Browsing by Author "Srinivasan, D."

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    Thermal stability and high-temperature wear of Ti-TiN and TiN-CrN nanomultilayer coatings under self-mated conditions
    (Elsevier Ltd, 2007) Srinivasan, D.; Kulkarni, Trupti.G.; Anand, K.
    Ti-TiN and TiN-CrN nanomultilayers were thermally stable retaining uniform and sharp layer interfaces up to 24 h at 773 K, without any oxidation or phase transformation accompanying each individual layer. Decreasing the multilayer spacing resulted in an increase in the hardness in both cases. The coating hardness was found to be independent of the substrate type, when applied on HS718, Ti64 and HCHCr substrates. In scratch testing, the multilayers displayed a better resistance to the onset of failure, as compared to the monolayer TiN. The substrate plasticity played an important role in determining the coating failure mode. Self-mated wear tests revealed the CrN-TiN system to exhibit the best wear behaviour, both at room temperature and at 773 K. The Ti-TiN coatings are more accommodative with all three substrates, as compared to TiN-CrN and TiN. © 2006 Elsevier Ltd. All rights reserved.
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    Understanding the Residual Stress in DMLS CoCrMo and SS316L using X-ray diffraction
    (2019) Chimmat, M.; Srinivasan, D.
    Laser additive manufacturing (LAM) is the next in line revolutionary technology for various turbine applications, as an enabler of new designs and parts and during repair and refurbishment of service returned parts. In LAM process, residual stresses play a key role during component build up as well as while removing the components from the build plate, to ensure distortion free parts, as a standalone or as a hybrid build on an existing part. The present study comprises an experimental determination of residual stresses of two direct metal laser sintered (DMLS) alloys, CoCrMo and SS316L, using the X-ray diffraction sin2 ? technique. In both cases, the process parameters were optimized to result in dense (> 99.95%) samples. Surface residual stress measurements were carried out on the DMLS samples in the as printed condition and after heat treatment. While SS316L measured a surface tensile stress of 127 MPa, CoCrMo showed a tensile stress of 265 MPa, in the as printed condition. Upon grit blasting, both samples undergo a peening effect and record a compressive stress of 300-400 MPa. Heat treatment of SS316L at 650�C, tends to relieve these stresses and results in zero stress, whereas for CoCrMo there was a systematic variation in the response to heat treatment at different temperatures, correlating with the microstructural evolution. At 1050�C CoCrMo shows compressive stresses because of partial recrystallization and at 1150�C having a completely recrystallized microstructure comprising equiaxed grains of around 40 �m and a completely stress relieved condition. � 2019 The Authors. Published by Elsevier B.V.
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    Understanding the Residual Stress in DMLS CoCrMo and SS316L using X-ray diffraction
    (Elsevier B.V., 2019) Chimmat, M.; Srinivasan, D.
    Laser additive manufacturing (LAM) is the next in line revolutionary technology for various turbine applications, as an enabler of new designs and parts and during repair and refurbishment of service returned parts. In LAM process, residual stresses play a key role during component build up as well as while removing the components from the build plate, to ensure distortion free parts, as a standalone or as a hybrid build on an existing part. The present study comprises an experimental determination of residual stresses of two direct metal laser sintered (DMLS) alloys, CoCrMo and SS316L, using the X-ray diffraction sin2 ψ technique. In both cases, the process parameters were optimized to result in dense (> 99.95%) samples. Surface residual stress measurements were carried out on the DMLS samples in the as printed condition and after heat treatment. While SS316L measured a surface tensile stress of 127 MPa, CoCrMo showed a tensile stress of 265 MPa, in the as printed condition. Upon grit blasting, both samples undergo a peening effect and record a compressive stress of 300-400 MPa. Heat treatment of SS316L at 650°C, tends to relieve these stresses and results in zero stress, whereas for CoCrMo there was a systematic variation in the response to heat treatment at different temperatures, correlating with the microstructural evolution. At 1050°C CoCrMo shows compressive stresses because of partial recrystallization and at 1150°C having a completely recrystallized microstructure comprising equiaxed grains of around 40 µm and a completely stress relieved condition. © 2019 The Authors. Published by Elsevier B.V.