Study of mechanical behavior of molybdenum coating using sliding wear and impact tests

Surface treatments and coatings are a practical approach used to extend the lifetime of components and structures especially if the surface is the most solicited part of the considered engineering component. Thermally sprayed molybdenum coating is one of the most wear resistance coating widely used in many practical mechanical applications. This paper aims to study the influence of post-thermal spraying parameters on the metallurgical and mechanical behavior of molybdenum coating formed by flame spraying on a 35CrMo4 steel substrate. These post-deposition parameters concern the influence of an annealing at 850 degrees C for 1 h in vacuum followed by air cooling and also the role of an oil lubricant. Metallurgical study is essentially based on the microstructure and hardness of molybdenum coating and mechanical behavior concerns its tribological resistance through sliding wear and impact fatigue resistance. The obtained results showed that flame sprayed molybdenum coating was very hard and has a good tribological behavior either for sliding wear or impact tests. Post-annealing has contributed to redistribution of pores and oxides and to homogenize coating microstructure but did not show a great influence neither on the wear resistance nor on the impact resistance. Oil lubricant has no significant influence on friction wear of molybdenum coating but has altered severely its impact fatigue resistance by evacuating continuously the generated powder and debris outside craters under indenter repetitive blows so that its deformation was consequently facilitated. (C) 2007 Elsevier B.V. All rights reserved.