Alloy Friction Research Articles

Workability improvement on Al alloy inhomogeneous blanks by cryogenic forming

ABSTRACT A novel cryogenic forming method is proposed to improve the workability of Al-Cu-Mn alloy friction stir-welded (FSW) blanks in this paper. Experiments were conducted to study the formability, deformation processing, and microstructure evolution of FSW blanks at liquid nitrogen temperatures. The cryogenic tensile properties of the joints showed that the plastic efficiency increased from 70.6% to 91.1%. The longitudinal weld fracture strain increased, and the ultimate tensile strength difference between the weld and base material decreased by 77.5% at −196°C. The cryogenic limiting dome height of the FSW blank increased from 25.4 mm at room temperature to 36.3 mm. The strain inhomogeneity of the bulged part decreased at −196°C. The FSW blank exhibited synergistic enhanced formability and deformation uniformity because of the improved plasticity of the weld zone and the smaller strength differences of the base material zone and weld zone at −196°C. The easy multiple slips in the nugget zone decreased the localized slips and increased the plasticity during cryogenic deformation. The decreased strength differences at cryogenic temperature were attributed to the significant dislocation strengthening of the coarse-grained base material.

Efficient friction and wear reduction of Al-Si alloy via tribofilms generated from synergistic interaction of ZDDP and chemically functionalized h-BN additives

Zinc dialkyldithiophosphate (ZDDP) and molybdenum dithiocarbamate (MoDTC) are conventional lubricant additives for reducing friction and wear of metallic components. However, their efficacy for lightweight aluminum (Al)-based alloys is limited due to the wear of soft Al matrix regions. The present work reports significant improvement in the tribological properties of Al-Si alloys (ADC12) under liquid lubricants containing a combination of ZDDP and hexagonal boron nitride (h-BN) nanosheets. In situ monitoring of tribofilm growth, friction, and wear was carried out using atomic force microscopy (AFM)-based measurements. At high temperature (110 °C), experiments were carried out at the Al matrix and Si phase of ADC12 alloy under the lubricant containing ZDDP (1 wt%) and tert-butoxy (TBO) functionalized h-BN nanosheets [(h-BN-TBO), (0.02 mg/mL and 0.05 mg/mL)]. The addition of h-BN-TBO in ZDDP containing lubricant significantly improved the tribological properties due to the synergistic interaction between h-BN-TBO and ZDDP; leading to the formation of lubricious and robust antiwear tribofilms on Si and Al phase regions. A synergistic combination of h-BN-TBO and ZDDP as lubricant additive showed superior performance compared to ZDDP or a combination of ZDDP and MoDTC-based lubricant systems.

Molecular structure insight into the tribological behavior of sulfonate ionic liquids as lubricants for titanium alloys

The wide industrial application of titanium alloys requires lubricating materials with superior performance. Although ionic liquids have been recognized as potential choices for excellent lubricants, research on their tribological properties as applied to titanium alloys is not mature and systematic. In this work, a series of halogen-free sulfonate IL lubricants with different anions and cations were designed, synthesized, and applied to the titanium alloy (Ti-6Al-4V) friction pairs. From the perspective of molecular structure, the influencing factors on their physicochemical properties (thermal stability, viscosity) and tribological performances (friction-reducing and anti-wear performances) were explored, including the influences derived from their active element, chain length, molecular rigidity and branched chain structure. The lubricating mechanism contributed by the IL molecules and the Ti surfaces during sliding were analyzed by means of SEM, XPS, ECR and QCM. The results showed that physical adsorption and tribo-chemical reactions were involved during the sliding process. And the lubricating performances of the synthesized ILs may largely depend on their ability to form physical/chemical adsorption films on the titanium interfaces. The rigid benzene ring structure and flexible alkyl chain are conducive to strengthening the stability and efficiency of the formed interfacial tribo-film.

Rapidly improved tensile strength of 6N01 Al alloy FSW joints by electropulsing and artificial aging treatment

The tensile strength of 6N01 Al alloy friction stir welded joints is obviously improved in a short time by combining electropulsing and artificial aging treatment, which is attributed to the transformation of precipitates from rod-like β' to needle-like β''. Benefiting from the athermal effect of electropulsing, rapid solid solution of β' is achieved in 3 s below 110°C.

High entropic coatings FeCrNiTiZrAl and their properties

In our proposed empirical model, the anisotropy of the surface energy and the thickness of the surface layer of the high-entropy FeCrNiTiZrAl alloy are calculated. The thickness of the surface layer of this alloy is about 2 nm, which is an order of magnitude greater than the thickness of the surface layer of complex crystals, but is of the same order of magnitude as that of metallic glasses. The hardness and other properties of the high-entropy alloy are the same as for metallic glasses, but are 2-3 times higher than the hardness of stainless steels. The surface energy of the high-entropy FeCrNiTiZrAl alloy is about 2 J/m2, which corresponds to the surface energy of magnesium oxide and other crystals with a high melting point. However, unlike these crystals, the friction coefficients of a high-entropy alloy (~ 0.06) are much lower than that of ordinary steels (~0.8). We have theoretically shown that the friction coefficient is proportionally dependent on the surface energy and inversely proportional to the Gibbs energy, which significantly decreases for a high-entropy alloy, leading to low friction. The high hardness and low coefficient of friction of the high-entropy alloy facilitates the deposition of coatings from them on structural metal products, which contributes to their widespread use.

Grain orientation and texture analysis of 6082 aluminum alloy friction plug welded joints

Electron backscatter diffraction (EBSD) was used to study the grain morphology, grain boundary characteristics, and texture compositions of different regions in 6082-T6 aluminum alloy friction plug welded joints made using shoulder-assisted heating. The results showed that the material at the plug and hole junction underwent thermoplastic deformation, dynamic recovery, and recrystallization, with significant refinement of the joint grains. In addition, inter-grain misorientation deviated from random distribution to a noticeable preferred orientation. The welded nugget zone had a dominant recrystallized texture, and deformation and recrystallization textures were both observed in the junction zone, while the deformation texture accounted for a large proportion of the thermo-mechanically affected zone.

Effect of ultrasonic impact treatment on microstructure and corrosion behavior of friction stir welding joints of 2219 aluminum alloy

Ultrasonic Impact Treatment (UIT) was performed to improve the corrosion resistance of 2219 aluminum alloy friction stir welding (FSW) joints. Results showed that the coarse grains on near surface of FSW joints were obviously modified and refined after UIT, and the thickness of the modified layer of different sub-regions was ranged from 90 to 120 μm. UIT increased intergranular corrosion resistance of 2219 aluminum alloy FSW joints in salt spray corrosion atmosphere. Free-corrosion potential of heat-affected zone (HAZ), which presented the worst corrosion resistance, was increased from −0.653 to −0.628 V, and the corrosion current density was decreased from 7.48 to 6.18 mA cm−2. The sensitivity index of stress corrosion cracking (SCC) of the joints was decreased from 0.139 to 0.129 in 3.5% NaCl solution after UIT, and the risk of crack initiation during SCC process was significantly inhibited. UIT improved the SCC resistance of 2219 aluminum alloy FSW joints by surface plasticity improvement, grain refinement and precipitates dissolution and redistribution.

An insight into the effect surface morphology, processing, and lubricating conditions on tribological properties of Ti6Al4V and UHMWPE pairs

The effects of surface topography, processing, and environment conditions during tribological contact between Ti6Al4V titanium alloy and UHMWPE friction pairs were systematically evaluated. Hence, in this research the polyethylene samples (blocks) having a constant surface roughness were rubbed against counter-bodies (rollers) made of titanium alloy with different roughness of surfaces. The counter-samples were manufactured using either dry machining and/or minimum quantity lubrication (MQL) conditions. Such cutting conditions are harmless to humans and the environment. Simulated body fluid (SBF) and distilled water was used to simulate the tribological trials. We have noted that the lubricant applied to protect the integrity of machined parts, the rollers, have only minor impact on the tribological features of the friction pairs tested. Further, the samples produced with dry machining demonstrated a slightly lower momentary friction coefficient and temperature. In contrast, the MQL method enable reduced friction surface and significant wear accumulation. Further, it was found that the minimum and maximum values of the Sa texture parameter associated to tribological parameters do not exceed 21% and 4%, when is used dry and MQL methods, respectively. Nevertheless, the distilled water revealed a much better wear resistance when comparing to SBF, and the later one trigger as well as an accentuated wear progress with different patterns. The results of the study are important in the design of new biomedical components produced by finish turning.

Effect of the modification structure for Newton's metal on some its properties for industrial applications

Newton's metal is important for industrial applications that is the reason for studying the effect of modified structure of it’s on mechanical and thermal properties. Microstructure, mechanical properties such as elastic modulus Vickers hardness, internal friction and melting temperature of Bi50Pb34Sn16, Bi50Pb28Sn22, Bi50Pb22Sn28 and Bi50Pb16Sn34 alloys have been studied and analyzed. X-ray analysis of these alloys show that, it contained different phases with formed a solid solution. Elastic modulus variable decrease, melting temperature varied, internal friction and Vickers hardness increased due to modified Newton's metal (Bi50Pb31.2Sn18.8) alloy.

Tribological Properties of Different-Sized Black Phosphorus Nanosheets as Water-Based Lubrication Additives for Steel/Titanium Alloy Wear Contact

Titanium alloys are extensively used in the aerospace, chemical, and biomedical industries. However, it has always been a challenge in the manufacturing and machining of titanium alloys because they exhibit poor friction and wear characteristics, which results in serious problems and significantly restricts their further production and application. Therefore, in the present study, the wear contact between GCr15 steel and Ti6Al4V alloy is specifically studied by considering black phosphorus nanosheets (BP-NS) as water-based lubrication additives, which is expected to have a great potential application in manufacturing and machining titanium alloys. The influence of BP nanosheet size on the coefficient of friction (COF) and wear rate of Ti6Al4V alloy has been comprehensively studied, based on comparisons among adding large BP nanosheets (L-BP) (2–4 μm), medium BP nanosheets (M-BP) (300–500 nm), and black phosphorus quantum dots (BPQDs) (6–10 nm). Compared with ultrapure water, the COF and wear rate of Ti6Al4V alloy are reduced by 42.4% and 82.3%, respectively, when BPQDs are used as water-based lubrication additives. This paper also shows that a lower COF and wear rate is achieved with the addition of BPQDs than the other two BP nanosheet sizes. Derived from the friction tests and worn surface analysis of Ti6Al4V alloy, lubrication mechanisms of different-sized BP lubricants were proposed. The interlaminar shearing between BP-NS and the adsorbed films were the main mechanisms for L-BP and M-BP lubricants, while the adsorption, repair, and ball-bearing effects were mainly presented in the BPQD lubricants. The discoveries in this paper would be beneficial to developing novel lubricants for the manufacturing and machining of titanium alloys.

Braking behaviours of C/C–SiC mated with iron/copper-based PM in dry, wet and salt fog conditions

C/C–SiC composites have enormous potential as a new generation of brake materials. It is worth studying the friction and wear behaviours of these materials in special environments to ensure the safe and effective braking of trains in practical applications. In this study, the braking behaviours and wear mechanisms of C/C–SiC mating with iron/copper-based PM in dry, wet and salt fog conditions are compared in detail. The results show that the coefficient of friction (COF) in the wet condition is reduced by 14.13% compared with that under the dry condition. The COF value of the first braking under salt fog condition is increased by 12.27% and 30.75% compared to the dry and wet conditions, respectively. Additionally, the tail warping phenomenon of the braking curve disappears in wet condition, which is attributed to the weak adhesion of friction interfaces and the lubrication of the water film. The main wear mechanisms of C/C–SiC mating with iron/copper-based PM under dry condition are adhesive, fatigue and oxidation wear. However, the dominant wear in wet condition is abrasive wear. The cooling and lubrication of water reduce the tendency of thermal stress, and weaken adhesive and fatigue wear. Furthermore, salt fog can accelerate the corrosion of alloy friction film, leading to the damage of friction film. Meanwhile, the third body particles formed in salt fog condition participate in the braking process. The wear mechanisms in salt fog condition are dominated by abrasive and delamination wear.

Effect of microstructure evolution on corrosion behavior of 2195 Al-Li alloy friction stir welding joint

In this study, the microstructure and corrosion behavior of 2195-T8 aluminum‑lithium alloy friction stir welding (FSW) joint were investigated by the microscopy and salt spray corrosion tests. Results indicated that the base metal was mainly composed of Al2CuLi and Al2Cu phases. New phases of Al3Li, Al3Zr, Al2CuMg and residual Al2CuLi and Al2Cu phases were found in HAZ, and WNZ exhibited Al3Li and Al3Zr phases. The salt spray corrosion tests showed that BM exhibited the highest corrosion susceptibility, which could be attributed to the macro-galvanic effect between different regions. The corrosion rate of the FSW joints was calculated by conducting salt spray corrosion tests in 3.5% NaCl solution at different pH values and spraying time. The corrosion rate decreased with increasing pH values and the average corrosion depth is positively correlated with the corrosion rate. It was also found that the corrosion rate decreased with increasing spraying time, but the average corrosion depth tended to increase with increasing spraying time. In addition, an empirical relationship was established to predict the corrosion rate of 2195-T8 AlLi alloy FSW joints, which can be used to predict the corrosion rate of the FSW joints.

Microstructural, mechanical and tribological characterization of ZrB2 reinforced AZ31B surface coatings made by friction stir processing

Among the different surface modification techniques, Friction Stir Processing (FSP) is one of the promising techniques for magnesium materials. In the present work, an AZ31B magnesium alloy is reinforced with 3 wt.% micro-sized Zirconium diboride (ZrB2) particles through the Friction Stir Processing technique. The effect of tool passes (single pass and double pass) on microstructural, mechanical, and tribological properties were investigated. The microstructural study revealed that the average grain size of double-pass AZ31B/ZrB2 surface composite was reduced from 12 to 6 µm as compared to the AZ31B magnesium alloy. The microhardness test results revealed a 50% improvement in hardness in the double-pass AZ31B/ZrB2 surface composite than in the single-pass reinforced composite and base alloy. The tensile test result revealed a 19% improvement in the strength of the double-pass AZ31B/ZrB2 surface composite and 13.5% improvement in the strength of the single-pass AZ31B/ZrB2 surface composite in comparison to the base alloy. A ductile mode of fracture was observed in fractured tensile specimens. The friction and wear performance of base alloy and AZ31B/ZrB2 surface composites were evaluated using a pin-on-disc tribometer. Tribological behaviour exhibited that the wear rate of a double-pass AZ31B/ZrB2 surface composite was 60% lower than the base alloy. The coefficient of friction of the double-pass AZ31B/ZrB2 surface composite was 24% lower than the base alloy. SEM images of the worn surface revealed delamination, micro-cracks, and ploughing in AZ31B/ZrB2 surface composites.

Influence of Graphite Morphology on Hyperthermal Friction and Wear Behaviors of Aluminum-high Silicon Alloys

Influence of Graphite Morphology on Hyperthermal Friction and Wear Behaviors of Aluminum-high Silicon Alloys

SURFACE STRENGTHENING AND FRICTION WEAR OF THE INNER WALL OF LIQUID SODIUM HYDROSTATIC BEARING

Sodium hydrodynamic bearings are parts which are easy to wear in order to improve the wear resistance of the inner wall and prolong the service life. In this paper, high-temperature element W was used as a variable to prepare cobalt-based alloy coatings with different contents of W. By testing the hardness and anti-wear performance of the coatings at high temperature, the microstructure and wear mechanism of the coatings were further analyzed in combination with crystal phase diagram and microscopic morphology diagram. The results show that the coefficient of friction of cobalt-based alloy coating decreases with the increase of W content under high-temperature dry rubbing, while the wear quantity increases with the increase of W content. Under high-temperature oil lubrication, the coefficient of friction of cobalt-based alloy coating is the lowest when the W content is 12%. The wear amount of cobalt-based alloy coating decreases with the increase of W content, and the wear mechanism changes from adhesion wear to abrasive wear with the increase of W content.

Controllable in situ fabrication of self-lubricating nanocomposite coating for light alloys

Intrinsic friction and corrosion issues of light alloys impede their application in tribological and corrosive environments, thus a proper ceramic coating is normally required to overcome these issues for practical engineering deployment. Here, we developed a new approach to fabricate controllable and self-lubricating nanocomposite coating by combining in-situ synthesis of MoS2 and plasma electrolytic oxidation (PEO) process. It is found that the coefficient of friction of this new coating is only about a quarter of the coatings obtained by traditional PEO process due to the self-lubricating characteristic of gradient MoS2. More importantly, this ceramic coating exhibits excellent interfacial strengthen through edge-pinning by noncoherent, which endows excellent tribological and adhesive properties. This facile technique provides a new strategy to fabricate self-lubricating ceramic coating for light alloys, and is believed to have great potential applications in wide engineering sectors and open new avenues for designing novel alloy systems for extreme conditions.

Investigation of the friction and wear properties of nitrided 7075-T6 aluminum alloy under vacuum and ambient air

Investigation of the friction and wear properties of nitrided 7075-T6 aluminum alloy under vacuum and ambient air

Microstructure and Mechanical Properties for Thick Plate 5083 Aluminum Alloy Friction Stir Welding Joint along the Thickness Direction

Microstructure and Mechanical Properties for Thick Plate 5083 Aluminum Alloy Friction Stir Welding Joint along the Thickness Direction

The Evolution of Precipitates in 2195-O Al-Li Alloy Friction Stir Welding Joints

The Evolution of Precipitates in 2195-O Al-Li Alloy Friction Stir Welding Joints

Microstructural Thermal Stability of Aluminum Alloy Friction Stir Welding Joint

Microstructural Thermal Stability of Aluminum Alloy Friction Stir Welding Joint