Papers by Keyword: Micro-Texture

Abstract: Take water hydraulic slide valve core as the research object. Laser surface texturing (LST) technology was used to improve the valve core carrying capacity and hydrodynamic lubrication characteristics, which can process micro-texture on the surface of the core. And CFD method was taken to calculate flow field of smooth and laser surface texturing core respectively. For studying the influence of valve core micro-texture and valve core overlap lengths on hydrodynamic lubrication characteristic and carrying capacity of the core, core surface pressure distribution, surface pressure and friction force curves were drawn. Results show: The smooth valve core does not produce hydrodynamic lubrication effect, but textured valve core can bring the oil film load capacity, so as to make the effect of mixed friction between valve core and sleeve weaken. And along with the decrease of the core overlap length, the carrying capacity on the surface of the textured valve core does not decrease but increase when the valve core overlap length amount is greater than 2.5mm.The results provide important theoretical reference of studying and applying LST process technology to the valve core friction pair’s lubrication performance.

Abstract: the effects of turning on the gradients of micro-texture and grain size of Al alloy 7075 processed by turning is studied. Analytical models based on Boussinesq equation and stress/force transformation, predict that the equivalent von-Mises stress penetrate almost 1 mm below the machined surface with a maximum of 1400 MPa. The induced temperature below the surface is and reaches up to 240°C. As a result of deformation below the machined surface, the grains below the surface show a preferred grain shape orientation different from the grains in the central region. The normalized population of (121) plane increases at the machined surface compared to the central part of the sample. Orientation distribution functions reveal that at the central part of the sample, the material is mostly randomly oriented and the closest texture component is the recrystallized texture. On the other hand, the strongest texture attribute at the machined surface is β-fiber torsion. The average grain size shows a 10% decreases moving away from center while below the machined surface there is a 50% increase in the average grain size. This can be due to the grain growth caused by higher temperatures right below the machining tool. The reported results provide a toolset to determine the final properties of the material after machining in addition to providing means to more accurately describing the machining mechanics.

Abstract: Hard machinability of titanium alloys severely limits its development in the field of aviation. It has been proved that micro-texture has a good effect on friction-reducing in turning under the conditions of Minimum Quantity Lubrication (MQL). In this paper, cutting tool with micro-texture on its rake face is fabricated and then experiments are carried out under the conditions of dry continuous turning titanium alloys. A dynamometer is set under the workpiece to measure three components of the cutting forces and the data is processed by Business software MATLAB. Average coefficient μ is calculated according to the mechanical model. Experimental results show that under the dry conditions, micro-texture plays a role in the specific cutting parameters while losing its role in most cases. Also the reasons which lead to the failure of improving the friction properties are analyzed.

Abstract: Plane-strain compression testing on HSLA steel samples using single-pass and multi-pass hot-deformation schedules showed that heavy deformation of metastable austenite below A_e3, developed ultra-fine ferrite grains (<3 µm), increased the fraction of high-angle (>15º misorientation) boundaries (>70%), and encouraged the formation of beneficial g-fibre ((ND//<111>) components along with {332}<113> and {554}<225> texture components, minimising the intensity of harmful ‘cube’ texture.

Abstract: High resolution EBSD analysis was carried out under specific experimental conditions (15 to 5 kV) on the skeleton of the modern carbonate brachiopod Gryphus vitreus and resolved nano- to microscale preferred crystallographic orientation patterns undetcted so far. As biologic superstructures are formed by controlled nanoparticle assembly it is essential to resolve their internal structure and texture with the highest possible spatial resolution. Low kV EBSD (15 kV and at 5 kV) provides the required resolution. We observe in the investigated carbonate skeletons a strongly interlocking microstructure of concave/convex grains. The interface topology of the interdigitating structure reaches below the micrometer scale. Individual grains reach sizes up to 20 µm (or even more) in one dimension. They show a mosaic spread of several degrees such that they must be addressed as mesocrystals. Even though the shell consists of three different microstructures with completely different crystal morphologies and grain boundary topologies the crystallographic texture of the three layers is similar. This indicates that distinct control mechanisms prevail when the shell is formed.

Abstract: This study investigates the changes in radial micro-texture via Kearn’s f-factors during single cold pilger reduction of a titanium Ti-3-2.5 alloy as a result of strain path changes from tooling modifications. EBSD results confirm that the texture intensity as well as the radial f-factors can be increased by modifications of pilgering tooling. In addition a switch between the secondary prism planes which lie normal to the pilger direction in the starting tube to primary prism planes after pilgering has been observed.

Abstract: Micro-texturing self-lubricated cutting tools named MTR-1 and MTR-3 were designed and made based on micro-texturing lubricating idea and laser micro-texturing technology. Dry cutting tests on 45^# hardened steel were carried out with these self-lubricated cutting tools and conventional cemented carbide tools named MT0. The cutting temperatures and the morphology of chips were measured. The results indicated that the cutting temperatures with the micro-texturing self-lubricated cutting tools were reduced compared with that of MT0 cemented carbide tools, and the chip coiling was improved.

Abstract: By using techniques of severe plastic deformation a metallic material can be subjected to an enormous strain that is not achievable by conventional methods of deformation. In this study nickel single crystals with different crystallographic orientation and nickel polycrystals were deformed by high pressure torsion. All nickel samples were processed up to the evolution of a saturation microstructure where no further hardening of the material can be observed. In this region all samples develop a similar microstructure and micro-texture. The differences in the fragmentation of the microstructure and the micro-texture development between the single crystals and the polycrystalline aggregate were examined using EBSD. A major difference between single crystals and polycrystals was not only the microstructure evolution at low equivalent strains, but also the development of a stable micro-texture, which is achieved earlier by the use of a polycrystalline aggregate.

Abstract: Local orientation distributions of two neighbouring grains initially orientated near (01l)[100] and (210)[001], in a pure Al poly-crystal aggregate rolled by a reduction of 65% at room temperature have been investigated using electron backscatter diffraction (EBSD) technique. It was found that the rotation angles of zones adjacent to both sides of initial boundary (BP) are less than that of zones remote from the boundary (IP), which reveals that rotation incompatibility and heterogeneity of local orientations within individual grains during rolling. A type of improved Taylor type crystal plasticity models, in which an added prescribed shear (APS) depending on distances from grain boundary proposed, was established to illustrate development of micro-textures in each grain. The results simulated by the APS-Taylor models well agree with the micro-textures examined by EBSD.