Characterization of Thermal Spray Coatings for Cylinder Running Surfaces of Diesel Engines
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JTTEE5 19:866–872 DOI: 10.1007/s11666-010-9488-x 1059-9630/$19.00 Ó ASM International
Characterization of Thermal Spray Coatings for Cylinder Running Surfaces of Diesel Engines Mareike Hahn and Alfons Fischer (Submitted July 9, 2009; in revised form August 24, 2009) Future demands of diesel engines are about low-friction and wear-resistant materials in order to increase the efficiency and achieve environmentally sound solutions. Thus, thermally sprayed Fe-base coatings are investigated for application as cylinder running surfaces in cast aluminum crankcases. They should allow the desired combination of structural, productional, and topographical properties required in Diesel engines. To understand the influence of the characteristic microstructures on the integrity of the composites the coatings have to be examined in laboratory tests in terms of different loading situations. Cavitation tests were carried out where the tribological stability of these coatings and their ability to resist high-frequency cyclic impact stresses are revealed. Composite samples (base material and coating) were investigated in terms of crack initiation in a scanning electron microscope with an in situ 3-pointbending test. The endurance under cyclic mechanical stresses was tested with a 4-point-bending stress controlled test.
Keywords
coating characteristics, Fe-base coatings, thermal spray
1. Introduction Versatile thermal spray processes and material combinations have been applied in automotive engineering. Wear protection as well as reducing friction are of major concern and led to the development of powder and wire consumables adapted to the specific features of the different spraying processes for manufacturing and repair (Ref 1). The structure and, therefore, the properties of metal sprayed coatings are governed by the thermal and kinetic energy introduced. Particle velocities might vary from 150 m/s for Twin Wire Arc Spraying (TWAS), 450 m/s for Plasma Transferred Wire Arc (PTWA) up to 750 m/s for High Velocity Oxygen Fuel (HVOF). Mean particle temperatures are about 2000 °C for TWAS and PTWA but kept in the vicinity of the material melting point within HVOF spraying. This leads to differing characteristic features (particles size, pore and oxide fraction and size, lamella or splat thickness) within such coatings (Ref 2-4). Coating characteristics depend on bonding between the splats and the substrate as well as between the individual splats whereas voids and splat
Mareike Hahn and Alfons Fischer, University of DuisburgEssen, Institute of Product Engineering, Materials Science and Engineering, Lotharstr. 1, 47057 Duisburg, Germany. Contact e-mails: [email protected] and [email protected].
866—Volume 19(5) September 2010
grain boundaries play a significant role in fatigue behavior of these coatings (Ref 5). Hitherto low alloyed carbon steels with 0.9 wt.% carbon have been successfully used for cylinder coatings. Many wear-resistant coatings make use of hard phases which are either introduced by alloying (e.g., C
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