WC-Co AISI 1020
steel
AISI 1020
steel WC-Co
Microstructural Evolution and Mechanical Behavior of WC-Co / AISI 1020 Steel Joint obtained by … 46
Figure 3. The interfaces of AISI 1020 steel/filler alloy and filler alloy /WC-Co obtained by brazing
Figure 4. EDS linescane analysis of the interface WC-Co/filler alloy obtained by GTAW process
While in the brazed joint, the EDS analysis (Figure 5) indicate any element diffusion. However, Mehmet Uzkut found a diffusion of Co element, in the SAE 1040/WC-C0 brazed joint when the temperature of work is 775 °C [4]. Although, the EDS linescane analysis done on the interface obtained by the GTAW, reveal the migration of Co and WC to the
filler alloy interface and a small diffusion range of Ni towards the carbide. That can be explained by the diffusion of cobalt in metal (filler alloy) is easier than the diffusion of Ni in cermet (WC-Co), which gives a large distance of diffusion on Co in filler alloy and small ones of Ni in WC-Co [11].
Xu relates the migration of WC to the use of shielding gas [12]. Moreover, Przybyłowicz found that, the heat activation involves the dissolution of great amount of carbide[13], however in joint obta-ined by the GTAW process we noticed the rearran-gement of the W beside the filler alloy which is probably caused by the temperature. Furthermore, Buytoz noted that when the energy input decreases the carbide remains undissolved when he applied a melted tungsten carbide powders on the surface of carbon steel, using tungsten inert gas[14].
Therefore, it can be said that the high temperatu-re and the use of shielding gas activate migration of some elements and dissolution of carbides.
Figure 6 shows the microhardness distribution across the joints. The curves exhibit a similar ten-dency for both procedures, i.e. the higher value of microhardness is recorded in the carbide side with 1510 HV0.3.Then, it decreases until the filler alloy.
This difference is due to the ductile nature of elements present in the filler alloy such as Cu, Ni, Zn [3] After that, it increases closer the AISI 1020 steel where it remains nearly constant at 200 HV0.3.
Figure 5. EDS analysis from the WC-Co to the filler alloy obtained by brazing.
In the brazing joint closer the WC-Co, the micro-hardness achieves 210 HV0.3, increasingly moving away from this interface, the microhardness decree-ses and stabilizes at 162 HV0.3. Whereas, for the joint obtained by the GTAW process, the behavior in the hardness shows two different regions at the interface, the first is the inter-diffusion zone where the hardness is intermediate between the WC-Co and the filler alloy ones. The hardness recorded in this zone (530 HV0.3) is relatively similar to the
0 5 10 15 20 25 30
0 50 100 150 200 250
Composition
Distance (µm)
Ag Co W Cu Ni
Pores
7 8 9 10 11 12 13 14 15 16
0 20 40 60 80 100 120
Composition)
Distance (µm)
Ag Co Ni Cu W
AISI 1020Steel
Filler alloy
WC-Co
B. Cheniti, D. Miroud, D. Allou 47
tungsten ones, which its presence was confirmed by the EDS microprobe analysis. The second is the HAZ where the hardness was high and achieves a 1570 HV0.3. Similar results found by Mehmet Uzkut, who referred this value to passage of Co element along the connection line in this region indicating the mobility of this element [4].
Figure 6. Microhardnes destrubution across the WC-Co/
filler alloy interface.
The higher microhardness of the filler alloy after brazing compared to GTAW (162-140 HV0.3) is due to the fast cooling rate caused by the low range of temperature (650°C) which gives finer microstruc-tures then the one obtained by the GTAW process.
The results obtained through shear testing indi-cate that the maximum value was recorded in the joint obtained by brazing with 260MPa. While the GTAW process once was 168MPa. The reason can be related to the presence of the HAZ and the cracks in the joint. Thereby confirming the measure-ments of micro-hardness already obtained
4. Conclusion
The comparison of the microstructures and mec-hanical properties results between those two pro-cedures support the following conclusions:
Based on the EDS microprobe analysis of the GTAW interface, the higher the temperature the greater amount of carbide dissolution is. Further, it activates the rearrangement of the WC beside the interface.
It can be seen that the use of shielding gas and the high range of temperature activate the migration of some elements as well as the Ni and the W.
Thus, the inter-diffusion zone formed between the WC-Co and the filler alloy. However, at low tem-perature the WC remains undissolved.
The special shear test showed that the maximum shear strength value obtained for the joint made by brazing compared to the one obtained by the GTAW
process. It is interesting to note that for the both processes, the fracture happened in the filler alloy zone cross the WC-Co side and the presence of the HAZ in the GTAW joint makes this joint weak and fragile.
5. References
[1] L. J. Prakash, “Application of fine grained tungsten carbide based cemented carbides,” International Journal of Refractory Metals and Hard Materials, vol.
13, no. 5, pp. 257–264, Jan. 1995.
[2] J. X. Zhang, R. S. Chandel, and H. P. Seow, “Effects of chromium on the interface and bond strength of metal–ceramic joints,” Materials Chemistry and Physics, vol. 75, no. 1–3, pp. 256–259, Apr. 2002.
[3] W. B. Lee, B. D. Kwon, and S. B. Jung, “Effects of Cr3C2 on the microstructure and mechanical properties of the brazed joints between WC-Co and carbon steel,” Int. Journal of Refractory Metals and Hard Materials, vol. 24, pp. 215–221, 2006.
[4] M. Uzkut, N. S. Köksal, and B. S. Ünlü, “The determination of element diffusion in connecting SAE 1040/WC material by brazing,” Journal of Materials Processing Technology, vol. 169, pp. 409–413, 2005.
[5] H. Chen, K. Feng, J. Xiong, and Z. Guo,
“Characterization and stress relaxation of the functionally graded WC-Co/Ni component/stainless steel joint,” Journal of Alloys and Compounds, vol.
557, pp. 18–22, 2013.
[6] S. Ouallam, “Etude du soudage TIG et laser Nd-YAG de l’alliage d’aluminium 2024 T3,” Algiers: Ecole Nationale Polytechnique ENP, 2009.
[7] C. Just, E. Badisch, and J. Wosik, “Journal of Materials Processing Technology Influence of welding current on carbide / matrix interface properties in MMCs,” vol. 210, pp. 408–414, 2010.
[8] A. Khorram, M. Ghoreishi, M. J. Torkamany, and M.
M. Bali, “Optics & Laser Technology Laser brazing of inconel 718 with a silver based fi ller metal,” Optics and Laser Technology, vol. 56, pp. 443–450, 2014.
[9] J. Lemus-ruiz, L. Ceja-cárdenas, and V. H. López-morelos, “Interfacial and mechanical evaluation of WC-Co/Ni joints,” Journal of Engineering and Technology, pp. 91–99, 2011.
[10] J. Nowacki and M. Kawiak, “Microstructure and characteristics of high dimension brazed joints of cermets and steel,” Manufacturing Engineering, vol.
37, no. 2, pp. 448–457, 2009.
[11] J. Lemus, L. C.- Cárdenas, E. B. Becerril, and V. H.
López, “José Lemus -Ruiz, Leonel Ceja- Cárdenas, E. Bedolla - Becerril, Víctor H. López -Morelos,” pp.
91–99, 2011.
[12] P. Q. Xu, “Dissimilar welding of WC-Co cemented carbide to Ni42Fe50.9C0.6Mn3.5Nb3 invar alloy by laser-tungsten inert gas hybrid welding,” Materials and Design, vol. 32, pp. 229–237, 2011.
[13] J. Przybyłowicz and J. Kusiński, “Structure of laser cladded tungsten carbide composite coatings,”
Journal of Materials Processing Technology, vol. 109, no. 1–2, pp. 154–160, Feb. 2001.
[14] S. Buytoz, M. Ulutan, and M. M. Yildirim, “Dry sliding wear behavior of TIG welding clad WC composite coatings,” Applied Surface Science, vol. 252, pp.
1313–1323, 2005.
WC-Co
Filler alloy AISI 1020 steel
Microstructural Evolution and Mechanical Behavior of WC-Co / AISI 1020 Steel Joint obtained by … 48