TITANIUM AND TITANIUM ALLOYS BASIC INFORMATION AND TUTORIALS


Titanium alloys are important industrially because of their high strength-weight ratio, particularly at temperatures up to 427°C. The density of the commercial titanium alloys ranges from 4.50 to 4.85 g/cm3, or approximately 70% greater than aluminum alloy and 40% less than steel.

The purest titanium currently produced (99.9% Ti) is a soft, white metal. The mechanical strength increases rapidly, however, with an increase of the impurities present, particularly carbon, nitrogen, and oxygen.

The commercially important titanium alloys, in addition to these impurities, contain small percentages (1% to 7%) of (1) chromium and iron, (2) manganese, and (3) combinations of aluminum, chromium, iron, manganese, molybdenum, tin, or vanadium.

The thermal conductivity of the titanium alloys is low, about 15 W/m ⋅ K at 25°C, and the electrical resistivity is high, ranging from 54 mΩ ⋅ cm for the purest titanium to approximately 150 mΩ ⋅ cm for some of the alloys.

The coefficient of thermal expansion of the titanium alloys varies from 2.8 to 3.6 x 10–6 per degree Celsius, and the melting-point range is from 1371 to 1704°C for the purest titanium. The tensile modulus of elasticity varies between 100 to 120 GPa (15 to 17 # 106 lb/in2).

The mechanical properties, at room temperature, for annealed commercial alloys range approximately as follows: yield strength 760 to 965 MPa (110,000 to 140,000 lb/in2); ultimate strength 800 to 1100 MPa (116,000 to 160,000 lb/in2); elongation 5% to 18%; hardness 300 to 370 Brinell.

On the basis of the strength-weight ratio many of the titanium alloys exhibit superior short-time tensile properties as compared with many of the stainless and heat-resistant alloys up to approximately 427°C.

However, at the same stress and elevated temperature, the creep rate of the titanium alloys is generally higher than that of the heat-resistant alloys. Above about 482°C, the strength properties of titanium alloys decrease rapidly. The corrosion resistance of the titanium alloys in many media is excellent; for most purposes, it is the equivalent or superior to stainless steel.

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