1. 6 Advisor : 戴子堯 Advisee : 張博翔 Department of Mechanical Engineering & Institute of Nanotechnology, Southern Taiwan University of Science and Technology, Tainan, TAIWAN Date ﹕ 2015/06/08 Paper Survey 1 Spark plasma sintering of tungsten/graphite joints with a SiC ceramic interlayer Ceramics International41(2015)4651–4655 Tomoyuki Okunia, YoshinariMiyamotoa,n, HiroyaAbeb, MakioNaitob

2. 2 Tungsten powders were successfully sintered and simultaneously joined to a graphite disk using an interlayer of SiC ceramic powder,which contained Al2O3 and Y2O3 as sintering aids for the SiC.The tungsten/graphite joints were prepared at30MPa and temperatures ranging from 1700 1C to2000 C for 5min using spark plasma sintering(SPS).The tensile strength of the joints prepared at1700 1C reached 21MPa.The suggested joining mechanism of the joints prepared below 1800 C is as follows:both the sintered W metal layer and the SiC ceramic interlayer are chemically bonded together accompanying reaction phases of WC,W2C andW5Si3. A physical bond is achieved between the SiC interlayer and graphite when the SiC powder fills the open pores of the graphite and is sintered there.Although a similar joining mechanism is suggested when the joining temperature exceeds1900 C, the SiC interlayer disappears,and the broad reaction layer consisting of WC,W2C and trace W5Si3 is formed. Abstract

3. Experimental procedure 3 Fig. 1.SPS setup for joining between W and graphite(a)and the enlarged figure of the test sample(b). Fig. 2. Schematic drawing of the jigs used for the tensile testing of the joints. Epoxy resin adhesive 80 °C for 24 h

4. 4 Fig. 3.Cross-sectional SEM images and elemental analyses of W,Si and C at the interface of the W/graphite joint prepared at 1700 °C (a)and 1900 °C (b). Results and discussion C Si 1700°C1900°C

5. 5 Results and discussion Fig. 5.Average tensile strength of the W/graphite joints as afunction of joining temperature.

6. 6 Results and discussion Fig. 6.SEM images of the joints prepared at1700°C (a)and1800 C°(b)after the water-quenching test. 1700°C1800°C

7. Results and discussion Fig. 7.Schematic illustrations of the joining mechanism for the W/graphite joints prepared below 1800C (a)and above 1900C (b). 1800°C1900°C

8. 8 Conclusions In the present work,tungsten and graphite joints were successfully obtained using a SiC interlayer processed by SPS. Asaresult,the following conclusions were obtained: (1) No cracking or delamination was observed at the interfaces of the joints.The reaction phases including WC,WC and W5Si3 were produced between the W and graphite. (2) The tensile strength reached a maximum of 21 MPa when joined at 1700 ° C and then decreased with an increasing joining temperature.All the fractures occurred in the graphite near the interface due to the residual stress. (3) The joining mechanism was explained as follows: Below 1800 ° C, the sintered W metal layer and SiC ceramic interlayer were bonded mainly in a chemical manner, producing reaction phases at the interface.In addition, the SiCinterlayerandgraphitewerephysicallybondedby the anchoring effect.This was formed by the SiC powder penetrating into the open pores of the graphite and sintering.Whenthejointswerepreparedabove1900 ° C, the SiC interlayer disappeared,but a broad reaction layer including WC,W2C andW5Si3 was formed there.

9. 9 (4) The thermal shock test severely attacked the SiC interlayer and lowered the tensile strength of the W/Graphite joints below 7MPa.The best preparing temperature for joining W and graphite with a SiC interlayer is suggested to be 1800 ° C. Conclusions

10. 10 Thanks for your attention !!