J. Appl. Cryst.の発刊に際して

This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

Over the last 40 years, the commercial production of titanium and its alloys has increased steadily. Whilst these materials have some very attractive properties, enabling applications in many industries, they are seldom used in mechanical engineering applications because of their poor tribological properties. This paper starts with an introduction to the titanium material and a review of the different types of surface treatment. The processes of nitriding, oxidation and carburizing are among the most popular thermochemical treatments aiming at improving the surface properties of Ti-alloys. Different kinds of nitriding are investigated like plasma nitriding, ion nitriding, and laser and gas nitriding. The kinetics of nitriding and the conditions for the formation of nitrided layers are studied. The influence of the main processing parameters such as temperature, time on the microstructure and the formation of new phases during the processes of nitriding is discussed. Also based on investigations presented in the literature, the effects of nitriding on the microhardness and the corrosion resistance of titanium and titanium alloys are analyzed. The improved mechanical properties, which arise from these thermochemical treatments, are discussed in relation to the potential for applying these alloys to different industries.

Enhancing the microstructure and properties of titanium alloys through nitriding and other surface engineering methods

Design and evaluation of tribological coatings

This review article exemplifies the importance of self-cleaning materials and coatings. Self-cleaning coatings are becoming an integral part of our daily life because of their utility in various applications such as windows, solar panels, cements, and paints. In this review, various categories of materials for the fabrication of hydrophilic, hydrophobic, oleophobic, amphiphobic and multifunctional coatings and their synthesis routes have been discussed. Furthermore, different natural organisms exhibiting superhydrophobic behaviour have been analysed. This review also covers the fundamentals of self-cleaning attributes such as water contact angle, surface energy, and contact angle hysteresis.

A review on ‘self-cleaning and multifunctional materials’

Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For this purpose, ion nitriding by a d.c. glow discharge is generally efficient for numerous materials. However, for some metals and alloys, the processing temperature, dominated by the discharge parameters, is too high and cannot be controlled independently from the plasma reactivity. This paper reviews the following solutions for low-temperature plasma-assisted nitriding: pulsed d.c. discharge, thermionically assisted d.c. triode arrangements, plasma implantation, electron cyclotron resonance systems and thermionic arc discharges. We focus on metallurgical results obtained by these techniques on austenitic stainless steel and aluminium.

Low-temperature plasma-assisted nitriding

In this paper the mechanisms of ion nitriding are discussed, particular attention being paid to d.c. diode nitriding. Recent trends in the analysis of the mechanisms of d.c. diode nitriding are reviewed, emphasizing the importance of the cathode fall region. Diagnostics of active species and calculation of their densities in the plasma are presented and related to modelling. The hydrogen effect and plasma-solid interaction are also discussed. New developments and alternatives to d.c. diode nitriding such as triode nitriding are highlighted.

Progress in the analysis of the mechanisms of ion nitriding

This paper reviews the low-pressure (<10 Pa), high-density plasma-assisted nitriding processes recently developed for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For that purpose, plasma generation is most frequently ensured by d.c. glow discharges at relatively high pressure (100–1000 Pa) with the underlying limitations associated with this technology. Nevertheless, more flexibility and control are required for plasma nitriding of promising non-ferrous materials such as titanium, aluminium and their alloys. These requirements are fulfilled by the recently developed enhanced or intensified plasma nitriding processes that operate at lower pressures (<10 Pa) such as: thermionically assisted d.c. triode arrangements (TAT), plasma immersion ion implantation (PIII) or plasma source ion implantation (PSII), electron cyclotron resonance (ECR) systems and thermionic arc discharges (TAD). The purpose of this paper is to review these new nitriding processes from both technological and fundamental points of view. Plasma parameters and plasma–surface interactions are considered for these processes.

Low-pressure, high-density plasma nitriding: mechanisms, technology and results

Structural analogies are revealed between 310 stainless steel-nitrogen deposits prepared by reactive sputtering and diffusion layers resulting from low temperature plasma nitriding of the same grade of stainless steel Both the coatings and the diffusion layers show high nitrogen supersaturations in the fcc lattice of austenite and present a rather favourable compressive stress and a good level of microhardness An interesting corrosion resistance is also expected With these properties, future applications can be considered

Properties of sputtered stainless steel-nitrogen coatings and structural analogy with low temperature plasma nitrided layers of austenitic steels

AISI 316L stainless steel (SS) and titanium nitriding were studied in a low pressure arc-assisted nitriding process where the substrate temperature and the plasma parameters are uncoupled. Lower nitriding temperature limits were explored for constant plasma parameters in Ar–N2 gas mixtures and substrates at floating potential. Nitrogen superficial concentration, layer thicknesses and X-ray diffraction analyses were performed on SS specimens nitrided at two temperatures (580 and 680 K) for different times and titanium nitriding was studied in the temperature range 750–1025 K. At low temperature, the nitriding performances are limited by a plasma–surface phenomenon that probably involves recombination of nitrogen atoms.

H. Michel

Papers

Low-temperature plasma-assisted nitriding

Progress in the analysis of the mechanisms of ion nitriding

Low-pressure, high-density plasma nitriding: mechanisms, technology and results

Properties of sputtered stainless steel-nitrogen coatings and structural analogy with low temperature plasma nitrided layers of austenitic steels

Low temperature nitriding of AISI 316L stainless steel and titanium in a low pressure arc discharge