Tribological Behavior of Boronized Fe40Mn20Cr20Ni20 High-Entropy Alloys

The tribological behavior of hot-rolled and boronized Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) sliding against a Si3N4 ball was investigated in the air, deionized water and seawater. The results showed that the hot-rolled Fe40Mn20Cr20Ni20 HEA was composed of an FCC (face-centered cubic) phase. In addition, the boronized HEA was composed of a great number of borides, including CrB, FeB, MnB, Fe2B, Fe3B and MnB2. The hardness increased from 139 HV to 970 HV after boronizing. In air, the wear rate decreased from 4.51 × 10−4 mm3/Nm to 0.72 × 10−4 mm3/Nm after boronizing. The wear mechanism transformed from abrasive wear and oxidative wear to the polishing effect. After boronizing, in the deionized water, the wear rate decreased from 1.27 × 10−4 mm3/Nm to 8.43 × 10−5 mm3/Nm. The wear mechanism transformed from abrasive wear and delamination wear to delamination wear. In the seawater, the wear rate decreased by about ten times that of hot-rolled alloy.

Effects of inert gas environment on the sliding wear behavior of AZ91/B4C surface composites

Tribological characteristics of AZ91/B4C surface composites were studied under air and argon gas environments. Tests were conducted under a constant normal load of 10 N, with a sliding velocity of 0.06 m/s using a linear reciprocating tribometer. Wear tracks and debris were analyzed using scanning electron microscopy, three-dimensional contour topography, and energy-dispersive X-ray spectroscopy in order to understand the wear mechanisms. The wear rate of the specimen tested under the argon environment was found to be lower (∼60%) in comparison with that of the specimen tested under the open-air environment. The value of the friction coefficient was found to be minimum under the argon environment compared with the air environment. In the air environment, the major material loss from the test specimen was attributed to oxidation wear; whereas under the argon environment, strain-hardening effect was dominant, and the material was found to be removed by delamination wear. In addition, the worn surface morphology of the wear tracks and counter surfaces showed the involvement of abrasion and adhesion wear mechanisms. The results of the study pave the pathway for the design of lightweight surface composite material systems such as AZ91/B4C toward an efficient and robust tribo-pair applicability for a controlled environment.

The Wear of Seal Fins during High-Speed Rub between Labyrinth Seal Fins and Honeycomb Stators at Different Incursion Rates

Labyrinth seals as a noncontact sealing technology are widely used in aero-engine. To improve the efficiency of the aero-engine, the clearance between the rotor and stator must be as small as possible. However, the change of the clearance between the rotor and stator because of thermal expansion, vibration, mechanical loading may lead to undesirable high-speed rub, which will lead to the cracking of the seal fins. This paper focuses on the wear of the seal fin after the rub and presents the rubbing tests between seal fins and the metal honeycomb under rubbing speed of 380 m/s and incursion rates between 20 and 180 μm/s, with an incursion depth of 1500 μm and a temperature of 350 °C. The rubbing force and temperature were recorded, and the seal fins were checked by SEM and EDS. The results show that the wear mechanism of seal fins changed from oxidation wear and adhesive wear to delamination wear and then to metal wear with the increasing incursion rate. The axial cracks appeared on the worn surface of the seal fins due to the cracking of tribo-layers under periodic thermomechanical stress. The wear mechanism of the seal fin also has a great influence on the rubbing force and temperature.

Effect of Variation of SiC Reinforcement on Wear Behaviour of AZ91 Alloy Composites

In this investigation, the extensive wear behaviour of materials was studied using SiC reinforced magnesium alloy composites fabricated through the stir casting process. The wear properties of AZ91 alloy composites with a small variation (i.e., 3%, 6%, 9% and 12%) of SiC particulates were evaluated by varying the normal load with sliding velocity and sliding distance. The worn surfaces were examined by scanning electron microscope to predict the different wear mechanisms on the pin while sliding on the hard disk in the dry sliding wear test condition. The microhardness of the SiC reinforced AZ91 composites was found to be more than the un-reinforced AZ91 alloy. Pins tested at load 19.62 N, and 2.6 m/s exhibited a series of short cracks nearly perpendicular to the sliding direction. At higher speed and load, the oxidation and delamination were observed to be fully converted into adhesion wear. Abrasion, oxidation, and delamination wear mechanisms were generally dominant in lower sliding velocity and lower load region, while adhesion and thermal softening/melting were dominant in higher sliding velocity and loads. The wear rate and coefficient of friction of the SiC reinforced composites were lower than that of the unreinforced alloy. This is due to the fact of higher hardness exhibited by the composites. The wear behaviour at the velocity of 1.39 m/s was dominated by oxidation and delamination wear, whereas at the velocity of 2.6 m/s the wear behaviour was dominated by abrasion and adhesion wear. It was also found that the plastic deformation and smearing occurred at higher load and sliding velocity.

Investigation of Two-Dimensional Ultrasonic Surface Burnishing Process on 7075-T6 Aluminum

A novel two-dimensional ultrasonic surface burnishing process (2D-USBP) is proposed. 7075-T6 aluminum samples are processed by a custom-designed 2D-USBP setup. Parameter optimization of 2D-USBP is conducted to determine the best processing strategy of 7075-T6 aluminum. A uniform design method is utilized to optimize the 2D-USBP process. U13(133) and U7(72) tables are established to conduct parameter optimization. Burnishing depth, spindle speed, and feed rate are taken as the control parameters. The surface roughness and Vickers hardness are taken as the evaluation indicators. It establishes the active control models for surface quality. Dry wear tests are conducted to compare the wear-resistance of the 2D-USBP treated sample and the original sample. Results show that the machining quality of 2D-USBP is best under 0.24 mm burnishing depth, 5000 r/min spindle speed, and 25 mm/min feed rate. The surface roughness Sa of the sample is reduced from 2517.758 to 50.878 nm, and the hardness of the sample surface is improved from 167 to 252 HV. Under the lower load, the wear mechanism of the 2D-USBP treated sample is mainly abrasive wear accompanied by delamination wear, while the wear mechanism of the original sample is mainly delamination wear. Under the higher load, the accumulation of frictional heat on the sample surface transforms the wear mechanisms of the original and the 2D-USBP treated samples into thermal wear.

Friction and wear performance of a copper-based bond emery wheel for rail grinding

In this paper, a copper-based bond emery wheel was prepared by vacuum hot pressing sintering through powder metallurgy. The effects of various bond contents on the grinding performance of the copperbased bond grinding wheel were studied using a self-made experimental device; the friction coefficients between the friction pairs and roughness of the grinded rail surface were also obtained. The results show that the grinding wheel had the best grinding performance when the content of the copper-based bond was at 35 wt.-%, the friction coefficient 0.29, the grinding ratio 81.34, and the surface roughness 7.191 μm, which meet the roughness requirements of rail grinding. The microstructure of the rail surface and debris after grinding were studied by scanning electron microscope and energy spectrum analysis. Adhesive wear, abrasive wear, oxidation wear and delamination wear occurred during the friction and wear process. The grinding behavior of grinding wheels was analyzed in accordance with the experimental results.

Experimental study on triblogical behaviors of PA6 and PTFE polymers in the case of rolling friction

Rolling/sliding contacts, such as rolling-element bearings or gears, are a keystone of many machines, which could not properly operate in absence of these components. Machine elements of this kind are typically made of certain variants of steel, whereby hardening processes are carried out in order to increase lifetime and reduce wear. Furthermore, proper lubrication of these tribo-systems is inevitable in order to guarantee a safe operation throughout the component’s lifetime. In recent years high performance polymers, such as Polyether ether ketone (PEEK) or polyamid 46 (PA46), have become an option for application in rolling/sliding contacts. Due to the low density and effective manufacturing processes, such as injection moulding, polymers enable lightweight design solutions under relatively low cost. A comparative investigation based on tribological properties including the friction and wear behaviour of two polymers (Polyamide 6, Polytetrafluoroethylene) was researched in this study. Where samples were prepared by machining for precast cylinders of these materials, and experiments were carried out using a device designed for this purpose, with two parameters (rolling speeds and loads) in select. The morphology of the polymeric transfer film which plays a lubricating role in the dry operation conditions was observed for both materials. The obtained results showed that the friction feature of PTFE was better than that of PA 6 which released high sounds during testing duo to adhesion bonds with metallic counterface. The main wear mechanism of polyamide was micro mechanical machining and deformation, while was adhesive wear for PTFE, and the wear rate of PTFE was very high compared to PA 6 which suffered from delamination wear in some cases