Titanium alloys are materials composed primarily of titanium mixed with other elements to achieve superior strength, temperature resistance, and lightweight properties. The question of their melting point is complex because “titanium alloy” refers to a large family of materials, not a single substance. Unlike pure elements, which transition from solid to liquid at one sharp temperature, alloys melt over a range of temperatures defined by their metallurgical composition. This melting range is bounded by the solidus temperature, where melting first begins, and the liquidus temperature, where the material becomes fully molten.
Melting Point of Pure Titanium
Establishing a baseline for the thermal properties of titanium begins with the pure metal, known as Commercially Pure Titanium (CP-Ti). Pure titanium has a single, precise melting point that serves as a reference for all its alloyed forms. The melting temperature of commercially pure titanium is approximately 1,668°C (3,034°F).
This high thermal stability makes titanium attractive for high-performance applications. The strong metallic bonds require a significant amount of energy to break, leading to this elevated melting temperature. For a pure element, the solidus and liquidus temperatures are identical, creating a sharp transition from solid to liquid, which contrasts with the broader melting ranges observed in alloys.
The Role of Alloying Elements
The specific melting behavior of a titanium alloy is fundamentally altered by the addition of other elements, which establishes the solidus and liquidus temperatures. Alloying elements modify the crystal structure of titanium, which exists in a hexagonal close-packed alpha (\(\alpha\)) phase at room temperature and a body-centered cubic beta (\(\beta\)) phase at higher temperatures. These elements are categorized based on how they affect the phase transformation temperature, known as the beta transus.
Elements like aluminum are classified as alpha stabilizers because they favor the lower-temperature \(\alpha\) phase. Conversely, elements such as molybdenum, vanadium, and chromium are beta stabilizers that lower the beta transus temperature and favor the \(\beta\) phase. Introducing these elements shifts the thermal equilibrium, resulting in a temperature range where the solid and liquid phases coexist. The distance between the solidus (where liquid first forms) and the liquidus (where the last solid disappears) defines the melting range.
Specific Melting Ranges of Major Titanium Alloys
The exact composition of a titanium alloy dictates its thermal performance, resulting in unique melting ranges for various commercial grades. The most widely used alloy, Ti-6Al-4V (Grade 5), an \(\alpha+\beta\) alloy, has a melting range from 1,604°C (2,920°F) to 1,660°C (3,020°F). This range is slightly lower than that of pure titanium, showing how alloying elements modify the thermal profile.
The high-strength \(\beta\) alloy Ti-5Al-5V-5Mo-3Cr (Ti-5553) is known for its deep hardenability and has a reported melting point around 1,630°C. Its melting behavior remains close to the pure metal’s melting point. Conversely, the high-temperature \(\alpha\) alloy Ti-1100, which contains aluminum, tin, and zirconium, has a liquidus temperature of 1,637°C (2,978°F). Overall, the melting ranges for titanium alloys fall between 1,600°C and 1,800°C (2,912°F and 3,272°F).
Manufacturing Considerations and High Temperature Use
The high melting points of titanium alloys present distinct manufacturing challenges that require specialized processing techniques. Titanium exhibits strong chemical reactivity with oxygen, nitrogen, and carbon at elevated temperatures, which can lead to contamination and embrittlement. Therefore, melting must be performed in controlled environments, typically using vacuum arc remelting (VAR) or electron beam (EB) melting furnaces.
These methods ensure the metal is melted under a vacuum or an inert atmosphere, managing the metal’s high-temperature reactivity and preserving its mechanical properties. This high thermal resistance is why titanium alloys are selected for extreme environments, such as aerospace engine components, where service temperatures can approach 600°C (1,112°F). The melting point and the beta transus temperature directly determine the maximum temperature an alloy can withstand while maintaining structural integrity.