Thermal Conductivity Of Alloys Research Articles

Evolution of precipitate orientation and its effect on thermal conductivity of Mg-5Sn alloy

The evolution of precipitate orientation and its effect on the thermal conductivity of Mg-5Sn alloys under different treatments were systematically investigated. The results show that for the alloy subjected to aging prior to twinning (Sample AT), the basal precipitates are precisely regulated to be the prismatic precipitates, and the lath-shaped precipitates experience a rigid rotation of 3.7° to accommodate the twinning shear. For hexagon-shaped precipitates with a larger thickness in Sample AT, the precipitate only experiences a small rigid rotation of 0.2°, due to the development of stacking faults releasing part of the strain at the precipitate/twin interface. In addition, the orientation of precipitates has a significant effect on the thermal conductivity of the alloy. When the measurement direction of thermal conductivity is parallel to extrusion direction (ED), the precipitates lying on the basal plane, perpendicular to ED, are more beneficial to the improvement of thermal conductivity than precipitates lying on the prismatic plane parallel to ED. Sample TA (aging after twinning) with precipitates lying on the basal plane shows the best thermal conductivity of 137.81 W/(m·K).

Improving thermal conductivity of Mg-Si-Zn-Cu alloy through minimizing electron scattering at phase interface

The primary cause of the decrease in thermal conductivity of conventional thermal conductive magnesium alloys is electron scattering brought on by solute atoms. However, the impact of phase interface on thermal conductivity of magnesium alloys is usually disregarded. This study has developed a Mg-Si-Zn-Cu alloy with high thermal conductivity that is distinguished by having a very low solute atom content and a significant number of phase interfaces. The thermal conductivity of the Mg-1.38Si-0.5Zn-0.5Cu alloy raises from its untreated value of 133.2 W/(m·K) to 142.2 W/(m·K), which is 91% of the thermal conductivity of pure Mg. This is accomplished by subjecting the alloy to both 0.8wt% Ce modification and T6 heat treatment. The morphology of eutectic Mg2Si phase is changed by Ce modification and heat treatment, and as a result, the scattering of electrons at the Mg2Si/Mg interface is reduced, resulting in increase of the alloy's thermal conductivity.

Thermal conductivity of Zr52.5Ti5Cu17.9Ni14.6Al10 alloy in as-cast glassy, relaxed and crystallized states

The thermal transport property of amorphous alloys is significant to understand the glass-forming ability and developing the thermal insulation coating. However, systematic studies on the thermal conductivity of alloys in as-cast glassy, relaxed and crystalline states are still scarce. Here, we systematically investigated the thermal conductivity behaviors in the temperature range of 10–300 K for as-cast glassy, relaxed, partially-crystallized and well-crystallized Zr52.5Ti5Cu17.9Ni14.6Al10 alloys. The total thermal conductivity (κ) of the as-cast Zr52.5Ti5Cu17.9Ni14.6Al10 metallic glass is approximately 5.66 Wm−1K−1 at room temperature and is slightly lower than that of the structurally relaxed sample, which can be attributed to the opposite changes in electronic thermal conductivity (κe) and phonon thermal conductivity (κp). In contrast, the total thermal conductivity of the partially-crystallized and well-crystallized Zr52.5Ti5Cu17.9Ni14.6Al10 alloys improves significantly owing to the abrupt decrease of electrical resistivity. In addition, the well-crystallized sample exhibits larger grains than the partially-crystallized sample, which will further enhance the phonon thermal conductivity. Our results lay a foundation for further understanding the mechanism of thermal conductivity evolution with the microstructure of metallic alloys.

AZ Serisi Döküm Magnezyum Alaşımlarının Termal Özellikleri

Bu çalışmada, AZ serisi döküm magnezyum alaşımlarının ısıl davranışları (ısıl yayılma ve ısıl iletkenlik) üzerine deneysel bir araştırma sunmaktadır. Deneyde kullanılan alaşım bileşenlerinden Al’nin değişimi (ağırlıkça % 1-9 arasında) alaşımların ısıl yayılma ve ısıl iletkenliklerini nasıl etkilediğini, yoğunluk ve sertlik üzerindeki değişimler incelenmiştir. Alaşımların mikroyapı değişimlerinin ve mikroyapıda görülen intermetalik fazın (Mg17Al12) alaşımların ısıl yayınım, ısıl iletkenlik, yoğunluk ve sertlik üzerine etkisi olduğu görülmüştür. Alaşımın ısıl özellikleri, alaşımdaki Al içeriğine bağlı olarak değişmiştir. Alaşımların termal özellikleri sıcaklık artışına bağlı olarak (sıcaklık değişimi 25 °C- 400 °C arası) artmıştır. En yüksek termal yayılma AZ61 alaşımında gözlenmiştir.

Elucidating thermal conductivity mechanism of Al-9Si based alloys with trace transition elements (Mn, Cr, V)

The effects of trace transition elements (Mn, Cr, V) on the solidification microstructure and the thermal conductivity of Al-9Si based alloys have been investigated. It was found that the effect of Mn, Cr, V on the solidification behavior and solidification microstructure is mainly related to α-Al grains via affecting heterogeneous nucleation and growth restriction, while no significant effect on the solidification behavior and microstructure of eutectic Si was observed. Compared with factors including grain size of α-Al and morphology characteristics (e.g. size, spacing, and shape factor) of eutectic Si, the solid solubility in Al matrix is confirmed to be one of the most important factors affecting thermal conductivity. Due to the larger partition coefficient of V compared with Cr and Mn, the solid solubility and the lattice distortion of α-Al in Al-9Si-xV alloy were increased significantly, thus the thermal conductivity of alloy was decreased steeply from 171.7 to 152.3 W/m·K with the content of V increasing from 15 to 1010 ppm. A linearly fitted curve reflecting the relationship between the content of the transition elements and the thermal conductivity of alloys has been proposed, which can be used to optimize the alloy composition in subsequent remelting or recycling process. Furthermore, two thermal conductivity models (H-S model and Maxwell model) also have been used to evaluate the effect of Mn, Cr, V on thermal conductivity, in which the thermal conductivity of α-Al was corrected based on the measured solid solubility. In this way, the data correlation between the experimental and fitted value based on H-S model and Maxwell model is increased from 0.18 to 0.96. These obtained results could be helpful to precisely control the composition and further improve the thermal conductivity of Al-Si based alloy during the primary production and / or recycling process.

Influence of Second Phase Particles on Thermal Conductivity of Bi Alloys

High-Bi alloys are being explored to understand their potential as replacement for high-Pb alloys in high-temperature die-attach applications. Thermal conductivity of these alloys is an important consideration for die-attach applications, where heat dissipation is necessary for reliable operation of the devices. Pure Bi has a thermal conductivity of about 8 W/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\cdot \text{K}$ </tex-math></inline-formula> , which is the lowest among metals. The addition of the alloying elements to Bi had been explored to tailor its thermal, mechanical, and other physical properties. In this study, the role of Cu and Sb on the effective thermal conductivity of the resultant alloys was investigated. The thermal conductivities of these alloys in the bulk form and the three-layer die-attach form were measured using a flash diffusivity technique. Test specimens were developed to replicate a die-attach assembly between the Ni-metallized Si die and Cu substrate using the Bi– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> Sb–10Cu alloy (where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x =10$ </tex-math></inline-formula> –20 wt%). The three-layered structure was modeled with the unknown diffusivity of an intermediate layer of the Bi alloy. The alloy microstructure comprises a composite of Bi–Sb solid solution filled with Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sb intermetallic particles. The presence of these intermetallic phases is responsible for an effective increase in thermal conductivity of this alloy. With the optimized microstructure developed, the resultant thermal conductivity was obtained at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 24$ </tex-math></inline-formula> W/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\cdot \text{K}$ </tex-math></inline-formula> , which is a threefold increase compared to pure Bi.

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The thermoelectric properties of the solid solution Sn1−x Pbx Sb4Te8 and Sn1−x Pbx Sb4−y Biy Te8 (y = 0.4, 0.8, 1.2) were measured in a wide temperature range (100−800 K). The substitution of Bi atoms for Sb atoms leads to an increase in the thermo-emf coefficient and a decrease in the lattice component of thermal conductivity in comparison with the corresponding properties of the solid solution Sn1−x Pbx Sb4Te8. The lower values of the lattice thermal conductivity in alloys y = 1.2 in comparison with the solid solution Sn1−x Pbx Sb4Te8 are associated with distortions due to the difference in the atomic masses and sizes of Sb and Bi atoms. With an increase in the Bi content in solid solutions, the lattice thermal conductivity decreases and, accordingly, the thermoelectric efficiency increases. Thermoelectric figure of merit Sn1−x Pbx Sb4−y Biy Te8 (y = 1.2) has a maximum value of = 3.2 · 10−3 at 300 K.

Effect of Short T6 Heat Treatment on the Thermal Conductivity and Mechanical Properties of Different Casting Processes Al-Si-Mg-Cu Alloys

The thermal conductivity of alloys is gradually becoming appreciated. It is often assumed that heat treatment can improve the thermal conductivity of Al-Si-Mg-Cu alloys, but there has been little relevant research. This paper studies the effects of different casting processes and short T6 heat treatment (ST6) on the thermal conductivity and mechanical properties of Al-Si-Mg-Cu alloys. The results show that a microstructure with fine α-Al crystal grains can be obtained by semi-solid die casting (SSDC), improving the mechanical properties of the Al-Si-Mg-Cu alloy in the as-cast state. After SSDC, the size and aspect ratio of eutectic silicon can be reduced by ST6 treatment, effectively improving the thermal conductivity and mechanical properties of the alloy. Finally, the influence of eutectic silicon on electron transport is analyzed in detail. With the SSDC + ST6 processing technology, Al-Si-Mg-Cu alloys with excellent thermal conductivity and mechanical properties can be obtained.

Thermal Conductivity of Double Continuous Disordered Solid Solutions

A way of calculating the thermal conductivity of alloys (double continuous disordered solid solutions) is proposed. The procedure serves to estimate the thermal conductivity of different alloys (continuous solid solutions) as early as the stage of developing new materials with predetermined properties, using the minimum amount of initial information. It also allows the time and cost of creating trial samples and measuring their properties to be reduced considerably.

A new model to describe composition and temperature dependence of thermal conductivity for solution phases in binary alloys

Modelling temperature- and composition-dependent thermal conductivity in alloys is challengeable and is seldom studied systematically. In the present work, a new model is developed to describe the temperature and concentration dependence of thermal conductivity for binary alloys. In this new model, firstly thermal conductivity of pure metals was modelled as the function of temperature for each phase and each magnetic state by the corresponding physically sound model. Secondly, in order to describe the composition and temperature dependence of thermal conductivity for solid phases, the combination of the theories of Nordheim and Mott for electric conductivity of alloys with the Wiedemann-Franz law was performed. Thirdly, the reliability of the new model was verified by presently measured thermal conductivities for pure Co, Ni and Co-Ni alloys at 300, 600, 900 and 1100 K as well as for binary Al-Zn, Mg-Zn and U-Zr systems using the data taken from the literature. The calculated thermal conductivities can well reproduce the measured ones in one-phase regions of a series of Co-Ni alloys. The thermal conductivity in a two-phase region of the Co-Ni system is reasonably predicted as well. It is demonstrated that the new model can be utilized to evaluate the thermal conductivity over the whole investigated composition and temperature ranges for the first time and is expected to be extended to ternary and multicomponent systems by CALPHAD method, which contributes significantly to the development of computational design of materials.

Comparison in characteristic and atomization behavior of metallic powders produced by plasma rotating electrode process

In this study, characteristics of powder for additive manufacturing from three typical alloys Ti-6Al-4V, 316-steel and Co-29Cr-6Mo produced by plasma rotating electrode process (PREP) at 4 rotation speeds are compared in details. The results indicate that for a given rotation speed, alloy with higher ratio of surface tension and density (γρ) is capable of producing powder with larger particle size and narrower particle size distribution δ (D90-D10). The formation mechanism of the satellite and irregular particle produced by PREP are discussed in detail. The satellite powder is confirmed to be formed by collisions between two particles, and the volume fraction of the satellite powder is lower in the alloy with higher (γρ) and high thermal conductivity. The formation of irregular powder is possibly related to the peeling of liquid film, which is strongly dependent on the thermal conductivity of alloy.

Microstructure, Thermal Conductivity and Mechanical Properties of the Mg–Zn–Sb Ternary Alloys

A novel Mg alloys of Mg–xZn–ySb (x = 0, 2, 4, 6; y = 0, 0.2, 0.5, 0.8, 1.2) were designed and their microstructure, thermal conductivity and mechanical properties were systematically investigated in the present study. The as-cast Mg–Zn–Sb ternary alloys consist of α-Mg, Mg4Zn7 and Mg3Sb2 phases. Sb addition can refine the eutectic structure (α-Mg + Mg4Zn7) by the growth of Mg4Zn7 on Mg3Sb2 phases. The thermal conductivity of Mg–Zn–Sb alloys decreased with increasing Sb content. There existed an interactive effect of Zn/Sb on the thermal conductivity of the Mg–Zn–Sb alloys. The negative effect of Sb addition on thermal conductivity of alloys was getting smaller with increasing Zn content in alloys. The negative effect of Mg3Sb2 phases on the thermal conductivity of alloys could be weakened by the formation of weak-scattering Mg4Zn7 coated on Mg3Sb2 phases. The best refinement effect on microstructure could be obtained with 0.8 wt%Sb addition. Mg–4Zn–0.8Sb alloy possess the best comprehensive properties with thermal conductivity of over than 120 W/(m·K) and UTS of 185.6 MPa.

Effect of the Impulsive Magnetic Field in the Course of Crystallization of Aluminum Alloys on Their Physical Properties

We present the results of experimental investigation of the electric resistance and thermal conductivity of A356.0 and A413.1 aluminum alloys crystallized in impulsive magnetic fields. We show that the electric resistance of alloys processed by magnetic fields increases and their thermal conductivity decreases as compared with the initial state. We give a qualitative explanation of changes in the electric resistance and thermal conductivity of the analyzed alloys. The obtained temperature dependences of specific electric resistance do not contradict the existing theoretical concepts about the nature of the phenomenon of electron transfer in metals below and above the Debye temperature. The temperature dependences of the thermal conductivity for the analyzed alloys cannot be explained from the viewpoint of the quantum theory of heat transfer by the conductivity electrons for pure metals. In this connection, it is assumed that the thermal conductivity of alloys is determined not only by conductivity electrons, but also by the phonon component.

Evolution of the microstructure, texture and thermal conductivity of as-extruded ZM60 magnesium alloy in pre-compression

A systematic study on the influence of pre-compression on the microstructure evolution, texture and thermal conductivity of as-extruded ZM60 alloy was performed. The results indicated that the lenticular shaped {10–12} extension twins were generated during the pre-compression along ED (extrusion direction), resulting in the formation of c-axis//ED texture component and the volume fraction of {10–12} extension twins increased as the pre-compression strains increased from zero to 8.3%. Such microstructure evolution led to a crystal orientation deflection of alloy, and the probability of electrons and phonons being scattered by defects in this direction became much lower, and the mean free path of electrons and phonons in this direction was improved, leading to an increase in the thermal conductivity of alloy. Upon further increase of pre-compression strain, a small amount of the {10–12}-{10–11} contraction twins and {10–12}-{10–11}-{10–12} ternary twins were observed, which introduced a reorientation of the c-axis of grains by ∼56° and ∼38°, respectively. So the mean free path of electrons and phonons decreased, due to the decrease of volume fraction of grains with c-axis parallel to ED, and the thermal conductivity of the alloy decreased. Therefore, the thermal conductivity of alloy first increased and then decreased with the increase of pre-compression strain, and the alloy with pre-compression strain of 8.3% showed the best thermal conductivity of 108.8 W/(m·K).

Effect of extrusion temperature on the microstructure and thermal conductivity of Mg–2.0Zn–1.0Mn–0.2Ce alloys

Abstract This study investigated the effect of extrusion temperature on the microstructure and thermal conductivity of Mg–2.0Zn–1.0Mn–0.2Ce. The thermal conductivity of the alloy was measured using the flash method at room temperature. Results indicated that the volume fraction of un-recrystallized grains decreased and the average grain size of recrystallized grains gradually increased with increasing extrusion temperature. The thermal conductivity of Mg–2.0Zn–1.0Mn–0.2Ce alloys initially increased, reached the maximum value of 131 W/(m·K) when the extrusion temperature increased from 340 °C to 400 °C, and then decreased to 125 W/(m·K) when the extrusion temperature further increased to 430 °C. The obtained maximum thermal conductivity meets the requirement for Mg alloy radiating module of LED lights. A micro-hardness of approximately 59 HV is maintained at extrusion temperature lower than 400 °C, while it sharply increases up to 74.0 HV when the alloy is extruded at 430 °C. The extrusion temperature changes the microstructure and solid solution of elements, which comprehensively affect the thermal conductivity of as-extruded alloys.

Thermoelectric Properties and Microstructure Studies of Spinodally Decomposed PbTe&lt;SUB&gt;0.38&lt;/SUB&gt;S&lt;SUB&gt;0.62&lt;/SUB&gt; Alloy

PbTe is a premiere mid-range temperature thermoelectric material and recent studies have proven nanostructing as an effective approach to reduce thermal conductivity of alloys. Whereas, little attention has been given to long-term thermal stability of secondary phases and microstructural evolution. Interestingly, replacing Te with S in PbTe provides an opportunity to form nanostructures in the bulk material through spinodal decomposition, which appears in binary phase diagrams of the PbTe–PbS system. Herein, the critical composition of PbTe_(0.38)S_(0.62) alloy is fabricated to n-type by chlorine doping. Thermoelectric transport properties of the alloy are investigated in the 300–850 K temperature range and the maximum zT achieved at 800 K is 0.75 with a predicted zT ∼ 0.85 at 750 K from single parabolic band model. The microstructure of the sintered samples was studied by FEG-SEM for both the as sintered and post transport properties measurement. The experimental results are compared with estimates from the parallel and series models for heterogeneous composites of single phase PbTe and PbS. The Seebeck coefficient is in agreement with the models predictions, but the resistivity is higher and the thermal conductivity is much lower than predicted values. We propose that this is attributed to the phonon and electron scattering on solute atoms in solid solutions and at interfaces.

Controlling Thermal Conductivity of Alloys via Atomic Ordering

Many random substitutional solid solutions (alloys) will display a tendency to atomically order given the appropriate kinetic and thermodynamic conditions. Such order–disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order–disorder transition on phononic transport properties of Lennard–Jones type binary alloys is explored via nonequilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that by varying the degree of ordering, the thermal conductivity of a binary alloy of fixed composition can be tuned across an order of magnitude at 10% of the melt temperature, and by a factor of three at 40% of the melt temperature.

Developing castability index for magnesium diecasting alloys

A partial castability index has been developed for magnesium diecasting alloys based on alloy characteristics such as solid thermal conductivity, non-equilibrium freezing range and hot tear sensitivity. The partial castability index IC for thin walled castings was developed using an industrial diecasting defect index IDD of five different alloys and regression analysis to give IC −0·08(ΔF)+0·58Δκ+0·01ΔHTS+0·06ΔT′ with R2=0·9977, where ΔF=(freezing range for AZ91)−(freezing range for alloy); Δκ=(thermal conductivity of alloy)−(thermal conductivity of AZ91); ΔHTS=(hot tear sensitivity of AZ91)−(hot tear sensitivity of alloy); ΔT′=(non-equilibrium freezing range of alloy)−60°C. The hot tear test and its hot tearing susceptibility (HTS) rating determined using a constrained rod casting mould can also assess the trend in diecastabilty of magnesium alloys in thin walled castings but the prediction is not as good as the partial diecastability index IC. The HTS rating correlates with the industrial diecasting defect index IDD as IDD=0·9HTS0·5.

Optimum composition of a Bi2Te3 − x Se x alloy for the n-type leg of a thermoelectric generator

The reliability of determination of model parameters for the Bi2Te3 − xSex alloys is improved by extending the concentration and temperature ranges in experimental studies and, correspondingly, in calculations of kinetic coefficients based on the two-band model of the electronic spectrum. The obtained results served as a motivation for a study of the thermoelectric figure of merit for the above-mentioned alloys with x = 0.3, 0.45, and 0.6 and with the electron concentration varied in the range (1–50) × 1018 cm−3 at temperatures 300–550 K. Comparison of the results showed that the highest efficiency is exhibited by the Bi2Te2.7Se0.3 alloy with the absolute value of the thermoelectric power of about 165 μVK−1 at 300 K, and the dimensionless efficiency is equal to 1.2 at 410 K. An appreciable decrease in thermal conductivity in alloys with x = 0.6 at 410 K is related to a larger band gap and could beneficially affect the figure of merit. However, the magnitude of this effect is found to be too small to compensate a decrease in electrical conductivity due to a large fraction of heavy electrons in the concentration and to a high content of selenium.

Thermal conductivity of an alloy in relation to the observed cooling rate and glass-forming ability

The glass-forming ability (GFA) of an alloy in this case is the largest diameter of a rod which can be cast fully glassy. The present work shows that the thermal conductivity of a liquid alloy has a strong effect on GFA by influencing the cooling rate upon mould casting. The initial cooling rates (for the first 70–100 K of temperature decrease), obtained for Cu-, Zr- and Au-based bulk glass-forming alloys in the liquid state, are found to scale linearly with the thermal conductivities of the liquid base elements. However the low cooling rate found for Ni-based alloy suggests that the heat transfer at the melt–mould interface may also influence the cooling rate. The low thermal conductivity of Ni-based alloys and the correspondingly low cooling rate obtained compared to Cu-based counterparts explains their lower GFA. In the literature, many factors influencing the GFA of alloys have been discussed. To these factors, the present study adds the thermal conductivity of the molten alloy and the melt–mould heat-transfer coefficient. Moreover, the cooling rate depends on temperature and, thus, the critical cooling rate itself is not a suitable parameter for indicating GFA. The cooling can be better described by an appropriate fitting of the cooling curve to an exponential temperature decay function.