Key Engineering Materials Vol. 642

Abstract: Large amount of unsaturated and polar component of oils enhance the lubrication of ferrous materials. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetal oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC sliding against 440C stainless steel ball. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases in both coatings but the wear rate increases in the a-C:H and decreases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. The degree of graphitization increases with increasing temperature. Graphitization occurs in the tribological contact because of friction-induced heating under contact and high contact stress conditions.

Abstract: In this study, the multi-pass friction stir processing (MP-FSP) technique was performed on ADC6 aluminum alloy + 5 wt% fly ash composite (A5FC) castings to increase their surface area. The dry sliding wear behaviors of the ADC6 alloy, A5FCs, and MP-FSPed A5FCs were evaluated. Dry sliding wear tests were performed using a ring-on-washer machine at a constant rotation speed of 100 rpm for 60 min, and the normal load was 10, 20, 30, and 40 N. The results showed that the MP-FSPed A5FCs had the lowest wear rates in the load range from 10 to 40 N, and adhesive wear was the major wear mechanism in these tests. The increased wear resistance was mainly due to grain refinement and elimination of casting defects after subjecting the ash composite to MP-FSP. The microstructure of the MP-FSPed A5FCs reveals that the sizes of the added raw fly ash particles decreased from micro-to nanoscale levels, and the nanoscale fly ash was uniformly dispersed in the aluminum matrix.

Abstract: The elastic-plastic finite element and atomistic models for the frictionless contact of a deformable sphere pressed by a rigid flat is presented. The evolution of the elastic-plastic contact with increasing interference is analyzed using two different analysis tools. The simulation results show that deformation mechanisms revealed in the two different analysis tools are quite different from each other. The physical phenomena “jump-to-contact” and “force drops during dislocation emission” are observed in our atomistic simulations which can not be seen in the continuum analysis.

Abstract: Surface texturing has been shown to reduce friction and increase the film thickness in various tribological applications (hydrodynamic bearings, mechanical seals, and cylinder-liner contacts). Studies have reported that surface-texture can reduce the resistance of sliding friction pair, increase the oil film thickness, increase the bearing’s capacity. Surface texture structure’s design and layout are very important, unfavorable design may lead to be counterproductive. In this paper, in combination with the 650mm seal structure, we are using the main design of groove type to seal the inner surface texture, so as to study the geometry structure and distribution's influence on seal property.

Abstract: The poor quality of machining surfaces caused by the surface wear of the pressing dies and the corrosion of the pressing parts has been a major concern for manufacturing engineers. In order to decrease the surface wear of the pressing dies and the corrosion of the pressing parts, the drawing oil is always used during the pressing process. It is well known that the properties and the distributions of the drawing oil significantly influence lubrication, cool down, cleanness and stabilization for the pressing dies and parts. Therefore, it is very important for the operating limitation of the pressing process. This paper is base on the above statements to further investigate the effects of the high viscosity drawing oil on the tribological properties and the adhesions between the dies and parts. The results have not only an added advantage of technology of pressing process, but they are also very helpful in design the pair of the dies and parts in the future. Moreover, the purpose of better quality and faster product speed of the pressing process can then be obtained for the industry.

Abstract: Not only fatigue of the metal materials but also inferior quality of the lubricant oils will be occurred for the machines after the long-term operation. Therefore, the self-developed reciprocating friction tester with the measurement system was used to experimental study the tribological properties for the automobile oil regeneration in this study. The major parameters are the reciprocating speeds and the three types of the oil. The ball specimens were made of SUJ2 and the plate specimens were made of SUS304. The variations of friction coefficient and electrical contact resistance were simultaneously recorded during dynamic friction process. After each friction test, the OM was used to observe the worn surface. According to the experimental results, the differences between the new oil, the old oil and the regeneration oil can be clarified. The viscosity, density and color were quite similar for the old oil and the regeneration oil. However, the tribological properties of the regeneration oil were significantly improved. Moreover, it also showed stable during the dynamic friction tests. Even compared with the new oil, the regeneration oil sometimes showed better lubrication under the operation conditions. The wear resistance of the regeneration oil does show great potentials.

Abstract: A series of a-C:H:Zr-x coatings (the x in the term a-C:H:Zr-x is the Zr target current varied in the deposition process) have been deposited on AISI M2 steel used unbalanced magnetron sputtering system (UBMS). During deposition process, different a-C:H:Zr-x topcoats were deposited by varying the Zr target current from 0.0 A to 0.5A while maintaining the remaining process conditions at the constant settings. The microstructure, adhesion and tribological properties of the a-C:H:Zr-x coatings were found to vary with the Zr content. The tribological properties of the coatings had been tested against AISI 52100 or Si₃N₄ counterbody under ball-on-disk point contact wear mode using an oscillating friction and wear tester. Of the various coatings, the a-C:H:Zr-0.4 coating provided the best tribological properties, including the lowest wear depth, the friction coefficient and the longest lifetime. Compare to the coatings sliding against both counterbodies, all of coatings possessed the high wear depth as sliding against Si₃N₄, but it displayed longer wear lifetime than sliding against AISI 52100.

Abstract: A model of the problem of variable load line contact EHL with single asperities is established. The influences of the single asperities and variable load on the pressure and film thickness are investigated. Numerical results reveal that the existence of single asperities can lead to pressure change drastically and film thickness become thin in the vicinity of asperities. The effects of the variable load on the pressure and film thickness are discussed. The comparison of the variable load and steady load is given.

Abstract: The surface of high-pressure crystallized ultra-high molecular weight polyethylene (UHMWPE) was modified for application as an artificial cartilage material. A UHMWPE surface pretreated by a series of processes, including treatment with O₂-plasma and ethylenediamine solution, was coated with hyaluronic acid (HA). After that, adipic acid dihydrazide (AAD) was added to partially crosslink the HA coating in order to enhance its durability. The modified samples were verified by water contact angle measurement and Fourier transform infrared spectrometry. Both HA layers, original and crosslinked, were also quantitatively evaluated by carbohydrate chemistry assay according to the absorbance of the incident light. The tribological performance of the samples was evaluated by a pin-on-disk test rig lubricated by normal saline under an average pressure of 18 MPa and at a sliding speed of 0.03 m/s for 45 h. The wear resistance of the HA-coated UHMWPE specimens promoted by the crosslink process was superior to that of the original HA-coated sample, and that resistance was maintained after immersion in saline solution for one month.

Abstract: The friction coefficient of tribology pair between silicon nitride ceramic and stainless steel was researched with bovine serum albumin, saline and water lubricants. The coefficient of friction of silicon nitride in bovine serum albumin is lower than those in saline and water. Using digital microscope, the worn surfaces of silicon nitride and stainless steel were viewed. The groove depths of worn stainless steel surface were measured. The depth with bovine serum albumin is shallower than those in saline and water. The results showed that ceramic in bovine serum albumin has good tribological characteristic. This research provides the reference for the development of ceramic artificial joint.