Direct Current and Pulsed Direct Current Plasma Nitriding of Ferrous Materials a Critical Review

Nowadays, the improvement of ferrous materials performance is a problem of high interest. One of well-known wear- and corrosion properties improving technique is plasma nitriding, in which elemental nitrogen is introduced to the surface of a metal part for subsequent diffusion into the material. As a result, a compound, “white” layer and a diffusion zone are formed at the detail’s surface. Most of the authors positively describe the effects of surface ion nitiding. On the other hand, there are also reports on adverse effects of direct current and pulsed direct current plasma nitriding on ferrous materials performance. Therefore, an attempt to provide comprehensive summary on direct current and pulsed direct current ion nitriding and its influence on ferrous materials’ mechanical and corrosion properties has been made. According to the results, some of the technique drawbacks are hard to avoid in mass production

Review of Recent Research on AlCoCrFeNi High-Entropy Alloy

High-entropy alloys (HEAs) have gained significant interest in recent years because of their outstanding properties. The AlCoCrFeNi alloy is one of the most studied HEAs. The effect of the manufacturing methods and heat treatment on the properties of the high-entropy AlCoCrFeNi alloy is under intense scrutiny. The effect of varying component content on properties of the alloy is frequently analysed. Aluminium is most popular due to its impact on alloy microstructure and occurrence of phases. Research is also conducted on the influence of alloying additives, such as boron and titanium, on the properties of the AlCoCrFeNi alloy. High-entropy alloys also have excellent mechanical properties at high temperatures. Excellent structural and functional properties make them suitable for application in the most demanding conditions. The research conducted on HEAs still provides a lot of new and valuable information on the properties and structures of these alloys. This article summarizes the most important information about HEAs, specifically the AlCoCrFeNi alloy

Effect of Plasma Nitriding Process Conditions on Corrosion Resistance of 440B Martensitic Stainless Steel

Martensitic stainless steels are used in a large number of various industrial applications, e.g. molds for plastic injections and glass moldings, automotive components, cutting tools, surgical and dental instruments. The improvement of their tribological and corrosion properties is a problem of high interest especially in medical applications, where patient safety becomes a priority. The paper covers findings from plasma nitrided AISI 440B (PN-EN or DIN X90CrMoV18) stainless steel corrosion resistance studies. Conventionally heat treated and plasma nitrided in N2:H2 reaction gas mixture (50:50, 65:35 and 80:20, respectively) in two different temperature ranges (380 or 450°C) specimens groups were examined. Microscopic observations and electrochemical corrosion tests were performed using a variety of analytical techniques. As obtained findings show, plasma nitriding of AISI 440B stainless steel, regardless of the process temperature, results in reduction of corrosion current density. Nevertheless, applying thermo-chemical process which requires exceeding temperature of about 400°C is not recommended due to increased risk of steel sensitization to intergranular and stress corrosion. According to the results, material ion nitrided in 450°C underwent leaching corrosion processes, which led to significant disproportion in chemical composition of the corroded and corrosion-free areas. The authors suggest further research into corrosion process of plasma nitrided materials and its degradation products

The Effect of Dynamic Recrystallization on Monotonic and Cyclic Behaviour of Al-Cu-Mg Alloy

The paper presents an investigation that was conducted to determine the possibility of the occurrence of the process of dynamic recrystallization in 2024 alloy during monotonic tensile and creep tests at the elevated temperatures of 100 °C, 200 °C, and 300 °C. As-extruded material was subjected to creep process with constant force at elevated temperatures, until two varying degrees of deformation were reached. After cooling at ambient temperature, the pre-deformed material was subjected to monotonic and fatigue tests as well as metallographic analysis. The process of dynamic recrystallization was determined in monotonic tests to occur at low strain rate (0.0015/s) only at the temperature of 300 °C. However, in the creep tests, this process occurred with varying efficiency, both during creep at 200 °C and 300 °C. Dynamic recrystallization was indicated to have a significant influence on the monotonic and cyclic properties of the material

Investigation of the Structure and Corrosion Resistance of Novel High-Entropy Alloys for Potential Biomedical Applications

High-entropy alloys are a new generation of materials that have attracted the interest of numerous scientists because of their unusual properties. It seems interesting to use these alloys in biomedical applications. However, for this purpose, the basic condition of corrosion resistance must be fulfilled. In this article, selected corrosion properties of self-composed high-entropy alloys are investigated and compared with conventional biomedical alloys, that is titanium alloys and stainless steels. Corrosive parameters were determined using the potentiodynamic method. X-ray diffraction studies were performed to characterize the crystal structures. Microstructures of the prepared materials were examined using a scanning electron microscope, and surface hardness was measured by the Vickers method. The results show that investigated high-entropy alloys are characterized by simple structures. Three out of four tested high-entropy alloys had better corrosion properties than conventional implant alloys used in medicine. The Al0.7CoCrFeNi alloy was characterized by a corrosion potential of −224 mV and a corrosion current density of 0.9 μA/cm2; CoCrFeNiCu by −210 mV and 1.1 μA/cm2; TiAlFeCoNi by −435 mV and 4.6 μA/cm2; and Mn0.5TiCuAlCr by −253 mV and 1.3 μA/cm2, respectively. Therefore, the proposed high-entropy alloys can be considered as potential materials for biomedical applications, but this requires more studies to confirm their biocompatibility

Polyurethanes from the crystalline prepolymers resistant to abrasive wear

The research aimed at the selection of polyurethanes synthesized from poly(tetramethylene ether) glycol (PTMEG), as well as from two different isocyanates 4,4′-methylenebis(cyclohexyl)isocyanate (HMDI) and 4.4′-methylenebis(phenyl isocyanate) (MDI) in order to obtain polyurethane with increased resistance to abrasive wear and degradation for bio-medical application. Polyurethanes were fabricated from crystalline prepolymers extended by water. The paper presents preliminary results on polyurethane surface wettability, friction coefficient for different couples of the co-working materials such as polyurethane-polyurethane, polyurethane-titanium alloy, polyurethane-alumina, in comparison to commonly used polyethylene-titanium alloy. Shear strength of polyurethane-alumina joint, as well as viscosity of prepolymers were also measured. The values of friction coefficient were compared to literature data on commercially available polyurethane with the trade name Pellethane. Polyurethanes obtained are characterized by low abrasive wear and low friction coefficient in couple with the titanium alloy, what makes them attractive as possible components of ceramic-polymer endoprosthesis joints

Polyurethanes from the crystalline prepolymers resistant to abrasive wear

The research aimed at the selection of polyurethanes synthesized from poly(tetramethylene ether) glycol (PTMEG), as well as from two different isocyanates 4,4′-methylenebis(cyclohexyl)isocyanate (HMDI) and 4.4′-methylenebis(phenyl isocyanate) (MDI) in order to obtain polyurethane with increased resistance to abrasive wear and degradation for bio-medical application. Polyurethanes were fabricated from crystalline prepolymers extended by water. The paper presents preliminary results on polyurethane surface wettability, friction coeffi cient for different couples of the co-working materials such as polyurethane–polyurethane, polyurethane–titanium alloy, polyurethane–alumina, in comparison to commonly used polyethylene–titanium alloy. Shear strength of polyurethane–alumina joint, as well as viscosity of prepolymers were also measured. The values of friction coeffi cient were compared to literature data on commercially available polyurethane with the trade name Pellethane. Polyurethanes obtained are characterized by low abrasive wear and low friction coeffi cient in couple with the titanium alloy, what makes them attractive as possible components of ceramic-polymer endoprosthesis joints