1、Designation: C 1212 98 (Reapproved 2004)Standard Practice forFabricating Ceramic Reference Specimens ContainingSeeded Voids1This standard is issued under the fixed designation C 1212; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 the year of last 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 practice describes procedures for fabricating bothgreen and sintered test bars of silicon carbide a
3、nd siliconnitride containing both internal and surface voids at prescribedlocations.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of thi
4、s 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:2B 311 Test Method for Density Determination for PowderMetallurgy (P/M) Materials Containing Less than TwoPercent Porosit
5、yC 373 Test Method for Water Absorption, Bulk Density,Apparent Porosity, and Apparent Specific Gravity of FiredWhiteware Products3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 green specimena ceramic specimen formed as origi-nally compacted prior to high-temperature densifica
6、tion.3.1.2 internal voida cavity in a specimen with no connec-tion to the external surface.3.1.3 seeded voidsintentionally placed discontinuities atprescribed locations in reference specimens.3.1.4 sintered specimenformed ceramic specimen afterfiring to densify and remove solvents or binders.3.1.5 s
7、urface voida pit or cavity connected to the externalsurface of a specimen.4. Significance and Use4.1 This practice describes a method of fabricating knowndiscontinuities in a ceramic specimen. Such specimens areneeded and used in nondestructive examination to demonstratesensitivity and resolution an
8、d to assist in establishing properexamination parameters.5. Apparatus5.1 Aeroduster, moisture-free.5.2 Die, capable of exerting a pressure of up to 120 MPa,that will not contaminate the compacted material.5.3 Optical Magnifier, capable of providing 10 to 30Xmagnification.5.4 Tubing, latex, thin-wall
9、, capable of withstanding iso-press.5.5 Carver Press or similiar type of appartus capable ofexerting the necessary pressure to consolidate the sample.5.6 Cold Isostatic Press, capable of maintaining 500 MPa.5.7 Vacuum Oven or Furnace which can maintain a tem-perature of 525C.5.8 Imaging Equipment wi
10、th the capability of producing ahard copy output of the image (that is, 35mm camera, CCDcamera outputted to a video printer, a stereo microscope with 4X 5 instamatic film, etc.).5.9 Sintering Furnaces capable of reaching temperatures of14002200C. Depending on the ceramic system chosen, thefurnace ma
11、y be required to operate in a vacuum and/or underinert gas atmospheres at pressures as high as 200 MPa.5.10 Commercial or similar device capable of measuringwithin .01 mg. Measuring densities according to Archimedesprinciple requires the use of a sample holder suspended inwater attached to the scale
12、.6. Materials6.1 Silicon Carbide or Silicon Nitride Powders, of appro-priate purity and particle size, prepared with sintering aids andbinder representative of the product to be inspected and in amanner appropriate for dry pressing with granule size less than100-mesh.1This practice is under the juri
13、sdiction of ASTM Committee C28 on AdvancedCeramics and is the direct responsibility of Subcommittee C28.02 on Design andEvaluation.Current edition approved May 1, 2004. Published June 2004. Originallyapproved in 1992. Last previous edition approved in 1998 as C 121298.2For referenced ASTM standards,
14、 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
15、28-2959, United States.6.2 Styrene Divinyl Benzene Spheres, with diameters asnecessary. Other material with low vaporization temperaturesmay be substituted, but pressing characteristics and final voidsizes may be different.7. Fabrication of Surface Voids7.1 Green Specimens:7.1.1 The test piece geome
16、try must be appropriate for thesize and geometry limits of the NDE test method. If thepurpose of the test is to determine if the NDE method issuitable for the detection of voids in a particular part/sample,ideally the test sample should be identitcal to the part/sample.If this is not feasible due to
17、 fabrication or testing limitations,the test sample should be similar to the part/sample in chemicalcomposition, density, and thickness (the thickness of the testsample should be the same as the thickness in the area of thepart/sample being examined.7.1.2 Procedure:7.1.2.1 Prepare the test specimen
18、bars by pouring ceramicpowder into a die in an amount sufficient to make a specimenof the desired thickness. Level the surface and press at anominal pressure of 60 MPa.7.1.2.2 Remove the ram to expose the specimen. Clean thespecimen of all particles that are not flush with the top surface;this can g
19、enerally be performed with a moisture-free aero-duster.7.1.2.3 Place large spheres in the desired location on thespecimen surface. Small microspheres may be moved to thedesired position with a single human hair taped to a stiff plasticrod, using the assistance of an optical magnifier.7.1.2.4 Press t
20、he spheres into the surface at a suitablepressure to obtain the desired strength for handling of the greencompact (typically 120 MPa).7.1.2.5 Remove the bar from the die and clear the surfacesof extraneous particles. An aeroduster or brush should beadequate.7.1.2.6 Place the specimen in a thin-wall
21、latex tube andevacuate the air. Seal the tube end. Cold isopress at a pressuresuitable for a specific material (nominally 210420 MPa).7.1.2.7 Remove the specimen from the tubing and heat it ina vacuum to decompose the spheres (525C for 45 min forstyrene divinyl benzene).7.1.2.8 Mark the specimen ori
22、entation with a scribe mark orby beveling a corner or edge. Remove extraneous particlesfrom all surfaces with an aeroduster or brush. Light sandingmay be necessary, for adherent particles.7.1.3 Void MeasurementMeasure the lateral dimensionsin two orthogonal directions. The depth can be measured byfo
23、cusing a microscope alternately on the specimen surface andon the bottom of the crater and noting the difference in thevertical position of the tube. Use a magnification suitable formeasuring depth within 2 m.7.1.4 Measure the bulk density of the specimen from directvolume and weight measurements.7.
24、2 Sintered Specimens:7.2.1 Procedure:7.2.1.1 Follow the steps given in 7.1.2 to produce greenspecimens.7.2.1.2 Sinter green samples under suitable conditions toachieve full densification. Nominal sintering conditions forsilicon nitride are 17001900C for1hinaninert atmosphereat 0200 MPa; for silicon
25、carbide, sintering temperatures of20002200C for 0.5 h under vacuum are commonly used. Thesintering aids used will dictate the firing conditions. Measurethe bulk density using either Test Method B 311 or TestMethod C 373 or from volume and weight measurements.7.2.2 Void MeasurementSee 7.1.3.7.3 Surfa
26、ce Void Characteristics (for Both Green and Sin-tered Specimens):7.3.1 Surface voids produced by this procedure are notspheroidal in shape. The final dimensions are a function of thecompressibility of the seeded spheres and the compressibilityand sintering characteristics of the powders that compris
27、e thebulk material.7.3.2 Silicon Nitride Test BarsMade from 100-mesh pow-der containing yttria and silica sintering additives: The lateralsurface dimensions of voids smaller than 100 m are up to10 % greater than the diameter of the seeded styrene divinylbenzene spheres. Surface dimensions of larger
28、voids areapproximately equal to the seeded sphere diameter. The depth-to-width ratio increases from 0.6 to 0.8 as the seeded spheresize increases from 50 to 115 m.7.3.3 Silicon Carbide Test BarsMade from 100-meshalpha silicon carbide powder; in green specimens, the lateralsurface void dimensions are
29、 approximately 25 % greater thanthe diameter of seeded divinyl benzene spheres, while insintered specimens they are approximately 10 % greater. Thedepth-to-width ratio is approximately 0.4 in both green andsintered specimens.7.3.4 Compaction and burn-off usually cause powder par-ticles to accumulate
30、 in the craters of green samples. If these arenot removed prior to sintering (7.1.2.8) they will fuse to thewalls, resulting in an irregular void with less volume.8. Fabrication of Internal Voids8.1 Green Specimens:8.1.1 Procedure:8.1.1.1 Prepare the test specimen bars by pouring powderinto a die in
31、 an amount sufficient to position the voids at thedesired distance from the specimen surfaces. If the voids to beseeded are smaller than 200 m in diameter, level the surfaceand press at 60 MPa to facilitate positioning of the spheres.Pressing is not necessary if the diameter is greater.8.1.1.2 To po
32、sition spheres, follow 7.1.2.2 or 7.1.2.3, orboth.NOTE 1If voids smaller than 100 m are being seeded, it is advisableto insert discrete spheres at least 250 m in diameter in selected locationsto provide markers detectable with X rays.8.1.1.3 Press the microspheres into the surface at a pressureof 60
33、 MPa to hold them in position.8.1.1.4 Record the positions of the spheres photographicallywith the use of imaging equipment or other suitable means.8.1.1.5 Add ceramic powder in an amount sufficient toseparate the adjacent layers of the voids. If this is the final layerof powder, press to provide ha
34、ndling strength to the greencompact (nominally 120 MPa); otherwise, press at 60 MPa andC 1212 98 (2004)2repeat the steps given in 8.1.1.2 through 8.1.1.4 until thedesired number of void layers is obtained.8.1.1.6 After final pressing, remove the specimen from thedie and place it into thin-wall latex
35、 tubing, evacuate the air, andseal the end. Cold isopress at 420 MPa or a pressure mostsuitable for the specific material.8.1.1.7 Remove the specimen from the tubing and heat it ina vacuum at 525C for 45 min. to decompose the styrenedivinyl benzene spheres.8.1.1.8 Follow the procedure described in 7
36、.1.2.8.8.1.2 Void MeasurementTo estimate the total void vol-ume, remove extraneous particles from the specimen surfacesby sanding or brushing, and measure bulk density. Controlspecimens without seeded voids should be fabricated forcomparison. Internal void dimensions can be inferred fromdirect measu
37、rements on selected samples by sanding offsurface layers to expose the cavities. Alternatively, specimenscan be broken so that void dimensions can be measured on bothfracture surfaces.8.2 Sintered Specimens:8.2.1 Procedure:8.2.1.1 Follow 8.1.1.8.2.1.2 Follow 7.2.1.2.8.2.2 Void MeasurementTo estimate
38、 the total void vol-ume, sand off any bumps that may cling to the surfaces andmeasure the bulk density. Control specimens without seededvoids should be fabricated for comparison. Internal voiddimensions can be inferred from direct measurements onselected samples by grinding and polishing off surface
39、 layers toexpose the cavities.8.3 Internal Void Characteristics (for Both Green andSintered Specimens):8.3.1 Characterization is complicated by the following fac-tors:8.3.1.1 Due to initial compaction by unidirectional pressing,the shape of the cavities is that of an oblate ellipsoid. The wallsare n
40、ot smooth-sided and thus resemble natural fabrication-induced voids.8.3.1.2 During decomposition of the seeded spheres, someof the surrounding powder may be drawn into the cavity,resulting in a partially filled void.8.3.2 Sintering reduces the size of the voids as well as thatof the bar as a whole.
41、The following3,4observations were madeon specimens made from 100-mesh silicon nitride powdercontaining yttria and silica sintering aids and from 100-meshalpha silicon carbide powder. The minor axis of voids seededwith 80-m spheres was reduced by as much as 75 % in siliconnitride and 35 % in silicon
42、carbide. The shrinkage of largerseeded voids was less. In the case of 200-m seeded spheres,the reduction in the minor axis was approximately 35 % insilicon nitride and 20 % in silicon carbide.9. Reporting Voids9.1 Report the location of the voids. (For surface voids, usephotographic methods.)10. Pre
43、cision and Bias10.1 Insufficient data exist to establish consensus measuredvalues for precision and bias.11. Keywords11.1 advanced ceramics; reference specimen; seeded voids;voidsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item me
44、ntionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committe
45、e and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeti
46、ng of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO
47、 Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).3R
48、oth, D. J., Klima, S. J., Kiser, J. D., and Baaklini, G. Y., “Reliability of VoidDetection in Structural Ceramics by Use of Scanning Laser Acoustic Microscopy,”Materials Evaluation, Vol 44, No. 6, May, 1986, pp. 762769. NASA TM 87035,1985.4Baaklini, G. Y., Kiser, J. D., and Roth, D. J., “Radiographic Detectability Limitsfor Seeded Voids in Sintered Silicon Carbide and Silicon Nitride,” AdvancedCeramic Materials, Vol 1, No. 1, 1986. NASA TM 86945, 1984.C 1212 98 (2004)3
