ICMCTF2016 Session EP: Symposium E Poster Session

The purpose of this research work is to prepare titanium zirconium nitride (TiZrN) coatings by DC magnetron sputtering using argon as inert gas and nitrogen as reactive gas. The power of titanium(Ti) target was kept constant at 275W whereas power of zirconium (Zr) target was varied from 275W to 450W . The structural characterization of TiZrN coatings were done by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The evolution of well intense (200) and (311) peaks of TiZrN coatings were observed with increase in power of Zr target. Tribological properties of TiZrN coatings such as friction and wear were investigated by pin on disc tribometer. Tribological properties of TiZrN coatings were examined within the permissible limits of various testing parameters such as load values of 10-30N and speed of 500-1000rpm.

The unique combination of hardness, toughness and wear resistance exhibited by WC-Co cemented carbides (hardmetals) has made them a preeminent material choice for extremely demanding applications, such as metal cutting/forming tools or mining bits, where improved and consistent performance together with high reliability are required.

The remarkable mechanical properties of hardmetals result from a two-fold effectiveness associated with its composite character. On the one hand in terms of composite nature: combination of a hard WC particles and a tough Co layer with optimal interface properties. On the other hand, as related to composite assemblage: two interpenetrating-phase networks where toughnening through constrained deformation of the ductile phase is highly effective.

Although extensive research has been conducted on the mechanical behavior of hardmetals, information on their small-scale mechanical response is rather scarce. This is particularly true for the metallic binder layer, phase whose deformation is stringly constrained by surrounding carbides. In this regard, microstructure-hardness correlations has been proposed on the basis of intrinsic hardness of constitutive phase obeying Hall-Petch relations, but without experimental evidence to support it. It is clear that such knowledge is crucial not only to improve the performance of WC-Co grades but also to design new cemented carbide systems, which will lead to highly desirable improvements in the cost and time on the materials development cycle.

In the present work a systematic study of the mechanical properties of WC-Co hardmetals is conducted at the micro- and nanometric length scale. The intrinsic hardness for the constrained metallic cobalt binder layer is determined on four microstructurally different WC-Co grades through massive nanoindentation tests and subsequent statistical analysis of the experimental data. In doing so, established thin film models (mainly Korsunsky and Puchi-Cabrera models) are employed to isolate the influence of surrounding carbide grains and extract the real hardness for the metallicbinder layer with different constrining degree. Experimental results are found to validate the description of microstructural effects on flow stress for the metallic binder on the basis of Hall-Petch relation, as directly related to the role played by ceramic-metal phase boundaries as obstacles for dislocation movement.

Hardened steel substrates for forging and cutting tools for high-temperature applications are often protected using hard nanostructured ceramic coatings. While a moderate amount of knowledge exists for material deformation properties at room temperature, significantly less is known about such systems under an applied load at the elevated temperatures generated during service. For rational engineering design of such tooling, it is therefore important to have methodologies for testing these materials to understand their properties under such conditions (i.e. high strain rate, temperature or impact).

In this work, we present our first results using a newly developed Alemnis piezo actuated nanoindenter device which utilizes dynamic indentation testing at frequencies approaching 10 kHz. A sinusoidal displacement amplitude input is provided, while a stage heater allows for sample temperatures exceeding 500 °C. Thermal drift can be minimized through high frequency, and therefore low contact time, impacts. We investigated a thin (4.65 μm) physical vapor deposited chromium nitride (CrN) ceramic coating, which had been deposited onto plasma-nitrided heat-treated tool steel.

Forces of approximately 400 mN were applied sinusoidally at 500 Hz using a 5 μm diameter diamond flat-punch at room temperature, 200°C, 300°C, 400°C and 500°C. Force-deformation data was collected at a sampling rate of 50 kHz. It was found that increasing the number of impacts led to plastic deformation and fatiguing of the hard ceramic coating. At 300°C a transition to increased material flow and consequently larger crater size, and crack initiation and propagation in the ceramic, was observed. These ceramic deformation results are understood using high-resolution scanning electron microscopy (HR-SEM) to investigate radial cracking and plastic flow, transmission electron microscopy (TEM) of residual indents to look at dislocations in the ceramic, elastic simulations of the indentation system, and large scale batch processing of force-deformation data which are generated during high-frequency measurement. The results are further put into context by understanding recently measured small-scale high-temperature fracture toughness and yield strength properties of both thin CrN films and nitrided steel.

Laser Cladding (LC) is a novel additive manufacturing process that produces metallic components depositing melted metallic powder layer by layer on a substrate material. LC has also been used as a surface treatment process for many years to improve the wear resistance of a variety of components by depositing hardfacing layers on the targeted parts using high power laser beam. Nickel based Tungsten Carbides (Ni-WC) is a metal matrix composite (MMC) that has been used frequently for the surface treatment of many industrial components under severe abrasive conditions. This paper investigates the laser cladded single coat Ni-WC on a medium carbon steel substrate. A 4 kW fibre connected Diode Laser coupled to an articulated robotic arm was used for laser cladding. The microstructural phase evolution and micro-hardness were measured and analyzed by X-ray diffraction (XRD), Energy Dispersion Spectroscopy (EDS), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM) and Vickers hardness tester. Wear behavior of the hardfacing alloy were studied with the dry sliding wear tests using a ball-on-disk configuration. The effect of process parameters (laser power, powder feed rate, laser speed, focal length of lens and contact tip to work distance) were studied and correlated with the microstructural and wear behavior of the Ni-WC. Variations in bead geometry including dilution zone of laser cladded Ni-WC was also correlated with the process parameters. It has revealed that the single coat Ni-WC has superior hardness and wear resistance compare to the steel substrate in all respective process parameters. This superior resistance to abrasion results from the fast solidification rate and very low dilution in the laser cladding process.

Nowadays, many kinds of PVD coated cutting tools with some post-coat treatments for improving their machining performance are used in industry. A dry micro-blasting, one of the post-coat treatment methods, enables us to control several physical properties like surface roughness, residual stress and hardness of coatings. Although there are many previous works about the micro-blasting effect on the machining performance of PVD coated cutting tools, the performance is often evaluated in the wear resistance rather than in the fracture resistance. The dry micro-blasting effects on the fracture resistance of PVD-AlTiN coated cemented carbide cutting tools were studied. PVD-AlTiN coatings are widely used for various machining situations due to their high hot hardness and compressive residual stress.

The AlTiN films were deposited using cathodic arc evaporation method onto WC-Co substrates of K15 quality (WC 89.2, Co 10.0, balance 0.8 [wt%]). The composition of the cathode was Al60-Ti40. The coating thickness on the substrates was approximately 3 μm. The two types of coatings, which had a compressive residual stress of 0.1 GPa (low-σ) and 2.6 GPa (high-σ), were prepared. The coated samples were subjected to the dry micro-blasting treatment by Al₂O₃ grains at pressures of 0.11 MPa, 0.14 MPa, and 0.17 MPa. A milling test was carried out for evaluating the fracture resistance of the prepared samples. The workpiece material was AISI 4140 (42CrMo4) steel with the hardness of 270 ± 10 HB. The tool life was determined by the occurrence of cutting edge fracture. The tool life cutting length of as-deposited low-σ and high-σ samples was 1.0 m and 8.8 m, respectively. The result indicated that the tool life strongly depends on the residual stress of coating. The tool life of low-σ sample micro-blasted at 0.14 MPa and 0.17 MPa was 2.9 m and 7.2 m, respectively, largely extended as compared to that of as-deposited low-σ sample. However, the tool life of high-σ sample micro-blasted at 0.14 MPa was 8.6 m, almost same with that of as-deposited high-σ sample. It was found that the dry micro-blasting effect on the fracture resistance was larger for low-σ coating than for high-σ one. The correlation between the cutting performance and the several physical properties will be discussed.

Diamond-like carbon (DLC) films are effectively utilized for improving tribological properties of materials due to their low friction coefficient, good wear resistance and high hardness. On the other hand, in recent years, different pre-treatments such as plasma assisted diffusional processes have been used to increase long-term durability of these coatings. In the present work, DLC films were deposited on untreated and plasma nitrided at 400, 500 and 600 °C for 1 and 4 hours, AISI 4140 low-alloy steel samples using physical vapour deposition method (PVD). The effect of nitrided layers on the structural and mechanical properties of DLC films were examined by XRD, SEM, microhardness tester and reciprocating tribotester. The wear tests were performed under dry, saltwater and lubricant environments. The microhardness test results indicated that surface hardness considerably increased after duplex treatment and this caused to increase plastic deformation resistance of the material. The reciprocating test results showed that DLC films deposited on untreated and plasma nitrided samples reduced the coefficient of friction because of the formation of transfer film between sliding/mating surfaces. Also, wear rates were importantly enhanced after duplex treatment in consequence of high plastic deformation resistance of duplex treated samples. The highest wear resistance was obtained from lubricated condition while the lowest wear resistance was for the samples tested in dry conditions.

Assessment of coating adhesion is one of the main challenges when applying hard PVD coatings like hydrogen-free tetrahedral amorphous carbon (ta-C). Coating failure could not only result from weak adherence of the coating to the substrate, but can also follow from many other sources such as abrasive wear, internal cracks, intrinsic stresses, and plastic deformation of the substrate under load. These mechanisms are hard to distinguish afterwards, which is the main limiting factor of the classical scratch testing method. Therefore, comparability of measured critical loads is restricted to identical test parameters only, and depends on coating thickness, Young’s Modulus, and yield strength of the substrate. Typically, such conditions are found in serial production, but not in a research environment.

In this work we present a careful investigation of failure mechanisms during scratch testing of ta-C coatings with thickness in the range of 1 to 10 µm and Young’s Modulus in the range of 450 to 900 GPa. Characteristic features of the scratch track are discussed with respect to plastic substrate deformation and coating thickness.

A new method for quantification of adhesive failure area by means of optical segmentation is discussed. It is shown that this value is independent from coating thickness and Young’s Modulus within a certain range. Furthermore, it is characteristic for delamination outside the scratch-induced substrate plasticity and strongly correlates with shear stresses in the interface plane.

By this new method it became possible to distinguish coating processes with two different plasma pretreatments regarding their adhesion.

The formation of boride coating and adhesion at the surface of API X60 microalloyed steels obtained by dehydrated paste pack were studied in this work. The thermochemical treatment was carried out at temperatures 1073, 1123, 1173, and 1223 K with exposure times 1, 3, 5, and 7 h, respectively. The mobility of the boron in the boride coatings is determined by the mass balance equation in the corresponding interphases with their respective concentration of boron. The presence of the boride coatings were revealed with the classic metallographic techniques and observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) on the boride coatings/substrate were applied. Finally, the adherence of the boride coating on the API X60 substrate was qualitative evaluate by VDI 3198 norm using the Rockwell C indentation technique.

Thermal barrier coatings (TBCs) are applied on aircraft and industrial gas turbine engines protecting the operating components from demanding high temperature environments. TBCs insulate turbines and combustion engine components from hot gas streams and improve durability and energy efficiency of these engines. However, the thermal mismatch in the thermal barrier coatings (TBC) leads to generation of stresses in the TBCs resulting in micro-crack initiation in the TBC which subsequently grow and coalesce, leading to ultimate failure of the coating by delamination. To counteract this, TBCs have been embedded with molybdenum disilicide (MoSi₂) particles to provide a crack healing mechanism. The high temperature oxidation that occurs during engine operation leads to MoSi₂ decomposition and the formation of silica (SiO₂), which fills and repairs the cracks created during thermal cycling.

It has been reported that MoSi₂ has relatively low strength and fracture toughness below the brittle-to-ductile transition temperature (~1000^oC), therefore it is important to understand its effect on the mechanical performance of YSZ.

In this work, we investigate the mechanical properties of pure YSZ and YSZ composites containing different volume ratios of MoSi₂ particles, produced by spark plasma sintering (SPS). Micro-indentation has been chosen to investigate material hardness and elastic modulus. Fracture toughness data has been acquired by measuring the length of radial cracks as a function of load after Vickers indentation. The microstructure of the composite materials has been examined using optical microscopy and scanning electron microscopy combined with image correlation analysis to measure area fraction, shape and distribution of healing particles.

These results show a significant impact of the embedded MoSi₂ particles on the elastic behaviour of the composite material. This is attributed to the MoSi₂ volume fraction, reported to have elastic modulus values of approximately 440 GPa (more than double that of bulk zirconia).

In this paper we analyzed films of Si and Si + W deposited on glass by magnetron co-sputtering. A 4 "diameter and ¼" thick target of Si (99.99% pure) to which one to three, small pieces of W (0.7 X 2.5 cm) were added on to one section of the racetrack: the internal and external diameters of which were 0.9 cm and 5.0 cm. The glass substrates (7.5 X 2.5 cm) were placed 5.5 cm below the target, such that one end was directly below the pieces of W. All the depositions were carried out in 30 mT of pure Ar using a DC plasma power of 20 W. The variation of the thickness and composition of the deposited films were measured with a Dektak profilometer 150 and by Rutherford BackScattering, RBS, using a 2 MeV beam of alpha particles, and Energy Dispersion Spectroscopy, EDS respectively. The tribological and mechanical properties of the different parts of the samples were measured by scratch testing, with simultaneous measurement of the friction force, and nanoindentation. The 0.5 cm long scratch tests were performed with loads of 0 - 30 N, with 1/16” diameter counter bodies of AISI 52100 and alumina. The results of the hardness and scratch tests were correlated to the thickness and the composition of the tested area of the films. The details and dimensions of wear tracks were characterized by optical microscopy and profilometry, and the chemical composition of selected areas of scratch debris were analysed by EDS.

In the adhesion tests it is observed that for the preparation conditions that corresponded to the highest concentration of tungsten, the adhesion of the film to the substrate was greater than the fracture resistance of glass substrate. SEM and EDX analysis of the Lc3 critical load point indicated that the detached material was glass rather than the Si-W coating.

Coatings of Ta and TaN are widely studied in the last two decades due their mechanical properties and their biocompatibility, however single layers coatings of TaN and Ta are hard with low ductility, and soft and ductile respectively. Recent investigations of hard coatings have studied multilayer hard coatings with a hierarchical configuration, this helps to improve adhesion to the substrate and reduce the effects that generates a sharp change in a conventional multilayer coating. Furthermore combining soft and hard layers in a multilayer coating can generates toughness mechanisms that can stop crack propagation and reduce stress across the coating. In this study is analyzed the mechanical properties by nanoindentation and micro wear under dry and simulated body fluid (SBF) of coatings made by magnetron sputtering with a single layer of Ta, bilayer of TaN/Ta, and TaN/Ta with a hierarchical architecture or configuration. The substrates were biomedical alloys of CoCrMo and Ti6Al4V. There is a lack of knowledge about micro-wear of coatings immerse in SBF solutions. TaN/Ta hierarchical coating showed the lowest wear rate of the coatings and substrates of this investigation. There was no evidence of lubrication effects under SBF conditions, since the wear rates in dry and wet conditions remained with same values or increase in SBF. We can conclude that the hierarchical configuration in TaN/Ta coatings is highly desirable for micro-tribology applications under dry and wet conditions.

Ni-P/nanoSiC composite coatings were electroplated at different pulse frequencies (1-100 Hz). The mechanical and tribological properties of the as-plated and annealed (400 °C) coatings were compared in order to optimize the pulse frequency and determine the effect of the heat treatment. The results indicated that the hardness of the as-plated Ni-P/SiC coatings (6.9-7.6 GPa) is proportional to the pulse frequency, whilst the annealed coatings always yielded a higher hardness (8.3-11.4 GPa) due to the formation of a Ni₃P phase. However, the friction coefficient of the annealed coatings (1.02-1.15) was greater than that of the as-plated coatings (0.86-1.02), which was inversely proportional to the pulse frequency. More importantly, the wear resistance of the as-plated coatings, regardless of pulse frequency, deteriorated after annealing at 400 °C even with an improved hardness. Moreover, the wear rate of the annealed coatings increased gradually ( 7.57×10^-6-2.09×10^-5 mm³/Nm ) with increasing pulse frequency. It is deduced that the lower toughness, i.e., the fragility of the annealed coatings led to the higher wear rate in addition to an increase in debris, which was deemed as the major cause of the higher friction coefficient experienced. In contrast, the higher pulse frequency exhibited, a stronger wear resistance in the as-plated coatings presented, especially the Ni-P/nanoSiC coatings electroplated at 10Hz and 100 Hz, which were found to have an unmeasurable wear. Therefore, the Ni-P/nanoSiC coating electroplated at a higher pulse frequency (100 Hz) without subsequent post heat treatment is expected to present a promising tribological performance in industrial applications.

The purpose of this work is to study the influence of abrasive wear modes on the coefficient of friction (μ) of thin films. Ball-cratering wear experiments were conducted with thin films of TiN, CrN, TiAlN, ZrN, TiZrN, TiN/TiAl, TiN/TiAl (multi-layer), TiHfC and TiHfCN using a ball of AISI 52100 steel and abrasive slurries prepared with black silicon carbide (SiC) particles and glycerine. The aim of this design was to produce grooving abrasion and rolling abrasion on the surface of thin films. The normal force (N) and the tangential force (T) were monitored throughout the tests, and the coefficient of friction was calculated as μ = T/N. The results show that the abrasive slurry concentration affected the abrasive wear modes (grooving abrasion or rolling abrasion) and, consequently, the magnitude of the coefficient of friction: i) a low abrasive slurry concentration was related with grooving abrasion and a relatively high coefficient of friction; ii) a high abrasive slurry concentration was related with rolling abrasion and a relatively low coefficient of friction.

Keywords: Micro-scale abrasion; two-body abrasion; three-body abrasion; PVD coatings.

Roll coatings are typically developed on work roll surfaces during hot rolling of aluminum alloys. The thickness and properties of the coatings are believed to influence the surface quality of the aluminum hot rolled products. The development of these coatings has been noted to be influenced by rolling load, friction and the emulsion used. The structure and composition of these coatings have long been subjects for research, but the tested materials have mostly been limited to commercial-purity aluminum. Analysis of roll coatings has long been limited to scanning electron microscopy and X-ray microanalysis.

In the present study, a hot rolling tribo-simulator, with a roll-on-block configuration, was used to study the development of the roll coating, in its initial stages, during hot rolling of an Al-Mg alloy. AISI 440C and D2 steel work rolls with surface roughness (Ra) of 0.01 µm were used to hot roll Al-Mg samples under similar lubricated conditions for a rolling schedule of 20 passes. Both steel rolls possessed various carbide protrusions on their surfaces, which has previously been observed to contribute to increased aluminum adhesion to the work roll surfaces. Scanning electron microscopy (SEM), focus ion beam (FIB) microscopy, and high resolution transmission electron microscopy (HR-TEM) were used to investigate the roll coating. The generated roll coatings were patchy, discontinuous, and streaked in the rolling direction on the work roll surfaces, covering the carbide protrusions. The roll coatings distribution was mapped with energy dispersive spectrometry analysis and confirmed to be mainly composed of aluminum and magnesium oxides, lying on a thin carbon layer. The microstructure of the initial roll coating buildup was evaluated and its relationship to the carbide protrusions and polymerised lubricant films were studied.