Initial Wear Stage Research Articles

Wear of diamond wheels in creep-feed grinding of ceramic materials II. Effects on process responses and strength

Alumina specimens were ground with a resin bonded diamond wheel using three different work speeds in creep-feed up-cut mode. For each work speed, the wheel surfaces and the process responses were evaluated at five different wear states, which were generated by grinding 0, 29.6, 59.2, 88.8, and 118.4 cm 3 volume of a selected silicon nitride material. The mechanisms of wheel wear have been studied and reported in Part I (Wear 211 (1997) 94–103). This paper investigates the effects of wheel wear on process responses and ground ceramic quality, particularly the flexural strength. Strong relationships between the wheel surface conditions and the process responses are found. During the initial stage of wheel wear (from the as-dressed state to the first 29.6 cm 3 volume of material removal), the surface density of diamond grits, surface roughness and flexural strength decreased, and the specific normal force, specific tangenitial force, force ratio, and specific energy increased. The largest change in most of process responses, except the roughness, occurs at the lowest work speed. Right after grinding 29.6 cm 3 volume of sillicon nitride material, process responses stayed approximately the same with some degree of expected fluctuation due to the competing influence of attritious wear and the wheel's self-sharpening effect. The effect of wheel wear on the flexural strength of ground alumina specimens is found to be dominated by the effect of work speed.

Nanotribology: an UHV-SFM study on thin films of C 60 and AgBr

We performed scanning force microscopy (SFM) in ultrahigh vacuum (UHV) on C 60 and AgBr thin films deposited on NaCl(001) substrates. The morphology of the initial growth stage and the nanotribological properties of these thin films are characterized and discussed. A novel experimental approach is presented where local friction coefficients are determined: the lateral (frictional) forces are measured as a function of normal load, controlled by an external ramp generator. The local friction coefficient can be extracted by means of the two-dimensional histogram technique. In the low load regime, friction coefficients of 0.15 ± 0.02, 0.33 ± 0.07 and < 0.03 were found between probing SiO x tip and C 60, AgBr and NaCl, respectively. The two-dimensional histogram reveals significant details about the force regime of wear-less friction and the initial stage of wear on these thin films.

Nanotribology: an UHV-SFM study on thin films of AgBr(001)

We performed scanning force microscopy (SFM) in ultrahigh vacuum (UHV) on AgBr thin films which were in situ deposited on NaCl(001) substrates. The morphology of the initial growth stage and the nanotribological properties of these thin films are characterized and discussed. The lateral (frictional) forces are measured as a function of normal load. The local friction coefficients are extracted by means of the two-dimensional histogram technique. In the low load regime, friction coefficients of 0.33 ± 0.07 and <0.03 are found between probing SiO x tip and AgBr and NaCl, respectively. The two-dimensional histogram reveals the transition from the force regime of wearless friction to the initial stage of wear on this thin film system. High-resolution SFM images of AgBr(001) are presented which reveal the atomic-scale periodicity of an unreconstructed AgBr(001) surface. The stick-slip nature of the frictional force is demonstrated.

Friction and wear of Langmuir-Blodgett films observed by friction force microscopy.

Lubrication is documented on a microscopic scale with a friction force microscopy: A reduction in friction is observed for Langmuir-Blodgett film-covered surfaces, compared to the bare substrates. Film defects not detected in the AFM topographic mode are clearly recorded in the friction force mode. With applied forces over 10 nN, the initial stages of wear are observed. Small islands of bilayer height are moved in the entirety, conserving the normal orientation of the aliphatic chains. This collective motion of molecules allows the shear strength of the films to be determined. The observed ability of the molecules to remain in the ordered state illustrates one of the fundamental origins of boundary lubrication.

Monitoring the wear of sintered high-speed-steel tools

This paper presents the results of a detailed investigation into the relationship between the wear of sintered T15 high-speed-steel cutting tools and the associated cutting forces. The equations for the cutting forces are established taking into account the influence of both crater and flank wear. The experimental results show that during the initial stage of wear, crater wear promotes a decrease of the cutting forces. This behaviour of the cutting forces is related to the change of the actual side-rake angle, which depends on the crater depth and width. When the true rake-angle reaches a maximum, the cutting forces tend to stabilize, unless flank wear progresses at a high wear-rate, in which case the cutting forces increase until the failure of the cutting tool. According to the proposed model, the measurement of cutting forces could provide an adequate control variable for monitoring the wear of high-speed-steel tools.

Influence of alloying of iron with niobium and tungsten in ion beam mixing on surface properties

1. The microhardness of the specimens weakly depends upon the material of the film sprayed on iron but is determined by machining of the specimens and the kinetics of accumulation of radiation defects. 2. The intensity of wear of the specimens after ion-beam mixing decreases sharply in comparison with the wear of the original specimens with films sprayed on the surface. The initial stages of wear occur under conditions of wear-free fraction and with a further increase in the path of friction the specimens after ion-beam mixing wear to a lesser degree than the original.

Optimum tool geometry of CBN tool for continuous turning of carburized steel

The optimum geometry of a CBN tool for continuous turning of a carburized steel bar was determined for the angle and width of negative land, the nose radius and the honing radius. Fine turning by a tool with such an optimum geometry could be fully substituted for a grinding process on the basis of tool life and roughness of the finished surface. Tool wear as a controlling factor of tool life was analyzed. Particularly in the initial wear stage, frequent chipping of the cutting edge strongly influenced the life of tools with small negative land angles.

Wear properties of silicon nitride in rolling contact

The wear properties of silicon nitride were examined in dry rolling contact. The wear coefficient of silicon nitride in pure rolling was of the order of 10 −6 at the initial stage of wear and of the order of 10 −8 at the steady stage of wear under hertzian pressures of 1.06, 1.30, 1.50 and 1.83 GPa. The wear coefficient of silicon nitride in rolling-sliding was of the order of 10 −3 under hertzian pressures of 1.06, 1.50 and 1.83 GPa. The original grinding marks were decreased by the initial wear. Then a very smooth surface appeared in the steady state and its centre-line average roughness R a was 0.02 μm. In contrast, pitting and the adhesive accumulation of thin film debris on the surface started to occur in the steady stage of wear. Three typical types of wear debris were distinguished. One of these, which was a glassy film, was confirmed to have an SiO 2 structure.

The unlubricated reciprocating sliding wear of 316 stainless steel in CO 2 at 20–600°C

The friction and wear behaviour of 316 stainless steel in CO 2 has been investigated in the load range 8–50 N from 20 to 600°C. Wear transitions occurred at all temperatures but were load-dependent. At and below 300°C, wear transitions only took place at low loads, whereas above 300°C transitions were observed at all loads. The low temperature wear transition, representing an order of magnitude decrease in wear rate, was associated with a change in friction behaviour. The friction force across the specimen was initially widely fluctuating but after a time, which did not necessarily coincide with the wear transition, became much smoother. The smoother sliding is thought to indicate a trend to oxide-oxide contacts. At higher temperatures wear transitions result in a two orders of magnitude reduction in wear. The corresponding friction transition was similar to the low temperature friction change but also included a marked temporary drop in the coefficient of friction. Pits or troughs up to 450 μm deep were seen in wear scars above 400°C. It is proposed that isolated sections of grooves formed during the initial stages of wear become back-filled with loosely adhering oxide particles. These troughs are then further deepened, possibly by abrasive fretting action of the semi-fluid oxide material.

WEAR CHARACTERISTICS OF SLURRY PUMP PARTS AT SHIELD TUNNELING WORK

Long life and reliability in pumping abrasive slurry are more important than initial cost and efficiency. Here, several wear tests for impeller, reducer and frontliner of unshrouded centrifugal pump were executed at 2 sites of shield tunneling work. The influences of soil and metal including some surface coatings properties on the wear characteristics of pump parts were investigated. As the results, the effects of surface coatings treated on a reducer are displayed remarkably at initial stage of wear. To prevent the eccentric wear at a bottom of reducer or frontliner, it is necessary to increase the flow velocity at the inlet of pump not to occur a state of bed-load slurry movement, or to rotate their setting positions periodically.

Variation in friction coefficient with tool wear

The acceleration component resulting from flank wear alone is isolated from vertical tool vibration signals collected by an accelerometer mounted safely away from the cutting process. The friction force and friction coefficient are computed from this component to show that they decrease at the initial stages of wear, reach a minimum near the critical wear, and increase again. Empirical models are proposed and estimated with the computed values. The importance of these models in predicting the coefficient in the hazardous region of large wear, from data collected in the safe region below critical wear, is delineated. Possible mechanisms for this behavior based on the current theories of friction and wear are discussed.

Transfer of semicrystalline polymers sliding against a smooth steel surface

The interrelationships between transfer and wear in polymers were studied using a pin-disk-type wear testing apparatus. The wear rates of polymers except polytetrafluoroethylene (PTFE) were high for up to about the first 100 revolutions of the disk and decreased gradually until the steady low wear rates which generally occurred after about 2000 revolutions. However, PTFE exhibited an almost constant high wear rate throughout the wear process. The thickness of transferred polymer increased rapidly with increasing number of revolutions in the initial wear stage but after about several hundred revolutions remained constant. A coherent transfer film was formed in most parts of the friction track after about 100 revolutions. It was found that polymer wear could occur in polymers sliding on a transferred polymer layer. All polymers except PTFE exhibited smaller wear rates when sliding on the transferred layer. The load dependence of the thickness was very small compared with that of the wear rate. PTFE produced a very dense and coherent transferred layer compared with that of other polymers. However, there was no clear relationship between friction and the thickness of the transferred polymer layer.

Abrasive wear of tungsten carbide-cobalt composites. I. Wear mechanisms

The anomalies arising from the previous observations of two wear mechanisms during rotary drilling of sandstone with sintered tungsten carbide tools have been resolved by further work on the initial stages of abrasive wear: selective cobalt removal and microfracture of the carbide skeleton are two stages in the overall wear mechanism. In the initial stages of wear, fine abrasive particles preferentially remove cobalt from the surface, thus forming small pits with intergranular facets. This is the rate-controlling step in the wear process. The removal of cobalt appears to lower the fracture strength of the surface layers. Intergranular cracks propagate from the pits, leading to microfracture of the carbide skeleton and a microspalling type of failure of the surface layer. The results indicates the importance of cobalt content and distribution, abrasive debris size and environmental factors in controlling the amount of abrasive wear in rock drilling.

Some observations concerning the friction and wear characteristics of sliding systems involving cast ceramic

A study has been performed to determine if cast ceramic parts can provide desirable wear characteristics in high-speed mechanisms. While economically advanageous for production of small, complicated parts, key factors in utilization of cast ceramics is their friction and wear characteristics when sliding against similar ceramics, hardened steel or other hard surfaces. This study showed that the wear in a steel- ceramic system is primarily governed by the transfer of steel to the ceramic part and that this wear can be quite severe. The ceramic-ceramic mode of wear was found to be predominately surface fatigue. The surface finish of the ceramic affects the wear of the steel in the ceramic-steel system but only in the initial stages of wear whereas the surface finish of the ceramic-ceramic and ceramic-tungsten carbide systems influenced the wear throughout the entire wear test range.

セラミック工具の初期摩耗に及ぼす切れ刃仕上精度の影響

Application of ceramic tools is limited at present, because ceramics are comparatively weak against mechanical and thermal shocks. The wear mechanism of ceramic tools is also different from that metallic tools.In this study, theoretical and experimental investigations on the relation between the roughness of initial cutting edge and that of worn cutting edge with alumina-based ceramic tools have been made.The change of roughness of cutting edge at the initial stage of wear has been analyzed theoreticaly under such assumption that the wear of ceramic tool at the first stage of cutting is caused by cleavage and separation of alumina grains. And the result of the theoretical calculation has been confirmed by the orthogonal cutting tests of a steel.The main findings are as follows : (1) The experimental results on the behaviour of the roughness of cutting edge as the tool wear proceeds coincide qualitatively with those calculated.(2) The roughness of worn tool edge becomes to be almost constant regardless of its initial state of finish, and the final value of roughness seems to be related with the grain size of alumina.

The mechanisms of wear of cast iron in dry sliding

The present study has been made on the mechanisms of wear of cast iron in dry sliding. The results of the study show that under mild wear conditions plastic deformation occurs in the sliding surface. Under heavy wear conditions destruction of the sliding surface by thermal shock takes place. Maintaining the wear condition in such a state that oxidative wear would occur at the initial stage of wear, it has been found that the phenomenon of adhesive wear becomes increasingly evident with increase in the sliding length.

Study on wear of casting aluminium alloys

In the first report, the wear characteristics of aluminium alloys against the same alloys and against carbon steel ware described. In the case of aluminium alloys against carbon steel, the wear loss of each of the materials is vrey small irrespective of the sliding speed and the contact pressure. When aluminium alloys excepting hyper-eutectic aluminium-silicon alloy are combiend against the same alloys, partial welding phenomena (scuffing) can easily occur on the frictional surface as the sliding speed is increased.In this report, frictional characteristics such as the frinctional coefficient, the surface appearance and the surface roughness. The results obtained from this experiment are summerized as under:1. It has been thought that there are not always definite relationships between the frictional coefficient and the wear. However, in this experiment it is made clear that there exist intimate corelations between the two. In the case of aluminium alloys against the same alloys, the frictional coefficient increases along with the increasing of wear loss, especially where scuffing occurs, the frictional coefficient as well as the wear loss show a rapid increase. However, in the case of hyper-eutectic aluminium-silicon alloys against the same alloys and of aluminium alloys against carbon steel, the frictional coefficient decreases in conformity with the deminution of wear loss as the sliding speed is increased.2. In the case of aluminium alloys excepting hyper-eutectic aluminium-silicon alloy against the same alloys, scuffing can easily occur under a high sliding speed and at high contact pressure, and surface roughness in creases. The hyper-eutectic aluminium alloys sach withhard spots coming about on the frictional surface thereon, does not generate scuffing, for the hard spots on the either alloy come into touch with each other. While in the case of aluminium alloys against carbon steel, not only the wear losse but also the frictional coefficient are very small since the frictional surface is protected by an oxidized layer.3. Though unstable at the initial stage of wear, the surface roughness may get to the constant value when wear reaches astationary stage, and the value may be controlled according to the experiment conditions.