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Today, the technology of hardening the surface layers of parts and the creation of protective coatings on the surface with high physical, mechanical and chemical properties is particularly effective. The article reviews the most promising innovative technologies for surface hardening of aluminum alloys – plasma electrolytic oxidation (PEO). Possible conditions and mechanisms for the formation of protective coatings on the surface of aluminum alloys are considered. The influence of the main parameters of PEO processing (electrical parameters, composition and concentration of electrolyte, the influence of alloying elements) on the structure and properties of oxide-ceramic coatings has been studied. The qualitative characteristics of the surface layer of samples and finished products made of aluminum alloys have shown the effectiveness of the PEO technology, which makes it possible to obtain ceramic coatings with high hardness, strength, increased wear and corrosion resistance. Possible areas of application of high-performance technologies for the deposition of protective PEO coatings on the surface of products made of aluminum alloys are proposed.

Process optimization is one pathway to maximizing strength of a given alloy. Thixomolding® is a semi-solid casting process that combines pores reduction with a typical bimodal grain size distribution that can lead to enhanced strength. AZ91D and AZX911 were processed via Thixomolding® using two different processing conditions to change fraction solid of primary particles at the point of injection into the mould. The tensile properties, creep resistance and corrosion behaviour of the alloys were investigated. The creep resistance was measured in the range of 135–150 °C for stresses of 50–85 MPa. The corrosion behaviour was measured via hydrogen evolution for the two alloys and was smaller than that for die-cast AZ91. The AZX911 alloy showed improved creep resistance compared to the AZ91D. The differences in the property profile of the chosen alloys are correlated with their chemical compositions as well as with different microstructures obtained through the different processing conditions.

An attempt was made to understand the effect of silicate based plasma electrolytic oxidation (PEO) coating on the stress corrosion cracking (SCC) behaviour of an AZ61 wrought magnesium alloy. The SCC behaviour of untreated and PEO coated specimens was assessed using slow strain rate tensile tests at two different nominal strain rates, viz. 1 × 10−6 s−1 and 1 × 10−7 s−1, in ASTM D1384 test solution at ambient conditions. The PEO coating was found to improve the general corrosion resistance to a significant extent; however, the improvement in the resistance to stress corrosion cracking was only marginal.

The current trend in biomaterial development is moving toward the use of degradable materials that have extended functionalities and advantages in the fields of tissue engineering and drug delivery. These functionalities are not only realized by metal-based materials but more and more by specific and tailor-made polymer-based coatings. The great advantage of those systems is their flexibility in mechanical properties, degradation behavior, physicochemical functionalities, and their potential to realize influencing and activating specific phenotype characteristics of cells and tissues. The latter opens a huge area for the progress in new therapeutic strategies such as induced autoregeneration and personalized medicine. Furthermore, multifunctionality of the materials will combine cell and tissue specific properties with specific drug delivery concepts and diagnostic methods. Therefore, an interdisciplinary knowledge-based scientific approach has to be realized to benefit from this potential. Useful polymer systems, as well as examples of most important parameters and degradation characteristics, will be discussed and completed by actual applications and future perspectives.

It is shown that oxide-ceramic coatings on magnesium alloys are, in general, characterized by high corrosion resistance depending on the porosity of the coating. The surface topology of oxide-ceramic coatings on IMV2 and VMD10 alloys is studied to reveal discontinuities by using special procedures of immersion and electrochemical deposition. Craters detected as a specific feature of the topology of the coatings and not always through and, in this case, they do not affect the corrosion resistance of the alloys. Isolated pores are formed, most often around the craters, in the process of oxidation under the action of high thermal stresses. On the basis of the comparative analysis of various materials and corrosive media, it is possible to make a conclusion that the corrosion resistance of magnesium alloys with oxide-ceramic coatings in acid media is mainly determined by the chemical composition of the alloy. At the same time, in neutral media, it is determined by the porosity of the coatings.

Ferritic alloys with different contents of carbon, aluminum and chromium are nitrided by plasma immersion ion implantation at 300 °C for 3 h. The thermal stability of the nitrided surface layers is evaluated by annealing the specimens in vacuum and in air both at 400 °C. The composition and the structure of the surface layers is studied by means of GDOES-spectroscopy and X-ray diffraction. In comparison to the nitrided reference specimens the nitrogen concentration decreases after heat treatment at 400 °C in air as well as under vacuum condition. The possibly main reasons are outward (degassing) and inward diffusion of nitrogen at elevated temperature. The e-nitride layer of a Fe–Cr alloy with high chromium content transforms to a stable Fe–Cr–N solid solution.

The result of nitriding ferritic steels using a PI3 treatment depends strongly on the composition of the steel. For chromium containing steels, an expanded ferrite phase was found for higher chromium contents (about 3.6%Cr) under certain treatment conditions. Standard metallography did not reveal any precipitation and the treated surface layer possessed a uniform microstructure. The expanded ferrite phase exhibits high hardness and thus good wear resistance.

The influence of imperfect and annealed structure on the phase composition of α-iron after nitrogen implantation is studied. The surface phase composition of α-iron specimens is investigated by the glancing angle X-ray diffraction and Conversion Electron Mossbauer Spectroscopy (CEMS). The nitrogen depth profile is obtained by Rutherford backscattering spectroscopy. The high density of surface defects induced by grinding and polishing facilitates the formation of a predominantly paramagnetic e-Fe 2 N phase during and after nitrogen implantation. The structure of the annealed surface does not trap such a high content of implanted nitrogen atoms and the ferromagnetic Fe-N phases with lower nitrogen concentrations are detected as dominant in the surface layers. Similar results are obtained for the mechanically treated surface after electrochemical etching that removes partly the defect structure.

Nitride formation was studied in various steels with different alloying elements. Results of PI 3 nitriding, r.f. nitriding with self bias and DC voltage at 300 and 400°C were compared. It was found that nitriding of ferritic steels depends strongly on the formation of surface nitride layers. The habit of the nitrides and the supersaturation of nitrogen is strongly influenced by the HV pulsing during PI 3 and thus also the treatment depth and layer properties.

Expanded austenite can be formed either by nitrogen or carbon plasma immersion ion implantation (PI3 ™) from a nitrogen or methane plasma at elevated temperatures. The structure and properties of nitrogen and carbon expanded austenite layers produced on austenitic stainless steel X5CrNi189 are compared. A new structural model of expanded austenite based on a defect rich face centred cubic (fcc) lattice is proposed. Although the structure of the two expanded austenite layers is similar, there is a remarkable difference in the uptake of nitrogen or carbon, despite the use of similar treatment conditions. The modified surfaces have different hardness, corrosion and wear properties.

Plasma immersion ion implantation has been used for simultaneous implantation of carbon and nitrogen into austenitic stainless steel X5CrNi189 at 400°C. Duplex layer structures are formed with a nitrogen-rich layer close to the surface and a carbon-rich layer at greater depth. The influence of different gas compositions on the structure and phase composition of the layers is examined and compared with results from pure nitrogen and methane. The results provide further information about ‘expanded austenite’ (S-phase) which is formed during the low temperature nitriding of austenitic stainless steels.

The thermal stability and the magnetic nature of metastable nitrided surface layers produced by plasma immersion ion implantation at 300°C on an austenitic X6CrNiTil810 (f.c.c.) and a ferritic X10CrA118 (b.c.c.) stainless steels were examined. The surface phase analysis was performed by the Conversion Electron Mossbauer Spectroscopy (CEMS) and the results were correlated with X-ray diffraction and microhardness measurements. The dominant phase in the as-nitrided surfaces of both steels was found to be expanded austenite (S-phase). The first structure changes of phase composition of the surface of the ferritic X10CrA118 steel were detected after an annealing at 200 °C while in the case of the austenitic X6CrNiTi1810 steel at 250°C. The lower stability of the ferritic steel is ascribed to higher diffusion of nitrogen atoms in b.c.c. structure and to a lack of other austenite stabilising elements besides nitrogen.

Plasma immersion ion implantation is an effective surface treatment for stainless steels. The influence of treatment parameters (temperature, plasma density and pressure) on the sliding wear resistance are studied here. At moderate temperatures, nitrogen remains in solid solution without forming nitrides. This increases the surface hardness and the wear resistance without affecting the passivation of the steel. This may allow the use of such steels in applications where their poor wear resistance would normally prohibit their use.

Nichtrostende Stahle konnen zur Erhohung ihrer Harte und Verschleisbestandigkeit bei Temperaturen ≤ 400 °C nitriert werden, ohne das ihre ausgezeichnete Korrosionsbestandigkeit dabei vermindert wird. Die Struktur und die Eigenschaften von in diesem Temperaturbereich durch Plasmanitrieren und eine PIII-Behandlung erzeugten Randschichten wurden untersucht. Trotz unterschiedlicher Wirkprinzipien der hierfur angewendeten Verfahren bestehen keine nennenswerten Unterschiede im Aufbau der erzeugten Randschichten. Im Gegensatz dazu unterscheiden sich die Randschichten unterschiedlicher Stahle deutlich. Die Randschicht ferritischer Chromstahle besteht vorrangig aus e-Nitrid. Kennzeichnend fur die Randschichten austenitischer und ferritisch-austenitischer Stahle ist dagegen der expandierte Austenit. Die Korrosionsbestandigkeit der Stahle wird durch die Nitrierung nur bei nachweisbarer CrN-Bildung herabgesetzt. Structure and properties of stainless steels after plasma immersion ion implantation and plasma nitriding Stainless steels can be nitrided at temperatures ≤ 400 °C to increase their hardness and wear resistance without a decreasing of their excellent corrosion resistance. Structure and properties of the surface layers produced by plasma nitriding and plasma immersion ion implantation in this temperature range were tested. There are negligible differences in the structure of the produced surface layers in spite of different interaction principles of the used technologies. However there are clear differences between the case of different steels. The case of ferritic chromium steels mainly consists of e-nitride. Whereas the cases of austenitic and ferritic austenitic steels are characterized by expanded austenite. The corrosion resistance of the steels is reduced by nitriding only, if evident CrN-formation occurs.

A study of the response of the nitriding steel, 34CrAlNi7, to two different nitriding techniques revealed remarkable differences. The techniques used were pulsed plasma nitriding and plasma immersion ion implantation over a range of temperatures from 300 to 500°C. The surface produced by the pulsed plasma nitriding consisted of a nitride layer whose thickness varied with temperature, with an underlying diffusion zone. Plasma immersion ion implantation treatment, however, formed nitrides only at the lowest temperature, with most of the nitrogen in solid solution. Although quite different surface structures resulted from the two treatments, similar improvements in wear performance were obtained.

A thin nitride layer containing high amounts of oxygen is formed on the surface of A199.5 treated by Plasma Immersion Ion Implantation (PIII) at temperatures up to 500°C. Below this layer, nitrogen is found in a diffusion zone several microns thick but does not form nitrides. The thickness of the diffusion zone is dependent on the treatment temperature. Microhardness measurements reveal a decrease in hardness due to a loss of work-hardening. In spite of this annealing, both the wear and corrosion resistance are improved.

Most low alloy steels are tempered at relatively low temperatures, limiting the opportunities for improving their wear resistance and surface hardness by traditional heat treatment processes. In this work, we use plasma immersion ion implantation (PI 3 ) to apply a hybrid ion implantation/thermochemical diffusion treatment to ball bearing steel 100Cr6 (1% C, 1.5% Cr). By a judicious choice of implantation voltage, temperature and time, it is possible to combine the PI 3 treatment with the tempering stage of heat treatment, without compromising the hardness of the alloy. Up to 200 °C, the bulk hardness (750 HV tempered) of the material is maintained, and nitrogen implantation increases the surface hardness due to the precipitation of fine Fe 2 N. At 300 °C, where enhanced nitrogen and carbon diffusion can occur, the bulk hardness decreases, although in many applications this can be compensated by the increase in surface hardness to around 900 HV0.1 due to Fe 3 N and Fe 4 N formation. Wear and corrosion tests reveal significant improvements in comparison with untreated steel.

Macro test samples of magnesium alloy AM60B were melted and quenched at maximum instantaneous cooling rates ranging from -5°C/s to -500°C/s and the resultant cooling curves were analyzed. Characteristic reactions on these curves corresponding to formation of individual phases were identified with the aid of literature data as well as metallographic and micro-chemical analysis. The results indicate that these phases, their size and location in the micro structure, their chemistry and their relative proportions all change in response to the increase in the cooling rate. These rapid cooling rates are typical of real industrial solidification processes such as die casting. These findings can be used to improve future computer models of casting solidification processes for magnesium and for other alloys.

Ultrahigh molecular weight polyethylene (UHMWPE) has been the material of choice in orthopaedic joint prostheses for over three decades owing to its proven low friction and excellent wear resistance when coupled with smooth Co-Cr-Mo alloy or austenitic stainless steel surfaces in vivo [1]. However, it is gradually recognized that the principal constraint on the longevity of total joint replacements is the body’s reaction to debris, which is mostly UHMWPE [2]. Therefore, how to improve the wear resistance of UHMWPE and thus reduce the volume of wear debris, which promotes implant loosening, is a timely task from both a scientific and technological point of view. Nitrogen ion implantation of UHMWPE has been proved to improve its tribological properties in terms of low friction and extremely low wear rate [3], however, it is difficult in practice to uniformly treat such three-dimensional objects as hip joint sockets without using sophisticated manipulating devices. Recently, an innovative hybrid technology, plasma immersion ion implantation (PI3), has been developed, which can, to a large extent, address the problems with ion implantation of components with complex shapes [4]. However, there appears to have been little, if any, work reported on the surface modification of UHMWPE using the innovative, hybrid PI3 technology with a view to improve its mechanical and tribological properties [5]. In the present investigation, an attempt has been made to explore the feasibility of surface modification of UHMWPE using the novel PI3 technology. The material used in the study was medical grade UHMWPE (GUR-412) in the form of 12.5 diameter, extruded and annealed rod which was obtained from Poly Hi Solidur Ltd (GB). The density of the homogeneous material and the average molecular weight are 0.932 g cm−3 and 3.6× 106 g mol−1, respectively. Specimens were treated in a Mark 1 PI3 unit at the Technical University of Clauthal with the pulse source being (PI3 treatment) or not being (plasma treatment) applied. Specimens were immersed in a low pressure (0.17 Pa) radio frequency plasma discharge, which was generated by a 300 W r.f. power at 13.56 MHz. Table I lists the treatment conditions for plasma treatment (PT) and PI3 treatments. By selecting appropriate pulse length and pulse frequency, the treatment temperature was controlled at below 90 ◦C. Although it has been claimed that ion implantation can decrease the surface roughness of polymeric materials [6], such an improvement was not observed in the present study. Indeed, surface relief appeared on PI3-H specimens largely because of the ion etching effect resulting from nitrogen ion bombardment. Slight surface discoloration was observed for all surface treated specimens, increasing in the order of PT, PI3-L and PI3-H. In view of the fact that the surface modified layers of UHMWPE material usually are very thin and the substrate very soft, the mechanical properties of the untreated and treated UHMWPE specimens were measured using a NanoTest 500. A standard procedure developed by Oliver and Pharr was adopted to process the load-depth data [7]. Fig. 1 depicts characteristic load versus depth hysteresis curves, showing the loadingunloading response of the PI3 treated as well as untreated material. It can be clearly seen that, to reach the same penetration depth (250 nm), a higher load was need for the treated surface relative to the untreated surface. It also demonstrated that PI3 treated material exhibited a higher elastic recovery and less creep during the dwelling time (10 s) than the untreated material.

The formation of non-equilibrium phases at surfaces of austenitic X6CrNiTi1810, ferritic XIOCrA118 and austenitic-ferritic X2CrNiMoN2253 stainless steels modified by nitrogen plasma immersion ion implantation at 300 °C and 400 °C is studied using Conversion Electron Mossbauer Spectroscopy. The nitrogen depth profiles are followed by Rutherford Backscattering Spectroscopy. The results of the phase analysis are related to the surface hardness measured for each treatment.

Detailed surface structure investigations by microscopic methods and microhardness measurements of modified Fe-6at.%Si steel samples are presented here. It is found that a preceding mechanical and heat treatment of the samples influence drastically the surface morphology, phase composition and properties after ion implantation at 300°C in pure nitrogen plasma and in a mixed plasma of nitrogen and silicon.