# Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting

^{1}

^{2}

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## Abstract

**:**

^{7}of Ti6Al4V manufactured by DMLS was slightly better than that of Ti6Al4V manufactured by EBM, and the fatigue strength of both the DMLS and EBM specimens was improved by about two times through cavitation peening, compared with the as-built ones. An experimental formula to estimate fatigue strength from the mechanical properties of a surface was proposed.

## 1. Introduction

^{7}cycles was in the order of shot peening, HIP, tribofinishing, electropolishing, and as-built surfaces [46]. Thus, peening methods are some of most effective tools for improving the fatigue properties of AM Ti6Al4V.

## 2. Materials and Methods

#### 2.1. Titanium Alloy Manufactured by DMLS and EBM

#### 2.2. Cavitation Peening

^{−2}m

^{3}/min and injected into a chamber filled with water. The injection pressure was controlled by the rotational speed of the invertor motor of the plunger pump. When the high-speed water jet was injected into the chamber, cloud cavitation was generated inside the nozzle and/or in the shear layer around the jet. A submerged jet with a cavitation bubble is called a cavitating jet [70]. On the impinging surface, cloud cavitation became a ring vortex cavitation, then collapsed. Thus, the area treated by the fixed cavitating jet shows an annular shape [70], and the scanning cavitating jet can treat the surface uniformly [78]. In the present paper, the specimen, which was put in a recess to make a flat surface, was placed perpendicular to the jet in the chamber. The specimen was treated by scanning the nozzle, which moved horizontally at a constant speed v. The throat diameter of the nozzle was 2 mm. As the cavitator and the guide pipe can enhance the aggressive intensity of the cavitating jet [79], both of them were installed in the nozzle. The diameter of the cavitator was 3 mm, which was optimized in a previous study [79]. As the geometry of the outlet bore at the nozzle affects the aggressive intensity of the cavitating jet, the length L and the diameter D of the bore were optimized as L = 16 mm and D = 16 mm [80]. As the cavitating flow was separated at the upstream corner of the nozzle, the standoff distance s was defined by the distance from the upstream corner of the nozzle to the surface of the specimen. When the specimen is set too close to the nozzle, even though there is the cavitating jet, the specimen is treated by water jet peening, in which water columns peen the target. The classification map, in which cavitation peening and water jet peening were classified using the normalized standoff distance and cavitation number, was proposed [73]. The standoff distance chosen in the present experiment was s = 222 mm, which was the same in a previous report [13], and this was the cavitation peening condition.

_{p}is defined as follows.

_{p}= 10 s/mm, which was the same in a previous study [13], was used to compare the cavitation peening effect on Ti6Al4V manufactured by DMLS and EBM.

#### 2.3. Laser Peening

^{−3}m

^{3}/min to remove particles caused by the ablation. It should be noted that the water was degassed to minimize the cushion effect at the bubble collapse. The focal distance of the final convex lens was 100 mm. In order to minimize damage to the mirrors and lenses due to the reflection between the final convex lens and the chamber, the convex was placed as shown in Figure 3. In the present laser peening, the distances in air s

_{a}and in water s

_{w}were 84 mm and 19 mm, respectively, which was the same in a previous study [13]. In the present condition, the diameter of the laser spot on the specimen surface was about 0.8 mm. The specimen was placed on a stage, which was moved by linear stepping motors in the vertical and horizontal directions. The pulse density d

_{L}was controlled by the horizontal speed v

_{s}and the stepwise movement in the vertical direction s

_{v}using the stepping motors. As the repetition frequency was 10 Hz, d

_{L}was defined by Equation (2).

_{L}was set to 5 pulses/mm

^{2}, with n = 1, v

_{h}= 4.46 mm/s, and s

_{v}= 0.448 mm, which were the same in a previous study [13], to compare the laser peening effect on Ti6Al4V manufactured by DMLS and EBM.

#### 2.4. Shot Peening

_{p}was defined by the scanning speed v and the number of scans n, as shown in Equation (1). In the present experiment, t

_{p}was set to 1 s/mm, which was the same in a previous study [13], to compare the shot peening effect on Ti6Al4V manufactured by DMLS and EBM.

#### 2.5. Fatigue Test and Evaluation of Surface Characteristics

_{a}at the test was calculated from the bending moment M, the width of the specimen b (i.e., 20 mm), and the thickness δ measured by a digital caliper, with an accuracy of 0.01 mm, as shown in Equation (3).

_{R15N}. The hardness was measured five times in each case to obtain the mean value and the standard deviation.

_{R}on the surface was measured by the 2D method [84] using an X-ray diffraction apparatus, with a two-dimensional detector, as the sin

^{2}ψ − 2θ diagram of the laser peened metal was curved [85]. The optimal conditions for residual stress measurement using a 2D method, considering the error, were already reported [86]. The X-ray tube used was Cu Kα, and it was operated at 35 kV and 40 mA. The diameter of the collimator was 0.8 mm, and the diffraction from the 8 mm × 8 mm area on the surface was obtained by moving the specimen perpendicularly to the X-rays. The lattice plane (h k l) used for the measurement was the Ti (2 1 3) plane, and the diffraction angle, without strain, was 139.5 degrees. The depth for the 90% contribution to the diffracted X-rays was 12.4 µm in the present condition. The 24 diffraction rings from the specimen at various angles were detected, and the exposure time per frame at each single position was 5 min. As mentioned above, the bending stress was applied in the longitudinal direction of the specimen, and the residual stress in the longitudinal direction of the specimen are discussed in the present paper.

## 3. Results

#### 3.1. Surface Characteristics of Ti6Al4V Manufactured by DMLS and EBM

_{R15N}is shown in Figure 8. As the surface of Ti6Al4V is very rough, the scatter band of H

_{R15N}in each case is relatively large. The hardness of the as-built DMLS specimen is H

_{R15N}= 67.1 ± 7.0, and this is slightly harder than that of the EBM specimen (i.e., H

_{R15N}= 61.8 ± 6.3). The H

_{R15N}of the DMLS specimen produced by cavitation peening was about 10% larger than that of the as-built Ti6Al4V, and the increment for the EBM specimen by cavitation peening was 4%. In the case of laser peening, H

_{R15N}was decreased in the DMLS specimen, and it was increased in the EBM specimen. This might be caused by local melting and local plastic deformation due to the pulse laser. In the case of shot peening, H

_{R15N}was increased in both the DMLS and EBM specimens. It should be noted that H

_{R15N}was affected by the surface profile, such as the skewness R

_{sk}[13], and the H

_{R15N}at R

_{sk}< 0, as in the case of shot peening, was larger than that at R

_{sk}> 0, even though the hardness was equivalent. Thus, the increment on H

_{R15N}by shot peening was caused by the work hardening and deformation of the surface. In any case, the peening treatments caused a work hardening effect on both the DMLS and EBM surfaces.

_{R}is also important factor for improving the fatigue strength of metallic materials by peening methods, Figure 9 shows the residual stress on the surface of the DMLS and EBM specimens, with and without treatments. The σ

_{R}of the as-built DMLS and EBM specimens is nearly zero. After cavitation peening, grinding, and shot peening, compressive residual stress was introduced. In the case of laser peening, the σ

_{R}of the DMLS specimen was tension, and the σ

_{R}of EBM was compression. As laser peening produces ablation and plastic deformation at the same time, tensile residual stress was introduced by the ablation, and compression was introduced by the peening through the plastic deformation. When 70 µm of the surface of the laser-peened specimen was removed, the σ

_{R}of EBM was −187 ± 11 MPa. It should be noted that the depth for the 90% contribution in the residual stress measurement was about 12 µm, and the Ra of the as-built, cavitation peening and laser peening are similar. Thus, it can be concluded that the measured value of the residual stress was affected by the roughness, but all the treatments for the DMLS and EBM specimens introduced compressive residual stress into the surface (see Appendix A).

#### 3.2. Fatigue Properties of Ti6Al4V Manufactured by DMLS and EBM

_{a}in Figure 10 was calculated by Equation (3) using δ, which was measured by the calipers. When the fatigue life and fatigue strength of the as-built specimen manufactured by DMLS and EBM were compared, those of the DMLS specimen were better than those of the EBM specimen. In the case of the DMLS specimen, the fatigue life at σ

_{a}≈ 450 MPa was improved by 10 times through cavitation peening after grinding, 5.9 times through cavitation peening, 4.7 times through shot peening, 3.5 times through laser peening, and 1.5 times through grinding, compared with the as-built specimen. The fatigue strength σ

_{f}

_{1}at N = 10

^{7}was calculated using Little’s method [87], as shown in Table 1. The improvement ratio R

_{1}in Table 1 means the ratio of the fatigue strength, compared with the as-built specimen, for each DMLS and EBM specimen. The ratio R

_{2}in Table 1 shows the ratio between the fatigue strength of DMLS and EBM for each treatment. As shown in Figure 10 and Table 1, in the case of the DMLS specimen, the fatigue strength at N = 10

^{7}was improved by 1.97 times through cavitation peening, 1.93 times through laser peening, 1.92 times through shot peening, and 2.41 times through cavitation peening after grinding, compared with the as-built specimen. In the case of EBM, it was improved by 1.75 times through cavitation peening, 1.87 times through laser peening, and 1.95 times through shot peening. In sum, all treatments improved the fatigue strength, and the fatigue strength of the DMLS specimen was slightly better than that of the EBM specimen, as shown in Table 1.

#### 3.3. Cracks of Ti6Al4V Manufactured by DMLS and EBM

_{d}was measured by the fractured surface using SEM, it was 206 ± 43 µm for the DMLS specimen and 188 ± 22 µm for the EBM specimen. As shown in Figure 7b, the Rz of the as-built specimen was 56.5 ± 2.7 µm for the DMLS specimen and 116.1 ± 9.9 µm for the EBM specimen. Importantly, the δ

_{d}was remarkably larger than the Rz for both the DMLS and EBM specimens.

## 4. Discussion

#### 4.1. Fatigue Strength Considering the Depth of the Surface Defect

_{f}

_{1}in Table 1 was calculated with the thickness of the specimen, measured by the caliper as δ in Equation (3). In particular, the δ in Figure 15 was used as the δ in Equation (3). In the previous report, the core part δ and the surface roughness Rz were considered to calculate the bending stress, as shown Equation (4). Thus, δ was used as δ in Equation (3) [13]. In the present paper, the fatigue strength σ

_{f}

_{2}, considering Rz, is shown in Table 2. As the core part is thinner than the thickness of the specimen, the increase of σ

_{f}

_{2}, compared with σ

_{f}

_{1}, was 3–9% for the DMLS specimen and 8–43% for the EBM specimen.

_{d}is much larger than Rz. This means that the actual core part is thinner than δ

_{2}. Then, the fatigue strength σ

_{f}

_{3}was recalculated using δ

_{3}, which was defined by Equation (5), instead of δ

_{2}. σ

_{f}

_{3}is shown in Table 2. It should be noted that δ

_{d}is 206 µm for the DMLS specimen and 188 µm for the EBM specimen in the present study.

_{f}

_{3}of the DMLS specimen was 561 ± 12 MPa for cavitation peening after grinding and 497 ± 12 MPa for cavitation peening. Elsewhere [88], the fatigue strength at 10

^{7}of the bulk material made of Ti6Al4V through heat treatment was 545 ± 10 MPa. The fatigue strength of the present Ti6Al4V manufactured by DMLS was about 50% of the bulk Ti6Al4V, and it was improved by up to 90% of the bulk Ti6Al4V by cavitation peening, and it came to have a nearly equivalent strength to the bulk Ti6Al4V.

#### 4.2. Experimental Formula to Estimate Fatigue Strength Improved by Mechanical Surface Treatments

_{f}

_{est}by mechanical surface properties was proposed in Equation (6). In Equation (6), σ

_{f}

_{0}is the fatigue strength of the reference condition. It was reported that the fatigue strength was decreased with the maximum surface roughness [39], equivalent crack length of the defect [43], and root area parameter [44]. Thus, the parameter of the surface roughness should be placed in the denominator, as shown in the second term of the right-side member of Equation (6). The hardness suggests the tendency of the increase of the yield stress of the surface by the mechanical surface treatments, and the hardness is expressed in Equation (6) as in the third term. As the residual stress affects the fatigue properties of AM Ti6Al6V [15], σ

_{R}is placed in the fourth term. ΔRz’ and ΔH

_{RNT}’ are the differences in Rz and H

_{RNT}between the reference condition and the estimated condition, normalized by the reference condition, as shown in Equations (7) and (8). The Δσ

_{R}is the difference in residual stress between the estimated condition and the reference condition. In particular, the second term of the right-side member of Equation (6) reveals the effect of surface roughness. The third term shows the effect of work hardening (i.e., an increase of hardness). The fourth term reveals the effect of residual stress. The second term and the third term were normalized by the reference values.

_{f}

_{1}, σ

_{f}

_{2}, and σ

_{f}

_{3}and the estimated fatigue strength σ

_{f}

_{1 est}, σ

_{f}

_{2 est}, and σ

_{f}

_{3 est}is shown in Figure 16. The error bars in Figure 16 were calculated from the standard deviation of the measured values (i.e., σ

_{f}

_{1}, Rz, H

_{RNT}, and σ

_{R}) using error analysis [89]. In Table 3 and Figure 16, the values of the as-built EBM specimen were used as the reference condition to estimate the fatigue strength. In the estimation, the residual stress of laser peening was −187 ± 11 MPa, as compressive residual stress was introduced in the near surface, although the surface was abraded by laser ablation. As shown in Figure 16, the relations between the experimental fatigue strength and the estimated fatigue strength for all three cases (i.e., σ

_{f}

_{1}− σ

_{f}

_{1 est}, σ

_{f}

_{2}− σ

_{f}

_{2 est}, and σ

_{f}

_{3}− σ

_{f}

_{3 est}, are roughly on the line. These results show that the improved fatigue strength of the AM titanium alloy, enhanced by surface mechanical treatments, can be estimated from the fatigue strength of the as-built specimen by measuring the surface roughness, surface hardness, and surface residual stress of the treated one using Equation (6). Now, let us investigate the effect of the surface roughness, surface hardness, and surface residuals stress in the improvement of the fatigue strength. As mentioned above, although the surface roughness of the cavitation peened and laser peened specimens were scarcely changed, the fatigue strength was drastically improved by both peening methods. This means that the effect of the surface roughness was smaller than the others in the present study. This is why a is relatively smaller than b and c. When the absolute values of a, b, and c were compared, the absolute value of b was relatively larger than the others. In particular, the contribution of H

_{R15N}was relatively large, and the scatter band of H

_{R15N}was relatively large, as shown in Figure 8. Thus, the scatter band of the estimated fatigue strength was relatively large, as shown in Figure 16. As the compressive residual stress (i.e., negative value) enhances the fatigue strength, c is negative. As shown in Table 3, the absolute value of c was 0.34 for σ

_{f}

_{1}− σ

_{f}

_{1 est}, 0.38 for σ

_{f}

_{2}− σ

_{f}

_{2 est}, and 0.39 for σ

_{f}

_{3}− σ

_{f}

_{3 est}. As the plane bending fatigue test was used in the present study, and the maximum bending stress was applied at the surface, the fatigue strength was improved by 34–39% of the introduced compressive residual stress. As shown in Figure 16, the laser peening points for both the DMLS and EBM specimens are slightly further than the others, as the measured work hardening was not so large, compared with the other treatments. The correlation coefficient between the experimental fatigue strength and the estimated value was 0.896 for σ

_{f}

_{1}− σ

_{f}

_{1 est}, 0.766 for σ

_{f}

_{2}− σ

_{f}

_{2 est}, and 0.823 for σ

_{f}

_{3}− σ

_{f}

_{3 est}. As the number of the dataset was nine in the present study, the probability of a non-correlation is less than 0.1% for σ

_{f}

_{1}− σ

_{f}

_{1 est}, 1.6% for σ

_{f}

_{2}− σ

_{f}

_{2 est}, and 0.6% for σ

_{f}

_{3}− σ

_{f}

_{3 est}. When the probability of a non-correlation is less than 1%, it can be concluded that the relationship is highly significant. Thus, it can be concluded that the relationship between the experimental fatigue strength and the estimated fatigue strength is highly significant. In particular, the improved fatigue strength treated by the present post-processing can be estimated by the surface roughness, surface hardness, and surface residual stress.

## 5. Conclusions

- (1)
- Cavitation peening, laser peening, and shot peening can improve the fatigue strength of Ti6Al4V manufactured by DMLS and EBM. In the case of DMLS, the improvements in the fatigue strength at N = 10
^{7}, compared with that of the as-built specimen, were 97% for cavitation peening, 93% for laser peening, and 92% for shot peening in the present condition. In the case of EBM, they were 75% for cavitation peening, 87% for laser peening, and 95% for shot peening in the present condition. - (2)
- The fatigue strength of Ti6Al4V manufactured by DMLS is slightly better than that manufactured by EBM, with and without peening. The difference in fatigue strength at N = 10
^{7}between the DMLS and EBM specimens was +9% for the as-built specimen, +23% for the cavitation peening specimen, +13% for the laser peening specimen, and +8% for the shot peening specimen. - (3)
- The fatigue strength of the Ti6Al4V manufactured by DMLS treated by cavitation peening was improved to the same level as that of wrought Ti6Al4V, when the depth of the surface defects was considered in the calculation of the fatigue strength. The fatigue strength at N = 10
^{7}of the DMLS specimen was 497 MPa for cavitation peening and 561 MPa for cavitation peening after grinding the surface. - (4)
- The improvement of the fatigue strength of AM Ti6Al4V caused by the treatments can be estimated using the surface roughness, surface hardness, and residual stress.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Appendix A

**Figure A1.**X-ray diffraction pattern for the Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peening (SP) grinding (G), and cavitation peening after grinding (G + CP), compared with the as-built specimen.

**Figure A2.**Schematic diagram of X-ray diffraction, considering the surface roughness and depth of the contribution to the diffracted X-ray.

## Appendix B

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**Figure 1.**Geometry of the fatigue specimen for the displacement-controlled plane bending fatigue test. The thickness was 2.6 ± 0.2 mm for the direct metal laser sintering (DMLS) specimen and 2.0 ± 0.2 mm for the electron beam melting (EBM) specimen.

**Figure 4.**Schematic diagram of the peening head of the recirculating shot peening accelerated by a water jet.

**Figure 5.**Aspects of the specimen manufactured by DMLS, observed by a laser confocal microscope. (

**a**) As-built; (

**b**) cavitation peening; (

**c**) laser peening; (

**d**) shot peening; (

**e**) grinding; (

**f**) grinding and cavitation peening.

**Figure 6.**Aspects of the specimen manufactured by EBM, observed by a laser confocal microscope. (

**a**) As-built; (

**b**) cavitation peening; (

**c**) laser peening; (

**d**) shot peening.

**Figure 7.**Surface roughness of the as-built Ti6Al4V manufactured by DMLS and EBM and the Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peeing (SP), grinding (G), and cavitation peening after grinding (G + CP). (

**a**) Arithmetical mean roughness Ra. (

**b**) Maximum height of the roughness profile Rz.

**Figure 8.**Surface hardness of the as-built Ti6Al4V manufactured by DMLS and EBM and the Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peeing (SP), grinding (G), and cavitation peening after grinding (G + CP).

**Figure 9.**Surface residual stress of the as-built Ti6Al4V manufactured by DMLS and EBM and the Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peeing (SP), grinding (G), and cavitation peening after grinding (G + CP).

**Figure 10.**Improvement of the fatigue properties of Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peening (SP) grinding (G), and cavitation peening after grinding (G + CP), compared with the as-built specimen.

**Figure 11.**Aspects of the surface near the fracture of the specimen manufactured by DMLS, observed by scanning electron microscope (SEM). (

**a**) As-built (σ

_{a}= 301 MPa, N = 162,400); (

**b**) cavitation peening (σ

_{a}= 370 MPa, N = 291,600); (

**c**) laser peening (σ

_{a}= 400 MPa, N = 352,200); (

**d**) shot peening (σ

_{a}= 361 MPa, N = 764,800); (

**e**) grinding (σ

_{a}= 350 MPa, N = 141,000); (

**f**) grinding and cavitation peening (σ

_{a}= 450 MPa, N = 310,000).

**Figure 12.**Aspect of the surface near the fracture of the specimen manufactured by EBM, observed by SEM. (

**a**) As-built (σ

_{a}= 224 MPa, N = 510,300); (

**b**) cavitation peening (σ

_{a}= 328 MPa, N = 319,300); (

**c**) laser peening (σ

_{a}= 320 MPa, N = 420,900); (

**d**) shot peening (σ

_{a}= 350 MPa, N = 505,700).

**Figure 13.**Aspects of the fractured surface of the specimen manufactured by DMLS, observed by SEM. (

**a**) As-built (σ

_{a}= 301 MPa, N = 162,400); (

**b**) cavitation peening (σ

_{a}= 370 MPa, N = 291,600); (

**c**) laser peening (σ

_{a}= 400 MPa, N = 352,200); (

**d**) shot peening (σ

_{a}= 361 MPa, N = 764,800); (

**e**) grinding (σ

_{a}= 350 MPa, N = 141,000); (

**f**) grinding and cavitation peening (σ

_{a}= 450 MPa, N = 310,000).

**Figure 14.**Aspects of the fractured surface of the specimen manufactured by EBM, observed by SEM. (

**a**) As-built (σ

_{a}= 224 MPa, N = 510,300); (

**b**) cavitation peening (σ

_{a}= 328 MPa, N = 319,300); (

**c**) laser peening (σ

_{a}= 320 MPa, N = 420,900); (

**d**) shot peening (σ

_{a}= 350 MPa, N = 505,700).

**Figure 15.**Schematic diagram of the thickness of the specimen for the calculation of the bending stress.

**Figure 16.**Relationship between the experimental fatigue strength and fatigue strength estimated from the surface roughness, surface hardness, and surface residual stress.

**Table 1.**Fatigue strength and improvement ratio of the as-built Ti6Al4V manufactured by DMLS and EBM and the Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peeing (SP), grinding (G), and cavitation peening after grinding (G + CP).

Number of Specimens | Fatigue Strength σ_{f}_{1} MPa | Improvement Ratio R_{1} | Ratio R _{2} = σ_{f}_{1 DMLS}/σ_{f}_{1 EBM} | |
---|---|---|---|---|

DMLS, as-built | 8 | 185 ± 9 | 1 | 1.09 |

DMLS, CP | 5 | 365 ± 8 | 1.97 | 1.23 |

DMLS, LP | 5 | 357 ± 6 | 1.93 | 1.13 |

DMLS, SP | 7 | 355 ± 10 | 1.92 | 1.08 |

DMLS, G + CP | 4 | 445 ± 8 | 2.41 | — |

EBM, as-built | 8 | 169 ± 14 | 1 | 1 |

EBM, CP | 6 | 296 ± 13 | 1.75 | 1 |

EBM, LP | 6 | 317 ± 7 | 1.87 | 1 |

EBM, SP | 5 | 329 ± 1 | 1.95 | 1 |

**Table 2.**Fatigue strength considering the roughness and defect of the as-built Ti6Al4V manufactured by DMLS and EBM and the Ti6Al4V manufactured by DMLS and EBM through cavitation peening (CP), laser peening (LP), shot peeing (SP), grinding (G), and cavitation peening after grinding (G + CP).

Fatigue Strength σ_{f}_{2} MPa | Fatigue Strength σ_{f}_{3} MPa | |
---|---|---|

DMLS, as-built | 202 ± 10 | 262 ± 18 |

DMLS, CP | 392 ± 9 | 497 ± 13 |

DMLS, LP | 389 ± 6 | 494 ± 8 |

DMLS, SP | 366 ± 10 | 467 ± 12 |

DMLS, G + CP | 459 ± 8 | 561 ± 12 |

EBM, as-built | 221 ± 19 | 262 ± 17 |

EBM, CP | 388 ± 18 | 442 ± 16 |

EBM, LP | 451 ± 6 | 474 ± 30 |

EBM, SP | 355 ± 1 | 468 ± 7 |

**Table 3.**Constants to estimate the improved fatigue strength of the Ti6Al4V manufactured by DMLS and EBM through mechanical surface treatment using the surface roughness, surface hardness, and surface residual stress.

Constant | σ_{f}_{1 est} | σ_{f}_{2 est} | σ_{f}_{3 est} |
---|---|---|---|

a | 0.01 | 0.01 | 0.01 |

b | 2.59 | 1.17 | 1.95 |

c | −0.34 | −0.38 | −0.39 |

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## Share and Cite

**MDPI and ACS Style**

Soyama, H.; Takeo, F.
Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting. *Materials* **2020**, *13*, 2216.
https://doi.org/10.3390/ma13102216

**AMA Style**

Soyama H, Takeo F.
Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting. *Materials*. 2020; 13(10):2216.
https://doi.org/10.3390/ma13102216

**Chicago/Turabian Style**

Soyama, Hitoshi, and Fumio Takeo.
2020. "Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting" *Materials* 13, no. 10: 2216.
https://doi.org/10.3390/ma13102216