terms of mechanical characteristics. The added palladium gives it increased corrosion resistance. Grade 19contains 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, and 4% molybdenum. Grade 20 contains 3% aluminium, 8% vanadium, 6% chromium, 4% zirconium, 4% molybdenum and 0.04% to 0.08% palladium. Grade 21 contains 15% molybdenum, 3% aluminium, 2.7% niobium, and 0.25% silicon. Grade 23 also known as Ti-6Al-4V-ELI or TAV-ELI contains 6% aluminium, 4% vanadium, 0.13% (maximum) Oxygen. ELI stands for Extra Low Interstitial. Reduced interstitial elements oxygen and iron improve ductility and fracture toughness with some reduction in strength. TAV-ELI is the most commonly used medical implant-grade titanium alloy. Ti-6Al-4V-ELI standard specifications include: AMS: 4907, 4930, 6932, T9046, T9047 ASTM: B265, B348, F136 MIL: T9046 T9047 Grade 24 contains 6% aluminium, 4% vanadium and 0.04% to 0.08% palladium. Grade 25 contains 6% aluminium, 4% vanadium and 0.3% to 0.8% nickel and 0.04% to 0.08% palladium. Grades 26, 26H, and 27 all contain 0.08 to 0.14% ruthenium. Grade 28 contains 3% aluminium, 2.5% vanadium and 0.08 to 0.14% ruthenium. Grade 29 contains 6% aluminium, 4% vanadium and 0.08 to 0.14% ruthenium. Grades 30 and 31 contain 0.3% cobalt and 0.05% palladium. Grade 32 contains 5% aluminium, 1% tin, 1% zirconium, 1% vanadium, and 0.8% molybdenum. Grades 33 and 34 contain 0.4% nickel, 0.015% palladium, 0.025% ruthenium, and 0.15% chromium . Grade 35 contains 4.5% aluminium, 2% molybdenum, 1.6% vanadium, 0.5% iron, and 0.3% silicon. Grade 36 contains 45% niobium. Grade 37 contains 1.5% aluminium. Grade 38 contains 4% aluminium, 2.5% vanadium, and 1.5% iron. This grade was developed in the 1990s for use as an armor plating. The iron reduces the amount of Vanadium needed as a beta stabilizer. Its mechanical properties are very similar to Grade 5, but has good cold workability similar to grade 9. Heat treatment Titanium alloys are heat treated for a number of reasons, the main ones being to increase strength by solution treatment and aging as well as to optimize special properties, such as fracture toughness, fatigue strength and high temperature creep strength. Alpha and near-alpha alloys cannot be dramatically changed by heat treatment. Stress relief and annealing are the processes that can be employed for this class of titanium alloys. The heat treatment cycles for beta alloys differ significantly from those for the alpha and alpha-beta alloys. Beta alloys can not only be stress relieved or annealed, but also can