SINGLE CRYSTAL ARTICLES HAVING CONTROLLED SECONDARY CRYSTALLOGRAPHIC ORIENTATION

摘要

Alignment of the [001] crystal axis of a face centered cubic metal with the primary z axis of a single crystal article provides good thermal fatigue resistance along the z axis, and minimizes cracking transverse to the axis. However, significant cracking is still observed parallel the z axis in severe applications. This cracking can be reduced by controlling the secondary crystallographic orientation (i.e., orientation of crystal axes within x-y planes transverse to the z axis), to make the [110] crystal axis tangent to the article surface in the region most prone to thermal fatigue cracking. Algorithims derived from empirical relationships enable calculation of the orientation likely to produce improved fatigue resistance. More durable single crystal gas turbine blades result when the [110] crystal axis is made tangent to the blade surface in the critical crack prone regions just behind the leading edge of the airfoil at about 40-80% of the airfoil span. A representative improved gas turbine blade will have a secondary orientation angle alpha of -10 to +20 degrees, where alpha is the angle between the [100] crystal axis and the y axis.