The single crystal superalloys, used in the manufacture of advanced gas turbine blades, are known to suffer from poor weldability and have a tendency to form cracks during and after welding. These cracks are largely related to the amount of heat input and metallurgical reactions that occur in the Heat Affected Zone (HAZ) adjacent to the weld. Experience has shown that cracks can be avoided by minimizing the HAZ through the use of proper heat management or process control.
Automation systems can offer the level of process control necessary to significantly reduce weld cracking. The systems have proven to be more repeatable, reliable, and efficient, compared to conventional techniques or earlier attempts at automation. In order to succeed, welding automation requires a complete integration of the process, consisting of tooling, robotic accuracy, vision measurement system, filler material, and welding parameter control. With the proper process control technology, it is possible to weld the tips of single crystal blades with difficult to weld oxidation resistant alloys as well as repair conventional compressor, high pressure and low pressure turbine blades.
This paper describes the welding of LT101 single crystal gas producer (GP) blade tips with highly alloyed filler metals for greater oxidation resistance. Results are presented for blades welded using a Laser beam with powder feed and compared to those welded using Micro-Plasma with the same filler alloys in wire form. The experience emphasizes the need for proper selection and integration of the welding processes, and confirms the importance of total process control to achieve the desired results in difficult and unique welding applications.