types-of-hollow-material-flawsDirection of dendritegrowthCavityDendrites(fir tree structure)Cavity or gas pore? These are considerably differenttypes of material flaw.Gas pores are usually spherical.They are created by gas bubblesin the melt. They tend to form in part zones where gas bubbles cancollect, such as at the part surface.Cavities usually have sharp edges. Theirshape is usually determined by the dendritestructure. They are created in solidified castmaterial due to a lack of residual melt. Theytend to occur in thick part zones becausesolidification begins at the surface.Cavities, shrinkage cavities, shrinkage porosity: Gas pores:Spherical gas pores