ANX-RAY FRACTOGRAPHY STUDY OF A SINTERED COMPOSITES. SYSTEM OF Al204 Sic (WHISKER)

Transcription

1 Copyright(c)JCPDS-International Centre for Diffraction Data 2,Advances in X-ray Analysis,Vol ISSN ANX-RAY FRACTOGRAPHY STUDY OF A SINTERED COMPOSITES ABSTRACT SYSTEM OF Al24 Sic (WHISKER) Toshiya Mori, Mikio Kawasaki, Toshihiko Sasaki and Yukio Bose Department of Mbterials Science andengi~eeting Kanazawa University Kbkmna-machi, K anazawa , Jqan X-ray methods were used to measure the residual stress near a fracture surface of a sintered composite system of A&3/ Sic. A specimen bent at three points with different notch radii was used to measure h-acture toughness. Effects of the notch radii on the stress intensity factor Kp were measured during the initiation of the crack. Experimental results agreed with fracture mechanics theory. INTRODUCTION Brightness is a defect in ceramic materials. Al,O&iC (w)/zrq composite material reinforced the Sic whisker, and has good toughness as a result of crack deflection and drawing. Hot press processing can produce anisotropic Sic whiskers. We assume that material strength is controlled by the cutting direction. We studied the influence of the distribution of Sic (w) on toughness. We evaluated the 6acture mechanism by applying fracture mechanics. In the field of fracture mechanics, KIC indicates the minimum stress intensity factor which exists when the crack occurs. A li-acture toughness test by the IF method was done on a AI,OdSiC (w)/zq composite ceramic material. In addition, the influence of crack radius on the stress intensity factor was considered. X-ray fiactography technique was used to measure fracture surface. The relationship between an X-ray parameter (residual stress) and fracture mechanics parameter were investigated. EXPERIMENTAL PROCEDURE Materials and specimens Alz3 /Sic(w) reinforced composite specimens prepared by the hot press method were studied. Table 1 shows the volume fraction of the chemical compositions. Two kinds of specimen components were prepared using a different crack growth direction. They were perpendicular (Sample A) and parallel (Sample B) to the hot press direction as shown in Fig. 1. Specimens had a uniform size and shape. The notch radius p was between.1 and.75 mm as shown in Fig. 2. Specimens were notched with diamond blades. Compositions were analyzed with a scanning electronic microscope to observe the distribution of the Al and Si in the sample. A&O3 and Sic element were seen to disperse uniformly as shown in Fig. 3.

2 ISSN This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 Copyright(c)JCPDS-International Centre for Diffraction Data 2,Advances in X-ray Analysis,Vol ISSN Table 1 M.ixture ratio of A&Ox, Sic(w), ZrO, I Al,2 Sic(w) ZrO- Volumefi-action, vol. % Hot press direction =,Hot press dinxtion Cutting direction cutting direction Hot press direction Sample A Sample B Fig. 1 Relation between cutting direction and Hot press direction(unit: mm). Fig. 2 Geometry of specimens (unit : mm). Fig. 3 Results of the analysis on Al and Si components by energy dispersive X-ray analysis. (Dots indicate each element) Table 2 Result of Vickers hardness and fracture toughness value by IF method. Vickers hardness, HV Fracture toughness value, KI,, MPa& Sample A Sample B

4 Copyright(c)JCPDS-International Centre for Diffraction Data 2,Advances in X-ray Analysis,Vol ISSN The IF method was therefore used to measure fi-acture toughness. Table 2 shows fracture toughness values obtained by the IF method. S ecimen Fracture toughness test of notched specimen P Displacement(u Fig. 4 shows the schematic of the fracture toughness test. The cross head speed used was.5 mm/min. A x-y -l-44 three point bending test was adopted. Load P was ~~~b~~~: pq obtained by changing measure with the load cell. - Crack opening displacement was measured usiig a clip gage. Symbol u indicates crack opening displacement u. The fracture toughness K value was calculated using Fig. 4 Schematic illustration of fi-acture toughness measuring equipment. the following equation4: K=&-FFMPafi) (1) where a is crack length (unit: mm), Wis the width of the specimen (unit: mm), S note the pin-span distance (unit: mm), B is the thickness of specimen(unit: mm), P denotes load (unit: N), F (a/w) is a coefficient to correct for the shape of the specimen. X-ray stress measurement The residual phase stress during crack growth was measured using the sin2w technique5 under the conditions shown in Table 3. Measurements were made with a (Shimadzu-XD-61) iso-inclination method &I goniometer. The X-ray irradiation area is 2 X 4mm as shown in Fig. 5. Peak angle 2 was determined Table 3 Operating parameters. corn the pesk profile ofthe A~,o, phase using the half Method Parallel beam method value width method. Residual stress was calculated Chamcter&icradiatior 1 Cu Ka using the phase X-ray elastic constant Kroner model? Dtiadion, hkl A12,: 146, SiC:2,,47 A depth profile of residual stress was obtained by use Radiation filter of chemical etching. A laser displacement meter was Tube voltage Ni foil 3, kv (const.) used to measure the depth of the area polished. Tube current scanning speed 2, ma.6, degimin (29

5 Copyright(c)JCPDS-International Centre for Diffraction Data 2,Advances in X-ray Analysis,Vol ISSN h-&lent X:ray beam I- I I / I I I I I I , deg Figure. 5 Schematic illustration of X-ray irradiated area (unitmm). Figure. 6 Peak profile of AI,O,,/SiC whisker /Zr2 composite materials. RESULTS AND DISCUSSION Relation between fracture toughness and notch radius Fig. 7 shows the relationship between load P (unit: N) and crack opening displacement (u) in the notch radius (&O. 1 (unit: mm) specimen. Displacement (u) to the fracture was very small on all specimens in the crack produced. There was a liner relationship between P and u to the crack generation point. Load P (shown by the arrow) was assumed to be a fracture load, corresponding to the crack produced. Thus, a conventional stress intensity factor Kp was obtained. The maximum of the load increased with p Figure. 7 ;;a2 co** Displacement u (mm) Displacement u (mm) (a) Sample A (b) Sample B Relationship between load and crack-opening displacement 1 mm specimen. Fig. 8 shows the relationship between fi and tiacture toughness value Kp A ceramic specimen of and two kinds of AI,OJSiC whisker /Zr2 were compared7. Kp increased with notch radius in all specimens. A relationship of fi-acture toughness value K, and p was observed. Toughness increased when changing for a siigle phase A123 to the phase of A123 SiC(w)/ZrO,.

6 Copyright(c)JCPDS-International Centre for Diffraction Data 2,Advances in X-ray Analysis,Vol ISSN A change of the fracture toughness value with distribution of Sic was also confirmed. The fracture toughness value in the sample B is larger than that of Sample A The relationship can be roughly approximated by a straight line. KP is proportional to fi. X-ray Fractography of fracture surface Fig, 9 shows a distribution of residual stress. The tensile stress on the fracture surface was measured. Tensile stress changed into compressive stress as a deeper layer was measured. At a certain depth, it became a local maximum compressive stress point that gradually reduced and approached a constant value...**...- I.5 1 Square root notch radi& p, Jmm Fig. 8 Relationship between fi-acture toughness and the square root of the notch-tip radius. 5 8 I 5 I _ m m -!i 4 I aa - P - l l,..? 4 *AaBAA.6A oaoh 6 x - A f o l OA.+++AA _ gaa f 3 A 7 _ A -cr s p =O.lO,mm 4 g* P. p=.5,mm [1: AA d A p =.75, mm.x4-, I I I 23-5 D&th from fracture s:tiaoe w,bf mm depth from fracture%tface w, hfm (a) Sample A (b) Sample B Figure. 9 The distribution of residual stress in the A&O3 phase near the surface 7. Plastic zone depth Residual stress almost becomes constant, and is assumed to be the plastic zone depth. q is define as the depth of the plastic zone onn>. The relationship between q and KJoB of the notched specimen is shown in Fig. 1. The relationship between q and the slope KJoB is approximately a straight line in both logarithm plots. The relationship can be shown as follows:

7 . Copyright(c)JCPDS-International Centre for Diffraction Data 2,Advances in X-ray Analysis,Vol ISSN *, =a 2 K 2 ( OB 1 (3) 2 I I I I Illll!I,2 l y 7 :lr h where M indicates the constant in the material. E 8- We obtained a value of.44 in Sample B, and.43 in Sample $ 2 A. They are nearly the same for the A&O3 single-phase material7 8 4 _ (~.47). Since the two values are nearly equal, we found that the a value in the plastic zone depth is not influenced by the 2 *s 2 Sample A B p=o.lo, mm l p=o.5, mm + p=o.75, mm A A distribution of the Sic whisker. We were able to determine the 1 I I 11,111, fracture toughness of these materials from the X-ray parameter &/cb, mm near the fracture surface. Figure. 1 Relationship between plastic CONCLUSIONS zone depth and stress intensity factor divided by bending stress. (1) Fracture toughness was found to the square root of notch radius in composite rnaterial(al~o~sic). This value was influenced by the specimen cutting direction during the hot press process. (2) X-ray fiactography can be used to measure tensile stress on the surface of the Al~O~SiC/ZrO~ composite ceramics material. The plastic zone size, q was determined from a measurement of the residual stress. 9 was found to be related to both fracture toughness K, and the bending stress o, by the following equation: w, = a(k, /ubb)2 where P.44 for the specimen A, E.43 for the specimen B. Both the values are smaller than A&OS bulk material (~.47). REFERENCES [l] Y. Hirose and Tanaka K. -prz&c. Mat. Sci., 1979,29, [2] Y. Hirose, K. Tanaka and K. Okabayashi, Jpn. &ML& A&, 1978,27, [3] K. Tanaka, Establish of Analysis of Accident Fracture by X-m Fractogrqhf, Science Stu& Expenses Subsi@ S thsis Report(A), 1987,46. [4] T. Kunio, H. Nakazawa, et. al. Fracture Medmnics Experimental Procedure, 1984, 81, Asakura-shoten. [5] Japan Material Science Society, X-ray StressMeasurement Youkendo, 1981, [6] E. KrGner, 2 Physik 1958, Bd151, [7] T. Mishima, Y. Nanayama, Y. Hirose and K Tanaka, +,S&. A4a2: Sti., l%7,36, A