General Electric and PCC Airfoils (GE-PCC) teamed up to address the challenges of bringing cost-effective single crystal (SX) technology to land-based gas tur-bine engine applications. As noted by General Electric, the require-ments for grain perfection and those for accurate part geometry compete with one another and create formi-dable challenges to successful, wide-spread use of large, directionally solidified (DS) and single crystal (SX) parts.
The GE-PCC work has pro-duced a number of findings and ad-vances in casting technology that will enable General Electric to in-corporate higher-yield SX and DS components into their ATS unit. Early work determined that signifi-cant improvement in oxidation re-sistance resulted from reducing sulfur levels to 1.0–0.5 ppm in the super nickel alloy used. GE-PCC developed a low-cost melt desulfu-rization process to replace expen-sive heat treatment methods for sulfur removal.
In parallel, GE-PCC advanced the casting and silica core processes to enable SX manufacture of com-plex-cored and solid airfoils for land-based turbine applications. Also explored was the use of alu-mina ceramic formulated core ma-terials to provide enhanced stability and dimensional control. Prototype testing showed promise for com-mercial application. Liquid metal cooling (LMC) was evaluated for application to DS processing. LMC provides increased thermal gradi-ents without increasing the casting metal temperature by improving heat input and removal from cast-ings. Casting of large stage-2 buck-ets for a 9G prototype machine was successfully demonstrated.
Siemens Westinghouse is de-veloping a process to fabricate com-plex SX blades and vanes from small, readily producible castings using transient liquid phase bond-ing. Transient liquid phase bond-ing was developed in the 1970s by Pratt & Whitney for aircraft engine components. The bonding media contains a melting point depressant and a carefully selected subset of the parent metal chemistry to attain 90 percent of the base metal properties. In the fabricated component ap-proach, bond planes are placed in insensitive locations.
Howmet Research Corpora-tion is pursuing ways to enhance SX and DS casting technology toward improving yields for the large ATS hot gas path components. Activities are focused on: (1) improving cur-rent Vacuum Induction Melt (VIM) furnace capability and control; (2) 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址:Advanced Turbine Systems 先进的涡轮系统(10)