In the present study, laser cladding of Inconel 718/TiC metal matrix composite coating on SS 304 was carried out using a 2 kW Yb-Fiber laser by preplaced and blown powder method. The molten pool ...thermal history during the deposition process was monitored using an IR pyrometer and correlated with the evolution of microstructure. The effect of various process parameters, viz. laser power ‘P’ (400 W – 1200 W), scanning speed ‘V’ (200 mm/min to 1400 mm/min) and powder feeding rate (8 g/min – 20 g/min) on the molten pool lifetime and cooling rate is investigated. Molten pool lifetime increased and cooling rate decreased with the decrease of scanning speed and increase of laser power. However, scanning speed had dominant effect on the molten pool lifetime and cooling rate compared to laser power. Moderate molten pool lifetime resulted in the formation of shell-core structure between Inconel 718 matrix and TiC particles. The longer molten pool lifetime (>0.45 s) resulted in complete decomposition of TiC particles rendering brittleness to the coating. The feasibility of detecting TiC particle decomposition in Inconel 718 matrix from the recorded thermal cycles based on multiple solidification shelfs is discussed. At the end, a process map based on a combined process parameter, PD/V2 (spot diameter D) and molten pool lifetime (τ) was developed. An optimum range of molten pool lifetime i.e. 0.25 s < τ ≤ 0.45 s was found to result in a good quality of coating with the formation of shell-core structure both in case of preplaced and blown powder laser cladding method.
•Laser cladding of Inconel 718/TiC MMC coating is carried out.•Influence of process parameters on molten pool thermal history is reported.•Decomposition of ceramic particles is correlated with molten pool lifetime.•Process map based on the molten pool lifetime is developed.•Reproducibility and repeatability of results with respect to molten pool lifetime is reported.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mild steel substrates were coated with commercially available alumina and chromia powders using the powder flame spraying process. The top layers of the flame sprayed coatings were remelted using a ...2 kW fiber laser. Thermo-cycles of the laser remelting process were monitored on-line using an infrared pyrometer. Cooling rates were varied using different laser scanning speeds. Surface morphology, microstructure and phases of the laser treated and as-sprayed coatings were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction and X-ray tomography. Surface residual stress of the as-sprayed and laser treated coatings was measured using X-ray diffraction. The inherent defects like porosity and inter-lamellar boundary diminish to a great extent upon laser remelting. Surface residual stress of the remelted coatings tends to increase with increase in cooling rate. Surface crack density of the laser treated coating was reduced appreciably when coatings were preheated prior to laser remelting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Surface properties play a critical role in the structural integrity of any component and this becomes even more critical for weld joints. Laser shock peening (LSP) is one of the non-contact methods ...which is getting popular in industries to enhance surface properties for improving service life, mainly fatigue of engineering components. In the present study, electron beam welding (EBW) of commercially pure (cp) titanium was carried out at constant line energy with varying scan speeds ranging from 1000 to 1600 mm/min and welding currents from 25 to 40 mA. The influence of the EBW parameters on microstructure, surface micro-hardness, tensile, and fatigue strength was investigated. The effect of LSP on mechanical and corrosion properties of EBW cp titanium was studied. LSP induced a significant amount of compressive residual stresses at the surface through plastic deformation and led to significant improvement in micro-hardness (7–10%) at the sub-surface region of the fusion zone due to finer grain structure. Further, appreciable enhancement in tensile strength (~ 15%) and fatigue life (~ 43%) due to strain hardening and changes in microstructure like twinning within grains was realized.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The study is aimed to analyse the comparative behaviour of the high-temperature abrasive wear of H13 steel surfaces modified by laser melting and cladding with Stellite 6 and Stellite 6 + 30 wt% WC. ...3-body abrasive tests were conducted at room temperature, 450 °C, 550 °C, and 650 °C. The microstructural evolution, microhardness, wear surface morphology and mechanisms, and various phases formed during laser surface modifications were also studied. The laser remelting of H13 steel surface increased its room temperature microhardness to 750 ± 35 HV0.01, whereas laser cladding of Stellite 6 powder yielded hardness of around 600 ± 20 HV0.01 in the clad layer; and Stellite 6/WC composite clad layer had marginally higher hardness than the Stellite 6 clad layer in the matrix and much higher hardness of ~3000 HV0.01 at the sporadically distributed WC particle sites. Though the room temperature microhardness of laser remelted H13 surface is the highest, the volumetric wear loss in it was comparable to that of the Stellite 6 cladding. However, Stellite 6/WC composite layer recorded a relatively less volumetric loss as WC particles resisted the abrasive wear. With increasing temperature, the wear loss in laser remelt surfaces increased at a fast rate, while that in Stellite 6 and composite clad layers varied marginally with no definite trend. Overall, Stellite 6/WC composite cladding performed better than others in the current temperature range.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Significance of the molten pool thermal history in mitigation of cracks and improving the surface properties during laser surface alloying of AISI 1020 steel with in-situ synthesized TiN has been ...investigated. The molten pool thermo-cycle was monitored using an IR pyrometer and from this heating and cooling rates and molten pool lifetime were estimated for different process parameters. Good correlation was found between the molten pool lifetime and the evolved microstructure and mechanical properties. Molten pool lifetime was found to have an optimum range for crack-free alloyed layer formation with maximum volume fraction of TiN in the matrix that could provide improved hardness and wear resistance. Molten pool lifetime below this range resulted in Fe-Ti intermetallics formation and micro-cracks while the above resulted in heavy dilution resulting in a relatively low volume fraction of Ti in Fe and overall TiN content, both of which found to deteriorate the hardness and wear characteristics of the coating. Based on the results, a process map with molten pool lifetime as a function of a combined process parameter, Pd/V2, is developed, where P, d and V respectively are laser power, beam diameter and scan speed.
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•Effects of process parameters on laser surface alloying of AISI 1020 steel with in-situ synthesised TiN is reported.•Peak surface temperature, heating and cooling rates and molten pool lifetime during laser surface alloying are reported.•Influence of molten pool lifetime on crack mitigation, formation of TiN and mechanical properties was reported.•Process map with respect to a combined parameter and molten pool lifetime is established.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Online monitoring of thermal history during laser cladding of Inconel 718/TiC metal matrix composite (MMC) produced by in-situ process was carried out. Effects of weight percentage of Ti+C and ...process parameters on the thermal history, and its correlation with the evolution of microstructure were studied. Further, changes in the evolution of microstructure and excessive dilution were identified online by monitoring various features of the thermo-cycle profile, i.e. occurrence of undercooling with change in microstructure from dispersed fine particles to dendritic structure caused by assembling of floating TiC particles at slow cooling, molten pool lifetime and shift in solidification shelf location because of compositional changes caused by excessive dilution. Coating with dispersed fine TiC particles exhibited high hardness and good wear characteristics compared to the one with dendritic structure. Further, dendritic growth of TiC particles resulted in embrittlement of the coating. Cladding was also carried out in laser power modulated mode to enhance the cooling rate, thereby refining the microstructure. Identification of optimum parameters through real-time monitoring of molten pool thermal history and its physical state (liquid/solid) during laser power modulation to ensure refinement of microstructure was studied. SEM and XRD analyses were carried out for analysing the microstructure and phases.
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•Thermal history in laser cladding of Inconel 718+ in-situ TiC was studied.•Changes in microstructure were identified from the recorded thermo-cycle.•Influence of microstructure on mechanical properties was studied.•Excess dilution was identified by the shift in solidification shelf location.•Effect of laser pulsing on microstructure was also studied.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Real-time monitoring of bending mechanism in multi-scan laser forming was investigated.•Effect of laser modulation on bending mechanism was investigated.•Influence of heat accumulation and strain ...hardening on bending angles is reported.•Transition in bending mechanism due to heat accumulation is investigated.
Laser forming is a non-contact type process used for bending, spatial forming, and alignment of metallic components through a controlled application of laser energy. The process involves localized rapid heating and cooling, inducing thermal strains exceeding the elastic strain of the material resulting in plastic deformation. The process is broadly governed by the temperature gradient mechanism (TGM), buckling mechanism (BM), and upsetting mechanism (UM). However, in the case of multi-pass laser forming process, heat accumulation and variation in the flow stress because of consecutive thermal cycles and strain hardening due to multiple bending cycles makes the process highly complicated. While operating laser in modulated mode may be a wise choice to handle the heat accumulation, inter-pulse cooling cycles along with variation in peak and average power with change in duty cycle affects the bending mechanism and angle significantly. Therefore, in the present study, a real-time monitoring system was developed to investigate the bending mechanism for a multi-pass laser forming process carried out in laser modulated mode. Also, the effect of average power, peak power, heat accumulation, strain hardening on bending mechanism and bending angle were investigated. Keeping the peak power constant, variation in duty cycle from 100% to 40% resulted in reduced average energy and strain hardening was found to be dominant, decreasing bending angle per pass. On contrast, variation in duty cycle by keeping the average power constant resulted in heat accumulation dominating the bending mechanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Laser forming is an advanced metal forming technique that uses the energy from high-power laser to permanently deform the components by inducing localized thermal stresses. One of the major ...challenges in laser forming is attaining a targeted bending angle. Unlike the conventional processes, the targeted angle in the case of laser forming has to be achieved through multiple laser scans. However, due to strain hardening, heat accumulation and sheet thickening near the processing zone, the bending angle per scan keeps on varying, making it difficult to achieve the desired angle. In order to overcome these limitations as well as to automate the process, the current study aims to develop a real-time monitoring setup and investigate the bending mechanism based on real-time detection of temperature gradients and bending angle with the scan number. This was achieved through two non-contact type IR pyrometers, one focused on the top and the other on the bottom surface of the sheet being bent, monitoring the temperature gradient. Real-time bending of the sheet as the laser beam scans it was captured using a non-contact type displacement sensor. Further, the study investigates the effect of process parameters, i.e., laser power and scan speed, on the bending angle. Also, the effect of inter-pass delay and its effect on bending angle was investigated. Among laser power and scanning speed, laser power has a higher effect on the bending angle. Also, it was observed that higher-thickness sheets exhibit lesser bending angles due to higher section modulus. Further, inter-pass cooling is also found to affect the bending angle significantly as it mitigates the heat accumulation effect, thereby strain hardening dominating the bending angle achieved per pass leading to a reduced bending angle.
•Real-time monitoring of bending mechanism in multi-scan laser forming process•Real-time monitoring of temperature gradients and its influence in laser forming•Effect of heat accumulation and strain hardening on bending mechanism is investigated.•Efficacy of inter-pass delay in laser forming process is investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In the present study, laser cladding of Inconel 718/TiC metal matrix composite coating on SS 304 was carried out using a 2 kW Yb-Fiber laser by preplaced and blown powder method. The molten pool ...thermal history during the deposition process was monitored using an IR pyrometer and correlated with the evolution of microstructure. The effect of various process parameters, viz. laser power 'P' (400 W – 1200 W), scanning speed 'V' (200 mm/min to 1400 mm/min) and powder feeding rate (8 g/min – 20 g/min) on the molten pool lifetime and cooling rate is investigated. Molten pool lifetime increased and cooling rate decreased with the decrease of scanning speed and increase of laser power. However, scanning speed had dominant effect on the molten pool lifetime and cooling rate compared to laser power. Moderate molten pool lifetime resulted in the formation of shell-core structure between Inconel 718 matrix and TiC particles. The longer molten pool lifetime (>0.45 s) resulted in complete decomposition of TiC particles rendering brittleness to the coating. The feasibility of detecting TiC particle decomposition in Inconel 718 matrix from the recorded thermal cycles based on multiple solidification shelfs is discussed. At the end, a process map based on a combined process parameter, PD/V2 (spot diameter D) and molten pool lifetime (τ) was developed. An optimum range of molten pool lifetime i.e. 0.25 s < τ ≤ 0.45 s was found to result in a good quality of coating with the formation of shell-core structure both in case of preplaced and blown powder laser cladding method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Pre-placed powder laser cladding is one of the simplest laser-based deposition techniques, having high material usage efficiency and capable to provide sound clad quality. However, the quality along ...with the geometrical aspects of the deposited layer depends on various energy transfer mechanisms controlled by process parameters. Energy transfer phenomena include the partial absorption of the laser radiation by metal powder layer, melting of the powder layer and transmission of energy to the substrate, along with the losses, like convective heat transfer to the atmosphere and conductive heat transfer to the bulk material. Theses phenomena all together defines the molten pool temperature, which needs to be analyzed to control the geometrical features of the clad and dilution by optimizing the process parameters. Therefore, a lumped parametric analytical model has been formulated and presented in this work for the pre-placed laser cladding process considering energy transfer and loss mechanisms along with the surface tension phenomena of the molten material to predict the molten pool temperature, clad geometry and substrate dilution. The developed model is validated using the experimental results of molten pool temperature of the clad layer, clad width and height as well as the percentage dilution. A continuous mode Yb-Fiber laser system with maximum available laser power of 220 W is used for the deposition of Inconel 625 powder on AISI 304 stainless steel substrate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
