Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600°C

Wear, 2009

Since the term 'lubricious oxides' was introduced to tribology in order to describe expected low coefficients of friction (COF) and high wear resistances in unlubricated (dry) sliding conditions numerous studies have been carried out on bulk materials and thermal spray coatings of the Ti-O system. Recently, studies were performed on the binary TiO 2-Cr 2 O 3 system, as well as with (Ti,Mo)(C,N)-NiMo cermets or TiC-based thermally sprayed hardmetal coatings, which might form beneficial titanium suboxides as a result of tribo-oxidative and/or high-temperature reactions. In this paper, we shortly summarize the characteristics and dry sliding wear resistance of thermally sprayed oxide coatings of the Ti-O and TiO 2-Cr 2 O 3 systems, as well as of (Ti,Mo)(C,N)-Ni(Co) hardmetal coatings. The prediction of solid lubrication properties of titanium suboxides was inspired from the planar oxygen defects present in the Magnéli-phases of titania, e.g., so-called crystallographic shear planes. While such structures with some limitations can be realised in coatings, the significant disadvantage is that TiO x tends to re-oxidize in air above ∼380 • C. The iso-structural phases in the TiO 2-Cr 2 O 3 phase diagram can be prepared in air and have stable oxygen content. However, as can be concluded from the phase diagram, during thermal spraying phase transformations occur as well. In this paper, the wear resistance of alumina dry sliding against APS-sprayed coatings of three compositions in the TiO 2-Cr 2 O 3 systems (compositions 75Cr 2 O 3 /25TiO 2 , 27Cr 2 O 3 /73TiO 2 and 23.5Cr 2 O 3 /76.5TiO 2) is studied from room temperature up to 800 • C and sliding speeds in the range of 0.1-7.5 m/s. The results are compared with those of a chromia and a titania suboxide coatings, as well as with (Ti,Mo)(C,N)-Ni(Co) coatings and bulk (Ti,Mo)(C,N)-NiMo cermets as self-mated couples.

Wear, 2007

Five thermally sprayed coatings, considered for application in earth moving vehicle undercarriage components, undergoing consecutively lubricated and dry sliding wear, were prepared and investigated. Four different wear tests were employed to reveal the factors controlling the wear response under different contact conditions. An approach considering the local and overall strength of the coating in connection with the knowledge of contact stresses helped to understand the major wear modes under specific contact conditions for the materials tested. The testing illustrated that in situations with lower contact stresses the contact response of the coating may not be directly related to the intersplat binding strength and hardness, but rather to the local splat properties. It has been shown that a porous structure although limiting the wear resistance of nickel aluminum coating in dry under high contact stress may be beneficial in quasi-lubricated sliding. High local splat hardness measured for the molybdenum carbide coatings appeared to be crucial for its enhanced wear resistance. The testing configuration 'rotating ring on flat' newly employed in this study has been proven to be a highly reproducible and efficient way of wear testing for thermal spray coatings.

Metallurgical and Materials Transactions A, 2014

In this paper, we show that duplex surface treatment, combining oxygen diffusion hardening with the subsequent deposition of thick, low-friction nanocomposite nc-MeC/a-C coatings to improve the tribological properties of the Ti-6Al-4V alloy. We have synthesized, in a magnetron sputtering process, the nanocomposite nc-MeC/a-C coatings (where Me denotes W or Ti transition metal) consisting of two dissimilar materials (nanocrystallites of transition metal carbides MeC and an amorphous carbon matrix a-C). The nano and microstructure of the substrate material and coatings were examined with the use of scanning and transmission electron microscopy as well as by X-ray diffractometry. It was found that different carbide nanocrystals of the same transition metal were embedded in an amorphous carbon matrix of both coatings. The HRTEM analysis indicated that the volume fraction of tungsten carbides in the nc-WC/a-C coating was equal to 13 pct, whereas in the nc-TiC/a-C one the volume fraction of the titanium carbides was equal to just 3 pct. The tribological properties, hardness, and scratch resistance of the coatings were investigated as well. The coefficient of friction (COF) of the coatings during dry sliding against 6 mm diameter alumina ball reached very low value, 0.05, in comparison with an oxygen-hardened alloy, whose COF was equal to 0.8. This lowfriction effect of the coatings has been attributed to the formation of a self-lubricating film in sliding contact. The coatings exhibited similar failure morphology in the scratch tests. Even though the hardness was rather low, the coatings exhibited a very good wear resistance during sliding friction. The wear rate of the nc-WC/a-C coating was equal to 0.08 9 10 À6 mm 3 N À1 m À1 and for the nc-TiC/a-C one it was 0.28 9 10 À6 mm 3 N À1 m À1 .

Tribology in Industry, 2021

The effect of high temperature on the sliding wear and friction behaviour of NiCrBSiFe powder coating on stainless steel 316L substrate was investigated. The NiCrSiBFe coatings were obtained using a thermal spray technique. The sliding wear tests were performed as per ASTM G99 on the pin on disc tribometer from room temperature (28 ℃) to 700 ℃ temperature condition. The coating characterization was carried out with X-ray diffraction, scanning electron microscopy, porosity analysis and nanoindentation. A 3D non-contact analysis was performed on the wear-track to obtain the wear rate of the coating at different temperatures. The coefficient of friction and wear rate was obtained for the coatings against silicon nitride (1580 HV 0.3) material. The coefficient of friction was obtained as 0.68, 0.15 and 0.51 at room temperature, 300 ℃ and 700 ℃, respectively. The mild wear range confirms the efficacy of the coating at high temperature. The wear rate and coefficient of friction of the coatings were influenced by the oxidation and mechanical properties at the hightemperature conditions. The wear rate increases from 300 o C to 700 o C as the substantial amount of material loss from the coating surface occurred due to the coatings thermal softening and the fragmentation of oxides like CrO3, SiO2 and NiO.

Surface & Coatings Technology, 2006

In the present study, the wear behaviour of nanocrystalline coatings of the composition (Ti,Mo)(C,N) -45 vol. % NiCo, prepared by vacuum plasma spraying (VPS) and high-velocity oxy-fuel (HVOF) spraying of high-energy-milled powder, is characterized and compared to microcrystalline coatings of the same composition. Two-body abrasive wear tests, as well as scratch tests, are applied to produce wear traces on the surfaces of the nano-and microcrystalline coatings. While nanocrystalline HVOF coatings are weaker than their microcrystalline counterparts, nanocrystalline VPS coatings show superior wear resistance. The worn surface morphologies are investigated with optical microscopy, scanning electron microscopy and atomic force microscopy. The wear mechanisms and failure of nano-and microcrystalline coatings are distinctly different and are discussed in detail. D

Materials Today: Proceedings, 2019

The wear breakdowns of dissimilar gears employed for automotive and aerospace services operating under severe environments could be minimised by applying WC based coatings. The tribological performance of WC-Cr 3 C 2-Ni composite coatings deposited by High-Velocity Oxy-Fuel (HVOF) technique has been investigated. The coatings were characterized with esteem to nano-hardness, surface roughness, microstructure, and porosity. The dry sliding experiments were in accordance with ASTM G99 on the ball-on-disc tribometer at room temperature with alumina ball as a counter body. The contact stress is principal factor affecting severe wear of gears and consequently, variable contact pressure has been applied to simulate concrete effect. Experimental analysis proved that coated specimens exhibited higher hardness, lower coefficient of friction and better anti-wear properties which enhance life span of gears.

Wear, 2007

High velocity oxygen-fuel (HVOF)-sprayed wear resistant Co-28%Mo-17%Cr-3%Si and Ni-32%Mo-15%Cr-3%Si coatings, both as-sprayed and after heat treatments at 600 • C for 1 h, have been studied. Particularly, their dry sliding wear behaviour has been compared by ball-on-disk tests against different counterbodies (100Cr6 steel and sintered alumina), and differences were discussed based on microstructural characteristics and micromechanical properties (Vickers microindentation and scratch test responses). As-sprayed coatings contain oxide stringers, are mostly amorphous and display rather low Vickers microhardness (about 7.4 GPa for the Co-based and 6.2 GPa for the Ni-based), toughness and elastic modulus. Heat-treated ones display sub-micrometric crystalline intermetallics, improving hardness (9.6 GPa and 7.4 GPa, respectively) and elastic modulus. Scratch tests indicate greater brittleness of the Ni-based alloy (higher tendency to cracking). Due to low hardness and toughness, both as-sprayed coatings undergo wear loss against steel and alumina counterparts. The more plastic Co-based alloy undergoes higher adhesive wear against steel and lower abrasive wear against alumina; the situation is reversed for the Ni-based alloy. After heat treatment, the wear loss against steel is very low for both coatings; abrasive wear still occurs against alumina.

Wear, 2016

This paper provides a comprehensive characterisation of HVOF-and HVAF-sprayed Cr 3 C 2-25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr 3 C 2 than the feedstock powder, possibly due to the rebound of some Cr 3 C 2rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter-and intra-lamellar cohesion, being higher (Z 70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (E5x10 À 6 mm 3 /(Nm)). At 400°C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from E0.7 to E 0.5. The thermal expansion coefficient of the coatings (11.08x10 À 6°C À 1 in the 30-400°C range) is sufficiently close to that of the steel substrate (14.23x 10 À 6°C À 1) to avoid macro-cracking.

Wear, 2010

An extended study on tribological properties of carbon nitride coatings under oscillating sliding conditions has been carried out. The coatings were prepared by reactive magnetron sputtering with graphite target using nitrogen as reactive gas in an argon/nitrogen atmosphere during the deposition process to deposit carbon nitride, CN x . Coating thickness was about 2 m. A 200-300 nm thick Ti interlayer was used to enhance adhesion. The nitrogen flow during the deposition was varied to control the amount of nitrogen in the coating. Maximum amount of N-content was about 28 at%, achieved at a maximum N 2 flow rate. Other deposition parameters were target to substrate distance, substrate temperature during deposition and bias voltage. The results show a large variation of hardness depending mainly on the nitrogen content and bias voltage. Higher bias voltage produced harder coatings as did lower nitrogen content. The tribological properties were tested unlubricated and lubricated by paraffin oil under gross slip fretting conditions at room temperature against alumina as counter material. Most coatings, but not all, showed a more or less pronounced dependence of wear on relative humidity with wear rates from 10 −5 to 10 −6 mm 3 /Nm. The best coatings with regard to a low wear rate and the least dependence upon relative humidity were carbon nitride coatings deposited at elevated substrate temperatures up to 350 • C. The wear resistance of these coatings was increased under the most severe conditions by about one order of magnitude. The results are discussed on the basis of a transfer layer formation. The results show clearly that wear is not significantly correlated to the coating hardness which itself is strongly dependant on the nitrogen content. However, under lubricated conditions with paraffin oil, wear rates were generally very low with wear coefficients at about 10 −8 mm 3 /Nm.

Wear, 1976

The role of metallic coatings in sliding wear is examined experimentally. The results indicate that the tribological behavior of soft coatings is consistent with the delamination theory of wear, especially the critical nature of the plating thickness. It is shown that a reduction in wear rate of three orders of magnitude is possible when the coating material is softer than the substrate and thinner than a critical thickness. The optimum plate thickness is found to be of the order of 0.1 p for cadmium, silver, gold or nickel plated on various types of steel. Cadmium, silver and nickel reduce wear only in non-oxidizing environments, whereas gold reduces wear both in air and in inert atmospheres. The roughness of the substrate surface prior to plating and the nature of the coating/substrate bond have significant effects on the life of these coatings. The life of the coatings is increased by polishing the substrate to 0.1 fl (c.1.a.) prior to plating, and also by diffusion of the plated material into the substrate, which increases the coating/substrate bond strength.