Preparation and Mechanical Properties of Misch Metal Based Bulk Metallic Glasses

Bulk metallic glasses(BMGs)have been devel-oped in many alloy systems during past decade.Among these systems,rare-earth(RE)metal-basedBMGs are ones of those found earliest and with betterglass forming ability(GFA).For example,La-basedBMGs were the first a…     

Thermodynamic and Topological Modeling and Synthesis of Cu-Zr-Ti-Ni–Based Bulk Metallic Glasses by Mechanical Alloying

In the present investigation, thermodynamic and topological concepts have been used together to understand the formation of bulk metallic glasses. The article attempts to develop a parameter that combines chemical mixing enthalpy (ΔH _chem), mismatch entropy normalized by Boltzmann constant (ΔS _σ /k_B), and configurational entropy (ΔS _config/R), which can be effectively used to identify the best bulk glass forming compositions in multicomponent systems. The ΔH _chem for multicomponent systems has been calculated by extending the Miedema’s macroscopic model, and ΔS _σ /k_B was obtained from Mansoori’s approach. The iso-ΔH _chem, iso-ΔS _σ /k_B, and iso-ΔS _config/R contours have been developed. The product of ΔH _chem and ΔS _σ /k_B in the ΔS _config/R range of 0.9 to 1.0 can be correlated strongly to glass forming ability. This has been demonstrated in the case of the quaternary Cu-Zr-Ti-Ni bulk glass forming system to determine the bulk metallic glass forming compositions. Mechanical alloying is used to prepare the bulk amorphous powder at the compositions predicted by the model in order to validate the model. This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India.

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Cooling Process and Cast Structure of Zr-Al-Ni-Cu–Based Bulk Metallic Glasses Produced in Various Atmospheres

Cooling process in the production of Zr₆₅Al_7.5Ni₁₀Cu_17.5-based bulk metallic glasses (BMGs) was investigated in various chamber atmospheres in Cu mold casting. Two different cooling modes, consisting of the direct heat transfer between the melt and Cu mold in the high temperature and indirect transfer via cavity in the low-temperature regions, are suggested. In the later case, the cooling effect should depend on the chamber atmosphere, which results in the formation of glassy structure with large relaxation enthalpy casting under the ambient Ar and He atmospheres due to a good thermal conductivity. The less relaxed BMGs produced by an improved cooling effect are also expected to contain a large amount of free volume for significant deformability. Actually, it is clarified that the compressive plastic deformation is improved with an increase of the relaxation enthalpy. The present study indicates a necessity of development of the glassy structure, i.e., relaxation state, and provides a new technique of the formation of less relaxed glassy structure for the improvement of plasticity in BMGs.     

Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100−xAlx Metallic Glasses

Metallurgical and Materials Transactions A - In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to...     

Solidification Behaviour of Ti–Cu–Fe–Co–Ni High Entropy Alloys

For the first time, we report here that the development of the novel Ti?CCu?CFe?CCo?CNi high entropy alloys (HEAs) via vacuum arc melting technique using non consumable tungsten electrode under high purity Ar atmosphere on a water-cooled copper hearth. Ti?CCu?CFe?CCo?CNi multicomponent alloys with varying Ti/Cu (x) molar ratio (x?=?1/3, 3/7, 3/5, 9/11, 1, 11/9 and 3/2) have been prepared through the tailoring of microstructure to get understanding of the phase formation and the microstructural evolution of these multicomponent HEAs. X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopic results confirm the presence of (Cu)_ss, (Co)_ss and (??-Ti)_ss dendrites with ultrafine eutectic between cubic (Cu)_ss and Laves phase (Ti₂Co type). The solidification pathways of novel alloys are critically discussed as follows. For x?=?9/11, 1, 11/9 and 3/2; firstly, (??-Ti)_ss dendrite is formed from the liquid, followed by the liquid phase separation between the cobalt-rich solid solution (Co)_ss and copper-rich solid solution (Cu)_ss and finally, the remaining liquid undergoes eutectic reaction between copper solid solution (Cu)_ss and the Laves phase (Ti₂Co Type), whereas for x?=?1/3, 3/7 and 3/5; (??-Ti)_ss dendrite is formed first from the liquid and then remaining liquid undergoes the liquid phase separation resulting two different dendrites of (Cu)_ss and (Co)_ss phases. Detailed thermodynamic calculations have been carried to rationalize the formation of stable solid solution phases of these newly developed multicomponent Ti?CCu?CFe?CCo?CNi HEAs.     

Prediction of Bulk Metallic Glass Formation in Cu–Zr–Ag–Hf System by Thermodynamic and Topological Modeling

Cu based bulk metallic glasses (BMGs) are widely studied because of their high glass forming ability (GFA) and interesting combination of properties such as high strength coupled with good ductility and low cost. With these attributes, Cu based BMGs are being projected as promising materials for practical applications. The process of glass formation in metallic systems is a challenging task and alloys should be cooled from the liquid state at rates faster than a critical cooling rate (R_c) to resist crystallization. Interestingly, composition plays an important role in achieving easy glass formation, which is usually measured in terms of R_c. In the present work, attempt has been made to identify the composition for easy glass formation in Cu based quaternary system by theoretical approach. A GFA parameter P_HS, which is a product of enthalpy of chemical mixing (?H_chem) and mismatch entropy normalized with Boltzmann??s constant (?S_??/k_B) is used to identify the best glass forming composition in Cu?CZr?CAg?CHf system. Further, a new parameter P_HSS, which is a product of P_HS and configurational entropy (??S_config/R) is found to illustrate strong correlation with GFA. An attempt has also been made to correlate P_HSS parameter with critical diameters and R_c using reported data in Cu?CZr?CAg?CHf system.     

Structural Relaxation, Glass Transition, Viscous Formability, and Crystallization of Zr-Cu–Based Bulk Metallic Glasses on Heating

In this article, we summarize our recent findings on relaxation, glass transition, viscous flow, and crystallization of Zr-Cu?Cbased metallic glasses on heating. At least two processes related to the diffusivities of different alloying elements take place in the glass-transition region of a Zr-Cu-Al-Ni glassy alloy. Also, we report an unusual solidification behavior of the bulk glassy alloy produced using low-purity Zr in which both primary and eutectic-type structural constituents were formed simultaneously during solidification of the melt. In addition, viscous flow and structure changes in the Zr-Cu-Al-Ag glassy alloy are examined in both the glass-transition and supercooled liquid regions. This alloy is found to exhibit localized phase separation leading to nanocrystallization before massive crystallization of the entire sample.     

Study on the Effects of Squeeze Pressure on Mechanical Properties and Wear Characteristics of Near Eutectic Al–Si–Cu–Mg–Ni Piston Alloy with Variable Mg Content

In the present work, the effects of pressure on the wear resistance characteristics, mechanical properties and the microstructures of Al–Si piston alloys that have variable Magnesium (Mg) content are studied. The paper begins with an explanation of the desirable properties of eutectic Al–Si alloys and why these chemical and mechanical properties are desirable in the fabrication of light weight machine components. The methods for further strengthening the alloys using alloying elements such as Ni, Cu and Mg, and applying heat treatment are also discussed. The paper also emphasises on the addition of Magnesium, and compares the traditional gravity die casting with a novel hybrid technology known as squeeze casting. In the results and discussion section, the microstructure properties of the Al–Si both as-cast and after heat treatment conditions are discussed. The mechanical and wear properties as well as the implications of pressure on the alloys are also discussed in details. SEM analyses of wear surface and fracture behavior on the as cast Al–Si alloys and after heat treatment, reveal that squeeze pressure increases fracture ductility as well as resistance to wear; more so upon heat treatment. It is also determined that the hardness and UTS values increases with increase in Magnesium content and reaches the maximum values when Mg content is at 1 % of the alloy’s composition.     

Effect of Samarium on the Properties of Mg–Y–Gd–Zr Alloys

The microstructure, the aging kinetics, and the strength properties of Mg–Y–Gd–Zr cast alloys, in particular, a samarium-alloyed IMV7-1 alloy, at room and high (250, 300°C) temperatures after homogenization without and with subsequent aging are studied. Alloying with samarium accelerates the decomposition of the supersaturated magnesium solid solution and enhances the properties of the Mg–Y–Gd–Zr alloys.     

Thermodynamic Assessment of the Mg–Ni–Si System

Powder Metallurgy and Metal Ceramics - The thermodynamic assessment of the Mg–Ni–Si system has been developed in the framework of the CALPHAD method. The critical review of the...     

Comparison on Hot Tearing Behavior of Binary Mg–Al,Mg–Y,Mg–Gd,Mg–Zn,and Mg–Ca Alloys

Metallurgical and Materials Transactions A - Mg–1Al, Mg–0.9Y, Mg–2Gd, Mg–1.5Zn, and Mg–0.5Ca binary alloys were chosen to clarify the hot tearing mechanism since they...     

Features of the Sintering of Fe–Cu–Sn–Ni and Cu–Ti–Sn–Ni Powders during Hot Pressing

Powder Metallurgy and Metal Ceramics - The efficiency and durability of a diamond tool fabricated using powder metallurgy methods depend on several factors. These are the quality of diamond...     

High temperature properties of ductile CuAlNi shape memory alloys with boron additions

The use of polycrystalline CuAlNi alloys for high temperature applications is restricted to very small shape changes due to their brittle nature. Additions of alloying elements such as manganese and boron have been introduced to improve the ductility of the material. The behaviour of these alloys has been studied in terms of the influence of these elements on the stability of the microstructure after high temperature annealing or after room and high temperature deformation. The results show that the martensitic structure produced by quenching the alloy from the β-temperature has a lower degree of order than that obtained after further annealing at 300°C for up to an hour. Also, the alloys containing higher boron concentrations present a lower degree of order in all cases. Similarly, the ductility has been much influenced by the boron content. The ductility is greater, in particular at high temperatures, in the alloys with lower concentration of boron.     

Effect of Aging Time on Mechanical Properties and Wear Characteristics of Near Eutectic Al–Si–Cu–Mg–Ni Piston Alloy

Al–12Si–3Cu–1 Mg–1.78Ni alloy is widely used for piston parts in automobile industry. The present paper investigates the effect of aging time for 1–16 h at 180 °C after solution treatment of the alloy at 500 °C for 5 h, on alloys prepared by gravity casting and squeeze casting. The wear rate of the alloy shows a minimum at an intermediate aging time. The hardness and ultimate tensile strength showed a peak at intermediate aging time. Mechanical properties and wear resistance are found to be better in squeeze cast alloy. The result are explained based on the microstructure developed during casting process and on heat treatment for various durations.     

Mechanisms of formation of hardening precipitates and hardening in aging of Al–Li–Cu–Mg model alloys with silver additions

The mechanisms of the influence of silver additions on the phase transformations that occur in aging are revealed. The contribution of Ω'-phase particles to the deformation stress in Al alloys is estimated. The mechanisms of the effect of low (up to 0.5 wt %) silver additions and the copper content on the structure of the Ω'-phase precipitates in Al alloys are found. According to the proposed model, silver atoms remain immobile during the decomposition of a solid solution and nucleation centers of the Ω' phase form near them in low-temperature aging. Upon hardening aging, fragmented Ω'-phase particles intersect with each other, and the contribution of the intersection regions to the hardening of alloys by Ω'-phase particles is principal.     

Analysis of the Influence of Element’s Entropy on the Bulk Metallic Glass (BMG) Entropy,Complexity, and Strength

Metallurgical and Materials Transactions A - Bulk metallic glasses (BMGs) are disordered compounds without a long-range crystalline order. In this paper, we study the effect of an element’s...     

Indentation creep behaviors of Mg61Cu28Gd11 and （Mg61Cu28Gd11）99.5Sb0.5 bulk metallic glasses at room temperature

The room temperature creep behaviors of Mg61Cu28Gd11 and(Mg61Cu28Gd11)99.5Sb0.5 bulk metallic glasses(BMGs) were revealed by means of nanoindentation technique.The creep mechanism was explored by characterization of creep rate sensitivity,creep compliance and retardation spectra.The results showed that the experimental creep curves could be well described by a generalized Kelvin model.The low creep rate sensitivity of both Mg-based BMGs indicated that their room temperature creep was dominated by localized shear flow.In addition,the(Mg61Cu28Gd11)99.5Sb0.5 glassy alloy exhibited lower creep rate sensitivity,creep compliance and milder retardation peak,indicating its higher creep-resistance and less relaxed state.Furthermore,the creep retardation spectrum consisted of two relatively separated peaks with the well defined characteristic relaxation times.     

Effect of Barothermal Treatment on the Structure and the Mechanical Properties of a High-Strength Eutectic Al–Zn–Mg–Cu–Ni Aluminum Alloy

The effect of barothermal treatment by hot isostatic pressing (HIP) on the structure and the properties of castings of a promising high-strength cast aluminum alloy, namely, nikalin ATs6N4 based on the Al?Zn–Mg–Cu–Ni system, has been studied using two barothermal treatment regimes different in isothermal holding temperature. It is shown that the casting porosity substantially decreases after barothermal treatment; eutectic phase Al3Ni particles are additionally refined during exposure to the barothermal treatment temperature: the higher the HIP temperature, the more substantial the refinement. The improvement of the casting structure after HIP increases their mechanical properties. It is found, in particular, that the plasticity of the alloy in the state of the maximum hardening increases by a factor of more than 8 as compared to the initial state (from 0.82 to 6.9%).     

Effect of Solid Solution Treatment on Microstructure of FeNi Based High Strength Low Thermal Expansion Alloy

The influence of solid solution treatments on the dissolution of carbides precipitates, the grain size, and the hardness of high strength low expansion alloy were investigated through XRD analysis, microstructure observations, and theoretical computation. It was seen that most primary Mo2C type carbide band dissolved in a temperature range of 1 100-1 150 ℃. When the temperature was over 1 200 ℃, the grain size increased remarkably, which led to the reduction of hardness.