Deformation behavior of Zr-based bulk metallic glass in an undercooled liquid state under compressive loading

High temperature deformation behavior of a Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk amorphous alloy has been studied in a temperature range between 355 and 460°C under compressive loading after rapid heating. A transition of flow behavior, viz. from, a Newtonian to a non-Newtonian flow, has been reported by many researchers as the temperature is decreased at a given strain rate. In the present study, two different theoretical relations based on a viscous flow model and a transition state theory have been applied to analyze the transition behavior of deformation in terms of viscosity and flow stress. An experimental deformation map was then constructed to specify the boundaries between Newtonian and non-Newtonian flow, based on the relationship between the flow stress and strain rate in an undercooled liquid state. It has further been confirmed that the stress overshoot phenomena can be observed mostly in a non-Newtonian flow regime appearing in an intermediate temperature and strain rate region in this deformation map.     

Microstructural heterogeneities governing the deformation of Cu47.5Zr47.5Al5 bulk metallic glass composites

Cu_47.5Zr_47.5Al₅ rods with different volume fractions of crystalline B2 CuZr phase were prepared by copper mould casting. Based on microstructural investigations a solidification mechanism is proposed for these bulk metallic glass (BMG) composites. The composite microstructure enhances the compressive plasticity (plastic strain up to 14%) and both plastic strain as well as yield strength scale with the crystalline volume fraction. Yield strength and fracture strain were successfully calculated using a strength model, which considers percolation and an empirical three microstructural element body approach, respectively. Furthermore, B2 CuZr was synthesized by means of a thermal cycling treatment and uniaxial compression tests were carried out at room temperature. The intrinsic work-hardenability caused by a martensitic transformation has strong implications on the deformation behaviour of the investigated Cu_47.5Zr_47.5Al₅ BMG composites.     

Arrhenius activation of Zr65Cu18Ni7Al10 bulk metallic glass in the supercooled liquid region

In the current research, the dynamic mechanical spectrum and compressive deformation of Zr₆₅Cu₁₈Ni₇Al₁₀ bulk metallic glass in the supercooled liquid region (SLR) are investigated. The experimental results prove the existence of transition from Newtonian flow to non-Newtonian flow in the metallic glasses. In addition, we found that the characteristic stress σ_tc, which is obtained by a stretched exponential function based on the normalized viscosity, can be regarded as a transition point from Newtonian to non-Newtonian flow. The correlation between strain rate sensitivity exponent and corresponding strain rate was obtained at a certain temperature. It is noted that the variation of transition strain rate from Newtonian to non-Newtonian flow with different absolute temperatures follows the Arrhenius equation. The activation energy is in good accordance with that using the mechanical spectroscopy method.     

Homogeneous deformation of Ti41.5Cu37.5Ni7.5Zr2.5Hf5Sn5Si1 bulk metallic glass in the supercooled liquid region

The homogeneous deformation behavior of Ti_41.5Cu_37.5Ni_7.5Zr_2.5Hf₅Sn₅Si₁ BMG has been investigated by compression tests. The results show that its high-temperature deformation behavior is strongly dependent on strain rate and temperature, and there exists a transition from non-Newtonian flow to Newtonian flow with decrease in strain rate, which can be explained based on the transition state theory. In addition, this alloy can reach a large compressive strain than 0.8 at high strain rate; however the much higher flow stress and lower value of S parameter compared with typical BMGs indicates its worse formability in the SLR. A beneficial domain (temperature and strain rate) for optimum hot workability of this alloy has been roughly located by constructing the power dissipation efficiency map, where the power dissipation efficiency is larger than 0.8.     

Influence of Superheat on Microstructure and Mechanical Properties of Ductile Cu47.5Zr47.5Al5 Bulk Metallic Glass-Matrix Composite

Generally bulk metallic glasses (BMGs) posses very less ductility and toughness at room temperature. Over the recent past years to improve up on these properties in many alloy system BMG composites have been developed. It was also reported that Cu_47.5Zr_47.5Al₅ BMG composite shows a very high strength together with an extensive work hardening-like behavior of large ductility around 18%. In this study, the influence of superheat on microstructure and the resulting mechanical properties in Cu_47.5Zr_47.5Al₅ bulk metallic glass-matrix composite alloy has been studied. The Cu_47.5Zr_47.5Al₅ melt solidifies into a composite microstructure consisting of crystalline precipitates embedded in an amorphous matrix. The crystalline phase consists of B2 CuZr (cubic primitive with CsCl structure) with a small amount of monoclinic CuZr martensitic structure embedded in an amorphous matrix. The volume fraction of crystalline phases varies with melting current as well as position along the length of the as-cast rod, depending on the local cooling condition. The volume fraction and the distribution of the crystalline precipitates are heterogeneous in the amorphous matrix. Room temperature uniaxial compression tests revealed high yield strength ranging from 796 to 1900 MPa depending upon the volume fraction of the crystalline phases present. The presence of the dendritic B2 CuZr significantly improved the ductility. The BMG composites show a pronounced plastic strain up to 14% for the higher volume fraction of crystalline phase.     

DEFORMATION BEHAVIOR AND CONSTITUTIVE EQUATION FOR Zr55Cu30Al10Ni5 BULK METALLIC GLASS IN SUPERCOOLED LIQUID REGION

Zr₅₅Cu₃₀Al₁₀Ni₅块体非晶合金(BMG)在过冷液态区内的单向压缩实验表明: 材料在过冷液态区内的形变行为强烈依赖于温度和变形速率. 随着应变速率的增加, 材料的流变特征由Newtonian流变转变为非Newtonian流变.利用扩展指数本构方程模型建立了非晶合金的流变应力、应变速率和温度的关系.     

Flow Stress and Processing Map of a PM 8009Al/SiC Particle Reinforced Composite During Hot Compression

Hot compression tests of 8009Al alloy reinforced with 15% SiC particles (8009Al/15%SiC_p composites) prepared by powder metallurgy (direct hot extrusion methods) were performed on Gleeble-3500 system in the temperature range of 400-550 °C and strain rate range of 0.001-1 s^?1. The processing map based on the dynamic material model was established to evaluate the flow instability regime and optimize processing parameters; the associated microstructural changes were studied by the observations of optical metallographic and scanning electron microscopy. The results showed that the flow stress increased initially and reached a plateau after peak stress value with increasing strain. The peak stress increased as the strain rate increased and deformation temperature decreased. The optimum parameters were identified to be deformation temperature range of 500-550 °C and strain rate range of 0.001-0.02 s^?1 by combining the processing map with microstructural observation.     

Hot deformation behavior of Ni–Fe–Ga-based ferromagnetic shape memory alloy – A study using processing map

Ni–Fe–Ga-based alloys form a new class of ferromagnetic shape memory alloys (FSMAs) that show considerable formability because of the presence of a disordered fcc γ-phase. The current study explores the deformation processing of this alloy using an off-stoichiometric Ni₅₅Fe₁₉Ga₂₆ alloy that contains the ductile γ-phase. The hot deformation behavior of this alloy has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression tests in the 1123–1323 K temperature range and strain rate range of 10⁻³–10 s⁻¹ and using a combination of constitutive modeling and processing map. The dynamic recrystallization (DRX) regime for thermomechanical processing has been identified for this Heusler alloy on the basis of the processing maps and the deformed microstructures. This alloy also shows evidence of dynamic strain-aging (DSA) effect which has not been reported so far for any Heusler FSMAs. Similar effect is also noticed in a Ni–Mn–Ga-based Heusler alloy which is devoid of any γ-phase.     

Constitutive equations of flow stress of magnesium AZ31 under dynamically recrystallizing conditions

Constitutive equations for the relationship between flow stress, strain, strain rate and temperature for magnesium AZ31 alloy under hot working conditions where dynamic recrystallization is prevalent have been developed. Equation development data were obtained using isothermal plane strain compression (PSC) tests carried out at 300–500 °C with strain rates ranging from 0.5 to 50 s⁻¹, to an equivalent strain of 0.7. The predicted flow stress curves show good comparison with the experimental isothermal flow curves in terms of peak, steady state stress and flow softening behaviour but at higher Zener–Hollomon (Z) values (>10¹¹ s⁻¹) the predicted peak stress deviates from the isothermal value in the range of 14–25 MPa suggesting a breakdown in the hyperbolic sine equation at those Z values. The developed constitutive equations for the valid thermomechanical conditions were adopted in a finite element model to simulate the PSC conditions. The distributions of strain, strain rate and temperature qualitatively suggest higher strain rate at the centre of the sample which agrees well with that of the quantitative analysis of the dynamically recrystallized grain size.     

Superplasticity in a bulk amorphous Pd-40Ni-20P alloy:a compression study

Compressive deformation behavior of a cast Pd₄₀Ni₄₀P₂₀ bulk metallic glass in the supercooled liquid region (589–670 K) was investigated at strain rates ranging from 10⁻⁴ to 10⁻² s⁻¹. The material exhibited excellent mechanical formability in the supercooled liquid region. However, in contrast to a Newtonian behavior generally observed in oxide glasses, the present alloy also showed a non-Newtonian behavior, depending upon the temperature and applied strain rate. Specifically, the alloy is like a Newtonian fluid at high temperatures, but becomes non-Newtonian at low temperatures and high strain rates. Structures of the amorphous material, both before and after deformation, were examined using X-ray diffraction and high-resolution transmission electron microscopy. The non-Newtonian behavior is proposed to be associated with the glass instability during deformation.     

Thermomechanical deformation behaviour of DH36 steel during friction stir welding by experimental validation and modelling

Friction stir welding is a solid state thermomechanical deformation process from which the plasticisation behaviour of the stirred material can be evaluated through the study of flow stress evolution. Flow stress data also supporting the development of a local microstructural numerical model have been generated. Hot compression testing of DH36 steel has been performed at a temperature range of 700–1100°C and strain rates from 10^?3 to 10² s^?1 to study the alloy’s thermomechanical deformation behaviour in conditions that simulate the actual friction stir welding process. It has been found that the evolution of flow stress is significantly affected by the test temperature and deformation rate. The material’s constitutive equation and constants have been calculated after analysis of these data. Preliminary numerical analysis results are in good agreement with experimental observations.     

35% SiC_p/2024A1复合材料的热变形行为(英文)

采用Gleeble-1500D热模拟试验机,对35%SiCp/2024A1复合材料在温度350~500°C、应变速率0.01~10s-1的条件下进行热压缩试验,研究该复合材料的热变形行为与热加工特征,建立热变形本构方程和加工图。结果表明,35%SiCp/2024A1复合材料的流变应力随着温度的升高而降低,随着应变速率的增大而升高,说明该复合材料是正应变速率敏感材料,其热压缩变形时的流变应力可采用Zener-Hollomon参数的双曲正弦形式来描述;在本实验条件下平均热变形激活能为225.4 kJ/mol。为了证实其潜在的可加工性,对加工图中的稳定区和失稳区进行标识,并通过微观组织得到验证。综合考虑热加工图和显微组织,得到变形温度500°C、应变速率0.1~1 s-1是复合材料适宜的热变形条件。     

The mechanical properties of single phase γ Ti47Al51Mn2 polycrystals

The mechanical properties of polycrystalline samples of the single phase γ-Ti₄₇Al₅₁Mn₂ alloy have been studied during compression tests in a wide range of temperatures (120–1270 K). The flow stress and the work hardening rate are measured during imposed strain rate tests, while the strain rate sensitivity of the stress is examined using both strain rate jumps and stress relaxation experiments. From the temperature, strain and stress dependence of these parameters, it is shown that the investigated temperature domain can be divided into three régimes corresponding to different deformation mechanisms. The results are compared to the data available in the literature and are found to be in good agreement with the dislocation structures and dislocation motion mechanisms that we have previously reported.     

Characterization of mechanisms of hot deformation of as-cast nickel aluminide alloy

The hot deformation behavior of as-cast Ni₃Al alloy has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing in the temperature range 1100–1250°C and strain rate range 0.001–10 s⁻¹. The mechanisms of hot working have been evaluated using four generations of materials modeling techniques, which included shape of stress–strain curves, kinetic analysis, processing maps and dynamical systems approach. The material exhibited a steady-state flow behavior at slower strain rates but flow softening associated sometimes with broad oscillations, was observed at higher strain rates. The flow stress data did not obey the kinetic rate equation over the entire regime of testing but a good fit has been obtained in the intermediate range of temperatures (1150–1200°C). In this range, a stress exponent value of 6.5 and an apparent activation energy of about 750 kJ/mol have been evaluated. Microstructural investigations have shown that the matrix γ′ phase undergoes dynamic recovery in the presence of harder γ colonies The processing maps revealed four different domains out of which three are interpreted to represent cracking processes. The fourth domain, which has a peak efficiency of about 44%, occurred at 1250°C/0.001 s⁻¹. Microstructural observations revealed that this domain represents dynamic recrystallization (DRX) of γ phase and is desirable for hot working the material. The material exhibits flow instabilities when deformed in the intermediate temperature regime at strain rates higher than 1 s⁻¹ and these are manifested as shear localization.     

镁基大块非晶合金在过冷液相区流变行为本构关系

研究了Mg60Cu30Y10大块非晶合金在过冷液相区的流变行为.结果表明:随着温度升高和应变速率增加,平衡态的牛顿流转变为非平衡态的非牛顿流;其流变行为对于温度和应变速率非常敏感.由粘度与应变速率的关系,根据Arrhenius型VFT方程,确定了流动应力、应变速率和温度的关系.Mg60Cu30Y10大块非晶合金在过冷液相区的流变性能依赖于温度与变形速率,其微观机制可由自由体积模型解释,为大块非晶合金流变成形工艺的实现提供理论依据:温度高于玻璃转变温度以后,自由体积的增加使非晶合金变形过程中能够移动的原子数目随之增加,自由体积周围的原子沿外力的作用方向移动,即宏观上的塑性流变行为.应变速率增加,由热激活引起的自由体积增加不能满足更多原子流变所需的空间体积,导致牛顿流向非牛顿流转变.     

TC17钛合金高温变形行为研究

采用Gleeble 3500D热模拟试验机对TC17钛合金进行了高温压缩试验。其变形温度为973～1223 K,应变速率为0.001～10 s~(-1),应变0.9。结果表明:TC17钛合金高温流变应力对应变速率和变形温度非常敏感。在温度为1123,1183和1223 K,应变速率为10 s~(-1)时,TC17钛合金的流动应力出现了明显的应力不连续屈服现象。利用Zener-Holloman参数建立了TC17钛合金的高温本构方程,与试验结果对比表明:该方程可以准确地描述TC17钛合金的的高温流动行为。基于动态模型,建立了TC17钛合金的热加工图,并结合微观组织分析验证了加工图的准确性。     

Deformation behavior of Zr55.9Cu18.6Ta8Al7.5Ni10 bulk metallic glass matrix composite in the supercooled liquid region

A Zr_55.9Cu_18.6Ta₈Al_7.5Ni₁₀ bulk metallic glass (BMG) composite with an amorphous matrix reinforced by micro-scale particles of Ta-rich solid solution was prepared by copper-mold casting. Isothermal compression tests of the BMG composite were carried out in the range from glass transition temperature (∼673 K) to onset crystallization temperature (∼769 K) determined by differential scanning calorimetry (DSC). The compressive deformation behavior of the BMG composite in the supercooled region was investigated at strain rates ranging from 1 × 10⁻³ s⁻¹ to 8 × 10⁻² s⁻¹. It was found that both the strain rate and test temperature significantly affect the stress–strain behavior of the BMG composite in the supercooled liquid region. The alloy exhibited Newtonian behavior at low strain rates but became non-Newtonian at high strain rates. The largest compressive strain of 0.8 was achieved at a strain rate of 1 × 10⁻³ s⁻¹ at 713 K. The strain rate change method was employed to obtain the strain rate sensitivity (m). The deformation mechanism was discussed in terms of the transition state theory based on the free volume.     

A thermoplastic forming map of a Zr-based bulk metallic glass

A thermoplastic forming (TPF) map of a Zr₃₅Ti₃₀Be_26.75Cu_8.25 bulk metallic glass was constructed through systematic hot-embossing experiments, spanning a wide range of strain rates and temperatures in the supercooled liquid region. By comparison with the corresponding deformation map, it is found that Newtonian flow, non-Newtonian flow and inhomogeneous flow regions correspond well to fully filled, partially filled and non-filled regions, respectively, in the hot-embossing TPF map. Furthermore, the spatio-temporally homogeneous flow facilitates the thermoplastic formability of the Zr-based bulk metallic glass, which is rationalized in terms of free volume theory as well as by finite element simulations. Finally, our results are corroborated by potential application tests.     

Compression behaviour of semisolid YL112 die casting aluminium alloy following isothermal heat treatment

Abstract

The semisolid compression deformation behaviour of YL112 die casting aluminium alloy with the non-dendritic and dendritic structures has been compared in tests using a Gleeble-1500 thermomechanical simulator. The non-dendritic structure was obtained by isothermal treatment at 570°C for 120 min. In tests up to compressive strains of 0·8, the semisolid compression stress of the alloy with non-dendritic structure initially increases rapidly with increasing strain, then decreases, before reaching a plateau value. Under different deformation temperatures and deformation rates, the maximum compressive stresses are obtained in all cases at strain values of ～0·07. The semisolid deformation stress decreases with increasing deformation temperature and increases with increasing deformation rate. The compression behaviour of the two types of alloy differs. The semisolid compression stress of the alloy with dendritic structure is higher than that of the alloy with non-dendritic structure; and for strains >0·07, the semisolid compression stress increases and decreases with increasing strain for alloys with dendritic and non-dendritic structures respectively.     

高温变形对(Cu50Zr50)92Al8等温晶化行为及其力学性能的影响

研究了(Cu50Zr50)92Al8非晶合金在过冷液相区中,经过牛顿流变和非牛顿流变后的等温晶化行为及其对该合金力学性能的影响。结果表明,牛顿型流变对(Cu50Zr50)92Al8非晶合金的结构没有明显的影响;而非牛顿流变对该非晶的显微结构及其等温晶化行为有显著影响:非牛顿流变促进了(Cu50Zr50)92Al8非晶合金的晶化,其主要晶化相为体心立方结构的CuZr相(B2相)和CuZr马氏体相;经非牛顿流变及真空热处理试样,在室温压缩过程中,应力诱发了部分B2相的马氏体相变,从而使其在室温下表现出超弹性,当预塑性应变量为8%时,其总可回复应变为5%左右。