ASTM C1525-04 (Reapproved 2013)

Designation: C1525 − 04 (Reapproved 2013)Standard Test Method forDetermination of Thermal Shock Resistance for AdvancedCeramics by Water Quenching1This standard is issued under the fixed designation C1525; 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.1. Scope1.1 This test method describes the determination of theresistance of advanced ceramics to thermal shock by waterquenching. The method builds on the experimental principle ofrapid quenching of a test specimen at an elevated temperaturein a water bath at room temperature. The effect of the thermalshock is assessed by measuring the reduction in flexuralstrength produced by rapid quenching of test specimens heatedacross a range of temperatures. For a quantitative measurementof thermal shock resistance, a critical temperature interval isdetermined by a reduction in the mean flexural strength of atleast 30 %. The test method does not determine thermalstresses developed as a result of a steady state temperaturedifferences within a ceramic body or of thermal expansionmismatch between joined bodies. The test method is notintended to determine the resistance of a ceramic material torepeated shocks. Since the determination of the thermal shockresistance is performed by evaluating retained strength, themethod is not suitable for ceramic components; however, testspecimens cut from components may be used.1.2 The test method is intended primarily for dense mono-lithic ceramics, but may also be applicable to certain compos-ites such as whisker- or particulate-reinforced ceramic matrixcomposites that are macroscopically homogeneous.1.3 Values expressed in this standard test method are inaccordance with the International System of Units (SI) andStandard IEEE/ASTM SI 10.1.4 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. Referenced Documents2.1 ASTM Standards:2C373 Test Method for Water Absorption, Bulk Density,Apparent Porosity, andApparent Specific Gravity of FiredWhiteware Products, Ceramic Tiles, and Glass TilesC1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCeramicsC1322 Practice for Fractography and Characterization ofFracture Origins in Advanced CeramicsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE616 Terminology Relating to Fracture Testing (Discontin-ued 1996) (Withdrawn 1996)3IEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System2.2 European Standard:EN 820-3 Advanced Technical Ceramics—MonolithicCeramics—Thermomechanical Properties—Part 3: Deter-mination of Resistance to Thermal Shock by WaterQuenching43. Terminology3.1 Definitions:3.1.1 The terms described in Terminologies C1145, E6, andE616 are applicable to this standard test method. Specific termsrelevant to this test method are as follows:1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onMechanical Properties and Performance.Current edition approved Aug. 1, 2013. Published September 2013. Originallyapproved in 2002. Last previous edition approved in 2009 as C1525 – 04 (2009).DOI: 10.1520/C1525-04R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at [email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from European Committee for Standardization (CEN), 36 rue deStassart, B-1050, Brussels, Belgium, http://www.cenorm.be.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.2 advanced ceramic, n—a highly engineered, highperformance, predominately non-metallic, inorganic, ceramicmaterial having specific functional attributes. C11453.1.3 critical temperature difference, ∆Tc,n—temperaturedifference between the furnace and the ambient temperaturewater bath that will cause a 30 % drop in the average flexuralstrength.3.1.4 flexural strength, σf,n—a measure of the ultimatestrength of a specified beam specimen in bending determined ata given stress rate in a particular environment.3.1.5 fracture toughness, n—a generic term for measures ofresistance to extension of a crack. E6163.1.6 slow crack growth (SCG), n—subcritical crack growth(extension) which may result from, but is not restricted to, suchmechanisms as environmentally-assisted stress corrosion ordiffusive crack growth.3.1.7 thermal shock, n—a large and rapid temperaturechange, resulting in large temperature differences within oracross a body. C11453.1.8 thermal shock resistance, n—the capability of materialto retain its mechanical properties after exposure to one ormore thermal shocks.4. Summary of Test Method4.1 This test method indicates the ability of an advancedceramic product to withstand the stress generated by suddenchanges in temperature (thermal shock). The thermal shockresistance is measured by determining the loss of strength (ascompared to as-received specimens) for ceramic test specimensquickly cooled after a thermal exposure.Aseries of rectangularor cylindrical test specimen sets are heated across a range ofdifferent temperatures and then quenched rapidly in a waterbath. After quenching, the test specimens are tested in flexure,and the average retained flexural strength is determined foreach set of specimens quenched from a given temperature. The“critical temperature difference” for thermal shock is estab-lished from the temperature difference (exposure temperatureminus the water quench temperature) that produces a 30 %reduction in flexural strength compared to the average flexuralstrength of the as-received test specimens.5. Significance and Use5.1 The high temperature capabilities of advanced ceramicsare a key performance benefit for many demanding engineeringapplications. In many of those applications, advanced ceramicswill have to perform across a broad temperature range withexposure to sudden changes in temperature and heat flux.Thermal shock resistance of the ceramic material is a criticalfactor in determining the durability of the component undertransient thermal conditions.5.2 This test method is useful for material development,quality assurance, characterization, and assessment of durabil-ity. It has limited value for design data generation, because ofthe limitations of the flexural test geometry in determiningfundamental tensile properties.5.3 Appendix X1 (following EN 820-3) provides an intro-duction to thermal stresses, thermal shock, and criticalmaterial/geometry factors. The appendix also contains a math-ematical analysis of the stresses developed by thermal expan-sion under steady state and transient conditions, as determinedby mechanical properties, thermal characteristics, and heattransfer effects.6. Interferences6.1 Time-dependent phenomena such as stress corrosion orslow crack growth may influence the strength tests. This mightespecially be a problem if the test specimens are not properlydried before strength testing.6.2 Surface preparation of test specimens can introducemachining flaws which may have a pronounced effect on themeasured flexural strength. The surface preparation may alsoinfluence the cracking process due to the thermal shockprocedure. It is especially important to consider surface con-ditions in comparing test specimens and components.6.3 The results are given in terms of a temperature differ-ence between furnace and quenching bath (∆T). However, it isimportant to notice that results may be different for the same∆T but different absolute temperatures. It is therefore specifiedin this test method to quench to room temperature.6.4 The formulae presented in this test method apply strictlyonly to materials that do not exhibit R-curve behavior, but havea single-valued fracture toughness. If the test material exhibitsa strong R-curve behavior, that is, increase in fracture tough-ness with increasing crack length, caution must be taken ininterpreting the results.6.5 Test data for specimens of different geometries are notdirectly comparable because of the effect of geometry on heattransfer and stress gradients. Quantitative comparisons ofthermal shock resistance for different ceramic compositionsshould be done with equivalent test specimen geometries.7. Apparatus7.1 Test Apparatus:7.1.1 The test method requires a thermal exposure/quenching system (consisting of a furnace, specimen handlingequipment, and a quench bath) and a testing apparatus suitablefor measuring the flexural strength of the test specimens.7.1.2 The test method requires a furnace capable of heatingand maintaining a set of test specimens at the requiredtemperature to 6 5K(6 5°C). The temperature shall bemeasured with suitable thermocouples located no more than 2mm from the midpoint of the specimen(s) in the furnace.Furnaces will usually have an open atmosphere, because airexposure is common during the transfer to the quench bath.NOTE 1—If air exposure is detrimental, a special furnace-quench systemcan be set up in which both the furnace and the quench unit are containedwithin an inert atmosphere container.Acommon design for such a systemconsists of a tube furnace positioned vertically above the quench tank, sothat the test specimen drops directly into the tank from the furnace.7.1.3 The method requires a test specimen handling equip-ment designed so that the test specimen can be transferred fromthe furnace to the quenching bath within 5 s.C1525 − 04 (2013)27.1.4 A water bath controlled to 293 6 2 K (20°C 6 2°C)is required. The water bath must have sufficient volume toprevent the temperature in the bath from rising more than 5 K(5°C) after test specimen quenching. It is recommended thatthe bath be large enough for the test specimens to have cooledsufficiently before reaching the bottom of the bath, or containa screen near the bottom to prevent the test specimens fromresting directly on the bottom of the bath.7.1.5 The universal test machine used for strength testing inthis test method shall conform to the requirements of PracticeE4. Specimens may be loaded in any suitable test machineprovided that uniform test rates, either using load-controlled ordisplacement-controlled mode, can be maintained. The loadsused in determining flexural strength shall be accurate within61.0 % at any load within the selected load rate and load rangeof the test machine as defined in Practice E4.7.1.6 The configuration and mechanical properties of thetest fixtures shall be in accordance with Test Method C1161 foruse with the standard four-point flexure specimens. If largertest pieces (sizes A or C below) are employed, the test fixtureshall be scaled accordingly. There are currently no standardfixtures for testing cylindrical rods in flexure; however, thefixtures to be used shall have the appropriate articulation. Testfixtures without appropriate articulation shall not be permitted;the articulation of the fixture shall meet the requirementsspecified in Test Method C1161.7.1.7 The method requires a 393 K (120°C) drying oven toremove moisture from test specimens before (if needed) andafter quench testing.7.1.8 A micrometer with a resolution of 0.002 mm (or0.0001 in.) or smaller should be used to measure the test piecedimensions. The micrometer shall have flat anvil faces. Themicrometer shall not have a ball tip or sharp tip since thesemight damage the test piece if the specimen dimensions aremeasured prior to fracture. Alternative dimension measuringinstruments may be used provided that they have a resolutionof 0.002 mm (or 0.0001 in.) or finer and do no harm to thespecimen.8. Test Specimens8.1 The ceramic test specimens shall be pieces specificallyprepared for this purpose from bulk material or cut fromcomponents.8.1.1 Specimen Size—Three specimen geometries are de-fined for use in this test method:8.1.1.1 Type A—Rods 10 6 0.13 mm in diameter, 120 mmlong.8.1.1.2 Type B—Bars 3 6 0.13 mm × 4 6 0.13 mm in crosssection, minimum 45 mm long with chamfered edges, inaccordance with type B in Test Method C1161.8.1.1.3 Type C—Bars 10 6 0.13 mm × 10 6 0.13 mm incross section, 120 mm long, with chamfered edges.NOTE 2—The test specimens of A and C type are intended to be largeenough to produce a materials ranking that is basically independent ofspecimen size and appropriate for larger test specimens (1, 2)5. Testspecimens of B type may require greater quenching temperature differ-ences in order to produce strength reduction. These test specimens maynot correctly rank the relative behavior of larger components. Only TypeB coincides with Type B in Test Method C1161.NOTE 3—Under some circumstances the edges of prismatic testspecimens or the ends of cylindrical test specimens may be damaged byspallation during the quench test. These specimens should be discardedfrom the batch used for strength testing if the damage will interfere withthe strength test. In any case such spallation must be noted in the report.Spallation problems can be alleviated by chamfering sharp edges.NOTE 4—The parallelism tolerances on the four longitudinal faces are0.015 mm for B and C and the cylindricity for A is 0.015 mm.8.2 Test Specimen Preparation—Depending on the intendedapplication of the thermal shock data, one of the four testspecimen preparation methods described in Test MethodC1161 may be used: As-Fabricated, Application-MatchedMachining, Customary Procedures, or Standard Procedures.8.3 Handling Precautions—Care shall be exercised in stor-ing and handling of test specimens to avoid the introduction ofrandom and severe flaws, such as might occur if test specimenswere allowed to impact or scratch each other.8.4 Number of Test Specimens—A minimum of 10 speci-mens shall be used to determine as-received strength at roomtemperature. A minimum of 30 is required if estimates regard-ing the form of the strength distribution is to be determined (forexample a Weibull modulus).Aminimum of 5 specimens shallbe used at each thermal shock temperature. It is recommendedthat as ∆Tcis established, additional 5 specimens be tested atthis as well as the adjacent temperature intervals. This willallow for determination of the mean and standard deviation. Ifestimates regarding the form o