TC4 titanium alloy, an α-β type titanium alloy, was successfully developed by the United States in 1954. It comprises 6% α stable element and 4% β stable element V. The nominal composition of TC4 titanium alloy is equivalent to 7.0 aluminum, with a molybdenum equivalent of 2.9. In its annealed state, the alloy contains 10%-15% beta phase. The addition of aluminum enhances the strength at room temperature and thermal strength properties of the alloy by strengthening the α phase through solid solution in the Ti-Al-V system. On the other hand, V serves as one of the few alloying elements that improves both strength and plasticity in titanium alloys. Unlike most alloying elements, V has a beneficial effect on the plasticity of titanium alloys as it reduces the c/a-axis ratio of the α-state lattice, promoting the formation of α-phase and preventing long-term alloy embrittlement during use.
TC4 titanium alloy stands out for its exceptional overall performance and favorable process characteristics. This alloy exhibits moderate strength at room temperature and high strength at elevated temperatures. It demonstrates admirable resistance to creep and thermal stability, along with high fatigue resistance and crack propagation resistance in seawater. Moreover, it boasts satisfactory fracture toughness and thermal salt stress corrosion resistance. TC4 titanium alloy also showcases reduced hydrogen sensitivity compared to TC2 and TC1 alloys. Consequently, it finds suitability in manufacturing various components that operate within a broad temperature range of -196 to 450 °C, particularly parts designed with the principle of damage tolerance limit in mind.
Furthermore, TC4 titanium alloy displays excellent ductility and superplasticity, making it suitable for shaping using various pressure processing methods. It also lends itself well to welding and machining operations, offering versatility in fabrication techniques.
TC4 titanium alloy is available in different semi-finished forms, including bars, forgings, sheets, thick plates, profiles, and wires. Additionally, it finds application in castings (referred to as ZTC4).
TC4ELI Titanium Alloy
TC4ELI is an enhanced version of TC4 titanium alloy, distinguished by its altered aluminum content and reduced levels of interstitial elements such as iron (Fe), nitrogen (N), hydrogen (H), and oxygen (O).
TC4ELI titanium alloy has gained prominence as a preferred material for medical surgical implants due to its exceptional biocompatibility, low elastic modulus, lightweight nature, corrosion resistance, non-toxicity, high yield strength, extended fatigue life, considerable room temperature plasticity, and ease of formability. In the medical field, TC4ELI titanium alloy sheets are predominantly employed for applications like skull repair and bone fixation, where stringent requirements exist for strength, fatigue life, and plasticity.
Titanium alloy, comprising titanium as the base element along with other alloying elements, exhibits two isomorphic crystal structures. Below 882 °C, titanium adopts a close-packed hexagonal lattice structure known as α-titanium, while it transforms into a body-centered cubic lattice structure called beta-titanium above 882 °C. By carefully incorporating appropriate alloying elements to modify the phase transition temperature and component composition, titanium alloys with different structures can be obtained, capitalizing on the distinctive characteristics of these two structures.
Building upon the foundation of TC4 alloy, TC4ELI titanium alloy reduces the presence of interstitial elements such as carbon (C), oxygen (O), and nitrogen (N), as well as impurity element iron (Fe), resulting in a reduction in strength. However, this adjustment significantly enhances the capacity and toughness of the alloy. TC4ELI exhibits excellent plasticity, toughness, welding performance, and low-temperature performance, making it widely applicable in crucial fields such as low-temperature engineering, medical treatments, ships, and aircraft.
While TC4 alloy is suitable for use in ordinary or high-temperature environments, TC4ELI alloy is specifically designed for ultra-low-temperature environments.
Comparable grades to TC4 titanium alloy and TC4ELI titanium alloy include T-6A-4V/Grade 5 (American grade), BT 6 (Russian grade), IMI 318 (British grade), and TiAI6V4 (German grade).
In the realm of medical equipment manufacturing, titanium and titanium alloys find extensive use in addressing bone and joint damage caused by trauma and tumors. Artificial joints, bone plates, and screws are commonly made from titanium and titanium alloys, which have gained wide acceptance in clinical practice. These materials are employed in hip joints (including femoral heads), knee joints, elbow joints, metacarpophalangeal joints, interphalangeal joints, mandibles, artificial vertebral bodies (spinal orthoses), pacemaker housings, artificial hearts (heart valves), artificial dental implants, titanium-nickel dental orthodontics, and titanium mesh for cranioplasty. The high specific strength, excellent biocompatibility, and resistance to corrosion by bodily fluids make titanium and titanium alloys increasingly sought-after materials.
Ti 6Al-4V ELI is a variant of Ti 6Al-4V alloy that features a narrower structural gap, enabling it to achieve maximum toughness. This grade is particularly well-suited for applications in seawater and low-temperature environments. Typically, Ti 6Al-4V ELI is utilized in the annealed state and is an excellent choice for medical implants.
The production process involves relaxation annealing, where the alloy is air-cooled at temperatures ranging from 900 to 1200 degrees Fahrenheit for a duration of 1 to 4 hours. For round bars and forgings, a double annealing process is employed. Initially, solution annealing is conducted at a temperature of 50 to 100 degrees Fahrenheit above the beta transition point. The material is held at this temperature for a minimum of 1 hour before being air-cooled. Subsequently, the alloy is reheated to 1300-1400 degrees Fahrenheit for at least 1 hour and then air-cooled. Relaxation annealing is recommended following welding operations.
