**3. Physical vapor deposition coatings**

The acronym PVD comes from the English expression Physical Vapor Deposition, knowing by this name a wide range of coating techniques that have in common the use of physical methods to obtain some of the components of the deposited layer. PVD coatings are made in high-vacuum chambers (10–50 mbar), working with average process temperatures in the range of 450°C to room temperature. By using this deposition technique, films from very thin thickness (10 nm) up to several microns with controllable composition can be perfectly obtained. In **Figure 4**, a schematic representation of PVD chamber is presented.

Basically, the PVD coatings are formed as follows. Firstly, a material is evaporated starting from a solid source (Ti, TiAl, Cr) by means of different physical methods as a function of the deposition technique employed which are electron beam evaporation or arc electric, pulverization (sputtering) by ionic bombardment, etc. The atmosphere of the treatment chamber consists of high vacuum in which there are partial pressures of controlled gases (mostly nitrogen and argon). The evaporated metal and the reactive gas of the chamber react condensing on the surface of the components to be coated. According to this process, the most known PVD coatings of typical industrial use are TiN, TiAlN, TiCN, or CrN, among others [50–55].

Concerning to the PVD processes, there are three main methods that are more widespread such as the electron beam (EB), the cathodic arc (CA), and the magnetron sputtering (MS), respectively. On the other hand, new concept in magnetron sputtering systems has been developed using high-power pulses (HIPIMS), making possible a significant increase in plasma ionization, and as a result, a considerable enhancement in the resultant adhesion of the coatings has been obtained [56, 57]. In **Figure 5**, a comparison between high-power impulse magnetron sputtering (HIPIMS), direct current magnetron sputtering (DCMS), and modulated pulsed power magnetron sputtering (MPPMS) is presented as function of power and time, respectively.

One of the research lines where PVD coatings have shown a high degree of novelty is in the protection against joint wear. The first experiences date back to the decade of the 1980s of the last century where TiN in total join arthroplasty was used as well as clinical trials were started in the 1990s in knee and hip arthroplasty [58, 59].

**Figure 4.** Scheme of the Metaplas Ionon MZR 323 arc evaporation PVD system. Courtesy of AIN.

**3. Physical vapor deposition coatings**

for PSHA coatings (c). Reprinted with permission of [41].

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The acronym PVD comes from the English expression Physical Vapor Deposition, knowing by this name a wide range of coating techniques that have in common the use of physical methods to obtain some of the components of the deposited layer. PVD coatings are made in high-vacuum chambers (10–50 mbar), working with average process temperatures in the range of 450°C to room temperature. By using this deposition technique, films from very thin thickness (10 nm) up to several microns with controllable composition can be perfectly

**Figure 3.** SEM intermediate micrograph (a) high magnification micrograph (b) and IFM three-dimensional reconstruction

Basically, the PVD coatings are formed as follows. Firstly, a material is evaporated starting from a solid source (Ti, TiAl, Cr) by means of different physical methods as a function of the deposition technique employed which are electron beam evaporation or arc electric, pulverization (sputtering) by ionic bombardment, etc. The atmosphere of the treatment chamber consists of high vacuum in which there are partial pressures of controlled gases (mostly nitrogen and argon). The evaporated metal and the reactive gas of the chamber react condensing on the surface of the components to be coated. According to this process, the most known PVD coatings of typical industrial use are TiN, TiAlN, TiCN, or CrN, among others [50–55].

obtained. In **Figure 4**, a schematic representation of PVD chamber is presented.

**Figure 5.** Power versus time in direct current magnetron sputtering (DCMS), high-power impulse magnetron sputtering (HIPIMS), and modulated pulsed power magnetron sputtering (MPPMS), respectively.

Subsequently, diamond-like carbon (DLC) coatings were introduced, following the strategy of favoring sliding with very low coefficients of friction (0.1), maintaining relatively high hardness (H > 15 GPa). Although these specific coatings showed high efficacy in laboratory tests, the clinical tests performed to date for hip and knee prostheses showed undesirable results, being the decohesion of the layers and the subsequent localized corrosion the main cause of the failure.

On the other hand, TiN and DLC coatings showed very good biocompatibility so they are being marketed in other types of prostheses such as dental implants and heart valves. For these specific purposes, the absence of high loads which can delaminate the coating as it happened in the case of hip and knee prosthesis enables its introduction into the market. In **Figure 6**, two representative examples of Ti dental implants obtained which are coated by TiN (left) or DLC (right) magnetron sputtering can be clearly appreciated.

However, one of the main problems concerned to this type of coatings is the adhesion and corrosion behavior, being one of the hot topics in the community scientific their implementation and introduction of them in a massive way in the market of hip and knee prostheses. One of the most promising approaches is the use of the aforementioned HIPIMS. This PVD technology allows obtaining layers of much greater adhesion and density, giving excellent results in terms of corrosion and wear resistance. A representative example is shown in **Figures 7** and **8**, respectively. In **Figure 7** is shown a cross section of a sample coated with TaN DC magnetron sputtering (left), where a columnar growth with micron-sized grains can be appreciated. On the other hand, the photograph on the right shows a layer of TaN coating by HIPIMS where a greater density and compactness can be observed. The corrosion resistance in terms of polarization resistance as a function of time (4, 24, and 168 h, respectively) is shown in **Figure 8**.

Another research line which is showing promoting results is ceramic coatings doped with bactericidal elements (mostly Ag or Cu) in the form of nanoparticles embedded in the TiN or CrN. The controlled release of Cu or Ag ions provides a bactericidal effect which makes possible the prevention of infections due to bacterial proliferation on the surfaces of the prostheses. Doped metal nitrides and carbonitrides deposited by pulsed magnetron sputtering are widely tested [60, 61]. In addition, Cu and Ag concentrations between 5 and 25% have been shown to be highly efficient, avoiding the proliferation of different contagious types of bacteria such as *S. aureus*, *P. aeruginosa*, and *S. epidermis*, increasing bactericidal efficacy with increased concentration of Ag and Cu, respectively. Finally, another extended solution is the coatings of diamond-like carbon(DLC) doped with Ag because the experimental results of depositing these layers by means of magnetron sputtering point to the fact that silver segregates in the form of nanoparticles (order of 3 nm), and in high concentrations appear nanofibers of Ag on the surface, showing very good antibacterial behavior [62].

**4. Ion implantation techniques**

sample (AISI 304, black color), respectively. Courtesy of IK4-TEKNIKER.

respectively. Courtesy of IK4-TEKNIKER.

(mostly in aeronautical or biomedical sector).

Ion implantation techniques consist in the superficial modification of materials by ion bombardment. By means of these techniques is possible to improve surface properties of different materials [63, 64]. Although these techniques have their origin in the nuclear industry [65, 66], the first works on semiconductor applications appeared in Bell Laboratories in 1948 when Kingsbury and Ohl carried out studies of implantation of light ions on wafers of Si [67, 68]. Metallurgical application of ion implantation was firstly reported simultaneity in the 1970s by Harwell laboratory (UK), and Naval Research Laboratory (USA). These early works were mainly focused on nitrogen implantation of steels. From these first results up to today ion implantation techniques have been introduced in many different industrial applications

**Figure 8.** Evolution of corrosion resistance for TaN HIPIMS sample (blue color), TaN DCMS (red color), and pristine

**Figure 7.** Cross-sectional SEM images of TaN DC magnetron sputtering (left) and TaN HIPIMS coating (right),

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Ion implanters equipment consists of a series of characteristic elements (see **Figure 9**) such as a source of ions (capable of producing sufficient quantities of certain types of ions), one

**Figure 6.** TiN magnetron sputtering coating (left) and diamond-like carbon (DLC) magnetron sputtering coating (right) on Ti dental implant. Courtesy of the commercial company Flubetech.

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**Figure 7.** Cross-sectional SEM images of TaN DC magnetron sputtering (left) and TaN HIPIMS coating (right), respectively. Courtesy of IK4-TEKNIKER.

**Figure 8.** Evolution of corrosion resistance for TaN HIPIMS sample (blue color), TaN DCMS (red color), and pristine sample (AISI 304, black color), respectively. Courtesy of IK4-TEKNIKER.
