha grades or alloys. The alpha (0) grades or alloys are generally weldable and nonheat treatable. They are materials with relatively large amounts of alpha stabilizers and low concentrations of beta (B) stabilizers. They are sometimes referred to as having predominately an alpha phase. They have medium strength, good notch toughness, and good resistance to creep at elevated temperatures. Silicon is sometimes added to enhance creep strength. A common alpha alloy is commercially pure (CP) titanium.
allotrope. An allotrope is a structurally different form of an element such as graphite and diamond which are allotropes of carbon. As can be seen with the example of carbon allotropes, certain physical properties can vary dramatically from allotrope to allotrope. Alpha and beta allotropes of titanium have very different properties. Alpha and beta allot-ropes are also referred to as phases.
alpha phase. The low-temperature allotrope of titanium with a hexagonal close-packed (HCP) crystal structure. The alpha phase promotes increased weldability and higher creep strength.The interstitial alloying elements of the alpha stabilizing type are oxygen, nitrogen, and carbon. Interestingly, these are the same elements we guard against intro-ducing during welding.
alpha-beta grades or alloys. Most of the alpha-beta alloys are considered heat treatable with a wide range of possible properties. Their strength levels are medium to high but their creep strength is not as good as most alpha alloys. Their forming qualities are acceptable but generally exhibit a significant amount of spring-back.
beta grades or alloys. The beta (B) or near-beta alloys have a high percentage of beta-stabilizing elements, resulting in a microstructure that is predominantly beta after solution annealing. During subsequent heat treatment, extensive strengthening can occur by the precipitation (formation) of alpha (0) within the beta microstructure. Care should be taken when welding these alloys due to the tendency to form alpha from the heat of welding. Post fabrication heat treatment (aging heat treatments) of these alloys is common. Beta alloys are more dense, respond to a greater extent to heat treatment (e.g.. properties are altered), have higher short-term rupture strength, a greater strain-rate sensitivity and improved fabricability (especially in the solution treated condition) than do the alpha alloys.AWS G2.4-G2.4M pdf download.