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The curved and tribologically highly stressed surfaces of bearing components pose a major challenge for steel alloys or tribological resistant coatings like tetrahedral amorphous carbon (ta-C) coatings which in particular have an increased risk of delamination due to the significantly increased residual stresses. A possibility to prevent coating failure is the use of dopants while maintaining or even increasing tribological properties. This study aims to compare the tribological behavior of several doped diamond-like-carbon coatings with an undoped ta-C coating under varying slip conditions and Hertzian pressure up to 1800 MPa.

For this purpose, the tribological behavior was studied using of a ball-on-disc tribometer and a two-disc test rig under mixed/boundary conditions. The tests were conducted with coated specimens against uncoated 100Cr6 steel. Additionally, the influence of lubrication additives was studied due to the use of two fully formulated PAO-based oils, one without and one with molybdenum containing additives. The friction was measured in situ, and the wear was analyzed trough laser scanning microscopy and tactile measurement.

It was shown that the use of doped ta-C coatings exhibited a tendency for a more favorable tribological behavior compared to undoped ta-C coatings, with no general dependence on the lubricants used. The use of the most suitable coatings reduced the wear of the steel counter-body considerably.

To the best of the authors’ knowledge, this is the first approach of testing the tribological behavior of these doped ta-C coatings, developed for friction efficiency, in dependency on lubrication additives under the given load collective. The approach is relevant to determine whether the friction reduction and the wear inhibition of these coatings are suitable for higher contact pressures and load cycles.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0336/

The evaluation of the haptics of water taps and wear-related changes during usage usually involves time- and cost-intensive testing. The purpose of this paper is to abstract the tribo-system between technical ceramic disks of water tap mixer cartridges to the model level and study the tribological behavior.

The friction and wear behavior was studied by means of an alumina ball-on-original alumina disk setup at different temperatures as well as under dry conditions and under lubrication by different greases. Thereby, the frictional behavior was measured in situ, and the wear losses were analyzed by means of laser scanning microscopy.

It was shown that friction and wear can behave in a contrasting way, whereby one grease might lead to low friction, that is, an easy-going movability of the water tap, but to increased wear losses. The latter, in turn, is an indicator for the usability and service life, which cannot be explained from friction alone. Thereby, the viscosity of the base oil, the grease consistency and additives were identified as relevant grease formulation parameters to allow for fluid film (re-)formation and removal of wear particles.

To the authors’ best knowledge, this is the first approach to systematically analyze the friction and wear behavior of technical ceramic disks of water tap mixer cartridges in dependency on the temperature as well as the used lubricating grease. This approach is relevant for developing screening test strategies as well as for the selection of lubricants for water tap applications.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0334/

Synthetic and semi‐synthetic fluids are known to be less sensitive to bacterial growth than soluble oils. However they often offer poor lubricating properties, especially in the extreme pressure (EP) regime. In this paper, we introduce an innovative sulfur based additive demonstrating outstanding EP performances despite being completely water soluble. In combination with oiliness and anti‐wear agents, such as phosphate esters or alkyl thio acids, it exhibits a wide range of lubricating properties which are requested for multifunctional lubricants. Finally, we show that synthetic and semi‐synthetic fluids containing this type of additive can be considered for severe metalworking operations.

Reliable modeling of induction hardening requires a multi-physical approach, which makes it time-consuming. In designing an induction hardening system, combining such model with an optimization technique allows managing a high number of design variables. However, this could lead to a tremendous overall computational cost. This paper aims to reduce the computational time of an optimal design problem by making use of multi-fidelity modeling and parallel computing.

In the multi-fidelity framework, the “high-fidelity” model couples the electromagnetic, thermal and metallurgical fields. It predicts the phase transformations during both the heating and cooling stages. The “low-fidelity” model is instead limited to the heating step. Its inaccuracy is counterbalanced by its cheapness, which makes it suitable for exploring the design space in optimization. Then, the use of co-Kriging allows merging information from different fidelity models and predicting good design candidates. Field evaluations of both models occur in parallel.

In the design of an induction heating system, the synergy between the “high-fidelity” and “low-fidelity” model, together with use of surrogates and parallel computing could reduce up to one order of magnitude the overall computational cost.

On one hand, multi-physical modeling of induction hardening implies a better understanding of the process, resulting in further potential process improvements. On the other hand, the optimization technique could be applied to many other computationally intensive real-life problems.

This paper highlights how parallel multi-fidelity optimization could be used in designing an induction hardening system.

Environmental protection regulations are becoming increasingly strict. Using water instead of a hydraulic mineral or biodegradable oil in power‐control hydraulic systems is a very positive step towards complying with these regulations. Since water hydraulics has many specifics, primarily related to lower viscosity and lubricity of water compared to oil, which greatly affects the leakage, and even more the friction and wear in these systems, a dedicated test rig is required for performing research with the real‐scale components. The purpose of this paper is to present some preliminary representative results on dynamic responses of the two hydraulic circuits with and without a mass load.

The paper presents the newly developed dedicated test rig and its dynamic characteristics when used with water and oil as hydraulic fluid. Hydraulic pressures and motions of spool and piston in the two different fluids were of special interest.

The results clearly show their dependence on friction properties of selected materials in different hydraulic fluids. While the oil valve worked perfectly, water valve has some irregularity, linked with the small gap, the shape irregularity, the surface roughness and the poorer lubrication conditions in the water hydraulics compared to the oil system.

The observed irregularity of the movement of the spool in the water hydraulic valve has almost no influence on the movement of the piston rod of the water cylinder, which is a very promising result for future research on water hydraulics.

Environmentally adapted lubricants (EALs) have been a slowly growing segment of the lubricants business since the early 1970s. The evolution of environmental thinking has led to the change of focus, from biodegradability to renewability. In the future, the focus will be more on fuel economy and lower emissions. Technical development drivers include the availability of suitable base fluids and additives for lubricants formulation and the adaptation of technical standards, OEM specifications and eco‐labels. Important non‐technical development drivers include environmental management tools and eco auditing. Environmental policy, and procurement guidelines for cities and government organizations, clearly has a large impact. EALs have been repeatedly heralded as one of the few future growth segments of the lubricants business, hence the relatively large increase in R&D activity over the last decade. In sales terms, growth has been slow, limited by high cost and several other factors. For a good future development, both technical and political hurdles must be overcome.