Dimensional inspection follows. Then, a combination of heat treating, hot isostatic pressing, machining, or coating completes the journey. The Growth of Crystals In an equiax turbine blade, the grain boundaries control the strength, said John Corrigan, Howmet's vice president of engineering. Creep is the principal failure mode. For equiax crystals, failure occurs ultimately at the grain boundaries.
Grain structures are visible.
We pour alloy into the mold, it starts to cool down and solidify, and we start to get nuclei through the melt. Eventually, the alloy solidifies into small grains oriented at random. When we pour, we get growth in the vertical direction. Unlike equiax casting, though, d.s. uses a graphite cylinder surrounded by an induction coil to keep part of the casting hot. On a d.s. part, we have a starter about 2 to 3 inches long and that's where the d.s.