Temperature dependent friction and wear of magnetron sputtered coating TiAlN/VN

In this paper, a magnetron sputtered nano-structured multilayer coating TiAlN/VN, grown on hardened tool steel substrate, has been investigated in un-lubricated ball-on-disk sliding tests against an alumina counterface, to study the friction and wear behaviours at a broad range of testing temperatures from 25 to 700 ◦C, followed by comprehensive analysis of the worn samples using FEG-SEM, cross-sectional TEM, EDX, as well as micro/nano indentations. The experiment results indicated significant temperature dependent friction and wear properties of the coating investigated. Below 100 ◦C, the coating showed low friction coefficient at �≤0.6 and low wear rate in the scale of 10−17m3 N−1m−1 dominated by mild oxidation wear. From 100 to 200 ◦C, a progressive transition to higher friction coefficient occurred. After that, the coating exhibited high friction of �= 0.9 at temperatures between 200 and 400 ◦C, and simultaneously higher wear rates of (10−16 to 10−15) m3 N−1m−1. The associated wear mechanism changed to severe wear dominated by cracking and spalling. From 500 ◦C and so on, accelerated oxidation of the TiAlN/VN became the controlling process. This led first to the massive generation of oxide debris and maximum friction of �= 1.1 at 500 ◦C, and then to fast deterioration of the coating despite the lowest friction coefficient of �< 0.3 at 700 ◦C

Hybrid HIPIMS and DC magnetron sputtering deposition of TiN coatings: Deposition rate, structure and tribological properties

High power impulse magnetron sputtering (HIPIMS) has the advantage of ultra-dense plasma deposition environment although the resultant deposition rate is significantly low. By using a closed field unbalanced magnetron sputtering system, a hybrid process consisting of one HIPIMS powered magnetron and three DC magnetrons has been introduced in the reactive sputtering deposition of a TiN hard coating on a hardened steel substrate, to investigate the effect of HIPIMS incorporation on the deposition rate and on the microstructure and mechanical and tribological properties of the deposited coating. Various characterizations and tests have been applied in the study, including XRD, FEG-SEM, cross-sectional TEM, Knoop hardness, adhesion tests and unlubricated ball-on-disk tribo-tests. The results revealed that, both the DC magnetron and hybrid-sputtered TiN coatings exhibited dense columnar morphology, a single NaCl-type cubic crystalline phase with strong (220) texture, and good adhesion property. The two coatings showed similar dry sliding friction coefficient of 0.8 – 0.9 and comparable wear coefficient in the range of 1 – 2× 10-15 m3N-1m-1. The overall deposition rate of the hybrid sputtering, being 0.047 μm/min as measured in this study, was governed predominantly by the three DC magnetrons whereas the HIPIMS only made a marginal contribution. However, the incorporated HIPIMS has been found to lead to remarkable reduction of the compressive residual stress from -6.0 to -3.5 GPa and a slight increase in the coating hardness from 34.8 to 38.0 GPa

Mechanical properties of heat treated and worn PVD TiN, (Ti, Al)N, (Ti, Nb)N and Ti(C, N) coatings as measured by nanoindentation

Steered arc ion plated TiN, (Ti50, Al50)N, (Ti85, Nb15)N and Ti(C60, N40) coatings were heat treated in an inert argon atmosphere at temperatures up to 900-degrees-C. The hardness, Young's modulus and plasticity of the coatings were measured with nanoindentation after heating. As the coatings were annealed at higher temperatures, the hardness decreased and the plasticity increased. X-ray diffraction of the coatings showed that this corresponds to a decrease in internal stress and a change of crystallographic texture. The nanohardness of the cutting edge of coated drills was also measured after these were used in AISI 4140 steel. Scanning electron microscopy demonstrated the presence of a silicate layer located near the cutting edge of (Ti85, Nb15)N coated drills. Nanoindentation showed that the mechanical signature of the surface film further away from the cutting edge corresponded to a heat-treated coating covered with an oxide layer.status: publishe

Dry sliding wear of TiN based ternary PVD coatings

ln order to understand the tribological characteristics of TiN, (Ti, Al)N, (Ti, Nb)N and Ti(C, N) coatings, ball-on-disc experiments were performed under dry sliding ambient conditions. The coefficient of friction and the wear resistance against a corundum counterbody were determined as a function of coating composition and sliding speed. The wear of the (Ti, Nb)N coatings was found to be comparable to that of the TiN coatings and this was related to the formation of a similar type of oxide in the tribo-contact. In the case of the (Ti, Al)N coatings, the wear volume increased markedly as the aluminium in the coating increased, and the tribo-oxide formed was found to be Al2TiO5. Ti(C, N) coatings exhibited an extremely low wear against corundum because of the low coefficient of friction. A mild-oxidational wear model was found to give a qualitative fit to the experiments. Measuring the coating wear as a function of sliding speed opens the possibility of calculating the activation energy for tribo-oxidation processes of thin coatings.status: publishe

Tribological and structural characterization of a physical vapour deposited TiC/Ti(C,N)/TiN multilayer

A physical vapour deposited TiC/Ti(C,N)/TiN multilayer was investigated and compared with a PVD TiN monolayer coating in a ball-on-disc test. Wear and friction against a corundum ball were measured as a function of time and sliding velocity. In these experiments, the coefficient of friction remained constant at 0.2 as long as the ball was sliding on TiC or intermediate Ti(C,N) layers. When the TiN layer was reached, the coefficient of friction became unstable and rose to an average value of 1-1.5, which is characteristic for a TiN/Al2O3 contact. Wear rates for the multilayer were found to be three to four times smaller as compared to the reference TiN. The multilayer morphology of the TiC/Ti(C,N)/TiN was revealed in a low-angle cross-section resulting from a prolonged ball-on-disc test. In that way, it was shown that the multilayer consisted of nine separate sublayers.status: publishe

Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining

Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining was carried out to investigate microfracture, residual damage, and surface roughness associated with material removal and surface generation. Brittle versus plastic deformation was studied using Vickers indention and nano-indentation. To characterize the abrasive machining response, the 6H-SiC (0001) substrates were ground using diamond wheels with grit sizes of 25, 15 and 7 mum, and then polished with diamond suspensions of 3 and 0.05 mum. It is found that in indentation, there was a scale effect for brittle versus plastic deformation in 6H-SiC substrates. Also, in grinding, the scales of fracture and surface roughness of the substrates decreased with a decrease in diamond grit size. However, in polishing, a reduction in grit size of diamond suspensions gave no significant improvement in surface roughness. Furthermore, the results showed that fracture-free 6H-SiC (0001) surfaces were generated in polishing with the existence of the residual crystal defects, which were associated with the origin of defects in single crystal growth. (C) 2003 Elsevier Ltd. All rights reserved

Galvanotechnische nikkel-indium deklagen

SIGLEKULeuven Campusbibliotheek Exacte Wetenschappen / UCL - Université Catholique de LouvainBEBelgiu

High-quality grinding of polycrystalline silicon carbide spherical surfaces

The objective of this study was to develop high-quality grinding protocols for polycrystalline silicon carbide spherical surfaces in order to achieve nanometre surface roughness and submicron form accuracy. Plastic deformation and fracture damage associated with the material removal mechanisms were studied using nano-indentation and Vickers indentation. Spherical grinding was conducted with a CNC grinding machine using metal-bond diamond tools with grit sizes of 25 and 15 mum under the machining conditions selected. The ground spherical surfaces were examined using laser interferometry, WYKO optical interferometry, and scanning electron microscopy to measure form accuracy, surface roughness, and residual defects as a function of grinding conditions. Ground silicon carbide spherical surfaces with form accuracy peak-to-valley (PV) of 0.21-0.59 wave (0.13-0.37 mum) and surface roughness of 9.92-17.22 nm R-a were obtained. Low machining-induced damage was found on the ground silicon carbide where defects were mainly associated with microstructural defects such as pores. The topography of the diamond tools was examined using a scanning electron microscope (SEM) to evaluate the performance of diamond wheels in grinding. This work provides technological insights into precision engineering for rapid manufacturing of ceramic components without the need or with less need for subsequent lapping and polishing. (C) 2003 Elsevier B.V. All rights reserved

Influence of microstructure on ultraprecision grinding of cemented carbides

The influence of microstructure on the ultraprecision grinding response of a series of cemented carbides for spherical mirrors was characterized by means of optical and laser interferometry, atomic force microscopy, scanning electron microscopy and Xray diffraction. Surface roughness, form accuracy, grinding-induced residual stress and material removal behaviors were studied as a function of tungsten carbide (WC) grain size. In connection with the removal mechanisms in ultraprecision grinding, microindentations performed on each material showed similar deformation patterns, all in the plastic regime. The microstructure of WC-Co materials was found to have little influence on the nanometre surface roughness and submicron form accuracy. However, the X-ray stress measurements indicated that the microstructure of carbide materials had a significant influence on the grinding-induced residual stresses; i.e. an increase in grinding-induced residual compressive stress with an decrease in WC grain size. No grinding-induced cracks were observed in the ground cemented carbide surfaces. The material removal in ultraprecision grinding was considered to occur within the ductile regime. The formation of microgrooves and plastic flow regions via slip bands of WC grains along the cobalt binder without visible resultant microfracturing of WC grains were the dominant removal mechanisms. (C) 2003 Elsevier Ltd. All rights reserved