Pure titanium rods and titanium alloy rods are being used more and more widely in the industrial, medical, and aerospace sectors. In the following, we will examine the differences between the two.
Pure titanium: Pure titanium is 99% titanium and offers high corrosion and acid resistance. The industrial-grade pure titanium commonly used in industry is Gr2, which is relatively easy to machine due to its moderate corrosion resistance and overall mechanical properties.
Gr2 is an industrial-grade titanium with a single α phase. It is the industrial-grade pure titanium most commonly used in industry due to its moderate corrosion resistance and overall mechanical properties. TA3 can be used when higher wear resistance and strength are required. Gr1 can be used when better formability is required.
"Low thermal conductivity" means that heat transfer is slow. Slow heat transfer causes localized heat buildup during machining, which can easily burn out the cutting tools. Therefore, to prevent excessive heat generation, cutting speeds are kept very low when machining titanium alloys, resulting in very long machining times.
Industrial-grade pure titanium is classified into three grades-Gr1, Gr2, and Gr3-based on impurity content. The levels of interstitial impurity elements gradually increase across these three grades, resulting in a corresponding stepwise increase in mechanical strength and hardness, but a corresponding decrease in ductility and toughness.
Gr2 is the most commonly used grade of industrial pure titanium in industry due to its moderate corrosion resistance and overall mechanical properties. Gr3 may be used when higher wear resistance and strength are required. Gr1 may be used when better formability is required.
Gr1, Gr2, and Gr3 in the Chinese National Standard correspond to Gr1, Gr2, and Gr3 in the UNS system.
Gr1 and Gr2, with iron content ω of 0.095%, oxygen content ω of 0.08%, hydrogen content ω of 0.0009%, and nitrogen content ω of 0.0062%, exhibit excellent low-temperature toughness and high low-temperature strength, making them suitable for use as structural materials at temperatures below -253°C.
Characteristics of Industrial-Grade Pure Titanium:
It has moderate strength but good plasticity, making it easy to process, form, stamp, and weld, with good machinability. It exhibits good corrosion resistance in atmospheric air, seawater, moist chlorine gas, and oxidizing, neutral, and weakly reducing media; its oxidation resistance is superior to that of most austenitic stainless steels. However, it has poor heat resistance, so operating temperatures should not be too high.
Applications of Industrial-Grade Pure Titanium:
Industrial-grade pure titanium is primarily used for stamped parts and corrosion-resistant structural components operating at temperatures below 350°C that are subject to low stress but require good ductility. Examples include: aircraft frames, skins, and engine accessories; seawater-corrosion-resistant pipes, valves, pumps, hydrofoils, and components for seawater desalination systems in the marine industry; in the chemical industry, heat exchangers, pump bodies, distillation columns, coolers, agitators, tees, impellers, fasteners, ion pumps, compressor valves, as well as diesel engine pistons, connecting rods, and leaf springs.
Titanium Alloys: Titanium alloys consist of 90% titanium and feature high strength and high hardness. They offer a range of advantages, including excellent corrosion resistance, low density, high specific strength, and good toughness and weldability.
GR5 titanium alloy is widely used in industrial and scientific research fields. The rapid development of titanium alloys has been recognized by international industries and the aerospace sector. In particular, GR5 titanium alloy bars and GR5 titanium forgings have promising market prospects. Made of Ti-6Al-4V, the GR5 alloy possesses the following unique properties:
(1) Ti-6Al-4V is an α+β-type alloy and is widely used.
(2) GR5 has good processability; its conventional hot deformation occurs in the two-phase region, and the deformation must exceed 50% to transform the coarse original Widmanstätten structure into an equiaxed structure.
(3) After deformation, GR5 can undergo stress-relief annealing (held at 600°C, air-cooled), conventional annealing (held at 700–800°C, air-cooled), recrystallization annealing (held at 940°C, furnace-cooled to 480°C, then air-cooled), and double annealing (held at 940°C, air-cooled, followed by holding at 700°C, air-cooled), among other heat treatment processes. The microstructure obtained from stress-relief annealing and conventional annealing is non-recrystallized or partially recrystallized, resulting in higher strength; Recrystallization annealing yields an equiaxed α + intergranular p microstructure, which exhibits good plasticity; double annealing results in an equiaxed α + β microstructure, approaching a dual-phase structure, and offers good overall properties (t_u approximately 900–1000 MPa, δ 10%, ψ approximately 35%–45%).
(4) When GR5 undergoes strengthening heat treatment, its strength can be increased by 20%–30%. It is generally accepted that aging at 850–950°C yields a microstructure with an appropriate amount of primary α and good overall properties. GR5 alloy has poor hardenability; therefore, the cross-sectional area of parts subjected to strengthening heat treatment is generally no greater than 40 mm.
(5) GR5 alloy has good weldability; the temperature in the weld zone is no less than 90% of that of the matrix, and its ductility is similar to that of the matrix metal.
(6) The corrosion resistance of GR5 is close to that of pure titanium; it can operate for extended periods at temperatures below 400°C, and short-term operating temperatures can reach 700–750°C. When the oxygen and nitrogen content in the alloy is low, the GR5ELI alloy can maintain good plasticity even at –196°C, making it suitable for the manufacture of low-temperature, high-pressure vessels.
Titanium alloys are used in some large factories, where liquid nitrogen is employed for machining and cooling to improve processing efficiency. Additionally, if cooling is inadequate, the minute particles of titanium alloy debris generated during machining can ignite at temperatures around 200°C. This results in very high processing costs, and titanium alloys are widely recognized in the machining industry as one of the most difficult materials to machine. Their processing costs can range from several to dozens of times the value of the material itself.
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