ASTM_C_664_-_10_2015.pdf

Designation:C66410(Reapproved 2015)Standard Test Methods forThickness of Diffusion Coating1This standard is issued under the fixed designation C664;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONDiffusion coating is a thermally activated means of protecting certain iron,nickel,and cobalt basedalloys against severe operating conditions.It creates a chemically bonded,tenacious coating that actsas a diffusion barrier against oxygen and other elements into the substrate to provide superioroxidation,corrosion and erosion resistance up to 2100F(1150C).It is commonly used for gasturbine components,power generation components,and diesel engines.This test procedure providesa mean of determining the thickness of a diffusion coating.1.Scope1.1 These test methods cover two procedures for measuringthe thickness of diffusion coatings.1.2 Test Method A is the determination of the dimensional-change thickness,defined as the difference in the thickness ofthe part before and after coating.(The terms micrometerthickness and part growth are considered synonymous withdimensional change thickness.)1.3 Test Method B is the determination of total coatingthickness,defined as the distance between the observablyunaffected substrate and the exterior surface of the coating.This includes the total of all included phases,zones and layers.(The term case depth is considered to be synonymous with totalcoating thickness.)The total coating thickness is determined bycross-sectioning the coating,preparing a metallurgical mountand microscopically measuring the coating thickness.1.4 The total coating thickness as determined microscopi-cally from a cross-section will usually be greater than,or equalto,the dimensional change thickness determined by partgrowth.When the coating is produced primarily by reactionwith the substrate,the substrate-coating interface recedes as thesubstrate is consumed in the reaction.In such cases thedifference between the total coating thickness and the dimen-sional change thickness is the thickness of the substrateconsumed.1.5 Diffusion coatings are usually formed at elevated tem-peratures for service at elevated temperatures.This means thatdiffusion coatings are dynamic systems which are continuallyundergoing changes while in an elevated-temperature environ-ment.It is necessary to know that certain phases are growing atthe expense of others and to know the previous history of acoating to understand the significance of coating thicknessdata.1.6 Values in SI units are to be regarded as the standard.Inch-pound units are provided for information only.1.7 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D374 Test Methods for Thickness of Solid Electrical Insu-lation(Withdrawn 2013)3E3 Guide for Preparation of Metallographic Specimens3.Significance and Use3.1 A diffusion coating is one produced by causing anelement or elements to react with or diffuse into,or both,thesurface of a metallic substrate,thus chemically altering thesubstrate adjacent to the surface.To appreciate the significanceof coating thickness measurements one must understand thecontributions to a particular coating of solid-solution zones inthe substrate and reaction products such as intermetalliccompounds.1These test methods are under the jurisdiction of ASTM Committee B08 onMetallic and Inorganic Coatings and are the direct responsibility of SubcommitteeB08.12 on Materials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved May 1,2015.Published June 2015.Originallyapproved in 1970.Last previous edition approved in 2010 as C664 87(2010).DOI:10.1520/C0664-10R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.Test Method A4.1 ApparatusThe instrument shall be a machinists typemicrometer without a locking device.If calibrated in inches,itshall be constructed with a vernier reading to 0.0001 in.(0.1mil).If calibrated in metric units,it shall be capable of readingto 0.01 mm.It shall have a ratchet or similar mechanism,suchas a friction thimble,for controlling measuring pressure andshall have anvil and spindle surfaces 6.00 6 0.03 mm(0.250 60.001 in.)i