PSI - Issue 13

Milan Uhríčik et al. / Procedia Structural Integrity 13 (2018) 1571 – 1576 Milan Uhríčik / Structural Integrity Procedia 00 (2018) 000 – 000

1572

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austenite and ferrite formers. They are alloyed with chromium, nickel, molybdenum and sometimes with copper, titanium, niobium and nitrogen.These steels have very good mechanical and technological properties combined with good corrosion resistance (Lima et al. 2005; Rashid et al. 2012; Zatkalíková et al. 2014). Biomaterials are materials used for making devices that can interact with biological systems. The surgical implants are usually made from metallic materials, such as austenitic stainless steel, cobalt based alloys, and commercially pure titanium and its alloys. They are mainly used for implant devices replacing failed hard tissue, for example, artificial hip joints, artificial knee joints, bone plates, screws, dental implants, etc. It is important to choose the proper material by considering its mechanical behaviour, chemical stability, biocompatibility and the corrosion resistance. Human body represents an aggressive environment and so the implanted material can interact with this environment, which results in negative response to immune system. On the other hand, the aggressive environment can affect the properties of the implanted material, as well. Some of the devices are intended to remain inside the body for a substantial period of time and some of them for long-term period (Park et al. 2003). By measuring the internal damping processes of microplastics are evaluated and examined and the energy dissipation within the metal is also evaluated. The mechanism of microplasticity can be evaluated by various dependencies (frequency, time, temperature and amplitude), which characterize the kinetic of accumulation of fatigue damage in long-time loading. By measuring the energy dissipation in a material, it is possible to determine elastic characteristics, the modulus of elasticity, the degree of stress relaxation in the material and others (Puškár et al. 1981). The ability of the solid to irreversibly disperse energy under mechanical stress is called the internal damping. The time that is required to reach the equilibrium value of deformation is determined by various processes related to the redistribution of atoms, magnetic moments and temperature of the solid under external stresses (Soviarová 2015). For the study and measurement of internal damping the commercially available austenitic stainless steels, namely AISI 304, AISI 316L and AISI 316Ti, were used as experimental materials. They are often used as biomaterials. The AISI 304 is a chrome-nickel steel, which has a reduced content of molybdenum. This steel is suitable for various medical and surgical instruments. It has a high strength and is well machinable and wroughtable in various shapes, so it is ideal for the production of operating dishes, tools and various medical containers. In the healthcare, it is is used where the high corrosion resistance, good formability, strength, reliability and hygienic safety are important. The AISI 316L is a chrome-nickel-molybdenum steel with low carbon content in order to increase the resistance to intercrystalline corrosion. This steel is often used in medical environments such as orthopedic implants, bone fixation implants (splints, bolts, needles), catheters and various surgical instruments. The AISI 316Ti is a chrome-nickel-molybdenum steel stabilized by titanium. The content of the stabilizing element in the steel, in this case Ti, should be 5 x C. The addition of the stabilizing element is by reason of increasing of the resistance to intercrystalline corrosion, because titanium carbides are preferably formed, thereby maintaining the proper distribution of chromium throughout the structure. The chemical composition of steels was examined by spark emission spectrometer SPEKTROMAXx and results are shown in Table 1. 2. Experimental material

Table 1. The chemical composition of all austenitic stainless steels. C [%] Cr [%] Mn [%] Mo [%] Ni [%]

P [%]

S [%]

Si [%]

Ti [%]

Fe [%] balance balance balance

AISI 304 AISI 316L AISI 316Ti

0.05 0.03 0.03

19.59 17.41 17.83

1.57 1.34 1.54

0.49 2.38 2.36

7.84 9.91

0.05 0.07 0.06

0.03 0.03 0.03

0.29 0.51 0.44

- -

10.62

0.14

Microstructures of individual steels are shown in Figure 1, which were evaluated by a light microscope NEOPHOT 32. This analysis shows that structures are made of polyhedral grains of austenite of different sizes, which represent a certain inhomogeneity of the structure. Microstructures are affected by previous technological processing, by hot rolling, as indicated by the manufacturer.