Ni53Mn22Ga25磁性形状记忆合金的相变内耗

研究了Ni53Mn22Ga25磁性记忆合金在190～390K温度范围的内耗行为。结果表明．当合金发生正、逆马氏体相变时出现明显的内耗峰,并伴随模量变化出现极小值。马氏体相变后继续降温。在215K附近出现新的内耗峰,模量明显增高。合金在居里温度发生顺磁及铁磁正反转变时．内耗及模量均不发生变化。对上述现象进行了分析和讨论。     

高硅马氏体型热作模具钢回火转变的内耗研究

研究了含硅量为1.5%(质量分数)的高硅马氏体型热作模具钢(SDH3)的内耗谱与显微结构之间的关系.实验用SDH3钢采用1060℃保温30min油冷淬火和不同回火工艺处理.试样的温度-内耗谱(TDIF)的测量在振动仪上进行,采用自由衰减法,测量温度区间为室温至750℃.实验结果表明:SDH3钢的TDIF谱线主要是Snoek峰和SKK峰这两种机制的内耗峰;随着回火温度的升高,内耗峰峰高均逐渐降低,并且峰位也发生改变;当回火温度达到650℃时,内耗峰完全消失而只剩下背景内耗;随着回火保温时间的延长,内耗峰峰高和峰位都发生变化,并从扩散控制再分配机理的角度对这些变化进行了分析讨论.     

钇对工业纯钛中氧内耗峰的影响

工业纯钛中存在一个峰温为440C(f=1Hz)激活能为203kJ/mol的内耗峰,加入微量稀土元素钇后峰温向高温移动,峰高下降。用O—Y原子对模型对上述现象进行了说明。     

高强海工钢EH36中氢扩散行为研究

通过显微组织表征明确了高强海工钢EH36厚板心部和表面组织的差异,进而通过氢渗透测试、内耗、氢脆敏感性指数测定等实验研究了EH36厚板心部和表面位置的氢扩散行为。结果表明,EH36厚板的表面和心部组织分别为贝氏体组织和铁素体+珠光体组织。心部组织的氢陷阱数量较少,组织溶氢能力较弱,氢扩散系数较高,氢扩散穿透时间较短。钢中间隙氢原子的扩散导致了充氢后实验钢的内耗峰在低温区出现了H-Snoek峰,同时氢的存在使得SKK峰发生偏移。相比于心部位置,由于实验钢表面的组织中所含界面较多,导致其内耗谱在高温区出现较弱的晶界峰。实验钢心部粗大的铁素体+珠光体组织导致其氢脆敏感性指数较高,抗氢脆失效能力较弱。此外,钢中氢原子的大量存在会显著弱化柯氏气团对可动位错的钉扎作用,降低实验钢的屈服点延伸率。     

BNb与BNbRE钢轨踏面区的内耗

测量了BNb钢和BNbRE钢重轨踏面区使用(热轧)态及其700℃、30min WC、室温变形态试样的内耗。发现,两种钢轨热轧态试样都有Snoek—Kê—Kster(SKK)峰;但这两种钢热轧态样品的内耗,有较明显的差异:未加稀土的BNb钢轨的SKK峰明显地大于加丁稀土的BNbRE钢轨的峰,前者的峰温度也较后者高约20℃;但后者有可测的Snoek峰,而前者则没有此峰。两种钢变形态样品的SKK峰大致相同。对结果做了讨论。     

高碳高合金马氏体钢回火过程连续性转变的内耗行为研究

高碳高合金马氏体钢淬火后在回火过程中存在过饱和碳原子偏聚现象,碳原子偏聚于位错附近的间隙位置,回火过程中以碳化物形式沉淀析出.通过内耗研究表明,随着回火温度的增加,Snoek峰驰豫强度下降并消失,SKK峰驰豫强度降低并随回火温度的升高而宽化.由该结果可知由于大量碳原子偏聚于位错处,随后以细颗粒碳化物形式在位错处析出.随...     

预处理对Fe－15Cr－4Al合金475℃脆性的影响和钇的作用

１１００℃预处理的Ｆｅ－１５Ｃｒ－４Ａｌ合金在５００℃时效后迅速脆化，８００℃预处理的合金则无脆化倾向。高温处理的合金有明显的Ｓｎｏｅｋ内耗峰，α相中碳、氮的浓度较高。时效后Ｓｎｏｅｋ峰降低，在主峰的高温侧还分裂出一小峰。这表明４７５℃脆化包括碳、氮析出和α＇相析出两个过程。前者在时效初期有极强的脆化作用，后者在时效数百小时后才显示出微弱的影响。中温预处理的合金无Ｓｎｏｅｋ峰，碳、氮已充分析出，它们不再发生时效析出。含０．２和０．４ｗｔ％Ｙ的合金不出现４７５℃脆性。内耗无Ｓｎｏｅｋ峰，合金中碳化物、氮化物极少。Ｙ－Ｆｅ相俘获杂质原子，消除碳、氮的时效析出，是钇抑制４７５℃脆性的原因。     

热处理对添加少量Cr、Fe的Ti-Ni合金组织和力学性能的影响

采用真空熔炼法制备Ti_(45)Ni_(55)Cr_(0.3)和Ti_(45)Ni_(52)Fe_3合金(元素含量为摩尔分数)铸锭,对其进行均匀化处理以及850℃/1 h固溶和水淬后,分别采用3种不同的工艺进行热处理:1)850℃/1 h固溶,2)375℃/1 h时效,3)25%冷轧+375℃/1 h退火,研究热处理工艺对合金的相变特性、力学性能、内耗性能和微观组织的影响。结果表明,Ti_(45)Ni_(55)Cr_(0.3)和Ti_(45)Ni_(52)Fe_3合金的基体均由B2与R相组成;Ti_(45)Ni_(55)Cr_(0.3)合金经过375℃/1 h时效或25%冷轧+375℃/1 h退火处理后,析出Cr3Ni2粒子,时效后抗拉强度为1 385 MPa,时效升温过程的峰值内耗达到0.53;Ti_(45)Ni_(52)Fe_3合金经过25%冷轧+375℃/1 h退火后析出Ti3Ni4相,抗拉强度为770 MPa;与其它热处理工艺的升温过程相比,Ti_(45)Ni_(52)Fe_3合金的时效升温过程峰值内耗最高,达到0.158;降温过程中,Ti_(45)Ni_(55)Cr_(0.3)合金在时效降温过程中发生B2→R→M相变,退火的降温过程中发生B2?R相变,而Ti_(45)Ni_(52)Fe_3合金在退火的降温过程中发生B2→R→M相变。     

温度和加热速度对CuZnAl形状记忆合金相变内耗的影响

本文探讨了CuZnAl合金相变过程中内耗的变化规律、产生机制以及加热速度对内耗的影响。结果表明:CuZnAl合金高内耗的产生是由其特有的相变机制引起的,并和加热速度有关。     

Fe-RE系合金的力学谱特征

利用多功能内耗仪测量,分析了不同稀土含量对Fe-RE系合金内耗峰的影响,在此基础上,探讨了稀土在纯铁晶界处的存在状态与微合金化机理。结果表明,纯铁在551.4℃(频率为2 Hz)出现纯铁晶界峰;当纯铁中稀土含量为0.0084%时,纯铁晶界峰接近于消失,峰温不变,峰值减小,说明有部分稀土固溶在晶界处;当稀土含量为0.0135%时,出现固溶晶界峰和第二相沉淀晶界峰,此时稀土以固溶形式和第二相沉淀的形式存在于晶界。     

Sarcomere relaxation in hamster diaphragm muscle

We characterized instantaneous sarcomere relaxation over the load continuum in isolated hamster diaphragm muscles by means of laser diffraction. In afterloaded twitches, sarcomere relaxation displayed two consecutive phases. The bulk of sarcomere lengthening occurred during the first phase and corresponded in time to muscle lengthening. The second phase of sarcomere relaxation was slower and corresponded in time to tension decay. At initial muscle length, the peak velocity of sarcomere lengthening (SVL) was linearly related to both the maximum extent of sarcomere shortening (delta SL) and sarcomere length at peak shortening (SLmin; each P < 0.01). Varying preload modified the SVL vs. SLmin relationship but not the SVL vs. delta SL relationship. At a given preload, muscle tension decay began at a similar sarcomere length, regardless of the afterload level. In conclusion, our results support the role played by sarcomere length in regulating the diaphragm muscle-lengthening rate but not the rate of tension decline.     

Simulation of the γ–α‐transformation using the phase‐field method

Phase transformation is a powerful tool to change the properties of steels. Of the known transformations especially the γ–α‐transformation is utilised. It occurs in a temperature range relevant for heat treating and hot deformation processes. In this paper an approach is presented in which the γ–α‐transformation is simulated with Micress. This software applies the multicomponent multiphase‐field model, which is based on the reduction of total free enthalpy. Two different steels have been selected for the simulations, an ULC and an IF steel. Dilatometric tests serve as a basis for the simulations. These tests have shown that the transformation behaviours of the two steel grades are governed by two different kinetics. The transformation kinetics of the IF grade is influenced by the microalloying concept applied, resulting in a very slow start of the transformation. This has also been incorporated in the simulations by choosing two different grain boundary mobilities, one main parameter of the simulation. The simulation results of the ULC grade show the huge influence of nucleation undercooling as another one of the main parameters. Both simulation results are satisfying. They show that the phase‐field method offers a strong simulation tool in the area of phase transformation.     

Temperature,Stress and Distortion of Ti–6Al–4V Alloy Low-Temperature Friction Stir Welding Assisted by Trailing Intensive Cooling

The low-temperature friction stir welding (FSW) in which peak temperature is lower than the transus temperature of β phase was achieved using rotational speed of 100 rpm and welding speed of 30 mm/min. Trailing intensive cooling with liquid nitrogen was successfully applied to FSW under the low-temperature welding conditions. Comparisons of the temperature field, plastic strain, residual stress and welding distortion between intensive and conventional cooling were investigated by experiment and simulation. Results reveal that trailing intensive cooling is attributed to shrink high-temperature area and reduce the value of peak temperature and plastic strain. Longitudinal residual stress presents M shape, and the reduction of maximum tensile residual stress reaches 4.8%. The welding distortion shows an anti-saddle shape, and the decrement of welding distortion in transverse direction is 34.5%.     

Comparison of Hot Rolled Textures in Different Grades of High Formable Steels

During hot rolling of steels phase transformation takes place. Hot band texture and hot band grain size largely influence the texture formation of cold rolled and annealed steels. Generally, a strong crystallographic relationship exists between the parent austenite phase and the product ferrite phase. The present investigation incorporates a comparative study of hot band texture formation in austenitic zone in extra deep drawing (EDD), interstitial free (IF) and interstitial free‐ high strength (IF‐HS) steels. The intensities of hot band texture in IF‐HS steel [f(g) = 19.6] were found to be much stronger in comparison to EDD [f(g) = 3.9] and IF [f(g) = 1.4] steels.     

Hefting for a maximum distance throw: A smart perceptual mechanism.

Objects for throwing to a maximum distance were selected by hefting objects varying in size and weight. Preferred weights increased with size reproducing size-weight illusion scaling between weight and volume. In maximum distance throws, preferred objects were thrown the farthest. Throwing was related to hefting as a smart perceptual mechanism. Two strategies for conveying high kinetic energy to projectiles were investigated by studying the kinematics of hefting light, preferred, and heavy objects. Changes in tendon lengths occurring when objects of varying size were grasped corresponded to changes in stiffness at the wrist. Hefting with preferred objects produced an invariant phase between the wrist and elbow. This result corresponded to an optimal relation at peak kinetic energy for the hefting. A paradigm for the study of perceptual properties was compared to size-weight illusion methodology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoluminescence properties of a blue-emitting phosphor Eu2+-activated Ca3ZnAl4O10

A new aluminate host material Ca3ZnAl4O10 doped with Eu2+ was prepared by a high-temperature solid-state reaction method, and a pure crystalline phase of Ca3ZnAl4O10 was confirmed with X-ray powder diffraction (XRD) measurement. The luminescent property was investigated with excitation and emission spectra. The phosphor could be excited by UV light from 220 nm to 400 nm and emitted a blue luminescence peaked at 450 nm, which corresponded to the 4f65d1→4f7 transition of Eu2+ ions. The dependence of luminesce...     

Delta-ferrite recovery structures in low-carbon steels

The development of delta-ferrite recovery substructures in low-carbon steels has been observed in-situ utilizing laser scanning confocal microscopy (LSCM). Well-developed sub-boundaries with interfacial energies much smaller than that of delta-ferrite grain boundaries formed following transformation from austenite to delta-ferrite on heating. It is proposed that transformation stresses associated with the austenite to delta-ferrite phase transformation generate dislocations that subsequently recover into sub-boundaries by a process of polygonization. Experimental evidence in support of this proposal was found in a ferritic stainless steel. Thermal cycling through the high-temperature delta-ferrite/austenite/delta-ferrite phase transformation leads to the development of a well-defined recovery substructure, which, in turn, modifies the low-temperature austenite decomposition product from Widmanstätten to polygonal ferrite, with a commensurate change in hardness.     

Transformation superplasticity of zirconium

A tensile strain of 270 pct was achieved for coarse-grained zirconium subjected to transformation superplasticity conditions, where strain increments are accumulated upon repeated thermal cycling around the allotropic transformation temperature under the biasing effect of a uniaxial tensile stress. The strain increment per cycle was found to consist of two equal contributions from transformations on heating and cooling and to increase linearly with the applied stress. The measured strain increments are in good quantitative agreement with predictions based on the average internal stress during the transformation, which was determined independently from experimental transformation times. As the cycling frequency is raised, the average strain rate increases (a maximum value of 1.3·10⁻⁴ s⁻¹ was measured), but the strain increment per cycle decreases above a critical cycling frequency, for which the sample gage section undergoes only a partial phase transformation. The resulting reduction in internal mismatch and increase in internal stress are modeled using the experimental observation that β-Zr deforms by a mixture of diffusional and dislocation creep in the stress range of interest.     

Extracting instantaneous mean frequency information from Doppler signals using the Wigner distribution function

The Wigner distribution function (WDF) does not require the analysed signals to be stationary within the time segment used for analysis, and instantaneous frequency (IF) information can be obtained from it. Because of the influence of the cross-power of the signal components, however, the interpretation of the IF results is physically clear only for monocomponent signals with infinite data lengths. The IF results for multicomponent signals also suffer from spike problems and are quite unstable even when the signal-to-noise ratio is high. It is suggested that a "pseudo-instantaneous mean frequency," which uses the positive part of the WDF to follow the power distribution changes among frequency components, is used as a simple and rapid way to track frequency changes of Doppler signals. Simulation results show that the pseudo-instantaneous mean frequency does not have the same spike problems and gives stable and relatively accurate information about frequency changes when the sampling frequency is properly chosen.