This study systematically investigates the tribological performance of titanium doped diamond-like carbon monolayer and multilayer coatings with superior mechanical properties. The coatings were lubricated in poly alpha olefin grade 4 (PAO4) base oil, containing three concentrations of two organic, ashless, and sulfur free (low SAPS) antiwear, and extreme pressure additives with different amounts of phosphorus and nitrogen (Duraphos (R) 178 and Duraphos (R) OAP). The multilayer Ti-doped DLC coatings exhibited superior tribological performance compared to uncoated steel, undoped DLC, and monolayer Ti-DLC coatings. They exhibited coefficient of friction values which were in the range of 0.013 and 0.006 (superlubricity) for formulations with Duraphos (R) OAP. Duraphos (R) 178 significantly lowered the specific wear rates of both the monolayer and multilayer coatings.

To address modern tribological challenges-reducing friction and wear to conserve resources while minimising environmental impact-cobalt-doped DLC (Co-DLC) coatings were developed. These nanometric multilayer coatings, designed to retain key properties such as hardness, reduced modulus, and substrate adhesion, were fabricated using non-reactive DC magnetron sputtering (DCMS). The multilayer structure was achieved by controlling the planetary substrate holder's rotational speed. Characterisation of microscopic, chemical, structural, and mechanical properties was performed using techniques including FEI-SEM, EDS, XRD, TEM, Raman spectroscopy, scratch adhesion testing, and nanoindentation. Tribological performance was evaluated under boundary and fully flooded lubrication using PAO4 base oil and formulations with ashless, sulphur-free AW and EP additives. The coatings exhibited a granular surface morphology, columnar cross-sections, and amorphous structure. Increased dopant concentrations slightly enhanced graphitisation and significantly improved adhesion, though hardness and reduced modulus decreased. Tribological testing revealed superlubricity in several coating-oil combinations and significantly reduced wear rates with higher dopant levels and new additives. A phosphate ester additive without an amine group achieved the lowest COF values, while one with an amine group yielded minimal wear rates. These findings highlight the potential of Co-DLC coatings and tailored additives to minimise friction and wear effectively.

This study aims to evaluate the tribological behavior of polyphthalamide (PPA) and polyetheretherketone (PEEK) lubricated with biodegradable synthetic esters. Tribological tests were performed at 23 degrees C and 100 degrees C with new and aged samples to assess the effects of increased temperature and polymer aging on friction and wear. The results of tests at room temperature and the SEM images of the wear scars show that synthetic esters provide better wear resistance to PEEK than synthetic mineral oil (polyalphaolefin, PAO). FTIR and XPS analyses suggest the formation of a physisorbed protective film by the esters. Trimethylolpropane-based ester (TMP) was shown to adsorb better to both polymers than propylene glycol-based ester (PG), but this did not translate into a better tribological performance. When compared to room temperature, tests at 100 degrees C showed a higher wear coefficient for both polymers, irrespective of the oil. However, the friction coefficient increased for PEEK due to a higher adhesion, while it decreased for PPA because of the material's softening. The aging of samples at 100 degrees C degraded the tribological performance of the polymers, especially aging in PG ester, which caused an increase in friction for PEEK and an increase in friction and wear for PPA. PG ester was found to have caused oxidation of both polymers to a greater extent than PAO or TMP ester.

Two sets of nanoscale multilayer Ti-DLC/DLC coatings, with similar chemical composition but different periods between consecutive layers (0.4 and 5.5 nm), were deposited by non-reactive direct current magnetron sputtering using different rotational speeds of the substrate holder (12 and 1 rpm, respectively) in this work. The results show that the overall Ti content in the coatings varied from approximate to 2.9 to approximate to 8.2 at. % in both cases. Significant fluctuations in the Ti concentration between the middle points of the DLC and Ti-DLC layers were observed for the coatings deposited at 1 rpm. All the coatings deposited were mainly amorphous, presenting a columnar structure and a cauliflower-like granular surface morphology. The sp 2 /sp 3 ratio increased as the concentration of Ti rose. The coatings deposited at 1 rpm demonstrated better mechanical properties (up to 33 % improvement in hardness and up to 25 % improvement in the elastic modulus) when compared to the equivalent coatings deposited at 12 rpm. The multilayer titanium doped coating (deposited at 1 rpm) with 5.9 at. % Ti presented the most significant improvement in mechanical properties when compared to pure DLC and monolayer coatings deposited at 12 rpm. The results confirmed that it is possible to tune the performance of this type of coatings by depositing alternating layers of pure DLC and Ti-doped DLC.

Laser powder bed fusion (LPBF) involves depositing, melting, and solidifying metal powder particles layer by layer to create 3D components. In this study, a deep fundamental understanding on how process parameters-laser power, scan speed, and hatch spacing-affect the melt pool, densification, microstructure, hardness, and thermal behavior of 420 stainless steel (420SS) parts produced by such technology is provided. The conducted investigation considers five levels of laser power and hatch spacing, and four scan speeds. Optimal single tracks, based on geometry and profile, are achieved with laser powers between 40 and 80 W and a scan speed of 10 mm s-1. In the multitrack analysis, it is indicated that a dense, smooth surface is obtained with a hatch spacing of 250 mu m, corresponding to an overlapping rate of approximate to 30%. The 420SS samples show high densification (approximate to 99%) and low surface roughness (approximate to 3.62 mu m). The microstructure consisted of martensite laths and retained austenite. The hardness and thermal conductivity of the samples are measured at 540 HV and 15.3 W m-1 K-1, respectively. In this study, the understanding of the process-structure-property relationships in LPBF of 420SS is expanded. Laser powder bed fusion involves depositing, melting, and solidifying metal powder particles layer by layer to create 3D components. In this study, a deep fundamental understanding on how process parameters-laser power, scan speed, and hatch spacing-affect the melt pool, densification, microstructure, hardness, and thermal behavior of 420 stainless steel parts produced by such technology is provided.image (c) 2024 WILEY-VCH GmbH

In this study, samples of 420 stainless steel were obtained by hot pressing from powder at temperatures from 1,100 to 1,200 degrees C. The aim was to explore the influence of the processing temperature on their grain size, microstructure, densification and mechanical properties. The results showed that it is possible to produce dense samples at these sintering temperatures. The sintering temperature influenced the density, grain size, structural phases, and hardness of the samples. Martensite and austenite were present in the samples sintered at 1,100, 1,150, and 1,180 degrees C. Precipitation of Cr23C6 was observed after sintering at 1,200 degrees C. This sample was the one with the highest density (99.7% densification) and hardness (771.9 HV).

This study investigated the mechanical and tribological properties of 3D-printed Poly (lactic acid) (PLA) composites reinforced with different concentrations of carbon fibers (SCF) and graphene nanoparticles (GNP) (0.5 to 5 wt.% of each filler). The samples were produced using FFF (fused filament fabrication) 3D printing. The results showed a good dispersion of the fillers in the composites. SCF and GNP promoted the crystallization of the PLA filaments. The hardness, elastic modulus, and specific wear resistance grew with the increase in the filler concentration. A hardness improvement of about 30% was observed for the composite with 5 wt.% of SCF + 5 wt.% GNP (PSG-5) compared to PLA. The same trend was observed for the elastic modulus with an increase of 220%. All the composites presented lower coefficients of friction (0.49 to 0.6) than PLA (0.71). The composite PSG-5 sample showed the lowest value of specific wear rate (4.04 × 10−4 mm3/N.m), corresponding to about a five times reduction compared to PLA. Therefore, it was concluded that the addition of GNP and SCF to PLA made it possible to obtain composites with better mechanical and tribological behavior.

This work proposes the design of laser-textured patterns for the development of surfaces with high anchor densities capable of promoting solid mechanical bonding of highly abrasive sintered diamond/carbide-reinforced. Cu-based composite coatings with excellent wear resistance. The results show the development of dense and well-adhered coatings onto the patterns and how the higher nucleation of TiC/Fe3C on the diamond surfaces favours its greater bonding within the matrix, preventing its graphitization, and detachment. Reductions above 40% and 60% in the CoF were observed, under dry conditions, for coatings reinforced with 10 & 30 wt% of diamonds, respectively. Depending on the percentage of diamond used, the best glass/coating and alumina/coating wear volume ratios were around 20 and 6. These values would indicate that these composite coatings show high performance and therefore could be used to make tools for grinding and/or cutting glass and ceramic materials.

Multi-material structures make it possible to obtain effective solutions to engineering problems by combining the benefits of different materials to meet the requirements of different working conditions. The aim of this multifunctional 420 stainless steel-copper structure is to create a hybrid solution in which copper acts as heat-transfer enhancer (through cooling channels) while maintaining the required mechanical properties of the steel matrix. This work focuses on a combined engineering process consisting of CNC machining through holes on a 420 stainless steel surface substrate and subsequent filling with copper by hot pressing. The influence of the copper filling on the physical, chemical, microstructural, mechanical, and thermal properties of this multi-material solution was analysed. The machined area (5% of the total surface area) consisted of nine holes with a diameter of approximately 1 mm. The multi-material samples showed high densification, homogeneous microstructures, and a well-defined and sharp interface between the two materials. The microhardness values measured for the 420 stainless steel and copper were 759 and 57 HV, respectively, and the thermal conductivity of the multi-material was ≅ 59% higher than the 420 stainless steel (39.74 and 16.40 W/m K, respectively).

A CuCoBe–diamond composite was used to reinforce a laser textured 410 stainless steel piston ring by hot-pressing. Different hot-pressing parameters were used to optimize the sintering process of the CuCoBe particles ( P = 25 and 50 MPa, T = 820 and 980 °C, and t = 15 and 30 min). The results showed an increase in the hardness of the hot-pressed samples (50.5% and 48.5% for P = 25 and 50 MPa, respectively). Three textures with different track widths and distances between them were produced by laser on the compression piston rings’ surface. The composite powders were used for the reinforcement of the textures by hot-pressing at the optimized sintering parameters ( T = 980 °C, P = 25 and 50 MPa, and t = 15 min). The tribological results revealed that larger texture dimensions led to enhanced tribological performance.

The aim of this study was to fabricate different self-lubricating poly (lactic acid)-based bio-composites reinforced with mono- and multi-fillers of carbon fibers, graphene nanoparticles, and a soft Sn-based brazing alloy (Sn89-Zn8-Bi3) using a two-step process consisting of mechanical alloying followed by casting. The results showed that the incorporation of the different fillers on the PLA surface by mechanical alloying was quite homogenous. The volume ratio between the PLA and the fillers was 1:0.02, respectively. The PLA sample reinforced with short carbon fibers and graphene nanoparticles presented the highest hardness (84.5 Shore D, corresponding to a 10% increase compared to PLA) and the lowest specific wear rate (1.5 × 10−4 mm3/N·m, one order of magnitude lower than PLA). With regard to the coefficient of friction, the lowest value was obtained for the sample reinforced with graphene (0.43, corresponding to a decrease of 12% compared to PLA).

This review provides a critical overview of the influence of the laser powder bed fusion (LPBF) processing parameters on the final properties of the three steels used in the plastic injection mould industry (420 stainless steel, H13, and P20 steels). The main objective is to provide an engineering overview concerning the response of the parts made from the materials produced by this technique. A comprehensive summary of LPBF processing parameters and their influence on the physical, mechanical, tribological, corrosion, and thermal properties of the LPBFed parts is presented and discussed. An analysis of the suitability of these steels for the production of components for the plastic injection mould industry is also presented. This review shows that, despite the increase research about these steels over recent years, there are still some shortcomings and issues that require further investigation, such as the behaviour of LPBFed parts in-service conditions, their thermal behaviour, and the influence of the processing parameters and their surroundings on the final properties of the parts.

The surface of an annealed 420 stainless steel plate was textured using a fibre laser in this work. Four hundred textures were produced from eighty different combinations of processing parameters (laser power, scan speed, line spacing and number of passes). The most promising textures (fourteen combinations of the processing parameters) were obtained with laser power values of 16 and 64 %, scanning speeds up to 2,000 mm/s, number of passes of 8 or higher and line spacings of 40 and 50 µm. The lower the laser power, the lower the scanning speed and the high number of passes and line spacings were required for a suitable ablation process. High laser powers were responsible for the dissolution of the chromium carbides in the laser tracks (top and edges of the unmachined areas). The hardness of these regions was 320 ± 11 HV against 255 ± 5 HV for the unmachined zones.

A novel multi-material design concept to be applied in plastic injection moulds is proposed combining the mechanical resistance of the 420 stainless steel alloy and the high thermal conductivity of copper, in a single component, fabricated in just one event by means of homemade 3D Multi-Material Laser Powder Bed Fusion equipment. The processing strategy and the interface region between both materials are analysed and discussed both from a metallurgical and mechanical point of view. The results show a good metallurgical bonding between the two materials, with a diffusion zone of about 10 mu m, capable of providing mechanical interlocking, i.e. entrapment of one material in the other, creating a physical link between them. Both materials have low porosity and the pores detected present a sub-micrometre size distribution. A few pores and cracks on both the top and cross-section surfaces were detected with some tens of micrometres in size, at the interface zone. The hardness of the 420 stainless steel and copper varied from 482 to 532 HV and 99 and 116 HV, respectively.

Hydrophobic composites are prepared from Ultra High Molecular Weight Polyethylene (UHMWPE) and onion-like carbon (OLC), employing a solvent-free mechanochemical process consisting of milling at 250 rpm for 60 min. The encapsulation of OLC on the surface of UHMWPE microspheres increased with the increasing composition of OLC from 0.5 to 5 wt.%, thereby mimicking the core-shell structure. The consolidated composite with 5 wt.% of OLC exhibited a higher water contact angle (WCA) of about 111.18 degrees, compared to pure UHMWPE (94.80 degrees). (C) 2022 The Authors. Published by Elsevier B.V.

AISI 420 martensitic stainless steel is widely used in the mould industry due to its high tensile strength, hardness, and corrosion properties. Another requirement concerning any material used for this type of application is high thermal conductivity to minimise the time between consecutive injection cycles. The surfaces of some parts of the mould may be textured and reinforced with a material with higher thermal conductivity to achieve this aim. The results of a detailed study on the texturing of annealed 420 stainless steel using a Nd:YVO4 fibre laser are presented in this work. The influence of the laser's processing parameters (laser power, scanning speed, number of passes, and line spacing) on the dimensions of the track, microstructure, and hardness of the modified surfaces was studied. Based on the continuity and dimensions of the machined grooves, several promising textures could be produced with laser power values from 5 to 30 W, scanning speeds of 500 to 2000 mm/s, 8 passes or more, and line spacings of 40 and 50 µm. High laser powers were responsible for the dissolution of chromium carbides in the laser tracks, the incorporation of chromium in austenite, and the consequent hardening of the microstructure.

ABSTRACT Porous Si100-xSnx samples with x = 15, 30 and 40 at.% were produced from Si and Sn elemental powders by mechanical alloying followed by two different compaction and sintering processes: cold uniaxial pressure and subsequent sintering at 220°C, and hot pressing at 240°C. The results showed that it is possible to produce samples with a major porosity of close to 0.1 μm. The porosity of the Si70Sn30 sample that was mechanically alloyed for 12 h and synthesized by the former process is in the mesoporous region. The structure of all the final samples is composed of the Si, Sn and SnO phases.

The aim of this work was the development, production and characterisation of a multi-functional surface, consisting of a 420 stainless steel surface textured by laser and subsequently filled with pure copper by hot pressing, for plastic injection moulds. The influence of pure copper on the physical, chemical, surface, mechanical and thermal properties was analysed. The textured pattern consisted of unidirectional lines with a machined volume of approximately 12%. The steel and pure copper interface after sintering were well defined and sharp, and no significant diffusion was observed in the multi-material part produced. The pure copper zones exhibited grains of a quite heterogeneous size (lower than 50 µm) with twins and micropores at the grain boundaries, while the 420 stainless steel consisted of an iron-rich matrix (grains lower than 10 µm) and Cr 23 C 6 . The hardness values of the 420 stainless steel and copper measured were 385 HV and 84 HV, respectively, and the thermal conductivity of the multi-material solution was ≅ 4 times higher than the 420 stainless steel (62.54 and 15.72 W/m K, respectively).

The development of iron and titanium carbides nanoparticles reinforcements during the mechanosynthesis Cu-10Sn-15Ti/diamonds composite powders from a mixture of blended Cu/Sn/Ti powders and synthetic diamonds (10 wt.%) was studied in this work. The analysis of the microstructure evolution showed that mechanical alloying performed at high-energy ball milling (600 rpm) allows developing different metastable phases depending on the SA content and milling time. For 3 wt.% of SA, XRD patterns revealed a metastable Cu(Sn) solid solution is produced after 5 h of MA while Fe2.939O4, FeTiO3 and TiH0.66 nanophases were formed for milling times higher than 15 h as a result of degradation of the SA in form of gaseous products (CO, CO2, H-2, and lighter hydrocarbons (HC's)). XRD confirm that the release of these gases, along the SA degradation, and high carbon content carbon favors the carbothermic reduction of Fe2.939O4 for producing amorphous Fe3C nanoparticles at low-temperature thanks to the high-energy transferred in each impact during the MA process. For 1 wt.% of SA, XRD patterns showed the formation of Cu (Ti, Sn), from the very beginning of the process (5 h), is accompanied by the release of carboxyl groups (-COOH) and crystallization of long heptadecane chains, CH3(CH2)(15)CH3. The high boiling point of this heptadecane chains and the low Fe released during milling, produces a lower content of amorphous Fe3C nanoparticles. DSC and SAED patterns performed in the mixture of both alloyed powders after heating up to 1000 degrees C showed the carbothermic reduction of FeTiO3 for producing TiC nanoparticles takes place preferably when a 3 wt.% of SA is used. In both cases, the resulting alloyed powders are composed by a mixture of crystalline Cu13.7Sn + Fe + Fe3C + C + TiC phases with an Fe, and Fe3C and TiC content lower in the case of the powders processed with 1 wt.% SA. The development of this dissimilar Fe3C and TiC content produces the mixture with 3 wt.% of SA shows a higher stiffness.