The Inconel 718 is a nickel-based superalloy . The alloying elements are mainly chromium (15% ~ 30%), the rest are cobalt, iron, molybdenum, tungsten, titanium and niobium, the total content is 3% ~ 20%. Chromium can guarantee the elastic modulus at high temperature and prevent plastic deformation. Titanium and aluminum can form the dispersion phase of Ni3(A1, Ti), which is co-lattice with the matrix and plays a strengthening role. Used in serving under high temperature (1100 ℃) and high stress situations, such as gas turbine turbine disk, blade, etc.
Nickel-based super alloy creep performance is good, its working temperature is 850 ℃, and its melting point is 1280 ℃, that is, to a high ratio of the material such as selection of 0.72 TM root hard, it is difficult to use the usual methods of processing, to be cast into the final shape. The lost wax casting method is often adopted: a precise wax mold of the blade is embedded in the paste AI2O3, and the paraffin is melted to leave a precise cavity and then poured into the nickel-based superalloy limb. Blades made this way are expensive, costing around 150 pounds or $330 a blade, with material costs of just 10 pounds mostly manufacturing costs. There are 102 blades on the turbine disc and the total cost is 15,300 pounds.
Nickel-based super king of reinforcement can successfully suppress dislocation creep, but under 850 ℃ diffusion creep into the main problems, diffusion creep is mainly under the high strength, through the grain boundary after shield room for directional flow in a dynamic and failure in rolling the solution is to increase the grain size, even can make the blade has no boundary, in order to avoid failure or arrange the grain direction parallel to the external force, to do that, only in the directional solidification technology. Because of the large diffusion distance, the rate of diffusion creep can be greatly reduced. Directional solidification alloys are expected to be used in civilian aircraft in the near future.