The hot compression tests of Ti-12Mo-4Zr-5Sn alloy were tested on the thermo-mechanical simulator of Gleeble-3500 under isothermal and constant strain rate. We studied this alloy’s behavior during thermal deformation at the conditions of T = 670~820 °C, ε ˙ = 0.001~10 s−1, and deformation degree 70%. The rheological stress curves of the alloy were modified, the characteristics of the rheological stress curves were analyzed, and the activation energy map of hot deformation was established. A physical constitutive model of the alloy based on strain compensation was established, which has taken the relationship between Young’s modulus and self-diffusion coefficient and temperature into account. Moreover, the intrinsic hot workability ξ map of the alloy was established based on the polar reciprocity model. The results show that this alloy’s rheological stress will descend when the temperature of deformation rises and grow when the strain rate increases, and has negative sensitivity of temperature and positive sensitivity of strain rate. According to the error calculation, the physical constitutive model’s correlation coefficient is 0.9910 and the average relative error is 3.97%, which has good accuracy. Through the analysis of the microstructures of the instability zone and the stability zone, it was found that the instability mode of the instability zone was dominated by the local flow, and the deformation mechanism of the stability zone was dominated by the dynamic recrystallization. The optimum processing parameters of the alloy known from ξ map and metallographic structure are the following: T = 790~820 °C and ε ˙ = 0.001~0.01 s−1.
Equal channel angular pressing(ECAP) is a promising technology for producing bulk ultra-fine grained(UFG) materials. The process and die structure are of its own characteristics. Reasonable die structure plays important role in developing uniformity of deformation, enhancing effectiveness of UFG production, reducing the cost of process, optimizing the process and so on. In this paper, the various ECAP dies are introduced in detail, especially, one-angle die structure characteristics and the relation among structure parameters of square channel are emphasized. The deficiency and further application prospects of the ECAP die also are discussed. which has a significant contribution to the optimization of the technology and die design.
The isothermal constant strain rate compression test of Ti-2.7Cu alloy was carried out by Gleeble-3500 thermomechanical simulator. The hot deformation behavior at temperature of 740–890 °C and strain rate of 0.001–10 s−1 was studied. The results show that the flow stress of the alloy is more sensitive to the deformation temperature and strain rate. The flow stress will decrease with the increase of deformation temperature, and increase with the increase of strain rate. The constitutive equation of Ti-2.7Cu is derived by using the Arrhenius hyperbolic sine function, and the activation energy at a strain of 0.4 is 412.32 kJ/mol. Based on the experimental data, the power dissipation efficiency and the instability parameter were investigated. Processing maps were established by superimposing the instability map and the power dissipation map. Through processing map prediction and microstructure observation, the unstable zones are mainly flow localization (740–750 °C /0.56 s−1–10 s−1) and mechanical instability (825 °C–890 °C /0.32 s−1–10 s−1), and the deformation mechanism of the stable zone is mainly dynamic recrystallization. It is found that the suitable deformation parameters of Ti-2.7Cu alloy are as follows: deformation temperature 780 °C–825 °C, strain rate 0.001 s−1–0.056 s−1.
Graphene nanoplatelets (GNPs) have many outstanding properties, such as high mechanical strengths, light weight, and high electric conductivity. These unique properties make it an ideal reinforcement used for metal matrix composites (MMCs). In the past few years, many studies have been performed to incorporate GNPs into metal matrix and investigate the properties of obtained metal matrix composites. Meanwhile, fabrication of MMCs through laser-assisted additive manufacturing (LAAM) has attracted much attention in recent years due to the advantages of low waste, high precision, short production lead time, and high workpiece complexity capability. In this study, the two attractive features are combined to produce GNPs reinforced MMC using selective laser melting (SLM) process, one of the LAAM processes. The target metal matrix material is Inconel 718, a nickel-based Ni–Cr–Fe austenitic superalloy that possesses excellent workability and mechanical performance, and has wide applications in industries. In the experiment, pure Inconel 718 and GNPs reinforced Inconel 718 composites with two levels of GNPs content (i.e., 0.25 and 1 wt. %) are obtained by SLM. Note that before the SLM process, a novel powder mixture procedure is employed to ensure the even dispersion of GNPs in the Inconel 718 powders. Room temperature tensile tests are conducted to evaluate the tensile properties. Scanning electron microscopy (SEM) observations are conducted to analyze the fracture surface of materials and to understand the reinforcing mechanism. It is found that fabrication of GNPs reinforced MMC using SLM is a viable approach. The obtained composite possesses dense microstructure and significantly enhanced tensile strength. The ultimate tensile strengths (UTSs) are 997.8, 1296.3, and 1511.6 MPa, and the Young's moduli are 475, 536, and 675 GPa, for 0 wt. % (pure Inconel 718), 0.25 wt. %, and 1 wt. % GNP additions, respectively. The bonding between GNPs and matrix material appears to be strong, and GNPs could be retained during the SLM process. The strengthening effect and mechanisms involved in the composites are discussed. Load transfer, thermal expansion coefficient mismatch, and dislocation hindering are believed to be the three main reinforcing mechanisms involved. It should be noted that more work needs to be conducted in the future to obtain more comprehensive information regarding other static and dynamic properties and the high-temperature performances of the GNP-reinforced MMCs produced by SLM. Process parameter optimization should also be investigated.
Abstract To realize the accuracy forming of diverse bent tubular components, the influences of geometrical parameters including the bending angle θ , the relative bending radius R/D , the outside diameter of tube D and the wall thickness of tube t on springback behaviors of high strength TA18 tube in numerical control (NC) bending are explored by finite element (FE) numerical simulation method. The results show that with increasing the θ or the R/D , the springback angle linearly increases, which can be described as a linear equation. With increasing the t , the springback angle first reduces and then increases, while the springback angle fluctuates mildly with increasing the D. Under the same D/t , the springback angle declines with increasing the D and t proportionally.
AIM To approach the effects of multi-site synchronous ventricular pacing on myocardial mechanics and cardiac work. METHODS Five modes of multi-site synchronous ventricular pacing were randomly performed in 12 dogs with anesthetized, opened chest and artificial-ventilation. Some parameters were measured simultaneously including: the peak of left ventricular pressure rise and fall (+/- dp/ dt(max)), the time constant of left ventricular relaxation(tau), the muscle tensile force in left/right ventricular wall (V-tensile force, V-TF), SV, LVSW and RVSW. RESULTS The myocardial systolic mechanical parameters: +dp/dt(max) and LV-TF of cHisB-LVPL and RVA-LVPL pacing by biventricular pacing modes were increased than that of cHisB-RVA pacing in right ventricular bifocal pacing mode. +dp/dt(max) in above two groups of biventricular pacing was increased than that in cHisB-RVA pacing. Tau value of cHisB-LVPL and RVA-LVPL pacing modes were shorted than that of cHisB-RVA pacing. The above parameters of cHisB-RVA-LVPL and cHisB-RVA-LVA biventricular trifocal pacing were superior to that of cHisB-LVPL and RVA-LVPL biventricular pacing. The +dp/dt(max), LV-TF and RV-TF of cHisB-RVA-LVPL pacing were increased as compared with that of cHisB-RVA-LVA pacing (P > 0.05). The -dp/dt(max) in cHisB-RVA-LVPL pacing were increased by 6.0% and tau value was shorted by 3.7% compared with those in cHisB-RVA-LVA pacing (P > 0.05). SV, LVSW and RVSW of cHisB-LVPL and RVA-LVPL biventricular pacing were increased than those of cHisB-RVA bifocal pacing. The above parameters of cHisB-RVA-LVPL pacing were increased than that of cHisB-RVA-LVA and cHisB-LVPL pacing. CONCLUSION It was explained that the cHisB-RVA-LVPL biventricular trifocal sites synchronous pacing mode would increase the velocity of ejection and filling during myocardial contraction and relaxation and enhance cardiac work by maintaining normal VSS.
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