Effect of vacuum annealing temperature on tribological behaviors of sintered polycrystalline diamond compact

The sintered polycrystalline diamond compacts (PDCs) were annealed at 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C under vacuum environment. The friction and wear behaviors of the annealed PDCs sliding against Si₃N₄ balls were evaluated by a ball-on-disc tribometer in ambient atmosphere. The compositions, microstructures and surface morphologies of PDC discs and wear scars on Si₃N₄ balls were characterized by energy dispersive spectroscopy (EDS), Raman spectroscopy, and scanning electron microscopy (SEM), respectively. The experimental results demonstrated that the steady friction coefficient decreased at the annealing temperature of 200 °C and increased with annealing temperature increasing. While, the wear rate of PDCs and Si₃N₄ balls increased at 200 °C, and sharply decreased from 300 to 800 °C. The surface morphologies and Raman spectra revealed that the variation law of friction coefficient curves at different annealing temperatures was attributed to carbonaceous transfer films formed on Si₃N₄ balls. The residual stress on PDC surface was reduced after the annealing treatment, thus fine diamond grains were easily extracted from PDC surface onto the contact area during the tribotest which led to the wear of PDC and abrasive wear for both counter parts. These results revealed that the friction and wear behaviors of PDC were significantly affected by the vacuum annealing temperature.     

Influence of normal load and sliding speed on the tribological property of amorphous carbon nitride coatings sliding against Si3N4 balls in water

Amorphous carbon nitride (a-CN_x) coatings were deposited on Si₃N₄ disks by an ion beam assisted deposition system. The composition, structure and hardness of the a-CN_x coatings were characterized by Auger electronic spectroscopy, Raman spectroscopy and nano-indentation tester, respectively. The influences of normal load and sliding speed on the friction coefficients and the specific wear rates for the a-CN_x/Si₃N₄ tribo-pairs were investigated and analyzed synthetically by ball-on-disk tribometer. The worn surfaces were observed by optical microscope. The results showed that the a-CN_x coatings contained 12 at.% nitrogen, and their structure was a mixture of sp²and sp³ bonds. The a-CN_x coatings’ nanohardness was 29 GPa. The influence of sliding speed on the friction coefficients and the specific wear rate of the CN_x coatings was more obvious than that of normal load. The friction coefficients and the specific wear rate of the CN_x coatings decreased as the sliding speed increased. At a sliding speed higher than 0.1 m/s, the friction coefficients were less than 0.04. The specific wear rates of the a-CN_x coatings were higher than those of Si₃N₄ balls at a sliding speed below 0.1 m/s, while the specific wear rates of the a-CN_x coatings and the Si₃N₄ balls all fluctuated around a lower level of 10^− 8 mm³/Nm as the sliding speed increased beyond 0.2 m/s. To describe the wear behavior of a-CN_x coatings sliding against Si₃N₄ balls in water with normal loads of 3-15 N and sliding speeds of 0.05-0.5 m/s, the wear-mechanism map for the a-CN_x/Si₃N₄ tribo-pairs in water was developed.     

Tribological Properties of Ni<Subscript>3</Subscript>Al Matrix Composite Sliding Against Si<Subscript>3</Subscript>N<Subscript>4</Subscript>, SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> at Elevated Temperatures

The Ni₃Al matrix self-lubricating composite was fabricated by powder metallurgy technique. The tribological behavior of the composite sliding against commercial Si₃N₄, SiC and Al₂O₃ ceramic balls was investigated from 20 to 1000 °C. It was found that the composite demonstrated excellent lubricating properties with different friction pairs at a wide temperature range, which can be attributed to the synergetic effect of Ag, fluorides, and molybdates formed by oxidations. The Ni₃Al matrix self-lubricating composite/Si₃N₄ couple possessed the stable friction coefficient and wear rate.     

Tribological Behavior of Babbitt Alloy Rubbing Against Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and Steel Under Dry Friction Condition

The tribological behavior of Babbitt alloy rubbing with Si₃N₄ ball and steel ball with various sliding speeds at dry friction condition was investigated. It was found that B88 alloy rubbing with Si₃N₄ ball and steel ball possesses a low sliding wear resistance at dry friction. The wear rate is above 10^?4 mm³/Nm, and the friction coefficient is from 0.2 to 0.4. At low sliding speed of 0.05-0.1 m/s, the mainly wear mechanisms are microgroove and fatigue wear, while at high sliding speed of 0.5 m/s, the wear mechanisms depend on plastic deformation and delamination. The high wear rate indicates that it is needed to prevent Babbitt alloy from working at dry friction conditions, while the low friction coefficient suggests that it is not easy to the occurrence of cold weld.     

Self-lubricating mechanisms via the in situ formed tribo-film of sintered ceramics with hBN addition in a high humidity environment

Sliding wear tests against monolithic Si₃N₄ and austenitic stainless steel, respectively, were performed on Si₃N₄ ceramic with the addition of hBN solid lubricants. The friction coefficients and wear rates were measured. The wear surface features were examined by scanning electron microscopy (SEM) and laser scanning microscopy (LSM), and the chemical characterization of worn surface was made by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Results showed that the friction coefficient and the wear rate decreased with the increase of hBN up to 20 vol% at high relative humidity (RH95%). When Si₃N₄-hBN ceramic composites sliding against stainless steel, with further increases in hBN content, the wear rate increased rapidly. The mechanism responsible were determined to be an in-situ formed tribo-chemical film composed of B-O and Si-O compounds between the pin-disc sliding couple. SEM observations showed that a black surface film is formed on the wear surface depending on the hBN content. The surface film associated with small friction coefficient of 0.03 and low wear rate with the magnitude of 10^− 6 mm³/Nm was formed by the releasing and smearing of the tribo-chemical reaction products of hBN and moisture on the wear surface when with 20 vol%hBN content. This tribo-chemical film acted as solid lubricant film between the sliding couple, and thus the couple entered to a state of boundary lubrication. Hence, the friction coefficient and the wear rate were significantly reduced. For Si₃N₄-hBN/stainless steel sliding pair, even at high relative humidity, no tribo-chemical film was observed on samples with 30 vol%hBN content, just because of a large degradation of mechanical properties of the composite with higher hBN content. At low relative humidity (RH25%), the wear mechanism for Si₃N₄-hBN sliding couple was mainly dominated by mechanical wear (abrasive or adhesive wear) due to the absence of tribo-chemical film on the wear surfaces, and higher friction coefficient and wear rate were obtained.     

Friction and wear of Si3N4 ceramic/stainless steel sliding contacts in dry and lubricated conditions

Austenitic stainless steel AISI 321 is one of the most difficult-to-cut materials. In order to investigate the wear behavior of Si₃N₄ ceramic when cutting the stainless steel, wear tests are carried out on a pin-ondisk tribometer, which could simulate a realistic cutting process. Test results show that the wear of Si₃N₄ ceramic is mainly caused by adhesion between the rubbing surfaces and that the wear increases with load and speed. When oil is used for lubrication, the friction coefficient of the sliding pairs and the wear rate of the ceramic are reduced. A scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), and an energy dispersive x-ray analyzer (EDXA) are used to examine the worn surfaces. The wear mechanisms of Si₃N₄ ceramic sliding against the stainless steel are discussed in detail.     

Enhanced tribological behaviors of sintered polycrystalline diamond by annealing treatment under humid condition

The tribological behaviors of the 700 °C annealed sintered polycrystalline diamond (PCD) at various relative humidity (RH) levels were systematically investigated. The comparison of tribological behaviors between the 700 °C annealed PCD and the pristine PCD was made to further understand the tribological mechanisms. The results reveal that the friction inducing carbonaceous transfer film and oxidation and hydrolysis induced tribochemistry reaction dominant the tribological behaviors of the annealed PCD at various RH levels. The low coefficient of friction (COF) obtained in dry environments is attributed to carbonaceous transfer film on the worn Si₃N₄ surface, which was formed by the layers shearing action of massive tiny diamond grains exfoliated from the annealed PCD surface. The graphitization, oxidation and stress relaxation of the PCD induced by the 700 °C annealing treatment make the tiny diamond grains more easily to exfoliate and be grinded on the Si₃N₄ interface. It facilitates the formation of friction reducing carbonaceous transfer film, and finally results in the 30% lower COFs than those of pristine PCD at low RH levels (5%–50% RH). Meanwhile, an enhanced wear resistance of PCD can be achieved after 700 °C annealing treatment. The tribochemistry reaction induced by the oxidation and hydrolysis of Si₃N₄ governs the tribological behaviors of the annealed PCD at high RH levels (60%–99.9% RH). It reveals higher COFs accompanied with serious wear of Si₃N₄ ball and nearly no wear loss of annealed PCD. The produced SiO₂ and silicic acid embeds into massive spalling pits on the annealed PCD surface, resulting in slighter wear of the PCD and Si₃N₄ than that of the pristine PCD/Si₃N₄. These results propose that the tribological behaviors of PCD under humid environment can be significantly improved by the 700 °C annealing treatment.     

Effects of tribochemical reaction on tribological behaviors of Si3N4/polycrystalline diamond in hydrochloric acid

The interfacial tribo-chemistry significantly affects the tribological behaviors of polycrystalline diamond (PCD)/Si₃N₄, especially introducing acid solution. The results indicate that the friction coefficient rises with increased PH while Si₃N₄ wears severer and then slighter. Besides, when the hydrogen ions were introducing in the testing environment, the hydrolysis reaction of Si₃N₄ and oxidation reaction of PCD were promoted on the surfaces with the formation of Si-OH and C-OH. The tribo-pair surfaces absorded hydrogen ions by protonation reaction to form the double electron layer in this process, during which significantly affect the tribological behavior of Si₃N₄. This work elucidates that the protonation effect of hydrogen ions and bridge effect of hydroxyls, leading to the friction and wear mechanism of PCD/Si₃N₄.     

Investigation of the friction and wear characteristics of Si3N4-hBN ceramic composites under marine atmospheric environment

The tribological properties of Si₃N₄-hBN in marine atmosphere and deionized water atmosphere were investigated by using Pin-On-Disc (POD) tribometer. In comparison, the friction coefficients of the sliding pairs in marine atmosphere were lower than that in the deionized water atmosphere. Furthermore, the tribo-chemical films were observed on the worn surface of titanium alloy against Si₃N₄–20 wt%hBN in marine atmosphere, which provided a certain bearing capacity between sliding pairs. Meanwhile, it can be concluded that the tribo-chemical films possessed lower shear force through theoretical analysis. Thus, the lower friction coefficient and wear rate were obtained in this study.     

The Sliding Wear and Friction Behavior of M50-Graphene Self-Lubricating Composites Prepared by Laser Additive Manufacturing at Elevated Temperature

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si₃N₄ ball from 25 to 550 °C at 18 N–0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10^?7 mm³ N^?1 m^?1. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10^?7mm³ N^?1 m^?1). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer.     

载荷、摩擦副及介质环境对多层Ti掺杂类石墨薄膜的摩擦学行为影响EI北大核心CSCD

针对非晶碳基薄膜高内应力和低膜基结合强度的问题,采用闭合场非平衡磁控溅射系统在316L不锈钢基体上制备多层结构掺杂类石墨薄膜(GLC),探究载荷、摩擦副和介质环境对薄膜摩擦学行为的影响。结果表明,制备得到的多层结构GLC薄膜结构致密均匀,膜基之间没有明显缺陷,且力学性能良好。薄膜在干摩擦条件下的摩擦因数曲线呈明显的三阶段特征,分别对应于轻微的磨粒磨损、薄膜的剥离以及对磨球上碳质转移膜的形成。薄膜的平均摩擦因数随载荷的增加而显著提高,磨损率呈先减小后增大的趋势。相对于ZrO_(2)陶瓷球,Si_(3)N_(4)陶瓷球因其较高的黏着倾向和较大的赫兹接触半径导致其较高的摩擦因数和磨损率。GCr15金属球因其较低的硬度,导致碳质转移膜随金属磨削的剥离而脱落,造成相对较高的摩擦因数和磨损率。相对于室温空气环境下,GLC薄膜在NaCl溶液中由于受到水溶液的冲洗和腐蚀介质Cl^(-)的侵蚀,导致薄膜从基体的快速剥离,造成更高的摩擦因数和磨损率。研究成果可为提高非晶碳基薄膜在不同工作环境下的服役寿命和使用效率提供理论指导。     

Structural transformations and tribological properties of amorphous alloys upon wear at room and cryogenic temperatures

The abrasive wear resistance of the Fe₆₄Co₃₀Si₃B₃, Co_86.5Cr₄Si₇B_2.5, Fe_73.5Nb₃Cu₁Si_13.5B₉, and Fe_82.6Nb₅Cu₃Si₈B_1.4 commercial amorphous alloys (ribbon 0.03 mm thick and 12 mm wide) has been investigated under the conditions of abrasive and adhesive wear upon sliding friction. The character of fracture of the surface and structural transformations that occur in these materials upon wear have been studied by the metallographic and electron-microscopic methods. It has been shown that at room and cryogenic (−196°C) temperatures of tests the abrasive wear resistance of the amorphous alloys is two-three times lower than that of tool steels Kh12M and U8. A comparatively small abrasive wear resistance of the amorphous alloys is explained by local softening of these materials in the process of wear. Under the conditions of adhesive wear of like friction pairs at room temperature in air and argon, the amorphous alloys are characterized by the rate of wear that is smaller approximately by an order of magnitude than in steels 12Kh13 and 12Kh18N9. It has been established that upon wear the deformed surface layer of the alloys under study retains a predominantly amorphous state but in local sections of this layer nanocrystalline structures that consist of crystals of bcc and fcc phases and borides are formed. The possible effects of this partial crystallization on the microhardness, friction coefficient, and wear resistance of these alloys have been considered.     

不同纳米WS2含量Ni-P-Ti N-WS_(2)复合化学镀层的制备及其摩擦学性能EI北大核心CSCD

Ni-P-TiN化学复合镀层具有比Ni-P镀层更高的硬度和耐磨性,但其表面粗糙度大,与对偶件之间的摩擦因数高,应用潜力受到限制。通过在化学镀液中添加不同用量的纳米WS_(2)颗粒和固定用量的TiN颗粒,在低碳钢表面制备Ni-P-TiN-WS_(2)复合镀层。采用X射线能谱仪(EDS)、扫描电子显微镜(SEM)和X射线衍射仪(XRD)对镀层的化学成分(质量分数)、表面形貌及微观结构进行表征,并利用球盘式摩擦磨损试验机测试复合镀层的摩擦磨损性能。结果表明:纳米WS_(2)颗粒与纳米TiN颗粒的共沉积可使镀层表面更加致密、平整。随着镀液中纳米WS_(2)用量的增加,复合镀层的硬度先减小后增大,与氮化硅陶瓷球的摩擦因数则先升后降,磨损率显著下降,耐磨性增强。镀液中纳米WS_(2)粉末的用量为2.5 g/L时复合镀层的摩擦学性能最佳。纳米WS_(2)颗粒的加入及用量优化可显著改善复合镀层的综合性能,可为发展高耐磨低摩擦因数的先进涂层提供借鉴。     

Optimization of friction and wear behaviour of Al–Si3N4 nano composite and Al–Gr–Si3N4 hybrid composite under dry sliding conditions

The tribological behaviour of gravity die stir cast LM6 alloy with graphite (Gr) and silicon nitride nanoparticles was investigated. Al–Gr–Si₃N₄ hybrid composite, Al–Si₃N₄ nanocomposite and Al–Gr nanocomposites were separately fabricated to investigate their frictional and wear characteristics under dry sliding conditions. EDS was used to ensure the uniform presence of nano Si₃N₄ and graphite in the cast. L9 orthogonal array method was chosen to conduct the experiments to study the effect of different applied loads (20, 30 and 40 N) and sliding distances (1, 2 and 3 km). The results showed that the respective wear rate and coefficient of friction (COF) decreased by 25% and 15% for hybrid composite when compared with those of Al–Si₃N₄ nanocomposite whereas the wear rate and COF of Al–Gr was found to be very minimal. The micro Vickers hardness of the hybrid composite was 14% more than that of the simple nanocomposite and there was not much notable variation for Al–Gr and Al–Si₃N₄ nanocomposite materials. Scanning electron microscope was used to analyze the worn surface and subsurface, from which it was noted that the predominant wear mechanisms observed were abrasive for nanocomposite and both abrasive and adhesive mechanism for hybrid composite. Analysis of variance (ANOVA) and F-test were used to check the validity model and to determine the significant parameters affecting the wear rates.     

Tribological performance of hybrid filtered arc-magnetron coatings. Part II: Tribological properties characterization

Nano-structured coating architectures were developed to provide a best blend of corrosion and wear resistance for high chromium content steels used in aerospace bearing and gear applications. A hybrid filtered arc-magnetron deposition process was employed to deposit functionally graded, multilayered and nanocomposite TiCrN/TiCrCN + TiBC cermet coatings on carburized steel substrates. Coatings exhibited excellent adhesion to the carburized surfaces and had hardness in the range of 23-25 GPa. Tribological properties of the coatings were characterized by: pin-on-disk COF, lubricated sliding, reciprocating sliding, and 3 ball half thrust bearing tests in dry and lubricated environments at high contact stresses. Both polyester and perfluoropolyalkylethers (PFPAE) based lubricants were used to evaluate coating performance with neutral and chemically aggressive lubrication. Sliding friction and reciprocating sliding wear tests were performed using modified disk-on-ring and point-on-disk arrangements, respectively. Contact stresses were estimated using the Hertzian contact formula (sliding friction), and through direct measurements of contact areas by SEM (reciprocating sliding). Low-speed thrust bearing high load rolling contact was evaluated at 350 °C, using Si₃N₄ balls and PFPAE-based lubricant, at contact stresses of ∼ 3.2 GPa. Aggressive corrosion testing was performed on coated samples using MIL-STD-810F “salt-fog” testing. Wear and corrosion behavior was investigated using SEM/EDS, EDX, AFM, profilometry, and optical microscopy. The influence of coating architecture on wear properties was investigated. Multifold improvements in the surface dry and lubricated wear life, reduction of the dry friction coefficient, prevention of corrosion attack from the products of PFPAE lubricant degradation, and improvement of salt-fog corrosion resistance are demonstrated.     

Unlubricated friction and wear behaviors of Al2O3/TiC ceramic cutting tool materials from high temperature tribological tests

The unlubricated friction and wear behaviors of Al₂O₃/TiC ceramic tool materials were evaluated in ambient air at temperature up to 800 °C by high temperature tribological tests. The friction coefficient and wear rates were measured. The microstructural changes and the wear surface features of the ceramics were examined by scanning electron microscopy. Results showed that the temperature had an important effect on the friction and wear behaviors of this Al₂O₃ based ceramic. The friction coefficient decreased with the increase of temperature, and the Al₂O₃/TiC ceramics exhibited the lowest friction coefficient in the case of 800 °C sliding operation. The wear rates increased with the increase of temperature. During sliding at temperature above 600 °C, oxidation of the TiC is to be expected, and the formation of lubricious oxide film on the wear track is beneficial to the reduction of friction coefficient. The wear mechanism of the composites at temperature less than 400 °C was primary abrasive wear, and the mechanisms of oxidative wear dominated in the case of 800 °C sliding operation.     

Dense Si3N4 coatings with high friction coefficient deposited by high-velocity pulsed plasma spraying

A novel electromagnetically accelerated plasma spraying technique was applied to mixtures of αSi₃N₄, and alumina, yttria, and silica additives to deposit thin coatings (50–100 μm) onto mirror-polished stainless steel surfaces. The dense coatings consisted of crystalline αSi₃N₄ with minor amounts of β'SiAlON, traces of βSi₃N₄ and Y₃Al₅O₁₂ as well as a quinary Si−Al−N−O−Y glass. The adhesion strengths depended on the powder particle size showing values of>77 MPa for coarse powders (median grain size 25 μm) and>67 MPa for fine powders (median grain size 8 μm). The average indentation hardnesses were 450 HV_0.025 (coarse powder) and 620 HV_0.025 (fine powder); the sliding wear resistances were comparable to those of sintered Si₃N₄ used as counterbody in a pin-on-disc friction test. The friction coefficient showed surprisingly large values (1.0–1.1 in water and 1.3–1.4 in air), suggesting application of such coatings as tribological high-friction surfaces.     

Sliding wear resistance of porous biomorphic sic ceramics

Porous biomorphic SiC ceramics were fabricated from four different wood precursors, three natural woods and one recycled wood product, by reactive infiltration of molten silicon into a carbon preform obtained from wood pyrolysis. Sliding wear resistance when sliding against a Si₃N₄ ball in air was studied. Tribological experiments were done with a pin-on-disk apparatus, under normal loads of 1 and 2 N, at a sliding velocity of 100 mm/s. The wear properties and the volume fraction of porosity were correlated. A commercial sintered SiC ceramic was also tested for comparison. The measured values of friction coefficient were in the range reported in literature for monolithic SiC ceramics under similar dry contact conditions. Two concurrent wear mechanisms are taking place: abrasion from the SiC debris and soft ploughing. The presence of an oxide tribolayer was assessed using energy dispersive X-ray analysis. Wear rates were found to scale with the composite porosity.     

TiN-Coating Effects on Stainless Steel Tribological Behavior Under Dry and Lubricated Conditions

The tribological properties of magnetron sputtered titanium nitride coating on 316L steel, sliding against Si₃N₄ ceramic ball under dry friction and synthetic perspiration lubrication, were investigated. The morphology of the worn surface and the elemental composition of the wear debris were examined by scanning electron microscopy and energy dispersive spectroscopy. TiN coatings and 316L stainless steel had better tribological properties under synthetic perspiration lubrication than under dry friction. Among the three tested materials (316L, 1.6 and 2.4 μm TiN coatings), 2.4 μm TiN coating exhibits the best wear resistance. The difference in wear damage of the three materials is essentially due to the wear mechanisms. For the TiN coating, the damage is attributed to abrasive wear under synthetic perspiration lubrication and the complex interactive mechanisms, including abrasive and adhesive wear, along with plastic deformation, under dry friction.     

Effect of Atmospheric Plasma Spraying Power on Microstructure and Properties of WC-(W,Cr)2C-Ni Coatings

WC-(W,Cr)₂C-Ni coatings were prepared by atmospheric plasma spraying (APS) with different spraying powers. The effect of spraying power on microstructure, phase composition, hardness, fracture toughness, and oscillating dry friction and wear behaviors of the coatings were studied. Simultaneously, the microstructure and properties of the as-sprayed coatings were compared with those of WC-17Co coating prepared under the optimal spraying power. It was found that spraying power had significant effect on the molten degree of feedstock powder and phase composition as well as microstructure and properties of WC-(W,Cr)₂C-Ni coatings. WC-(W,Cr)₂C-Ni coating deposited at a moderate spraying power of 22.5?kW had the highest fracture toughness and the best wear resistance. WC-17Co coating obtained under the moderate spraying power had poor fracture toughness and wear resistance. Moreover, the four kinds of coatings were all dominated by subsurface cracking and removal of materials when sliding against Si₃N₄ ball under unlubricated conditions.