Journal of the European Ceramic Society 18(1998) 1915-1921 Pinted in Great taesvier rignts reserved Printed in Great Britain. All rights reserved p:0955-2219(98)00130-7 0955-2219/98/5- see front matter Graceful Failure of Laminated Ceramic Tubes Produced by Electrophoretic Deposition Luc J. Vandeperre* and Omer O. Van Der Biest Departement Metaalkunde en Toegepaste Materiaalkunde Katholieke Universiteit te Leuven, De Croylaan 2, 3001 Heverlee,Belgium Abstract which makes it possible to obtain ceramic lami- nates of complex shape at low cost. Electrophoretic The production of silicon carbide laminated ceramic deposition is investigated, therefore, as a produc- tubes by electrophoretic deposition was investigated. tion process for complex shaped ceramic laminates Alternating deposition of SiC and graphite layers was since it has been shown that complex shapes can be obtained by depositing Sic from an acetone based obtained2and that this technique is very well suited suspension and by depositing the graphite interlayers to forming layered materials. Moreover, electro- oretic deposition has been used also to infiltrate nated tubes fibre preforms with a ceramic or glass-ceramic tubes were Electrophoretic deposition consists of applying graphite an electric field to a suspension of a charged cera- ponse to this electric field, the and supported lations powder particles move (electrophoresis)and for the expecte Heposit at the electrode of opposite charge. Shap- Elsevier Science Limited. ing is possible because the deposit takes the shape of the depositio Keywords: A. Shaping, B. Composites, C. Tough-E ent of a sus- ness, Toughening, D. SiC, electrophoretic depo-pension for electr of SiC, 6 the sition from which high epo 1.e graphit s and have a 1Introduction satistactory and electrophoretic deposit ed plates.?In Ceramic laminates have been introduced as a sim- this contribution deposition of ple way to obtain tough ceramic composites C/graphite lam d tubes is described, and Laminates consist of layers of ceramic material in the behaviour of rings cut from these tubes in between which weak interlayers are introduced. diametral compression is investigated. These materials show a tough behaviour because when a crack propagates through a strong layer, it flected into the Is dene nterlayer. As a result the 2 Experimental ther layers are ck and can continue to The electrode set-up consisted of a hollow graphite The processing techniques available today, how- cylinder as deposition electrode with a stainless ever, allow only relativel shapes to be steel rod situated in the centre as the counter elec- obtained. Taking into account possible applica-trode (Fig. 1). Poly-tetrafluorethylene(PTFE) tions for these. materials such as tubes for he exchangers and nozzles in chemical processing, it Further they provide support for the deposit dur- becomes apparent that there is a need for a process, ing drying he electrode set.up is attacthed an in-house developed automated deposition ce *To whom correspondence should be addressed. which controls the residence time in the different 1915
1916 0.0. Van Der biesi 3 Results and discussion Figure 2 shows some examples of laminated tubes consisting of 19 Sic and 18 graphite layers pro- duced by electrophoretic deposition 3.1 Laver thicknes For the first tubes the deposition time was 2 min per SiC layer. Due to depletion of the suspension the deposition rate drops and therefore, the thick ness of the Sic layers de The layer thick () curve so that the deposition time per layer can be adapted in order to obtain layers of equal and pre- selected thickness. To test the master curve, the deposition times were calculated in order to obtain Sic layers of 100 um. The actual average Sic layer Fig. 1. Electrode set-up for electrophoretic deposition of tubes thickness was 95+/-12 um(Fig 3). The equation (a)automated electrode positioner capable of moving the electrodes to one of four suspensions, (b) top PTFE cover, (c) describing the master curve is aphite cylindrical deposition electrode,(d)suspension,(e) stainless steel rod serving as counter electrode, (f bottom FE cover T=T0(1-e-k) suspensions, and is able to move the electrodes where T is the cumulative Sic layer thickness, t is from one suspension to another with a maximum the cumulative deposition time from one suspe of 4 suspensions. Deposition occurs on the inside sion, whilst To(1500 um)and k(0 121 min )are of the graphite cylinder fitting constants determined by fitting to experi Sic layers are obtained by deposition from a mental data. The thickness of the graphite layers suspension of a Sic powder(Superior Graphite, was 10+/-3 um HSC-0598, 50g)in acetone with 5 vol%n butylamine and 20 vol% iso-propyl alcohol. The 3.2 Mechanical testing iso-propyl alcohol is not required for deposition of Figure 4 shows the result of a mechanical test on a SiC, but is added to the acetonic suspension in ring cut from a laminated tube, and Fig. 5 shows order to match the drying rate of the SiC layers the sample after testing. The load-displacement better to the drying rate of the graphite layers, which are deposited from a commercial colloidal graphite suspension(Superior Graphite, N210) based on iso-propyl alcohol and diluted furt with iso-propyl alcohol (70 vol%) A laminated tube is obtained by consecutive deposition of SiC and graphite layers by applying钟时e 145 V so that the graphite deposition electrode is the positive electrode. After deposition of the required number of Sic and graphite layers, the deposit is dried and removed from the electrode The tubes are sintered in a graphite furnace under vacuum at 2050.C for 30 min For evaluation of the layer thickness, the tubes are cut into a number of rings with equal width and the layer thickness is measured using an opti al microscope (LOM). chaliCe evaluation 23×x119×5mm) are tested in diametral compres sion by placing the ring between two parallel hori zontal plates which move towards each other ig. 2. Some examples of SiC/graphite laminated tube while the resulting load is measured with a load sting of 19 SiC layers(95 +/-12 um)and 18 graphite (10+/-3 um). The outer diameter is 23 mm; the inner eter is 19 mm and the length of the standing tube is 35mm
Graceful Failure of Laminated Ceramic Tubes produced by Electrophoretic Deposition 1917 2000 1750 E99 1250 0 Cummulative deposition time(min (mm) Fig 3. Calculated(solid line)and experimental ( dots)cumula- ig. 4. Example of a load-displacement diagram recorded tive Sic layer thickness versus cumulative deposition time during a diametral compression test on a laminated ring(dots) After 9 SiC layers the SiC suspension was replaced by a new Sic and calculated overlay (solid line)showing that the slope suspension whilst the deposition experiment was continue changes due to failure can be reproduced accurately if the proposed failure mechanism is used for calculation diagram is of the saw-tooth type typical for lami The relations between the displacement, applied nates: as a Sic layer fails, the crack is deflected into force and stress can be derived by combining the the graphite interlayer. The rest of the ring can solution for an O-ring and a C-ring. The maxin continue to carry load until all SiC layers have tensile stress in an O-ring is related to the applied failed one by one. As a result the work to failur force by: 2 increased and a graceful failure is obtained. The deflection of cracks at the graphite interlayers is very apparent in the photograph of a sample after failure Whilst rather complete descriptions of the bel y+ro iour of laminated ceramic plates in bending -cos e exist, 10 as well as some predictions on their 丌r+h2 behaviour in tensile tests, no description of the behaviour of laminated rings in diametral com vith pression was found in literature. Based on visual r2: the outer radius of the ring(mm); damage observation during the test, stereoscopic r1: the inner radius of the ring(mm); investigation of the damage after the test, and by ro the average radius of the ring(mm)(=(1+r2)/2); taking into account the stress distribution during y: the distance from the average radius(mm) loading of a ring (see below), a more complete description of the failure mechanism is proposed to S: the surface area of the ring(mm2)(=(r2-r1).r); consist of the following sequence of failure events t: the thickness of the ring(mm); (Fig. 6): when the strength of the inner Sic layer is eg: the stress in the 0 direction(MPa, see Fig. 7) reached, it fails and the crack is deflected into the and graphite interlayer. As a result one obtains a thin- er ring and two thin C-rings inside this ring which are still retained by the outer layers. As the strength of the next inner layer of the full ring is reached, 42=1ods=)h(3-2 ro+y again that layer fails and the crack is deflected in the next graphite interlayer, resulting in the formation of a new pair of thin C-rings. Finally the ring will The displacement is related to the force through have been transformed completely in a series of thin C-shaped layers, which will then fail layer by layer The latter because the horizontal plates also retain d he C-rings so that they can still carry load ES2(8x6+h2
1918 L.J. Vandeperre, O.O. van Der Biest 体钟 pression for an infinite Weit a laminated ring in diametral com- eibull modulus:(a) elastic loading of the ring, (b)the strength is reached and the most in Fig. 5. Detail of a ring after testing showing the occurrence of in the formation of 2 C-rings of 1 layer thickness, (c) 灬= crack deflection into the graphite interlayers layer fails, (d) the last layer fails, (e) the strength of the outer C ring is reached, (f) the next C-ring fails, (g) the last C-ring fails with E: Y d: displacement of the loading plate(mm) For a C-ring these relations can be derived from the exact solution for a C-ring under end shear (7b) loading: the effect of a concentrated force is only important close to the point where the con centrated force acts on a body (st. Venants princi ple). The solution for the stresses is ri+r Or sine(5a) and the relation between the strain and the displacements F(-(r2+r2) F(—6+ cos e(5c) with Explication of the expressions for the stress [eqn R=(r-r2)+(+r2)ln2) (5)in eqn(7)], followed by substitution of th result in eqn(8)and partial integration leads to the following expression for the displacement in the In order to obtain the resulting displacement, we direction of the radius, ur, and in the direction of used the definitions of the strain the circumference, ue
Graceful Failure of Laminated Ceramic Tubes produced by Electrophoretic Deposition 1919 with a finite Weibull modulus, a random strength value is taken from the Weibull distribution for h layer. As the graphite interlayer from one layer to another each layer will indeed only fail when its strength is r2 In order to predict what the next failure event will be, the program calculates for all layers what the total displacement of the loading plate should be in order to reach a maximum stress within that Fig.7. Conventions for the calculation of the stresses and layer equal to the strength of that layer. The layer displacements in O-and showing the lowest displacement required to reaching a stress equal to its strength, is taken as the next layer which fails. Note that the first layer n=BE(4(1-mr+B(-3 to fail is not necessarily the layer with the lowest (9a) strength, since also the position of the layer and the +0=0)-m0+o tress distributie ring has Initially, when the ring is intact, the graphite interlayers are assumed to be capable of perfect load-transfer so that the stress can be evaluated A(1-D)=A(I-v)Inr if it were a monolithic ring. The maximum stress each layer of the intact ring as a function of the +Br2(5+u)+5(1+v))+-sin6 displacement can be evaluated by using eqns(2) and(4), where y is varied as a function of the position of each layer within the ring Normally it is expected that the inner ring will fail first, as the stress is at maximum in this laye (7+冂) Upon failure of the inner layer, the deflection of RI stela removing the inner layer from the ring, and re B (ly cing this layer by two thin C-rings clamped within the now thinner O-ring. Further, it is assumed, that 2(r2+n2) once a crack has been deflected in a graphite inter- layer, the graphite interlayer is no longer capable of load transfer. Hence the force required to Ar2 deform the now thinner O-ring together with the 2(7+n2 (12) newly created C-rings can be found by super position of the force required to deform each of these components independently. During further as a result the relation between displacement and calculations the program will now evaluate for force is(displacement in the r-direction for 0=I) each layer in the O-ring and for each of these newly created C-rings, what the required displacement is r2) order to reach the strength of that layer in the E (13) O-ring or the strength of each of the c If instead of the inner layer, a layer in the centre of the ring fails, e.g. because it has a very low Using the above relations, simulations of load-dis- strength, this layer is removed from the ring placement diagrams for laminated rings in diame- However, as no load transfer is assumed to occu tral compression can be made. A computer by graphite interlayers in which a crack has program was written which assembles the ring as a Deen defected. this results in the creation of number of layers. In order to define the geometry two O-rings: one consisting of all layers from the of the ring, the inner diameter is stored in a data- outer layer until the layer next to the failing layer, base together with the strength and the thickness of and one consisting of all layers starting with the each layer. If an equal strength value is given to all layer one further than the failing layer until the layers, this simulates a material with an infinite most inner layer. Further the failed layer is Weibull modulus. In order to simulate a material replaced by two C-rings in between these O-rings