Residual stress and stress relaxation in cemented carbide composites

"Cemented carbides (cermets or hardmetals) are a class of materials consisting of large fractions of transition metal carbide surrounded by a small fraction of iron-group metal or alloy. These composites possess the wear resistance of carbides combined with the toughness of a ductile metal binder. They are employed where high stationary and fatigue loadings are encountered - such as in the oil drilling industry as drill bit inserts - thus exploiting their dual composite nature. Actual mechanical properties arise from the relative sizes, amounts, and distributions of carbide and binder as well as from the carbide-binder interactions [1]. Grain sizes of carbide particles are typically on the order of 0.5 to 5.0 pm. Cemented carbides for technical applications normally contain from 5 to 25 weight percent binder (usually cobalt). Theories on carbide distribution include in the extremes both the existence of a rigid carbide skeleton [2] and the immersion of carbide particles in a binder matrix [3], It is now generally accepted that a continuous carbide phase exists and that the grain boundaries between carbide crystals are binder rich. This compromise view recognizes the strength contribution of the carbide while acknowledging the importance of binder deformation and carbide-binder interactions on composite behavior. Central to the description of material behavior is an understanding of bulk residual stresses in the cermet. Studies have shown that residual stresses first arise in the manufacture of the composite."--Introduction.