Serpentine, whose main component is magnesium silicate hydroxide (MSH), has excellent friction properties. To explore the self‐repair mechanism of pure MSH under natural working conditions, MSH was synthesised by hydrothermal method and modified with oleic acid (OA). The optimal concentration of OA‐MSH was added to the air‐conditioning compressor simulator. The self‐repairing layers were studied by scanning electron microscope, Raman, and transmission electron microscope. The results show that OA‐MSH is well uniformly dispersed in lubricating oil and has significant anti‐friction performance. When the concentration is 1.0 wt%, the friction performance is best. The surface self‐repairing layer is composed of a 1.5 μm thick transition layer and a 20 nm amorphous carbon‐based film under the conditions of air‐conditioning compressors. There are dislocation cells, nanocrystals, and Mn2(Fe2+, Mg)5Si8O22(OH)2 in the transition layer. The formation mechanism of the self‐repairing layer on piston surface can be divided into three stages: nano‐crystallisation, mechanical alloying and lubricating oil crack deposition.

Using magnesium silicate hydroxide as additive of lubricating oils for reducing friction in engineering equipment/machinery has been researched intensively. However, some mechanism relating to the growth of the self-repairing layers on the won surfaces is still not clearly explained. At the same time, using magnesium silicate hydroxide (MSH) in the form of nanorods showed great promise in reducing friction and wear. In this study, surface-modified MSH in the form of nanorods was used as additive of polyolester oil (POE) which was then used for the lubrication of compressor vanes. The sample parts were studied on the morphology and the microstructure of the self-repairing layer in a great depth. The results showed that self-repairing layers with different thicknesses were generated on the worn surfaces when the POE with 1 wt.% nanorods-MSH was used. It was found that the self-repairing layers consist of organic–inorganic composite membranes, and with increase of working time of the compressor vanes, the self-repairing layers become denser and thicker, while their micro-structural form remains to be similar. The situ-repairing capability of the metal surfaces (roller-vane pair of the compressor) enforced by the MSH nanorods is very significant, indicating high potential for industrial applications where boundary and mixed lubrications are needed.

Magnesium silicate hydrosilicate (MSH) was added into a lubricating oil as an additive for testing self-repairing capability of a friction pair when it is lubricated. A systemic examination of the structure and chemical composition of the surfaces with self-repairing layers was carried out with an expectation of reducing the wear and even fully repairing the surfaces through the newly grown layers. The wear behaviour of the surfaces, including that having the deposited self-repairing layers, was examined with reference to the lubricated steel friction pairs, being loaded under different working conditions. The treated surfaces and their chemical composition were examined using scanning electron microscopy (SEM) and EDS/XRD, respectively. The results showed that the level of the concentration of the additive in the lubricating oil does not affect the chemical composition of the self-repairing layer formed, and lubricating oil with 1.0% MSH is an optimal concentration value for reducing friction and wear for the friction pairs examined. At the same time, the grown self-repairing layers become more uniform as the duration of sliding between the two parts in a friction pair increases.

Induction heating is one of the most popular metal heating technologies due to its high heating rate and high energy efficiency. This method is suitable for heating workpieces/blanks in different shapes, sizes and materials. Although induction heating of metal sheets has already been investigated by various research organizations and industrial companies, information concerning the induction heating of aluminium blanks is limited. Considering that hot stamping of aluminium sheets for automotive and aerospace applications is currently attracting a lot of attentions, it is timely important to gain more understanding on this technology by conducting in-depth investigations. Especially, investigations are required to address issues relating to the uneven temperature distributions developed in the metal sheets when they are heated, so that optimum designs could be obtained to improve the technology and its applications. This paper presents an in-depth analysis conducted recently for the investigation into heating schemes and process parameters in induction heating of aluminium sheets, mainly using 3D FE simulations, based on a general experimental validation. Different material, coil geometric and power-setting factors were considered during the modelling and analysis to examine their effects on the heating efficiency and developed temperature profiles. It was revealed from the simulations that design features of the induction coils affect the uniformity of the developed temperatures in the metal sheets. It is shown that an optimised combination of the coil design and the power setting could help to achieve higher heating rates, at the same time, also to achieve higher temperature-distribution uniformity. At the end of this paper, a discussion of practical factors that affect applications of induction heating of aluminium sheets for hot stamping applications is presented.

Induction heating is one of the most popular metal heating technologies because of its high heating rate and high energy efficiency. This method is suitable for heating workpieces/blanks in different shapes, sizes and materials. Induction heating of metal sheets has been investigated by various research organizations and industrial companies. However, information concerning the induction heating of aluminium blanks is limited. Further, investigations were required by industries to address the issues relating to the uneven temperature distributions developed in the metal sheets so that an optimized design could be developed to help the enhancement of the technology. Aiming at the study of the induction heating process for hot stamping, especially the temperature distribution developed in the aluminium sheets, this paper presents in-depth analysis of induction heating using 3D FE simulations, involving uses of DEFORM and COMSOL. Different coil arrangements, level of powers, frequencies, cycle times, etc. have been modelled and simulated to examine their effects on the heating efficiency and developed temperature profiles in the Aluminium sheets. It is revealed from the simulations that design features in the induction coils like shapes of cross-sections and angles of coil corners affect the uniformity of the developed temperatures in the metal sheets. Heating with an optimized combination of the coil design and the power setting could help to achieve higher heating rates and temperature uniformity. Nevertheless, the application could be constrained by some practical factors.

In this study, investigations were conducted to evaluate a new type of rapid treatment designed to alter the microstructures of cemented carbides for improved milling and mechanical performances. The effects of a treatment that combined a pulsed magnetic field and a pulsed current (MCT) on the milling performance, mechanical properties, and conductivity of the cemented carbides (WC-6Co) were studied. The results show that the wear loss of the cemented carbides decreases by nearly 35 pct and the milling force decreases significantly after MCT. The hardness and transverse rupture strength are enhanced by approximately 2 and 12 pct, respectively. The conductivity of the electromagnetically treated sample exhibits a decrease of 5 pct. Microstructural analysis reveals that the electromagnetic treatment tends to increase the dislocation density within the cemented carbides, which strengthens the material and decreases the conductivity.

As demands on miniature products increase significantly, a rapid prototyping and production system for highly flexible and cost-efficient production of micro components made from a wide range of materials is needed. In present work, the Micro-forming Fields Activated Sintering Technology (Micro-FAST) with the coupling effects of electrical and pressure fields as the dominant driving force, has been proved to be very successful in the fabrication of the nearly full-density micro-cylinder parts from WC-8Co-xTi-nC powders (x=4, n=2 or x=6, n=0). The influence of heating rate and composition of titanium and carbon has been investigated. Based on the analysis of the relative density, microstructure and mechanical properties, high density (up to 99.7%), fine grain sizes and good mechanical properties could be obtained by Micro- FAST to sinter WC-TiC-Co Cemented Carbide bodies under a low sintering temperature (1200 ℃).

The effects of magnetic field(M), electropulsing(E) and electromagnetic(EM) treatment on the microstructure , lattice parameter, dislocations and microhardness of the undeformed solid TC11 alloy were investigated . The results show that the volume fractions of primary α phase increase by 4% and 3%, respectively, after E and EM treatment, indicating that the external fields can provide additional driving force for the phase transformation of β to α. The axis ratio c/a of α phase increases after the treatments, implying strengthened α phase by solid solution. Meanwhile, the dislocation entanglement density decreases and the surface microhardness is reduced after the EM treatment. A 2.6% decrease in hardness is produced. The presented study shows external field treatment can impose significant influence on the properties of the materials by altering microstructures and movement of dislocations of the material.

目的 分析不同工况对表层自修复层的影响,探究羟基硅酸镁纳米管在摩擦磨损过程中的作用机理.方法 以人工合成的羟基硅酸镁纳米管Mg3Si2O5(OH)4为自修复添加剂,在油润滑实验条件下进行铁基金属摩擦副摩擦磨损实验.利用SEM、EDS、激光拉曼光谱仪及显微维氏硬度计分别对自修复层厚度、自修复层元素组成、自修复层表面结构及自修复层表面显微硬度进行表征.结果 在转速为1000、2000 r/min时,载荷为200、300、400 N的实验条件下,表层均有自修复层的生成.在转速为2000 r/min、载荷为400 N时,表层自修复层的厚度最大.实验过程中,摩擦副得到修复,出现负磨损,自修复层的主要元素为C、O、Fe等.高转速载荷工况下,其摩擦系数相比基础油下降0.008.自修复层为类金刚石结构,其平均硬度值在673HV左右,为基体的1.87倍.结论 羟基硅酸镁、基础油及磨屑三者共同作用,在高能摩擦作用下合金化,形成高硬度的类金刚石结构修复层,能有效保护摩擦副工作面,并延长寿命.加大实验载荷与实验转速,能加速自修复层的形成,实现摩擦副负磨损,并降低摩擦系数.

In this study graphene platelet (GPL)-reinforced yittria stabilised zirconia (YSZ) composites were fabricated using a spark plasma sintering furnace to evaluate a new type of structural material for engineering applications. The effects of the content of GPLs on the microstructures and mechanical performances of the GPL/YSZ ceramic composites were investigated. It is found that GPLs are well dispersed in the YSZ matrix and GPL/YSZ composites are nearly fully consolidated. The addition of GPLs significantly refines the ceramic matrix and a higher percentage of GPLs lead to a finer microstructure. GPLs retain their structural integrity during the high temperature processing and phase transformation of YSZ from the tetragonal to monoclinic occurs with the presence of GPLs. Both hardness and toughness of the YSZ matrix are improved by adding GPLs. A maximum improvement of around 7% and 60% in hardness and toughness are achieved respectively.