This article deals with the testing of surface layers produced on technical titanium Ti99.2 under glow discharge conditions. In order to determine the effect of process temperature on the produced surface layers, nitriding processes were carried out at 700°C and 800°C and for 3 and 5 hours. The research results on evaluating the properties of the obtained surface layers and the characterization of their morphology were presented. The impact of the adopted nitriding process variant on the quality of the obtained layers was evaluated. It was demonstrated that the use of the supplementary potential during the ion nitriding process reduces the unwanted edge effect, which results in a significant increase in the homogeneity of the nitrided layers and improves the functional properties of the technical titanium Ti99.2.
Biocompatible coatings produced on the basis of the chemically extracted natural hydroxyapatite (HAp) from the animal bones were deposited using multiplex method comprising glow discharge nitriding (GDN) of the titanium alloy substrate and pulsed laser deposition (PLD) of HAp on the formerly fabricated titanium nitride layer (TiN). The TiN interlayer plays an important role improving adhesion of HAp to substrate and preserves the direct contact of the tissue with metallic substrate in the case of possible cracking of HAp coating. Surface morphology of deposited layers, crystallographic texture and residual stress were studied in relation to the type of laser applied to ablation (Nd:YAG or ArF excimer), laser repetition, temperature of substrate and atmosphere in the reactive chamber.
Group of steel balls with different chemical composition, diameters and nitriding treatment parameters were investigated with using magnetic resonance and magnetization methods. Emerging nitrided regions consists of diffusion and surface layer of iron nitrides. The thickness of the individual layers depends on the type of steel and process parameters. Resonance signal shape and position were successfully described in the ferromagnetic resonance regime expected for dense iron magnetic system. Influence of the sample size, thermal treatment and carbon content on the absorption signal has been analyzed. Significant magnetic anisotropy has been revealed, as well as non-usual increasing of the magnetization as a function of temperature. It suggests, that overall antiferromagnetic ordering, destroyed by thermal movement, lead to increasing of the ferromagnetic region.
Thermo-chemical treatments are known to increase the fatigue life of industrial parts. Due to the imprecise consideration of residual stresses in predicting the durability of components subjected to cyclic loading and their effect on the fatigue life, the authors developed a numerical model combining the influence of residual stresses with stresses caused by bending. The authors performed the numerical simulation with the use of Finite Element Method to analyse material behaviour during cyclic loading. The residual stress state developed during nitriding was introduced onto cross-section of the numerical specimen. The goal of this work was better understanding of the real conditions of the nitride steel fatigue processes and improving the knowledge about numerical predicting of the fatigue life for parts with residual stresses. The results of simulation were compared with plane bending fatigue tests. The presented method indicates the possibility of increasing the accuracy of the fatigue analysis of elements after surface treatment, increasing its certainty and the ability to perform better optimization of service life.
Rising technical standards of customers, legal requirements and the trend to minimize maintenance effort raise the thermal, mechanical and tribological loads on components of combustion engines. In this regard, emphasis is laid on improving the piston ring - cylinder liner tribosystem, one with the highest energy losses. An efficient performance has to be guaranteed during its lifetime. Tribological investigations could be carried out on engine test benches, but they are highly cost-intensive and time-consuming. Therefore, a damage-equivalent test methodology was developed with the analogous tribological model, "ring-on-liner". The research was carried out under two characteristic operating conditions. One with a "standard" operating system, modelled in line with ideal lubrication conditions, and the other "extreme abrasive" operating system, typical to a system running on a lubricant contaminated by abrasive particles. To optimize the tribological loading capacity of the cylinder liner, with focus on these two operating conditions, numerous nitride coatings have been investigated. The key aspects being seizure resistance, running-in characteristics and long term wear behaviour.
Deep cryogenic treatment (DCT) is gaining popularity as a treatment used to modify structures obtained during heat or thermo-chemical treatment. The article presents the influence of DCT, carried out during heat treatment before and after gas nitriding processes, on the formation of gas nitrided layers on X153CrMoV12 steel. It was found that the use of DCT between quenching and tempering performed prior to gas nitriding processes, increases the hardness, thickness and wear resistance of the nitrided layers. At the same time, if we apply cryogenic treatment during post-heat treatment of nitrided layers, we also get very high wear resistance and increased thickness of nitrided layers, in comparison with conventional gas nitriding of X153CrMoV12 steel. In this case, DCT significantly increases also the hardness of the core by the transformation of retained austenite and the precipitation of fine carbides of alloying elements.