超高压水压泵柱塞副间隙泄漏占比的仿真计算

考虑间隙内水介质黏度、间隙受压形变在柱塞轴向沿程变化,用AMESim软件对超高压水压泵细长型柱塞副在工作压力从0~120 MPa变化时的间隙、泄漏占理论排量的比值进行了计算预测。结果表明:随着工作压力升高,柱塞间隙内水介质黏度沿程变化引起的泄漏量呈近似线性增长,在120 MPa时间隙泄漏增大25%;间隙高压形变引起的泄漏量快速增长,在120 MPa时间隙泄漏增加3倍;当配合间隙为3,5,7μm时,间隙泄漏占比为3.51%,8.93%和18.51%;超高压工况下,影响柱塞间隙泄漏的主要因素是柱塞副间隙大小、间隙高压变形量、柱塞副接触长度、柱塞偏心量,减小柱塞副配合间隙、间隙高压变形量,增大柱塞副接触长度,可显著减小泄漏,提高容积效率。

Deformation defects and electron irradiation effect in nanostructured Al-Mg alloy processed by severe plastic deformation

In order to explore the exact nature of deformation defects previously observed in nanostructured Al-Mg alloys subjected to severe plastic deformation, a more thorough examination of the radiation effect on the formation of the planar defects in the high pressure torsion （HPT） alloys was conducted using high-resolution transmission electron microscopy （HRTEM）. The results show that high density defects in the HRTEM images disappear completely when these images are exposed under the electron beam for some duration of time. At the same time, lattice defects are never observed within no-defect areas even when the beam-exposure increases to the degree that holes appear in the areas. Therefore, it is confirmed that the planar defects observed in the HPT alloys mainly result from the significant plastic deformation and are not due to the radiation effect during HRTEM observation.

Strain rate-dependent high temperature compressive deformation characteristics of ultrafine-grained pure aluminum produced by ECAP

To explore the effect of strain rate ε on the high temperature deformation characteristics of ultrafine-grained materials, the deformation and damage features as well as microstructures of ECAP-treated pure Al at different temperatures T and strain ratesε were systematically studied through compression tests and microscopic observations. The increase in ε eliminates strain softening at T≤473 K, and largely enhances the yield strength and flow stress at 473?573 K. The shear deformation dominates the plastic deformation of ECAP-treated Al. Many cracks along shear bands (SBs) are formed at T≥473 K and secondary SBs basically disappear at 1×10?3 s?1; however, at 1×10?2 s?1, cracks are only observed at temperature below 473 K, and secondary SBs become clearer at T≥473 K. The microstructures of ECAP-treated Al mainly consist of sub-grains (SGs). The increase in ε inhibits the SG growth, thus leading to the increases both in yield strength and flow stress at high temperatures.

Flow instability criteria in processing map of superalloy GH79

Hot compression tests were conducted on a Gleeble-1500D thermal simulating tester.Based on the deformation behavior and microstructural evolution of superalloy GH79,different types of instability criteria of PRASAD,GEGEL,MALAS,MURTY and SEMIATIN were compared,and the physical significance of parameters was analyzed.Meanwhile,the processing maps with different instability criteria were obtained.It is shown that instability did not occur when average power dissipation rate was larger than 60%in the temperature range of 900-930°C and 960-1080°C,corresponding to the strain rate range of 5×10 -4 -1.8×10 -1 s -1 and 5×10 -4 -1.5×10 -1 s -1 ,respectively.The two domains are appropriate for the processing deformation of superalloy GH79.

Microstructure evolution and dislocation configurations in nanostructured Al-Mg alloys processed by high pressure torsion

Microstructure evolution and dislocation configurations in nanostructured Al–Mg alloys processed by high pressure torsion （HPT） were analyzed by transmission electron microscopy （TEM） and high-resolution TEM （HRTEM）. The results show that the grains less than 100 nm have sharp grain boundaries （GBs） and are completely free of dislocations. In contrast, a high density of dislocation as high as 1017 m^-2 exists within the grains larger than 200 nm and these larger grains are usually separated into subgrains and dislocation cells. The dislocations are 60° full dislocations with Burgers vectors of 1/2〈110〉and most of them appear as dipoles and loops. The microtwins and stacking faults （SFs） formed by the Shockley partials from the dissociation of both the 60° mixed dislocation and 0° screw dislocation in ultrafine grains were simultaneously observed by HRTEM in the HPT Al–Mg alloys. These results suggest that partial dislocation emissions, as well as the activation of partial dislocations could also become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. The grain refinement mechanism associated with the very high local dislocation density, the dislocation cells and the non-equilibrium GBs, as well as the SFs and microtwins in the HPT Al-Mg alloys were proposed.

High temperature deformation behavior and optimization of hot compression process parameters in TC11 titanium alloy with coarse lamellar original microstructure

The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the temperature range of 950-1100 ℃ and the strain rate range of 0.001-10 s-1. The processing maps at different strains were then constructed based on the dynamic materials model, and the hot compression process parameters and deformation mechanism were optimized and analyzed, respectively. The results show that the processing maps exhibit two domains with a high efficiency of power dissipation and a flow instability domain with a less efficiency of power dissipation. The types of domains were characterized by convergence and divergence of the efficiency of power dissipation, respectively. The convergent domain in a＋fl phase field is at the temperature of 950-990 ℃ and the strain rate of 0.001-0.01 s^-1, which correspond to a better hot compression process window of α＋β phase field. The peak of efficiency of power dissipation in α＋β phase field is at 950 ℃ and 0.001 s 1, which correspond to the best hot compression process parameters of α＋β phase field. The convergent domain in β phase field is at the temperature of 1020-1080 ℃ and the strain rate of 0.001-0.1 s^-l, which correspond to a better hot compression process window of β phase field. The peak of efficiency of power dissipation in ℃ phase field occurs at 1050 ℃ over the strain rates from 0.001 s^-1 to 0.01 s^-1, which correspond to the best hot compression process parameters of ,8 phase field. The divergence domain occurs at the strain rates above 0.5 s^-1 and in all the tested temperature range, which correspond to flow instability that is manifested as flow localization and indicated by the flow softening phenomenon in stress-- strain curves. The deformation mechanisms of the optimized hot compression process windows in a＋β and β phase fields are identified to be spheroidizing and dynamic recrystallizing controlled by self-diffusion mechanism, respectively. The microstructure observation of the deformed specimens in different domains matches very well with the optimized results.

Effects of hot compression on carbide precipitation behavior of Ni-20Cr-18W-1Mo superalloy

The effect of hot compression on the grain boundary segregation and precipitation behavior of M6C carbide in theNi-20Cr-18W-1Mo superalloy was investigated by thermomechanical simulator, scanning electronic microscope （SEM） and X-raydiffraction （XRD）. Results indicate that the amount of M6C carbides obviously increases in the experimental alloy after hotcompression. Composition analyses reveal that secondary M6C carbides at grain boundaries are highly enriched in tungsten.Meanwhile, the secondary carbide size of compressive samples is 3？5 μm in 10% deformation degree, while the carbide size ofundeformed specimens is less than 1 μm under aging treatment at 900 and 1000 ℃. According to the thermodynamic calculationresults, the Gibbs free energy of γ-matrix and carbides decreases with increase of the compression temperature, and the W-rich M6Ccarbide is more stable than Cr-rich M23C6. Compared with the experimental results, it is found that compressive stress accelerates theW segregation rate in grain boundary region, and further rises the rapid growth of W-rich M6C as compared with the undeformedone.

Hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy

The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.

Prolonged high-pressure balloon angioplasty of femoropopliteal lesions：Impact on stent implantation rate and mid-term outcome

Objectives To assess the impact on stent implantation rate and mid-term outcomes of prolonged high pressure angioplasty of femoropopliteal lesions. Methods We retrospectively enrolled 620 consecutive patients from January 2011 to December 2011 （75.6 ±12.3 years, 355 males, 76.5%in Rutherford class 5-6）, referred for critical limb ischemia and submitted to prolonged high-pressure angioplasty of femoropopliteal lesions. The definition of prolonged high-pressure angioplasty includes dilation to at least 18 atm for at least 120 s. Proce-dural data, and clinical and instrumental follow-up were analyzed to assess stent implantation rate and mid-term outcomes. Results The preferred approach was ipsilateral femoral antegrade in 433/620 patients （69.7%） and contralateral cross-over in 164/620 （26.4%） and pop-liteal retrograde＋femoral antegrade in 23/620 （3.7%）. Techniques included subintimal angioplasty in 427/620 patients （68.8%） and endolu-minal angioplasty in 193/620 patients （31.2%）. The prolonged high pressure balloon angioplasty procedure was successful in 86.2%（minor intra-procedural complications rate 15.7%）, stent implantation was performed in 74 patients （11.9%）, with a significant improvement of ankle-brachial index （0.29 ±0.6 vs. 0.88 ±0.3, P〈0.01） and Rutherford class （5.3 ±0.8 vs. 0.7 ±1.9, P〈0.01）, a primary patency rate of 86.7%, restenosis of 18.6%on Doppler ultrasound and a target lesion revascularization of 14.8%at a mean follow-up of 18.1 ±6.4 months （range 1-24 months）. Secondary patency rate was 87.7%. Conclusions Prolonged high pressure angioplasty of femoropopliteal lesions appears to be safe and effective allowing for an acceptable patency and restenosis rates on mid-term.

Influence of high pressure and manganese addition on Fe-rich phases and mechanical properties of hypereutectic Al-Si alloy with rheo-squeeze casting

The influence of high pressure and manganese addition on Fe-rich phases(FRPs)and mechanical properties of Al-14Si-2Fe alloy with rheo-squeeze casting(RSC)was investigated.The semi-solid alloy melt was treated by ultrasonic vibration(UV)firstly,and then formed by squeeze casting(SC).Results show that the FRPs in as-cast SC alloys are composed of coarseβ-Al5(Fe,Mn)Si,δ-Al4(Fe,Mn)Si2 and bone-shapedα-Al15(Fe,Mn)3Si2 phases when the pressure is 0 MPa.With RSC process,the FRPs are first refined by UV,and then the solidification under pressure further causes the grains to become smaller.The peritectic transformation occurs during the formation ofαphase.For the alloy with the same composition,the ultimate tensile strength(UTS)of RSC sample is higher than that of the SC sample.With the same forming process,the UTS of Al-14Si-2Fe-0.8Mn alloy is higher than that of Al-14Si-2Fe-0.4Mn alloy.

Mechanical responses, texture and microstructural evolution of high purity aluminum deformed by equal channel angular pressing

Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.

High-pressure torsion deformation process of bronze/niobium composite

The deformation process in the material volume under high-pressure torsion(HPT)was studied.As a model object for the observation of deformation process,we used a composite comprising a bronze matrix and niobium filaments.The arrangements of the niobium filaments in the bronze matrix and their size have regular geometry.This allows us to monitor and measure the displacement of the niobium filaments in the sample volume,which results from HTP.The bronze/niobium composite samples were subjected to HPT at room temperature and 6 GPa,and the number of revolutions N=1/4,1/2,1,2,3 and 5.It was shown that HPT with revolution number of 1 leads to the 360° rotation of entire sample volume without sample slippage.Similar deformational behavior during HPT can be expected for high-ductility metallic materials.The increase in the number of revolutions more than 2 leads to twisting the niobium filaments in the sample volume and the formation of 'vortex' multilayer structure.The mechanisms for the formation of such structures were discussed.

Characteristics of thickness distribution of tailor-welded tube hydroforming

Both experimental and mechanical analyses were carded out to investigate the characteristics of thickness distribution for tailor-welded tube （TWT） hydroforming with dissimilar thickness. Then, the effects of weld-seam position and thickness difference were also revealed. A multiple-diameter tube was formed to reveal the characteristics and the regularity of thickness distribution during TWT hydroforming. It is indicated that there are obvious fluctuations in thickness distribution though the TWTs have the same expansion ratio. The thinning ratio of thinner tube is bigger than that of thicker tube especially in the zone closed to the weld-seam. The difference in thinning ratio between two tube segments can reach 9%. Consequently, sudden and large fluctuation of thickness appears in the zone nearby the weld-seam. The difference in thinning ratio between thinner and thicker tubes enlarges as the thickness difference increases, but improves as length ratio increases. Different strain states are the main reason to induce nonuniform thickness distribution. The difference in thickness is the main reason to induce different strain states on thinner and thicker tubes.

Special nanostructures in Al-Mg alloys subjected to high pressure torsion

Deformation twins and stacking faults were observed in nanostructure A1-Mg alloys subjected to high pressure torsion. These observations are surprising because deformation twinnings have never been observed in their coarse-grained counterparts under normal conditions. Experimental evidences are introduced on non-equilibrium grain boundaries, deformation twinnings and partial dislocation emissions from grain boundaries. Some of these features can be explained by the results reported from molecular-dynamics simulations of pure FCC metals. Special emphasis is laid on the recent observations of high density hexagonal and rhombic shaped nanostructures with an average size of 3 nm in the A1-Mg alloys processed by high pressure torsion. A possible formation process of these nanostructures is proposed based on molecular-dynamics simulations.

Deformation behavior and microstructural evolution of Al-Zn-Cu-Mg-Sc-Zr alloy during high temperature compression

The deformation behavior of a new Al-Zn-Cu-Mg-Sc-Zr alloy was investigated with compression tests in temperature range of 380?470 ℃ and strain rate range of 0.001-10 s-1 using Gleeble 1500 system, and the associated microstructural evolutions were studied by metallographic microscopy and transmission electron microscopy. The results show that true stress—strain curves exhibit a peak stress, followed by a dynamic flow softening at low strains (ε<0.05). The stress decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon exponential equation with the activation energy for deformation of 157.9 kJ/mol. The substructure in the deformed specimens consists of few fine precipitates with equaixed polygonized subgrains in the elongated grains and developed serrations at the grain boundaries. The dynamic flow softening is attributed mainly to dynamic recovery and dynamic recrystallization.

Subtransus deformation mechanisms of TC11 titanium alloy with lamellar structure

Isothermal compression tests are applied to study the deformation mechanisms of TCll titanium alloy with lamellar structure under the deformation temperature range of 890-995 ℃ and strain rate range of 0.01-10 s^-1. According to the flow stress data obtained by compression tests, the deformation activations are calculated based on kinetics analysis of high temperature deformation, which are then used for deformation mechanism analysis combined with microstructure investigation. The results show that deformation mechanisms vary with deformation conditions： at low strain rate range, the deformation mechanism is mainly dislocation slip; at low temperature and high strain rate range, twinning is the main mechanism; at high temperature and high strain rate range, the deformation is mainly controlled by diffusion offl phase.

Unified modeling of high temperature deformations of a Ni-based polycrystalline wrought superalloy under tension-compression, cyclic, creep and creep-fatigue loadings

The complex deformation behaviors under tension-compression, cyclic, creep and creep-fatigue loadings of a nickel-base polycrystalline wrought superalloy at 650℃ and 700℃ were experimentally investigated. To uniformly simulate the complex deformation behaviors, the modified viscoplastic constitutive model combined with both the Kachanov damage evolution equation and the Ohno-Wang modification was formulated on the basis of the Chaboche theory. The simulated results on ten-sion-compression behavior, cyclic viscoplastic and creep deformations showed comprehensive predicting ability. With the obtained material parameters, the deformations in creep-fatigue interaction under three dwell types were simulated and the capability of the modified model was further verified with good accuracy.