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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/

This study aims to investigate the surface modification on 20CrMnTi gear steel individually treated by diamond-like carbon films and nitride coatings.

For this purpose, the mechanical properties of a-C:H, ta-C and AlCrSiN coatings are characterized by nano-indentation and scratch tests. The friction and wear behaviors of these three coatings are evaluated by ball-on-disc tribological experiments under dry contact conditions.

The results show that the a-C:H coating has the highest coating-substrate adhesion strength (495 mN) and the smoothest surface (Ra is about 0.045 µm) compared with the other two coatings. The AlCrSiN coating shows the highest mean coefficient of friction (COF), whereas the ta-C coating exhibits the lowest one (steady at about 0.16). The carbon-based coatings possess excellent self-lubricating properties compared with nitride ceramic ones, which effectively reduce the COF by about 64%. The major failure mode of carbon-based coatings in dry contact is slight abrasive wear. The damage of AlCrSiN coating is mainly adhesive wear and abrasive wear.

It is suggested that the carbon-based film can effectively improve the friction-reducing and wear resistance performance of the gear steel surface, which has a promising application prospect in the mechanical transmission field.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0129/

The purpose of this paper is to obtain the optimal N₂/Ar ratio parameters for preparing Ta (C, N) coating. Three coatings with different N₂/Ar ratios were prepared on the TA15 substrate, and their effects on the wear properties of the coatings were discussed.

Ta(C, N) coatings with three different N₂/Ar ratios were prepared on TA15 substrates using the double cathode glow metallurgical plasma alloying technique (DGMPA) using a step-by-step diffusion method.

With the increase of N₂/Ar flow ratio, the hardness and elastic modulus of the coating first increase and then decrease. Compared with the S1 sample (N₂/Ar gas ratio 25: 75) and the S3 sample (N₂/Ar gas ratio 75: 25), the S2 sample (N₂/Ar gas ratio 50: 50) has better mechanical properties, with hardness increased by 48.45% and 6.8%, respectively, and elastic strain ratio increased by 22.8% and 28.5%, respectively. Moreover, the wear degree of the S2 sample is less than other samples. The wear rate of the S2 sample was 32.4% lower than the S3 sample at 300°C and 14.3% lower than the S3 sample at 500°C. Therefore, the S2 sample has the best mechanical properties and the best high temperature wear resistance.

Ta(C, N) coatings were prepared by DGMPA technology, and the wear mechanism of Ta(C, N) coatings with different N₂/Ar ratios was investigated to reduce the wear rate.

This study aims to introduce a strategy that permits well-defined contact areas in forming tools for improving both wear and friction properties by a selective laser treatment of a hydrogen-free diamond-like carbon layer (DLC), for substituting lubrication in forming processes. The need of lubricant substitution in forming processes is given because, besides the positive technological aspects, lubrication leads to numerous negative economic and ecological effects such as lubricant appliance and removal costs as well as its disposal.

Hydrogen-free DLCs with an sp³-ratio of 60-70 per cent are deposited on steel surfaces and subsequently micro-structured using direct laser interference patterning (DLIP). To find the optimal structure parameters for reducing friction and wear, line-like and cross-like patterns with three different structure sizes were fabricated onto the DLC layer. Tribological measurements are performed with a ball-on-disk tribometer on the differently DLIP-structured surfaces and compared to polished steel and unstructured DLC reference surfaces.

A reduction of the coefficient of friction, from 0.18 to 0.11, is observed for the laser-structured DLC surfaces, reaching values comparable to lubricated and polished steel surfaces, with a friction coefficient of 0.10.

Using DLIP, it was possible to show how this method can reduce friction on DLC-coated specimens. The observed characteristics are relevant to improve the tribological performance of forming processes, without usage of lubrication.

The purpose of this study is to investigate the tribological properties of tetrahedral diamond-like carbon (DLC) films in self-mated contacts in the presence of additivated and non-additivated vegetable oils. DLC films have high practical value due to low friction and low wear properties. On the other hand, vegetable oils are considered to be lubricants for future due to its resource renewability and biodegradability. Sometimes different chemical agents are added to vegetable oils to further improve its tribological properties. Thus, the tribological study of DLC films against additivated oils becomes important.

The tribology tests were conducted in a four ball tribo-meter under the boundary lubricated conditions.

Ta-C DLC exhibited 80 per cent lower wear rate under Zinc dialkyldithiophosphates (ZDDP)-added oil compared to that of base oil. In contrast, the friction coefficient under additivated oil was slightly higher than the base oil lubricated case. Moreover, the carbonyl band area as well as the viscosity change of ZDDP-added oil was much smaller than that of base oil. Therefore, ZDDP reduced the wear of DLC film and prevented the oxidation of base oil during tribotests.

This is the first work on the tribological properties of ta-C DLC lubricated with corn oil with and without anti-wear additives.

Facility location and re-location decisions are critical managerial decisions in modern supply chains. Such decisions are difficult in this environment as managers encounter uncertainty and risks. The study investigates establishing or moving distribution facilities in the global supply chain by considering costs, fulfilment, trade uncertainties, risks under environmental trade-offs and disruptive technologies.

This paper combines the possibilities and probabilistic scenarios for a supply chain network by proposing the novel Robust Optimisation and Mixed Integer Linear Programming (ROMILP) method developed under the potential uncertainty of demand while considering the costs associated with a four-tier supply chain network. ROMILP has been solved in a real-time logistics environment by applying a case study approach.

The solution is obtained using an exact solution approach and provides optimality in all tested market scenarios along the proposed global logistics corridor. A sensitivity analysis examines potential facility location scenarios in a global supply chain context.

Logistics managers can apply the ROMILP model to test the cost-benefit trade-offs against their facility location and relocation decisions while operating under uncertainty. Future research is proposed to extend the literature by applying data from the OBOR logistics corridor.

This study is the first to examine sustainable dimensions along the global logistics corridor and investigate the global container traffic perspective. The study also adds value to the Middle East logistics corridor regarding facility location decisions.

Young men of African‐Caribbean origin are over‐represented in mental health services (MHSs), often entering these services by coercive routes, such as under the Mental Health Act or via the criminal justice system. This pilot study focused on patients' narratives of their journey from first contact with primary care services. Our principal aim was to describe and compare early experiences of help‐seeking for serious mental health problems among young men of white and black ethnicity.In‐depth interviews were conducted (using a topic guide) with black and white men aged 18‐30 years old and who were accessing secondary care mental health services for the first time for a psychotic illness. Participants were recruited from the early intervention services serving inner‐city Birmingham. Seven participants were interviewed, and 12 themes were identified from transcripts. Six of these individuals had consulted their GP prior to accessing the early intervention service. Only one attendee received medication at initial consultation, and none were referred to specialist mental health services. Participants described the manner in which family or friends interceded on their behalf to advocate for and secure specialist help ‐ either by accompanying them to see their GP, contacting mental health services directly or taking them to the local accident and emergency department. The latter route was accessed by black but not white participants. Three out of four black participants and one out of three white participants were subsequently admitted to hospital. None of the participants were particularly satisfied with their experience of primary care. Communication was less than ideal, and participants were able to reflect on their own failure to disclose critical information to their doctor. By contrast, all participants confided in family or in their trusted friends that they were becoming aware that they were experiencing mental distress.Our findings confirm the difficulties faced by GPs and those who consult them in the early stages of first onset psychotic episodes, and the importance of having family or friends who are able to advocate on other people's behalf at times of crisis. Despite the advent of universal early intervention services across the UK, those most in need may still not be receiving the help that they need in the timeliest manner.