1、Designation: C1212 98 (Reapproved 2010)Standard Practice forFabricating Ceramic Reference Specimens ContainingSeeded Voids1This standard is issued under the fixed designation C1212; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he 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.1. Scope1.1 This practice describes procedures for fabricating bothgreen and sintered test bars of silicon carbide and
3、siliconnitride containing both internal and surface voids at prescribedlocations.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated wit
4、h 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:2B311 Test Method for Density of Powder Metallurgy (PM)Materials Con
5、taining Less Than Two Percent PorosityC373 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
6、 prior to high-temperature densification.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 an
7、d remove solvents or binders.3.1.5 surface 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 demo
8、nstratesensitivity and resolution and 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 30Xmagnif
9、ication.5.4 Tubing, latex, thin-wall, 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-perat
10、ure of 525C.5.8 Imaging Equipment with 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
11、ceramic system chosen, thefurnace may 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 sus
12、pended inwater attached to the scale.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-m
13、esh.1This practice is under the jurisdiction of ASTM Committee C28 on AdvancedCeramics and is the direct responsibility of Subcommittee C28.03 on PhysicalProperties and Non-Destructive Evaluation.Current edition approved Dec. 1, 2010. Published January 2011. Originallyapproved in 1992. Last previous
14、 edition approved in 2004 as C121298 (2004).DOI: 10.1520/C1212-98R10.2For 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
15、website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.2 Styrene Divinyl Benzene Spheres, with diameters asnecessary. Other material with low vaporization temperaturesmay be substituted, but pressing characteristics and final void
16、sizes may be different.7. Fabrication of Surface Voids7.1 Green Specimens:7.1.1 The test piece geometry 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/s
17、ample,ideally the test sample should be identitcal to the part/sample.If this is not feasible due to 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 thick
18、ness in the area of thepart/sample being examined.7.1.2 Procedure:7.1.2.1 Prepare the test specimen 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
19、 the specimen. Clean thespecimen of all particles that are not flush with the top surface;this can generally 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
20、human hair taped to a stiff plasticrod, using the assistance of an optical magnifier.7.1.2.4 Press the 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 extra
21、neous particles. An aeroduster or brush should beadequate.7.1.2.6 Place the specimen in a thin-wall 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
22、 to decompose the spheres (525C for 45 min forstyrene divinyl benzene).7.1.2.8 Mark the specimen orientation 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 M
23、easurementMeasure the lateral dimensionsin two orthogonal directions. The depth can be measured byfocusing 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 wi
24、thin 2 m.7.1.4 Measure the bulk density of the specimen from directvolume and weight measurements.7.2 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 sint
25、ering conditions forsilicon nitride are 17001900C for1hinaninert atmosphereat 0200 MPa; for silicon 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 B311 o
26、r Test MethodC373 or from volume and weight measurements.7.2.2 Void MeasurementSee 7.1.3.7.3 Surface 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 t
27、he seeded spheres and the compressibilityand sintering characteristics of the powders that comprise 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 % gre
28、ater than the diameter of the seeded styrene divinylbenzene spheres. Surface dimensions of larger 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 fro
29、m 100-meshalpha silicon carbide powder; in green specimens, the lateralsurface void dimensions are 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
30、 andsintered specimens.7.3.4 Compaction and burn-off usually cause powder par-ticles to accumulate 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 Gre
31、en Specimens:8.1.1 Procedure:8.1.1.1 Prepare the test specimen bars by pouring powderinto a die in 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 facili
32、tate positioning of the spheres.Pressing is not necessary if the diameter is greater.8.1.1.2 To position 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
33、markers detectable with X rays.8.1.1.3 Press the microspheres into the surface at a pressureof 60 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 tose
34、parate the adjacent layers of the voids. If this is the final layerof powder, press to provide handling strength to the greencompact (nominally 120 MPa); otherwise, press at 60 MPa andC1212 98 (2010)2repeat the steps given in 8.1.1.2 through 8.1.1.4 until thedesired number of void layers is obtained
35、.8.1.1.6 After final pressing, remove the specimen from thedie and place it into thin-wall latex 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
36、min. to decompose the styrenedivinyl benzene spheres.8.1.1.8 Follow the procedure described in 7.1.2.8.8.1.2 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 voi
37、ds should be fabricated forcomparison. Internal void dimensions can be inferred fromdirect measurements 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 Specime
38、ns: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 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 c
39、an be inferred from direct measurements onselected samples by grinding and polishing off surface 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
40、unidirectional pressing,the shape of the cavities is that of an oblate ellipsoid. The wallsare not 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
41、filled void.8.3.2 Sintering reduces the size of the voids as well as thatof the bar as a whole. 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 voi
42、ds seededwith 80-m spheres was reduced by as much as 75 % in siliconnitride and 35 % in silicon 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
43、 Voids9.1 Report the location of the voids. (For surface voids, usephotographic methods.)10. Precision 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
44、no position respecting the validity of any patent rights asserted in connection with any item mentionedin 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 respo
45、nsibility.This standard is subject to revision at any time by the responsible technical committee 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
46、 to ASTM International Headquarters. Your comments will receive careful consideration at a meeting 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 a
47、ddress shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO 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
48、), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).3Roth, D. J., Klima, S. J., Kiser, J. D., and Baaklini, G. Y., “Reliability of VoidDetection
49、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.C1212 98 (2010)3
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