Faculty Publications
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Item Wetting behaviour and evolution of microstructure of Sn-Ag-Zn solders on copper substrates with different surface textures(2010) Satyanarayan, S.; Prabhu, K.N.The effect of surface roughness on wetting behaviour and evolution of microstructure of two lead-free solders (Sn-2.625Ag-2.25Zn and Sn-1.75Ag-4.5Zn) on copper substrate was investigated. Both solders exhibited good wettability on copper substrates having rough surface and lower wettabilty on smooth surfaces. The contact angles of solders decreased linearly with increase in surface roughness of the substrate. The exponential power law, ?=exp(-K ?n), was used to model the relaxation behaviour of solders. A high intermetallic growth was observed at the interface particularly on copper substrates with rough surface texture. A thin continuous interface showing scallop intermetallic compounds (IMC) was obtained on smooth surfaces. With an increase in surface roughness, the IMC morphology changed from scallop shaped to needle type at the Sn-2.625Ag-2.25Zn solder/substrate interface and nodular to plate like IMCs for Sn-1.75Ag-4.5Zn solder matrix. Copyright © 2010 by ASTM International.Item Wetting behaviour and evolution of microstructure of Sn-Ag-Zn solders on copper substrates with different surface textures(ASTM International, 2011) Satyanarayan, S.; Prabhu, K.N.The effect of surface roughness on wetting behaviour and evolution of microstructure of two lead-free solders (Sn-2.625Ag-2.25Zn and Sn-1.75Ag-4.5Zn) on copper substrate was investigated. Both solders exhibited good wettability on copper substrates having rough surface and lower wettabilty on smooth surfaces. The contact angles of solders decreased linearly with increase in surface roughness of the substrate. The exponential power law, ?=exp(-KT -1), was used to model the relaxation behaviour of solders. A high intermetallic growth was observed at the interface particularly on copper substrates with rough surface texture. A thin continuous interface showing scallop intermetallic compounds (IMC) was obtained on smooth surfaces. With an increase in surface roughness, the IMC morphology changed from scallop shaped to needle type at the Sn-2.625Ag-2.25Zn solder/ substrate interface and nodular to plate like IMCs for Sn-1.75Ag-4.5Zn solder matrix. Copyright © 2010 by ASTM International.Item Effect of temperature and substrate surface texture on wettability and morphology of IMCs between Sn-0.7Cu solder alloy and copper substrate(2012) Satyanarayan, S.; Prabhu, K.N.In the present work, the effect of soldering temperature (270 and 298 °C) and substrate surface texture (0.02 and 1.12 ?m) on wetting characteristics and morphology of intermetallic compounds (IMCs) between Sn-0.7Cu lead-free solder on copper substrates was investigated. It was found that increase in temperature and substrate surface roughness improved the wettability of solder alloy. However, the effect of surface roughness on wettability was significant as compared to that of temperature. The spreading of solder alloy was uniform on smooth substrate, whereas spreading of the alloy on rough substrate resulted in an oval shape. The morphology of IMCs transformed from long needle shaped to short and thick protrusions of IMCs with increase in surface roughness of the substrate. Needle shaped and thick protruded intermetallics formed at the solder/Cu interface were identified as Cu 6Sn 5 compounds. The formation of Cu 3Sn IMC was observed only for the spreading of solder alloy at 298 °C which contributed to improvement in the wettability of solder alloy on both smooth and rough substrate surfaces. © Springer Science+Business Media, LLC 2012.Item Heat Transfer and Deposition Strategies for Enhanced Mechanical Performance of Wire Arc Additively Manufactured SS316L Alloy(Springer, 2025) Pai, K.R.; Vijayan, V.; Samuel, A.; Prabhu, K.N.The work investigates the effect of various deposition strategies for wire arc additive manufacturing of SS316L on an SS304 substrate for industrial applications. Droplet deposition of SS316L on an SS304 substrate at varying current values (60–130 A) identifies the operational range for line deposition. The wettability, contact angle and spread area are evaluated along with heat flux transients for each current value. Heat flow calculated during line deposition at 90 A for horizontal and vertical substrates was 34297 kJ/m2 and 24137 kJ/m2 respectively. The corresponding values of porosity and micro-hardness indicate superior deposition at 90 A. Further investigation on deposition strategies such as interlayer current change with and without dwell time, deposition at 90 A with a dwell time of 30 s for five cycles, preheated substrates and Continuous Multi-Pass Deposition with 2 s is explored. Heat flux transients are computed for every deposition cycle using an inverse solver. Heat flow was found to be 63260 kJ/m2 and 58863 kJ/m2 for the 15th layer of interlayer current change of 90 ± 10 A and constant current of 90 A with dwell time respectively. By altering deposition parameters such as interlayer time gap and current the chromium content achieved through high-current density deposition significantly increased from 17.2% to 26% and 25.4% respectively. The ultimate tensile strength for the 80A sample without deposition strategies was found to be lower. Columnar grain morphology with dendritic structure was observed at higher currents. Finer equiaxed grains with lower interlayer fusion were observed at lower currents. Finer grain growth across the layers was achieved by adjusting the current between cycles in response to observed heat flux transients. EBSD analysis reveals the formation of brass texture with {110} in deposition strategies involving time gap and interlayer current change, indicating directional solidification thereby enhancing the overall mechanical performance of the as-deposited SS316L. © ASM International 2025.