Question

Describe material advancements that increase resistance to creep

Answer 1

Creep is the natural tendancy of material to deform under steady loads for prolonged periods of time. Creep increases with the temperature of the application. It is a critical property, because the material should work reliably for longer time periods. The creep mechanism is mainly related to the grain boundaries, which is due to the grain boundary diffusion and sliding. So the material with large grain size indented to have less grain boundaries than material with small grains. Increasing the grain size is one of the way to improve creep resistance. Further, development of single crystal materials which is having crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. That's why super alloy based on nickel and titanium are widely used for turbine blade to resist creep deformation.

Another solution is directional solidification, where the nucleation of the grains and their growth is in the direction of temperature gradient. This leads to formation of elongated grains in the direction of temperatue gradient and improved creep resistance in direction parallel to the long grains. Solid solution alloying is another method to improve creep resistance by preventing the movement of discloction through lattice distortion. And disperion hardening involves the inclusion of small and hard particles, thus restricting the movement of dislocations by pinning grain boundaries.