Erosion-oxidation interaction in Ni and Ni-20Cr alloy
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I. INTRODUCTION
SOLID-PARTICLE erosion is an important material degradation mechanism experienced by a wide variety of engineering components, and, of them, a substantial number are subjected to erosion at elevated temperatures.[1–4] Over the last decade, a substantial amount of work on elevatedtemperature erosion of metals and alloys has been carried out.[5–35] A compilation of these investigations, providing details on the materials subjected to elevated-temperature erosion and the test conditions, are summarized in Table I. These tests cover a wide range of test conditions and test materials. In general, these results indicate the following with regard to the elevated-temperature erosion behavior of metals and alloys. (1) The erosion rate increases with increasing test temperature, although the rate of increase exhibits a wide range, depending on the material tested and the range of test temperatures in relation to the melting point of the test material.[4–6,9,10,14,20,21] (2) The erosion rate always increases with increasing impact velocity. For example, a perusal of the literature indicates that the velocity dependence of the erosion rate, characterized by the constant n (erosion rate E␣V n; V ⫽ impact velocity) varies from a value in the range of 2 to 3 (for room-temperature erosion tests) down to values as low as 0.8 to 1.2, especially for erosion tests conducted at very high temperatures, low impact velocities, and low particle feed rates.[8,17,18,24,26]
MANISH ROY, Scientist “D,” is with the Defence Metallurgical Research Laboratory (DMRL), Hyderabad 500 058, India. K.K. RAY, Professor, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology (IIT), Kharagpur 721 302, India. G. SUNDARARAJAN, Director, is with the International Advanced Research Centre for Powder Metallurgy & New Materials (ARCI), Hyderabad 500 005, India. Manuscript submitted December 6, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
(3) The dependence of erosion rate on impact angle exhibits a ductile behavior (i.e., the erosion rate exhibits a maximum at oblique impact angles) in the case of erosion tests conducted at room temperature and even at elevated temperatures, as long as a significant amount of oxide scale does not form.[4–6,9,10,12,14,20,21] In contrast, under erosion test conditions wherein a substantial amount of oxide scale forms, the erosion rate exhibits a brittle behavior.[8,16,24,28] (4) The elevated-temperature erosion rate is generally higher in an oxidizing atmosphere than in an inert atmosphere.[28] (5) Under erosion conditions, the oxide scale grows more rapidly than under static or dynamic oxidation conditions.[23] (6) The magnitude of the erosion rate, in the regime where oxidation has a strong effect, is dependent on the morphology of the oxide scale, with the segmented scale (as opposed to the continuous, consolidated scale) resulting in the lowest erosion rate.[17,18,23,24,26] The phenomenological modeling of the erosion behavior at elevated temperatures has been atte
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