Analysis of the laser-cladding process for stellite on steel

Abstract

Laser-cladding experiments have been performed with STELLITE 6 powder on mild steel substrates, using a 1.5 kW linearly polarized continuous wave CO 2 laser as a heat source. The clad height, the mass efficiency, the dimensions of the melt pool, as well as the global absorptivity, were measured as functions of the powder feed rate and the scanning speed. A quantitative analytical model of the process is proposed, based on the overall mass and energy balance. It allows the calculation of the mass efficiency and of the global absorptivity, taking into account the incorporation of the powder into the melt pool as well as the energy absorbed by the powder jet and the substrate. It successfully explains the experimental results and demonstrates the role played by the melt pool inclination with respect to the substrate. A processing diagram is given to find rapidly the optimal laser treatment conditions and the desired clad height. It is discussed with respect to the other limiting conditions of the process, the geometrical maximum powder efficiency, the porosity, the dilution, and the maximum power of the laser installation.

An overview of Direct Laser Deposition for additive manufacturing; Part I: Transport phenomena, modeling and diagnostics

“…For example, maximum/peak temperatures within a melt pool of AISI 316 SS can be around 2300 K which is about 40% above its melting temperature of 1673 K, while melt pool temperatures in single-line clads of Ni20 were found to have temperatures 30% higher than their liquids [33,115]. The powder injection contributes to the melt pool superheat [136], and M a n u s c r i p t increasing the powder feed rate will decrease the melt pool temperature [33]. In addition, the center-axis of the blown powder, or relative positioning of the powder nozzles to the center of the melt pool, will impact the melt pool temperature and its temperature profile [33].…”

Modeling of laser cladding with powder injection

“…Evaporation is not so dominant as in welding cases; however, it is still a significant phenomenon under laser cladding circumstances, especially under high laser power situations. The energy balance on the top free surface can be expressed as the following equation: [26] Here, the heat losses by convection and radiation are obtained through the following formulas:…”

“…The first term on the right-hand side in Eq. [26] therefore is given by [31] where P laser is the power of the laser beam, P atten is the power attenuated by the powder cloud, is the absorption coefficient of the substrate, r is the distance from the computational cell to the laser beam center, R is the radius of the laser beam spot, and the laser beam intensity is assumed to be the Gaussian distribution in this study.…”

“…Based on the experimental investigation, Frenk et al [26] suggested a practical equation to calculate the attenuated power in the situation of the side nozzle, which can be rewritten for the coaxial case as [32] Here, denotes the mass flow rate, l is the flight distance from the nozzle exit to the substrate, D p is the area diameter covered by the powder cloud, V p is the powder injection velocity, r is the radius of the powder particle, is powder density, and Q ext is the extinction coefficient. It is assumed that the extinction cross section is close to the actual geometrical cross section, and Q ext takes a value of unity.…”

Investigation into Heat Treatment and Residual Stress in Laser Clad AA7075 Powder on AA7075 Substrate

“…The composition of the powder can be the same as the substrate to rebuild a surface, or of a different composition to enhance the surface properties of a component. Typically, wear-resistant coatings [5] or corrosion-resistant coatings [6] are clad to enhance the surface characteristics. The process is complicated due to the interaction of many variables [7] including the laser power setting, the traversing speed, the amount of powder or wire being fed into the melt pool and the overlap distance between clad tracks.…”