Microstructure and tribological properties of gray cast iron specimens coated by aluminizing, boronizing, chromizing and
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Microstructure and tribological properties of gray cast iron specimens coated by aluminizing, boronizing, chromizing and siliconizing T. Murakami1, K. Matsuzaki1, Y. Gomi2, S. Sasaki2 and H. Inui2 1 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Ibaraki 305-8564, Japan 2 Department of Mechanical Engineering, Tokyo University of Science, Tokyo 102-0073, Japan 3 Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan ABSTRACT In this study, aluminized, boronized, chromized and siliconized gray cast iron plate specimens were prepared, and their microstructures and tribological properties were investigated. The surfaces of the aluminized, boronized, chromized and siliconized specimens mainly consisted of FeAl, Fe2B, (Cr, Fe)23C6 and FeSi phases, respectively. Also, the surface of the boronized specimen exhibited the highest microvickers hardness of all the specimens. The aluminized, boronized and chromized specimens exhibited friction coefficients as low as the non-coated specimens when sliding against AISI 52100 steel ball specimens in poly-alpha-olefin. In addition, the boronized and chromized specimens exhibited much higher wear resistance than the non-coated specimens. INTRODUCTION Gray cast iron has been used variously as a sliding material because of its low friction coefficient in various oils. However, gray cast iron has low strength and low wear resistance. Therefore, the gray cast iron surface is sometimes nitrided [1, 2] and quenched to increase the strength and wear resistance, although this does not sufficiently improve the corrosion resistance. Pack cementation [3-6] of gray cast iron may improve such problems because it is thought that adhesive and thick coating layers with high hardness, high wear resistance and high corrosive resistance can be formed using this process. However, the friction and wear properties of such coating layers have not been investigated sufficiently. In this study, gray cast iron specimens coated with Al-, B- and Cr-rich layers were prepared by aluminizing [3], Table 1 Pack cementation conditions used in this boronizing [4, 5] and chromizing [5] study. using an electric furnace, recpectively. Also, gray cast iron specimens coated with Si-rich layers were prepared by siliconizing [6] using a hot pressing machine at a pressure of 20 MPa because the Si-rich layers obtained using the electric furnace did not adhere adequately to the gray cast iron substrates as reported by Tatemoto et al [7]. After the coating, the microstructures, microvickers hardness
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and tribological properties of the coated specimens were investigated. EXPERIMENTAL PROCEDURES The gray cast specimens used in this study have a composition of Fe-4.6C-2.0Si (mass%). These specimens were cut from an ingot bar, polished using 4000-grit SiC papers and cleaned in a mixture of 50 vol% acetone and 50 vol% petroleum benzene using an ultrasonic cleaner for 1.2 ks before the pack cementation. The aluminizing, boronizing and chromizing and siliconizing w
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