扩张皮肤全耳廓再造后挤压塑形的心得体会

采用人工骨水泥和石膏纱布两种材料为１３例扩张皮肤法全耳再造术后立即进行挤压固定，维持新耳廓形态。挤压固定维持３～４周，这种方法使用简便，安全可靠，对于维持新耳廓的形态和防止术后皮肤收缩引起的耳廓形态改变具有较好的作用。

Equal channel angular extrusion of NiTi shape memory alloy tube

As a new attempt, equal channel angular extrusion （ECAE） of nickel-titanium shape memory alloy （NiTi SMA） tube was investigated by means of process experiment, finite element method （FEM） and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.

Effect of processing route on grain refinement in pure copper processed by equal channel angular extrusion

An experimental study of the microstructures in pure copper billets processed by 8 passes of equal channel angular extrusion （ECAE） via an extended range of processing routes with a 90° die is carried out. Each processing route is defined according to the inter-pass billet rotation angle （χ）, which varies from 0° to 180°. According to the generation of high-angle boundaries and reduction of grain size by electron backscatter diffraction （EBSD） measurements, the grain refinement is found to be most efficient for route with χ=90°and least efficient with χ=180°, among the seven routes studied. This trend is supported by supplementary transmission electron microscopy （TEM） measurements. Comparison of the EBSD and TEM data reveals the importance of considering the non-equiaxity of grain structures in quantitative assessment of microstructural differences in ECAE-processed materials.

Three dimensional finite element study on torsion extrusion processing of 1050 aluminum alloy

The capability of the torsion extrusion （TE） process as a severe plastic deformation （SPD） method was compared with the conventional forward extrusion （FE） process. The TE and FE processes were successfully performed on AA1050 alloy samples at room temperature. To simulate the above mentioned processes, finite element analysis was carried out using the commercial elasto-plastic finite element analysis ABAQUS/Explicit Simulation. It is shown that load requirement for the TE process is lower than that for the FE process. The equivalent plastic strain calculated by the FEA proved that higher values of strain are imposed to the sample in the TE process. The strain distribution for the TE sample at the final stage of extrusion shows smoother strain gradient in comparison with the one produced by the FE process.

Plastic deformation behavior of Mg97Zn1Y2 extruded alloys

The mechanical properties of the Mg97ZnlY2 extruded alloy containing the long-period stacking ordered phase, the so-called LPSO-phase, with a volume fraction of 24%-25%, were examined by compression tests and cyclic tension-compression deformation tests. The plastic behavior of the extruded alloys with compositions of Mg99.2Zn0.2Y0.6 and Mg89Zn4Y7 （molar fraction, %）, which were almost the same compositions of Mg matrix phase and LPSO phase in Mg97Zn1Y2 Mg/LPSO two-phase alloy, respectively, were also prepared. By comparing their mechanical properties, the strengthening mechanisms operating in the Mg97Zn1 Y2 extruded alloy were discussed. Existence of the LPSO-phase strongly enhanced the refinement of Mg matrix grain size during extrusion, which led to a large increment of the strength of alloy. In addition, the LPSO-phases, which were aligned along the extrusion direction in Mg97Zn1Y2 extruded alloy, acted as hardening phases, just like reinforced fibers.

Processing and characterization of AZ91 magnesium alloys via a novel severe plastic deformation method:Hydrostatic cyclic extrusion compression(HCEC)

Capability of a novel severe plastic deformation(SPD)method of hydrostatic cyclic extrusion compression(HCEC)for processing of hcp metallic rods with high length to diameter ratios was investigated.The process was conducted in two consecutive cycles on the AZ91 magnesium alloy,and microstructural evolution,mechanical properties and corrosion behavior were investigated.The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods.Its ability in improving strength and ductility simultaneously was also shown.The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen,respectively.Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%.The potentials derived from the polarization curves were high and the currents were much low for the processed samples.Also,the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples.The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC.HCEC is a unique SPD method,which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.

Inter-granular liquid phase aiding grain boundary sliding in superplastic deformation of fine-grained ZK60 Mg alloy

For 7475 Al alloy,there were micrographs showing filaments or whiskers formation during the separation stage of superplastic elongation.This indicates the presence of liquid phase which accommodates grain boundary sliding to reach superplasticity.On the other hand,there is no such phenomenon reported regarding Mg alloy in literatures.Scanning electron microscopic(SEM)fractography exceptionally exhibits a mark of grain boundary sliding and its accommodating mechanism of inter-granular liquid phase.Under the testing conditions of 350℃ and 1×10- 4s -1,the initially fine-grained structure(3.7μm)yields 642%superplastic elongation and exhibits fluffy appearance on the fractured surface.For other specimens showing less superplasticity,their fractured surfaces exhibit partial fluffy appearance.

Review on modified and novel techniques of severe plastic deformation

This review highlights very recent achievements and new developments of severe plastic deformation(SPD) technology for producing bulk ultrafine-grain(UFG) and even nanocrystalline(nc) materials.These numerous modified and novel SPD methods include cyclic forward-backward extrusion,axi-symmetric forward spiral extrusion,vortex extrusion,simple shear extrusion,planar twist extrusion,tubular channel angular pressing,cone-cone method,high-pressure tube twisting,tube channel pressing and elliptical cross-section spiral equal-channel extrusion.According to classification,these new methods are categorized into the extension of equal-channel angle pressing(ECAP),high-pressure torsion(HPT),twist extrusion(TE) and constrained groove pressing(CGP),respectively.The principles of various new SPD technologies are described in detail.In addition,the microstructure revolution characteristics and mechanical properties of materials produced by SPD process,as well as the applications of SPD techniques to UFG materials,are also reported.Furthermore,this article reviews recent progresses in determining the refinement and/or deformation mechanisms,e.g.dislocation deformation mechanism,twin deformation mechanism and grain boundary sliding and torsional deformation mechanism,and further orientation of SPD technology.