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 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 C 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

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

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

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 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 (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 Thanks for your attention !!