Zn-Al二元合金熔化过程的低频内耗研究

利用强迫振动扭摆方法对ZnAl二元合金熔化过程的低频内耗进行了研究.结果表明,ZnAl二元合金熔化过程的内耗峰与其固态相变内耗峰的特征有较大差异.结合该合金熔化过程的微观结构变化,初步分析了内耗峰的形成机理. 关键词： Zn-Al合金 低频内耗 熔化     

Zn-Al共析合金的黏滞流变行为

在连续升温条件下，测量了共析Zn-Al合金的应变速率和黏度随温度的变化曲线，在共析转变温区观测到伴随相变过程的黏度极小值，研究了应力对应变速率和升温速率对黏度极小值的影响，发现在相变温区材料的力学行为遵从Newton黏滞流变定律，用相界面的数量和性质解释了相变温区Zn-Al合金的黏滞流变行为．将相变激活能和相界面的流变激活能进行比较，说明界面的流动性是影响相变的主要因素．结合过去在非晶Pd-Cu-Si合金的结构转变过程中观测到的伴随玻璃转变和晶化过程的黏度极小值，说明伴随着结构转变或相变过程，黏度出现极小 关键词：     

泡沫铝的低频内耗特征研究

采用粉末冶金发泡法制备的泡沫铝试样，研究了室温下低频范围（0.04—4Hz）泡沫铝的内耗与孔结构（孔隙率和孔径）、频率、振幅之间的关系．结果表明泡沫铝的内耗具有以下特征：孔径一定时，内耗随孔隙率的增加而增大；孔隙率一定时，内耗随孔径的减小而增大；在测量频率范围内，内耗与频率近似无关；小应变振幅时内耗随振幅的增大而增大，具有正常振幅效应．提出了泡沫铝的内耗产生机制，根据等效夹杂方法和钉扎位错内耗特点进行了理论分析，较理想地解释了实验结果 关键词：     

Internal friction due to negative stiffness in the indium–thallium martensitic phase transformation

Internal friction and dynamic shear modulus in an indium–21?at.% thallium alloy were measured as functions of frequency and cooling rate using broadband viscoelastic spectroscopy during the martensitic transformation which occurs in this material occurs around 50°C. Microstructural evolution of martensitic bands was captured using time-lapse optical microscopy. The amplitude of damping peaks due to the temperature-induced transformation in the polycrystalline alloy was found to exceed those reported by others for single crystals of similar alloy compositions, in contrast to the usual reduction in damping in polycrystals. The high temperature portion of the damping peak occurs before martensitic bands are observed; therefore this portion cannot be due to interfacial motion. Constrained negative stiffness of the grains can account for this damping, as well as for amplification of internal friction peaks in these polycrystals and for sigmoid-shaped anomalies in the shear modulus at high cooling rates. Surface features associated with a previously unreported pre-martensitic phenomenon are seen at temperatures above martensite-start.     

快冷Fe71Al29合金中的两个内耗峰

用一个计算机控制的倒扭摆研究了快冷Fe71Al29合金中的两个内耗峰.在快冷的Fe71Al29样品中分别在180℃(P1)，340 ℃(P2)和510℃(P3)出现了内耗峰，而在慢冷的Fe71Al29样品中只发现了P3峰.快冷样品中的P1和P2峰在从650℃冷却下来的测量过程中或在350℃经过较长时间的时效后消失，其峰高随时效时间的增加 而下降，直至消失.P1和P2峰都有弛豫特征，它们的激活能分别为：H1=1．03±0．08eV(P1峰)；H2=1．64±0．05eV(P2峰).P1峰被认为是无序合金中Al原子在四面体点阵内的最近邻运动所引起，P2峰则是无序合金中Al原子在四面体点阵内的次近邻运动所引起. 关键词： Fe-Al合金 内耗     

Study of stabilization of CuAlBe alloy during martensitic transformation by internal friction

In this study, the internal friction (IF) of a CuAlBe alloy during reverse martensitic transformation (MT) was investigated under isothermal and non-isothermal conditions. It was found that the IF decreases regularly with the aging time in the temperature range of phase transformation. It is thought that this phenomenon is caused by the defect movement. The defects diffuse to the interfaces between martensite and austenite and pin there gradually, thus leading to the IF decrease.     

Internal friction in Al bicrystals with ⟨111⟩ tilt and twist grain boundaries

Internal friction measurements were performed on various ?111? tilt and twist grain boundaries in high-purity Al bicrystals. The temperature dependence of the grain boundary internal friction peak was determined, and the activation parameters of grain boundary relaxation were obtained. These parameters were found to change in a wide range depending on boundary geometry. The activation enthalpy of boundary relaxation and the pre-exponential factor of the relaxation time are related according to the compensation effect. The results are discussed in terms of the model of correlated relaxations. Bicrystals with vicinal Σ3 boundaries were observed to behave like single crystals, i.e. an internal friction peak did not appear. This evidences that both coherent and incoherent (60° ?111? tilt) twins possess a high mechanical resistance.     

Grain boundary relaxation in fine-grained magnesium solid solutions

Grain boundary relaxation at elevated temperatures in fine-grained pure magnesium and Mg–Al solid solutions was investigated by measuring damping capacity at low frequencies. A sharp increase in damping capacity caused by grain boundary relaxation was observed at above a certain temperature. The onset temperature depended on aluminum content; the onset temperature increased with aluminum content. It was demonstrated that aluminum was effective in suppressing grain boundary relaxation in magnesium alloys. However, additional measurement of the damping capacity of a dilute Mg–Y alloy revealed that yttrium was more effective in suppressing grain boundary relaxation.     

Mechanism of solid-state eutectoid transformation in an aluminium-zinc alloy

The growth rate of pearlite during isothermal transformation of an aluminium-zinc eutectoid has been determined experimentally. Different theoretical models, assuming either volume or boundary diffusion of zinc to be a rate controlling mechanism for the eutectoid transformation, have been applied. With volume diffusion models, the calculated growth rates were lower than the experimental growth rates by a factor of three orders of magnitude. Reasonable agreement between the calculated and experimental growth rates has been obtained on applying the boundary diffusion models. The activation energy for boundary diffusion of zinc in the aluminium-zinc alloy was estimated to be ≅11.6 kcals/mole.     

Tribological behavior of microarc oxidation coatings formed on titanium alloys against steel in dry and solid lubrication sliding

The coatings mainly composed of nanostructured TiO₂ were deposited on Ti6Al4V alloy by microarc oxidation (MAO). The duplex coatings of microarc oxidation combined with spraying graphite process were fabricated for the antifriction purpose. The tribological properties of unpolished, polished and duplex coating against steel under dry friction conditions were examined. It is found that antifriction property of the polished microarc oxidation coating is superior to that of the unpolished one. The improvement is attributed to the low surface roughness and the nanocrystalline structure of coatings. The duplex coating exhibits best antifriction property, registering a lower and steady friction coefficient of ≈0.12 than that of the polished microarc oxidation coating sliding in the similar condition. The good tribological property is attributed to the specially designed duplex structure, the coating adhering strongly to the substrate and serving as the load-supporting underlayer and the graphite layer on top of it working as solid lubricant.     

Effects of annealing and additions on dynamic mechanical properties of SnSb quenched alloy

The elastic modulus, internal friction and stiffness values of quenched SnSb bearing alloy have been evaluated using the dynamic resonance technique. Annealing for 2 and 4 h at 120, 140 and 160 °C caused variations in the elastic modulus, internal friction and stiffness values. This is due to structural changes in the SnSb matrix during isothermal annealing such as coarsening in the phases (Sn, Sb or intermetallic compounds), recrystallization and stress relief. In addition, adding a small amount (1 wt.%) of Cu or Ag improved the bearing mechanical properties of the SnSb bearing alloy. The SnSbCu₁ alloy has the best bearing mechanical properties with thermo-mechanical stability for long time at high temperature.     

Relaxation during short-range-ordering in Cu-30% Zn alloy

The internal friction measured in a vacuum torsion pendulum has been used to determine the kinetics of short range ordering in an Cu-30% Zn alloy. Curves of relative internal friction (Q^–1/Q ₀ ^–1 ) against annealing time have been determined for various annealing temperatures. Average activation energy of 1·7 eV was found for the ordering process, which equals to that derived for zinc diffusion in coarse grained copper.     

Microstructural stability and age-hardening behavior of Re-added dual two-phase Ni3Al and Ni3V intermetallic alloys

The effect of Re addition on the microstructure and hardening behaviour of the dual two-phase Ni₃Al (L1₂) and Ni₃V (D0₂₂) intermetallic alloy was investigated by scanning electron microscopy, transmission electron microscopy and Vickers hardness test. The two-phase eutectoid microstructure accompanying the Re-rich precipitates were observed in the channel region of the alloys in which Re substituted for Ni but not in those in which Re substituted for Al and V. The concomitant addition of Nb (or Ta) with Re more stabilized the two-phase eutectoid microstructure and consequently more induced the fine precipitates in the channel region. The annealing at temperatures below the eutectoid temperature was necessary to induce the fine precipitates in the channel region and thereby result in the precipitation hardening. The fine precipitation in the channel region and related hardening was attributed to the alloying feature so that Re is soluble in the A1 (fcc) phase at high temperatures and becomes less soluble in the two intermetallic phases decomposed from the A1 phase at low temperatures.     

Creep behaviour in a discontinuous SiC–Zn-22% Al composite

Creep experiments were conducted on Zn-22%?Al in which SiC particulates were introduced by variable co-deposition of multi-phase materials (VCM). The objective of the investigation is to determine the effect of SiC particulates on the creep behaviour in region I (the low-stress region) and region II (the intermediate-stress or superplastic region) of the sigmoidal plot between stress and strain rate, which was previously reported for the reinforcement-free Zn-22%?Al. The creep data show that the presence of SiC particulates has no effect on the sigmoidal trend between stress and strain rate; and that in region II, the stress exponent, n, and the activation energy for creep, Q, agree well with those reported for SiC-free grades of Zn-22%?Al; n?=?2.5 and Q?～?Q _gb, where Q _gb is energy for grain boundary diffusion in the alloy. However, the data indicate that the presence of the particulates results in narrowing region II and reducing maximum ductility. An analysis of the creep data reveals the presence of a threshold stress that depends strongly on temperature. The microstructural data inferred from an examination of the crept specimens by the means of transmission electron microscopy (TEM) suggest that the origin of τ ₀ may be related to the interaction between moving dislocations and dispersion particles. These particles are introduced in the material as a result of processing the material by thermal spray and deposition.     

铝一镁合金中的反常位错内耗峰

Al-0.03at％ Mg合金在倒扭摆上-65℃在原位进行拉伸,形变量为0.5％,然后在升温过程中测量内耗,于-30℃及60℃附近观测到内耗峰,随后从80℃的降温过程中仍在相同温度观测到内耗峰。研究了不同温度下的内耗-振幅曲线,在降温过程中出现内耗峰的温度范围内观测到了振幅内耗峰,并由此计算得到等效激活能分别为0.32及0.22eV。初步认为,当低温冷加产生的位错弯结在外力作用下作沿边往复运动时,“镁原子-空位”对和镁原子被拖曳运动是分别引起-30℃峰和60℃峰的可能的原因。 关键词：     

Photonuclear reaction yields from59Co at 35 MeV and 54 MeV

In energy loss measurements with 50 keV electrons the damping of the 15 eV volume plasma loss in Al was investigated by means of its energy half widthΔ E as function of the scattering angle?. For angles smaller than 1.5 · 10^?3 rad a damping is observed, which cannot be explained by former theories. It comes into play when the wavelength of the plasmons is larger than the mean crystal sized. — For large crystal size (d ≧250 Å) the half width of the plasma loss obtained at ?=0 was 0.53 eV.     

Anelasticity in grey cast iron and silicate mixtures

The findings from our investigations of the anelastic properties of graphite-containing composite systems (i.e., grey cast irons and graphite mixtures) are presented and analyzed. The nature of the temperature spectrum of internal friction between −120 and +40°C is shown to be similar for both graphite and graphite compositions based on iron (cast irons), and for graphite mixtures based on silicates (pencil lead). The mechanisms for the formation of thermally activated relaxation peaks within graphite, and the dissipation of energy in gray cast irons based on different compositions with lamellar-shaped graphite inclusions in the matrix, are discussed.     

马氏体式相变过程中所引起的内耗变化

用扭摆测量两种跌锰合金(Mn17.5％和12.8％)和一种铜铝合金(Al13％)的内耗,在发生正和反的马氏体相变的温度范围内各出现一个内耗峰。这种内耗峰出现的条件是必须伴随着马氏体式相变过程的进行。用含Mn17.5％的铁锰合金作了系统实验,观察到内耗峰的高度随升温(或降温)速度和应力的增加而增高,随振动频率和含碳量的增加而减低。可以用振动一周内试样中转变量愈多内耗也愈大的关系得到统一的解释。讨论了关于产生内耗峰的机构。认为主要由于马氏体相变是突然间完成,此时扭转的外力可视为常数,从应力和不均匀物质交互作用能的计算,可以证明外力所做的功必须损失一半,因而引起内耗。此外应力感生相变也可以引起很小一部分内耗。     

银、银-铝合金及其内氧化银-铝合金的内耗峯

用频率约为1周/秒的扭摆,测量了99.99％和99.95％两种纯银以及99.99％纯银分别加入0.01％、0.02％、0.05％、0.15％、0.5％铝和99.95％纯银加入0.5％铝的六种合金的内耗。并且,还比较了三种合金的多晶和其中一种合金的单晶在内氧化前和后,以及经过不同时间的内氧化处理后的内耗变化。实验的结果表明:(1)99.99％纯银试样在空气中测量,升温过程中在130℃左右出现一个内耗峯,从高温作降温测量这个峯不再明显地出现。(2)99.95％纯银试样和99.99％纯银加有少量铝的三种合金试样,在空气中作升温测量,都出现两个明显的内耗峯。低温峯出现在130℃到260℃的范围内,高温峯出现在380℃到430℃的范围内。这两种内耗峯的高度和巅值温度都随杂质含量的多少而改变。从高温作降温测量,高温峯可以重复出现,而低温峯就不再出现。加入合金元素一方面会引起一个新的高温峯,另一方面它又起着抑制低温峯出现的作用。当铝含量超过0.05％(即0.2原子％)时,就只出现一个高温峯。实验的结果指出,低温峯和氧在银中存在时的状态有关,可能是由于晶界上Ag₂O的变化导致晶界结构状态和空位的平衡浓度的改变而引起的。高温峯可能是由于富集在晶界或亚晶界处的合金元素,在一定温度的交变应力下向晶粒内扩散和反扩散所引起的。(3)经过内氧化处理后的合金试样,其内耗巅值是随处理时间的增加而减小。这种内耗的变化也是由于晶界处的铝和氧原子的平衡浓度和界面结构状态受到改变引起的。     

烧结β型Ti-Nb合金中由间隙原子引起的Snoek弛豫

用粉末冶金方法制备了不同Nb含量的Ti-Nb合金.用美国TA仪器公司的动力学分析仪Q800以单臂振动模式研究了不同Nb含量和不同热处理以及不同测量参数下的Ti-Nb合金的内耗行为,用X-射线衍射检测了不同样品的微观结构.实验表明,在水淬的和烧结态的Ti-Nb合金的内耗-温度曲线上均发现了弛豫型的内耗峰,这个内耗峰的高度与Nb含量有关,在低Nb含量的Ti-Nb合金样品中不出现,水淬样品内耗峰的最大值出现在Ti-35.4 wt.%Nb (以下称Ti-35.4Nb)的合金中,烧结态样品的内耗峰高度在实验成分范围内单调地随Nb含量而增加.水淬的Ti-35.4Nb合金的弛豫参数分别是激活能H_(wq)=(1.67±0.1) eV和指数前因子τ_(0wq)=1.1×10~(-17±1) s.另外,内耗峰的高度也与热处理有关,水淬的Ti-35.4Nb合金比具有相同成分的烧结态的合金的内耗峰高得多,淬火温度对内耗峰高度也有影响.研究发现,这个内耗峰与Ti-Nb合金中的β相有关,峰高取决于β相的稳定性及其含量,当β相的稳定性降低以及β相的量增加时,峰高增加.水淬Ti-35.4Nb合金中的β相是亚稳状态的β相(β_M),时效时β_M能转变成稳定的α相和稳定β相(β_S),烧结态合金中的β相是β_S.不同热处理状态下Ti-35.4Nb合金样品的微观结构的不同导致了内耗峰高度的差别.从微观结构分析,在淬火的合金中,峰高最大值出现在35 wt.%Nb含量附近的现象是由β相的稳定性和β_M相的量随Nb含量变化引起的.在烧结态的Ti-Nb合金中,峰高单调地随Nb含量的增加而增加的情况是由β_S的量决定的.在循环应力作用下,β_M或β_S相晶格点阵中氧原子的跳动和氧原子与替代原子的相互作用是产生内耗峰的根源.