Study on plastic deformation behavior of hot splitting spinning of TA15 titanium alloy

The plastic deformation behavior of hot splitting spinning of TA15 titanium alloy is a complex metal forming problem with multi-factor coupling interactive effects. In this paper, on condition of considering various thermal effects, a three-dimensional (3D) elastic–plastic coupled thermo-mechanical finite element (FE) model of hot splitting spinning of TA15 titanium alloy is established using the dynamic, temp-disp, explicit module of FE software ABAQUS. Based on the analysis of flow behaviors of TA15 titanium alloy, the mechanism and influence of materials plastic deformation behavior during the forming process are studied. The results show that, the flow stress of TA15 titanium alloy generally decreases with the increase of deformation temperature; at the same strain rate, the higher temperature is, the lower flow stress is. The temperature distributions along the circumferential direction of disk blank are even and the temperature of plastic deformation area is about 984 °C. The heat from plastic deformation and friction at local plastic deformation area is less than the dissipated heat, so the temperature just falls into approximately 945 °C. Radial spinning force as the driving force of plastic deformation increases gradually and reaches about 35 kN at the end. The maximum value of equivalent stress is presented in fillet part between disk blank and two mandrels. The distributions of equivalent plastic strain appear the large strain gradients and the obvious characteristics of inhomogeneous deformation. When friction factor on interfaces between disk blank and dies ranges from 0.4 to 0.6, the forming quality and precision are highest.     

A novel severe plastic deformation method for fabricating ultrafine grained pure copper

A novel severe plastic deformation (SPD) method entitled elliptical cross-section spiral equal-channel extrusion (ECSEE) was proposed to fabricate ultrafine grained (UFG) pure copper. The principle of ECSEE process was adopted to accumulate shear stress within the workpiece without any cross-section area change. In order to primarily demonstrate the deformation characteristic and refinement ability of ECSEE method, the simulated and experimental investigations were both done. In the case of simulation, the ECSEE-ed workpiece containing scribed grids was analyzed for the flow net change. Simulated results indicated the trend of effective strain distribution decreased from the circumferential area to the central area on the cross-section of ECSEE-ed workpiece. In experimental investigations of a single-pass of ECSEE, a significant grain refinement from 10–50 μm to 1–10 μm was mainly in the circumferential area of the cross-section for processed workpieces. During the ECSEE deformation, shear strain as an essential role conduced the grain refinement. Besides, a significant increase of hardness, from ∼40 Hv to ∼85 Hv, was examined. The distribution characteristic of refinement and hardness were both consistent with that of simulated effective strain.     

Cyclic deformation behavior of austenitic Cr–Ni-steels in the VHCF regime: Part I – Experimental study

A stable (AISI 316L) and a metastable (AISI 304L) austenitic stainless steel were investigated with respect to their VHCF behavior. The focus of the paper lies on the investigation of the cyclic deformation behavior of the two materials at very low stress amplitudes. The 304L steel is characterized by a pronounced cyclic softening during its initial stage of cyclic deformation. In the course of the following loading cycles, a phase transformation (γ-austenite → α′-martensite), accompanied by volume expansion is associated with the reduction of the global plastic strain amplitude and induces compressive stresses in the near surface layer. As a consequence, the material shows no failure up to 10⁹ cycles at 240 MPa. In contrast, the type 316L steel has a higher stacking fault energy and the microstructure remains fully austenitic during cyclic deformation when analyzed by means of magneto-inductive methods. In this case, very localized plastic shear occurs and the slip band topography reveals the formation of pronounced intrusions. Microcracks initiate from these intrusions in the VHCF regime and samples failed also beyond 10⁷ cycles. This study presents a comparative investigation of the damage evolution – including dislocation morphology and phase transformations – during cyclic loading for both materials. The combined effect of the individual deformation mechanisms is investigated for both materials in the context of a microstructure-sensitive simulation discussed in Part II of this study.     

T2铜箔精密微冲孔工艺

随着微机电系统的飞速发展,微孔类零件广泛应用于生物医疗、微电子以及纺织印染等领域中,要求尺寸精度高、断面质量和重复性好,并且能够实现低成本批量制造.微冲孔技术具有传统塑性加工工艺的优点,生产效率高,工艺简单,成形件性能好和精度高,非常适合微型零件的低成本批量制造.针对箔板微孔类零件,设计了一套精密微冲孔模具,采用微冲孔技术研究了冲裁条件对微冲孔工艺的影响规律.结果表明,微冲孔过程与传统冲裁类似,经由弹性变形阶段和塑性剪切阶段,最后断裂分离.微孔断面分布仍然包括圆角、光亮带、断裂带和毛刺.随着相对冲裁间隙的增加,最大剪切强度先降低后逐渐增加;随着冲裁速度的增加,铜箔微冲孔过程最大冲裁力和最大剪切强度逐渐减小,微孔断面光亮带高度增加,断面质量提高.最后,在最佳的冲孔工艺即冲裁间隙为5%、冲裁速度为20mm/s的条件下冲出直径为0.4mm质量良好的微孔.     

Nanostructured severe plastic deformation processed titanium for orthodontic mini-implants

Titanium mini-implants have been successfully used as anchorage devices in Orthodontics. Commercially pure titanium (cpTi) was recently replaced by Ti-6Al-4 V alloy as the mini-implant material base due to the higher strength properties of the alloy. However, the lower corrosion resistance and the lower biocompatibility have been lowering the success rate of Ti-6Al-4 V mini-implants. Nanostructured titanium (nTi) is commercially pure titanium that was nanostructured by a specific technique of severe plastic deformation. It is bioinert, does not contain potentially toxic or allergic additives, and has higher specific strength properties than any other titanium applied in medical implants. The higher strength properties associated to the higher biocompatibility make nTi potentially useful for orthodontic mini-implant applications, theoretically overcoming cpTi and Ti-6Al-4 V mini-implants. The purposes of the this work were to process nTi, to mechanically compare cpTi, Ti-6Al-4 V, and nTi mini-implants by torque test, and to evaluate both the surface morphology and the fracture surface characteristics of them by SEM. Torque test results showed significant increase in the maximum torque resistance of nTi mini-implants when compared to cpTi mini-implants, and no statistical difference between Ti-6Al-4 V and nTi mini-implants. SEM analysis demonstrated smooth surface morphology and transgranular fracture aspect for nTi mini-implants. Since nanostructured titanium mini-implants have mechanical properties comparable to titanium alloy mini-implants, and biocompatibility comparable to commercially pure titanium mini-implants, it is suggestive that nanostructured titanium can replace Ti-6Al-4 V alloy as the material base for mini-implants.     

Hydrogen‐enhanced plastic deformation during indentation for bulk metallic glass of Zr65Al7.5Ni10Cu17.5

The effect of hydrogen charging on shear bands and plastic zone during Vickers indentation for Zr₆₅Al_7.5Ni₁₀Cu_17.5 bulk metallic glass has been studied. The results showed that hardness increased gradually with charging time and reached saturation. The shear bands and the size of the plastic zone on the surface and subsurface of indentation increased evidently when charging time was less then 40 h at i = 10 mA/cm² or 10 h at i = 100 mA/cm², respectively. After that, the size of the plastic zone began to reduce with charging time because hydrogen blisterings began formation and growth.     

Densification mechanisms in spark plasma sintering of nanocrystalline ceramics

Effect of the particle size on the possible electric discharge during the SPS was examined. Nanoparticle compacts enable accumulation of high electric charge, and discharge under conventional voltages used for the SPS. The critical particle size for the electric discharge is both morphological and material dependent. The early stages of densification of the nanocrystalline powder compact proceed either by the plastic deformation or grain-rotation coalescence and sliding, aided by softening of the particle surfaces. The active densification mechanism depends on the changes both in the mechanical and electrical properties with temperature. Densification of 11 nm nc-MgO particles with low yield stress proceeds by plastic deformation already at 700 °C. However, densification of 34 nm nc-YAG particles with high yield stress proceeds by nano-grain rotation aided by particle surface softening. Densification at the final stages of SPS is associated with diffusional processes, where curvature driven grain growth predominates.     

Thermo-metallurgical and thermo-mechanical computations for laser welded joint in 9Cr–1Mo(V,Nb) ferritic/martensitic steel

Transient thermo-metallurgical and thermo-mechanical computations for laser welded joint, in 9 mm thick 9Cr–1Mo(V, Nb) ferritic/martensitic steel plate, in square-butt configuration, have been carried out by simulating the laser welding process on the 3-dimensional (3D) solid model using a finite element based welding and heat treatment simulation solution package – SYSWELD. The heat source has been modeled as a combination of a 3D Gaussian and a double ellipsoid profiles for realistic representation of fusion zone morphology. Phase and temperature-dependent physical and mechanical properties of this material were used in these computations. The results show very short residence time (<0.5 s) for the material in the heat affected zone (HAZ). The results clearly delineate the effects of different thermo-metallurgical processes like heating, softening, cooling and solid state phase transformation (SSPT) on temporal evolution of the stress-field resulting from laser welding. Longitudinal component of the residual stress is the most significant followed by the normal component and the transverse component is the least significant. Cross-weld residual stress profiles show a trough in the fusion zone and the heat affected zone (HAZ) with a peak in the parent metal region bordering the metallurgical HAZ. Also, the longitudinal and the normal components of the residual stress show nearly similar profile with different magnitudes. The computed residual stress profiles show reasonably good agreement with that measured by neutron diffraction. The results also show significant plastic deformation and strain-hardening of the austenitic phase-field prior to its transformation into martensite.     

Workability characteristics and mechanical behavior modeling of severely deformed pure titanium at high temperatures

In the present study, compression tests were performed at temperatures of 600–900 °C and at strain rates of 0.001–0.1 s⁻¹ to study the deformation and workability characteristics of commercially pure titanium after severe plastic deformation (SPD). It was found that the effects of temperature and strain rate are significant in dictating the steady state flow stress levels and the strain values corresponding to peak flow stress. The strain rate sensitivity (m) during hot compression of severely deformed Ti was shown to be strongly temperature dependent, where m increased with the increase in deformation temperature up to 800 °C. High temperature workability was analyzed based on the flow localization parameter (FLP). According to the FLP values, deformation at and below 700 °C is prone to flow localization. The flow behavior was predicted using Arrhenius type and dislocation density based models. The validities of the models were demonstrated with reasonable agreement in comparison to the experimental stress–strain responses.     

Deformation behavior and microstructural evolution of directionally solidified TiAlNb-based alloy during thermo-compression at 1373–1573 K

Alloy Ti44Al6Nb1.0Cr2.0V0.15Y0.1B is newly designed and melted by vacuum consumable melting method, and is then prepared by cold crucible directional solidification (CCDS) technology. Thermo-compression experiment is carried out on CCDS billets at 1373–1573 K. Experimental results show that, when compressing direction (CD) is perpendicular to columnar grains, higher deformation active energy of Q = 689.8 kJ/mol can be acquired which means excellent creep resistance in radial direction; the microstructural evolution with different lnZ parameters is investigated by electron back scattering diffraction and the deformation mechanism is discussed; the ordering temperature of B2/β phase is deduced to be in the range of 1200–1250 °C. When the CD is parallel to the columnar grains, a much higher peak stress is acquired which means more excellent creep resistance in the axial direction; the shearing deformation feature is presented and the schematic of deformation mechanism is given.     

Behavior and failure of uniformly hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C under various stress states,including RIA loading conditions

The anisotropic plastic behavior and the fracture of as-received and hydrided Cold-Worked Stress Relieved Zircaloy-4 cladding tubes are investigated under thermal–mechanical loading conditions representative of Pellet–Clad Mechanical Interaction during Reactivity Initiated Accidents in Pressurized Water Reactors. In order to study the combined effects of temperature, hydrogen content, loading direction and stress state, Axial Tensile, Hoop Tensile, Expansion Due to Compression and hoop Plane Strain Tensile tests are performed at room temperature, 350 °C and 480 °C on the material containing various hydrogen contents up to 1200 wt. ppm (hydrides are circumferential and homogeneously distributed). These tests are combined with digital image correlation and metallographic and fractographic observations at different scales. The flow stress of the material decreases with increasing temperature. The material is either strengthened or softened by hydrogen depending on temperature and hydrogen content. Plastic anisotropy depends on temperature but not on hydrogen content. The ductility of the material decreases with increasing hydrogen content at room temperature due to damage nucleation by hydride cracking. The plastic strain that leads to hydride fracture at room temperature decreases with increasing hydrogen content. The influence of stress triaxiality on hydride cracking is negligible in the studied range. The influence of hydrogen on material ductility is negligible at 350 °C and 480 °C since hydrides do not crack at these temperatures. The ductility of the material increases with increasing temperature. The evolution of material ductility is associated with a change in both the macroscopic fracture mode of the specimens and the microscopic failure mechanisms.     

Application of a small-timescale fatigue,crack-growth model to the plane stress/strain transition in predicting the lifetime of a tunnel-boring-machine cutter head

The crack-growth lifetime of a tunnel-boring-machine (TBM) cutter head accounts for more than 80% of a TBM cutter head's entire lifetime. Considering the ultrathick plate of a TBM cutter head, a small-timescale crack-growth model is modified to predict crack-growth lifetime based on the plane stress/strain transition condition. An improved quasistatic method is proposed to calculate the dynamic stress of the weak points of the cutter head, which is used as the input load. A plastic constraint factor α is introduced to change the yield stress value of the material. The transition of the stress/strain state in the crack tip is simulated, and the modified model is verified by a fatigue crack-growth test of the characteristic substructure, giving better prediction results. Finally, this method is applied to predict the crack-growth lifetime of a TBM cutter head in the Water Diversion Project in Northwest Liaoning Province, China, and the results show that when the crack of the cutter head's vulnerable part grows from 0.1 mm to 60 mm in depth, the TBM's useful driving distance is about 11.2 km.     

Constitutive modeling of deformation in high temperature of a forging 6005A aluminum alloy

The 6005A aluminum alloy is one of the most widely used alloys in aeronautic and railway industries, yet its plastic deformation behavior under hot compression is still not fully understood. Isothermal compression tests of 6005A aluminum alloy were performed using a Gleeble-1500 device, up to a 70% height reduction of the sample at strain rates ranging from 0.01 s⁻¹ to 10 s⁻¹, and deformation temperatures ranging from 573 K to 773 K. Several modeling approaches, including flow stress–strain curves, a constitutive Arrhenius-type equation model, and processing maps were used to characterize the deformation behavior of the isothermal compression of 6005A aluminum alloy in this study. The related material constants (i.e. A, β and α) as well as the activation energy Q for 623–773 K and 573–623 K temperature regimes were determined. Two sets of constitutive exponent-type equations for the 6005A aluminum alloy were proposed. Furthermore, a change in deformation mechanism occurred when changing the temperature range from 623–773 K to 573–623 K.     

Microstructure and mechanical properties of duplex stainless steel subjected to hydrostatic extrusion

The nanostructure and mechanical properties of ferritic-austenitic duplex stainless steel subjected to hydrostatic extrusion were examined. The refinement of the structure in the initial state and in the two deformation states (ε = 1.4 and ε = 3.8) was observed in an optical microscope (OM) and a transmission electron microscope (TEM). The results indicate that the structure evolved from microcrystalline with a grain size of about 4 μm to nanocrystalline with a grain size of about 150 nm in ferrite and 70 nm in austenite. The material was characterized mechanically by tensile tests performed in the two deformation states. The ultimate strength appeared to increase significantly compared to that in the initial deformation stages, which can be attributed to the grain refinement and plastic deformation. The heterogeneity observed in microregions results from the dual-phase structure of the steel. The results indicate that hydrostatic extrusion is a highly potential technology suitable for improving the properties of duplex steels.     

Fatigue crack initiation behaviors throughout friction stir welded joints in AA7075-T6 in ultrasonic fatigue

This paper presents the results of experimental investigation on fatigue behaviors of friction stir welded joints in AA7075-T6 with ultrasonic fatigue test system (20 kHz). Two kinds of particles, Fe-rich intermetallic compounds and Mg₂Si-based particles, governed the fatigue crack initiation. The plastic deformation and recrystallization during welding process led to the changes in particle size and micro crack occurrence between thermo-mechanically affected zone (TMAZ) and nugget zone (NZ). Therefore, the fatigue crack initiation sites leaned to be located at the TMAZ in short fatigue life, or at the NZ in very high cycle fatigue regime.     

Effects of thickness and texture on mechanical properties anisotropy of commercially pure titanium thin sheets

Simultaneous effects of thickness and texture on the anisotropy of mechanical properties and fracture behaviors of commercially pure titanium thin sheets were studied. The activation of different deformation systems, due to the split distribution of basal texture, led to mechanical properties anisotropy. The crack initiation and propagation energies, when the loading direction was parallel to the initial rolling direction, decreased with increasing thickness ranges from 0.25 to 1 mm. The changes of size, shape and distribution of dimples with increasing thickness confirmed the restriction of deformation systems and the development of triaxial stress state and plane-strain condition at the notch tip. However, in transverse-directed specimens, the energy release rate increased with increasing specimen thickness up to 0.75 mm and then decreased. The fractography of these specimens explained the simultaneous effects of thickness and texture on structural stability and high accommodated plastic deformation at the notch tip.     

Effects of initial grain size on hot deformation behavior of commercial pure aluminum

The effects of initial grain size of commercial pure aluminum on hot deformation behavior were investigated using hot compression tests. The hot compression tests were carried out on the pure aluminum samples with the initial grain sizes of 50, 150 and 450 μm using various strains, strain rates and different deformation temperatures. It was found that the hot deformation behavior of used material was sensitive to deformation conditions and initial microstructure. Results indicate that the initial grain size has significant effect on the flow stress. Flow stress decreases when the grain size decreases from 450 to 50 μm and when strain rate is lower than 0.05 s⁻¹. This procedure is reversed at strain rate of 0.5 s⁻¹. Furthermore, effects of other parameters like the strain rates and deformation temperatures on the flow stresses and hardening rates were investigated. It was also found that the inhomogeneity of microstructure distribution at different positions of the deformed specimens depended on the amount of deformation concentration at particular points and other processing parameters such as initial grain sizes, strain rates and deformation temperatures. In addition the geometric dynamic recrystallization (GDRX) was observed in the specimens highly strained (0.7) at elevated temperature (500 °C) using polarized light microscope and sensitive tint (PLM + ST).     

A new hybrid identification method for determining the material parameters of thin-walled tube under compressive stress state

Accurate and fast determination of material parameters of thin-walled tube under compressive stress state is essential for analyzing the compressive-type tube forming process. For the thin-walled tube with hollow structure, it is difficult to determine the material parameters directly from the experiment since buckling occurs easily when the tube suffers axial compressive loading. To accurately and rapidly identify the material parameters of thin-walled tube under compressive stress state, a hybrid inverse identification method is proposed based on tube lateral compression test with combining finite element simulation, regression analysis and genetic algorithm. By employing the proposed method, the Swift law hardening parameters of thin-walled tubes with different materials and specifications under compressive stress state are identified. Furthermore, the efficiency and accuracy of the proposed method are discussed in comparison with the previous researches. The results show that: (1) for 6061-T4 and 1Cr18Ni9Ti tubes, the maximum relative predicting errors of forces in tube lateral compression using the identified material parameters are less than 9%; (2) for aluminum tube ∅100 × 2 (diameter × thickness, mm), the maximum discrepancies between the simulated and experimental circumferential strains are less than 0.0274 for 30–70% reductions, and the simulated tube profiles deviate from the experiment less than 10% at reductions of 0–78%; and (3) the proposed method almost saves 80% computational time compared with the previous stepwise optimization method.     

Effects of formulation variables on surface properties of wood plastic composites

Degree of surface quality of wood plastic composites (WPCs) is a function of both raw material characteristics and the manufacturing variables. The WPC panels comprised of different panel densities (800, 950, 1000, and 1080 kg/m³), wood flour contents (50, 60, 70, and 80 wt.%), wood flour sizes (<0.5, ?0.5 to <0.8, 0.8–1, and >1 mm), and hot-pressing temperatures (190 and 210 °C) were manufactured using a dry blend/flat-pressing method under laboratory conditions. The surface smoothness of the WPC panels improved with increasing WPC density, plastic content, and hot-pressing temperature while it deteriorated with increasing wood flour size. The reduction in the particle size of the WF resulted in a more compact structure on the WPC surface. In general, the wettability of the samples increased by increasing surface roughness.