Microstructural Characterisations of Welded Shape Memory Alloys

Today, with the development of technology, different welding methods were applied for different alloys. In thiswork, changing of functional properties after using welding methods for NiTi alloy samples were aimed.However, two different welding methods were employed for the same alloy and results were compared to eachother and commented on them. In the present study, samples were welded with TIG and Laser welding and theircross section of welded zone was examined. Then these samples were examined in optical microscope andSEM. The advantages and disadvantages of both welding methods were reported. The basic distinction of TIGand laser welded samples examined in microscope were the scale of HAZ (Heat Affected Zone) of TIG weldedsamples. Nevertheless, due to more thermal input was applied for materials in TIG welded parts, more moltenmaterials were detected, or heat effects were attained in this practice. In laser welding, heat input was less, andthis could be recognized from the observed micrographs. When SEM figures were investigated, While HAZwas obviously distinguished from border of welding bath and the base metal was been separated from HAZ too.The twin structures were not observed in optical microscope; for that reason, they were investigated in SEM tosee these twins in laser welded area.

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1. Oliveira J P, Miranda R M, Braz Fernandes F.M. 2017. Welding and Joining of NiTi Shape Memory Alloys. A Review, Progress in Materials Science; 412–466.
2. Mehrpouya M, Gisario A, Mohammad E. 2018. Laser welding of NiTi shape memory alloy. Journal of Manufacturing Processes; 31: 162–186.
3. Jani. J.M.; Leary M.; Subic A.; Gibson M.A.; Mohd J.J.; Leary M.; Subic A.; Gibson M.A. A review of shape memory alloy research, applications and opportunities, Materials Design, 2014; 56, 1078–1113.
4. Patoor E, Lagoudas D.C, Entchev P.B, Brinson L.C, Gao X. 2006. Shape memory alloys, part I: general properties and modeling of single crystals. Mechanical Materials; 38: 391–429.
5. Sun Y, Luo J, Zhu J. 2018. Phase field study of the microstructure evolution and thermomechanical properties of polycrystalline shape memory alloys: Grain size effect and rate effect. Computational Materials Science; 145: 252–262.
6. Özgün Ö, Yılmaz R, Gülsoy H.Ö, Fındık F. 2015. The effect of aging treatment on the fracture toughness and impact strength of injection molded Ni-625 superalloy parts. Materials Characterization; 108: 8–15.
7. Cao S, Xinhua W, et all. 2018. Role of martensite decomposition in tensile properties of selective laser melted Ti6Al-4V. Journal of Alloys and Compounds; 744: 357-363.
8. Wang S.Q, Liu J.H, Chen D.L. 2014. Effect of strain rate and temperature on strain hardening behavior of a dissimilar joint between Ti–6Al–4V and Ti17 alloys. Materials and Design; 56: 174–184.
9. Mohd J.J, Leary M, Subic A, Gibson M.A. 2014. A review of shape memory alloy research, applications and opportunities. Materials and Design; 56: 1078–1113.
10. Saedi S, Sadi A, Taheri M, Shayesteh N. 2017. Texture, aging, and superelasticity of selective laser melting fabricated Ni- rich NiTi alloys. Materials Science Engineering A; 686: 1– 10.
11. Machado G, Louche H, Alonso T, Favier D. 2014. Superelastic cellular NiTi tube-based materials: Fabrication, experiments and modeling. Materials and Design; 65: 212–220.
12. Vidyarthy R.S, Dwivedi D.K. 2018. Microstructural and mechanical properties assessment of the P91 A-TIG weld joints. Journal of Manufacturing Processes; 31: 523–535.
13. Guoxin H, Lixiang Z, Yunliang F, Li Yanhong. Fabrication of high porous NiTi shape memory alloy by metal injection molding; School of Mechanical & Power Engineering, Shanghai Jiaotong University Press: Shanghai, China, 2008; pp 200-240.
14. Goryczka T, Humbeeckb J.V. 2008. NiTiCu shape memory alloy produced by powder technology. Journal of Alloys and Compounds; 456: 194–200.
15. Razorenov S.V, Garkushin G.V, Kanel G.I, Kashin O.A, Ratochka I.V. 2011. Behavior of the nickele titanium alloys with the shape memory effect under conditions of shock wave loading. Physic. Solid State; 53: 824-829.
16. Comer, A, & Looney, L. 2006. Crack propagation resistance of Zeron 100 weld metal fabricated using the GTA and SMA welding processes. Theoretical and applied fracture mechanics; 45(2): 139-147.
17. Tuissi, A, et al. 1999. Effect of Nd-YAG laser welding on the functional properties of the Ni–49.6 at.% Ti. Materials Science and Engineering A; 273: 813-817.
18. Falvo, A. Termomechanical characterization of NickelTitanium Shape Memory Alloys, Universita Della Calabria Press: Italy, 2007; pp 43-47.
19. Falvo, A, Furgiuele, F. M, & Maletta, C. 2005. Laser welding of a NiTi alloy: Mechanical and shape memory behaviour. Materials. Science and Engineering A; 412(1-2): 235- 240.
20. Hesse, T, Ghorashi M, Inman D.J, Intel, J. 2004 Shape Memory Alloy in Tension and Compression and its Application as Clamping-Force Actuator in a Bolted Joint. Materials Systems Structure;15: 577.