the airfoil and a convexly curved side termed the convex side 32 also sometimes known as the u201c suction u201d side of the airfoil a curved leading edge 31 separates the concave side 30 from the convex side 32 along one longitudinal margin of the airfoil a more sharply defined trailing edge 33 separates the concave side 30 from the convex side 32 along the other longitudinal margin of the airfoil 22 the airfoil 22 terminates in a tip 42 remote from the dovetail 24 in service the pressurized hot combustion gas from the combustors is directed against the concave side 30 this concave side 30 therefore requires more protection against the incident hot combustion gas than does the convex side 32 to provide this protection the concave side 30 is coated with a protective coating either in the form of an environmental coating or a thermal barrier coating fig2 schematically illustrates the airfoil 22 portion after the protective coating is applied on the concave side 30 there is a platinum layer 34 adjacent to a substrate 36 made of a base metal the base metal forming the substrate 36 is typically a nickel base superalloy such as rene 39 n5 the nickel base superalloy has more nickel than another element and is usually strengthened by gamma prime precipitation rene 39 n5 has a nominal composition in weight percent of about 7 5 percent cobalt about 7 percent chromium about 6 2 percent aluminum about 6 5 percent tantalum about 5 percent tungsten about 1 5 percent molybdenum about 3 percent rhenium about 0 05 percent carbon about 0 004 percent boron about 0 15 percent hafnium up to about 0 01 percent yttrium balance nickel and incidental.