**5. Laser cladding (LC)**

*Practical Applications of Laser Ablation*

used in the alloying process. The experimental result found that the LSA has been performed to form a defect free and uniform alloy zone. Compared to hardness of substrate, laser alloying produces the higher hardness due to the grain refinement [24]. The laser surface alloying is carried out on nodular cast iron by adding Ni-20%Cr alloy [20]. The laser parameters, power of 1.5 kW, scan speed of

600 mm/min, overlapping of 30% and defocus of 15 mm and argon gas are used to alloying the NCI surface. The microstructure of the laser alloyed specimen, worn out surface of substrate and laser alloyed specimen is shown in **Figure 18a**–**c** respectively. The ledeburite and pre-eutectic austenite are observed in the LSA surface. In addition, γ-phase (austenite) to M-phase (martensite) is transformation observed. The laser alloyed surface has produced the defect free and fine microstructure. The γ-phase has a higher percentage of Ni than cementite, whereas the Fe3C phase has Cr more and Ni less element. Hence, the presence of Fe3C on the laser-alloyed surface is rich in Cr and the γ-phase was supported through the solid solution of both alloy powders of Ni and Cr. The rapid solidification is the reason for obtaining the fine microstructure in the laser alloyed surface. The laser processed worn out surfaces have severe plastic deformation, wear track, delamination, grooves and adhesive particles. The NiCr alloying is also observed by using the LSA. The length of depth of hardness is increased by increasing the melted depth. The reasons are due to the refinement of grains through rapid re-solidification. The rate of cooling rate and thermal gradient also support the refinement of grains resulting in increased the hardness of the laser treated zone. Compared to hardness of substrate material, the laser processed depth has 2.62 time higher hardness due to the uniform grain structure. The wear loss is calculated for laser processed sample and untreated

*Microstructure of LSA specimen (a), worn out surface of substrate (b), and worn out substrate of LSA (c).*

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**Figure 18.**

Laser cladding is similar to arc welding. The laser is used to melt the clad material coated on the substrate. The powder, wire and strip form of clad materials are commercially available to perform by different laser processes. The major benefits of LC have low porosity, good surface uniformity and low dilution. The clad materials have rapid quench and cooling down after deposition resulted in a fine grained microstructure. The laser is used to deposit clad material on substrate through the interaction of powder with laser. The substrate permits the melt pool to solidify and form the solid track. The schematic of laser cladding process is shown in **Figure 19**. Compared to other different surface processing used to enhance the wear and corrosion resistance of substrate, LC is an attractive alternative method. This is due to the intrinsic properties of laser radiation. The LC benefits are high input energy, low distortion, and minimum dilutions observed between the substrate, processing flexibility and cladding on small areas. The LC can be used in surface alloys and composites in order to achieve the required properties. The LC produces desired properties are obtained by varying the process parameters such as laser beam power density, laser beam diameter at the workpiece surface and laser beam travel speed.

The laser solution strengthening, laser surface alloying and laser cladding have highly correlation to corrosion and erosion resistance. The laser solution strengthening and laser surface alloying are used to improve the erosion and corrosion resistance of old components without changing their sizes whereas laser cladding is used to repair wasted components by restoring their size. The high entropy alloy of CoCrFeNiNbx is coated to a pure titanium sheet by using laser cladding to study the hardness of the material. The laser cladding parameters such as power of 100 W, scanning speed of 8 mm/s, defocusing amount of +2 mm, pulse duration of 5 ms,

**Figure 19.** *Schematic of laser cladding process.*

frequency of 20 Hz, beam diameter of 1 mm power density of 127.4 W/mm2 and linear energy density of 12.5 J/mm are used in this process. The result found that the CoCrFeNiNbx HEA coated on titanium sheet produces higher hardness compared to the pure titanium. The Nb coating produces significant improvement in hardness compared to pure titanium due to the consisted phase of BCC solid solution with equiaxed bulk grain morphology and Cr2Ti Laves phase [25]. A comparison is performed between the thermal spray coating and laser cladding performance on steel. The laser cladding conditions, power of 780 W, cladding speed of 4.3 mm/s, powder feed rate of 6 g/min and argon gas are used. The thermal spray conditions, distance of 200 mm, acetylene (0.7 bar) and oxygen (4 bar) gas are used. The Metco 15E powder is used in both the processes. The result found that the cladded layer produced the high hardness, crack free, and good adherence to substrate whereas flame coating produces high porosity, minimum dilution and oxides inclusions [26]. The Inconel 625 coating performance on steel is evaluated by arc welding and laser cladding based on the microstructure, wear resistance and hardness. The parameters, power of 1200 W, scan speed of 2 mm/s, powder feed rate of 5 g/min, shielding gas flow rate of 5 L/min and powder feeding gas flow rate of 8 L/min are used. The result found that the arc welded and laser cladded Inconel 625 coatings have Ni (fcc) solid solution phase, and fine microstructure. The arc welded coating to Inconel 625 is produced slightly lower hardness compared to laser cladding coating. This is due to the microstructure developed in the arc welding. The laser cladded Inconel 625 coating is preferred due to its better mechanical performance such as hardness and wear resistance at both room and elevated temperature [27]. The 316 stainless steel powders coated on EN3 mild steel is to evaluate clad geometry and distribution of elements by laser cladding. The 2 kW continuous wave CO2 with laser power 1.8 kW, beam spot diameter 2–5 mm, powder feed rate 0.160–0.220 g/s, substrate traverse speed 7–40 mm/s are used. The stainless steel powder coating provides the sound coating and no porosity [28]. The Fe-Cr-Si-B alloy powder coating is performed on low carbon steel using laser cladding to evaluate the microstructure, hardness, wear resistance and corrosion resistance. The result identified that the Fe-Cr-Si-B alloy powder coating provides higher wear resistance, high hardness and high corrosion resistance compared to substrate [29]. The CPM 15 V, CPM 10 V, CPM 9 V, D2 and M4 coatings are provided on AISI 1070 carbon steel by laser cladding. The laser cladding conditions, power varying from 2.5–2.75 W, laser beam diameter varying from 2 mm, substrate traverse speed varying from 7.6–8.6 mm/s, powder feed rate varying from 20 to 9 g/min and overlap varying from 30 to 50% are used in the process. The abrasive wear resistance of the laser-clad CPM 15 V and CPM 10 V coatings is superior performance than D2 steel, whereas the wear resistance of the CPM 9 V and M4 coatings is inferior to that of the D2 [30].

**Figure 20a** shows the microstructure of Colmonoy 6 cladding on Inconel 625 [31]. The laser cladding parameters are 400 mm/min speed, feed rate of 4 g/min, power of 1000 W, argon pressure of 1 bar with flow rate of 25 lpm and 150 degrees preheating used in this process. The clad surfaces have no defects, uniform dendrite eutectic phases observed. There are two regions represented in the cladded surface such as darker region for boride content and lighter region for γ-nickel. The high quantity of intermetallic lave phase is observed in the cladded surface. **Figure 20b** shows the worn out surface of substrate Inconel 625. Compared to wear intensity of sample, laser cladded surfaces have lesser wear. The plow marks are also observed in the worn out surface substrate due to the less wear resistance and high plastic deformation. The higher material removal rate of the sample is observed than the cladded surface. **Figure 20c** shows the laser cladded worn out surface. The few debris particles, few depth of wear track and few grooves are observed in the cladded surface. This is due to the high hardness of the clad layer. Therefore, better

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*Laser Surface Modification of Materials DOI: http://dx.doi.org/10.5772/intechopen.94439*

due to weak intermetallic phases.

**Figure 20.**

*cladding (c).*

tance when compared to clad surface.

**6. Laser texturing**

protection is provided by the clad layer over the untreated surface. The more hardness is observed in the clad surface than the base metal. The reasons for increasing the hardness of clad surface is due to the defect free cladding, proper fusion and laves phase presented. The reason for decreasing the hardness of base material is

*Microstructure of Colmonoy 6 clad (a), worn out surface of substrate (b) and worn out surface of laser* 

The coefficient of friction (CoF) and wear behavior of coated and substrate found that the CoF is increased with increased sliding distance due to the reduced adhesion resistance and increasing heat between points of contact. The more CoF is observed in the substrate sample than clad sample due to the adhesion effect. The less CoF is observed in the clad sample due to the hard laves phases. It is found that low mass loss is observed in the clad sample compared to base material. The wear loss is highly related to the hardness and base material produces poor wear resis-

Laser texturing is a process that alters a material surface property by modifying its texture and roughness. The laser beam creates micro patterns on the surface through laser ablation, removing layers with micrometer precision and perfect repeatability. Typical patterns include dimples, grooves, and free forms. Laser surface texturing can be used to improve properties like adherence, wettability, electrical and thermal conductivity, and friction. For example, the method can increase surface adherence before applying common coatings like adhesives, paint or ceramic. Laser texturing can also be used to prepare surfaces for thermal spray coating and laser cladding as well as to improve the performance of mechanical seals. Surface treatments like abrasive blasting and chemical etching processes need *Laser Surface Modification of Materials DOI: http://dx.doi.org/10.5772/intechopen.94439*

**Figure 20.**

*Practical Applications of Laser Ablation*

and M4 coatings is inferior to that of the D2 [30].

**Figure 20a** shows the microstructure of Colmonoy 6 cladding on Inconel 625 [31]. The laser cladding parameters are 400 mm/min speed, feed rate of 4 g/min, power of 1000 W, argon pressure of 1 bar with flow rate of 25 lpm and 150 degrees preheating used in this process. The clad surfaces have no defects, uniform dendrite eutectic phases observed. There are two regions represented in the cladded surface such as darker region for boride content and lighter region for γ-nickel. The high quantity of intermetallic lave phase is observed in the cladded surface. **Figure 20b** shows the worn out surface of substrate Inconel 625. Compared to wear intensity of sample, laser cladded surfaces have lesser wear. The plow marks are also observed in the worn out surface substrate due to the less wear resistance and high plastic deformation. The higher material removal rate of the sample is observed than the cladded surface. **Figure 20c** shows the laser cladded worn out surface. The few debris particles, few depth of wear track and few grooves are observed in the cladded surface. This is due to the high hardness of the clad layer. Therefore, better

frequency of 20 Hz, beam diameter of 1 mm power density of 127.4 W/mm2

linear energy density of 12.5 J/mm are used in this process. The result found that the CoCrFeNiNbx HEA coated on titanium sheet produces higher hardness compared to the pure titanium. The Nb coating produces significant improvement in hardness compared to pure titanium due to the consisted phase of BCC solid solution with equiaxed bulk grain morphology and Cr2Ti Laves phase [25]. A comparison is performed between the thermal spray coating and laser cladding performance on steel. The laser cladding conditions, power of 780 W, cladding speed of 4.3 mm/s, powder feed rate of 6 g/min and argon gas are used. The thermal spray conditions, distance of 200 mm, acetylene (0.7 bar) and oxygen (4 bar) gas are used. The Metco 15E powder is used in both the processes. The result found that the cladded layer produced the high hardness, crack free, and good adherence to substrate whereas flame coating produces high porosity, minimum dilution and oxides inclusions [26]. The Inconel 625 coating performance on steel is evaluated by arc welding and laser cladding based on the microstructure, wear resistance and hardness. The parameters, power of 1200 W, scan speed of 2 mm/s, powder feed rate of 5 g/min, shielding gas flow rate of 5 L/min and powder feeding gas flow rate of 8 L/min are used. The result found that the arc welded and laser cladded Inconel 625 coatings have Ni (fcc) solid solution phase, and fine microstructure. The arc welded coating to Inconel 625 is produced slightly lower hardness compared to laser cladding coating. This is due to the microstructure developed in the arc welding. The laser cladded Inconel 625 coating is preferred due to its better mechanical performance such as hardness and wear resistance at both room and elevated temperature [27]. The 316 stainless steel powders coated on EN3 mild steel is to evaluate clad geometry and distribution of elements by laser cladding. The 2 kW continuous wave CO2 with laser power 1.8 kW, beam spot diameter 2–5 mm, powder feed rate 0.160–0.220 g/s, substrate traverse speed 7–40 mm/s are used. The stainless steel powder coating provides the sound coating and no porosity [28]. The Fe-Cr-Si-B alloy powder coating is performed on low carbon steel using laser cladding to evaluate the microstructure, hardness, wear resistance and corrosion resistance. The result identified that the Fe-Cr-Si-B alloy powder coating provides higher wear resistance, high hardness and high corrosion resistance compared to substrate [29]. The CPM 15 V, CPM 10 V, CPM 9 V, D2 and M4 coatings are provided on AISI 1070 carbon steel by laser cladding. The laser cladding conditions, power varying from 2.5–2.75 W, laser beam diameter varying from 2 mm, substrate traverse speed varying from 7.6–8.6 mm/s, powder feed rate varying from 20 to 9 g/min and overlap varying from 30 to 50% are used in the process. The abrasive wear resistance of the laser-clad CPM 15 V and CPM 10 V coatings is superior performance than D2 steel, whereas the wear resistance of the CPM 9 V

and

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*Microstructure of Colmonoy 6 clad (a), worn out surface of substrate (b) and worn out surface of laser cladding (c).*

protection is provided by the clad layer over the untreated surface. The more hardness is observed in the clad surface than the base metal. The reasons for increasing the hardness of clad surface is due to the defect free cladding, proper fusion and laves phase presented. The reason for decreasing the hardness of base material is due to weak intermetallic phases.

The coefficient of friction (CoF) and wear behavior of coated and substrate found that the CoF is increased with increased sliding distance due to the reduced adhesion resistance and increasing heat between points of contact. The more CoF is observed in the substrate sample than clad sample due to the adhesion effect. The less CoF is observed in the clad sample due to the hard laves phases. It is found that low mass loss is observed in the clad sample compared to base material. The wear loss is highly related to the hardness and base material produces poor wear resistance when compared to clad surface.
