1. School of Materials Science and Engineering Microstructural evolution and brazing mechanism of Ti 2 SnC-Ti6Al4V joint by using Cu pure foil Wenbo Yu, Shibo Li, Yann Aman, Zhipeng Guo, Shoumei Xiong School of materials science and engineering Tsinghua University Beijing China

2. School of Materials Science and Engineering MAX phases M n+1 AX n [1] X: C and/or N A: A Group element M: Early transition metal Ceramic + Metal properties Edge-sharing [M 6 X] octahedra interleaved with A layers Good oxidation resistance Good damage tolerance [1] M.W. Barsoum et al.,, Progress in Solid State Chemistry, 28 (1-4), 201-281, 2000

3. School of Materials Science and Engineering Pantograph: Good electrical conductivity Low friction coefficient Heating elements: Good oxidation resistance Motor: Low density Good resistance at high temperature Applications Al 2 O 3 TiC 0.67

4. School of Materials Science and Engineering Background Crack healing 800 ℃ /1h Ti 2 SnC [2] Ti 2 SnC/Al 2 O 3 composite [3] [2] Li, S., et al.,. Journal of the European Ceramic Society, 2016. 36(1): p. 25-32. [3] Bei et al. J. Am. Ceram. Soc. 98 (2015)1604-1610

5. School of Materials Science and Engineering sonication 10µm Widely biomedical application Such bone replacement 1200 ℃ /1h [4] Drawbacks: biotoxicity of vanadium Background [4] Gao et al.,. Journal of material research, 2002. 17(1): p. 25-32. [5] Zhao et al. Transaction nonferrous metal society. 2009 20(2)5p,414-417 Ti-6Al-4V 800 ℃ /1h [5 ] Possible: using Ti 2 SnC to replace Ti 3 SiC 2 The temperature can be strongly decreased

6. School of Materials Science and Engineering Experimental procedure Ti, Sn, C powders with a molar ratio of 2:1:1 Sintering condition: 1250 ºC /30 MPa /1h in vacuum High-frequency induction heating device 750ºC /5MPa under Ar atmosphere

7. School of Materials Science and Engineering layer I: migration of Cu atom into β-Ti layer II: Cu 4 Ti 3 Layer III : rich Cu and Ti Layer IV: CuTi 0.5 Sn 0.5 and Sn layer V: β-Cu(Sn) (bright area) and α-Cu(Sn) (grey area) Zhao et al. [5 ] 750ºC /5MPa/1h

8. School of Materials Science and Engineering 750ºC /5MPa/20mins and 750ºC /5MPa/40mins EPMA results show Sn atoms began to accumulate adjacent to TC4 side Chemical compositions of layers I II and III did not change Sn began to accumulate between layer IV and V

9. School of Materials Science and Engineering FIB procedure The side of Cu and Ti 2 SnC 1 In Fig(d), BSE images indicates two contrasts, Grain 1 was surrounded by white dots.

10. School of Materials Science and Engineering TEM results Ti:Sn=1:0.73 Sn atoms diffuse out from Ti 2 SnC grains Cu atoms could diffuse into Ti 2 SnC grain boundaries and form Cu(Sn) solid solution.

11. School of Materials Science and Engineering Shear test shear strength :85.7±10MPa. crack propagated in Ti 2 SnC Intergranular fracture mode.

12. School of Materials Science and Engineering The side adjacent to Ti 2 SnC, Ti 2 SnC → xSn +Ti 2 Sn 1-x C (1) Sn +Cu → β-Cu (Sn) + α-Cu (Sn) (2) The side adjacent to TC4, the interdiffusion between Ti and Cu resulted into the following reaction. Cu + βTi → βTi (Cu) (layer I) (3) 3Ti +5Cu → Ti 3 Cu 4 layer (II) + Cu (Sn,Ti) (layer III) (4) With the increasing processing time, Sn atoms began to accumulate into Cu(Ti) layer and form CuTi 0.5 Sn 0.5 intermetallic. 1.5Sn + Cu (Ti) → Sn +CuTi 0.5 Sn 0.5 (layer IV) (5) Conclusions

13. School of Materials Science and Engineering Thank you