WO2009021846A1 - Procédé permettant d'augmenter la solidité de céramiques, céramiques traitées par ce procédé et leur utilisation - Google Patents

Procédé permettant d'augmenter la solidité de céramiques, céramiques traitées par ce procédé et leur utilisation Download PDF

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Publication number
WO2009021846A1
WO2009021846A1 PCT/EP2008/059998 EP2008059998W WO2009021846A1 WO 2009021846 A1 WO2009021846 A1 WO 2009021846A1 EP 2008059998 W EP2008059998 W EP 2008059998W WO 2009021846 A1 WO2009021846 A1 WO 2009021846A1
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WO
WIPO (PCT)
Prior art keywords
ceramic
ceramics
shot peening
strength
treated
Prior art date
Application number
PCT/EP2008/059998
Other languages
German (de)
English (en)
Inventor
Philipp Spies
Volker Knoblauch
Ulrich Eisele
Original Assignee
Robert Bosch Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Publication of WO2009021846A1 publication Critical patent/WO2009021846A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
    • B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B7/00—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor
    • B24B7/20—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground
    • B24B7/22—Machines or devices designed for grinding plane surfaces on work, including polishing plane glass surfaces; Accessories therefor characterised by a special design with respect to properties of the material of non-metallic articles to be ground for grinding inorganic material, e.g. stone, ceramics, porcelain
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C11/00—Selection of abrasive materials or additives for abrasive blasts

Definitions

  • the present invention relates to a process for increasing the strength of ceramics, as well as ceramics treated by this process and their use.
  • lambda probes so-called Nernst or broadband probes, are used in the exhaust line upstream of the catalytic converter.
  • Probes are typically operated at temperatures between 750 0 C and 800 0 C. To ensure very low emissions, the lambda probe in front of the catalytic converter must show a very fast operational readiness after switching on.
  • the strength of the base ceramics conventionally used in sensor elements is not sufficient to ensure a thermoshock resistant probe in all operating cases and can not be increased to the required level. By design measures, the thermal shock can not be avoided by water hammer.
  • a method according to the invention for increasing the strength of ceramics by introducing a residual stress into the surface of the ceramic by mechanical treatment selected from the group comprising shot peening and / or grinding has the advantage that a thermoshock-resistant ceramic is produced by this method is made available from a thermoshock-proof probe can be made without having to apply additional protective layers on the sensor element. Since it is possible to dispense with the application of additional protective layers to the sensor element, sensor elements produced from a ceramic treated according to the invention have a fast operational readiness time with simultaneously good dynamic properties.
  • the invention can be increased by the invention by targeted reworking the surface of a base ceramic and the associated introduction of a near-surface residual compressive strength, the basic strength of a low-strength ceramic and thus expand the field of application of this formerly lower-strength ceramic for the load case thermal shock.
  • the increase in strength brought about by the method according to the invention is advantageously stable for a long period of time and for temperatures up to 1000 ° C.
  • Fig. 1a is a perspective view of a ceramic sensor element illustrating the thermal shock resulting stress distribution on the surface of the sensor element;
  • FIG. 1b is a perspective cross-section of the ceramic shown in FIG. 1a
  • FIG. 2 is a schematic view of a shot peening apparatus applicable to the invention of introducing a residual stress into a ceramic surface
  • Fig. 3 is a graph of the results of profile measurements of various samples and exemplifies the distortion caused by the method of the invention.
  • FIGS. 1a and 1b are perspective views of the ceramic sensor element in which the impact of a drop of water at the marked by an arrow point has triggered a thermal shock.
  • FIGS. 1a and 1b illustrate the stress distribution resulting from the temperature gradients of a thermal shock on the surface and in the interior of the ceramic sensor element.
  • Fig. Ia shows that the stress, and thus the stress, on the surface of the ceramic sensor element is very high.
  • FIG. 1b shows that the depth effect of the stress is low.
  • the maximum stress corresponding to the black colored area in FIGS. 1a and 1b is about 870 MPa at a temperature of. about 600 0 C.
  • the investigated, untreated ceramic (basic ceramic) has at this temperature but only a strength of about. 420 MPa, so that it comes to failure by cracking. A sensor element produced from such an untreated ceramic would therefore become unusable in the case of such a thermal shock.
  • Tensile stress determined. In the context of the present invention, it has been found that this tensile stress can be compensated for by superposition with an inherent stress (compressive prestress) in the ceramic surface, so that the total stress of the ceramic remains below the stress limit. That is, it turned out within the scope of the present invention, the failure of a ceramic, and thus a sensor element can be prevented when the sum of the basic strength of an untreated ceramic and by - A -
  • the inventive method introduced into the ceramic residual stress is higher than the introduced by the thermal shock tensile stresses.
  • a failure of the illustrated in Fig. Ia and Ib sensor element with a basic strength of about 420 MPa at a thermo shock induced tensile stress of about 870 MPa by an inventive overlay with an internal stress of more than 450 MPa can be avoided, as this the total strength of the ceramic on increased more than 870 MPa. Since the high stresses, as shown in Fig. Ib, occur only near the surface (in the region of the active zone of the thermal shock), it is sufficient to increase the overall strength of the ceramic by a near-surface residual stress in the context of the present invention.
  • machining processes such as turning, grinding or shot peening, which allow the material to be strengthened locally by targeted surface treatment.
  • the processing methods for metallic materials are based on a plasticization (plastic deformation) of the material.
  • the plasticization of metallic materials is due to dislocation movement along
  • ceramics are characterized by an extremely brittle, linear-elastic material behavior. Therefore, ceramics are known to be macroscopically not plastically deformable. In the context of the present invention, however, it turns out that even in ceramics microstructural dislocations can be achieved by machining methods, such as grinding or shot peening, and it is possible with these machining methods
  • the inventive method thus has the potential to close the gap to the required increase in strength of a ceramic for thermal shock-prone lambda sensors
  • Fig. 2 illustrates one for the inventive introduction of a residual stress in one
  • shot blasting agent balls 1 are shot at high pressure onto the surface of the base ceramic 2 to be treated, which is mounted on a sample holder 3.
  • shot blasting agent balls 1 are introduced from a shot blast container 4 through a flow nozzle 5 into a blasting nozzle 6, where they are accelerated by a pressure generated by a compressor 7 through the blasting nozzle 6 in the direction of the base ceramic 2 to be treated.
  • the width of the resulting, accelerated shot peening is set, for example, by an aperture 8, wherein the beam intensity is essentially determined by the shot peening distance 9, the shot peening means, the shot peening pressure and the peening time.
  • a plurality of disk-shaped samples (diameter: 15 mm) of a zirconium oxide film (thickness: 250 microns) in a shot blasting apparatus shown in Fig. 2 in a shot blasting distance of 24 cm shot peened.
  • tungsten carbide (WC) having a grain size of 0.65 mm or 0.75 to 100 ⁇ m was used.
  • Table 1 shows that when used tungsten carbide with a grain size of 0.65 mm to 100 microns, even with a shot peening pressure of 4 bar no damage to the ceramic occurs, whereas the use of tungsten carbide with a grain size in a range of 0.75 microns to 100 ⁇ m at 4 bar leads to damage to the ceramic and thus represents the more aggressive shot blasting medium.
  • the compressive prestress introduced into further samples and their temperature stability were investigated.
  • the induced residual stress was evaluated qualitatively in millimeters by means of curvature measurements and quantitatively in megapascals by X-ray diffraction measurements (measurement of the lattice constants, evaluation using Hooke's law). The measurement accuracy for the curvature measurements was about ⁇ 0.005 mm.
  • the treated samples were tempered at temperatures of 600 0 C to 1020 0 C and evaluated the residual stress after each temperature measuring trip qualitatively on the Verkurvungsunk. For all samples, the heating and cooling ramp was 300 K / h and the holding time at the specified temperature 30 min. In addition, a sample from 900 0 C was weighted by alumina rods.
  • Table 2 shows that with a shot peening pressure of 3 bar, more severe curvatures could be achieved than with a shot peening pressure of 2 bar. It can be seen from the curvature measurements that even at a temperature of 600 ° C., the previously introduced internal stress apparently decreases markedly. Up to a temperature of 800 0 C, the changes introduced residual stress in the context of measurement accuracy no longer significant. In a further increase in temperature to 900 0 C to 1020 0 C but then a further reduction of the residual stress is observed. A weighting of the samples had no influence.
  • FIG. 3 shows the results of profile measurements of a non-shot peened sample 10 and a sample 11, which were shot peened with a shot peening pressure of 3 bar for a beam duration of 560 s, shown.
  • FIG. 3 shows the result of a profile measurement of the shot-blasted sample 11 after annealing at 950 ° C.
  • FIG. 3 shows that the profile of the untreated sample 10 does not have any curvature within the scope of the measurement accuracy.
  • the non-annealed, shot-blasted samples 11 have the strongest curvatures.
  • the tempered, shot-blasted sample 12 has a weaker curvature than before tempering 11
  • Table 3 The residual stress results obtained by X-ray diffraction measurements are shown in Table 3 in megapascals. Table 3 gives each of the residual stress of a sample directly after shot peening and after annealing at different temperatures.
  • Table 3 shows that higher residual stresses could be achieved with a shot peening pressure of 3 bar than with a shot peening pressure of 2 bar. Table 3 further shows that even with an aging at 1020 0 C still quantitatively measurable residual stresses in the ceramic are present.
  • ⁇ o indicates the characteristic inert strength and m indicates the Weibull modulus of a Weibull distribution. The values are normalized to an effective volume of one. In brackets the 90% confidence interval is indicated. T denotes the average thermal shock temperature and ⁇ T the standard deviation of this.
  • the thermal shock resistance tests of the peened nonpaged samples showed two out of ten samples of the peened at 800 0 C annealed samples three out of ten samples and the shot-peened, at 1000 0 C annealed samples of ten samples no cracking at a maximum temperature of 800 0 C on.
  • the results of the inertness measurement show that an increase in inertance of more than 34% can be achieved by the method according to the invention.
  • This increase in inertness is independent of the aging temperature. After aging at 1000 ° C., the highest inert strengths are measured with the smallest scattering. The increase in inert strength here is 47% compared to untreated samples.
  • the thermal shock resistance can be increased by 17% by the process of the invention up to about 90 0 C.
  • the present invention relates to a process for increasing the strength, in particular for increasing the increase in inertness, of ceramics by introducing a residual stress into the surface of the ceramic by mechanical treatment selected from the group comprising shot peening and / or grinding.
  • internal stress is understood to mean that the surface of the ceramic has a different, for example greater, length extension than the ceramic volume lying below the surface and thereby causes a tension between the surface and the underlying ceramic volume.
  • the surface of the ceramic can be shot-blasted with the shot peening device for a shot peening time of> 50 s to ⁇ 1000 s, for example from> 150 s to ⁇ 800 s, in particular from> 250 s to ⁇ 600 s.
  • a material with a Rockwell C hardness of> 60 HRC, in particular a high-hardness abrasive having a Rockwell C hardness of> 60 HRC, for example tungsten carbide, can be used as the shot peening agent.
  • the shot peening pressure can be in a range from> 0.5 bar to ⁇ 4.0 bar, for example from> 1.0 bar to ⁇ 3.5 bar, in particular from> 1.5 bar to ⁇ 3.0 bar.
  • the shot peening distance (distance between the surface of the ceramic and the aperture / jet gland) may be in a range of> 10 cm to ⁇ 40 cm, for example from> 15 cm to ⁇ 35 cm.
  • a D91 to D25 grinding wheel can be used.
  • the grinding wheel can be resin bonded.
  • the feed rate of the grinding wheel in pendulum grinding in a range of> 1000 mm / min to ⁇ 25000 mm / min, for example from> 15000 mm / min to ⁇ 24000 mm / min, in particular from> 20,000 mm / min to ⁇ 22,000 mm / min , lie.
  • the speed of the grinding wheel can be in a range of> 25 m / s to ⁇ 40 m / s, for example, from> 30 m / s to ⁇ 37 m / s, in particular from> 33 m / s to ⁇ 35 m / s.
  • the process parameters such as shot peening means, shot peening bead size, shot peening pressure, shot peening time, shot peening, abrasive, abrasive grain,
  • the ceramic to be treated is a zirconium oxide ceramic, as a shot blasting agent, for example, tungsten carbide having a sphere size of> 0.01 ⁇ m to ⁇ 1.0 mm, for example> 0.1 ⁇ m to ⁇ 0.65 mm, in particular from> 0.75 ⁇ m to ⁇ 100 ⁇ m, for a shot peening time of> 50 s to ⁇ 1000 s, for example from> 150 s to ⁇ 800 s, in particular from> 250 s to ⁇ 600 s , at one of> 0.5 bar to ⁇ 3.5 bar, for example from> 1.0 bar to
  • tungsten carbide having a sphere size of> 0.01 ⁇ m to ⁇ 1.0 mm, for example> 0.1 ⁇ m to ⁇ 0.65 mm, in particular from> 0.75 ⁇ m to ⁇ 100 ⁇ m, for a shot peening time of> 50 s to ⁇ 1000 s, for example from> 150 s to ⁇ 800 s, in particular from> 250
  • ⁇ 3.25 bar in particular from> 2.0 bar to ⁇ 3.0 bar, in a shot peening distance of> 15 cm to ⁇ 35 cm, for example from> 20 cm to ⁇ 30 cm, in particular from> 22 cm to ⁇ 27 cm, can be used.
  • a further subject of the present invention is a ceramic treated by the process according to the invention.
  • the surface of the ceramic according to the invention has an internal stress in a range from> 50 MPa to ⁇ 5000 MPa, for example from> 150 MPa to ⁇ 4000 MPa, in particular from> 250 MPa to ⁇ 2500 MPa.
  • the ceramic according to the invention may have an inert strength of> 10%, for example>> 30%, in particular> 45%, higher than the untreated base ceramic and / or by> 5%, for example by> 8.5%, in particular by> 15%. , have higher thermal shock resistance than the untreated base ceramic.
  • inert and thermoshock resistance is temperature stable.
  • ceramics treated according to the invention can be heated up to a temperature of ⁇ 1200 ° C., for example ⁇ 1100 ° C., in particular ⁇ 1050 ° C., without losing the near-surface residual stress.
  • the surface of the ceramic treated according to the invention after reaching a temperature of> 500 0 C to
  • ⁇ 1200 0 C for example, from> 600 0 C to ⁇ 1100 0 C, in particular from> 800 0 C to
  • the ceramic treated according to the invention after being applied to a Temperature of> 500 0 C to ⁇ 1200 0 C, for example, from> 600 0 C to ⁇ 1100 0 C, in particular from> 800 0 C to ⁇ 1050 0 C, was heated, by> 10%, for example by> 30% , in particular by> 45%, higher inert strength than the untreated base ceramic and / or by> 5%, for example by> 8.5%, in particular by> 15%, higher thermal shock resistance than the untreated base ceramic.
  • the process according to the invention and the ceramics according to the invention are suitable for high-temperature applications.
  • Another object of the present invention is the use of the method according to the invention for increasing the strength, in particular increase in inertness, of ceramics in which high, near-surface stresses, such as thermal shock loads, contact loads, frictional loads or impact stresses occur.
  • Another object of the present invention is the use of a ceramic treated according to the invention for the production of lambda sensors, friction pairings, sliding pairings, rollers, valve seats, contact-loaded components and / or spark plugs.
  • the method according to the invention can be used for increasing the strength, in particular increasing the inertness, of zirconium oxide ceramics, alumina ceramics, silicon carbide and / or silicon nitride ceramics.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)

Abstract

La présente invention concerne un procédé qui permet d'augmenter la solidité de céramiques en introduisant dans la surface d'une céramique une contrainte propre créée par un usinage mécanique choisi dans le groupe comprenant le grenaillage et/ou l'égrisage. Elle concerne aussi des céramiques traitées par ce procédé ainsi que leur utilisation.
PCT/EP2008/059998 2007-08-16 2008-07-30 Procédé permettant d'augmenter la solidité de céramiques, céramiques traitées par ce procédé et leur utilisation WO2009021846A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102007038533.3 2007-08-16
DE200710038533 DE102007038533A1 (de) 2007-08-16 2007-08-16 Verfahren zur Festigkeitssteigerung von Keramiken sowie durch dieses Verfahren behandelte Keramiken und deren Verwendung

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WO2009021846A1 true WO2009021846A1 (fr) 2009-02-19

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DE (1) DE102007038533A1 (fr)
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1421266A (fr) * 1963-07-09 1965-12-17 Engelhard Hanovia Inc Surfaçage de matériaux
US3922821A (en) * 1973-09-14 1975-12-02 American Optical Corp Grinding method and coolant therefor
EP1637258A1 (fr) * 2003-05-26 2006-03-22 Japan Science and Technology Corporation Procede de renforcement pour surface d'outil de coupe en metal fritte et outil de coupe en metal fritte d'une grande longevite
US20060293165A1 (en) * 2002-10-15 2006-12-28 Hiroyasu Saka Surface toughening method of ceramics and a ceramics product

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1421266A (fr) * 1963-07-09 1965-12-17 Engelhard Hanovia Inc Surfaçage de matériaux
US3922821A (en) * 1973-09-14 1975-12-02 American Optical Corp Grinding method and coolant therefor
US20060293165A1 (en) * 2002-10-15 2006-12-28 Hiroyasu Saka Surface toughening method of ceramics and a ceramics product
EP1637258A1 (fr) * 2003-05-26 2006-03-22 Japan Science and Technology Corporation Procede de renforcement pour surface d'outil de coupe en metal fritte et outil de coupe en metal fritte d'une grande longevite

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TW200922747A (en) 2009-06-01
DE102007038533A1 (de) 2009-02-19

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