Materialwissenschaft und Werkstofftechnik最新文献

Scientific studies involving hafnium have grown significantly in recent years due to the potential applications that this metal has. These potential applications come from the properties of this element, which for many years since its discovery were neglected in research. Among the factors that contributed to this was the high cost of extracting its ores from nature. One of the properties is the solubility of this metal in concentrated sulfuric acid, reacting to form hafnium(IV) sulfate and hydrogen gas. This acid is one of the few that can dissolve this metal, since hafnium is highly resistant to corrosion. The present work reports a chemometrically planned study on the surface of hafnium metal during its dissolution in sulfuric acid at different temperatures (13 °C, 25 °C and 97 °C) and for different times (5 minutes, 60 minutes and 120 minutes). Samples of metallic hafnium were completely immersed in sulfuric acid, subsequently characterized by scanning electron microscopy and the mass variation of the samples was analyzed. The corrosion of hafnium occurs only after the rupture of the protective film of hafnium(IV) oxide of the material, this rupture being faster as the temperature increases.

Quality machining on stainless steel AISI 304 is achieved by reducing the interface temperature generated due to high hardness and compressive frictional force. Temperature rise during the turning operation was observed to cause a weak tool nose, and machining surface. Enhanced lubricant properties can alleviate these issues and help reduce tool nose wear while increasing machined surface quality. Nano-lubricants have been prepared to meet the functional requirements for machining. Emulsifier oil-based nanofluids perform exceptionally well in heat transfer during machining. The present investigation focuses on copper oxide nanoparticles addition in “Society of Automotive Engineers 30” emulsifier oil at two different weight percentage: 1.5 wt.-% and 2.25 wt.-%, aiming to improve heat transfer and machined surface quality. In this experimental study, a computer numerical control machine tool, DCMT120404 insert, tool dynamometer, and infrared pyrometer are utilized for the machining operation. It was observed that 2.25 wt.-% copper oxide mixed emulsifier-nano cutting fluid exhibited minimum cutting force and work-tool interface temperature while enhancing the surface quality.

High-chromium cast iron is a good wear-resistant material. Its heat treatment regime has an important influence on the evolution of its microstructure and properties. This study investigates the microstructural attributes and properties of Fe–4.0 C–35.0Cr–0.5Si (wt.%) low-silicon hypereutectic high-chromium cast iron subsequent to quenching at 1050 °C, followed by tempering at diverse temperatures. The microstructure was examined using optical microscopy, scanning electron microscopy, and X-ray diffractometry across varied tempering conditions. Furthermore, microhardness and wear resistance were conducted via a microhardness tester and a wear testing machine. The results show that the quenching heat treatment promotes the transformation of the matrix from austenite to martensite, while also promoting the precipitation of secondary carbides of M₂₃C₆-type. The subsequent tempering heat treatment engenders transformations involving retained austenite to martensite, amplifies the precipitation and enlargement of secondary carbides, and induces martensite decomposition. As the tempering temperature increases, primary and eutectic carbides exhibit minimal changes, while the secondary carbide morphology evolves from granular to reticular. The matrix composition predominantly comprises martensite, interspersed with a minor fraction of austenite. It is worth noting that the alloy has the highest hardness and wear resistance after quenching at 1050 °C and then tempering at 400 °C.

Sensor placement is one of the vital concerns in civil structure monitoring. A sensor placement strategy based on a damage assessment method has been introduced for beam-like structures. An existing damage detection method adapted to multi-modes and different types of beam-like structures. Then, it is numerically verified to be suitable for detecting any damage location in a 100 degrees of freedom mass-spring system. Depending on the noise in the response and the limited measurements, the results demonstrate the validity of using the multi-mode damage indicator. However, there are limitations to this method due to mode shape saddle points. Sensor deployment schemes have been proposed to address the restriction. In contrast to the corresponding procedure, this method does not rely on the optimization algorithm. Sensor placement strategies involve the simultaneous use of accelerometers and large-area electronics.

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.