Effects of equal channel angular extrusion and aging treatment on R phase transformation behaviors and Ti3Ni4 precipitates of Ni-rich TiNi alloys

Ni-rich TiNi alloys were subjected to the effect of multiple equal channel angular extrusion (ECAE) treatments by B_C path at 500 °C. The characteristics of R phase transformation in aging treatment were dissimilar in the appearance and the temperature range to those counterparts induced by ECAE treatments. The fine lens-like shape Ti₃Ni₄ particles precipitated mainly in the regions of near grain boundaries and on the tangled grain boundaries after ECAE treatments. The effects and mechanisms of aging treatments and ECAE treatments on R phase transformation behaviors and Ti₃Ni₄ precipitates were investigated and discussed.     

等径道角挤压法制备半固态MB15-RE镁合金坯

研究了等径道角挤压法制备半固态MB15-RE镁合金坯，其中包括挤压前后力学性能对比和半固态球化过程微观组织演变规律。分析结果表明，等径道角制备得到的MB15-RE镁合金力学性能大大提高，抗拉强度由铸态的154.7MPa提高到312.5MPa，伸长率由7.3%提高到13.0%。半固态组织晶粒细小、均匀、圆整度好，最小晶粒尺寸可达到5～20μm，圆整度接近1.3。     

Investigation into Channel Angular Extrusion and the UREAD energy absorption technique

Channel Angular Extrusion (CAE) processes are characterised by imposing high level of strain into deformable materials using simple tools where the material is deformed through a specific path. Because of the high strains tool stresses could be critical. The process is capable of reducing the thickness of flat sheets or slabs, and using equal channels, it could be used for material refinement where internal grain size changes to nano-scale structure by intense shearing. In this paper, the applications of CAE have been extended to include the construction of Universal Re-usable Energy Absorption Devices (UREAD) using equal channels. An investigation is carried out into the distribution of contact stresses at the tool/material interface. The model employs the slab method of analysis and splits the material inside the channels, which intersects at 90°, into two zones; one causes the deformation while the other remains rigid. Normal stresses that may develop at the contact surface between the deformable material and the tools are analysed for various cases of CAE and are compared with those obtained by the Finite Element Analysis. Experimental investigation on UREAD devices using lead are also presented where the energy absorbed reached a maximum of 160 J for 100 mm cross-sectional area and 30 mm stroke. An experimental set up for measuring contact pressure in CAE/ECAE is introduced and measurements at different depth of the CAE entry channel are presented. The sensing mechanism is based upon the sensitive pressure pin technique.     

等通道转角挤压模具挤压力计算

介绍了利用上限法求解等通道转角挤压模具挤压力的方法,为等通道转角挤压模具强度设计提供了依据.     

Microstructure and Orientation Evolution of Unidirectional Solidification Pure Copper during ECAP

Experiment were conducted to unidirectional solidification pure copper during ECAP by route C, the samples were investigated by XRD and EBSD. The results shown that the effect of original microstructure on the subgrains orientation decrease with the increasing of strain. At low strain, in the column grain interiors first formed a band structure that the orientation quite different with the matrix. With the strain increasing, the boundaries of the band structure expanding towards to two sides, gradually part...     

间接ECAD方法可行性的试验研究

等通道转角挤压（ECAE,Equal Channel Angular Extrusion）是一种强塑性变形（Severe Plastic Deformation）加工技术,可细化合金组织,改善材料性能。针对传统的等通道转角挤压法难以对过长的材料进行加工的缺点,基于新近提出的间接ECAD方法的理念,设计出模具并进行试验。结果表明,间接（In—Direct）ECAD能够对试样进行剪切变形处理,并对处理试样长度没有限制,该方法是可行的。     

Untersuchungen zur Festigkeit von Schrauben aus ultrafeinkörnigem und konventionellem Aluminiumwerkstoff EN AW‐7075

Investigation into strength of bolts made of ultra fine grain as well as coarse grain aluminium material AA7075 Results of investigation into strength and fracture behaviour with high level mean load of rolled 7075‐aluminiumbolts M6 are given. Bolts made of coarse grain as well as ultra fine grain structure produced by Equal Channel Angular Extrusion (ECAE) were tested. The ultimate tensile strength for both grain sizes was of a similar level. As a result of the first fatigue tests it seems that the fatigue strength of the ultra fine grain material is lower that the fatigue strength of the coarse grain material. An endurance limit of 23 MPa was found for the bolts made of coarse grain material using a modified staircase method. Furthermore, fracture behaviour of aluminium bolts is discussed.     

Deformation macrolocalisation and fracture in ultrafine-grained armco iron

The banded structure formed in armco iron specimens as a result of equal-channel angular extrusion causes their strong shear localisation under quasi-static tension. Applying transmission electron microscopy technique, a fine structure of meso- and macroscopic shear bands was revealed. The character of shear band propagation was studied by calculation of the maximum in-plane shear strain through a digital image correlation procedure. It was shown two different patterns of macroband propagation: two parallel shear bands with oppositely directed shears or a cross of shear bands oriented along the conjugate direction of maximum tangential stresses. The necking was revealed to be caused by the disturbance of self-consistent propagation of deformation macrobands.     

A computational study of die geometry and processing conditions effects on equal channel angular extrusion of a polymer

Equal channel angular extrusion (ECAE) is an efficient process to obtain enhanced microstructures via super-plastic deformation. In view of its optimisation, it is of prime importance to assess the relationships between processing conditions and material flow. More precisely, detailed knowledge of the plastic strain distribution in the extruded material in relation to the ECAE processing variables is required. The key parameters of the ECAE process are primarily die geometry, ram speed, extrusion temperature, use of back-pressure, number of extrusion sequences and processing route (e.g. rotation of the sample between successive passes). A numerical investigation was achieved to check out the influence of these parameters on the homogeneity of plastic strain distribution in the case of a conventional thermoplastic polymer. Material parameters of a phenomenological elastic viscoplastic model were deduced from compressive deformation tests at different temperatures and strain rates on high-density polyethylene (HDPE). Recommendations on tool geometry and processing conditions can then be provided, according to the numerical results.It was found that optimum ECAE die geometry is strongly material dependent. The application of a back-pressure significantly contributes to reduce the corner gap and consequently promotes the homogeneity of the plastic strain field. A slight sensitivity of plastic strain to ram speed and friction conditions was pointed out. The extrusion temperature strongly influences the magnitude of the plastic strain and has a slight effect on its homogeneity. The number of passes has a significant effect on the magnitude of the plastic strain but has a negligible influence beyond a certain temperature. The extruded material reaches a stationary strain state after few passes. The homogeneity of the plastic strain field is strongly affected by the processing route.