Papers by Author: Tao Hong

Abstract: The cooling temperature field, microstructure and properties of an Al-12.7Si-0.7Mg alloy extrusion after an end-quenching experiment at 540 ^oC were investigated by means of an end-quenching test, hardness test, electrical conductivity determination and TEM observations. The results showed that the cooling rate of the alloy extrusion decreases sharply as the distance from the end-quenching spray point increased, when the distance from the end-quenching spray point is within 70 mm. Additionally, the cooling rate of the alloy extrusion decreased slowly along the length of the alloy extrusion when the distance from the end-quenching spray point exceeded 90 mm. The cooling rate of the alloy extrusion at distances of 20 mm and 32.5 mm from the end-quenching spray point exceeded 34 ^oC/s and 24 ^oC/s, respectively. Both hardness and electrical conductivity of the alloy extrusion within 32.5 mm from the end-quenching spray point were comparable to those of the alloy extrusion of off-line quenching at over 520 °C. There was no obvious precipitate in the alloy extrusion matrix 20 mm from the end-quenching spray point, and there were few fine and heterogeneous short rod-like precipitates in the alloy extrusion matrix 32.5 mm from the end-quenching spray point. However, there were many precipitates with lengths of approximately 10 nm in the alloy extrusion matrix 45 mm from the end-quenching spray point, and the lengths of the precipitates increased to approximately 20 nm when the distance from the end-quenching spray point exceeded 57.7 mm. The critical cooling rate of the 4-mm thick Al-12.7Si-0.7Mg alloy extrusion should exceed 24 ^oC /s.

Abstract: In this article, some common defects, which are caused by material properties, and the mechanism of the defects occur are introduced. Author introduces how these defects are treated in conventional process, meanwhile, points out the disadvantages of the process. For the disadvantages, several special processes are introduced, including gas-assisted injection molding, rapid variotherm injection molding and hot runner technology, and their mechanism and advantages.

Abstract: This paper presents the parameters optimization by TRIZ theory in the precision lapping of sapphire in order to realize the high efficiency and low damaged lapping. The TRIZ theory was used to optimize processing parameters of sapphire precision lapping based on much experimental data of lapping, then the conflict matrix of internal contradictions was set up and the optimization parameters was obtained. The result of experiment indicated that the face quality of sapphire was improved greatly after optimized by TRIZ. There was a conclusion that TRIZ theory can be used to optimize the processing parameters of sapphire precision lapping which is important to enrich the processing theory of sapphire.

Abstract: This paper analyses the influence of indenter’s vertex angle on the ‘trap’ effect of the semi-fixed abrasive plate (SAP) with discrete element method. The indenters of different degree vertex angle are generated by discrete element method, then the indenter is applied processing velocity, which let the indenter press into the SAP, finally three curves of normal force and displacement are gained. From the curves, the normal force of the indenters doesn’t increase quickly and stay in stable in the beginning, because the SAP is full of pore, which let the indenter easily press into the SAP. Through the above indenter simulation, the relations between the lasting time of the ‘trap’ effect and the indenter’s vertex angle are in reverse proportion, if the indenter’s vertex angle is smaller, the lasting time of the ‘trap’ effect of SAP is longer, and the size of large grain is an influence factor in the ‘trap’ effect of SAP.

Abstract: This paper presents a finite element (FE) modeling of the nanoindentation test of sapphire, in which the finite element method was employed to study the mechanical characteristic of sapphire under the nanoindentation process. The results demonstrated that the nanoindentation FE models were able to simulate the indentation loading-unloading curves of the sapphire. The load and unload displacement curves of the simulation and experiment results can match with each other well, and then the properties used in the simulation should be the actual properties of the sapphire. The Mises stress field distribution of the sapphire sample was calculated to reveal the alteration from elastic region to plastic region, which are useful for indentifying the ductile to brittle change in the sapphire abrasive process.

Abstract: The formation mechanisms and properties of white layers produced in precision hard part machining of GCr15 hardened steels are not clearly understood to date. Microstructure of white layers formed during machining of GCr15 hardened steel (62±2 HRC) was investigated. Hard turned surface with white layer usually consists of three layers: a white layer (untempered martensite), a transition layer (over-tempered martensite), and the bulk material. Martensite, austenite and carbide are observed in the white layer, hardness of white layer is larger than that of bulk material and transition layer, it was caused by extremely small grain size and high dislocation density. The depth of white layer is about 7-14µm with the flank wear reached 0.1mm, the optimal width of the flank wear which generated low depth of white layer is essential to perform the super-finishing process.

Abstract: Surface integrity of Sapphire wafer is the frontier technology to grow high quality AlN/GaN films for high brightness light-emitting diode. Surface damage measurement methods for single crystal sapphire were introduced firstly. Classical types of surface deformation induced by abrasive machining, such as lattice deformation, strain, scratch, crack versus abrasive grits and chemical reaction were compared. With the development of modern grinding technology, depth of the damaged surface layer decreases from 10μm to 2μm or much less. Both crack, lattice deformation, twinning and strain were detected along the ground surface, only dislocation and strain were appeared for polished sapphire surface. Usually, depth of the damaged layer was less than 300nm using mechanical polishing process. Chemical mechanical polishing achieved the lowest depth of the damaged surface and best surface roughness, scratch depth was used to descript the damaged depth, which is about 1 nm, and so called no damage to the layer remains during chemical mechanical polishing process.

Abstract: Shot peening is a cold-work process in which a stream of small spherical shot is blasted against a metallic component to generate a high compressive residual stress regime at the surface of the target. This paper presents a computational modelling of the shot peening process, in which the finite element (FE) method was employed to study the elastic-plastic dynamic process of the shot impact on a metallic target, and the discrete element (DE) method was used to study the multiple particles dynamics. Statistical analyses of the shot impact data reveal the relationships between peening process parameters and peening intensity, which can be used to optimise these process parameters to produce an improved outcome.