A comparative study on the tribological behaviors of nitrided and sulfur-nitrided 35CrMo steel lubricated in PAO base oil with MoDTC additive

A nitrided layer on 35CrMo steel was prepared by the ion nitriding process, and then a sulfur-nitrided layer was obtained by low temperature ion sulfuration. The results showed that both the nitrided and sulfur-nitrided surfaces improved the wear resistance efficiently under PAO lubrication, and exhibited the best wear resistance and friction-reducing property under PAO with 0.75% MoDTC lubrication. Compared with the plain and nitrided surfaces, the sulfur-nitrided surface exhibited the best synergistic effect with MoDTC displaying the lowest friction coefficient and wear volume. The mechanism of the best effect was due to MoS₂ and FeS formed on the sulfur-nitrided surface.     

The Interactions Between Sulfur-Nitrided Layer on Steel Surface and MoDTC Lubricating Additive and Their Effects on Tribological Performance

Low temperature ion sulfuration and ion nitriding technologies were used to treat AISI 52100 steel. The tribological behaviors of the treated surface were investigated under lubrication with different MoDTC additive concentration. The morphologies and composition of worn surfaces were observed, and the valence states of tribofilm were identified. The results showed that the sulfur-nitrided surface was obviously improved in the friction-reducing property and exhibited the best synergistic effect when the concentration of MoDTC reached 1.0?%. The main reason is that MoS₂ and FeS were formed on the worn sulfur-nitrided surface.     

Tribological Behaviors of Different Diamond-Like Carbon Coatings on Nitrided Mild Steel Lubricated With Benzotriazole-Containing Borate Esters

Three synthesized benzotriazole-containing borate esters were separately added into poly-alpha-olefin (PAO) as additives, using molybdenum dithiocarbamate (MoDTC) as the comparison. The friction and wear behavior of Ti-DLC and Ti/Al-DLC coating on nitrided AISI-1045 steel sliding against AISI 52100 steel under the lubrication of PAO containing various additives was evaluated using a reciprocating ball-on-disk friction and wear tester. The morphology and chemical feature of the worn surfaces of the DLC coatings were observed and analyzed using a three dimensional (3D) surface profiler, a scanning electron microscope (SEM), and an X-ray photoelectron spectroscope (XPS). Results show that the three kinds of benzotriazole-containing borate esters as additives in PAO had much better tribological properties than MoDTC; the wear resistance of Ti/Al-DLC coating was better than Ti-DLC coating.     

Synergistic effects between sulfurized W-DLC coating and MoDTC lubricating additive for improvement of tribological performance

Low temperature ion sulfuration technology was used to obtain sulfurized layer on W doped diamond-like carbon (W-DLC) coating. The tribological behaviors of the pure W-DLC and sulfurized W-DLC coatings were investigated under PAO and MoDTC lubrication conditions. It shows that sulfurized W-DLC coatings can obviously improve their tribological performances under PAO with MoDTC lubrication. The primary reason is due to the formation of WS_x on the surface of sulfurized W-DLC coating, the decomposition of additives for formation a higher ratio of Mo sulfide/Mo oxide and the graphitization for a high ratio of sp²/sp³.     

Hydrogen influence on material interaction with ZDDP and MoDTC lubricant additives

In this paper the interaction of lubricant additives with hydrogen at the frictional interface has been investigated. Three different states of the base AISI 52100 alloy steel have been tested: untreated, nitrided and sulphonitrided, with different combinations of PAO6 base oil and ZDDP/MoDTC (Zinc DialkylDithioPhosphate and Molybdenum Dialkyldithiocarbamate) additives. Experiments have been carried out on pin-on-plate reciprocating tester, immersed in the lubricant heated to 100 °C. In the boundary lubricated regime the results showed the best friction behaviour for treated surfaces tested in presence of PAO6 with additives suggesting some interaction at the frictional interface of nitrided and sulphonitrided surfaces with lubricant additives. The minimum recorded value of coefficient of friction was as low as 0.05 for the sulphonitrided sample with PAO6+MoDTC oil. In the case of the treated surfaces a characteristic “low friction phase” has been observed when tested with PAO6 with additives. After a given time, the coefficient of friction was increasing to a higher steady-state value and the duration of this low friction phase varied from sample to sample. This can be explained by the mechanism of hydrogen interaction in the boundary lubrication regime, which was postulated for the base oil case by some of the authors in their previous papers. To validate the hypothesis, an experiment has been carried out where the test was stopped at the end of the “low friction phase” and during the hold period the sample was re-saturated with hydrogen. After resuming the experiment the low friction regime was again observed. The effect of a potential synergistic mechanism between hydrogen and ZDDP or MoDTC lubricant additives on frictional behaviour of nitrided and sulphonitrided surfaces is discussed in this paper.     

钻杆接头材料35CrMo钢硫氮共渗层的摩擦学性能

为了提高钻杆接头的使用寿命,利用离子渗氮和硫氮共渗技术在钻杆接头材料35CrMo钢表面制备了氮化层和硫氮共渗层。在油润滑条件下采用自制的球-盘磨损试验机考察了表面渗层的摩擦磨损性能。利用了XRD研究了表面层的相结构,采用了带EDS的SEM对表面改性层和磨损表面进行了分析。结果表明:35CrMo钢硫氮共渗层的摩擦学性能明显优于原始渗氮层;具有优良润滑作用的FeS固体润滑膜在高硬度氮化层的支撑下,可以有效地改善钻杆接头的摩擦磨损性能。     

Tribological properties of plasma nitrided stainless steel against SAE52100 steel under ionic liquid lubrication condition

1Cr18Ni9Ti stainless steel was modified by plasma nitriding. The phase composition of the plasma nitrided layer was examined by means of X-ray diffraction. The friction and wear properties of the modified and unmodified 1Cr18Ni9Ti stainless steel specimens sliding against SAE52100 steel under the lubrication of ionic liquid of 1-ethyl-3-hexylimidazolium hexafluorophosphate (L-P308) and poly α-olefin (PAO) were investigated on an Optimol SRV oscillating friction and wear tester, with the interactions among the modified surface layer and the ionic liquids and PAO to be focused on. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces of the modified steel surfaces were examined by means of X-ray photoelectron spectroscopy. Results showed that the modified sample had better anti-wear abilities than the unmodified one, but the modified sample had a slightly higher friction coefficient than the untreated one. This was partly attributed to the change in the hardness and phase composition of the stainless steel surfaces after plasma nitriding and tribochemical reactions between the steel and the lubricant. The resultant surface protective films composed of various tribochemical products together with the adsorbed boundary lubricating film contributed to reduce the friction and wear.     

Tribological properties of grey cast iron lubricated using organic compounds containing Mo and ZnDTP additives

The lubricating effectiveness of organic compounds containing Mo and ZnDTP in different ratios in poly‐alpha‐olefin (PAO) was investigated using an Optimol SRV‐IV (Optimol Instruments, Munich, Germany) reciprocating friction and wear tester. The morphologies of the worn surfaces were observed using a scanning electron microscope with energy‐dispersive X‐ray spectroscopy. The chemical states of several typical elements on the worn surfaces of grey cast iron discs were examined by means of X‐ray photoelectron spectroscopy (XPS). The results indicated that the grey cast iron discs exhibited different friction‐reducing and wear‐resistance capabilities when lubricated with PAO containing MoDTP and ZnDTP additives in different ratios. The lowest frication coefficient is only 0.072. XPS analyses indicated that ZnDTP + MoDTP and ZnDTP + MoDTC formed different chemical products. Copyright © 2012 John Wiley & Sons, Ltd.     

Lubrication of carbon coatings with MoS2 single sheet formed by MoDTC and ZDDP lubricants

The fuel economy and reduction of harmful elements of lubricants are becoming important issues in the automotive industry. One approach to these requirements is the potential use of low‐friction coatings in engine components exposed to boundary lubrication conditions. Diamond‐like carbon (DLC) coatings, extensively studied as ultra‐low friction films to protect ductile metals surfaces for space applications, are expected to fit the bill. The main purpose of this work is to investigate the friction and wear properties of DLC coatings lubricated with molybdenum dithiocarbamate (MoDTC) and zinc dithiophosphate (ZDDP) under boundary lubrication conditions. The mechanisms by which MoDTC reduces the friction in the centirange were studied using ultra‐high vacuum (UHV) analytical tribometer. The UHV friction tests were performed on a tribofilm previously formed on selected DLC material with MoDTC and ZDDP containing oil. Ex‐situ characterizations show that the composition of this tribofilm is similar to that of a tribofilm obtained on steel surfaces in the same lubrication conditions with MoS₂ single sheets dispersed inside zinc phosphate zones. However, analyses by X‐ray photoelectron spectroscopy (XPS) indicate that MoDTC and ZDDP additives seem to be more active on steel surfaces than carbonaceous ones. After UHV friction with the tribofilm formed on selected DLC and steel pin counterpart, the wear scars of both sliding surfaces were characterized by in‐situ analytical tools such as Auger electron spectroscopy, scanning Auger microscopy and micro‐spot XPS. Low friction is associated with the transfer of a thin MoS₂ film to the steel pin counterpart. Copyright © 2006 John Wiley & Sons, Ltd.     

In Situ Raman Observations of the Formation of MoDTC-Derived Tribofilms at Steel/Steel Contact Under Boundary Lubrication

ABSTRACT

In this study, the time-dependent formation process of molybdenum dithiocarbamate (MoDTC)-derived tribofilms at steel/steel contact under boundary lubrication was investigated by using an in situ Raman tribometer. Especially, we focused on the effects of zinc dialkyldithiophosphate (ZDDP) concentration in MoDTC solution on MoDTC tribofilm formation process. A laboratory-built in situ Raman tribometer was used to evaluate friction and the formation process of MoDTC-derived tribofilms. All our results clearly suggest that there is an optimum ZDDP concentration in MoDTC solution for promoting the formation of MoS₂ tribofilms on the sliding surfaces, and there is also a threshold value for the formation rate of MoS₂ on the sliding surface for achieving low friction under lubrication with MoDTC-containing lubricants.     

Evaluation of Local Mechanical Properties in Depth in MoDTC/ZDDP and ZDDP Tribochemical Reacted Films Using Nanoindentation

Local mechanical properties in depth and near the surface of MoDTC/ZDDP and ZDDP tribofilms, which exhibited obviously different friction coefficients in a pin-on-disc test, were determined by using a nanoindentation technique combined with in-situ atomic force microscopy (AFM) observation. Tapping-mode AFM observation revealed that the MoDTC/ZDDP film was much rougher than the ZDDP film. Nanoindentation measurement revealed that the MoDTC/ZDDP and ZDDP tribofilms possessed different elasto-plasticities around a depth of several nanometers from the surface, although both films showed the same hardness and modulus depth distributions except in the surface area. The same mechanical depth distributions indicated that both kinds of tribofilm were functionally graded materials; that is, they consisted of a layer near the surface with lower hardness and modulus and providing lubrication and a base layer with higher hardness and modulus and serving to modify property differences at the interface. Most importantly, the different elasto-plasticities near the tribofilm surfaces revealed that the MoDTC/ZDDP tribofilm possessed lower shearing yield stress than the ZDDP tribofilm. The results of this study suggest that the presence of some solid lubricants such as MoS₂ just below the MoDTC/ZDDP film surface reduced the boundary friction coefficient.     

全配方发动机油SJ/5W-30中二烷基二硫代甲酸钼的磨擦学特性研究(Ⅰ)——二烷基二硫代甲酸钼(MoDTC)的减摩抗磨特性

以渗氮层/灰铸铁摩擦副为对象,采用全配方矿物基发动机油SJ/5W-30作为基础润滑油,研究了油溶性有机钼添加剂二烷基二硫代甲酸钼(MoDTC)在125℃、250℃和320℃三种不同温度下的摩擦学特性。结果表明:MoDTC添加至全配方发动机油SJ/5W-30中能有效降低摩擦系数以及渗氮层/灰铸铁摩擦副的磨损程度。而且,温度越高,MoDTC的减摩抗磨作用越显著。磨损表面的SEM观察表明:温度升高,渗氮层与灰铸铁的磨损程度均增大。添加剂MoDTC的存在能显著减缓温度对磨损程度的影响。     

Comparison of the effects of ionic liquid and anti‐wear additives on the tribological properties of Cr―Mo―N coatings

Cr―Mo―N coating was prepared by magnetron sputtering, and its crystallinity and phase structure were analysed by X‐ray diffraction. The tribological properties of the coating separately lubricated with L‐P106 ionic liquid was compared with poly‐alpha‐olefin (PAO) and PAO‐containing MoDTP and ZnDTP additives with a ball‐on‐disc reciprocal friction and wear tester. It was found that the tribological properties of as‐prepared Cr―Mo―N coating vary with varying lubricant systems. Namely, the results indicated that the L‐P106 has better friction‐reducing and wear resistance properties than that of MoDTC and ZnDTP. The analyses indicated that Cr―Mo―N coatings and lubrication films can be considered as a solid–liquid duplex lubricating systems. Copyright © 2014 John Wiley & Sons, Ltd.     

全配方发动机油SJ/5W-30中二烷基二硫代甲酸钼的摩擦学特性研究(Ⅱ)--二烷基二硫代甲酸钼(MoDTC)的摩擦化学效应

EDX分析表明，摩擦磨损过程中二烷基二硫代甲酸钼(MoDTC)中的活性元素与摩擦副材料表面发生了摩擦化学反应。温度和摩擦机械作用能显著促进：MoDTC与摩擦表面的摩擦化学作用。MoDTC的存在促进了全配方发动机油SJ／5W-30中的多功能添加剂ZDTP的分解。采用添加MoDTC的油样润滑时，在铸铁磨损表面上能形成Mo的化合物(MoO3，MoS2)以及硫化物(FeS)；纯基础油样SJ/5W-30润滑时铸铁磨损表面上只有硫化物形成，而且所形成的硫化物除FeS之外，还有较多的硫酸盐(FeSO4)。MoDTC与ZDTP甲复配时边界反应膜的形成可采用Pearson的硬软酸碱(HSAB)原理来阐释。     

Tribological properties of Fe7Mo6-based-alloy lubricated with poly-alpha-olefin containing PN additive

Tribological properties of Fe–Mo type disk specimens were investigated against ASTM 52100 steel balls under the lubrication of poly-alpha-olefin (PAO) and PAO containing 1.5 mass% alkyl-phosphonic acid-triazole-methanamine (PN additive). Both the Fe₇Mo₆-based alloy and Mo disk specimens exhibited lower friction and lower wear rates than the Fe and gray cast iron disk specimens under the lubrication of PAO. The friction coefficients of the Fe₇Mo₆-based alloy disk specimens were reduced to 0.07 by adding 1.5 mass% PN additive to PAO. No wear volume loss was observed on the Fe₇Mo₆-based alloy disk specimens when they were lubricated with PAO containing 1.5 mass% PN additive.     

Wear behavior of AISI D2 steel by enhanced ion nitriding with atomic attrition

An experimental study was performed to investigate the effect of atomic attrition on wear behavior of AISI D2 steel. Wear tests were conducted under three different loads (5, 10, and 20 N) and sliding speeds (100, 200, and 500 rpm), using ball-on-disk type tester and SiC ball. After wear test, the specimen nitrided with ion bombardment showed superior wear behavior. The enhanced hardness by ion bombardment could have a beneficial effect on increased wear resistance. In addition, a wider and more adhesive oxide layer formed on the worn surface of ion-bombarded specimen, because of the rougher structure on the surface by ion bombardment, could lead the surface to withstand wear for longer duration time, acting as a protective layer.     

Transient processes of MoS2 tribofilm formation under boundary lubrication

A tribochemistry study that involves the application of Raman spectroscopy surface analysis has been undertaken to understand the time‐dependent tribochemical reactions, for lubrication by Molybdenum dialkyl‐dithiocarbamate (MoDTC) occurring in boundary lubricated conditions. Under the conditions of rubbing and high temperature, time‐resolved Raman spectroscopy results show the intermediate steps that lead to the MoDTC additive to be tribochemically structured on the wear scar of the contacting surface. A MoS₂ tribofilm with a lattice layer structure is observed on the wear scar whenever the lowest friction was achieved. An apparent shift of the A_1g and E_2g Raman modes, indicating qualitative and quantitative information on the MoS₂ tribofilm formed, is observed to be related to low friction. Detailed analyses of Raman spectra obtained on wear scars at different test durations and temperatures indicate that both temperature and rubbing are needed for the formation of low friction MoS₂ tribofilm. Copyright © 2016 John Wiley & Sons, Ltd.     

Tribological performance of three advanced piston rings in the presence of MoDTC-modified GF-3 oils

The piston assembly (piston ring and cylinder bore) is one of the key parts of the internal combustion (IC) engine. Its performance will directly determine the performance of the whole engine. The piston assemblys tribological performance will be influenced by both its mechanical properties and the tribochemical interactions that take place on their surfaces. In this paper, three kinds of advanced stainless steel piston rings with a single nitrided layer, CrN coating on the nitrided layer and a B₄C and CrN binary-layer coating on the nitrided layer, respectively, were employed. Their frictional behavior and wear performance, when sliding against the cast iron cylinder bore materials lubricated with two kinds of GF-3 category mineral-based engine oils (one of them blended with MoDTC friction modifier), were investigated on a SRV tribotester. The test conditions were set and maintained to simulate engine-operating conditions. SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray spectroscopy) were employed to characterize the morphology and elemental composition of the wear tracks. Tribotests and analysis results indicate that changes in both the mechanical properties of the tribomate (piston coatings) and tribochemical interactions (formulation of engine oils) have an impact on the tribological performance of the piston assembly. Tribochemical interactions will have a more obvious influence on friction coefficients while the mechanical properties of the tribomate have a more obvious influence on wear.     

渗氮GCr15钢在含氮硼酸酯添加剂润滑油作用下的摩擦学性能

针对提高滚动轴承使用寿命的问题,提出离子渗氮处理与添加剂结合的解决办法。用等离子渗氮炉在GCr15轴承钢表面制备了渗氮层,并用扫描电子显微镜(Scanning electron microscope, SEM )、X射线衍射仪(X-ray diffractometer, XRD)和显微硬度计观测了渗层的形貌、相结构和硬度变化。利用四球摩擦磨损试验机对比考察渗氮钢和未渗氮钢在含氮硼酸酯润滑条件下的摩擦学性能,并用X射线光电子能谱仪(X-ray photoelectron spectroscope, XPS)分析摩擦反应膜的成分与化学结合态。结果表明,渗氮层与润滑油添加剂之间发生了意想不到的良好交互作用,渗氮钢在质量分数为1.25%氮硼酸酯的润滑条件下表现出最低的摩擦因数和磨斑直径,比未渗氮钢分别降低了34%和45%;分析证明,渗氮层的摩擦表面生成了高BN质量分数的摩擦反应膜是获得优异摩擦学性能的主要原因,而在未渗氮钢摩擦表面未检测到BN。     

离子硫氮复合渗42CrMo钢的耐磨性和抗咬合性研究

研究了离子硫氮复合渗对42CrMo钢的耐磨性和抗咬合性的影响。数据表明，与42CrMo钢调质态和单一离子渗氮工艺状态相比，该钢经离子硫氮复合渗处理后可明显提高钢的耐磨性和抗咬合性。通过对渗层的组织结构分析，探讨了硫氮复合渗层对提高42CrMo钢的耐磨性和抗咬合性的作用机理。