B. K. Pant

Cavitation Erosion Behavior of HPDL-Treated TWAS-Coated Ti6Al4V Alloy and Its Similarity with Water Droplet Erosion

Twin wire arc-sprayed (TWAS) coating of commercially available SHS 7170-cored wire was obtained on Ti6AL4V alloy, and to improve its properties, it was further surface treated with high-power diode laser (HPDL). The cavitation erosion (CE) resistance of TWAS-coated samples was evaluated as per ASTM G-32-2003 and it was compared with laser-treated and untreated Ti6Al4V alloys. The CE resistance of TWAS-coated SHS 7170 samples after HPDL treatment has improved significantly. The main reasons for its improvement are elimination of pores, increased fracture toughness, reduced hardness, and brittleness. The CE resistance of HPDL-treated TWAS coating is compared with water droplet erosion resistance. It is observed that there is a similarity in the both the phenomenon.

High Power Diode Laser Surface Treatment to Minimize Droplet Erosion of Low Pressure Steam Turbine Moving Blades

This article deals with the high power diode laser (HPDL) surface treatment to overcome water droplet erosion of Low Pressure Steam Turbine (LPST) moving blades used in high rating conventional, critical and super critical thermal power plants. The materials generally used in these steam turbines are titanium alloy (Ti6Al4V), precipitate hardened stainless steel (17Cr-4Ni PH), X20Cr13 and X10CrNiMoV1222 steels. During incubation period as well as under prolonged testing, the HPDL surface treatment of these materials except for 17Cr-4Ni PH steel has enhanced the droplet erosion resistance significantly. This is due to increased hardness and formation of fine-grained martensitic phase due to rapid heating and cooling rates associated with laser treatment. The droplet erosion results of HPDL laser surface treatment of all these materials and their analysis form the main part of the article.

High-Power Diode Laser Surface Treated HVOF Coating to Combat High Energy Particle Impact Wear

High-velocity oxy-fuel (HVOF)-sprayed coatings have performed exceptionally well in low-energy particle impact wear and are accepted worldwide. However, their application for high-energy particle impact wear (HEPIW) requires a different approach and more efforts. HVOF-coating systems typically use WC-Co, WC-Co-Cr, WC-Ni-Cr, and FeCrAlY-Cr3C2 powders. WC-Co-Cr powders are preferred when there is a high demand for corrosion resistance. WC-10Co-4Cr coating powder has been selected in the current study. To improve coating properties such as microhardness, fracture toughness, and HEPIW resistance, a new approach of surface treatment with robotically controlled high-power diode laser (HPDL) is attempted. The robotically controlled HVOF-coating deposition and laser surface treatment were monitored using real-time diagnostic control. The HPDL-treated coating has been compared with “as-sprayed” HVOF coating for HEPIW resistance, fracture toughness, microhardness and microstructure. The coating characteristics and properties after laser surface treatment have improved many times compared with “as-sprayed” HVOF coating. This is due to the elimination of pores in the coating and formation of a metallurgical bond between coating and substrate. This new development opens up a possibility of using such laser treatments in specialized areas where HEPIW damages are acute. The fracture toughness and HEPIW resistance along with optical micrographs of HPDL-treated and untreated HVOF coatings are discussed and reported in this article. HEPIW resistance is observed to be proportional to the product of fracture toughness and microhardness of the HVOF coating.

Cavitation Erosion Characteristics of Nitrocarburized and HPDL-Treated Martensitic Stainless Steels

This article deals with plasma ion-nitrocarburising and high power diode laser (HPDL) surface treatment of 13Cr4Ni and X10CrNiMoV1222 martensitic stainless steels to enhance their cavitation erosion resistance. These steels are commonly used in hydro turbines and boiler feed pumps. These treated steels have been evaluated for cavitation erosion resistance and it has been observed that the plasma ion-nitrocarburising process has significantly enhanced the cavitation erosion resistance as compared to untreated steel whereas HPDL-treated steels have shown marginal improvement. This is due to formation of high hardness nitrides during nitrocarburising and formation of moderate hardness martensitic phase due to rapid heating and cooling rates involved in HPDL treatment. The cavitation erosion and micro-hardness data of plasma ion-nitrocarburized as well as HPDL-treated steel samples and their comparison with hard deposits such as stellite and HVOF coating form the main part of the article.

Effect of Laser Peening on Steel and Titanium Alloy for Power Applications

Low pressure steam turbine (LPST) blades are made of martensitic stainless steel and Ti6Al4V alloy for the different ratings of steam turbines due to their high strength and toughness. These blade roots have a fir tree profile and experience severe stress concentrations all along their notched sections during turbine operation. The fatigue life of these blades can be increased by introducing compressive stresses either by shot peening or by laser peening. The present work deals with laser peening of these two materials to understand its effect on their fatigue properties, surface roughness and hardness. It is observed that laser peening has significantly enhanced fatigue life of Ti6Al4V alloy at 550 MPa stress as compared to the shot peened sample. The penetration depth of residual stress due to laser peening in the Ti6Al4V alloy was twice that due to shot peening. However, the fatigue life of steel was found to be similar for both the shot peened as well as laser peened samples. Similar response was observed from testing at lower stresses (400 MPa). Since the depth of penetration of compressive residual stresses for both the laser peened as well as the shot peened samples were similar for steels, it can be concluded that the fatigue life is a strong function of the penetration depth.Copyright