6Advisor :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

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Spark plasma sintering of tungsten/graphite joints with a SiC ceramic interlayer

Ceramics International41(2015)4651–4655

Tomoyuki Okunia, YoshinariMiyamotoa,n, HiroyaAbeb, MakioNaitob

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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 interlayerand 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

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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 adhesive80°C for 24 h

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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°C 1900°C

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Results and discussion

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

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Results and discussion

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

1700°C 1800°C

Results and discussion

Fig. 7.Schematic illustrations of the joining mechanism for the W/graphitejoints prepared below 1800C (a)and above 1900C (b).

1800°C 1900°C

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ConclusionsIn the present work,tungsten and graphite joints weresuccessfully obtained using a SiC interlayer processed bySPS. Asaresult,the following conclusions were obtained:(1) No cracking or delamination was observed at the interfacesof the joints.The reaction phases including WC,WC andW5Si3 were produced between the W and graphite.(2) The tensile strength reached a maximum of 21 MPa whenjoined at 1700 ° C and then decreased with an increasingjoining temperature.All the fractures occurred in thegraphite near the interface due to the residual stress.(3) The joining mechanism was explained as follows: Below1800 ° C, the sintered W metal layer and SiC ceramicinterlayer were bonded mainly in a chemical manner,producing reaction phases at the interface.In addition,the SiCinterlayerandgraphitewerephysicallybondedbythe anchoring effect.This was formed by the SiC powderpenetrating into the open pores of the graphite andsintering.Whenthejointswerepreparedabove1900 ° C,the SiC interlayer disappeared,but a broad reaction layerincluding WC,W2C andW5Si3 was formed there.

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(4) The thermal shock test severely attacked the SiC interlayerand lowered the tensile strength of the W/Graphite jointsbelow 7MPa.The best preparing temperature for joiningW and graphite with a SiC interlayer is suggested to be1800 ° C.

Conclusions

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