Development of process maps based on molten pool thermal history during laser cladding of Inconel 718/TiC metal matrix composite coatings

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. © 2020 Elsevier B.V

Development of a Water-Jet Assisted Underwater Laser Cutting Process

We present the development of a new underwater laser cutting process in which a water-jet has been used along with the laser beam to remove the molten material through kerf. The conventional underwater laser cutting usually utilizes a high pressure gas jet along with laser beam to create a dry condition in the cutting zone and also to eject out the molten material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere while cutting radioactive components like burnt nuclear fuel. The water-jet assisted underwater laser cutting process produces much less turbulence and aerosols in the atmosphere. Some amount of water vapor bubbles is formed at the laser-metal-water interface; however, they tend to condense as they rise up through the surrounding water. We present the design and development of a water-jet assisted underwater laser cutting head and the parametric study of the cutting of AISI 304 stainless steel sheets with a 2 kW CW fiber laser. The cutting performance is similar to that of the gas assist laser cutting; however, the process efficiency is reduced due to heat convection by water-jet and laser beam scattering by vapor. This process may be attractive for underwater cutting of nuclear reactor components

Effect of Water-jet on Laser Paint Removal Behaviour

AbstractThe laser paint removal behaviour with water-jet assist laser has been investigated using Yb- fiber laser. The conventional laser paint removal process with gas-jet assist usually leaves behind traces of combustion product i.e. ashes on the surface. An additional post-processing such as light-brushing or wiping by some mechanical means is required to remove the residual ash. In order to strip out the paint completely from the surface in a single step, a hybrid laser process which utilizes a water-jet along with laser beam has been developed. A coaxial water-jet along with a high power fiber laser beam removed the paint and residual ashes very effectively. The specific energy, defined as the laser energy required removing a unit volume of paint was found to be marginally higher than that for the gas-jet assisted laser paint removal process. However, complete paint removal was achieved with the water-jet assist only