Abstract
Nickel-base wear materials are typically used as weld hardfacing deposits, or as cast or hot isostatically pressed (HIP) inserts that provide the needed wear resistance to a base material with the desired mechanical properties. Most nickel-base wear materials contain high levels of chromium, silicon, carbon, and boron, which results in complex microstructures that are comprised of high volume fractions of silicide, carbide, and/or boride phases. The volume fraction of nickel-phase dendrite regions typically ranges from 40 to 70 pct, and these dendrite-phase particles are individually isolated by a matrix of silicide, carbide, and boride phases. The continuous matrix of brittle silicide, carbide, and boride phases results in a low damage tolerance for nickel-base wear materials, which is a concern in applications that involve high stresses, thermal transients, or shock loading. Fatigue crack growth (FCG) and fracture toughness (K IC) testing in accordance with ASTM E399 methods has been used to quantify the damage tolerance of various nickel-base wear materials. Fractographic and microstructure examinations were used to define a generic toughening mechanism for nickel-base wear materials. The toughness of nickel-base wear materials is primarily controlled by the plastic deformation of the nickel-phase dendrites in the wake of a crack moving through the matrix of brittle silicide, carbide, and/or boride phases, i.e., crack bridging. Measured K IC values are compared with calculated K IC values based on the crack-bridging model. Microstructure examinations are used to define and confirm the important aspects of the crack-bridging model. This model can be used to predict the toughness values of nickel-base wear materials and direct processing methods to improve the K IC values.
Published Version
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