环境温度对M2052合金阻尼性能的影响

采用OLYMPUS光学显微镜、XRD以及倒扭摆法,研究了退火态M2052阻尼合金的阻尼性能随工况温度变化的情况.实验结果表明:M2052合金在室温下的阻尼性能良好.合金的阻尼性能随应变振幅的增加而快速升高后,随应变振幅的进一步增加而基本保持不变.当工况温度低于M2052合金马氏体向奥氏体转变温度时,随温度的升高,孪晶密度下降,孪晶界减少,阻尼性能减小;当工况温度高于马氏体向奥氏体转变温度时,马氏体开始向奥氏体转变,导致母相和马氏体界面和马氏体与马氏体界面减少,同时孪晶继续减少,M2052合金阻尼性能加速下降.     

轧制变形量对Mg-Zn-Y合金组织和性能的影响

使用光学显微镜、动态机械热分析仪、X射线衍射仪和扫描电镜研究了不同轧制变形量对Mg-4Zn-2Y和Mg-4Zn-4Y合金显微组织、力学性能及阻尼性能的影响。结果表明,经轧制后合金中出现片层状的LPSO相;两种合金阻尼性能中与应变振幅无关的阻尼性能Q^-1₀随着轧制变形量的增加,其变化趋势基本一致,与应变振幅相关的阻尼性能Q^-1_h随着轧制变形量的增加而降低,Mg-4Zn-2Y合金以及Mg-4Zn-4Y合金的阻尼机制为位错型阻尼;随着轧制变形量的增加,合金断口中的韧窝数量增加,解理面减少,主要断裂方式由脆性断裂转变为韧性断裂;相同轧制变形量下,Mg-4Zn-4Y合金的强度优于Mg-4Zn-2Y合金,而阻尼性能要低于Mg-4Zn-2Y合金。     

冷变形对汽车车身用Al-Mg-Si薄板烤漆硬化性的影响

针对T4态汽车车身用Al-1.3Mg-1.2Si-0.5Cu-0.7Mn合金板材,采用室温拉伸变形结合DSC测定分析研究了冷变形程度对其再经烤漆处理后的屈服强度及时效析出特点的影响规律。结果表明,当变形量较大时,T4态Al-1.3Mg-1.2Si-0.5Cu-0.7Mn合金板材具有较强的加工硬化能力;冷变形量超过15%后,由于加工硬化导致其屈服强度增加了近190 N/mm2;承受不同程度拉伸变形的T4态合金板经烤漆处理后均表现出比较明显的烤漆软化现象;虽然烤漆前的室温拉伸变形能促进T4态合金板材在随后烤漆处理时β″过渡相的析出,但仅能部分弥补由于软化过程所致合金板材屈服强度的降低,略有改善T4态合金板材烤漆硬化性的作用。     

高强阻尼铝合金轧制板材的组织与性能

采用气体雾化/粉末冶金（RS P/M）工艺研制Al-9.0Zn-2.5Mg-2.0Cu-0.1Ni-0.1Zr/Zn-30%Al（LZ7）高强阻尼铝合金,经挤压、轧制成5.0 mm板材。详细观察LZ7板材轧制和双重时效（T7态）两种状态下的组织,并测试了T7态室温拉伸性能和阻尼性能。结果发现：采用快速凝固气体雾化制备的LZ7合金主要强化相有η′相和η相;LZ7金属基复合材料具有较好的阻尼性能,室温-250℃,LZ7合金的阻尼性能为6.0×10-3-24.52×10-3;室温下：0σ.2〉465 MPa,σb〉490 MPa,5δ〉6.0%。     

固溶时效处理对Mg-4Zn-0.3Zr合金显微组织及阻尼性能的影响

采用光学显微镜、扫描电镜、动态热分析仪和X射线衍射仪研究了固溶时效处理对Mg-4Zn-0.3Zr合金显微组织和阻尼性能的影响。结果表明,铸态合金晶粒尺寸约121μm,晶界粗大且有MgZn、MgZn₂和Mg₇Zn₃相分布;固溶处理后,晶界处的MgZn、MgZn₂和Mg₇Zn₃相基本溶入基体;时效处理后,晶界处有少量的颗粒状MgZn和MgZn₂相析出。在低应变振幅区,铸态合金阻尼性能最好,在高应变振幅区,固溶态阻尼性能最好,固溶+时效态合金阻尼曲线的斜率最大;3种状态合金在低温区的阻尼峰均由晶界阻尼峰和位错阻尼峰叠加构成,固溶态和固溶+时效态合金在高温区的阻尼峰为弛豫型阻尼峰。     

Mg-3Y合金大应变量轧制过程中的孪生辅助动态再结晶及组织演变

采用预挤压加单道次大应变量热轧制的方法制备了Mg-3Y（质量分数,%）合金板材。并研究了大应变量轧制过程中不同孪晶类型对合金动态再结晶（DRX）及组织演变的影响。结果表明,在挤压比为8:1的预挤压过程中,合金内部发生了几乎完全的动态再结晶。而在接下来的大应变量热轧制过程中,孪生变形尤其是■压缩孪晶及■双孪晶在协调合金的塑性应变中发挥了重要作用。此外,大量动态再结晶在压缩孪晶及双孪晶内部发生,并扩展到非孪晶区域,有效缓解了轧制过程中的内应力集中。上述2个过程对提高合金在大应变量轧制中的成形性均起到了促进作用。     

电磁搅拌态Al-5Fe基合金轧制及组织与性能

利用电磁搅拌技术制备了Al-5Fe-1.2Si-1Mg-0.6Cu-0.5Mn合金轧制坯锭,研究Al-5Fe基合金的轧制变形能力及合金的组织性能。结果发现,Al-5Fe基合金在道次压下量较小时表现出较好的变形性能,随着压下量的增加,材料的变形性能变差。合金最佳变形温度范围在430～460℃之间;合金的道次压下量不宜过大,以2～3mm为宜。用电磁搅拌坯锭轧制的板材,其富Fe相的破碎效果较电磁搅拌合金有大幅度的改善。在道次压下量不变的情况下,采用轧制温度为460℃,道次压下量为2mm时制备的板材中富Fe相细小、均匀,且板材力学性能最好,其室温下的抗拉强度和伸长率分别达到314.5MPa和7.2%。     

轧制工艺对Mg-10Gd-4.8Y-0.6Zr合金显微组织和力学性能的影响

Mg-10Gd-4.8Y-0.6Zr铸态合金经525℃、16 h均匀化退火后,在500℃轧制成总变形量为84%的板材,轧制后在200℃进行时效处理。观察合金的微观组织变化,并测试合金的力学性能。结果表明:轧制变形明显细化了晶粒尺寸,轧制后组织中存在方块相和长条状相;轧制初期组织中存在大量孪晶,孪晶能很好地协调塑性变形,并诱发了孪生动态再结晶;随着轧制变形量的增大,孪晶数量减少,再结晶方式以晶界弓出形核为主。轧制T5态合金具有优异的高温力学性能,200、250、300和350℃时抗拉强度分别为392、381、251和112 MPa,350℃拉伸时伸长率达到107.0%。     

温度对大应变轧制Al-Mg-Si-Cu-Zr合金的组织及性能的影响

在250、300、400℃下分别对Al-0.75Mg-0.75Si-0.8Cu-0.7Zr合金进行大应变轧制变形,采用拉伸性能测试和扫描电镜(SEM)等研究了轧制温度对不同处理态合金显微组织和力学性能的影响。结果表明:在250℃轧制时,Al-0.75Mg-0.75Si-0.8Cu-0.7Zr合金的抗拉强度为204 MPa,伸长率为15.2%;随着轧制温度的升高,强度逐渐降低,而伸长率不断增大;合金经300℃热轧+510℃×80 min+195℃×13 h+冷轧加工后的晶粒最为细小,其综合力学性能最好,抗拉强度为475 MPa,伸长率为8.13%,断口上分布着大量细小均匀的韧窝。     

高速铁路接触网用铜合金的制备与性能

研究了室温冷轧、低温轧制、低温轧制+中间时效3种不同冷轧方式对时效态Cu-1Cr-0.15Zr合金显微组织和力学性能的影响。结果表明,低温轧制有助于时效态改善Cu-1Cr-0.15Zr合金的硬度,且经过中间时效处理后,时效态Cu-1Cr-0.15Zr合金的硬度和电导率会进一步提高;无论是冷轧态还是时效态,低温轧制+中间时效试样的抗拉强度都高于室温轧制和低温轧制试样,且峰时效态低温轧制+中间时效试样的电导率最高。室温轧制、低温轧制和低温轧制+中间时效试样的磨损体积分别为0.682、0.191和0.054mm~3,时效处理后的低温轧制+中间时效试样的耐磨性最好;其抗拉强度和耐磨性都高于室温轧制和低温轧制试样,这主要与合金中孪晶/基体片层间距较小以及弥散析出的细小壳状富Cr相有关。     

Effects of a small amount of Si or Ge addition on stability and hydrogen-induced internal friction of Ti34Zr11Cu47Ni8 glassy alloys

Effects of a small amount of Si or Ge addition on stability and hydrogen-induced internal friction behavior of Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys have been investigated by X-ray diffraction, thermal analysis and temperature dependence of internal friction. It is found that the addition of 1 at.% Si, 2 at.% Si or 1 at.% Ge is effective to stabilize the glassy state and that Si is more effective than Ge. The peak internal friction of the single glassy phase alloy increases with increasing hydrogen content below about 20 at.% H. It is found that (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₉Si₁ glassy alloys have lower peak internal friction than the Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys, while (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ and (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₉Ge₁ glassy alloys have much higher peak internal friction. It should be noted that a (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ glassy alloy containing 14.4 at.% H shows high internal friction, Q⁻¹ of about 4 × 10⁻². The peak temperature of the single glassy phase alloys decreases with increasing hydrogen content below about 20 at.%. It should be noted that the addition of an extremely small amount of Si is effective to increase the peak temperature of the single glassy phase alloys. The relationship between the tensile strength and specific damping capacity indicates that the hydrogenated (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ glassy alloys have almost the same potential for a damping material as crystalline Mn–Cu–Al and Cu–Al–Ni alloys and hydrogenated Zr–Cu–Al glassy alloys.     

Internal friction spectra of the Ni40Ti50Cu10 shape memory alloy charged with hydrogen

The temperature dependence of the dynamic Young’s modulus E, the elastic energy dissipation coefficient Q⁻¹ and the heat flow (DSC) has been studied between 90 and 370 K in an Ni₄₀Ti₅₀Cu₁₀ alloy containing various amounts n_H of H (n_H=H/Me=0; 0.004; 0.008; 0.013 and 0.018 at.). The Young’s modulus exhibits softening when the start temperature M_s of the B2→B19 martensitic transition is approached on cooling and a much steeper modulus decrease between M_s and M_f. This steep decrease appears to be associated with stress-induced motions of twin boundaries within the B19 martensite as it is drastically reduced by H pinning of these boundaries. No internal friction (IF) peak occurs at the B2→B19 transition and the values of Q⁻¹ are high in the B19 martensite (≅100×10⁻⁴). Two IF peaks, P_H and P_TWH, occur below M_s in the H-doped material; the first is likely due to stress-assisted reordering of H elastic dipoles within a hydride phase, the second to H dragging processes by twin boundaries.     

Phase transformation and damping behavior of lightweight porous TiNiCu alloys fabricated by powder metallurgy process

Porous TiNiCu ternary shape memory alloys (SMAs) were successfully fabricated by powder metallurgy method. The microstructure, martensitic transformation behavior, damping performance and mechanical properties of the fabricated alloys were intensively studied. It is found that the apparent density of alloys decreases with increasing the Cu content, the porous Ti₅₀Ni₄₀Cu₁₀ alloy exhibits wide endothermic and exothermic peaks arisen from the hysteresis of martensitic transformations, while the porous Ti₅₀Ni₃₀Cu₂₀ alloy shows much stronger and narrower endothermic and exothermic peaks owing to the B2-B19 transformation taking place easily. Moreover, the porous Ti₅₀Ni₄₀Cu₁₀ alloy shows a lower shape recovery rate than the porous Ti₅₀Ni₅₀ alloy, while the porous Ti₅₀Ni₃₀Cu₂₀ alloy behaves reversely. In addition, the damping capacity (or internal friction, IF) of the porous TiNiCu alloys increases with increasing the Cu content. The porous Ti₅₀Ni₃₀Cu₂₀ alloy has very high equivalent internal friction, with the maximum equivalent internal friction value five times higher than that of the porous Ti₅₀Ni₅₀ alloy.     

Elastic constants and internal friction of an SiC-fiber-reinforced Ti-alloy-matrix crossply composite: measurement and theory

The complete elastic-constant tensor C_ij and the corresponding internal friction Q⁻¹_ij for a crossply composite are measured. It consists of silicon-carbide fibers in a Ti–6Al–4V matrix; it contained 35 vol.% fibers. With tetragonal symmetry, this composite possesses six independent C_ij and Q⁻¹_ij. Principally, two measurement methods were used: noncontacting and point-contact resonance-ultrasound spectroscopy. Specimens were rectangular parallelepipeds measuring a few to several millimeters. By changing the magnetic-field direction, which is needed for the Lorentz-force coupling, a particular macroscopic-vibration-mode group among the eight groups for free vibration of a rectangular parallelepiped could be independently excited and detected. This provides a big advantage in identifying the vibration modes of the observed resonance peaks, whose frequencies yield the C_ij by solving an inverse problem. Contactless coupling allowed the measurement of intrinsic internal friction, avoiding the energy loss associated with contact coupling. The internal-friction tensor was determined by a free-decay method. Theoretical calculations were made using an extended Mori–Tanaka mean-field theory and good theory–measurement agreement was found.     

Observation of local internal friction and plasticity onset in nanocrystalline nickel by atomic force acoustic microscopy

Atomic force acoustic microscopy (AFAM) is a near-field microscopy technique exploiting the vibrational behavior of the atomic force microscope cantilever. With its tip in contact with a surface, it is sensitive to its elastic and anelastic properties. We show how AFAM can be used to investigate the onset of plasticity in nanocrystalline nickel. To this end cantilever resonance curves are recorded with varying tip-loading force P. From the resonance frequencies and the width of the resonance curves, one obtains the contact stiffness k¹ and the contact damping Q^?1. Plotting these quantities vs. P, one observes damping peaks, as well as a reduction of the contact stiffness at specific P (≈1 μN) due to the nucleation of partial dislocation loops at grain boundaries. The local Q^?1 value is most likely caused both by the nucleation and by the interaction of the loop with the phonon and the electron baths. There is a background damping which is related to the global ultrasonic absorption.     

Investigation on the low-frequency mechanical properties of La0.6Sr0.4Co1−xFexO3−δ materials

The low-frequency mechanical properties of La_0.6Sr_0.4Co_1−xFe_xO_3−δ (0 ≤ x ≤ 0.8) materials have been measured using a computer-controlled pendulum. For undoped sample, five internal friction peaks (P0, P1, P2, P3 and P4) were observed. However, with the Fe doping, only two peaks (P3 and P4) were found at high temperature. The peaks of P0 and P1 have the feature of phase transition-induced internal friction, while the peaks of P2, P3 and P4 are the relaxation-type. From the analysis, it is suggested that the peak of P0 is due to the phase separation and the peak of P1 is related to the ferromagnetic (FM)-paramagnetic (PM) phase transition. For the peaks of P2, P3 and P4, they were associated with the motion of domain walls. The formation of this kind of domain structure is a consequence of a transformation from the paraelastic cubic phase to ferroelastic rhombohedral phase.     

The internal friction peaks correlated to the relaxation of atomic defects in Fe47Al53 alloy

The internal friction behavior of a Fe₄₇Al₅₃ alloy was examined to understand the evolution of the atomic defects. It is found that the internal friction peak observed at around 410 °C is in fact composed of two relaxational peaks (P1 and P2) that shifted toward high temperature with increasing frequencies. The P1 peak originates from the stress-induced migration of Al antisite atoms between the vacancies while the P2 peak originates from the dissociation of the interstitial carbon atoms from the C–V complexes and subsequent diffusion.     

Mechanical spectroscopy and twin boundary properties in a Ni50.8Ti49.2 alloy

The internal friction (IF), Young's modulus (E) and heat flow (DSC) have been measured in a Ni_50.8Ti_49.2 alloy as a function of temperature after both ageing and solubilization followed by water quenching. The IF of aged material measured at kilohertz frequencies, besides hardly detectable peaks associated with the A↔R and R↔M transitions, displays two additional non-thermally activated peaks P_TWM and P_TWR, which appear to be due to stress-induced hysteretic motions of twin boundaries within the martensite and the R-phase, respectively. In the solubilized state a large peak corresponding to the A↔M transition is observed together with a thermally activated relaxation P_d occurring at around 100 K (for f=1.2 kHz). The activation energy and limit time of this peak are 0.11 eV and 10⁻¹⁰ s, respectively. Peak P_TWM was not observed in the solubilized state. Peak P_d, which is found to increase with the number of thermal cycles through the transition region undergone by the sample, is attributed to stress-induced motions of dislocations around their equilibrium positions within the B19′ structure of the martensite. The absence of a twin boundary peak in the martensite formed from the solubilized austenite, as well as the large difference in the strength of the transformation relaxations in the aged and solubilized states of the material are accounted for in terms of the different nature of the predominant twin boundaries in the two different states of the material.     

Investigation on microstructure and internal friction for low density TiB2/ZL114 composites

TiB₂/ZL114 composites with the density of 2.733 g/cm³ were fabricated through reaction of K₂TiF₄ and KBF₄ (LSM method). The composites were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The internal friction measurements were performed on DTM-II-J dynamic modulus damping analyzer and the mechanisms were investigated. Experimental results indicate that reinforced particles are well-distributed in the matrix and the internal friction value of TiB₂/ZL114 composites is up to a maximum of 9.04x10^-3, almost twice that of ZL114. The internal friction results form dislocation vibration within the material, the sliding of grain boundary and phase interface, and together with the micro-plastic deformation caused by difference in coefficients of thermal expansion and elasticity modulus of various phases. The average internal friction values of samples with the sizes of 40 mmx4 mmx2 mm, 40 mmx8 mmx2 mm and 40~mm$\times 25 mmx2 mm are 8.83x10^-3, 8.89x10^-3, and 8.93x10^-3, respectively. Thus, the developed composites are of low density, high internal friction, and the sizes of samples have no relation to the internal friction behavior.