HP/HVOF as a Low Cost Substitute for LPPS Turbine MCrAlY Coatings

Abstract

MCrAlY (M=Co, Ni) coatings have long been used in gas turbines to protect hot section components from hot corrosion and oxidation. Their complex chemistries, along with the thickness of the deposits, makes them reliable over long periods of time in engines used in power generation and in aircraft applications. A variety of techniques such as Electron Beam Physical Vapor Deposition (EBPVD), Low Pressure Plasma Spray (LPPS), and Argon Shrouded Plasma Spray have been used to deposit MCrAlYs over the years. Until recently, OEM’s have been reluctant to consider alternate deposition methods, but the prospect of lower cost, high quality coatings has merited reconsideration of some long-standing assumptions. In recent efforts, Howmet Thermatech has gained production approval to deposit a proprietary MCrAlY composition on an OEM’s latest generation gas turbine engine components using a TAFA JP-5000 High Pressure/High Velocity Oxygen Fuel (HP/HVOF) coating system. Tensile bond and hardness data are presented which substantiate the equivalence of this coating to its VPX® forerunner. Photomicrographs illustrate the levels of porosity, oxide content and interface quality currently in revenue service. Unpublished cost data from an established coating supplier reveal that MCrAlYs can be deposited by HP/HVOF at a fraction of the cost of VPX® alternatives.