Designation:C664−10(Reapproved2015)StandardTestMethodsforThicknessofDiffusionCoating1ThisstandardisissuedunderthefixeddesignationC664;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.INTRODUCTIONDiffusioncoatingisathermallyactivatedmeansofprotectingcertainiron,nickel,andcobaltbasedalloysagainstsevereoperatingconditions.Itcreatesachemicallybonded,tenaciouscoatingthatactsasadiffusionbarrieragainstoxygenandotherelementsintothesubstratetoprovidesuperioroxidation,corrosionanderosionresistanceupto2100°F(1150°C).Itiscommonlyusedforgasturbinecomponents,powergenerationcomponents,anddieselengines.Thistestprocedureprovidesameanofdeterminingthethicknessofadiffusioncoating.1.Scope1.1Thesetestmethodscovertwoproceduresformeasuringthethicknessofdiffusioncoatings.1.2TestMethodAisthedeterminationofthedimensional-changethickness,definedasthedifferenceinthethicknessofthepartbeforeandaftercoating.(Thetermsmicrometerthicknessandpartgrowthareconsideredsynonymouswithdimensionalchangethickness.)1.3TestMethodBisthedeterminationoftotalcoatingthickness,definedasthedistancebetweentheobservablyunaffectedsubstrateandtheexteriorsurfaceofthecoating.Thisincludesthetotalofallincludedphases,zonesandlayers.(Thetermcasedepthisconsideredtobesynonymouswithtotalcoatingthickness.)Thetotalcoatingthicknessisdeterminedbycross-sectioningthecoating,preparingametallurgicalmountandmicroscopicallymeasuringthecoatingthickness.1.4Thetotalcoatingthicknessasdeterminedmicroscopi-callyfromacross-sectionwillusuallybegreaterthan,orequalto,thedimensionalchangethicknessdeterminedbypartgrowth.Whenthecoatingisproducedprimarilybyreactionwiththesubstrate,thesubstrate-coatinginterfacerecedesasthesubstrateisconsumedinthereaction.Insuchcasesthedifferencebetweenthetotalcoatingthicknessandthedimen-sionalchangethicknessisthe...
