Surface Mechanical Properties Research Articles

Fatigue strength of hot-dip galvanized additively manufactured steel

This study investigated the fatigue resistance of additively manufactured steel plates with galvanized surfaces. Therefore, the effects of hot-dip galvanization (HDG) on the surface characteristics, mechanical properties, and fatigue resistance of the manufactured samples were investigated. This research involved measurements of the surface roughness and waviness before and after the HDG process to assess the impact of the zinc layer. Statistical analysis revealed no significant difference in the distribution of surface roughness; however, microscopic examination revealed sharper notches owing to the vertical growth of the zinc layer.Quasi-static tension tests demonstrated that HDG has a minimal influence on the yield strength, provided that the load transfer contribution of the soft zinc layer is excluded. Nonetheless, the mean elongation at fracture was slightly reduced in the HDG samples. Remarkably, a significant effect on fatigue resistance was observed with a detail category of 80 and an inverse slope of m = 3. This fatigue resistance aligned closely with that of the as-welded samples under high stress ranges while demonstrating a lower resistance under smaller stress ranges.

Preparation of GO‐SiO2 three‐dimensional point‐plane nanomaterials and enhancement of epoxy resin mechanical property

AbstractIn this research, mercapto‐anchoring graphene oxide (GO) and epoxy‐anchoring SiO2 nanoparticles (NPs) were assembled by mercapto‐epoxy click chemistry to form three‐dimensional (3D) point‐plane structure nanomaterials (GO‐SiO2), and epoxy resin (EP) composites were prepared using the auxiliary thermal blending method. The relationships among surface interfacial interaction, dispersion, and mechanical properties of composites were systematically investigated. The Research finding shows that SiO2 NPs covalently bonding with GO increases interface compatibility and dispersion, which explains epoxy composite strengthening. Compared to epoxy resin, 0.1 wt% GO‐SiO2/EP composite has 38.65%, 36.15%, 44.64%, and 61.61% higher tensile strength, flexural strength, flexural modulus, and impact strengths. The enhancement mechanism of GO‐SiO2 toward EP was analyzed.

Investigation of thermal annealing on the characteristics of ScxAl1−xN thin films

Good temperature stability is essential for radio-frequency (RF) devices working at high frequencies. AlN and Sc doped AlN (ScxAl1−xN) are widely used as piezoelectric thin films for their excellent performance, but the temperature characteristics of these two materials could be more precise. In this work, the effect of high-temperature thermal annealing on the characteristics of ScxAl1−xN thin films was investigated. ScxAl1−xN thin films with different Sc compositions were deposited and then annealed in different atmospheres at various temperatures. It was found that ScxAl1−xN thin films could maintain good temperature stability below 900 °C in vacuum or air, and AlN can even maintain up to 1300 °C under vacuum. When the annealing temperature exceeded 900 °C, the films’ crystallinity and lattice would appear to have apparent changes. Moreover, the introduction of oxygen at elevated temperatures could impair the surface morphologies and mechanical properties of the ScxAl1−xN thin films. The results revealed that the increased Sc composition decreased the temperature stability of the ScxAl1−xN thin films, and AlN was proved to have better temperature stability than the other two thin films. This work establishes a research foundation for utilizing ScxAl1−xN thin films in high-temperature applications.

Surface Characterization, Mechanical Properties, and Corrosion Behavior of Zn-Ni Alloy Coated Steel Using Electroplating-Hot-Dip Galvanizing

In this study, the processing of zinc-nickel alloys with an electroplated nickel layer as the first layer followed by hot-dip galvanizing on plain carbon steel (St37) is investigated. The effect of the nickel layer and the effect of the immersion time on the alloy layers of the coating obtained by this method are studied. In addition, some properties of the obtained coating, such as the overall thickness, hardness, surface uniformity, coating adhesion strength, and corrosion resistance, were investigated using the optical microscope, scanning electron microscopy, energy dispersive x-ray spectrometer analysis, and potentiostat. The results show that the 16-min immersion time is the optimum galvanizing time at which an alloy with a nickel content of 0.11 wt% is formed and that the overall thickness of the galvanized sheet, especially the alloy layers, decreases compared to the pure zinc sheet. In addition, a more ductile, corrosion-resistant, and smoother surface is obtained.

Durable and impact-resistant thermoset polymers for the extreme environment of low Earth orbit

Polymers degrade rapidly in low-Earth orbit (LEO) due to extreme thermal cycling, solar radiation, micrometeoroid and orbital micro-debris impact, and the synergistic erosive effects of atomic oxygen (AO) with UV radiation. In this work, we investigate the synergistic effect of (AO+UV)-induced erosion and high-velocity impact damage on a tough thermoset, polydicyclopentadiene (pDCPD), via erosion yield measurements after a long-term LEO exposure in the ram orientation aboard the International Space Station (ISS) followed by ground-based hypervelocity impact tests. The incorporation of SiO2 nanoparticles reduces the AO-erosion rate by an order of magnitude, while also mitigating the associated degradation of surface mechanical properties. Moreover, the resistance of pDCPD to AO-erosion increases with crosslink density. Hypervelocity impact tests using sub-millimeter laser-driven flyer plates launched at 4.5 km s−1 reveal that pDCPD has higher impact resistance than epoxies with comparable erosion resistance. Interestingly, both epoxy and pDCPD exhibit a statistically insignificant change in impact resistance following surface AO-erosion during direct exposure to space vehicle ram conditions (7.8 km s−1) in LEO.

Biodegradable zinc‐based materials with a polymer coating designed for biomedical applications

AbstractOver the last decades, biodegradable metals have gained popularity for biomedical applications due to their ability to assist in tissue healing. These materials degrade in vivo, while the corrosion products formed are either absorbed or excreted by the body, and no further surgical intervention is required for removal. Intensive research has been carried out mainly on degradable biomaterials based on Mg and Fe. In recent years, zinc‐based degradable biomaterials have been explored by the biomedical community for their intrinsic physiological relevance, desirable biocompatibility, intermediate degradation rate, tuneable mechanical properties and pro‐regeneration properties. Since pure Zn does not exhibit sufficient mechanical properties for orthopedic applications, various Zn alloys with better properties are being developed. In this work, the combined effect of minor Fe addition to Zn and a polyethyleneglycol (PEG) coating on the surface morphology, degradation, cytotoxicity and mechanical properties of Zn‐based materials was studied. There are several studies regarding the influence of the production of Zn alloys, but the effect of polymer coating on the properties of Zn‐based materials has not been reported yet. A positive effect of Fe addition and polymer coating on the degradation rate and mechanical properties was observed. However, a reduction in biocompatibility was also detected.

Selective laser sintering additive manufacturing of solid oral dosage form: Effect of laser power and hatch spacing on the physico-technical behaviour of sintered printlets

Selective laser sintering is a laser-based powder bed fusion 3D printing technique in which, the laser parameters plays a vital role in the fusion of polymeric powder particles and the behavior of the final printed object. Hence, the objective of the current study was to investigate the impact of laser power and hatch spacing on the fusion of particles, followed by their physicochemical and mechanical behavior investigations of the final sintered object made with dapsone and poly (1-vinylpyrrolidone-co-vinyl acetate) as a model drug and polymer, respectively. An increase in laser power and a decrease in hatch spacing improved particle fusion, resulting in smoother surface, increased density, and better mechanical properties. Interestingly, there was a loss of drug crystallinity was experienced in respect to varied laser parameters, highlighting the potential of laser-based powder bed fusion technique in developing amorphous solid dispersions. Despite extensive laser parameters, drug entrapment efficiency was found to be greater than 90 % for all sintered batches. No notable differences were observed in the dissolution behavior of all performed samples although it was anticipated to achieve as there was differences witnessed in porosity and disintegration time. Finally, the oral pharmacokinetics study revealed the comparable performance of the sintered dosage form with the tablet prepared with conventional direct compression techniques. Overall, these findings demonstrate that with varying laser parameters, various properties of the final sintered object can be manipulated which further showed the flexibility of this 3D printing technique to fabricate dosage form with a more personalized and customized needs.

Effect of molecular and atomic layer deposition thickness in zinc oxide hybrid films on surface cracks and mechanical properties of ultra-high molecular weight polyethylene

The integration of molecular/atomic layer deposition (MLD/ALD) techniques offers a versatile platform for the fabrication of functional organic-inorganic hybrid thin-film structures. In this study, we utilized a hybrid thin-film approach comprising of a zinc oxide (ZnO) ALD layer and a diethylzinc (DEZ) + hydroquinone (HQ) MLD layer to enhance the surface quality and mechanical properties. The objective of this research was to investigate the changes in surface crack pattern and mechanical properties of the hybrid thin films by varying the composition and number of MLD/ALD layers while maintaining a fixed MLD/ALD ratio of 1:5. The hybrid films were synthesized using the [(DEZ + HQ) m + (DEZ + H2O) 5 m]n structure, where the value of mxn was fixed at 200, and the value of m was varied between 5, 10, 20, 100, and 200. The hybrid films were designated as Hm, and their surface morphology was observed by scanning electron microscopy to identify the presence of cracks. The mechanical properties of the films were evaluated by measuring the hardness and elastic modulus of an ALD-coated ultra-high molecular weight polyethylene using nano-indentation examinations, and the films' behavior in the wear environment was studied through micro-scratch testing. The results indicate that H5 and H10 hybrid films exhibited no surface cracks, while serious surface cracks were observed in H20 and H100 films. X-ray diffraction analysis showed that structural changes occurred in the hybrid films, and it was speculated that this was related to surface failure. The hardness and elastic modulus values increased with an increase in the m value and showed significant differences between hybrid films. This study demonstrated that the MLD/ALD-based hybrid thin-film approach is an effective means of enhancing surface quality and mechanical properties. The findings of this study have significant implications for the development of advanced materials and coatings for various industrial applications.

Effect of pre-corrosion on the cavitation erosion performance of two aluminum bronzes in 3.5% NaCl solution

The cavitation erosion (CE) behaviors of two aluminum bronzes after pre-corrosion in 3.5% NaCl solution were studied. Results indicated that the CE rate was increased by a factor of 82% for the nickel aluminum bronze (NAB) and 26.73% for the manganese aluminum bronze (MAB) after 30 days’ pre-immersion, compared with the results of the corresponding fresh sample without pre-corrosion. Mechanical impact was dominantly responsible for the CE damage of the pre-corroded samples. Pre-corrosion increased the E/T (the contribution of pure erosion to the CE-corrosion damage) value from 42.66% to 65.20% for the NAB and from 72.46% to 80.13% for the MAB. After pre-immersion, pits appeared at the eutectoid microstructure in the NAB and the network-shaped β phases in the MAB because of selective phase corrosion. This increased the surface roughness and weakened the surface mechanical property. Therefore, large and deep cavities and remarkable material loss were created due to the collapse of eutectoid microstructure in the NAB and the detachment of κ phases and brittle fracture of β phases in the MAB. The grievous CE damage of the MAB samples was highly attributed to the inferior mechanical property. In contrast, pre-corrosion had a much greater influence on the CE behavior of the NAB, because the CE resistance was remarkably deteriorated as a result of the corrosion damage at the eutectoid microstructure.

Fabrication and optimization of multilayered composite scaffold made of sulfated alginate-based nanofiber/decellularized Wharton's jelly ECM for tympanic membrane tissue engineering

In this study, we fabricated a novel multilayer polyvinyl alcohol (PVA)/alginate sulfate (ALG-S) nanofiber/decellularized Wharton's Jelly ECM (d-ECM) composite for tympanic membrane perforations (TMPs) tissue engineering (TE). Initially, electrospun PVA/ALG-S scaffolds with different blend ratios were fabricated. The influence of ALG-S ratio on surface morphology, mechanical, physical and biological properties of the nanofibers was studied. Secondly, 3-layer composites were developed as a combination of PVA/ALG-S nanofibers and d-ECM to take synergic advantages of electrospun mats and d-ECM. As part of the evaluation of the effects of d-ECM incorporation, the composite's mechanical properties, in vitro degradation, swelling ratio, and biological activities were assessed. The MTT assay showed that PVA/ALG-S nanofibers with 50:50 ratio provided a more desirable environment to support cell growth. A composite containing 25 mg/cm2 d-ECM was determined as the optimal composite through MTT assay, and this composite was used for animal studies inducing TMP regeneration. According to the in vivo studies, the optimal composite not only stimulated the healing of TMPs but also shortened the healing period. These results suggest that a multilayer nanofiber/hydrogel composite could be a potential platform for regenerating TMPs.

Performance degradation mechanism of γ-ray irradiated sol-gel silica film

γ-ray radiation effect on sol-gel silica films was investigated at different absorbed doses ranging from 10 kGy to 1000 kGy. The defect and microstructure evolutions of silica films were analyzed to understand the performance degradation behavior and mechanism of the γ-ray irradiated silica films. The cracks appear on the silica film surface and further expand at larger γ-ray absorbed dose, while surface roughness slightly decreases. During γ-ray irradiation, the thermal effect and the increased rate of diffusion-controlled process lead to the condensation of Si-OH groups and the recombination of ODCs. However, the ionization of atoms leads to generation and accumulation of E′ centers and NBOHCs. γ-ray irradiation leads to the reductions of bond lengths and bond angles of Si-O-Si groups, thus causing the densification of films. The refractive index and mechanical property firstly enhance and then reduce with the increase of absorbed dose associated with the change of silica film density. After γ-ray irradiation, the decreased contact angle and increased surface free energy indicate the reduction of anti-pollution ability of silica films. The dose-dependent surface quality, defects and mechanical properties determine the variation in laser-induced damage threshold (LIDT) of silica film. The results provide a reference to control the structural damage and performance degradation of silica films, which is very important for the research of safe operation of high-power laser facilities for inertial confinement fusion (ICF).

A novel ultrafast laser ablation fracture polishing method to simultaneously smoothing and improving the surface quality of Al2O3 ceramics with high roughness

Al2O3 ceramics are widely used in industry due to their excellent mechanical and physical properties. However, microcracks, voids and high surface roughness (Sa) on the surface of Al2O3 ceramic parts produced in conventional industrial or additive manufacturing have been one of the technical bottlenecks limiting their high-performance applications. In this paper, a novel method of ultrafast laser ablation fracture polishing (ULAFP) of Al2O3 ceramic parts is proposed for improving the surface quality and enhancing the mechanical properties of the polished surfaces. The ULAFP method is developed with an ultrafast laser, which can be set up as a picosecond (PS) or a femtosecond (FS) laser. The PS laser is used to form a remelting layer on the surface to eliminate surface void defects. Combining laser ablation and laser thermal stress-induced crack extension effects, the FS laser is used to rapidly remove the remelted layer and obtain a surface free of crack defects and finally implement FS laser layer-wise ablation to achieve smoother surface finish. The FS laser energy density is controlled at a critical state close to the ablation threshold of the material to avoid surface defects. This ULAFP can reduce the surface roughness (Sa5.254 μm) polishing of Al2O3 ceramics to 0.80 μm, while controlling the total ablation depth of the polishing process to below 100 μm maintaining the dimensional accuracy of the part and dramatically improving the mechanical properties of the polished surface. Compared with the original surface, the hardness and elastic modulus of the polished surface improved by 104.6% and 63.9%, respectively.

Intelligent Additive Manufacturing Architecture for Enhancing Uniformity of Surface Roughness and Mechanical Properties of Laser Powder Bed Fusion Components

In the Laser Powder Bed Fusion (L-PBF) process, 3D components with complex geometries are fabricated in a layer-by-layer fashion by using a controlled laser beam to selectively melt particular regions of the metal powder bed. However, due to the stochastic nature of the L-PBF process, the top surface roughness of each solidified layer tends to be different even when the optimal processing conditions for the different positions on the build plate are employed. As a result, the mechanical properties of the built components frequently vary from one component to the next. Accordingly, this study proposes an Intelligent Additive Manufacturing Architecture (IAMA) for controlling the surface roughness of each build layer through an appropriate adjustment of the laser re-melting parameters. The IAMA architecture comprises five modules, namely In-Situ Metrology (ISM), Ex-Situ Metrology (ESM), Automatic Virtual Metrology (AVM), Additive Manufacturing Simulation (AMS) and Intelligent Compensator (IC). The feasibility of the proposed architecture is demonstrated by comparing the top surface roughness of cubic and mechanical strengths of tensile test samples built using the proposed method with those built using a traditional L-PBF approach without surface roughness control. It is found that the samples fabricated using the IAMA approach have an average top surface roughness of 1.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m and a standard deviation is 0.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m. By contrast, the samples produced using the traditional L-PBF approach have an average surface roughness of 13.45 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m and a standard deviation of 2.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m. In addition, the specimens produced with the assistance of IAMA architecture have an average tensile strength of 1013 MPa with a standard deviation of 69.5 MPa, while those printed without surface roughness control have an average tensile strength of 903 MPa with a standard deviation of 101.4 MPa <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —As L-PBF produce part in a layer-by-layer manner, therefore, the roughness on the top surface of previous layer have a strong influence on the printing quality of current layer. The variations of surface roughness will lead to the fluctuation of mechanical properties of the fabricated components. Additionally, to the best of author’s knowledge, current commercial L-PBF machines can not actively control the surface roughness of samples during the process. The proposed IAMA in this work can predict and control the roughness on the top surface of each layer during L-PBF process. Therefore, the constructed architecture has strong potential for integrating into the commercial L-PBF machine for controlling the surface roughness on the top of the parts during the manufacturing process. As a result, the quality of the fabricated components is expected to be in consistent. Accordingly, L-PBF machine equipped with IAMA will have a strong potential in applying for mass production of the components in aerospace and automobile industries.

К вопросу о биосовместимости керамических имплантатов при оказании ортопедической помощи.

When organizing orthopedic care, specialists should be aware of scientific data regarding the ability of the zirconia implant system used to osseointegrate. The biocompatibility of implants depends on various parameters such as the nature of the material, chemical composition, surface topography, chemical composition and loading, surface treatment, physical and mechanical properties. Zirconium has a high biocompatibility with soft tissues, resistance to bacterial biofilms. Zirconia implants are a promising alternative to titanium, especially for titanium allergic patients.

Effect of laser surface remelting on Microstructure, mechanical properties and tribological properties of metals and alloys: A review

Surface defects like porosity, cracks, coarse grains, surface roughness, etc. have a huge impact on the strength and performance of materials. Due to this, surface treatments have become an important part in the field of materials to attain certain desirable mechanical properties and surface properties. Surface of parts treated with laser surface remelting exhibits excellent surface and mechanical properties. It is a computer-based technique which provides the advantage of treating selective surfaces. Laser surface remelting tends to enhance corrosion resistance, microhardness, wear resistance, fatigue strength, and tensile strength of the materials. To achieve certain mechanical properties with laser surface remelting, an optimized set of laser processing parameters is essential. Laser surface remelting has become a compulsory treatment for parts manufactured by Additive Manufacturing (AM) processes as these processes provide poor surface, porosity, and hot cracking defects which ultimately affect the performance of parts. This paper critically evaluates the advancements which have been made in the field of laser surface remelting to get better surface quality, improved mechanical and tribological properties.

Effect of GO content on microstructure and mechanical properties of Ti6Al4V coating reinforced artificial joint.

In this study, we have innovatively proposed a method of in-situ synthesized TiC hard phase to improve the surface mechanical properties of artificial joint materials (Ti6Al4V). In order to explore the optimum graphene oxide (GO) addition, GO/Ti6Al4V composite powders with different proportions (0, 0.5, 1.0, and 1.5 wt.%) were prepared. The homogeneously dispersed GO/Ti6Al4V composite powder was prepared on Ti6Al4V substrate by laser cladding technology. The microstructure, phase composition, and mechanical behavior of GO/Ti6Al4V composite coatings were studied by scanning electron microscope (SEM), optical microscope (OM), energy dispersive spectrometer (EDS), tribometer, hardness tester, and surface profiler. The results showed that the addition of GO could significantly improve the mechanical properties of TC4 substrate. During the preparation of the coating, the grain size of in-situ TiC phase was nanoscale and was distributed between acicular martensite, which played a critical role in enhancing the mechanical properties of the coating. The TiC phase distributed between acicular martensite refine the grain size of phase and improve the cutting resistance of the coating. Nevertheless, excessive GO decreased the fluidity of the molten pool, and micro holes tended to generate in the coating, which had a negative impact on the mechanical properties of the coating. At the GO content of 0.5 wt.%, the microhardness of the GO/Ti6Al4V coating was 1.325 times that of pure Ti6Al4V. Under the friction environment of simulated body fluid solution, the average friction coefficient was approximately 0.307 and the wear rate decreased to 3.5 × 10-7 mm3/N · m.

Nanorheology and Nanoindentation Revealed a Softening and an Increased Viscous Fluidity of Adherent Mammalian Cells upon Increasing the Frequency.

The nanomechanical response of a cell depends on the frequency at which the cell is probed. The components of the cell that contribute to this property and their interplay are not well understood. Here, two force microscopy methods are integrated to characterize the frequency and/or the velocity-dependent properties of living cells. It is shown on HeLa and fibroblasts, that cells soften and fluidize upon increasing the frequency or the velocity of the deformation. This property was independent of the type and values (25 or 1000nm) of the deformation. At low frequencies (2-10Hz) or velocities (1-10µm s-1 ), the response is dominated by the mechanical properties of the cell surface. At higher frequencies (>10Hz) or velocities (>10µm s-1 ), the response is dominated by the hydrodynamic drag of the cytosol. Softening and fluidization does not seem to involve any structural remodeling. It reflects a redistribution of the applied stress between the solid and liquid-like elements of the cell as the frequency or the velocity is changed. The data indicates that the quasistatic mechanical properties of a cell featuring a cytoskeleton pathology might be mimicked by the response of a non-pathological cell which is probed at a high frequency.

Microstructure and mechanical properties of superficial surface and subsurface layers in the cutting of hardened steel under cryogenic cooling

Hardened steel parts extensively utilized in manufacturing fields, including automobiles and molds, are difficult to cut and process. Cryogenic cooling is an effective method for reducing tool wear and improving surface quality. However, knowledge about the microstructure and mechanical properties of the hardened steel cutting under a cryogenic cooling condition is severely limited. Herein, low-speed and high-speed cutting experiments with different wear tools were designed to investigate the characteristics and mechanisms of the microstructure, residual stress distribution, and hardness distribution of the superficial surface layer (SSL, including the white and transition layers) and subsurface layer (SL) of hardened steel cutting via cryogenic cooling. Results showed that microstructure changes caused by plastic deformation occurred in both the white and transition layers, whereas no changes occurred in the area below the transition layer. No phase transformation and recrystallization occurred in the white layer, the transition layer, and the area below the transition layer. The intense dislocation slip and strong plastic deformation are the keys to the formation of the white and transition layers. The hardness distribution curve included the surface hardening peak, SL softening valley, and SL hardening peak. The combined effect of fine grain strengthening and dislocation strengthening is the primary mechanism for forming the surface hardening peak. The peak residual tensile stress induces a SL softening valley in the hardness curve, whereas the peak residual compressive stress induces a SL hardening peak in the hardness curve.

Study on the process optimization and wear resistance of electron beam cladding AlCoCrFeNi coating on 253MA austenitic stainless steel surface

This study employs a continuous scanning electron beam to deposit AlCoCrFeNi composite cladding on the surface of 253MA austenitic stainless steel to enhance its surface properties. The characteristics were examined through a scanning electron microscope (SEM), backscattered electron diffraction (EBSD), and white light interferometric three-dimensional surface profile instrument. This study investigated the effect of electron beam process parameters on the surface organization and mechanical properties of 253MA steel. The sample surface was divided into four zones: overlay, bonding, thermal influence, and substrate, according to the results. Coarse columnar and island-shaped crystals composed the overlay zone, while equiaxed austenite grains primarily constituted the substrate. With the increase of the beam current, the microstructure's grain size decreased, the substructures increased, and the BCC phase transformed into the FCC phase. The grain size slightly decreased, substructures changed marginally, and the BCC phase increased as the scanning speed increased. Additionally, the microhardness and mechanical properties of the overlay layer increased significantly, and wear volume and wear rate decreased progressively with the increase in beam current and scanning speed. At a beam current of 18 mA and a scanning speed of 200 mm/min, the surface hardness of 253MA steel reached the maximum value of 520 HV. When the beam current was 24 mA, and the scanning speed was 200 mm/min, the wear volume and wear rate of the overlay sample were minimal, accounting for 37.4% of the original sample's, and its wear resistance was 2.67 times more than that of the substrate.

Forming of pure titanium tubes by combined spinning-ultrasonic surface rolling process: Microstructure and mechanical properties

Spinning-ultrasonic surface rolling process (S-USRP) combined forming technique, as a potential method for manufacturing thin-walled tubes with high performance, not only forms gradient nanostructures on the surface of materials, but also has advantages of reducing surface roughness and improving mechanical properties. In this work, the S-USRP was applied to manufacture thin-walled pure titanium tubes, and the surface morphologies, microstructure and mechanical properties of titanium tube formed by different forming methods (including spinning forming, USRP, and S-USRP) are investigated and compared. The results indicate that spinning ripples on the surface of CP-3 Ti tube can be improved obviously after introducing USRP treatment. Compared to USRP, the titanium tube formed by S-USRP has thicker gradient microstructure layer and finer grains, which is attributed to the spinning pre-deformation, resulting in decrease of strain threshold of grain refinement during USRP treatment. Microhardness after S-USRP varies more slowly between the plastic deformation layer and matrix compared with that after USRP. Tensile strength of titanium tube after S-USRP is promoted by 26.2 % owing to the grain refinement, deformation twins strengthening and synergy strengthening of gradient structured layer. However, the elongation reduced significantly because titanium thin-walled tube has the characteristics of coarse grains on one side and nanocrystalline on the other, leading to premature instability in the tensile process. In addition, the tensile strength and fracture strain of titanium tube after spinning-two passes ultrasonic surface rolling process are promoted compared to the spinning forming alone. This indicates that gradient microstructure with a certain thickness on the surface of components can achieve good strength-ductility synergy. The research in this article is of great significance to the development of high-performance forming processes for thin-walled tubes.