R. Freeman, A. Gregori, TWI Limited, Cambridge, United Kingdom

Summary:

Most high-pressure blades and nozzle guide vanes in the high pressure (HP) section of aeroengine, industrial derivative and power utility gas turbines are made from nickel superalloys. These materials have superior creep and strength properties at elevated temperature to combat the arduous conditions experienced in the HP sections of aeroengines and gas turbines. Unfortunately, many of the nickel superalloys are considered extremely difficult to weld because of their susceptibility to heat affected zone (HAZ) liquation cracking, weld metal cracking and cracking during postweld heat treatment. These problems have become more pronounced with the introduction of directionally solidified and single crystal alloys. The use of brazing techniques may circumvent cracking problems but usually at the expense of elevated temperature mechanical and corrosion properties of the repaired component.

The common view is that the reduction of the heat input and the use of high preheating temperatures are necessary for eliminating HAZ and weld metal cracking. It is also believed that the use of mechanised processes is key to achieving these goals. TWI has been developing procedures for minimising cracking during repair, overlay and build up of material using gas tungsten arc welding, plasma assisted welding and electrospark deposition. The high temperature performance of the welds and the effect of pre-weld and postweld heat treatments are also considered.

This presentation will provide results on the welding of materials such as Waspaloy, CMSX-10 and MAR-M-247 in order to give acceptable properties and extend component life. The potential savings incurred by improved production and repair procedures are considerable for the aircraft engine industry and associated maintenance, repair and overhaul organisations.