Sintered tungsten heavy alloys: Review of microstructure, strength, densification, and distortion

Abstract

Tungsten heavy alloys are fabricated using liquid phase sintering to form inertial, electrical, radiation, or structural components. The compositions, initially developed a century ago, are based on various W-Ni-(Fe/Cu/Co/Mo) alloys. Two classes, and W-Ni-Fe and W-Ni-Cu, remain the most popular. Nickel is key to sintering densification, producing the majority of sintering shrinkage prior to liquid formation. Sintering densification and distortion depend on the gravitational environment. Normal gravity induces distortion after densification, while sintering in microgravity fails to reach full density yet distorts. Mechanical properties are adjustable via changes to the composition, sintering cycle, or post-sintering treatment. Increased strength, with a loss of ductility, comes with post-sintering deformation and aging treatments. As shown here, a range of mechanical property combinations are possible. Processing options designed to improve strength invariably result in a loss of ductility, and vice versa. Peak property combinations are attainable over a broad tungsten content range, reflecting convergence to a self-similar microstructure.