Slurry Erosive Wear Evaluation of HVOF-Spray Cr 2 O 3 Coating on Some Turbine Steels
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JTTEE5 21:838–851 DOI: 10.1007/s11666-012-9795-5 1059-9630/$19.00 ASM International
Slurry Erosive Wear Evaluation of HVOF-Spray Cr2O3 Coating on Some Turbine Steels Deepak Kumar Goyal, Harpreet Singh, Harmesh Kumar, and Varinder Sahni (Submitted September 19, 2011; in revised form April 12, 2012) In this study, Cr2O3 coatings were deposited on CF8M and CA6NM turbine steels by high-velocity oxy-fuel (HVOF)-spray process and analyzed with regard to their performance under slurry erosion conditions. High Speed Erosion Test Rig was used for slurry erosion tests, and the effects of three parameters, namely, average particle size, speed (rpm), and slurry concentration on slurry erosion of these materials were investigated. SEM micrographs on the surface of samples, before and after slurry erosion tests, were taken to study the erosion mechanism. For the uncoated steels, CA6NM steel showed better erosion resistance in comparison with CF8M steel. The HVOF-sprayed Cr2O3-coated CF8M and CA6NM steels showed better slurry erosion resistance in comparison with their uncoated counterparts. It may be due to the higher hardness as a result of HVOF-sprayed Cr2O3 coating in comparison with the uncoated CF8M and CA6NM steels.
Keywords
erosion testing, HVOF-spraying, hydroturbine steel, slurry erosion, thermal spray coatings
1. Introduction Slurry erosion occurring as a result of high-velocity impact of hard and angular abrasive particles carried by water is a very common problem faced by the most of the hydropower plants. This problem becomes more severe during monsoon season for hydropower plants situated in the Himalayan region in India and often leads to shutdown of these hydropower plants (Ref 1, 2). Therefore, due to heavy economic losses associated with slurry erosion, this problem has attracted the attention of the researchers worldwide (Ref 3). From the experimental studies, many researchers concluded that wear depends upon hardness of the target material or hardness of the impacting solid particles or both (Ref 4-8). Moreover, it has also been observed that the surface hardening of materials plays a dominant role in the erosion process (Ref 9). CF8M and CA6NM grades of ASTM A743 steels are commonly used in hydraulic turbine components because of their excellent mechanical properties and resistance to corrosion. However, during longer hours of exposure, these steel are affected by slurry erosion
Deepak Kumar Goyal, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 140407, India; Harpreet Singh, Indian Institute of Technology Ropar, Rupnagar 140001, India; Harmesh Kumar, University Institute of Engineering and Technology, Panjab University, Chandigarh 160014, India; and Varinder Sahni, Sant Longowal Institute of Engineering and Technology, Longowal, Sangrur 148106, India. Contact e-mails: [email protected] and [email protected].
838—Volume 21(5) September 2012
because of their lesser hardness in comparison with very hard erodent particles of hardness of about 1100 HV. Therefore, there is
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