690合金材料的微动磨损特性研究

利用微动磨损试验机,在载荷50N以及位移幅值为60μm、100μm、150μm的工况下,研究了690合金材料在常温下的微动磨损行为及其动力学特性,采用激光共焦扫描显微镜(LCSM)和扫描电子显微镜(SEM)观察磨痕微观形貌。结果表明,载荷和位移幅值对微动特征有很大的影响,微动运行完全处于滑移状态。在滑移区,滑移磨损严重、磨痕面积大。690合金材料的磨损机制主要表现为磨粒磨损与剥层的共同作用。     

Friction and wear of Inconel 690 for steam generator tube in elevated temperature water under fretting condition

Recently, material of Inconel 690TT (thermal treatment) for the steam generator tubes in a nuclear power plant was substituted for the existing material of Inconel 600HTMA (high temperature mill-annealing). Inconel 690TT has more chromium than Inconel 600HTMA in order to improve the corrosion resistance. In this study, to evaluate the friction and wear characteristics of Inconel 690TT under fretting condition, the fretting tests as well as sliding tests were carried out in air and in elevated temperature water environment, respectively. Fretting tests of the cross-cylinder type were done under various applied normal loads, and sliding tests of pin-on-disk type were also carried out to compare with the results of the fretting test. In summary, the results of the fretting tests correlated with the results of the sliding tests. The wear mechanism of Inconel 690TT in air was delamination wear and the mechanism in water was affected by micro-pitting. Also, it was found that the fretting wear coefficients in water were increased with increase in the temperature of water.     

Experimental Study of the Fretting Wear Behavior of Incoloy 800 Alloy at High Temperature

The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.     

Fretting Wear Behavior and Mechanism of Inconel 690 Alloy Related to the Displacement Amplitude

Fretting wear tests on Inconel 690 alloy were carried out at different displacement amplitudes. The results indicated that with an increase in displacement amplitude, the ratio of tangential force to normal load and wear volume increased. The fretting mode gradually transformed from mostly stick, mixed stick–slip, to full sliding, showing the competition of fretting-induced fatigue cracking and fretting-induced wear. There was a gradient plastic strain created by fretting, which resulted in the formation of a nanocrystalline tribologically transformed structure (TTS) and plastic deformation layers. The plastic strain in the plastic deformation layer gradually increased with an increase in displacement amplitude.     

Experimental investigation on sliding and fretting wear of steam generator tube materials

In nuclear power steam generators, high flow rates can induce vibration of the tubes resulting in fretting wear damage due to contacts between the tubes and their supports. In this paper, the sliding and fretting wear tests were performed using Inconel 600HTMA and 690TT against STS 304, which are the steam generator tube materials. The sliding wear tests with a pin-on-disk type tribometer were carried out under various applied loads and sliding speeds at air environment. The fretting wear tests were carried out under various vibrating amplitudes and applied normal loads.

The result of sliding and fretting wear tests show that the heat-treated Inconel 690TT has better wear resistance than Inconel 600HTMA in air. The fretting wear regimes were plotted using the test results and the wear coefficient was calculated also. From the results, it was observed that the wear and tear by stick-slip has very strong effect on the fretting wear behavior.     

Effect of grain size and hardness on fretting wear behavior of Inconel 600 alloys

The effects of grain size and bulk hardness on fretting wear behaviors were investigated by solution annealing and subsequently fretting wear test in Inconel 600 alloys. The results indicated that, with increase of solution temperature, the grain size increased while the hardness decreased. The average friction coefficients were the almost same, independent of grain size and hardness; while the wear volume decreased with increase of grain size, but the hardness played little role. The smaller grain was conductive to formation of tribological transformed structure (TTS) layer, and produced shorter delamiantion cracks in the TTS layer than larger one.     

Effect of Cold Rolling on the Fretting Wear Behavior and Mechanism in Inconel 690 Alloy

The influence of cold rolling on the fretting wear behavior and mechanism of Inconel 690 alloy at 320?°C in air was studied. The wear volume and worn surface were obtained and analyzed using laser scanning confocal microscopy, electron back-scattering diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The grinding surface and strain distribution were also studied by electron back-scattering diffraction to analyze the mechanism of fretting damage. The results indicated that with an increase in cold rolling reduction, the microhardness was increased. However, the friction coefficient and wear volume first increased and then decreased. The characteristics of fretting areas changed from a gross slip regime to a partial slip regime. Accordingly, the damage mechanism in the gross slip regime was a combination of oxidative wear, abrasive wear, and delamination, whereas the damage mechanism in the partial slip regime was mainly adhesive wear.     

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component (such as carbon, nitrogen, sulphur and oxygen, etc) thermo-chemical treatment(LTGMTT) can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 (0.48%C) steel prepared by low temperature gas multi-component thermo-chemical treatment (LTGMTT) technology. The fretting wear tests of the modified layer flat specimens and its substrate (LZ50 steel) against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope(SEM), optical microscope(OM), X-ray diffraction(XRD) and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime(MFR) of the LTGMTT modified layer diminished, and the slip regime(SR) of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction(COF) of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime(PSR) was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.     

A study on wear coefficients and mechanisms of steam generator tube materials

Reciprocating sliding wear tests were performed to evaluate wear properties of Inconel 600MA and 690TT steam generator (SG) tube materials against 405 and 409 ferritic stainless steels. With increasing normal loads and sliding amplitudes, the wear rate of tube materials increased but a wear transition occurred only in Inconel 690TT. Subsurface deformation strengthening seemed to be an important factor that determines the wear resistance of tube materials. After the wear test, the worn surfaces were observed to investigate the wear mechanism of tube materials using SEM. The results indicated that there are different mechanisms of wear particle removal between the tube materials. The differences are related to the degree of work hardening due to the differences in chromium content in the tube materials. Based on the present results, wear coefficient values for the life estimation of SG tubes were calculated according to the work-rate model at each test condition. The wear rate is lower for Inconel 690TT compared to that for Inconel 600MA. Finally, parameters that should be considered for evaluation of wear coefficients were discussed.     

TiAlZr合金微动磨损性能研究

采用高精度液压式微动磨损试验机研究了TiA lZr合金在不同微动运行区域的微动磨损行为,建立了其运行工况微动图。试验结果表明:滑移区、混合区和部分滑移区的摩擦因数随循环次数变化呈现不同的规律,其中部分滑移区摩擦因数较低,磨损体积随着位移幅值的增大而增大;滑移区、混合区磨损体积随着法向载荷的增加而增大,而部分滑移区磨损体积随着法向载荷的增加而减小;滑移区磨屑堆积于中心区域,磨损以磨粒磨损和剥层机制为主;混合区磨损机制主要表现为粘着磨损与磨粒磨损并存;部分滑移区磨损轻微。     

Effect of Cold Rolling on the Fretting Wear Behavior and Mechanism in Inconel 600 Alloy

The fretting test was carried out using an SRV IV fretting test rig in order to investigate the fretting wear behavior and mechanism in Inconel 600 alloy at room temperature. The materials were rolled to different reductions before the test. The effect of cold rolling on the friction coefficient and wear volume was subsequently investigated. The surface and cross-sectional morphologies of the wear scar were studied by scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and electron back-scattering diffraction (EBSD). The results indicated that the cold rolling had a different effect on wear behavior in different slip regimes. In the stick regime, cold rolling strongly decreased the wear volume, although it did not affect the friction coefficient. The 25% rolled specimen had the minimum wear volume. The mechanisms of as-received and 50% rolled specimens were delamination and oxidation wear, whereas for the 25% rolled specimen, cracking was the main wear mechanism. In the gross slip regime, cold rolling had little effect on the friction coefficient or wear volume. The fretting wear process gave rise to a decrease in the Σ3 grain boundary, an increase in local misorientation, and a change in the crystal orientation.     

Modeling transient adhesive wear of tungsten carbide inserts tested with an angular setting

The standard transient adhesive wear equation had been used for modeling pins tested with a full contact with a counter disc. The wear volume against distance curve (wear curve) obtained from such a test can be divided into two regimes: the curvilinear transient regime and the linear steady-state wear regime. The slope of the wear curve at the beginning is a lot higher, and it gradually decreases with sliding distance towards the steady-state wear regime. On the other hand, for inserts tested with an angular setting, generally, the wear curve is in the form of a straight line with a constant slope. This is due to the limited volume of asperities available for wear initially, but as wear progresses, the volume of asperities available will also increase. Generally, the volume loss of inserts with an initial angular setting with the counter disc is lower, as compared with those obtained with a full contact setting. The wear volume also increases with load, speed and temperature. As the wearing conditions for both cases are different, a new exponential transient adhesive wear equation has, therefore, been developed to model the transient wear volumes of tungsten carbide inserts tested with an angular setting. Excellent results with an average correlation coefficient of 0.9964 and an average deviation of about 10% are obtained. Inferior results are obtained when the standard transient adhesive wear equation is used for modeling the inserts with an angular setting, as the assumption made in its derivation is no longer applicable. The modeling results obtained from using both equations, as well as some evidence obtained from SEM and optical examinations of the worn inserts and wear tracks will be discussed in details in this paper. The experimental wear data used to support this modeling work are obtained earlier from a high temperature wear testing rig, in which Sandvik tungsten carbide inserts are tested with an angular setting with a hot work tool steel counter disc. The experimental parameters used are: (i) Applied loads of 40 and 50 kgf, (ii) speeds of 100 and 130 m/min, (iii) temperatures of 25, 200, 400 and 600 °C, and (iv) distances from 1000 m to 16,000 m.     

Friction and wear behaviour of sintered steels submitted to sliding and abrasion tests

Fe–C–Mo and Fe–C–Cr steels were sintered by PM processes carried out using different values of temperature and pressure, leading to different microstructures and density values. Flat specimens were submitted to tribological tests in order to evaluate their behaviour under both dry sliding and abrasive wear conditions. A flat-on-cylinder tribometer was used for the sliding tests, while a micro-scale ball cratering device was used for the abrasion tests. The dry sliding wear resistance of the PM steels was mainly influenced by the composition and sintering conditions. In this regard, the best behavior was observed for the more hardenable Fe–C–Mo steels with higher Mo content, sintered under conditions giving rise to bainitic microstructures. A determining role was also played by the porosity content and pore shape: reduction in porosity (obtained by increasing the sintering temperature and the compacting pressure), as well as an increase in pore roundness, led to a significant improvement in the resistance to sliding wear. A mild oxidative wear regime were observed for all the sintered steels under relatively low values of the applied load, while an increase of the applied load led to a delamination wear regime. The resistance to abrasive wear was low for all the tested steels, irrespective of composition and sintering cycle.     

Fretting wear behaviors of steel wires under friction-increasing grease conditions

Fretting wear tests were performed on the self-made fretting wear rig to investigate fretting wear behaviors of steel wires under friction-increasing grease conditions. The results demonstrated that the fretting regimes were dependent on displacement amplitudes and normal loads. The friction coefficient exhibited different variation trends in different fretting regimes. Friction-increasing grease changed the fretting running behavior and had a very good wear resistance for steel wires. Wear was slight in partial slip regime. Mixed regime was characterized by plastic deformation, fatigue cracks and abrasive wear. Slip regime presented main damage mechanisms of abrasive wear, fatigue wear and oxidation.     

The Effects of Sodium Chloride Solution on Fretting Wear Behavior of Nickel Based Alloy in Partial Slip Regime

The investigations on fretting wear behaviors of nickel based alloy in NaCl solution and atmosphere indicated that wear mechanism and regional transformation from partial slip regime (PSR) to the mixed regime (MR) are significantly affected by NaCl solution. The crevice corrosion induced by synergy of chloride ion and deformed asperities caused wear mechanism changed from adhesive and oxidation wear (PSR in atmosphere) to abrasive and oxidation wear (PSR in NaCl solution) and to oxidation and delamination wear (MR in NaCl solution), meanwhile accelerated the regional transformation from PSR to MR. However, the annular fatigue crack was almost unaffected by NaCl solution, which propagated along the direction of 40-50^° to surface in the mode of transgranular and intergranular in all conditions.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Fretting Wear Behavior of UHMWPE—Influence of Load and Stroke

In this study, the tribological behavior of ultra-high-molecular-weight polyethylene (UHMWPE) against a GCr 15 steel ball during fretting wear conditions was investigated using an oscillating reciprocating tribometer. The aim of this study was to characterize the critical value of normal load and stroke corresponding to this transition in UHMWPE worn surface at room temperature. Results showed that there existed a critical value of load or stroke at fixed condition. The friction coefficient and wear volume loss of UHMWPE at or near the critical values of load and stroke exhibited extreme changes. Based on observation of the worn surface by scanning electron microscopy (SEM) and 3D surface profiler measurements, it can be found that damage to the worn surface can be linked to the contact load and stroke. In addition, results showed that during the process of fretting wear under different load or stroke conditions, the gross slip regime dominated throughout the whole test period.     

钛合金球与骨水泥界面之间的微动磨损机制研究

采用钛合金球与自制骨水泥试样以球/平面接触方式,在自制的微动摩擦磨损试验机上开展干摩擦和25%小牛血清介质中切向微动磨损试验研究,考察钛合金球与骨水泥界面之间的微动运行特性,并采用S-3000N型扫描电镜观察磨痕形貌来分析其微动磨损机制。结果表明:随着微动振幅的增加,微动运行由部分滑移区向混合区转变。随着接触载荷的增加,试样接触面之间更容易发生黏着。与干摩擦相比,在小牛血清溶液中部分滑移区向较大振幅区扩展。部分滑移区摩擦因数值较低且保持稳定,混合区的摩擦因数先增大后保持不变。稳定摩擦因数随着接触载荷的增加而减小,随微动振幅增大而增大。骨水泥试样的磨损量在小牛血清介质中比在空气中大,并且随接触载荷增大而增大。骨水泥在小牛血清介质中微动磨损的损伤机制主要为黏着磨损和疲劳磨损,溶液分子在应力作用下对骨水泥基体有削弱作用。     

On the wear characteristics of cobalt-based hardfacing layer after thermal fatigue and oxidation

High temperature wear characteristics of Stellite 6 alloy containing Cr₃C₂ after thermal fatigue and oxidation treatment at 700°C were investigated. The hardfacing layer was deposited by plasma transferred arc (PTA) process. After thermal fatigue treatment, cracks propagated along boundaries of incoherent chromium carbide particles. Significant oxidation occurred mainly on the clad layer containing Cr₃C₂. The wear test results revealed a slightly higher wear volume on Stellite 6 with Cr₃C₂ due to the existence of cracks. The formation of oxide on the surface could effectively reduce the wear volume by reducing the real contact area between mating surfaces. Lower sliding speed resulted in higher wear volume. The mechanism was interpreted by the friction coefficient change during sliding wear. Wear test results were further interpreted by investigating the wear trace via SEM. Possible wear mechanisms were postulated. Analysis of wear debris showed severe oxidation on the Stellite 6 with Cr₃C₂. It could be concluded that oxidation on the clad layer was beneficial to the wear resistance at elevated temperature. Thermal fatigue cracking on the surface might be detrimental to the wear resistance, however, this could be partly compensated by the existence of oxide.     

High temperature fretting wear behavior of WC-25Co coatings prepared by D-gun spraying on Ti-Al-Zr titanium alloy

Detonation gun (D-gun) spraying is one of the most promising spraying techniques for producing wear-resistance coatings. A thick layer (about 0.3 mm thickness) of WC-25Co with high hardness was covered on Ti-Al-Zr titanium alloy by D-gun spraying and the fretting wear behavior of WC-25Co coatings was studied experimentally on a high precision hydraulic fretting wear test rig. An experimental layout was designed to perform fretting wear tests at elevated temperatures from room temperature (25 °C) to 400 °C in ambient air. In the tests, a sphere (Si₃N₄ ceramic ball) was designed to rub against a plane (Ti-Al-Zr titanium alloy with or without WC-25Co coatings). It was found that the fretting running regimes of WC-25Co coatings were obviously different from those of Ti-Al-Zr titanium alloy. The mixed fretting regime disappeared in WC-25Co coatings, and the boundaries in the running condition fretting map (RCFM) showed hardly any change as temperature increased. The worn scars were examined using a laser confocal scanning microscope (LCSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the coefficients of friction (COF) of WC-25Co coatings at elevated temperatures were nearly constant in the partial slip regime and very low in the steady state. The fretting damage of the coatings was very slight. In the slip regime, the WC-25Co coatings exhibited a good wear resistance, and the wear volume of the coatings obviously decreased with increasing tested temperature. The fretting wear mechanisms of WC-25Co coatings were delamination, abrasive wear and oxidation wear at elevated temperature. The oxide debris layer formed at higher temperature was denser and thicker on top of WC-25Co coatings, thus providing more surface protection against fretting wear, which played an important role in the low fretting wear of the coatings.