喷射成形大尺寸镧基块体非晶过冷液相区内的塑性变形行为

研究了喷射成形大尺寸La62Al15.7(Cu,Ni)22.3非晶合金在过冷液相区内的塑性变形行为.结果表明,随加热温度的增加和应变速率的减小,该非晶合金由非稳态变形向单一稳态变形行为转变.当应变速率为5×10-3S-1,温度为443 K和挤压比为6.25时,喷射成形La62Al15.7(Cu,Ni)22.3非晶合金样品的密度由挤压前的5.723增加到挤压后的5.924 g/cm3,达到了同成分吸铸态非晶合金密度(6.134 g/cm3)的96.6%.挤压后非晶合金样品依然保持完全非晶态.     

DEFORMATION BEHAVIOR OF SPRAY–DEPOSITED La–BASED BULK AMORPHOUS ALLOY IN SUPERCOOLED LIQUID REGION

研究了喷射成形大尺寸La₆₂Al_15.7(Cu, Ni)_22.3非晶合金在过冷液相区内的塑性变形行为. 结果表明, 随加热温度 的增加和应变速率的减小, 该非晶合金由非稳态变形向单一稳态变形行为转变. 当应变速率为5×10^-3 s^-1, 温度为443 K和挤压比为6.25时, 喷射成形La₆₂Al_15.7(Cu, Ni)_22.3非晶合金样品的密度由挤压前的5.723增加到挤压后的5.924 g/cm³, 达到了同成分吸铸态非晶合金密度 (6.134 g/cm³) 的96.6%. 挤压后非晶合金样品依然保持完全非晶态.     

Effect of deformation temperature on the deformation behaviors of amorphous/crystalline composites

The amorphous/crystalline composite comprising amorphous particles of Cu54Ni6Zr22Ti18 embedded in the crystalline nickel matrix was produced and its temperature dependence of the plastic deformation behavior was studied in the supercooled liquid region (SLR) of the amorphous alloy. The flow stress of the amorphous alloy was quite sensitive to the testing temperature in the SLR. The deformation of the composites was dominated by the flow stress of the amorphous alloy. The deformation behavior of the composite was analyzed by finite element method (FEM) calculations.     

High Temperature Deformation Behavior of High Strength and Toughness Ti-Ni Base Bulk Metallic Glass CompositesEI北大核心CSCD

Room-temperature brittleness and strain-softening during deformation of bulk metallic glasses, and limited processability of shape memory alloys have been stumbling blocks for their advanced functional structural applications. To solve the key scientific problems, a new shape memory bulk metallic glass based composite, through the approach using transformation-induced plasticity (TRIP) effect of shape memory alloys to enhance both ductility and work-hardening capability of metallic glasses, and superplasticity of bulk metallic glass in supercooled liquid region to realize near net forming, was developed in this work. And the Ti-Ni base bulk metallic glass composites (BMGCs) rods were prepared by the levitation suspend melting-water cooled Cu mold process. Microstructure, thermal behavior, mechanical properties and high temperature deformation behavior of the alloy were investigated. The results show that the as-cast alloy microstructure consists of amorphous matrix, undercooled austenite and thermally-induced martensite. Besides, the size of the crystal phase precipitated on the amorphous matrix in-creases from the surface to the inside. The alloy exhibits excellent comprehensive mechanical properties at room temperature. The yield strength, fracture strength and the plastic strain of alloy are up to 1286 MPa, 2256 MPa and 12.2%, respectively. Under compressive loading in the supercooled liquid region, the composite exhibits approximate Newtonian behavior at lower strain rate in higher deformation temperature, and the optimum deformation temperature is T>480 degrees C and the intersection part with supercooled liquid region (SLR). When the temperature is 560 degrees C and the strain rate is 5x10(-4) s(-1), the stress sensitivity index m and the energy dissipation rate Psi are 0.81 and 0.895, respectively. Furthermore, the volume of activation is quantified to characterize the rheological behavior.     

镁基大块非晶合金在深过冷液相区的塑性变形

研究了Mg65Cu25Y7Nd3大块非晶合金在玻璃转化温度Tg附近及深过冷液相区的等温压缩变形行为。结果表明，Mg65Cu25Y7Nd3大块非晶合金的塑性变形与加热温度和加载时间紧密相关。在423K时该大块非晶合金具有一定的塑性，而在深过冷液相区则具有良好的塑性。通过系列试验，得出了Mg65Cu25Y7Nd3大块非晶合金的最佳加热温度为443～463K，加载时间约10min。对大块非晶合金在变形过程中的结构变化的分析表明，在本试验条件下，压缩变形对Mg65Cu25Y7Nd3大块非晶合金的晶化过程没有明显的影响。     

(Ti,Zr,Hf)-(Cu,Ni,Ag)-Al多组元合金体系的机械驱动非晶化

研究了由前过渡族金属和后过渡族金属按照等原子比替代的(Ti0.33Zr0.33Hf0.33)50(Ni0.33Cu0.33Ag0.33)40Al10多组元合金在机械研磨作用下的非晶化转变,并与由熔体急冷制备的同一成分玻璃态合金进行了对比.两种途径获得的玻璃态相似.在机械研磨的稳态产物中,仍残留有少量尺寸小于30 nm的晶体相颗粒,即非晶化转变未能完全实现.机械研磨形成的非晶相表现有明确的玻璃转变和约80 K宽的过冷液态温度区间,晶化过程分两步进行,第一步晶化转变完成后,剩余的非晶相亦具有玻璃态行为,呈现另一玻璃转变及约100 K宽的过冷液态温度区间.     

Finite-element analysis for high-temperature deformation of bulk metallic glasses in a supercooled liquid region based on the free volume constitutive model

A constitutive relation based on the free volume model was developed to describe the strain-rate-dependent deformation behavior of bulk metallic glasses (BMG) at temperatures within the supercooled liquid region (SLR). Validity of the present approach has consequently been assessed by comparing the numerical results obtained from finite-element analyses with the experimental results previously obtained from compression tests of Vitreloy-1 BMG alloy. Finite-element-method simulations combined with free volume constitutive relations were found to reproduce well the plastic deformation behavior of Vitreloy-1 alloy, exhibiting a Newtonian viscous flow without stress overshoot and also a non-Newtonian viscous flow with stress overshoot at temperatures within the SLR. The present approach appears to provide a powerful means of understanding plastic deformation behavior in relation to localized and uniform deformation and also of making reliable formability estimations of BMG alloys.     

Zr－Al－Ni－Cu大块非晶合金的变温晶化行为研究

研究了Zr-Al-Ni-Cu大块非晶合金在连续升温过程中的晶化行为。结果表明，随升温速度的加快，特征温度Ts，Tx，Tp均向高温区移动，晶化热焓增加，过冷温度区间扩大，并且峰值温度Tp对应的晶化体积分数减少。利用Kissinger曲线和Doyle曲线法计算合金的变温晶化激活能E，结果表明，晶化激活能随晶化过程的进行，其值先增加后降低，并且在晶化即将结束时，晶化激活能急剧降低。采用Kissinger曲线计算晶化激活能，由于特征温度在不同的加热速度下对应的晶化体积分数发生变化，从而导致了激活能计算值的偏大。     

Zr55Al10Cu30Ni5-xPdx块状非晶合金的玻璃形成能力和热稳定性

用铜模铸造方法制备了不同尺寸的Zr55Al10Cu30Ni5-xPdx(x=0,1,3,5)块状非晶合金，采用X射线衍射（XRD）、扫描差热分析（DSC）和透射电镜（TEM）分别为Zr55Al10Cu30Ni5-xPdx块状非晶样品的结构、热稳定性和微观组织进行了研究。结果表明：x=1时，合金具有最高的过冷液相区（高达100K）及最大的热稳定性，而对合金的玻璃形成能力影响不大，这说明用适量的Pd代表Zr55Al10Cu30Ni5合金中的Ni会提高合金的热稳定性；x=3时，合金的热稳定性有所提高，但降低了合金的玻璃形成能力；x=5时，非晶合金的热稳定性和玻璃形成能力同时降低。     

Influence of Processing Parameters on the Deformation Behavior of Ti14 Alloy Containing a Small Volume of Liquid

采用热模拟系统研究了半固态变形温度,应变速率和变形量对Ti14合金压缩行为和组织演变的影响。结果表明:温度和应变对Ti14合金半固态峰值应力影响较大,峰值应力随着温度的增加和应变速率的减小而降低。分析认为:半固态变形中,应变速率的变化会影响产生压缩变形所需的响应时间,而液相的含量受控于变形温度,随着变形温度的升高,组织中出现了网状晶界结构,使得变形机制由固相粒子的塑性变形转变为固液混合流动。此外,变形量对合金半固态变形的应力-应变影响较小,可以认为是液相的润滑作用和协调变形机制缓解了晶粒间的压缩应力和摩擦力,使得应力-应变变化不明显。     

新型铜合金/非晶复合材料的挤压成形特性

基于大块非晶在过冷液相区间具有较好的热塑性成形特点,选择铜基非晶Cu40Zr44Ag8Al8和铜合金,通过挤压成形工艺,制备出一种新型的铜合金/非晶复合材料;在703 K和挤压速度为0.4 mm/min下对该复合材料进行挤压,获得铜合金、非晶复合材料棒材.通过光学金相(OM)、X射线衍射(XRD)、示差扫描量热分析(DSC)和维氏硬度测试(HV)对挤压变形前、后芯部非晶进行形貌观察和结构分析.结果表明:芯部非晶在挤压前期呈不均匀分布,而后分布非常均匀;结合XRD、DSC和硬度的结果分析,在703 K下挤压后,芯部非晶没有发生晶化.     

Nanostructured bulk glassy Cu_(60)Zr_(30)Ti_(10) alloy with high strength and good ductility in cast state

1　INTRODUCTIONSinceaseriesofmetallicbulkglassyalloyswithexpectedmechanicalpropertiesandhighglassformingabilityhavebeenfound[13] ,particularattemptshavebeendonetoimprovethemechanicalpropertiesoftheglassyalloystomeetengineeringapplications .Bycrystallizingthemetallicglasses ,nanostructuredal loyscontainingnanocrystallinephasesandglassyma trixwereobtainedandthemechanicalpropertiesofthealloyswereenhancedbyhomogeneousdispersionofnanoscalemetallic particlesintheAl [4 ,5] ,Fe Ni [6 ] andMg [7]…     

半固态变形量对Ti14合金热稳定性的影响

研究新型阻燃钛合金Ti14(α+Ti2Cu)经不同变形量(45%～75%)半固态锻造后的热稳定性能,分析变形量对合金热稳定性能的影响。结果表明:变形量改变析出相的形态及晶粒尺寸,使合金具有不同的热稳定性能。随变形量的增加,Ti14合金热暴露后的强度呈先降低后升高的趋势,塑性有所改善。半固态变形量较小时(45%),合金晶粒粗大,Ti2Cu相呈长条状分布于晶界,高的强度取决于析出相强化作用;随变形量增大(75%),晶粒细化,Ti2Cu相呈颗粒状或短棒状弥散分布,产生细晶强化,使得强度和塑性都得到改善。断口分析表明:变形量较小,断口存在大量撕裂棱;变形量达到75%,断口以韧窝为主;表明析出相和晶粒尺寸共同决定Ti14合金的热稳定性能。     

Mechanical behavior of a bulk Cu–Ti–Zr–Ni–Si–Sn metallic glass forming nano-crystal aggregate bands during deformation in the supercooled liquid region

The deformation behavior of a bulk Cu₄₇Ti₃₃Zr₁₁Ni₆Sn₂Si₁ metallic glass, fabricated by injection casting, has been characterized in the supercooled liquid region. The alloy deforms homogeneously and exhibits large elongation above the glass transition temperature at constant true strain rate below 1×10⁻²s⁻¹, but it shows a variation of the flow stress during deformation. The flow stress reaches a peak just after yielding and then decreases significantly with increasing strain. After the plateau level of remarkably low flow stress, it rises again and then the alloy finally fails in a brittle manner. DSC data and TEM observations for the tested alloy reveal that the alloy evolves to being crystallized during deformation. Nano-crystals are aggregated and the aggregates are aligned along the load direction. When the volume fraction of the crystalline phase is in the range up to 0.5, the nano-crystal aggregates effectively slide over each other, lowering the apparent stress level. However, as the amount of the crystalline phase further increases, the flow stress continuously increases. This behavior can be explained based on the volume-fraction rule between the crystalline phase and the amorphous phase.     

Effect of hydrostatic pressure on the decomposition behavior of Cu54Zr22Ti18Ni6 bulk metallic glass alloy in supercooled liquid region

The effect that hydrostatic pressure has on the decomposition behavior in Cu₅₄Ni₆Zr₂₂Ti₁₈ bulk metallic glass (BMG) alloy was assessed using samples, which were isothermally annealed in the supercooled liquid region (SLR) with and without application of hydrostatic pressure. During subsequent annealing for the thermal analysis, the samples annealed under hydrostatic pressure displayed a slower crystallization process in the SLR, which is attributed to a retarded compositional decomposition of the BMG alloy under pressure.     

Zr基大块非晶合金在过冷液相区的静液挤压塑性变形研究

通过Gleeble1500热模拟试验,选择纯铁作为挤压包套材料,然后对非晶合金在390℃、应变速率8.9×10-1s-1的条件下进行了静液挤压。Zr非晶合金产生了塑性变形,但没有发生均匀粘滞性流动,而是断裂成两段。样品断口上随机分布着充分与未充分发展的“脉纹”状切变带,并且断面上出现了类似流动熔体凝固后的特征结构。高应变速率变形条件使非晶合金产生的非均匀流变,以及静液挤压时纯铁先于非晶合金的流动变形是造成非晶合金断裂的主要原因。挤压态非晶合金的过冷液相区减小,热稳定性有所降低。     

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.     

Cu-based bulk amorphous alloy with larger glass-forming ability and supercooled liquid region

The glassy rod with a maximum sample thickness of 11 mm and larger supercooled liquid region of 108 K was successfully fabricated when substituting Cu with minor amount of Ag in the Cu–Zr–Al–Gd alloy system. The value of γ reaches a maximum of 0.418 for the Cu_45.5Zr₄₅Al₇Gd₂Ag_0.5 bulk metallic glass (BMG) alloy. The high glass-forming ability (GFA) and larger supercooled liquid region are discussed from atomic size, negative mixing heat among constituent elements and thermodynamics.     

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.     

Co对Ti-Ni形状记忆合金相变和形变特性的影响

用热重分析仪、X射线衍射仪、示差扫描量热仪及拉伸试验研究了Co对Ti-49.8Ni(at%,下同)形状记忆合金相变和形变特性的影响。结果表明,中温退火态Ti-49.8Ni合金冷却/加热时的相变类型为A→R→M/M→A(A—母相,R—R相,M—马氏体相);随退火温度升高,该合金的马氏体相变温度升高,R相变温度先升高后降低;该合金室温相组成为马氏体,具有形状记忆效应(SME)。用1%Co置换等量Ti后所得Ti-49.8Ni-1Co合金冷却/加热时的相变类型为A→R→M/M→R→A,相变温度低,室温组成相为母相A,具有超弹性(SE)特性。退火温度低于600℃时,Ti-Ni基合金的SME和SE特性良好,退火温度超过600℃后,合金氧化加剧,SME和SE特性变差,塑性显著提高。