Effects of content and particle size of Si crystal on damping property of powder forged Al–Si alloy

Abstract

The effects of the Si content and Si crystalline size on the damping properties of powder forged (PF) Al–Si alloys has been investigated using a fast Fourier transformation (FFT) analyser. A quantitative image analysis method was used successfully to determine the mean diameter and distribution of Si crystals in the aluminium alloy. The damping capacity greatly depends on the mean diameter of Si crystals. The value of δ for heat treated specimens with Si crystals of 2–5 μm is 4 to 25 times less than that for the as forged specimens with Si crystals of 1–5 μm. This indicates that the vibration is absorbed at the interface between the Si particles and the aluminium matrix by a mechanism of internal friction. Therefore, a fine distribution of Si crystals and/or elimination of crystal coarsening should contribute to improved damping.     

铁基阻尼合金的研究现状及发展趋势

铁基阻尼合金具有良好的阻尼性能、力学性能和加工性能,在船舶减振降噪中可发挥重要作用。对铁磁类、层错类、复相类铁基阻尼合金的阻尼性能和力学性能进行了介绍,分析了3类铁基阻尼合金的阻尼机理,并对铁基阻尼合金的发展趋势,尤其在舰船方向的应用进行了展望。     

Damping characteristics of Ti50Ni49.5Fe0.5 and Ti50Ni40Cu10 ternary shape memory alloys

The damping characteristics of Ti₅₀Ni_49.5Fe_0.5 and Ti₅₀Ni₄₀Cu₁₀ ternary shape memory alloys (SMAs) have been systematically studied by resonant-bar testing and internal friction (IF) measurement. The damping capacities of the B19′ martensite and the B2 parent phase for these ternary alloys are higher than those for the Ti₅₀Ni₅₀ binary alloy. The lower yield stress and shear modulus of these ternary alloys are considered to be responsible for their higher damping capacity. For the same ternary alloy, the B19/B19′ martensite and R phase also have a higher damping capacity than does the B2 parent phase. In the forward transformations of B2 → R, R → 519′, and B2 → 519′ for Ti₅₀Ni₅₀ and Ti₅₀Ni_49.5Fe_0.5 alloys, the damping capacity peaks appearing in the resonant-bar test are attributed to both stress-induced transformation and stress-induced twin accommodation. The lattice-softening phenomenon can promote the stress-induced transformation and enhance the damping capacity peaks. The Ti₅₀Ni₄₀Cu₁₀ alloy had an unusually high plateau of damping capacity in the B19 martensite, which is considered to have arisen from the easy movement of twin boundaries of B19 martensite due to its inherently very low elastic modulus. The peaks appearing in the IF test for the Ti₅₀Ni₄₀Cu₁₀ alloy are mainly attributed to the thermal-induced transformation due to T ⊋ 0 during the test.     

Study of Fatigue in Metals Using Ultrasonic Technique

Abstract

An investigation of the basic mechanisms associated with cyclic and fatigue stressing was undertaken employing as a research tool a megacycle frequency internal friction method (ultrasonic wave attenuation). The materials used were plain high-carbon and alloy steels (SAE 1095 and SAE 4340). The behaviour of lattice imperfections, dislocations and interstitial atoms (carbon) in particular, was studied in more detail, since these are reported to have a strong influence on the fatigue characteristics of iron-base alloys.

Initially, static stressing conditions were studied. Using a dislocation loop pinning model, the conditions for the break-away of a dislocation loop from interstitial atoms in annealed and in cold-worked material were investigated. These findings were applied to the experimental results obtained on cyclic stressing and an interpretation is offered in terms of the formation of active dislocation loops and their immobilization by interstitial atoms.

The results are discussed with reference to improving fatigue characteristics of iron-base alloys and a similarity with the work of Mason (19) on non-ferrous metals is noted.     

Features and effect factors of creep of single-crystal nickel-base superalloys

The creep behavior of two single-crystal nickel-base superalloys with [001] orientation has been studied by measuring the creep curves, internal friction stress of dislocation motion, transmission electron microscopy (TEM) observation and energy-dispersive X-ray analysis (EDAX) composition analysis. The results show that over the stress and temperature range, there are different creep activation energies, time exponents, and effective stress exponents in two alloys at different creep stages. The size and volume fraction of the γ′ phase in the tantalum-free alloy is obviously decreased with the elevated temperature. This results in the decrease of the internal friction stress during steady-state creep. Higher levels of tungsten in the alloy result in a smaller strain value and lower directional-coarsening rate during primary creep. During steady-state creep, the primary reason for the better creep resistance of the other alloy is that it contains more Al and also Ta, which maintains a high volume fraction of γ′ phase. The dislocation climb over the γ′ rafts is the major deformation mechanisms during steady-state tensile creep. The fact that the strain rate is decreased with the increase of the size and volume fraction of the γ′ rafts may be described by a modified constitutive equation that is based on a model of the rate of dislocation motion.     

The internal friction of the pearlitic,bainitic and martensitic transformations in FeNiC alloys

The low frequency internal friction of the pearlitic, bainitic and martensitic transformations in three FeNiC alloys has been studied. The results show that the internal friction of the martensitic transformation is in correspondence with the model based on the hysteresis loss mechanisms associated with stress-induced motion of the interface dislocations, while that of the pearlitic and bainitic transformations obeys Postnikov's model. At a constant frequency, the internal friction peaks of the pearlitic and bainitic transformations increase as the cooling rate increases, but the temperature of the internal friction peaks decreases, and the Q_max⁻¹ is directly proportional to the T/f_mT_m. When the frequency increases, the Q_max⁻¹ of the pearlitic and bainitic transformations lowers apparently, and the temperature of the internal friction peaks increases. The internal friction of the isothermal bainitic transformation in a FeNiC alloy has also been studied, which proves that there appears a damping peak in the incubation period, and which may be attributed to the nucleation of bainite. Consequently it infers that the mechanism of the bainite reaction seems similar to that of pearlite.     

Solution Treatment Enhances Both Static and Damping Properties of Al–Si–Mg alloys

The static properties of Al–Si–Mg alloys have been widely studied, but their damping behavior is generally neglected. Although there is an increasing concern regarding the mitigation of vibration, the correlation between the damping properties and the load bearing capacity of an alloy is frequently neglected. This study explores this relationship using A356 alloy as an example. It is concluded that, owing to eutectic Si coarsening/spheroidization, Mg₂Si/π-phase dissolution, and α-Al solution strengthening, the solution treatment can enhance both static (yield strength) and dynamic (damping ratio) mechanical properties.     

Superplasticity and internal friction of a superplastic Zn-22% Al eutectoid alloy

Temperature spectrums of internal friction, in other words, specific points have been investigated and discussed in the wide temperature range from room temperature to equilibrium eutectoid isotherm for Zn-22% Al eutectoid alloy in order to measure grain boundary peaks. Three large grain boundary peaks of Pα, Pαβ and Pβ which are associated with superplasticity have been observed over the range of temperatures from 447K (174°C) to 525K (252°C). The Activation energies of Pα, Pαβ and Pβ have been calculated to be 109, 93 and 62 kJ·mol⁻¹ respectively in internal friction measurements. These peaks seem due to the grain boundary sliding which can be accommodated by the diffusive flux on a boundary between like phases, α/α, for Pα and β/β for Pβ, and on an interphase boundary, α/β for Pαβ. Furthermore, it has been indicated that a utilization of Pα as the damping alloys would be possible.     

Mechanism of damping capacity of high-chromium steels and α-Fe and its dependence on some external factors

The influence of heat treatment on the elastic and nonelastic parameters of internal friction of high-chromium ferritic alloys and α-Fe has been examined. Mechanisms of the formation of magnetoelastic and dislocation hysteresis have been investigated. Temperature ranges and temperature and amplitude critical points connected with different damping mechanisms have been established. Heat treatment for maximum damping capacity has been suggested, and the results of damping capacity of about 50 steels were generalized. Formerly with the Physics of Metals Department, Central Research Institute of Iron and Steel Industry, Moscow 107005, Russia.     

Creep and microstructure of magnesium-aluminum-calcium based alloys

This article describes the creep and microstructure of Mg-Al-Ca-based magnesium alloys (designated as ACX alloys, where A stands for aluminum; C for calcium; and X for strontium or silicon) developed for automotive powertrain applications. Important creep parameters, i.e., secondary creep rate and creep strength, for the new alloys are reported. Creep properties of the new alloys are significantly better than those of the AE42 (Mg-4 pct* Al-2 pct RE**) alloy, which is the benchmark creep-resistant magnesium die-casting alloy. Creep mechanisms for different temperature/stress regimes are proposed. A ternary intermetallic phase, (Mg,Al)₂Ca, was identified in the microstructure of the ACX alloys and is proposed to be responsible for the improved creep resistance of the alloys. All concentrations in wt. pct, unless otherwise stated. RE stands for a combination of rare earth elements, i.e., misch metal, in this case.     

Processing and damping behaviour of porous copper

Abstract

The well distributed open cellular porous copper was fabricated by present powder metallurgy technique based on space holder method, Depending on the volume fraction and size of the space holding particle, the porosity can be varied in the wide range of 30–85% and pore size from micron to millimetre in magnitude of order respectively. The damping behaviour and related relative dynamic modulus of the porous copper were investigated by a multifunction internal friction apparatus as a function of temperature from room temperature to 600°C. The results of investigation disclose that the porous copper can obtain a higher damping capacity than that of bulk one. In addition to this, an internal friction peak was found in the spectra of internal friction against temperature for the porous copper, it was proposed that the viscous sliding of the grain boundaries should be responsible for the appearance of the peak, and the dependence of the peak on porosity can be understood in terms of the anelastic relaxation mode of grain boundary.     

Effects of Fe Addition on the Snoek-Type Damping Behavior of Surface-Oxidation-Treated Ti-Mo Alloys

Effects of Fe addition on the oxygen diffusion and the Snoek-type relaxation damping behavior of the Ti-15 wt pct Mo alloy were investigated in this study. After surface oxidation treatment, the Ti-15 wt pct Mo-1 wt pct Fe alloy exhibits a higher damping capacity compared to the Ti-15 wt pct Mo alloy. The dual-phase zone and the oxygen-enriched β-phase zone in the surface-oxidation-treated Ti-Mo alloys were determined by electron backscattered diffraction (EBSD) and hardness measurements. Based on the oxygen distributions in both alloys obtained through a diffusion model, the relative damping capacity of different zones contributing to the beam sample damping was estimated to be proportional to the thickness of the oxygen dissolved zones. On the other hand, the substitutional solute of Fe in the Ti-Mo-Fe alloy is considered to affect the oxygen distribution by lengthening the oxygen diffusion zone and increasing the oxygen concentration in this zone. As a result, the addition of Fe in Ti-Mo alloy improves the damping capacity of the surface-oxidation-treated alloys.     

Hydrogen-solute interaction in nickel-based dilute alloys studied by internal friction technique

The internal friction has been measured for dilute NiM alloys (M = Ti, Si, Co, Cr, Cu, Fe, Mn, Pd, V) containing hydrogen over a temperature range from 60 to 400 K. An internal friction peak due to the interaction between substitutional solute atoms and interstitial hydrogen atoms (SI peak, SIP) is observed around 160K except for the NiCo alloy. Detailed measurements have been performed on the NiTi alloy; the binding energy for the TiH pair; evaluated from the solute and hydrogen concentration dependence of the peak height, is smaller than 2 kJ/mol. The relaxation strength of the SIP is comparable to the Snoek peaks in b.c.c. metals, and is closely related to the dilatation of the host Ni lattice by alloying. Below 120 K, a background internal friction is observed in specimens which show the SIP. The background is explained in terms of the magnetomechanical damping accompanied by the hydrogen reorientation around solute atoms under a static stress due to magnetostriction.     

THE STRUCTURE AND PROPERTIES OF SOME INTERNALLY OXIDIZED ALLOY POWDER COMPACTS

Abstract

The advantages of internally oxidized structures produced by powder-metallurgical techniques are briefly reviewed and discussed. A metallographic survey of the structures of some internally oxidized copper alloy and nickel alloy powder compacts is presented, and the effect of pressing and sintering variables upon the density and hardness of the product is established. Hot-hardness data up to 800°C, and also some tensile data up to 620°C, are presented for certain alloys.

It is concluded that although dispersion-hardened structures can be prepared by the pressing, sintering, and internal oxidation of appropriate alloy powders, and although the methods described offer a valid comparison of the properties of the various alloys studied, optimum mechanical properties are undoubtedly developed only after the powders are hot worked. The latter treatment densifies the product, removes any porosity in the structure, and increases the stored energy in the material.     

The effects of impurities and heat treatment on the internal friction of tungsten at high temperatures

An improved internal friction technique was used to study the relaxation processes in pure tungsten and the following alloys: commercially doped tungsten (218W), W-1 pct ThO₂, 218W-3 pct Re, and 218W-20 pct Re. Internal friction experiments were performed on worked and recrystallized specimens in the temperature range of 300° to 3000°K. The effects of impurities and alloying additions on the damping and recrystallization behavior of tungsten are demonstrated. It is further shown that the internal friction curves can conveniently be used to determine the temperature of primary and secondary recrystallization. The important effect of impurities on the microstructure and high temperature strength is also revealed by the temperature dependence of shear modulus.     

Effect of preferred orientation on the damping capacity of magnesium alloys

The torsional vibration damping of Mg-4.5 Ce alloys has been correlated with the texture orientation resulting from the method of fabrication. Forged and forged-plus-swaged alloys at vibratory stress levels of 1500 psi exhibit specific damping capacities, respectively, of 6 and 11 times that of an extruded alloy of similar composition. Pole figures show that the basal planes are oriented preferentially in the extruded alloys with a 20 deg tilt to the axis of the extrusion, while the basal planes are generally parallel to the rod axis for forged or forged-plus-swaged alloys. The correlations indicate that the major source of damping in these hexagonal magnesium alloys is stress-induced anelastic shear on the basal planes (probably by dislocation motion).     

Mechanisms of internal friction in a cu-zn-ai shape memory alloy

The internal friction in a Cu-Zn-AI shape memory alloy has been studied in various microstructural states in a wide range of stress amplitude. Simultaneous measurements of the corresponding shape change indicate correlations between internal friction and the deformation mechanisms. It is found that the observed stress-amplitude dependence of the internal friction cannot be represented by a single formalism. Rather, in different ranges of stress amplitude, where the internal friction mechanisms are different, separate formalisms are applicable. The comparison of the experimental results with a previously developed theory is presented.     

High-damping metals and alloys

High-Damping Metals (HIDAMETS) are the physical metallurgist’s answer to unwanted noise and vibrations. However, the characterization of the damping properties of metals and alloys is neither simple nor straightforward. This is mainly because the damping mechanisms involved depend upon the stress-induced movement of defects in the metal in question which, in turn, implies a dependence upon the microstructure (thermomechanical history) of the sample. To properly characterize the damping performance of a HIDAMET in a well-defined structural state, one must measure the mechanical damping as a function of vibration frequency, temperature, vibration strain amplitude, and static bias load over the ranges of these variables to be encountered in the application in question. This requires the use of a variety of equipment adapted to different modes of vibration and their overtones, especially when the damping is nonlinear (amplitude-dependent). Our approach to this problem is described and illustrated by test results obtained on several HIDAMETS. This paper is based on a presentation made in the symposium “Acoustic/Vibration Damping Materials” presented during the TMS Fall Meeting, Indianapolis, IN, October 1–5, 1989, under the auspices of the TMS Physical Metallurgy Committee.     

喷雾共沉积颗粒增强锌基复合材料的高频内耗

采用喷雾共沉积技术在ZA27合金中添加50mg．g-1Si制备了体积分数为10％的石墨、SiC增强锌基复合材料。用声频内耗仪对挤压前后材料的高频内耗行为进行了测量。结果发现,30℃时石墨、SiC增强复合材料的阻尼能力较常规铸造ZA27合金分别提高2．90和2.38倍;挤压后两种复合材料内耗值相当接近（约为常规铸造ZA27合金的4．3倍）。在微观组织形貌分析基础上探讨了石墨、SiC颗粒对复合材料内耗机制的影响。     

Centrifugal atomisation of metallic alloys in inductive plasma onto cooled disc

Abstract

A novel atomisation process for the production of high purity, fine powders of high melting point metallic alloys has been devised. This process associates centrifugal atomisation and inductive plasma techniques. The experimental equipment is described. Results obtained by atomising nickel base superalloy PER3, Ti–0·17%Pd alloy, and pure copper on a cooled copper alloy disc are presented. The effects of process parameters, such as the disc rotation speed and the aerodynamic environment of the disc, on the atomised product characteristics, are investigated. The alloys were melted drop by drop onto a water cooled disc. The atomisation of the dripped alloy can be characterised by three mechanisms: ultraquenched flakes and crusts solidified on the disc; spherical droplets formed by centrifugation; spherical droplets formed by aerodynamic erosion.