Ultrasonic Cold Forging Technology Research Articles

Improving corrosion resistance and biocompatibility of AZ31 magnesium alloy by ultrasonic cold forging and micro-arc oxidation.

Corrosion resistant and biocompatible AZ31 magnesium alloy surfaces were successfully prepared by ultrasonic cold forging and subsequent micro-arc oxidation. The properties of these ultrasonic cold forging pretreated (UCFT)AZ31 magnesium alloy surfaces containing Sr-Ca-P micro-arc oxide coating (MAO/UCFT/AZ31) were studied. Results showed that surface grain refinement of AZ31 Mg alloy in the depth of 400μm owing to the ultrasonic cold forging pretreatment was verified, and which provides more discharge channels for subsequent micro-arc oxidation. Comparing with the AZ31 magnesium alloy (AZ31) and ultrasonic cold forging technology treated AZ31 magnesium alloy samples (UCFT/AZ31), the corrosion resistance of MAO/UCFT/AZ31 significantly improved, which is also supported by the immersion experiments and electrochemical tests in simulated body fluid. Meanwhile, the MAO/UCFT/AZ31 samples also had excellent cytocompatibility as well as MAO/AZ31 samples. These results may beneficial to the developing of biodegradable medical materials in future.

Effect of Surface Nanocrystallization Pretreatment on the Tribological Properties of Plasma Nitrided AISI 316 L Stainless Steel Under Boundary Lubrication

It has been proved that surface nanocrstallization pretreatment is beneficial to plasma nitriding of steel by enhancing nitrogen diffusion, while the tribological properties of the nitrided nanostructured steel under boundary lubrication are not clear. In this work, AISI 316 L stainless steel with and without ultrasonic cold forging technology (UCFT) pretreatment was plasma nitrided at 500 °C for 4 h. The effects of UCFT pretreatment on the microstructure and properties of the nitrided layer and the tribochemical interactions between the nitrided layer and friction modifier molybdenum dithiocarbamate (MoDTC) and antiwear additive zinc dialkyldithio-phosphate (ZDDP) were investigated using SRV tribometer, scanning electron microscopy (SEM), vickers hardness tester, optical microscope, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Surface analyses confirm the formation of a 20 μm thick nitrided layer on the UCFT-pretreated sample and it had higher hardness than that on the unpretreated sample. Furthermore, the nitrided UCFT-pretreated sample presented better synergetic effect with MoDTC and ZDDP on tribological behaviors than the nitrided unpretreated sample. This is attributed to the higher contents of Mo, S, Zn, P, and MoS2/MoO3 ratio in the tribofilms on the nitrided UCFT-pretreated sample.

Improving Corrosion Resistance and Corrosive Wear Resistance of Aluminum Alloy Drill Pipe by Surface Nanocrystallization and Micro-arc Oxidation

To improve the corrosion and wear resistance performance of aluminum alloy drill pipes in geological and petroleum drilling applications, a strengthening coating was prepared on the surface of the 2618 aluminum alloy by combining treatment with ultrasonic cold forging technology (UCFT) and micro-arc oxidation (MAO). The effects of the strengthening coating on the corrosion and wear resistance of the aluminum alloy were evaluated by electrochemical and tribological tests. The results demonstrated that the corrosion and wear resistance of the aluminum alloy were improved by the UCFT and MAO technologies, especially the salt corrosion resistance. The corrosion morphology of the strengthening coating primarily included pitting, micro-cracks and NaCl attachment. In addition, the UCFT + MAO composite coating exhibited the best wear performance. The wear rate of the UCFT + MAO composite coating was lower than that of the aluminum alloy by 94%. The results provided support for this excellent surface treatment technology for the corrosion and wear resistance of aluminum alloy drill pipes, and they also present a feasible evaluation method for drill pipes.

Tribocorrosion behavior and mechanism of micro‐arc oxidation Ca/P coating on nanocrystallized magnesium alloys

In order to improve the corrosion and tribocorrosion resistance of magnesium alloy used as implant materials in human body, a calcium phosphate (Ca/P) containing coating was obtained by micro‐arc oxidation (MAO) on the nano‐layer pretreated by ultrasonic cold forging technology (UCFT). The metallographic structure of the UCFT‐treated sample was observed by metallographic microscope. The thickness of the nanolayer is about 100 µm and the grain size has become smaller than that of the untreated sample. The results show that OCP increases gradually under corrosion and will be up and down under tribocorrosion. PDP data show that the current density of UCFT‐MAO sample is the lowest under corrosion and tribocorrosion, and the current density of the sample under tribocorrosion is higher than that under corrosion. EIS shows that the impedance magnitude (|Z|) of the samples under tribocorrosion is much lower than that of under corrosion. These results indicate that corrosion resistant performance of the UCFT‐MAO sample can be reduced by wear. And a physical model of the tribocorrosion behavior was proposed.

Effects of nanocrystallized layer on the tribological properties of micro-arc oxidation coatings on 2618 aluminum alloy under high temperatures

A composite oxidized layer formed on a nanocrystallized 2618 aluminum alloy surface was prepared by a two-step method—the micro-arc oxidation (MAO) process and a pretreatment of the ultrasonic cold forging technology (UCFT). The tribological properties of samples were investigated under 25, 80, 160, and 200 °C by an MST-400 high temperature tribometer. The wear performance of MAO + UCFT aluminum alloy drilling rods was evaluated in the field drilling experiment. The morphologies and microstructures were measured by the scanning electron microcopy and optical microscope. The results show that UCFT treatment promotes the formation of α­Al2O3 phase, reduces the number of micro pores, and improves the hardness of MAO coatings. Both friction coefficients and wear rates of untreated and UCFT samples increase with the rise of temperature, but those of the UCFT samples are lower at the same temperature. The friction coefficients and wear rates of MAO and MAO + UCFT samples decrease with the rise of temperature, but those of the MAO + UCFT samples are lower at the same temperature. The main wear mechanism of untreated samples is severe adhesive wear, plastic deformation, and slight abrasive wear. Whereas, that of UCFT samples is some degree of adhesive wear, abrasive wear, and plastic deformation. Additionally, oxidative wear occurred on the untreated and UCFT samples. The main wear mechanism of MAO samples and MAO + UCFT samples is mild adhesive wear and abrasive wear.

Microstructure and corrosion model of MAO coating on nano grained AA2024 pretreated by ultrasonic cold forging technology

In order to study the effect of surface nano-structuring of aluminum alloy on the corrosion performance of MAO coating, ultrasonic cold forging technology (UCFT) was used as a pretreatment to produce a refined layer before a MAO coating was prepared on the surface of 2024 Al alloy (AA2024). The surface roughness was evaluated by atomic force microscope (AFM), and the average surface roughness value of the 5.00 × 5.00 μm area of UCFT treated sample is 7.477 nm. The grain size of the modified layer were observed by transmission electron microscope (TEM). The result showed that UCFT can refine the grains. The microstructure and phase component of the coated samples were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The observations showed that the micro-pore size of the MAO coating on UCFT treated Al alloy is smaller than that of MAO coating on untreated alloy. The phases of the coated samples with and without UCFT remain the same. The hardness of the samples measured by the micro-hardness tester showed that the UCFT-MAO sample possesses the highest micro-hardness among all the samples. The potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were employed to characterize the corrosion rate and the electrochemical impedance in a 3.5% NaCl solution. For the PDP testing, the sweep rate was 5 mV/s starting from −1.4 V to 0 V, while the EIS tests were carried out in the range of 0.01 Hz–100 kHz with AC voltage amplitude of 10 mV. The PDP and EIS results show that the UCFT-MAO sample has the best corrosion resistance with the lowest corrosion current density, 0.412 A/cm2. The largest electrochemical impedance is attributed to UCFT pretreatment prior to MAO process on aluminum alloys. The corrosion model of MAO coated AA2024 pretreated by UCFT was proposed.

Corrosion behavior and mechanism of MAO coated Ti6Al4V with a grain-fined surface layer

In order to enhance the corrosion behavior of Ti6Al4V, a MAO coating was prepared on the surface refined by ultrasonic cold forging technology (UCFT). The surface roughness value and the grain were evaluated by atomic force microscope (AFM) and transmission electron microscope (TEM). The microstructure and phase component of the coated samples were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion behavior of all the samples was examined by potentiodynamic polarization and electrode impedance spectroscopy (EIS) tests in a 3.5% NaCl solution. The results show that UCFT can reduce the surface roughness value and refine the grains. The micro-pore size of the UCFT-MAO sample is smaller and the pore number is less than those of MAO sample. The thickness of the coated sample is about 10 μm. The UCFT-MAO sample possesses the highest micro-hardness among all the samples. The UCFT-MAO sample has the best corrosion resistance with the lowest corrosion current density and the highest electrochemical impedance, which is attributed to UCFT pretreatment prior to MAO process on titanium alloys. The influence of UCFT on the corrosion process and corrosion mechanism were discussed.

Synergistic effects between sulfurized-nanocrystallized 316L steel and MoDTC lubricating oil additive for improvement of tribological performances

The synergistic effects between sulfurized-nanocrystallized 316L stainless steel and molybdenum dithiocarbamates (MoDTC) additive under boundary lubrication were investigated in this paper. The tribological behaviors of the treated steel were investigated on a ball-on-disc SRV tribometer. The chemical analysis of tribofilms was performed by X-ray photoelectron spectroscopy (XPS). The results showed that the sulfurized-nanocrystallized sample exhibited the lowest coefficient of friction (0.060) and the lowest wear rate under MoDTC lubrication. The sulfurized ultrasonic cold forging technology (UCFT) composite treatment provided a strong support to the soft FeS layer and prolonged its service time. The MoS2 decomposed by MoDTC can achieve the lowest coefficient of friction.

Effect of ultrasonic cold forging technology as the pretreatment on the corrosion resistance of MAO Ca/P coating on AZ31B Mg alloy

A calcium phosphate contained (Ca/P) coating was obtained on AZ31B Mg alloy by micro-arc oxidation (MAO) process under the pretreatment of ultrasonic cold forging technology (UCFT). The surface nanograins were introduced after UCFT pretreatment on AZ31B Mg alloy. Optical microscope (OM) was employed to observe the microstructures of the untreated and UCFT treated samples. Transmission electron microscopy (TEM) and atomic force microscope (AFM) were employed to observe the microstructures of nanograins and the surface roughness of the UCFT treated Mg alloys. The grain size of the UCFT treated Mg alloy is 48.67nm and the surface roughness is 17.03nm. The microstructures and the phase compositions of MAO samples were observed and analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The XRD results show that the coating include Ca/P phase, including hydroxyapatite (Ca10(PO4)6(OH)2), HA), tertiary calcium phosphate (Ca3(PO4)2, TCP) and calcium phosphate dehydrate (CaHPO4⋅2H2O, DCPD). The hardness of the samples was measured by the micro-hardness tester under the loads of 10g, 25g and 50g. 3D topographies of hardness indenter were characterized by 3D profiler. The immersion tests and potentiodynamic polarization tests were used to evaluate the weight loss rate and corrosion current density in simulated body fluid (SBF). The results show that the corrosion resistance of Ca/P MAO coating on Mg alloy was improved greatly by the pretreatment of UCFT.

Effects of surface nanocrystallization on tribological properties of 316L stainless steel under MoDTC/ZDDP lubrications

In this paper, 316L stainless steel (316LSS) is treated by a ultrasonic cold forging technology (UCFT) which is one of the methods of surface nanocrystallization. The tribological properties of UCFT sample are investigated by a SRV tribometer under lubrications with MoDTC and ZDDP. The chemical analysis of tribofilms is performed using X-ray photoelectron spectroscopy (XPS). The results show that the UCFT sample exhibits the lowest coefficient of friction (0.066) under MoDTC lubrication and the lowest wear rate under ZDDP lubrication, indicating that surface nanocrystallization has synergistic effects on low friction and antiwear performances of both MoDTC and ZDDP. The obviously synergistic effects between UCFT steel and MoDTC/ZDDP may be attributed to the higher hardness and surface reactivity of the UCFT surface.

The effect of nitriding temperature on hardness and microstructure of die steel pre-treated by ultrasonic cold forging technology

To promote the formation and growth of nitride layer, a befitting surface nano-crystallization process was introduced as a pre-treatment of nitriding, and an optimized nitriding temperature was investigated. A modification layer with a depth of 350μm was formed by ultrasonic cold forging technology (UCFT) on AISI D2 surface. A series of plasma nitriding experiments for both treated and untreated samples were conducted at various temperatures ranging from 350°C to 550°C for 4h. The influences of nitriding temperature on the hardness, microstructure, morphology and composition of the sample surface were investigated by micro-hardness tester, optical microscope (OM), 3D profile-meter and scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The diffusion of nitrogen and the formation of nitrides were markedly improved by UCFT pre-treatment. A thicker and harder nitrided layer was formed at a high nitriding temperature. However, as the nitriding temperature increased to 550°C, a stronger sputter occurred on the sample surface. The results presents that it is an optimized process to be pre-treated by UCFT and nitriding at 520°C for 4h.

Fatigue and mechanical characteristics of nano-structured tool steel by ultrasonic cold forging technology

Ultrasonic cold forging technology (UCFT) utilizing ultrasonic vibration energy is a method to induce severe plastic deformation to a material surface, therefore, the structure of the material surface becomes a nano-crystal structure from the surface to a certain depth. It improves the mechanical properties; hardness, compressive residual stress, wear and fatigue characteristics. Applying UCFT to a rolling process in the steel industry is introduced in this study. First, the UCFT specimens of a tool steel (SKD-61/equivalent H13) are prepared and tested to verify the effects of the UCFT in a variety of mechanical properties, the UCFT is applied to the trimming knives in a cold rolling process. It has been determined that UCFT improves the mechanical properties effectively and becomes a practical method to improve productivity and reliability by about two times compared with the conventionally treated tooling in the trimming process in a cold rolling line.

Nano structured surface modification of tool steel and its beneficial effects in mechanical properties

The industrial beneficial effects of nano-structured surface modification of tool steel (SKD 61) have been studying. Ultrasonic cold forging technology (UCFT) is one of severe plastic deformations for the improvement of mechanical properties by making nano-structure on surface. The basic mechanism of UCFT and experimental device for treatment of trimmer knives (SKD 61) are presented. Test results of UCFT treated knives in cold steel milling line and analysis why the improved service life is achieved are explained.