Study of the Properties of Thick Section Nickel Alloys for High Temperature Application

Nickel alloys are typically utilised for high temperature and pressure application due to their improved elevated temperature properties compared with their steel counterparts. Casting grades, certainly in thick section, have previously focused on nickel alloys which are predominately solid solution strengthened with only mild precipitation hardening characteristics.

However, current and future turbine application are driving for further improved creep performance which necessitates the development and use of cast precipitation hardened nickel alloys. These nickel alloys are more challenging to manufacture and success requires grades which are specifically designed to be produced as castings in heavy section and are weldable.

Castings have major benefits for critical duty applications since their geometries can be custom engineered to include smooth transitions to streamline flow stresses thereby reducing stress concentrations. Material can be added in specific locations required to improve local stiffness/ tensile and compressive performance, and removed from locations where it’s not required to optimise weight without compromising performance. Casting fabrication welds where casting/forged/wrought connections are made can be moved to lower stress concentration regions or locations of improved access to simplify weld procedures.

This work discusses the validation of precipitation hardening alloy G130 for application in high temperature turbine environments and discusses examples of geometry/ design benefits of castings over other product forms to enhance performance.