Laboratory galling tests of several commercial cobalt-free weld hardfacing alloys

Abstract

Since the mechanical properties of most wear materials are generally insufficient for structural applications, hardfacing alloys have been traditionally weld deposited to provide a wear resistant surface for a base material. An important attribute of a hardfacing alloy that is subjected to high load sliding contact is the resistance to adhesive (galling) damage. Although Co-base hardfacing alloys generally possess excellent galling wear resistance, there is interest in developing cobalt-free replacement hardfacings to reduce radiation exposure costs. A laboratory galling test has been developed for weld hardfacing deposits that is a modification of the standardized ASTM G98-91 galling test procedure. The procedure for testing a weld hardfacing deposit on a softer base metal using a button-on-block configuration is described. The contact stresses for the initiation of adhesive galling damage were measured to rank the galling resistance of several commercial Fe-base, Ni-base and Co-base hardfacing alloys. Although the galling resistance of the Fe-base alloys was generally superior to the Ni-base alloys, neither system approached the excellent galling resistance of the Co-base alloys. Microstructure examinations were used to understand the micromechanisms for the initiation and propagation of galling damage. A physical model for the initiation and propagation of adhesive wear is used to explain the lower galling resistance for the Ni-base hardfacings and to understand the influence of composition on the galling resistance of Ni-base alloys. The composition of some Ni base hardfacings was modified in a controlled manner to quantify the influence of specific elements on the galling resistance.