An alloy with a density about 60% that of steel, excellent specific strength and corrosion resistance. Depending on the proportions of the HCP α phase and BCC β phase, it is classified as α, α+β or β type.
Japanese name: チタン合金
Titanium alloy appears in 2 practice questions across 2 topics, including Metals and alloys, Glasses and amorphous materials.
Field: Metals and alloys
Pure titanium takes the HCP α phase below 882 °C and the BCC β phase above it. Alloying elements are divided into α stabilizers (Al, O, N, C), which raise this transformation temperature (the β transus), and β stabilizers (V, Mo, Nb, Ta, Fe, Cr and others), which lower it; Sn and Zr are neutral elements that hardly affect it. Alloys that are mainly α at room temperature are α alloys, those with both phases α+β alloys, and those that retain β to room temperature β alloys. The most widely used is the α+β alloy Ti-6Al-4V, which is said to account for about half of titanium alloy production.
Titanium alloys have a density of about 4.4–4.5 g/cm³, about 60% that of steel but about 1.6 times that of aluminum alloys. Their Young's modulus, about 110 GPa, is also about half that of steel, so their specific stiffness (Young's modulus/density) is almost the same as steel's and aluminum alloys'. Where titanium alloys excel is specific strength: Ti-6Al-4V reaches a tensile strength of about 900–1000 MPa and keeps its strength at temperatures of several hundred °C where aluminum alloys cannot be used, so it is also used for jet engine compressor parts. Titanium is chosen for being light, strong and corrosion resistant rather than light and stiff.
Thanks to its dense passive TiO₂ film, titanium shows very high corrosion resistance in seawater and chloride-containing environments and is used in chemical plant heat exchangers and desalination equipment. It also causes little galvanic corrosion in contact with carbon fiber, which suits it for fasteners in CFRP airframes. On the other hand, its thermal conductivity is low (about 7 W/(m·K) for Ti-6Al-4V), so cutting heat concentrates at the tool edge, and it reacts readily with tools at high temperature, making it difficult to machine. At high temperature it absorbs oxygen and forms a brittle surface layer (alpha case), and absorbed hydrogen causes hydrogen embrittlement.
For α+β alloys, working and heat-treatment temperatures are chosen relative to the β transus (about 1000 °C for Ti-6Al-4V), changing the morphology of the microstructure to balance strength, toughness and fatigue strength. Solution treatment and aging, which precipitate fine α, raise the strength further. Because titanium reacts violently with oxygen and nitrogen at high temperature, melting is carried out in vacuum or inert gas, and titanium sponge is made into ingots by vacuum arc remelting. This is one reason for its high price, and additive manufacturing from powder is now spreading as a way to reduce material waste and make complex parts.
Answer: B. About 1.4 times
The specific strength is 950/4.43 ≈ 214 kN·m/kg for the titanium alloy and 1200/7.85 ≈ 153 kN·m/kg for the steel, so the ratio is 214/153 ≈ 1.40, about 1.4 times (MPa divided by g/cm³ becomes kN·m/kg once units are made consistent). About 0.79 times compares only the tensile strengths (950/1200), ignoring weight. About 1.8 times takes only the density ratio (7.85/4.43 ≈ 1.77), ignoring the difference in strength. For a member carrying the same load, a higher specific strength allows a lighter design, which is why aircraft structures use titanium alloys, aluminum alloys and carbon-fiber composites. Material cost and ease of fabrication must also be weighed in the choice, however.
No. Their density, about 4.4 g/cm³, is higher than the roughly 2.7 g/cm³ of aluminum alloys and lower than the roughly 7.8 g/cm³ of steel, an intermediate value. Compared by specific strength, strength divided by density, they outperform many aluminum alloys.
They mean the alloy contains about 6% Al and about 4% V by mass. Al stabilizes the α phase and V the β phase, making it the representative α+β alloy. In Japan it is sometimes called “64 titanium”.
Pure titanium is weaker but easy to form and highly corrosion resistant, so it is used for chemical equipment, building materials and heat exchanger tubes. Alloys are used where high strength is needed, such as aircraft parts, bolts and artificial joints.
The specific strength is 950/4.43 ≈ 214 kN·m/kg for the titanium alloy and 1200/7.85 ≈ 153 kN·m/kg for the steel, so the ratio is 214/153 ≈ 1.40, about 1.4 times (MPa divided by g/cm³ becomes kN·m/kg once units are made consistent).
A titanium alloy has a tensile strength of 950 MPa and a de…For steel (yield stress 0.5 GPa, Young's modulus 200 GPa) it is about 0.25%, and even for a high-strength titanium alloy (0.9 GPa, 110 GPa) about 0.8%, so the elastic strain limit of the metallic glass is much larger.
A Zr-based bulk metallic glass has a yield strength of 1.8 …Metallic glass Young's modulus Dislocation Brass Columnar grains Recovery Recrystallization Solid-solution strengthening Stainless steel Work hardening