Erosion of amorphous nickel-phosphorus
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A. Mayer and R. B. Schwarz MST-7 and Center for Materials Science, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 5 May 1987; accepted 20 July 1987) The steady-state erosion rate of electrodeposited amorphous Ni g0 P 20 by angular alumina particles has been measured as a function of impingement angle from 15°-9O°, particle velocity from 50-100 m/s, and average particle diameter from 40-390/^m. The erosion rate can be described by a power law in velocity and particle size. The erosion rates in Ni g0 P 20 were compared to those measured for electrodeposited pure crystalline nickel. For all experimental conditions the erosion rate in the amorphous alloy exceeded that of nickel. The material removal in amorphous Ni g0 P 20 is attributed to formation of plastic shear bands below the impact areas. For the most energetic particles the erosion leads to the formation of melt, which seems to be a consequence of the localized shear.
I. INTRODUCTION Amorphous metallic alloys are finding increased applications as coatings because of their excellent resistance to corrosion.1'2 Amorphous nickel-phosphorus alloys were first electrodeposited by Brenner et al? These coatings have a high hardness,4 good corrosion resistance,1'2 and a dry-sliding-wear resistance comparable to or better than electroplated hard chromium.5 The wear resistance of amorphous nickel-phosphorus can be changed by at least an order of magnitude by altering the phosphorus content or by heat treatment.5 The fact that these materials have a high wear resistance suggests that they may have an equally high resistance to material degradation by solid-particle erosion. There is also interest in a fundamental investigation of erosion in amorphous materials because of their unique combination of ductility and high strength. The erosion characteristics of crystalline materials have been extensively studied. The main characteristics are as follows. The erosion rate of a ductile crystalline material has a maximum at an angle of incidence a^20°, depends on particle velocity V to the 2.0-2.5 power, and is independent of particle diameter D for values of D greater than a threshold (see, for example, Ref. 6). The steady-state erosion rate of a brittle crystalline material has a maximum for a — 90°, depends on V to the 2.4-3.2 power and on D to the \ power (see, for example, Ref. 7). A further difference is that the principal material property determining the erosion rate of a ductile crystalline material is hardness, whereas the erosion rate of a brittle crystalline material correlates closest with fracture toughness. Very little is known about the erosion properties of noncrystalline metals.8 For example, it is not known whether under erosive conditions amorphous metallic 818
J. Mater. Res. 2 (6), Nov/Dec 1987
http://journals.cambridge.org
alloys behave as a ductile or a brittle material. The objective of this investigation is to evaluate the erosion rate of an amorphous metallic alloy and to elucidate the fundamental mechanisms of material removal
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