**3.1. Wear volume analysis**

The values of normal force (N) were defined as a function of the density (*ρ*) of the ball material

(N) Normal force (N)—ball of AISI 316 L SS 0.25 (S) Sliding distance—(m) 8.0 (n) Ball rotational speed—(rpm) 50 (v) Tangential sliding velocity—(m/s) 0.1 (t) Test duration—(min) 10

The tests were conducted at t = 10 min. The sliding distance (S) was calculated based on the

All experiments were conducted without interruption, and the PBS solution was continuously agitated and fed between the ball and the specimen under a frequency of 1 drop/2 s. Both the normal force (N) and the tangential force (T) were monitored and registered constantly. Then,

The tribological behavior of the ISO 5832-1 austenitic stainless steel was also assessed by wear

the air, at 25°C, with counterbody of chrome steel 52–100 rotating ball shape, 2 mm in diameter, during 10 min, with normal force of 100.0 mN, distance equivalent to 2.4 m, and a scan

Vickers microhardness analyses were performed in a microdurometer coupled with optical microscope, Fisherscope HM 2000. The hardness values refer to the average of five measurements at a distance of 50 μm between each indentation, and applied load of 25.0 mN·0−1, for

speed of 4.0 cm.s−1. Both laser-textured and pristine materials were evaluated.

surfaces treated with laser and also for the untreated stainless steel specimens.

*<sup>N</sup>* (2)

). The tests were performed in

values of *v* = 0.1 m·s−1 and t = 10 min (t = 600 s) and was equal to 60 m.

**Figure 2.** ISO 5832-1 austenitic stainless steel textured by ytterbium optical fiber laser.

the friction coefficient (μ) was determined using Eq. 2:

**Table 2.** Test conditions selected for the ball-cratering wear experiments.

tests conducted in a nanotribometer (Anton Paar—model NTR2

*μ* = \_\_*<sup>T</sup>*

(AISI 316 L SS): *ρ*316L = 8 g ·cm−1.

68 Lubrication - Tribology, Lubricants and Additives

**Test condition**

**2.3. Nanotribometer**

**2.4. Microhardness (HV)**

The environment of implants usually induces wear deriving from the contact between the biomaterial and surrounding tissues, so that when manufacturing an implant, one has to choose a suitable area for laser treatment. **Figure 3** shows this biomaterial surface without texturizations (blank).

**Figure 4** presents the wear volumes (V) for the untreated and laser-textured samples after the ball-cratering wear tests. These values were determined according to Eq. (1). It is possible to observe that the wear volume decreased for the laser-textured specimens with respect to the untreated steel. This fact is likely to be associated with an increase in the surface hardness after laser texturing. As shown in **Table 3**, the microhardness of the laser-textured samples was higher than that of the untreated material. The highest values of wear volume were obtained for the untreated specimens. The wear resistance of the laser-textured surfaces was superior to that of the pristine material. Similar results were reported by Cozza et al. [13] using the same test for a different tribological system.

Microstructural and topographic modifications due to changes in some parameters of the laser beam were identified by Lima et al. [24]. They used a Q-switched Nd: YAG laser with different pulse frequencies. Similarly, they performed texturing treatment that consisted of

**3.2. Friction coefficient**

tion of some particles.

duced by the laser beam texturing.

Because wear is a surface phenomenon that occurs at the interface between the asperities of the surfaces in contact, biotribology results are strongly influenced by the surface finish pro-

Evaluation of the Biotribological Behavior and Cytotoxicity of Laser-Textured ISO 5832-1…

http://dx.doi.org/10.5772/intechopen.73140

71

Considering the ball-cratering wear test, the highest value of the friction coefficient was obtained for the untreated surface as shown in **Figure 5**. The laser-textured specimens presented lower friction coefficient. The lowest value was observed for specimen 3. There was no apparent relationship between the friction coefficient and the laser pulse frequency. Notwithstanding, it is possible to infer that the hardness increase can be related to this effect. Surface roughness, in turn, did not increase the friction coefficient, being the hardness effect more prominent to the friction characteristics of the treated surface. Values of such magnitudes were reported in

In the biomaterials' field for implantable medical or dental devices, tribological assays are of great value in providing an estimate of the normal, tangential, and frictional forces in relation to the volume of material that can be detached from the surface, migration, and accommoda-

This work also analyzed the evolution of the friction coefficient by nanotribometer wear tests of the surfaces of these biomaterials with laser texturing treatment. The results obtained are presented in **Figure 6**, and are compared with the blank specimen (without treatment).

No direct relationship between wear volume and friction coefficient was observed; i.e., the highest value of wear volume was not related to the higher value of coefficient of friction [25–28]. The variation of the friction coefficient with the test time is shown in **Figure 6** for the laser-textured and untreated samples. These results were obtained by means of the wear tests conducted in the nanotribometer. For the laser-textured surfaces, the values of friction coefficient were lower than those obtained for untreated surface, confirming the results of the ball-cratering wear test. For the laser-textured surfaces, **Figure 6**, the values of friction coefficient obtained were lower

literature [25–28], with the same type of test under different tribological systems.

than those obtained in the samples without treatment by the laser beam (blank).

**Figure 5.** Friction coefficient obtained by the ball-cratering wear test for untreated and textured specimens.

**Figure 3.** Wear test conducted on the ISO 5832-1 SS without laser treatment. Ball of AISI 316 L SS.

**Figure 4.** Wear volumes of the untreated and laser-textured surface determined after the ball-cratering wear tests.

juxtaposed lines on the surface of the AISI M2 tool steel. Changes in beam energies and intensities were observed. All conditions used produced metal fusion. They noticed that there was little roughness for the low intensities generated by the laser beam; however, there were "craters", that is, regions with high roughness at the higher intensities.

Allsopp and Hutchings [25] have suggested that surface roughness is interesting for improving adhesion between coatings and metallic alloys, and can be produced and controlled by laser beam. This effect is desirable on some biomaterials' surfaces for permanent fixture medical devices. The values of Ra shown in **Table 3** reveal that the average roughness increased after laser texturing, scaling up with the pulse frequency.


**Table 3.** Microhardness and roughness values for the untreated and laser-textured samples.
