1、Designation: F 1854 01Standard Test Method forStereological Evaluation of Porous Coatings on MedicalImplants1This standard is issued under the fixed designation F 1854; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers stereological test methods forcharacterizing the coating thickness, void content, and meaninter
3、cept length of various porous coatings adhering to nonpo-rous substrates.1.2 Porous coatings with significant gradients in the poros-ity from the substrate to the surface will require use of thealternate sample orientation method outlined in 8.2.1.3 The values stated in SI units are to be regarded a
4、s thestandard.1.4 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
5、. Referenced Documents2.1 ASTM Standards:E 3 Practice for Preparation of Metallographic Specimens2E 883 Guide for Reflected Light Photomicrography23. Terminology3.1 Definitions:3.1.1 fieldthe image of a portion of the working surfaceupon which measurements are performed.3.1.2 interceptthe point on a
6、 measurement grid line pro-jected on a field where the line crosses from solid to void orvice versa.3.1.3 measurement grid linesa evenly spaced grid ofparallel lines all of the same length.3.1.4 porous coatingcoating on an implant deliberatelyapplied to contain void regions with the intent of enhanc
7、ing thefixation of the implant.3.1.5 substratethe solid material to which the porouscoating is attached.3.1.6 substrate interfacethe region where the porous coat-ing is attached to the substrate.3.1.7 working surfacethe ground and polished face of themetallographic mount where the measurements are m
8、ade.4. Summary of Test Method4.1 Mean Coating ThicknessMeasurement grid lines areoriented perpendicular to the substrate interface. On each of thelines in the group, the distance from the substrate interface tothe last contact with the porous coating material is measured.The average of the line leng
9、ths over the group of lines is thelocal mean coating thickness.4.2 Volume Percent VoidA regular grid of points issuperimposed on a field from the working surface. Thepercentage of points that are in contact with void areas in thecoating correlates with the volume percent of void present.4.3 Mean Voi
10、d Intercept LengthMeasurement grid linesare oriented parallel to the substrate interface. The number oftimes the lines intercept voids is used with the volume percentvoid to calculate the mean void intercept length.5. Significance and Use5.1 These test methods are recommended for elementaryquantific
11、ation of the stereological properties of porous coatingsand the solid substrates to which they are bonded.5.2 These test methods may be useful for comparativeevaluations of different coatings or different lots of the samecoating.5.3 All three methods should be performed on the sameworking surface.5.
12、4 A statistical estimate can be made of the distributions ofthe mean coating thickness and the volume percent void. Noestimate can be made of the distribution of intercept lengthsunless the void is a regular geometric shape that can be definedmathematically.6. Apparatus6.1 The procedures outlined in
13、 this test method can beperformed manually or by an automated procedure. Thefollowing apparatus are necessary for manual calculations.6.2 Microscope, or other suitable device with a viewingscreen or photomicrographic capability of at least 125 by 175mm should be used to image the working surface.6.3
14、 Transparent Sheet, with measurement grid lines orpoints is superimposed on the viewing screen or photomicro-graph for the measurements. The grid lines grids of points1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct resp
15、onsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved October 10, 2001. Published February 2002.2Annual Book of ASTM Standards, Vol 03.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.should be uniforml
16、y spaced and parallel with at least fiveparallel lines.7. Metallography7.1 The procedures outlined in this test method for charac-terizing porous coatings require the preparation of metallo-graphic sections through the entire coating thickness into thesolid substrate. Good metallographic preparation
17、 techniques, inaccordance with Practice E 3 and Guide E 883 must be used toprevent deformation of the surface of the section or creation ofany other artifacts that will alter the stereological properties ofthe metallographic section. An example of an unacceptableartifact would be the absence of a po
18、rtion of the porouscoating, caused by its removal, thereby creating an artificialvoid area.7.2 Care must be taken to ensure that the working surface isperpendicular to the interface between the porous coating andthe solid substrate. In the case of the alternate mountingmethod shown in 8.4, extreme c
19、are must be taken to keep thesubstrate interface parallel to the final working surface.8. Sample Selection8.1 Normal Section Orientation:8.1.1 A description of type of sample from which the samplemetallographic sections are removed and the location of thosesample metallographic sections should be in
20、cluded as part ofthe results.8.1.2 For accurate coating thickness measurements, theorientation of sample working surfaces should be approxi-mately perpendicular to the substrate.8.2 Alternative Orientation Method:8.2.1 An alternate orientation is required for the volumepercent void and mean intercep
21、t length measurements ofcoatings with a varying amount of porosity in the coating. Theporous material and substrate should be mounted with thesubstrate interface parallel to the metallographic mount sur-face. The mount is ground parallel to the substrate interface andthe measurements are taken at a
22、fixed distance from thesubstrate interface. It is recommended that the measurementsbe made at 50 % of the mean coating thickness8.2.2 At least one surface must also be ground on the samemount at 90 to the measurement surface. These will confirmthat the interface surface is parallel to the working su
23、rface andallow measurement of the distance from the working surface tothe substrate. The working surface must be parallel within 65of the substrate.8.2.3 This test method is not suitable for substrate interfaceswith a radius of curvature less than 1 in. (25 mm).8.2.4 Since this test method also requ
24、ires more aggressiveporous surface removal to reach 50 % of the mean coatingthickness, it may be more susceptible to creation of metallo-graphic artifacts. Care should be exercised to assure that themetallographic sections that are used are free of artifacts.9. Procedure9.1 Mean Coating Thickness:9.
25、1.1 Appendix X2 includes two sets of typical measure-ment grids each with ten measurement lines, one set separatedby a distance of 1 cm and one set separated by a distance of 0.5cm.9.1.2 The magnification should be chosen such that thethickness of the coating in the image is at least 4 cm.9.1.3 The
26、transparency of the measurement grid lines issuperimposed on the field in an orientation approximatelyperpendicular to the substrate interface. The length of each linebetween the substrate interface to the last contact with theporous coating is measured on each line.9.1.4 If the angle between the su
27、bstrate interface and anyindividual line of the group of parallel lines is not between 80and 100, the individual measurement is invalid.9.1.5 The procedure is repeated on a minimum of ten uniquefields on each working surface.9.1.6 The average of all the measurements is the meancoating thickness for
28、that working surface. The standarddeviation estimator and the 95 % confidence interval should becalculated for each working surface. The equations for calcu-lating these values are as follows:T51Mxn(i51nti(1)where:ti= the individual magnified thickness line length,M = the magnification, andT = the m
29、ean coating thickness.S51n1(i51nFtiMi TG2(2)where:S = the standard deviation estimator.CI 5 23S=n(3)where:CI = the confidence interval.9.2 Volume Percent Void:9.2.1 X2.1 includes three different typical sets of 100-pointgrids. Two of the grids are spaced 10 by 10 (1.0 by 1.0 and 0.5-by 1.0-cm separa
30、tion) and the other is a 20 by 5 grid (0.5- by1.0-cm separation).9.2.2 If the void areas form a regular or periodic pattern onthe working surface, the use of a grid having a similar patternshould be avoided.9.2.3 The transparency is superimposed randomly on afields. The magnification of the field is
31、 chosen such that one ofthe available grids can fit completely within the porous coatingin the working surface.9.2.4 Grid height must be greater than 50 % of the meancoating thickness. For coatings consisting of regularly shapedparticles, or those having porosity gradients, care must be takennot to
32、influence results by nonrandom grid placement.9.2.5 The number of points in contact with void areas in theworking surface will be counted and recorded.9.2.6 Count any points falling on a boundary between voidarea and solid area as one half. Any doubtful point should becounted as one half.9.2.7 The n
33、umber of contact points, divided by the totalF 18542number of points on the grid times 100 gives the percentage ofgrid points on the void for that field. This should be calculatedfor each grid application.Pv5PaPT3 100 (4)where:P(a) = the total number of counted points,P(T) = the total number of grid
34、 points, andP(v) = the volume percent void.9.2.8 A minimum of 30 fields should be measured perworking surface.9.2.9 Fields to be analyzed should include as much of thecoating thickness as possible. When there are porosity gradi-ents are present, the accuracy of the measurement is related tothe amoun
35、t and repeatability of gradient in the portion of thecoating section analyzed in each field.9.2.10 The average percentage of the grid points on thevoids provides an unbiased statistical estimator for the voidvolume percentage in the three dimensional structure. Themean void percentage (Pv) for that
36、working surface, thestandard deviation estimator (S) and the 95 % confidenceinterval (CI) should be calculated for each working surface.The equations for calculating these values are as follows:Pv51n(i51nPvi(5)S51n 1(i51nPvi Pv#2(6)CI 5 23S=n(7)9.2.11 The volume percent void estimate is given by the
37、following relationship:Vv5 Pv(8)9.3 Mean Intercept Length9.3.1 Appendix X2 includes two sets of ten measurementlines, one set separated by a distance of 1 cm and one setseparated by a distance of 0.5 cm. A transparency can be madeof a group for manual work.9.3.2 The transparency is superimposed on e
38、ach of thefields. The measurement line grid should fit completely withinthe porous coating cross section.9.3.3 The magnification will be chosen such that the numberof counted intercepts per line should average five or more.9.3.4 The number of times that a void region is interceptedby the test lines
39、(Nv) is counted and recorded. There are twomethods that can be used for counting.9.3.4.1 The first method counts the number of intersectionsalong the grid lines. Each time the grid line goes from eithersolid to void or void to solid is counted as one intersection. Thenumber of intersections (ni) is
40、twice the number of intercepts(Nv).Nv5n12(9)9.3.4.2 In the second method the crossing direction of anyintersection on any line determines if it is counted as anintercept. If the beginning of the line starts on a void, count thetransitions from void to solid. If that same line ends on a void,count th
41、at as a one more intercept. If the beginning of a linestarts on solid, count the transitions from solid to void. If thesame line ends on a solid, there is no additional count.9.3.5 At least ten different fields should be counted on eachworking surface.9.3.6 For the alternative method, the orientatio
42、n of the gridshould be random.9.3.7 The mean intercept length (Lv) can be calculated fromthe total length of lines (LT), the number of intercepts (Nv), themagnification M, and the previously calculated volume percentvoid (Vv). The calculation is as follows:Lv5Vv3LtMNv(10)10. Report10.1 Report the ch
43、emical composition of the substratestructure and the coated material.10.2 The original morphological form of the coated material(that is, powder, wire, and so forth) and the method ofapplication will be reported.10.3 The number of fields of view for each measurement,the magnifications used, and the
44、grids and lines used shall bereported.10.4 The mean coating thickness and confidence interval,the volume percent void and confidence interval, and the meanlinear intercept will be reported.10.5 If curved substrates are used, that information must beincluded in the report, along with an estimate of t
45、he localradius of curvature.10.6 If the alternative orientation method is used, thatinformation must be reported together with the distance fromthe substrate for each set of measurements.10.7 For image analysis systems that measure on digitizedvideo images, the minimum measurement value, that is, th
46、edimension of a single pixel, must be reported at all magnifi-cations used in the measurements.11. Precision and Bias11.1 The following factors could significantly affect theresults obtained using this method:11.1.1 The presence of structural gradients or inhomogene-ities in the section can influenc
47、e the precision and accuracy ofthe measurements. If the amount of void in the porous coatingchanges with thickness, the alternative mounting method andserial grinding may be used to characterize the gradient.11.1.2 The quality of sample preparation can influenceprecision and bias.11.1.3 The counting
48、 of grid points and line ends at voidboundaries presents an opportunity for bias in the measure-ments. The method outlined in 9.3.4.1 and 9.3.4.2 must beused.11.1.4 The number of fields measured, the method of fieldselection, and their spacing can influence the precision andaccuracy. Random selectio
49、n of fields and, except where noted,F 18543random orientation of grids within the field can help eliminatebias.11.2 The results of an interlaboratory comparison, althoughnot comprehensive enough to support statistical statementsabout the precision of this method, are presented in AppendixX4 for information only.12. Keywords12.1 metallography; porosity; porous coatings; stereology;thicknessAPPENDIXES(Nonmandatory Information)X1. RATIONALEX1.1 Porous coatings are applied to the surface of medicalimplants. Standardized techniques should be available to char-acteriz
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