Abstract : The overall goal of this program is to increase the life of PCBN tools in friction-stir welding of high temperature metals. This will be achieved through the following objectives: (1) Understand the fundamental causes for limited lifetimes of PCBN tools during Friction-Stir Welding (FSW) of high temperature metals, including both wear and fracture. (2) Identify microstructural characteristics and defects in PCBN materials that affect lifetime in FSW. (3) Identify and develop simple mechanical/fracture test methods that can be used on PCBN materials as indicators of potential lifetime in FSW. (4) Use information gained in (1) to (3) to guide development of new grades of PCBN or modifications to existing grades or tool design to improve lifetime during FSW. We have formed a multidisciplinary team to tackle the problem of increasing the life of PCBN tools in FSW of high temperature metals. Studies in this program at Teledyne Scientific are being coordinated with complementary, collaborative studies on manufacturing improved grades of PCBN at Megadiamond, tool manufacture at Advanced Metal Products, and other ONR supported FSW studies at Brigham Young University. At a kick-off meeting held in February 2009, several materials and tools were selected for initial studies. Initial experiments have focused on materials from three lots of MS80 PCBN materials to identify relations between tool life, microstructure, and toughness measurements.