Triple yielding and deformation mechanisms in metastable Cu47.5Zr47.5Al5 composites

A triple yielding phenomenon resulting in high fracture strength (up to 2360 ± 10 MPa) and large ductility (up to 13.5 ± 0.5%) during compressive deformation is first discovered and systematically investigated in metastable Cu_47.5Zr_47.5Al₅ composites. Based on electron microscopy and X-ray diffraction studies, the major deformation mechanisms at the different stages of compression are revealed to be: (1) the constraint effect of the amorphous phase; (2) the pre-existence of a small number of microtwins and a small amount of martensitic phases; (3) the initiation and development of martensitic transformation; (4) the interplay between CuZr crystals and shear bands; and (5) the activation of partial detwinning, together with a high density of dislocations. The yield strengths of the composites are modeled as a function of the volume fraction of the constituent phases and a transition from the rule-of-mixtures to a load-bearing model is observed. The underlying ductile nature of the composites is further correlated with the unique electronic structure of the B2 CuZr intermetallics. The present results provide an understanding of the deformation mechanism of metastable CuZr-based composites and give guidance on how to improve the ductility/toughness of bulk metallic glasses.     

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.     

Zr5oTi5Cu18Ni17Al10块体金属玻璃的热稳定性和力学性能

采用差示扫描量热仪以连续加热的方式研究了Zr50Ti5Cu18Ni17Al10块体金属玻璃的热稳定性.其玻璃转变激活能(Eg)以及晶化激活能(Ep1和Ep2)分别为438±11,284±8和323+11 kJ/mol.采用压缩试验研究了金属玻璃的室温力学性能,初始应变速率为1×10-4 s-1.直径为3 mm的金属玻璃棒呈现良好的力学性能,最大塑性应变达3％,杨氏模量和断裂强度的最大值分别为90 GPa和1968MPa.多条剪切带的交织、分叉和滑移以及宽度为60 μm的较大临界剪切台阶是Zr50Ti5Cu18Ni17Al10块体金属玻璃具有较高压缩塑性的主要原因.     

Al原子在Cu44.25Ag14.75Zr36Ti5大块金属玻璃中的扩散

采用二次离子质谱仪(SIMS)离子剥落方式结合台阶仪研究了Al原子在Cu44.25Ag14.75Zr36Ti5大块金属玻璃(BMG)和晶态合金中的扩散行为。结果表明:在300～390℃,Al原子在金属玻璃中的扩散系数位于3.691×10-21～1.063-16×10-20m2.s-1;在晶态合金中的扩散系数位于2.038×10-16～5.674×10-16m2.s-1,其扩散系数和温度的关系符合单一的Arrhenius关系式。Al原子在Cu44.25Ag14.75Zr36Ti5BMG以原子团整体输运的方式扩散,在晶态合金中以空位和间隙扩散为主。     

结构驰豫对Cu58．1Zr35．9Al6块状非晶合金弹性性能的影响

本文系统地研究了结构驰豫对Cu58．1Zr35．9Al6块状非晶合金弹性性能的影响。将Cu58．1Zr35．9Al6非晶合金在150℃、300℃、450℃分别保温1h。测量退火样品的纵、横波声速,并推算其弹性性能。结果表明：随退火温度的升高,声速与弹性性能呈现逐渐增加的趋势。低温驰豫时声速与弹性性能变化缓慢,高温驰豫时增加明显。基于结构驰豫谱模型分析了上述现象的产生在于：提高温度,原子有足够的条件进行中程与长程扩散,通过发生原子的积聚重排,大量自由体积的湮灭,使非晶样品的有序度得到大大的改善。     

Thermomechanical characterization of Cu47.5Zr47.5Al5 bulk metallic glass within the homogeneous flow regime

We present a systematic study of the high temperature deformation behavior of a Cu_47.5Zr_47.5Al₅ ternary bulk metallic glass over a wide range of strain rates within the homogeneous flow regime. The apparent viscosity and the effective strain rate determined by thermomechanical analysis in the low stress regime strongly depend on the isothermal annealing temperature and the applied compressive force. Three distinct flow modes, viz. inhomogeneous, non-Newtonian and Newtonian flow, can be distinguished from compression tests. The strain rate–stress data, deduced from both thermomechanical analysis and quasi-static compression tests, were used to construct a Norton-type plot indicating a transition from Newtonian to non-Newtonian flow. The significance of these findings for the expected macroscopic shaping capability based on the dynamic materials model as well as the change of the amount of atomic-scale flow defects such as free volume is also investigated.     

Significant tensile ductility induced by cold rolling in Cu47.5Zr47.5Al5 bulk metallic glass

Significant tensile plasticity up to 0.7 ± 0.1% together with work-hardening and larger fracture strength was obtained in Cu_47.5Zr_47.5Al₅ bulk metallic glass (BMG) upon cold rolling with only 2.9 ± 0.3% thickness reduction. The good deformability could be attributed to the multiple pre-existing shear bands and structural inhomogeneity induced by rolling. The distributions of shear bands upon rolling can be predicted by a simplified rolling model. The underlying mechanism for the tensile plasticity was further discussed in the frame of potential energy landscape theory (PEL).     

轧制对Zr65Al7．5Ni10Cu17．5块体非晶合金硬度的影响

用等速率连续加热退火获得不同驰豫态的Zr65Al7.5Ni10Cu17.5块体非晶合金,在室温下对其进行轧制变形,分析变形后材料的结构.结果发现,最大变形量为95%时,该非晶合金仍然保持单一的非晶结构,不断进行的轧制变形仅是在其中引入了逐渐增多的剪切带,非晶合金的硬度也因此而不断下降.非晶合金在变形前的弛豫程度越高,硬度下降的越快.虽然非晶合金的自由体积在应变量大于80%时达到饱和,但随变形量的提高硬度继续下降.     

Be的添加对Mg_(58.5)Cu_(30.5)Y_(11)块体非晶合金微观组织和力学性能的影响

通过铜模铸造的方法制备了直径为3 mm的(Mg0.585Cu0.305Y0.11)100-xBex(x=3,5,7,10)合金的铸态试样。通过X射线衍射、差式扫描量热计、扫描电镜和电子试验机等,研究了合金的相组成、热性能、微观组织和力学性能。结果表明:在Mg-Cu-Y-Be铸态试样中,Mg Cu Y非晶基体里分布着包含Cu Y晶态相的Cu YBe非晶第二相。第二相的数量和尺寸随着Be的加入量的增大而增大。在单轴压缩载荷下,(Mg0.585Cu0.305Y0.11)100-xBex(x=3,5,7,10)合金的压缩断裂强度分别为866、954、1 086、953 MPa,而且在合金断口上观察到了韧性特征。表明Be的加入提高了合金的综合力学性能。     

退火工艺对Ni／Al复合涂层的组织和力学性能的影响

Ni/Al复合涂层经200℃以上温度退火后,可在Ni层和Al层的交界处形成Al3Ni和Al3Ni2两个稳定相以及Al9Ni2亚稳相。随着退火温度的升高,复合涂层中Ni和Al晶粒的长大使得涂层的强度和硬度降低。摩擦系数从退火前的0.36减小为退火后的0.27,涂层摩擦性能改善的主要原因是由于金属间化合物相的产生。     

Zr41.2Ti13.8Ni10Cu12.5Be22.5块状非晶合金的力学性能研究

在室温常压下，对Zr41．2Ti13．8Ni10Cu12．5Be22．5块状非晶合金在对称循环应力作用下的力学性能进行研究，获得了疲劳破坏寿命S-N曲线，并对其疲劳断口形貌进行了分析。结果表明，非晶合金具有与晶态合金相似的疲劳破坏过程。分析了非晶合金与晶态合金在疲劳寿命上的不同是因其显微结构上的差异所致，并从力学性能方面分析了其破坏机理。     

浇注保温时间对Zr-Cu-Ni-Al-Fe合金力学性能和组织的影响

在水冷铜坩埚中采用铜模吸铸法在相同的浇注温度下以不同的浇注保温时间制备出直径准3mm的Zr53.35Cu29.1Ni4.85Al9.7Fe3合金块体金属玻璃试样,研究了浇注保温时间对试样力学性能和组织的影响。结果表明,在相同的冷却速率和浇注温度下,浇注保温时间存在一个临界值,超过此临界值,合金开始晶化。随着浇注保温时间的延长,合金的非晶形成能力和热稳定性下降,当浇注保温时间从1 min延长至5 min时,过冷液相区△Tx从65 K降至50 K,约化玻璃转变温度Trg由0.560降至0.554,同时压缩断裂强度降低,塑性应变先升后降。     

Cu44.25Ag14.75Zr36Ti5非晶合金的晶化行为

采用铜模铸造法制备了直径为3mm的柱状Cu44.25Ag14.75Zr36Ti5块体非晶合金,X射线衍射证明试样为完全非晶态。利用差示扫描热分析仪(DSC)、X射线衍射,研究了该非晶合金的晶化行为。利用Kissinger和Ozawa方程求得Cu44.25Ag14.75Zr36Ti5第一晶化峰和第二晶化峰的晶化激活能。结果表明,该大块非晶合金具有良好的热稳定性,在10K/min的加热速率下,析出相主要是Cu8Zr3和Cu10Zr7。     

The Effect of Er Addition on the Air-Oxidation of a Zr55Cu30Al10Ni5-Based Bulk Metallic Glass

Air oxidation behavior of a (Zr₅₅Cu₃₀Al₁₀Ni₅)₉₈Er₂ bulk metallic glass was studied at 350–450 °C. The results showed that the oxidation kinetics of the alloy followed a multi-stage parabolic rate law, and the parabolic rate constants at the steady-state stage increased with temperature. The oxidation rates of the alloy were higher than those of the Zr₅₅Cu₃₀Al₁₀Ni₅ glassy alloy, indicative of poor oxidation resistance for the Er-containing alloy. The scales formed on the (Zr₅₅Cu₃₀Al₁₀Ni₅)₉₈Er₂ alloy consisted mostly of tetragonal ZrO₂ and minor monoclinic ZrO₂ and CuO at 350 °C, while Cu₂O and Er₂O₃ were present at T > 400 °C.     

结构驰豫对Cu58.1Zr35.9AI6块状非晶合金弹性性能的影响

本文系统地研究了结构驰豫对Cu58.1Zr35.9AI6块状非晶合金弹性性能的影响.将Cu58.1Zr35.9AI6非晶合金在150℃、300℃、450℃分别保温1 h.测量退火样品的纵、横波声速,并推算其弹性性能.结果表明:随退火温度的升高,声速与弹性性能呈现逐渐增加的趋势.低温驰豫时声速与弹性性能变化缓慢,高温驰豫时增加明显.基于结构驰豫谱模型分析了上述现象的产生在于:提高温度,原子有足够的条件进行中程与长程扩散,通过发生原子的积聚重排,大量自由体积的湮灭,使非晶样品的有序度得到大大的改善.     

奥－贝球铁焊缝的组织与力学性能

用Ｘ射线衍射仪、光学显微镜和电子显微镜，系统地研究了球铁焊缝金属等温贝氏体转变过程，等温温度及等温时间对焊缝组织与力学性能的影响。研究结果表明，球铁焊缝金属贝氏体相变快，等温时间在１５～２４０ｍｉｎ范围内焊缝基体组织主要为贝氏体铁素体和残余奥氏体且具有高的综合力学性能。随着等温温度从３１０℃增至４００℃，焊缝金属中残余奥氏体量增多，贝氏体铁素体条宽化，焊缝塑性提高，强度降低。     

Nanoindentation Mechanical Properties of Indium-Alloyed Cu-Based Bulk Metallic Glasses

In this paper, two Indium-alloyed Cu-based bulk metallic glasses, Cu₅₄Zr₃₇Ti₈In₁ and Cu₅₀Zr₃₇Ti₈In₅, have been evaluated with nanoindentation testing. Both bulk metallic glasses have homogenous nature in structure. Both hardness and Young’s modulus of bulk metallic glasses do not show a loading rate-dependent. Addition of In decreases hardness and Young’s modulus, but increases creep-resistance of bulk metallic glasses. Indentation creep of two bulk metallic glasses has also been investigated. The displacement-time curves of creep processes were described with generalized Kelvin model. The creep displacement, compliance spectrum, and retardation spectrum for each bulk metallic glass were discussed comparatively. The results showed that Cu₅₀Zr₃₇Ti₈In₅ has better creep-resistance at room temperature and a more relaxed state.     

Ti-Cu-Ni三元大块非晶合金的制备与力学性能

采用铜模喷铸法成功制备出成本较低、直径为2 mm的Ti基Ti50Cu42Ni8大块非晶合金.利用XRD、DSC及SEM等手段研究了Ti50Cu50-xNix(x=5, 8, 11)合金的非晶形成能力、力学性能与变形行为.结果表明:Ti50Cu42Ni8大块非晶合金具有明显且较高的玻璃转变温度Tg(659 K)、晶化初始温度Tx(716 K)、宽的过冷液相区ΔTx=Tx－Tg(57 K)、高的约化玻璃转变温度Trg=Tg/Tm(0.565)和压缩断裂强度(2008 MPa).