共查询到20条相似文献,搜索用时 562 毫秒
1.
Metal containing amorphous hydrocarbon films (Me‐C:H) have excellent tribological properties and an adjustable electrical
conductivity. Friction force microscopy investigations on gold‐ and tungsten‐C:H films show a non‐linear dependence of friction
on the load in the nanonewton‐range which can be explained by Hertz model of elastic contact. The effective friction coefficient
and the interfacial shear stress strongly depend on the type of metal and the metal concentration inside the film. Microfriction
and macrofriction (pin‐on‐disk) show a high qualitative correspondence.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Friction force microscopy measurements on the vacuum‐cleaved (001) surfaces of KF, KCl and KBr have been carried out. All
surfaces exhibit atomically flat terraces with monatomic steps aligned preferentially along low‐index lattice directions.
Stick‐slip lateral forces with the lattice periodicity are observed on all surfaces. Tip‐sample contact creates higher friction
domains on the terraces of all three materials. The structure, topography and degree of friction force contrast of these domains
is material dependent. The dependence of friction upon load generally does not coincide with the behavior expected for an
elastic contact. We propose that the observed domains result from surface structural changes created by low load tip‐sample
contact on these relatively soft materials.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
P. P. Sharin M. P. Akimova S. P. Yakovleva A. M. Bolshakov V. I. Popov 《Russian Engineering Research》2019,39(12):1034-1042
The intermediate layer formed when diamond is in contact with metals that are active with respect to carbon—such as iron and titanium—is investigated in a vacuum furnace. The conditions in the furnace match those employed in sintering with copper impregnation of the hard-alloy matrix of diamond tools. The results may be used in developing compositions and technologies such that tool materials based on tungsten–cobalt hard-alloy powder have a high diamond content in the matrix. 相似文献
4.
One of the fundamental postulates of friction is that at the microscopic or molecular level, the “real” area of contact is
proportional to the load applied over the macroscopic or “apparent” area. This has both theoretical and experimental support
and has formed the basis of many theoretical analyses, including an explanation of one of the most basic observations of everyday
friction, i.e., that the friction force F is proportional to the load L or weight of the moving object (Amontons' law) where
the ratio of F to L defines the coefficient of friction μ=F/L. We have carried out friction experiments between two molecularly
smooth non-adhering surfaces under conditions where all the relevant macroscopic and microscopic parameters were directly
measured. We find that even at the microscopic level the friction force is proportional to the net applied load and not to
the real area of contact. One implication of this finding is that Amontons' law is also obeyed directly at the molecular level
and does not emerge indirectly because of some fortuitous correlation between the net applied load and the local contact area
or shear strength, as is commonly supposed. A physical model, based on intermolecular forces and thermodynamic considerations,
is offered to explain why the friction force is proportional to the net applied load, and why the case of adhering surfaces
- where the friction force is found to be proportional to the molecular contact area -is quite different from that of non-adhering
surfaces.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
Friction Study of a Ni Nanodot-patterned Surface 总被引:3,自引:0,他引:3
Hengyu Wang Rahul Premachandran Nair Min Zou Preston R. Larson Andrew L. Pollack K. L. Hobbs Mathew B. Johnson O. K. Awitor 《Tribology Letters》2007,28(2):183-189
Nanoscale frictional behavior of a Ni nanodot-patterned surface (NDPS) was studied using a TriboIndenter by employing a diamond
tip with a 1 μm nominal radius of curvature. The Ni NDPS was fabricated by thermal evaporation of Ni through a porous anodized
aluminum oxide (AAO) template onto a Si substrate. Surface morphology and the deformation of the NDPS were characterized by
scanning electron microscopy (SEM) and atomic force microscopy (AFM), before and after friction/scratch testing. SEM images
after scratching clearly showed that, similar to what was assumed at the macroscale, the frictional force is proportional
to the real area of contact at the nanoscale. It was found that adhesion played a major role in the frictional performance,
when the normal load was less than 20 μN and plastic deformation was the dominant contributor to the frictional force, when
the normal load was between 60 μN and 125 μN. Surprisingly, a continuum contact mechanics model was found to be applicable
to the nanoscale contact between the tip and the inhomogeneous Ni NDPS at low loads. The coefficient of friction (COF) was
also found to depend on the size of the tip and was four times the COF between a 100 μm tip and the Ni NDPS. Finally, the
critical shear strength of the Ni nanodots/Si substrate interface was estimated to be about 1.24 GPa. 相似文献
6.
Measurements of atomic friction in the atomic force microscope frequently show periodic variations at the lattice spacing
of the surface being scanned, which have the saw‐tooth wave form characteristic of “stick–slip” motion. Simple models of this
behaviour have been proposed, in which the “dynamic element” of the system is provided by the elastic stiffness and inertia
of the cantilever which supports the tip of the microscope, in its lateral, i.e., torsional mode of vibration. These models
have been successful in predicting the observed motion, but only by assuming that the cantilever is heavily damped. However,
the source of this damping in a highly elastic cantilever is not explained. To resolve the paradox, it is shown in this note
that it is necessary to introduce the elastic stiffness of the contact into the model. The relationship between the contact
stiffness, the cantilever stiffness and the amplitude of the periodic friction force is derived in order for stick–slip motion
at lattice spacing to be achieved.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Ramasesha Sheela K. Srikari Tantri P. Jayasingh E. Moses Biswas S.K. 《Tribology Letters》2000,8(4):219-222
Wear tests were done in a pin‐on‐disc machine by sliding MoSi2 pins against hard‐steel discs in a normal load range of 5–140 N and a speed of 0.5 m/s under nominally dry conditions in
the ambient. The specific wear rate of the pin undergoes two transitions: severe to mild at low load and mild to severe at
high load. The mild‐wear domain is distinguished by the formation of a protective mechanically mixed layer of steel and its
oxides, transferred from the counterface in particulate form. Increasing the hardness by densification and TiB2 reinforcement lowers the specific wear rate and expands the mild‐wear load domain. However, even when the volume wear rate
is normalised with respect to the real contact area (load/hardness) the non‐dimensional wear factor is still seen to decrease
with densification and reinforcement. This indicates that fracture toughness may also play an important role in determining
the wear‐resistance of these materials. The surface coverage on the pin by the mechanically mixed layer increases with densification
and reinforcement.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
The behavior of an elastic–plastic contact between a deformable sphere and a rigid flat under combined normal and tangential
loading with full stick contact condition is investigated theoretically. Sliding inception is treated as a plastic yield failure
mechanism, which allows static friction modeling under highly adhesive conditions. Several contact parameters such as: junction
tangential stiffness, static friction force and static friction coefficient are extensively investigated. The phenomenon of
junction growth and the evolution of the plastic zone in the contact region are briefly described. It is found that at low
normal dimensionless loads the static friction coefficient decreases sharply with increasing normal load, in breach with the
classical laws of friction. As the normal load further increases the static friction coefficient approaches a constant value
that is about 0.3 for many material properties combinations. 相似文献
9.
I.I. Garbar 《Tribology Letters》1998,5(2-3):223-229
The connection between the structure and abrasive wear resistance of steels was studied. Samples of AISI 1020, 1040 and 1080
steels were tested. The initial hardness of the samples ranged from HV221 – for annealed steel AISI 1020, to HV868 – for water
quenched and tempered at 180°C steel AISI 1080. Two‐body abrasive tests on silicon carbide abrasive paper of grit size 1200–240
were carried out on a friction machine under identical conditions for all specimens. X‐ray studies of the specimens were conducted
before and after these tests. It was shown that characteristics such as the integral width of diffraction lines could be used
as a universal indicator of abrasive wear resistance for steels, independently of their heat treatment. The compressive residual
stresses in the surface layers of the steels were observed. The results showed that there is a correlation between abrasive
wear resistance and the sign and magnitude of residual stresses in the surface layers of steels, as well as between abrasive
wear resistance and the structural changes in these layers.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Kazuhisa Miyoshi Masao Murakawa Shuichi Watanabe Sadao Takeuchi Shojiro Miyake Richard L.C. Wu 《Tribology Letters》1998,5(2-3):123-129
The main criteria for judging coating performance were coefficient of friction and wear rate, which had to be less than 0.1
and 10-6 mm3/(N.m), respectively. Carbon‐ and nitrogen‐ion‐implanted, fine‐grain, chemical‐vapor‐deposited (CVD) diamond and diamondlike
carbon (DLC) ion beam deposited on fine‐grain CVD diamond met the criteria regardless of environment (vacuum, nitrogen, and
air).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
In sliding of organic self-assembled monolayer against a probe the friction force is generally found to vary linearly with
normal load. Here, lateral force microscopy is used to track the physical changes at the interface brought about when an octadecyltrichlorosilane
monolayer, self-assembled on a silicon wafer, is slid against a Si3N4 tip in the 0–30 nN load range. Regarding a morphologically heterogeneous monolayer domain to be made up of tiles of characteristic
friction forces, each tile is in a unique physical state; the variation of area fraction (in a scan area) of each tile is
tracked as a function of normal load. The area averaged friction force at a load is obtained by summing the fractional forces
of constituent friction tiles. The friction force obtained thus, is found to vary linearly with normal tip load. It is observed
that this force is dominated by the low-friction crystalline tiles at low loads and by the high friction more amorphous tiles
at high loads. This suggests that for a self- assembled monolayer the load governance of friction as implied by the Amontons
Law may be attributed to the physical changes that are brought about at the interface by changing the normal load. 相似文献
12.
A number of WC–Ni based cemented carbide grades with distinctive binder contents were tested with the goal to evaluate their
dry reciprocating sliding friction and wear behaviour against WC–6 wt.%Co cemented carbide using a Plint TE77 tribometer and
distinctive normal contact loads. The generated wear tracks were analysed by scanning electron microscopy and quantified volumetrically
using surface scanning topography. The experimental results revealed one WC–Ni grade with superior wear performance. 相似文献
13.
The adhesion and wear of colloidal silica nanoparticles (50 nm diameter) dispersed in a film have been directly studied using
atomic force microscopy (AFM) under aqueous solution conditions. The adhesion between surface‐bound silica particles and the
AFM tip is found to peak in strength between pH 4 and 5. Using the JKR contact mechanics model, the energy for a single Si–OH/Si–OH
interaction was estimated to be 0.4 ± 0.1 kcal/mol. Tribochemical wear of the silica particles, and their displacement from
the film, is enhanced at high pH due to the increased facility of silica dissolution and the concomitant increase in attendant
inter‐particle repulsion.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
14.
The friction behavior of two different materials, mica and ultra-high molecular weight polyethylene (UHMWPE), was evaluated
at the nanoscale with an atomic force microscope and with a custom-built ball-on-flat microtribometer at the microscale. The
same counterface (Si3N4 probe), environmental conditions (25 °C, RH < 10%), and similar load ranges were maintained for all experiments. The friction-force
data obtained were analyzed for contact-area dependence. Friction force between silicon nitride and mica at the nanoscale
showed initial non-linearity with normal load up to a certain load, beyond which surface damage was observed resulting in
a linear dependence of friction force on normal load. At the microscale, the friction force of the mica–silicon nitride interface
exhibited linear dependence on normal load. Friction force between silicon nitride and UHMWPE exhibited non-linearity with
normal load at both the length scales, for the applied load ranges of our experiment. An appropriate contact mechanics theory
was applied to calculate an interfacial shear strength value for the material pair at both the scales. The values at both
the scales were similar, when the conditions were carefully maintained to be the same across scales. 相似文献
15.
基于DMT接触模型,在理论上计算金刚石表面纳米摩擦的摩擦力和摩擦因数;采用原子力显微镜,以金刚石探针和片状金刚石试件作为摩擦副,在大气环境下分别研究机械抛光和聚焦离子束(FIB)刻蚀的金刚石试件的摩擦学特性,并比较实验结果和DMT接触模型计算结果。结果表明:金刚石试件的摩擦因数均随着载荷的增加而减小,这与以往对金刚石微观摩擦的研究结果相符合;DMT接触模型计算结果与机械抛光表面试验结果吻合较好,而略高于FIB刻蚀表面试验结果,验证了DMT模型在金刚石纳米摩擦研究中的适用性。通过表面粗糙度和碳原子化学状态分析,得出粗糙表面对探针滑动的阻碍作用和FIB刻蚀过程中生产的非晶碳的减摩作用是DMT模型应用于上述2种加工表面产生差异的原因。 相似文献
16.
The progression of local cartilage surface damage toward early stage osteoarthritis (OA) likely depends on the severity of
the damage and its impact on the local lubrication and stress distribution in the surrounding tissue. It is difficult to study
the local responses using traditional methods; in situ microtribological methods are being pursued here as a means to elucidate
the mechanical aspects of OA progression. While decades of research have been dedicated to the macrotribological properties
of articular cartilage, the microscale response is unclear. An experimental study of healthy cartilage microtribology was
undertaken to assess the physiological relevance of a microscale friction probe. Normal forces were on the order of 50 mN.
Sliding speed varied from 0 to 5 mm/s, and two probes radii, 0.8 and 3.2 mm, were used in the study. In situ measurements
of the indentation depth into the cartilage enabled calculations of contact area, effective elastic modulus, elastic and fluid
normal force contributions, and the interfacial friction coefficient. This work resulted in the following findings: (1) at
high sliding speed (V = 1–5 mm/s), the friction coefficient was low (μ = 0.025) and insensitive to probe radius (0.8–3.2 mm) despite the fourfold
difference in the resulting contact areas; (2) the contact area was a strong function of the probe radius and sliding speed;
(3) the friction coefficient was proportional to contact area when sliding speed varied from 0.05 to 5 mm/s; (4) the fluid
load support was greater than 85% for all sliding conditions (0% fluid support when V = 0) and was insensitive to both probe radius and sliding speed. The findings were consistent with the adhesive theory of
friction; as speed increased, increased effective hardness reduced the area of solid–solid contact which subsequently reduced
the friction force. Where the severity of the sliding conditions dominates the wear and degradation of typical engineering
tribomaterials, the results suggest that joint motion is actually beneficial for maintaining low matrix stresses, low contact
areas, and effective lubrication for the fluid-saturated porous cartilage tissue. Further, the results demonstrated effective
pressurization and lubrication beneath single asperity microscale contacts. With carefully designed experimental conditions,
local friction probes can facilitate more fundamental studies of cartilage lubrication, friction and wear, and potentially
add important insights into the mechanical mechanisms of OA. 相似文献
17.
Nanofriction Mechanisms Derived from the Dependence of Friction on Load and Sliding Velocity from Air to UHV on Hydrophilic Silicon 总被引:1,自引:0,他引:1
This paper examines friction as a function of the sliding velocity and applied normal load from air to UHV in a scanning force
microscope (SFM) experiment in which a sharp silicon tip slides against a flat Si(100) sample. Under ambient conditions, both
surfaces are covered by a native oxide, which is hydrophilic. During pump-down in the vacuum chamber housing the SFM, the
behavior of friction as a function of the applied normal load and the sliding velocity undergoes a change. By analyzing these
changes it is possible to identify three distinct friction regimes with corresponding contact properties: (a) friction dominated
by the additional normal forces induced by capillarity due to the presence of thick water films, (b) higher drag force from
ordering effects present in thin water layers and (c) low friction due to direct solid–solid contact for the sample with the
counterbody. Depending on environmental conditions and the applied normal load, all three mechanisms may be present at one
time. Their individual contributions can be identified by investigating the dependence of friction on the applied normal load
as well as on the sliding velocity in different pressure regimes, thus providing information about nanoscale friction mechanisms. 相似文献
18.
Friction force measurements were performed on 2-hydroxy stearic acid (2-HSA) and 12-hydroxy stearic acid (12-HSA) coated silica
surfaces in air using an atomic force microscope. The 2-HSA displayed viscoelastic behaviour with a yield point as the static–dynamic
friction transition. Steady sliding motion was replaced by microscopic stick–slip at lower velocities and higher loads. Stick–slip
motion was successfully described and fitted to a phenomenological model ascribed to interfacial material melting and freezing
in periodic cycles. The stick–slip periodicity is of the same order as the contact diameter. The 12-HSA did not experience
a yield point and exhibited steady sliding over the entire load and velocity regime. We attribute these observations to the
difference in molecular configuration, shear strength and adsorption density of the stearic acid layers.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Ruths Marina Ohtani Hiroko Greenfield Michael L. Granick Steve 《Tribology Letters》1999,6(3-4):207-214
Dilute solutions of two polar end‐functionalized linear alkanes (1‐hexadecylamine and palmitic acid), each dissolved in tetradecane,
were confined between two mica surfaces and investigated using a surface forces apparatus modified to study shear nanorheology.
These two solutions showed similar nanorheological properties that differed from those observed for pure n‐alkanes. In static measurements, a “hard wall”, rather than an oscillatory force, was observed as a function of film thickness.
The polar alkane component formed a weakly adsorbed single layer at each mica surface, disrupting the layered structures found
in neat n‐tetradecane. In dynamic experiments at low shear amplitude, the storage modulus G' exceeded the loss modulus G" at low frequencies;
above some characteristic frequencies G' increased such that g' ≈ G", indicating significantly more energy loss through viscous
modes at higher frequency. When the amplitude was varied at fixed frequency, no stick–slip was observed and the limiting value
of the shear stress at high effective shear rate was an order of magnitude less than for unfunctionalized n‐alkanes at similar loads. Together, these results show that the addition of a small amount of polar alkane component, by
disrupting the layered structures that would have been formed in the neat n‐alkane, is effective in suppressing static friction and reducing kinetic friction in the boundary lubrication regime.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated
with the film structure. The film consists of a monolayer of the red form of N‐(2‐ethanol)‐10,12‐pentacosadiynamide, prepared
on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy,
the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and
below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbones. We propose that
this effect is due to anisotropic film stiffness, which is a result of anisotropic side chain packing and/or anisotropic stiffness
of the backbone itself. Friction anisotropy is therefore a sensitive, optically‐independent indicator of polymer backbone
direction and monolayer structural properties.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献