Materialwissenschaft und Werkstofftechnik最新文献

Conventional liquid lubricants prove inadequate for effective lubrication in conditions characterized by high temperatures and high vacuum environments. In such extreme scenarios, powder lubricants emerge as a more viable solution. The present study is to conduct a series of experiments using a reciprocating wear test setup and evaluate the capability of four different machine learning models in analysing the tribological attributes of metals when lubricated with three distinct powder types: zirconium dioxide, copper oxide, and molybdenum disulfide, specifically under conditions of elevated contact pressures and dry environments. The experiments were systematically carried out encompassing a range of load and temperature combinations. Four different machine learning models (MLP, KNN, extreme gradient boosting and light gradient-boosting machine) were used for predicting the coefficient of friction of metals lubricated with different powders. Extreme gradient boosting machine learning model gives better result than the other models with mean absolute error, root mean squared error, R² value and average absolute deviation percentage of 0.0215, 0.0278, 0.9962 and respectively.

Due to their low thermal conductivity and high thermal expansion, austenitic chromium-nickel steels have an increased tendency to distortion during welding. In industrial sectors such as rail vehicle construction, there is a high demand for geometrical precision that is not met by distorted components. Introducing a low transformation temperature (LTT) effect in the weld seam influences the stress distribution, which effects the formation of welding distortion. The low transformation temperature effect is achieved by in situ alloying using commercially available materials. The demonstrators made of stainless steel (X2CrNiN18-7/1.4318) were welded with a low-alloy filler metal G4Si1. The low transformation temperature effect is assessed by energy dispersive x-ray spectroscopy and hardness measurements. The effect on distortion was investigated by measuring the demonstrators with a coordinate measuring system and the results were compared with the reference stainless steel demonstrators with stainless filler metal. The alloying process resulted in a reduction of the alloy content to 14.4 m% chromium and 5 m% nickel and a medium-high hardness of 361 HV 0.2 to 383 HV 0.2. The low transformation temperature effect achieved leads to a significant reduction in welding distortion of up to 78 % compared to the similar reference demonstrators.

This paper systematically studies cladding materials prepared by mixing 316 L and 2Cr13 alloy powders in different ratios. The powder was melted and deposited on a Q235B carbon steel substrate using laser melting deposition with a high Ni transition layer and appropriate laser process parameters. Bimetallic plates with a thickness of 10 mm ±0.5 mm was prepared. The microstructure of different parts of the bimetallic plates and the impact toughness and hardness were observed and tested under different alloy ratios. The results indicate that the Nickel-Chromium equivalence ratio increased, the hardness and wear resistance of the bimetallic plates increased, and the degree of eutectic segregation in the eutectic structure also increased. When the ratio of 2Cr13 reached 60 %, the impact toughness increased significantly, and the needle-like second phase appeared in the structure. X-ray diffractometer analysis determined that this second phase was (Fe, Cr)₇C₃. After Charpy impact testing, the fracture microstructure showed many dimples, indicating micropore aggregation fracture. This study guides preparing large-thickness cladding layers on iron and steel parts using laser melting deposition.

To enhance the friction and wear performance of TC4 titanium alloy, micro-arc oxidation(MAO) coating was fabricated on its surface, which was subsequently sealed with a modified graphene/epoxy resin coating to form a composite coating of micro-arc oxidation -modified graphene/epoxy resin. The friction and wear performance of samples sealed by different methods are analyzed and characterized using a scanning electron microscope, an energy spectrometer, and friction and wear tester. The results indicate that the modified graphene/epoxy resin coating successfully combines with the micro-arc oxidation coating and fills the pores, thereby enhancing the friction and wear performance of the composite coating. In tribological tests, compared with other samples, this composite coating has a lower friction coefficient and specific wear rate, showing excellent friction and wear performance, and its main wear mechanism is adhesive wear. Therefore, the fabrication of a micro-arc oxidation -modified graphene/epoxy resin composite coating can improve the friction and wear performance of TC4 titanium alloy.

Stainless steel grade 304, is one of the most utilized grades of stainless steel and it is chosen for its corrosion resistance. The ideal option is 304, since its lower carbon content lowers intergranular corrosion, especially if corrosion resistance is a top goal for a project. This research work investigates the mechanical and microstructural characteristics of a novel double side fiber laser welded stainless steel 304 plates. Double side fiber laser welding technique is used to fabricate a butt joint with plates of thickness 5 mm. With a laser frequency of 25 Hz, speed of 6 mm ⋅ s⁻¹, and a heat input of 1.4 kW in terms of power is applied to the joint, resulting in a maximum depth of penetration of 2.7 mm. The same parameter is applied on both sides of the plate. The dendritic structures are observed through micrographs of weld and pure metal captured using an optical microscope. Experiments such as tensile, bend, microhardness and impact test have been conducted to ensure the quality of weldment. The weldment consists of austenite and δ-ferrite. X-ray diffraction reveal presence of both austenite and ferrite in the weldment. Ductile mode of fracture occurred during failure of tensile samples.

In this paper glass/chicken feathers reinforced epoxy composite and glass/chicken feathers reinforced polyester composite was prepared in the laboratory at different percentage of the glass and chicken feathers. Tensile properties, flexural properties, shore hardness and impact strength of the glass/chicken feathers reinforced epoxy composite and glass/chicken feathers reinforced polyester composite was studied experimentally and compared at different percentage of the glass and chicken feathers. The composite will be used in humid and corrosive environment; therefore, water absorption and acid corrosion test were performed. To understand the degradation behaviour of the composite, soil test was performed. Scanning electron microscopy analysis was carried out to find the fracture and interfacial characteristics of the composites after tensile test. This hybrid composite can be used in automobile, structural and defense sector.

This work is carried out to investigate the anisotropic hardening behavior of MS1180 steel through experiment and analytical modeling. Dogbone and hydraulic bulging specimens were machined to test the mechanical behavior of MS1180 steel plate under different loading directions and stress states. The loading process was recorded by the three-dimensional digital image correction system. The result uncovers that the strength under equi-biaxial tension is larger than that under uniaxial tension. Mechanical behavior under different loading directions presents the obvious difference related to the plastic strain. Hardening behavior under uniaxial tension and equi-biaxial tension is characterized by the Swift-Voce and polynomial equations, respectively. Three yield functions are adopted to describe the anisotropic behavior, including Yld2000-2d, S-Y2009, and CQN-Chen. A convexity analysis method based on geometric definition is used to determine the convex region of the CQN-Chen yield surface under large strain. By comparing the yield surfaces of the three yield functions under different plastic strain, the CQN-Chen yield function possesses a more flexible and reasonable characterization ability than the Yld2000-2d and S-Y2009 yield functions. The anisotropic hardening behavior of MS1180 steel plate is modeled with an error of less than 0.03 by the CQN-Chen yield function, showing high prediction accuracy.

Due to its high energy intensity and the associated high welding depth, electron beam welding is particularly suitable for welding steel plates with high wall thicknesses. These are used, for example, in offshore wind power systems. However, due to the cooling conditions, the required cold toughness for offshore applications is often not achieved. The aim is to develop S355 ML steels – within the EN10025 4 standard – for welding monopiles for wind turbines. For this purpose, three parameters with different energy input are developed on three steels. The tests are carried out on plates with a wall thickness of 80 mm, whereby a full penetration weld must be achieved. The resulting top and bottom bead of the welds meet the standard DIN EN ISO 13919-1. The parameters have an energy per unit length of 9.5 kJ mm⁻¹ to 15.5 kJ mm⁻¹. The resulting weld seams have an average width of 5.5 mm to 7.5 mm, and burn-off of the manganese alloy element is observed, particularly on the top side of the seam. In addition, T8/5 times close to the weld seam of 11 s to 27 s are estimated using a simulation.

The biomass composites were prepared by hot molding with a pressure of 10 MPa, a temperature of 125 °C, a time of 15 minutes using soybean straw powder, poplar wood fibers, and soy protein as raw materials. The effects of different straw species, the ratio of soybean straw powder to poplar wood fibers, the particle size of soybean straw powder, and the theoretical density on the performance of biomass composites were investigated. The experimental results show that under the condition that the ratio of soybean straw powder and poplar wood fibers is 1 : 1, 20 mesh to 40 mesh soybean straw powder and 20 mesh to 60 mesh wood fibers are selected to copolymerize and strengthen the soy protein biomass composites when the theoretical density is 0.80 g/cm³, the actual density of the biomass composites is 0.90 g/cm³, the tensile strength was up to 22.04 MPa, and the bending strength was up to 44.92 MPa. Biomass composites have good water resistance while obtaining excellent mechanical properties. The above figures not only meet the relevant technical requirements of automotive interior parts but also enable the lightweight design of automobiles and the sustainable development concept of green, low carbon, and environmental protection.

In the current experimental work, using secondary phase hard nano titanium carbide (TiC) particles as reinforcement, two different magnesium metal matrices i. e., AZ31B/TiC and AZ61 A/TiC composite materials were synthesized by friction stir processing. Using the traditional testing approach for the developed materials, the simultaneous gain in metallurgical, mechanical, electrical, and tribological characteristics compared to the base substrate was examined. The microstructure study results for AZ31B/TiC and AZ61 A/TiC composites showed a uniform distribution of reinforced particles as well as an evolution in grain size, from 82 μm to 4.2 μm and from 74 μm to 3.7 μm, respectively, which consequently contribute in a significant gain in the microhardness of both composites i. e., around 2.2 times and 2.67 times respectively, greater than the base metal. When compared to monolithic alloys, the synthesized AZ31B/TiC and AZ61 A/TiC composites showed improvements in the areas of tensile strength, compressive strength, and coefficient of friction up to 1.81 times, and 1.64 times, 1.74 times and 1.58 times, and 57.92 % and 58.47 %, respectively. Furthermore, these improvements in characteristics also increase the final strengthening of the nanocomposite and reduce electrical conductivity.