The influence of grain size on the erosion rate of metals
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INTRODUCTION
SOLID particle erosion of ductile metals and alloys is an important and common material degradation mechanism encountered by the engineering industry. Erosion of turbine and compressor blades in aircraft engines ~and erosive wear of pipes in pneumatic bulk transport systems: are the typical examples of such a phenomenon. The metallurgical aspects of erosion have received sustained attention only during the last decade. Correlation of erosion resistance with metallurgical microstructure in particular has received even less attention. Levy and coworkers TM noted that the steady state erosion rate of 1075 carbon steel, impacted at a velocity and angle of 30 m/s and 30 deg, respectively, with 240/xm SiC particles, was dependent on its microstructure. For example, spheroidized microstructure resulted in a 30 pct higher resistance to erosion when compared to lamellar pearlite structure. In a more comprehensive study, McCabe, Sargent, and Conrad 5 investigated the effect of microstructure of a 1078 steel on its erosion resistance using 30/xm Al:O3 particles at various impact angles and velocities. Their results indicated that the steel microstructures can be ranked in order of increasing erosion rate as follows: spheroidite, pearlite, tempered martensite, and martensite. Emiliani and Brown 6 examined the erosion behavior of Ti6A1-4V alloy in two microstructural forms, equiaxed a + /3 and a basket weave a + /3 structure, using spherical silica particles of 210/xm in diameter, a velocity of 61 m/s, and an impact angle of 90 deg. The erosion rate was significantly higher in the case of equiaxed structures when compared to basket weave structures. The erosion rate of an aluminum 6061 alloy subjected to various heat treatments was characterized by Salik, Buckley, and Brainard. 7 The erosion rate was the lowest in the solution treated condition and increased with increased aging time, thereby indicating the adverse influence of the precipitate structure. One important microstructural feature whose influence on the solid particle erosion behavior that is yet to be studied is the grain size. As is well known, grain size refinement not only increases the strength of the material but also its ductility. On this basis, grain refinement should result in higher resistance to erosion. But, the extent to which the A. VENUGOPAL REDDY and G. SUNDARARAJAN are Scientists with Defence Metallurgical Research Laboratory, Kanchanbagh P.O., Hyderabad-500 258, India. Manuscript submitted June 10, 1986. METALLURGICAL TRANSACTIONS A
grain refinement will be beneficial at high strains and high strain rates relevant to erosion is not known, since no data exist. Therefore, there is a real need for characterizing erosion behavior of metals and alloys as a function of their grain size. In this regard it must be noted that Preece and coworkers 8 have studied the effect of grain size on the cavitation erosion resistance of pure metals like iron, nickel, and zinc. Their data indicate a grain size independent erosion rate in iron while in
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