Optical Detections From Worn and Unworn Titanium Compound Surfaces

Wear-induced roughness in terms of grooves, sharp ridges, and edges leads to scattering of the reflected light and leads unavoidably to a reduction of the optical signals in a standard specular geometry. However, by using a double-layer system consisting of titanium aluminum nitride (TiAlN) on top of a titanium nitride (TiN) layer we obtain an increase in the reflected light as a result of wear. The relative change of reflectance of light from the tribological TiAlN coated surface to the underlying layer of TiN is similar for non-worn surfaces and for surfaces exposed to an abrasive wear process. The induced roughness reduces the signals from worn samples, in a standard specular geometry, by up to 30% compared with unworn samples. Our model system of TiAlN coatings on top of ‘optical’ signal layers of TiN deposited on a 100Cr6 steel substrate, was exposed to a reciprocating wear process with up to 10⁵ repetitive cycles in a linear tribometer. The worn TiAlN layers of thicknesses up to 3 μm, with strongly developed grooves and ridges, were subsequently used for the reflectance measurements. The results show that optical reflectance monitoring is a potential technique for intelligent determination of a residual thickness of realistic tribological coatings prior to complete wear.     

Monitoring of Wear Characteristics of TiN and TiAlN Coatings at Long Sliding Distances

TiN and TiAlN thin hard coatings have been widely applied on machine components and cutting tools to increase their wear resistance. These coatings have different wear behaviors, and determination of their wear characteristics in high-temperature and high-speed applications has great importance in the selection of suitable coating material to application. In this article, the wear behavior of single-layer TiN and TiAlN coatings was investigated at higher sliding speed and higher sliding distances than those in the literature. The coatings were deposited on AISI D2 cold-worked tool steel substrates using a magnetron sputtering system. The wear tests were performed at a sliding speed of 45 cm/s using a ball-on-disc method, and the wear area was investigated at seven different sliding distances (36–1,416 m). An Al₂O₃ ball was used as the counterpart material. The wear evolution was monitored using a confocal optical microscope and surface profilometer after each sliding test. The coefficient of friction and coefficient of wear were recorded with increasing sliding distance. It was found that the wear rate of the TiAlN coating decreases with sliding distance and it is much lower than that of TiN coating at longer sliding distance. This is due to the Al₂O₃ film formation at high temperature in the contact zone. Both coatings give similar coefficient of friction data during sliding with a slight increase in that of the TiAlN coating at high sliding distances due to the increasing alumina formation. When considering all results, the TiAlN coating is more suitable for hard machining applications.     

Origin of Friction in Running-in Sliding Wear of Nitride Coatings

To investigate the origin of running-in friction in unlubricated sliding wear, a magnetron sputtered multilayer coating TiAlN/VN was tested on a ball-on-disc tribometer for a series of sliding durations from 10 to 1000 cycles, followed by careful observation of the obtained worn surfaces using an field-emission gun scanning electron microscope. Three steps of friction variation were found: (1) prior to wear particle generation, low initial friction coefficient was around 0.2–0.25 purely attributed to the asperity contact; (2) then it increased steeply to a range of 0.4–0.5 in the first 100 cycles following the generation, breaking and agglomeration of wear particles, and in particular the scaling-up of fish-scale-like tribofilm; (3) eventually it approached to a steady-state value around 0.5 when the friction was governed by the viscous shearing of the tribofilm. It is concluded that, under unlubricated sliding wear, the friction behaviour of transition metal nitride hard coating is dominated by the viscous shearing of tribofilm adhesively bonding to the parent nitride coating.     

Non-ferrous coating/lubricant interactions in tribological contacts: Assessment of tribofilms

Use of low friction non-ferrous coatings for engine tribo-components exposed to boundary lubrication is becoming popular in automotive industries. The excellent tribological behaviour of some non-ferrous coatings also reduces dependence on some harmful components of lubricants. In this work, hydrogenated diamond like carbon (HDLC) and chromium nitride (CrN) coatings sliding against cast iron counterbody have been used to study the interaction with friction modifiers (Moly dimer and Moly trimer) and antiwear additive zinc dialkyldithiophosphate (ZDDP) under boundary lubrication condition. The tribological results of the non-ferrous coatings are compared with those of uncoated steel. Tribofilms are formed using a reciprocating pin-on-plate tribometer. The chemical analysis of the tribofilms has been accomplished using X-ray photoelectron spectroscopy (XPS). The XPS analysis shows that the friction modifiers form a low friction tribofilm on the non-ferrous coatings. No antiwear tribofilm derived from ZDDP was observed on the HDLC coating but a stable antiwear tribofilm was found on the CrN coating. Moly dimer together with ZDDP+Base Oil showed the lowest friction coefficient for the CrN coating while Moly trimer along with ZDDP+Base Oil gave the lowest friction for the HDLC coating. This study will investigate the generic differences between the tribofilms formed on the DLC and CrN coatings by two additive-containing oils.     

钛合金铣削加工的PVD涂层适应性研究

利用电弧法沉积制备Al Cr N、Al Cr Si N、Al Cr N/Ti Al N、Al Cr N/Ti Si N四种用于钛合金切削加工涂层,研究了涂层的基本特性及切削使用效果。结果表明,Al Cr N涂层呈柱状生长,通过添加Si等元素或采用多层交替沉积有利于形成细化晶粒组织,提升涂层纳米硬度。切削试验表明,在低速铣削钛合金TC4时,Al Cr N/Ti Al N复合涂层表现最好。在较高速铣削时,四种涂层的刀具表现性能接近。     

TEM-EELS study of low-friction superlattice TiAlN/VN coating: the wear mechanisms

A 20–50 nm thick tribofilm was generated on the worn surface of a multilayer coating TiAlN/VN after dry sliding test against an alumina counterpart. The tribofilm was characterized by applying analytical transmission electron microscopy techniques with emphasis on detailed electron energy loss spectrometry and energy loss near edge structure analysis. Pronounced oxygen in the tribofilm indicated a predominant tribo-oxidation wear. Structural changes in the inner-shell ionization edges of N, Ti and V suggested decomposition of nitride fragments.     

Reciprocating Sliding Wear Performance of Hard Coating on Modified Titanium Alloy Surfaces

The high strength, low weight, and outstanding corrosion resistance properties possessed by titanium alloys have led to a wide range of successful applications in aerospace, automotive, and chemical industries and in power generation. Titanium alloys are characterized by poor wear resistance properties and their utilization has been excessive in nontribological applications. Surface texturing is a well-known and effective means of surface modification to improve the tribological properties of sliding surfaces. In the present work, modification of titanium alloy surfaces (Ti6Al4V) was done by lapping and laser surface texturing. The wear-resistant coating, AlCrN, was applied over the modified titanium alloy surfaces, with and without a chromium interlayer. Linear reciprocating sliding wear tests were performed with ball-on-flat contact geometry to evaluate the tribological performance of the coated alloy. The tests were performed under different normal loads for a period of 105 cycles at a frequency of 5 Hz. The friction force between the contact pair and displacement of the ball were simultaneously observed using a force transducer and laser displacement sensor. Optical microscopy was used to quantify the wear volume by measuring the wear scar diameter on both the specimen and the counterbody. Scanning electron microscopy (SEM) was employed to study the morphology of the wear scar. The characteristic behavior of the AlCrN coating such as bonding strength, wear volume, wear rate, and coefficient of friction with the chromium interlayer was evaluated and compared with the coating directly applied over the substrate. The coating on the textured surface, with the chromium interlayer showed better tribological performance.     

Tribological performances of ZDDP and ashless triphenyl phosphorothionate (TPPT) as lubricant additives on Ti–N and Ti–Al–N coated steel surfaces

Abstract

In recent years, there has been much attention on the effects of lubricant additives on the friction and wear properties of surface coatings. However, little research has been conducted to investigate the influence of antiwear additives on the tribological performances of titanium nitride (Ti–N) and titanium aluminium nitride (Ti–Al–N) coatings. It has been reported that introducing aluminium into Ti–N coatings enhanced their oxidation resistance. In this study utilising a pin on cylinder tribometer, lubricants containing zinc dialkyl dithiophosphate (ZDDP) or a more environmentally friendly alternative, ashless triphenyl phosphorothionate (TPPT), were used. Experimental results revealed that ZDDP and TPPT helped to reduce wear on both coatings through the formation of a tribofilm, although it was also found that both additives increased the friction coefficient on both surfaces. Based on overall findings, this paper suggests the use of TPPT as a suitable ZDDP replacement for providing wear protection on Ti–N and Ti–Al–N coatings.     

Characterization of Tribofilms Generated from Serpentine and Commercial Oil Using X-ray Absorption Spectroscopy

The chemical and tribological properties of serpentine particles suspended in lubricating oil were investigated using a pin-on-disk high frequency friction machine at 100 °C. The wear scar width of the upper steel pins was measured by an optical microscope. The tribofilm was characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) elemental mapping, and X-ray absorption near-edge structure (XANES) spectroscopy. It was found that the addition of serpentine to commercial engine oil improves its tribological properties. The SEM and EDX elemental mapping shows that a tribofilm formed by the commercial oil with serpentine contains silicon, magnesium, oxygen, phosphorus, sulfur, zinc, calcium, and carbon on the worn surface, which is different from the tribofilm formed by the commercial oil without serpentine. The results of the XANES analysis show that the addition of serpentine to the commercial oil changes the chemical compositions of the tribofilms. This change may account for the better tribological properties of the lubricating oil containing serpentine. The formation mechanism of the tribofilm is discussed.     

Study of wear resistance of thermal-diffusion boron nitride coatings on titanium

The wear resistance of commercially pure titanium VT1-0 covered with boron nitride coatings in pair with steel U8 is studied. It is found that the boron nitride coatings deposited from amorphous boron by thermal-diffusion saturation in molecular nitrogen at temperatures of 800?C850°C using the noncontact method improve the wear resistance of titanium during boundary sliding friction. Their characteristics are compared with those of boride coatings on titanium deposited by the same method. It is shown that the high-gradient strengthened layers formed during contact thermal-diffusion boronitriding within the 900?C950°C temperature range affect adversely the tribological performance of the boron nitride coating-steel pair.     

Effect of alloyed target vis-à-vis pure target on machining performance of TiAlN coating

Typically closed-field unbalanced magnetron sputtering (CFUBMS) and controlled cathodic arc deposition techniques having four or six pure or alloyed targets are employed for commercial titanium aluminium nitride (TiAlN) coating of cutting tools. The role of the use of alloyed target vis-à-vis pure target on the coating characteristics and the machining performance of TiAlN-coated tools has not been studied in detail. In the present work, TiAlN coating has been deposited on cutting tools using a pulsed DC, dual-cathode CFUBMS system to capture the role of the type of target on machining performance. The deposition rate in the case of the alloyed target has been found to be much higher as compared to the pure target. Such coatings deposited from alloyed targets also provided significantly better machining performance in dry turning of low-carbon and high-carbon steel. Dry turning of SAE 1070 high-carbon steel at 160 m/min did not yield more than 100 μm of average flank wear on the same insert coated using alloyed targets for a machining time of more than 3 min.     

Boundary Tribological Behaviors of Untreated and Surface-Modified M50 Steel Lubricated by Fuel JP-10

To explore the possibility of using advanced surface engineering techniques (ASETs) to solve the wear problems caused by the poor lubricity of pure, low-viscosity aviation fuel JP-10, polished M50 bearing steel sample surfaces were treated with nitrogen ion implantation, TiAlN coating deposition, and Ta coating deposition followed by high current pulsed electron beam (HCPEB) irradiation, respectively. Boundary tribological behaviors of these ASET-treated and untreated steel samples sliding in pure JP-10 against a Si₃N₄ ball (ball-on-disc model) were investigated under 2.0 GPa in the atmosphere and the friction tests indicated that significant, reductions, although to different extents, in friction and wear were achieved by these modified surfaces. Simultaneously considering the tribological performance and potential pollution caused by wear debris to JP-10, HCPEB-treated Ta coating with a lowest average friction coefficient of 0.11 and a specific wear rate of around zero was the fittest to offset the inadequate lubricity of JP-10 itself under the laboratory condition.     

Effect of Operating Temperature on Tribological Behavior of As-Plated Ni-B Coating Deposited by Electroless Method

The present work investigates the tribological behavior of electroless Ni-B coating in its as-plated condition at elevated operating temperatures. Ni-B coating is deposited using an electroless method on AISI 1040 steel specimens. Coating characterization is done using scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction techniques. Vicker's microhardness and surface roughness are measured. Friction and wear tests are carried out on a pin-on-disc tribological test setup at room and elevated temperatures of 100, 300, and 500°C. The tribological behavior deteriorates at 100°C compared to room temperature. Electroless Ni-B coating shows excellent wear resistance at 300°C, which again degrades at 500°C due to severe oxidation and softening of the deposits. The worn surface of the coatings is analyzed using optical microscopy and scanning electron microscopy. Within the temperature range considered, the wear mechanism changes from adhesion to a combination of adhesion and abrasion as the temperature rises from ambient condition to 100°C, following which the wear mechanism is predominantly abrasive. The formation of a tribochemical oxide film also affects the tribological behavior of the coatings at high temperature.     

The effects of AlCrN coating,surface modification and their combination on the tribological properties of high speed steel under dry conditions

In this study, the effects of a combination of ultrasonic nanocrystalline surface modification (UNSM) technique and AlCrN coating on the tribological properties of high speed steel (HSS) were investigated. The AlCrN coating with a thickness of about 3 µm was deposited by the physical vapor deposition (PVD) technique onto the polished and UNSM-treated HSS specimens. The tribological and scratch tests results revealed that the AlCrN coating deposited onto the UNSM-treated specimen showed better tribological properties compared to that of the AlCrN coating deposited onto the polished specimen, which may be attributed to the modified surface beneath the AlCrN coating. Hence, it is expected that the results of this study can be applied to reduce the wear of fine blanking punches.     

Abrasive wear behavior of high speed steel and hard metal coated with TiAlN and TiCN

The wear behavior of M2 high speed HSS steel and WC hard metal coated with TiAlN and TiCN were investigated and compared, using the pin on disk standard test with different loads. The coating PVD process has been done by two different suppliers, using an industrial equipment unit with optimized conditions. The coated layers were measured and characterized. The load, sliding distance and velocity of 0.5 m/s were kept constant during the abrasion test in order to control these variables. The counterface disks used were electric steel sheets from three different suppliers. The lost volume and temperature at the pin end have been measured during the wear test. Comparisons of tribological performance for the coated HSS and hard metal were done, using a plot of lost volume versus sliding distance for substrates and coatings. The pin worn surfaces were observed using a scanning electron microscope. A significant increase in the wear resistance of M2 steel and WC hard metal when coated with TiAlN and TiCN was observed. Quality of these coatings depended upon the supplier. Excessive porosity has diminished the TiAlN counting wear resistance from one supplier. However, in general the performance of TiAlN is superior to TiCN. The pin wear rate depended on the disk microstructure.     

Tribofilm Formation and Run-In Behavior in Ultra-Low-Wearing Polytetrafluoroethylene (PTFE) and Alumina Nanocomposites

Polytetrafluoroethylene (PTFE) and alumina nanocomposites have been of great interest to the tribological community due to the significant reduction in wear imparted by filling PTFE with low weight percentages of alumina nanofillers. The mechanisms of these three order, four order, and sometimes five order of magnitude reductions in wear have been commonly explored through evaluation of a transfer film. The present article evaluates the tribofilm formed on the wear surface of the polymer. PTFE composites with 2, 5, and 8 wt% alumina fillers were tested to evaluate wear of the polymer and how it is affected by the tribofilms formed on the wear surface of the polymer. Furthermore, the link between a transient “run-in” wear period and the formation of that tribofilm is observed and discussed. Nanomechanical measurements of the tribofilm reveal significant alterations in the mechanical properties of the surface films formed during sliding.     

Tribofilm formation from TiC and nanocomposite TiAlC coatings,studied with focused ion beam and transmission electron microscopy

This work demonstrate how two different carbide coatings respond very differently to tribological stress and their very different ability to provide low friction tribofilms in dry sliding against steel. Both coatings, TiC and TiAlC, were deposited by DC-magnetron sputtering, but while the TiC is a thermodynamically stable coating, the TiAlC is made metastable with the addition of Al, and therefore releases carbon upon tribological testing. Thus, the TiAlC coating is shown to be self-lubricating on the atomic scale which makes very low friction achievable. The primary interest in this study is the differences in the tribofilms formed on the steel balls that have been sliding against the two coatings. Cross-section samples for transmission electron microscopy were extracted from the ball tribofilms using a focused ion beam instrument. X-ray photoelectron spectroscopy and Raman analysis were employed to provide information on the chemical and structural characteristics of the tribofilms. It was shown that tribofilms on steel balls largely inherit the structure and composition that evolve in the coating wear tracks, that the tribofilm microstructure greatly affects the friction level. It was also shown that tribofilm delamination, occurring with tribofilm growth, was initiated in weak ribbon like regions inside the tribofilm.     

The Formation of Tribofilms of MoS2 Nanotubes on Steel and DLC-Coated Surfaces

Solid-lubricant nanoparticles as additives in oil provide good tribological properties based on the physical lubrication mechanisms in the contact. For this reason, they are strong candidates for use in the lubrication of diamond-like carbon (DLC) coatings, which only poorly interact with the traditional, chemically based additives. In this study, we focused on how a tribofilm formed from MoS₂ nanotubes is related to the tribological properties of these nanotubes, and then, we analysed such a tribofilm on steel and DLC-coated surfaces using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy. We demonstrated that when using oil containing MoS₂ nanoparticles, the formation of a tribofilm is a key factor in decreasing the friction for the steel and DLC-coated contacts. The major difference between the steel and the DLC contacts is the extent to which the MoS₂-based tribofilm covers the surface, which is 20 % in the case of the DLC/DLC contacts, but almost 40 % in the case of the steel/steel contacts. Moreover, the MoS₂-based tribofilm was found to be more oxidized on the DLC surface than on the steel surface. Nevertheless, we found that the chemical and functional properties of the MoS₂-based tribofilm are very similar, or even the same, for both the steel and DLC-coated surfaces. No direct evidence of any chemical reactions between the MoS₂ and the steel or DLC coating was observed.     

Wear behavior and cutting performance of nanostructured hard coatings on cemented carbide cutting tools in hard milling

The influence of nanolayer AlTiN/TiN and multilayer nanocomposite TiAlSiN/TiSiN/TiAlN hard coatings on the wear behavior and cutting performance of carbide cutting tools was investigated in face milling of hardened AISI O2 cold work tool steel (∼58 HRC) at dry conditions. Characterization of the coatings was performed using nanoindentation, scratch test, reciprocating multi-pass wear test. The chips forming during cutting process were also analyzed. Results showed that abrasive and oxidation wear are dominant tool failures. The nanolayer AlTiN/TiN coating gives the best adhesion to the substrate, the best wear resistance in machining and thus provides the longest lifetime with carbide inserts.     

Influence of counterbody material on wear of ta-C coatings under fretting conditions at elevated temperatures

The high temperature tribological performance of tetrahedral amorphous carbon coatings has been analyzed at elevated temperatures up to 250 °C in air against three different counterbody materials—steel 100Cr6, α-alumina and silicon nitride. The results show that the counterbody material influences the friction and wear behavior and therefore coating life time strongly. This effect is well known for these coatings at room temperature under dry environmental conditions, equivalent to conditions above 100 °C when water molecules desorb from the surface. However, the sharp difference in tribological performance between silicon nitride on the one hand and alumina and steel on the other hand cannot be understood in this context. Analyzing the friction behavior during the running-in phase, it is evident that only alumina and steel form a stable interface with constant low friction and relatively low wear rates. Silicon nitride forms an unstable interface with fluctuating COF and relatively high wear rates due to its own inherent tendency to tribo-oxidation.