**4. Numerical modeling of laser surface treatment processes**

Since LST processes are highly nonlinear processes, hence for clear understanding of the process, numerical modeling is essential [45]. Besides laser beam interaction with the substrate, LC and LSA impose additional constraints of clad and alloying materials that may be supplied in the form of preplaced powder or through powder feeder. In case powder is supplied through powder feeder, then the study of powder flow dynamics becomes important. Hence, LC and LSA processes can be broken in three stages: powder stream dynamics, melt pool region, and quality variables. Experimental study of laser surface treatments is not sufficient to understand complex phenomena such as powder stream pattern, laser and substrate interaction, heat transfer mode, and melt pool behavior. Hence, analytical models and numerical simulations have been developed. Some of the brief advancements and understandings in these areas are presented.

#### **4.1 Powder stream dynamics**

Powder stream dynamics is a significant area in the blown powder technique because we can predict powder stream characteristics such as motion, flow profile, powder with laser system interaction, etc. These parameters may be further used in optimization of parameters and calculate powder efficiency. The behavior of powder flow is governed by the type of nozzle employed. The turbulent flow of carrier gas can be assumed to be a continuum; hence Navier-Stokes equations can be used. A dispersed powder in carrier gas is generally solved using the Lagrangian equation [46]. During powder–laser interaction, attenuation of laser energy takes place due to absorption, reflection, radiation, beam scattering, and ricocheting of powder particles. Models based on particle attenuation [47], ray tracing [48], resolution [49], and light propulsion force model [50] have been reported to predict the behavior of attenuated laser energy fairly. Finally, powder substrate interaction depends on the standoff distance. For high convergence the substrate should lie at the focus of the nozzle [51].

#### **4.2 Melt pool**

The substrate melts due to absorption of remaining incident laser energy. The focuses of interest in this region are heat transfer, geometry of melt pool, fluid flow velocity, cooling rate, and solidification rate. These variables have been calculated using kinetic approach [52], volume method [53], and finite element method [54, 55]. Usually commercial multi-physics platforms such as ANSYS, COMSOL, FLUENT, and ABAQUS are employed for the problem.

#### **4.3 Quality variables**

The simulation of desirable properties is usually done in combination with developed thermal model. Phase transformation models along with thermal models provide base for the measurement of quality variables. Diffusion and diffusion-less phase transformations may occur in different material systems. Diffusion phase transformations have been modeled using the Johnson-Mehl-Avrami equation,

**247**

**Table 2.**

*Laser Surface Treatment*

**5. LST applications**

CMSX-4 (Ni-based super alloy)

Stellite-6/WC on B27 boron steel

NI40 and NI60 on C60 steel

CPM9V steel on H13 tool steel

Grade C wheel U75V rail with 316L, 420, 410

Mg-Zn-Dy alloy casted and laser melted

Powdered Co29Cr9W3Cu alloy

Ti powder on Ti6Al4V substrate

*Some applications of LST.*

Titanium hydroxylapatite on

Nitinol

*DOI: http://dx.doi.org/10.5772/intechopen.91800*

equations with phase transformation equations [60, 61].

Repair of tools for soil

Improvement of barrelscrew system in plastic injection molding

Repair of molds and dies used in hot and cold working

Repair of damaged railway wheels

Coating on Nitinol implants to restrict nickel release

Restrict in vitro degradation and improve tissue integration

Improve in vitro biocompatibility capacity of the titanium deposits to be used as medical implants

SLM is used to develop Co29Cr9W3Cu alloy joint prostheses

cultivation

while diffusion-less phase transformations are modeled using the Koinstinen Marburguer equation [56, 57]. Hardness measurement of a treated surface has been predicted by coupling thermo-kinetic relation and thermal model [58, 59]. Residual stresses develop in laser-treated parts; these lead to crack and distortion. The finite element method has been used to solve coupled elastic, plastic, and thermal strain

LST has a wide application in aerospace, automobile, medical, nuclear, oil recovery, and refinery industries [62–66]. Aluminum and its alloys are widely used in aerospace industry; they have been efficiently clad with other novel metals to improve their surface properties [67]. Stainless steel is used in automobile and household applications [68, 69]. Titanium and its alloys are used in the medical sector [70]. LC on Ti6Al4V has been studied frequently to improve its surface properties [71].

**Materials Application Improvement Author, year**

Repair of turbine blades This method helped to

CMSX-4

develop monocrystalline

Formation of intermetallic compounds improved the wear resistance

Ni-Cr alloy clad improved the microhardness

Presence of compressive stress due to formation of martensite phase

The wear rates decrease with increased hardness of the clad materials

Modulus of elasticity of coated samples falls in the range of 6–30 GPa which is similar to the natural bone

Improvement in in vitro degradation due to formation of insoluble protective layer

Initiation of crack is arrested due to plastic deformation caused by strain-induced martensitic

In vitro test of samples in Hank's solution shows that the leaching was within the desired values

transformation

Rottwinkel, 2016 [73]

Bartkowski, 2016 [74]

Zarini, 2014 [75]

Paul, 2017 [76]

Zhu, 2019 [77]

Chakraborty, 2019 [78]

Rakesh, 2019 [79]

Lu, 2019 [80]

Nyoni, 2016 [81]

while diffusion-less phase transformations are modeled using the Koinstinen Marburguer equation [56, 57]. Hardness measurement of a treated surface has been predicted by coupling thermo-kinetic relation and thermal model [58, 59]. Residual stresses develop in laser-treated parts; these lead to crack and distortion. The finite element method has been used to solve coupled elastic, plastic, and thermal strain equations with phase transformation equations [60, 61].
