PSI - Issue 14

Manojakumar Chimmat et al. / Procedia Structural Integrity 14 (2019) 746–757 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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4. Conclusions

Residual stresses in the DMLS CoCrMo and SS316L were evaluated and studied in the as printed and heat treated condition using the Sin 2  technique, for two geometries. Both the alloys were produced with a dense structure with little or no porosity (0.043% in CoCrMo and 0.038% in SS316L). The layer by layer structure of the as printed CoCrMo is seen to undergo partial recrystallization at 1050 °C followed by a completely recrystallized microstructure at 1150 °C . The residual stresses correlate with the microstructure evolution by measuring a tensile stress of  250 MPa and a showing a compressive behaviour with a similar magnitude (of  300 MPa), between the as printed and grit blasted conditions, in the CoCrMo samples. Upon heat treatment, a sinusoidal residual stress behaviour was noted, going from tensile (950  C) to compressive (1050  C) to a completely stress relieved state at 1150  C. The residual stress response was similar for both the geometries. Between the CoCrMo and SS316L, the optimized process parameters for a dense part indicated a residual stress that seemed to relate to the material yield strength, with the SS316L measuring only half (127 MPa) that of CoCrMo in the as printed condition. Overall, the role of processing parameters in influencing the residual stress and hence in distortion or defect free DMLS materials is brought out via this study. Acknowledgements This study was done during the internship tenure of Manojakumar Chimmat at the Repair Development Center (RDC), GE Power, Bangalore, India as part of his M.Tech thesis. The authors are thankful to the global RDC management for their sponsorship of the projects. INTECH, DMLS, is acknowledged for the DMLS samples provided for this study. References Basak, A., and Das, S. (2016) . “Epitaxy and Microstructure Evolution in Metal Additive Manufacturing.” Annu. Rev. Mater. Res. , 46(1), 125 – 149. Bawane, K. K., Srinivasan, D., and Banerjee, D. (2018). “Microstructural Evolution and Mechanical Properties of Direct Metal Laser-Sintered (D MLS) CoCrMo After Heat Treatment.” Metall. Mater. Trans. A . Bi, G., Sun, C. N., Chen, H. chi, Ng, F. L., and Ma, C. C. K. (2014). “Microstructure and tensile properties of superalloy IN 100 fabricated by micro- laser aided additive manufacturing.” Mater. Des. , 60, 401 – 408. FRARENDI. (2018). “Gas turbines first stage nozzles.” (Jul. 6, 2018). Gibson, I., Rosen, D., and Stucker, B. (2015). Additive Manufacturing Technologies . Addit. Manuf. Technol. 3D Printing, Rapid Prototyping, Direct Digit. Manuf. Second Ed. Grunberger, T., and Domrose, T. (2015). “Direct Metal Laser Sintering Identification of process phenomena by optical in - process monitoring.” Laser Tech. J. , 12, 45 – 48. King, W., Anderson, A. T., Ferencz, R. M., Hodge, N. E., Kamath, C., and Khairallah, S. A. (2015). “Overview of modelling and simulation of metal powder bed fusion process at Lawrence Livermore National Laboratory.” Mater. Sci. Technol. , 31(8), 957 – 968. Kumar, S., Chandrasekara, R., Reddy, A. S., Srinivasan, D., and Ananthanarayanan, D. (2018). “GTINDIA2017 - 4614.” 1– 10. Matsumoto, M., Shiomi, M., Osakada, K., and Abe, F. (2002). “Finite element analysis of single layer forming on meta llic powder bed in rapid prototyping by selective laser processing.” Int. J. Mach. Tools Manuf. , 42(1), 61 – 67. Monroy, K., Delgado, J., and Ciurana, J. (2013). “Study of the pore formation on CoCrMo alloys by selective laser melting man ufacturing process.” Procedia Eng. , 63, 361 – 369. Mukherjee, T., Zhang, W., and DebRoy, T. (2017). “An improved prediction of residual stresses and distortion in additive manufacturing.” Comput. Mater. Sci. , 126, 360 – 372. Protasov, C. E., Safronov, V. A., Kotoban, D. V., and G usarov, A. V. (2016). “Experimental study of residual stresses in metal parts obtained by selective laser melting.” Phys. Procedia , 83, 825 – 832. Reddy, S, A and Srinivasan, D. (2018) "Small scale mechanial testing of additively manufactured (Direct Metal Laser Sintered) monolithic and hybrid test samples." Structural intergrity. Procedia, (Temp ID : 496) . Schoinochoritis, B., Chantzis, D., and Salonitis, K. (2017). “Simulation of metallic powder bed additive manufacturing proces ses with the finite