Physical Metallurgy Considerations To understand the microstructure of any alloy system it is necessary to outline the phase relationships and constitution of the system being studied.

  Titanium can exist in two crystal forms. The first is alpha which has a hexagonal close-packed crystal structure and the second is beta which has a body-centered cubic structure. In unalloyed titanium, the alpha phase is stable at all temperatures up to 1620°F. (880°C.) where it transforms to the beta phase. This temperature is known as the beta transus temperature. The beta phase is stable from 1620°F. (880°C.) to the melting point.

  As alloying elements are added to pure titanium, the elements tend to change the temperature at which the phase transformation occurs and the amount of each phase present. Alloy additions to titanium, except tin and zirconium, tend to stabilize either the alpha or the beta phase. Elements called alpha stabilizers stabilize the alpha phase to higher temperatures and beta stabilizers stabilize the beta phase to lower temperatures.