Martensitic transformation behaviour of non-equilibrium heat treated Ni50·9Ti49·1 alloys

Abstract

Ni50·9Ti49·1 specimens were heat treated using a thermal simulator. The martensitic transformation behaviours of selected areas of the thermal simulating treated specimens were studied with resistivity temperature measurements. In the thermal simulating process specimens were heated by a large electric current to a given peak temperature (400, 500, 600, 800, 900 or 1100°C respectively) and immediately water cooled to room temperature. As the two ends of a NiTi alloy specimen were fixed in copper jigs, unequal heat treatment effect areas were formed in the specimen segments near its two ends. In the unequal area of an 800°C thermal simulating treated sample, a wide transformation temperature range phenomena appeared. The experimental results indicate that non-equilibrium heat treatment proves to be an effective method to fabricate transformation temperature gradient shape memory materials.     

Synergistic effects of binary oxygen carriers during chemical looping hydrogen production

The use of binary oxygen carrier allows for the materials of enhanced activity or stability during chemical looping process. However, the lack of mechanical understanding of the origin of the improvements hindered the rational design and control of the doping process in the oxygen carrier production. Here, we synthesized a series of M_0.6Fe_2.4O_y (M = Ni, Cu, Co, Mn) binary spinel materials and carried out various characterization techniques to study how the dopants influenced the material phase change, the oxygen transfer as well as the chemical looping performance. The results showed the chemical looping reactivity can be related to the oxygen transformation between lattice oxygen and oxygen vacancy, which was determined by the redox properties of both dopants and iron. The metal in tetrahedral site for Cu, Mn, Ni-doped sample were relatively stable, limiting oxygen transformation ability. In comparison, Co dopant promoted the reducibility of iron in tetrahedral site as well as metals in other sites, making almost all lattice oxygen rapidly transformed to oxygen vacancy during reduction. This was the main cause for the subsequent high hydrogen production rate (average ∼0.02 mmol. g⁻¹.s⁻¹) and yield (∼15.9 mmol.g⁻¹). Upon cycling, the phase separation of single oxides from Co_0.6Fe_2.4O_y and Mn_0.6Fe_2.4O_y spinels led to the decreased ability of oxygen transformation. However, the performance was extremely stable for Cu_0.6Fe_2.4O_y with reversible phase change between spinel and (Fe, Cu) wusitite by the Cu-Fe interaction. Based on the current results, this work points to a promising Cu-Co co-doping material with both good reactivity and stability.     

An effective approach for parameter determination of the digital phase-locked loop in the z-domain

In digital communication systems, typical methodologies in determining loop parameters of the digital phase-locked loop (DPLL) are based on the mapping transformation from the analog domain to the digital domain. However, such transform based algorithms are relatively complicated and not straightforward, and they also cause the problem that loop parameters are affected by the pre-detection integration time greatly. To solve these issues, an effective direct method of determining loop parameters of the second-order DPLL in the z-domain is proposed in this paper. Through ascertaining specific positions of the closed-loop system function's poles inside the right-hand side of the z-plane's unit circle, unknown parameters are calculated directly and flexibly in this method, which enables the DPLL to acquire good low-pass filtering characteristic and system stability. This novel method not only reduces the complexity of solving the parameters, but also eliminates the effect of the pre-detection integration time on loop parameters. Simulation results are provided to confirm the feasibility of the proposed method and to show that the DPLL obtained by this method achieves the similar tracking performance to the discretized PLL.     

Analysis of deformation induced martensitic transformation in stainless steels

Abstract

Many studies monitoring the formation of martensite during the tensile deformation of austenite report data which are, in principle, affected by both the applied stress and the resulting plastic strain. It is not clear in these circumstances whether the transformation is stress induced (i.e. the stress provides a mechanical driving force) or whether the generation of defects during deformation helps nucleate martensite in a scenario better described as strain induced transformation. The authors demonstrate in the present work that a large amount of published data relating the fraction of martensite to plastic strain can in fact be described in terms of the pure thermodynamic effect of applied stress.     

昙华林历史街区改造的反思

从武汉昙华林历史价值出发,结合国内创意产业园的成功案例,对造成昙华林被创意改造后的得失进行了分析,就其改造的规模、定位、功能、手法、配套等方面进行专项研究,最后尝试探寻昙华林历史街区改造的正确思路与方法,为昙华林开创一条复兴之路。     

GS30数控车床机电一体化改造研究

阐述了GS30型数控车床存在的问题及改造所要达到的目标,确定了改造的总体技术方案,选择了西门子840D数控系统作为控制装置,并配备了相匹配的各模块型号,做出了机床电气原理图,编制了PLC软件程序,对机床的各参数进行了设定,在完成机械部分和数字伺服系统的调试后,对该机床进行了验收,结果表明:通过改造,提高了机床的可靠性和精度,维修方便,能满足各元件的加工要求,机电一体化改造成本仅为同档次进口机床购价的四分之一。     

Precipitation behaviors in a quenched high Nb-containing TiAl alloy during annealing

The precipitation of γ phase and heterogeneous nucleation of ω_o phase within β_o phase areas are common phenomena in TiAl alloys. However, detailed explanation on the corresponding phase transformation mechanisms is still lacking. In this study, the precipitation behaviors of γ and ω_o phases in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy are investigated. The results show that large γ grains form after quenching whereas small γ particles can directly nucleate within the remaining β_o phase during annealing. Semi-coherent interfaces are observed between γ and β_o phases and the average distance between dislocations is evaluated. The heterogeneous nucleation of ω_o phase at the lamellar colony boundary is imaged by HRTEM. Edge-to-edge method is used to calculate the orientation relationship between γ and ω_o phases. The γ phase grows up faster than ω_o phase within the β_o phase areas during annealing at 800 °C.     

Effects of different particle deposition parameters on adhesion of resin cement to zirconium dioxide and phase transformation

This study evaluated the effect of air-abrasion parameters such as particle size, distance, and time on adhesion of resin cement to zirconium dioxide (Y-TZP) and t→m phase transformation. Y-TZP blocks (N = 80) (In-Ceram YZ, Vita) (4 mm^3?×?4 mm^3?×?3 mm³) were assigned into eight groups (n = 10): air-abrasion with 30 μm (CoJet Sand, S30) and 110 μm (Rocatec-Plus, S110) silica-coated alumina particles, applied for either for 10–20 s (T = time), from a distance of 10–20 mm (D = distance), composing the following groups: S₃₀T₁₀D₁₀, S₃₀T₁₀D₂₀, S₃₀T₂₀D₁₀, S₃₀T₂₀D₂₀, S₁₁₀T₁₀D₁₀, S₁₁₀T₁₀D₂₀, S₁₁₀T₂₀D₁₀, and S₁₁₀T₂₀D₂₀. Resin composite (RelyX ARC) was bonded to Y-TZP blocks in polyethylene molds. The specimens were aged (10,000 thermal cycles and water storage for 90 days) prior to shear bond test. Failure types were analyzed under stereomicroscope and SEM, and phase transformation was calculated. Data (MPa) were analyzed using 3-way ANOVA and Tukey’s tests. Air-abrasion with 110 μm silica particles (10.96) presented significantly higher bond strength (p = 0.0149) compared to 30 μm (8.96). Time (p = 0.403) and distance (p = 0.179) parameters did not affect the results significantly. Air-abrasion with 110 μm particles (12.3) promoted higher bond strength than that of 30 μm (6.4) when applied for 10 s from a distance of 10 mm (Tukey’s). Failure types were predominantly adhesive. Phase transformation ranged between 30.3 and 35.9% for 30 μm particles and 23.8–43.7% for 110 μm particles. While the size of silica-coated alumina particles were more relevant parameter for resin cement adhesion to Y-TZP, time (up to 20 s) and distance (up to 20 mm) appear to be less pertinent.     

基于SWT和Hilbert的密封磁阻马达式CRDM振动信号去噪

针对控制棒驱动机构滚轮振动信号采集过程受到噪声干扰的问题，提出了小波半软阈值（SWT）和Hilbert变换法相结合的去噪方法。该方法首先利用小波半软阈值算法在时频域对滚轮振动信号进行降噪处理，然后进行Hilbert变换求出其包络谱，分析寿命试验与缺陷验证试验中不同的滚轮振动信号。试验结果表明，该方法可有效消除噪声对振动信号的干扰，证明了小波半软阈值与Hilbert变换相结合的方法在驱动机构滚轮状态识别和故障诊断中的有效性，为驱动机构的状态判别提供了理论支持。     

建筑物内振动源变频改造前后楼板振动测试与分析

针对采取简单减振措施后的设备振动仍然会引起楼板明显振感的情况,在进行原因分析后,通过改变振动源工作频率,并取得了良好的减振效果。