Serration Behavior in Zr-Cu-Al Glass-forming Systems

The metallic glass matrix composites(MGMCs)and bulk metallic glasses(BMGs)were studied by statistical analysis during plastic deformation at the strain rates of 2×10~(-2),2×10~(-3),and 2×10~(-4) s~(-1),respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10~(-2) s~(-1).When deformed at the strain rate of 2×10~(-3) s~(-1),the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.     

Insight on Viscoelasticiy of Ti16.7 Zr16.7 Hf16.7 Cu16.7 Ni16.7 Be16.7 High Entropy Bulk Metallic Glass

High entropy bulk metallic glasses show promising mechanical and physical properties.Dynamic mechanical properties of Ti_(16.7)Zr_(16.7)Hf_(16.7)Cu_(16.7)Ni_(16.7)Be_(16.7)high entropy bulk metallic glass were investigated by mechanical spectroscopy(or called dynamic mechanical analysis).The main(α)relaxation was observed in the framework of the loss modulus G″,which is related to the dynamic glass transition behaviour for the glassy materials.From physical model point of view,dynamic mechanical properties of the Ti_(16.7)Zr_(16.7)Hf_(16.7)Cu_(16.7)Ni_(16.7)Be_(16.7)high entropy bulk metallic glass show good agreement compared with the quasi-point defects theory.     

Serration and Noise Behavior in Advanced Materials

正The Chinese Materials Research Society(C-MRS)Conference(2015)was held in the Guizhou Park Hotel International Conference Center,Guiyang,China,from July 10-14,2015.This conference consists of 30symposia,including 4international symposia.As one of 4international symposia,"Serration and noise behavior in advanced materials"     

Strip Casting of High Performance Structural Alloys

There exists a great need for the development of high performance alloys due to increasing demands for energy conservation and environmental protection. Application of strip casting shows a strong potential for the improvement of properties of existing alloys and also for the development of novel alloy systems with superior properties. The present paper reviews our Center's activities in the development of high performance alloys by strip casting. Examples include (1) Al alloys, (2) wrought Mg alloys, and (3) bulk metallic glass (BMG) alloys.     

Self-organized Criticality Behavior in Bulk Metallic Glasses

Serrated flows are known as repeated yielding of bulk metallic glasses (BMGs)during plastic deformation under different loading conditions,which are associated with the operation of shear banding.According to the statis-tics of some parameters,the shear avalanches can display a self-organized critical state,suggesting a large ductility of BMGs.The emergence of the self-organized criticality (SOC)behavior in different BMGs is due to the tempera-ture,strain rate,and chemical compositions.The SOC behavior is accompanied with the following phenomena:the interactions occur in the shear bands;the incubation time is longer than the relaxation time;the time interval is lac-king of typical time scale;and the spatial or temporal parameters should display a power-law distribution.     

Interactions of Shear Bands in a Ductile Metallic Glass

Shear bands play a key role in the plastic deformation of metallic glasses(MGs).Even though there are extensive studies on the initiation and propagation of shear bands,the interactions among them have not been systematically studied yet.The interactions between the primary shear bands(PSBs)and secondary shear bands(SSBs)in a ductile Zr-based MG were studied.The residual stress near PSBs can deflect the propagation direction and reduce the propagation velocity of SSBs,which contributes to the plasticity and toughness of the MG.It was demonstrated that the probability and strength of the interactions between PSBs and SSBs would become stronger for MGs with larger Young′s modulus and smaller shear modulus,i.e.,larger Poisson′s ratio.These results are valuable in understanding the plastic deformation of MGs and may be helpful in designing new MGs with desirable mechanical properties.     

钕对NiAl基共晶合金高温流变行为的影响

 研究了钕对NiAl 28Cr 55Mo 05Hf共晶合金显微组织及高温流变行为的影响。结果表明：NiAl 28Cr 55Mo 05Hf基体合金是由黑色的NiAl相和灰白色的Cr(Mo)相组成的共晶组织，在相界处聚集有白色的Ni2AlHf(Heusler)相，加入稀土钕可细化组织；NiAl 28Cr 55Mo 05Hf(wNd=005%)合金在较高的应变速率(=194×10-2 s-1和=194×10-3 s-1)下，含稀土合金的流变应力大于不含稀土合金的流变应力，而在低应变速率(=194×10-4 s-1)下，这种强化现象消失。幂指数规律和温度补偿的幂指数规律可以很好地描述各种合金的高温压缩流变行为。加入稀土可降低合金的应力指数和变形激活能，这是因为稀土偏聚在相界上，致使相界上的空位浓度发生变化。     

Rate Dependence of Serrated Flow and Its Effect on Shear Stability of Bulk Metallic Glasses

The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serra-ted flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,character-ized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the mi-croscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.     

激光熔覆AlCoCrFeNi高熵合金涂层的高温磨损性能

采用激光熔覆技术在42CrMo表面制备了Y掺杂AlCoCrFeNi高熵合金涂层,研究了涂层组织成分与高温摩擦磨损性能。结果表明：AlCoCrFeNi涂层主要由BCC相和B2相组成,900 ℃下涂层耐磨性约为基体的3.7倍,平均摩擦因数相比基体降低约22%。     

Corrosion Behavior of Fe-based Bulk Metallic Glass and In-situ Dendrite-reinforced Metallic Glass Matrix Composites in Acid Solution

The corrosion behavior study was conducted on a novel Fe_(77)Mo_5P_9C_(7.5)B_(1.5)in-situ metallic glass matrix composite(MGMC).This composite sample was developed by introduction of bccα-Fe dendrites as reinforcing phase.The corrosion behavior of this composite was compared to its monolithic counterpart and other Fe-based alloys such as 304 Land 2304Lstainless steels.The corrosion resistance of MGMCs in H_2SO_4 solution shows inferior to that of other Fe-based alloys.Experiments suggest that Fe-BMGs samples possess better corrosion resistance property than that of Fe-MGMCs.The possible underlying reasons can be the inhomogeneity induced by the precipitation ofα-Fe dendrites in the MGMCs.     

Cu基块体非晶合金的高温均匀塑性流变行为研究

本文选用非晶形成能力高,且在玻璃转变区和过冷液相区有高热稳定性的Cu46Zr47-x Al7块体非晶合金为研究对象,利用差示扫描量热分析（DSC）、高温真空压缩实验等方法,对其高温均匀塑性流变行为进行研究。结果表明,Cu46Zr47Al7块体非晶合金的高温均匀塑性形变行为依赖于温度和应变速率,随着温度的降低或应变速率的增大呈现出牛顿流变向非牛顿流变的转变,该行为可以用基于自由体积的过渡态理论来进行定量描述。根据过渡态理论拟合出来的驱动体积大致相当于25~50个原子,驱动能为551kJ/mol,说明控制合金高温均匀形变的原子不会脱离周围原子而单独跃迁,其扩散涉及到多原子的协同运动。     

Ti基大块金属玻璃的研究与应用

阐述了Ti基大块金属玻璃(BMG)的成分设计原则及制备方法，并对Ti基非晶合金及其部分晶化复合材料的力学性能及断裂机理进行了评述。结果表明：Ti基大块金属玻璃具有较高的断裂强度、弹性延伸率及一定的塑性延伸率，而经过部分晶化获得的非晶合金基纳米颗粒复合材料，其室温塑性获得很大的改善。在此基础上探讨了该合金目前所存在的问题、研究热点以及其应用前景。     

Ti-B25合金高温变形时的塑性流动软化行为

通过热模拟压缩实验,研究了变形温度、应变速率对Ti-B25合金高温变形时流动应力和峰值流动应力的影响,并结合组织演变规律揭示了其高温塑性流动软化机理.结果表明:流动应力和峰值流动应力均随变形温度的下降以及应变速率的增大而增大.应变速率为10.0 s-1时,随着变形温度的升高,流动软化程度减小,并且α+β两相区的软化程度...     

高Ni/Fe比W-Ni-Fe系重合金烧结行为

研究了钨质量分数为90%的高Ni/Fe比W-Ni-Fe系重合金在不同工艺参数(烧结温度、烧结时间等)下的烧结行为.研究结果表明:在相同烧结条件下,随粘结相中NiNe比增加钨合金烧结密度增加,致密化速率提高,同时烧结过程中W晶粒生长速率增大:当Ni/Fe比较低时,钨合金在循环烧结条件下难以实现完全致密化;但对高Ni/Fe比钨合金,循环烧结不仅可以获得比等温烧结更高的烧结密度,而且还可以有效地控制烧结过程中W晶粒的长大,获得细晶钨合金.     

Effect of Aluminium Addition on Glass Forming Ability of Nd55-x Al10＋x Fe15 Co20 （x = 0, 5, 10） Alloys

Nd55-x Al10＋x Fe15 （x =0, 5, 10） bulk glass-forming alloys with distinct glass transition in differential scanning calorimetry （DSC） traces were obtained by suction casting, The glass forming ability （GFA） of the alloys was investigated. It was found that the reduced glass transition temperature （Trg） and the parameter γ of the alloys increased with the increasing concentration of Al. The glass formation enthalpy of the alloys was calculated based on Miedema＇s model, and it was suggested that the GFA of the alloys could be enhanced by the decrease of the glass formation enthalpy with Al additions.     

Crystalline Behavior and Magnetic Properties of Nd60Fe30-x Al10Cox（x = 0,5,10） Bulk Amorphous Alloys

Crystalline behavior and magnetic properties of Nd60Fe30-xAl10Cox( x = 0, 5, 10) bulk amorphous alloys were investigated by differential scanning calorimeter (DSC), X-ray diffraction (XRD) and the vibrating sample magnetometer (VSM). Neither glass transition nor supercooled liquid region before crystallization was observed for the as-cast Nd60Fe30-xAl10Cox ( x = 0,5,10) bulk amorphous alloys. The glass forming ability can be improved significantly by the addition of Co. The as-cast Nd60Fe30-xAl10Cox (x = 0,5,10) alloys show hard magnetic behavior. With the addition of Co content, intrinsic coercivity (iHc) increases while the saturation magnetization(σs) and remanence (σr) decrease. The Curie temperature for the as-cast Nd60Fe30-xAl10Cox alloys increases from 451 K for x =0 to 468 K for x = 10. Some pre-cipitation of crystalline phases does not affect the hard magnetic properties of Nd60Fe30-xAl10Cox(x = 0,5,10) alloys, while the hard magnetic behavior disappears quickly after the alloys being completely crystallized.     

Ti对部分晶化Ni基非晶合金电化学腐蚀性能的影响

采用水冷铜模吸铸法制备出部分晶化的Ni55Nb30Sn5Ti5Zr5和Ni55Nb30Sn5Zr10块体非晶合金,并利用X射线衍射（XRD）分析和示差扫描量热仪分析（DSC）对合金的相组成及热物性参数进行了测量分析。采用极化曲线法研究合金在不同溶液中的腐蚀行为,并利用失重法测定合金在10%HCl溶液中的腐蚀速率,对腐蚀后的显微形貌及表面成分进行了扫描电镜（SEM）观察和能谱分析（EDS）。结果表明,Ni55Nb30Sn5Ti5Zr5合金比Ni55Nb30Sn5Zr10合金具有更宽的过冷液相区和更好的抗腐蚀性能。随着合金晶化相的增多,合金抗腐蚀性能降低。Ti元素的加入可在合金表面形成氧化钛的保护膜,从而使合金的抗腐蚀性能提高。     

Corrosion Behavior of Oxide Dispersion Strengthened Ferritic Alloys in Liquid Sodium

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TC4钛合金表面激光熔覆CoCrNi基合金涂层的温度场模拟

利用COMSOL对TC4表面激光熔覆制备CoCrNiMox及CoCrNi(WC)x高熵合金涂层的熔化与凝固过程的温度场进行模拟,建立了三维多物理场并存的瞬态模型,同时考虑了传热、流体传热、对流以及表面熔覆层生长过程,分析对比了扫描速度、激光功率等参数对添加不同含量Mo及WC的CoCrNi基合金温度场的影响。通过模拟结果可以得知,激光熔覆过程中熔池的主要驱动力为马兰戈尼力,提高Mo含量时会使涂层温度场的最大值降低,但同时速度场和压力场的最大值会上升。此外,使用CoCrNiMo2作为涂层粉末相比于熔覆CoCrNi(WC)2,会在温度场、速度场和压力场均观察到较低的数值;激光功率逐渐升高,激光熔覆产生的熔池的中心温度也随之升高,且熔池的宽度、深度也将有所升高;扫描速度逐渐升高时,熔池中心最高温度显著降低,熔覆层起始位置明显推迟,熔覆层厚度明显减少,熔池的几何尺寸变小且熔池底部形貌对称性变差。     

高钨合金砧模材料的研究

介绍了电热镦粗用的砧模材料，着重讨论了钨合金砧模材料的成分、工艺方法、材料的主要性能以及砧模的使用情况。钨合金是一种理想的砧模材料，具有高的红硬性，W232钨合金在500℃下，硬度HV达到198，在800℃下HV仍为168。W253、W232适用于排气门的生产．而W153、W132更适用于进气门的生产，其使用寿命是Cu-W80砧模的10～30倍，成品率由58％提高至98％．具有较好的经济效益。