**2. Selection of laser**

Many aspects are considered during selection of laser for LST processes. Some of the desirable characteristics are presented in the flow chart shown in **Figure 1**. The material to be processed is one of the factors for selection of laser type. Heatsensitive materials and refractory materials are generally processed in pulsed mode [10–15]. It is also observed that the solidified structure of developed materials may be different in the case of continuous and pulse laser modes [16]. **Figure 2** shows

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**Figure 2.**

**Figure 1.**

*Constraints considered in selection of laser source type.*

*Reflectance of substrate vs wavelength of radiation for some materials [20].*

*Laser Surface Treatment*

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

the relationship between reflectivity of a material and wavelength of radiation [17]. Materials such as aluminum which have very low absorptivity are usually processed with low wavelength pulses [18]. Besides, these desirable properties also signifi-

cantly affect the selection of laser for a particular application [19].

*Engineering Steels and High Entropy-Alloys*

*Characteristics of different techniques.*

**Table 1.**

components. There are wide varieties of surface modification techniques available. Some of these techniques are thermochemical coatings (nitriding, carburizing, cyaniding, etc.), electrodeposition, electroless deposition, spray coatings (flame spray, thermal spray coating, plasma spray coating, etc.), physical vapor deposition (PVD), chemical vapor deposition (CVD), laser surface modification (LSM), etc. These diverse techniques mutually form a branch termed as surface engineering. All these surface modification techniques have certain advantages and disadvantages. **Table 1** lists some of the desirable attributes and corresponding behavior observed with different processes. For precision coatings of thermally sensitive and multicomponent materials, usually laser material processing is employed. Due to its localized heating and rapid solidification rates, thermal distortion and segregation possibilities are diminished. Also, high energy density leads to melting of almost any metal [9]. High-energy-density laser beam produces high dilution and good bonding strength, and very low heat-affected zone can be developed. Other techniques usually suffer in one or the other reasons. Also, high repeatability and

**Attributes LSA Electrodeposition Thermal spray CVD PVD** Dilution High Nil High Nil Nil Bonding strength High Low Moderate Low Low Heat-affected zone Low Nil High Low Low Coating thickness Moderate Moderate High Low Low Repeatability High Low Moderate High High Controllability High Low Moderate High High

controllability makes it a suitable technique for industrial standards.

simulation and application of these techniques have been discussed.

With the development in the automation sector, lasers having high accuracy and precision are available. Thus, in the last decade, a large number of literature dealing with application of lasers in various fields are available. These lasers may also be used to develop layer by layer lamina to develop a desired 3D structure. Laser-based techniques employed in 3D printing are selective laser melting and sintering. A part program of the 2D structure to be manufactured is developed. These 2D structures of the same or varying sections are developed above one another. These adjacent layers join together and form a required 3D structure. Hence, laser printing is very similar to surface treatment processes. This chapter in particular presents the ongoing trends of laser surface treatments in melt regime, i.e., it discusses techniques such as laser surface alloying, laser cladding (LC), selective laser melting, and laser glazing. Although the basis of these techniques is same, these techniques differ from one another in the desirability of final surface properties achieved. Numerical

Many aspects are considered during selection of laser for LST processes. Some of the desirable characteristics are presented in the flow chart shown in **Figure 1**. The material to be processed is one of the factors for selection of laser type. Heatsensitive materials and refractory materials are generally processed in pulsed mode [10–15]. It is also observed that the solidified structure of developed materials may be different in the case of continuous and pulse laser modes [16]. **Figure 2** shows

**240**

**2. Selection of laser**

the relationship between reflectivity of a material and wavelength of radiation [17]. Materials such as aluminum which have very low absorptivity are usually processed with low wavelength pulses [18]. Besides, these desirable properties also significantly affect the selection of laser for a particular application [19].

#### **Figure 1.**

*Constraints considered in selection of laser source type.*

**Figure 2.** *Reflectance of substrate vs wavelength of radiation for some materials [20].*

The type of process also affects the selection of laser. Generally surface alloying requires a large amount of heat to melt considerable amount of substrate surface. Thus high-energy lasers are required. Glazing and sintering usually employ lowenergy lasers, whereas cladding uses intermediate-energy lasers.
