Fe-Co-B-Si-Nb-Cr块体非晶合金在纳米压痕过程中的变形行为

利用纳米压痕技术研究直径为3 mm的{[(Fe0.6Co0.4)0.75B0.2Si0.05]0.96Nb0.04}96Cr4块体非晶合金的变形行为以及加载速率对其塑性变形行为的影响规律.结果表明:该块体非晶合金在低加载速率下表现出显著的锯齿流变,而在高的加载速率下表现为连续的塑性变形;在纳米压痕过程中,该块体非晶合金出现室温蠕变现象,且其硬度值随着加载速率的增大而减小.     

纳米压痕法测量Ti6Al4V钛合金室温蠕变应力指数

主要通过恒加载速率纳米压痕法的保载阶段测量了Ti6Al4V钛合金在室温下的蠕变应力指数n。通过给金刚石Berkovich压头施加不同的加载速率使其达到不同的最大载荷,观察加载速率和最大载荷对实验结果的影响。在最大载荷下,给压头保载5 min,通过保载过程中材料的压痕应变率和硬度之间的关系得到了该材料在常温下的蠕变应力指数n。结果表明,在特定范围内加载速率和最大载荷的变化对实验结果的影响微乎其微,可以忽略不计。最终测得Ti6Al4V钛合金在室温下蠕变应力指数的分布范围为7.0513~7.216。     

U_(65)Fe_(30)Al_5非晶合金的纳米压痕蠕变行为研究

在室温下利用纳米压痕测试技术研究了峰值载荷和加载速率对U65Fe30Al5新型非晶合金蠕变行为的影响规律。结果表明,随着峰值载荷和加载速率的增加,在相同蠕变时间内,蠕变位移呈增大趋势,但当加载速率高于特定阈值时,蠕变位移不再增大。通过蠕变经验公式拟合发现,蠕变过程的应力指数随峰值载荷的增加不断变大,但随加载速率的增加先减小后基本恒定。与常规晶态合金相比,U65Fe30Al5非晶合金具有更大的应力指数,这反映出后者内部结构中富含自由体积。     

加载速率和峰值载荷对DD407镍基单晶高温合金纳米压痕蠕变行为的影响

在加载速率500～6000 uN/s和峰值载荷4000～12000 uN的条件下进行纳米压痕蠕变实验,研究DD407镍基单晶高温合金在室温下的蠕变行为.结果表明:DD407镍基单晶高温合金具有良好的蠕变抗力性能,但其蠕变性能对加载速率和峰值载荷敏感.依据Findley模型,得到拟合的蠕变参数随着加载速率和峰值载荷的增加...     

中频-直流磁控溅射铝涂层微米压入特性及低温循环性能

为预防TC4钛合金紧固件与机身铝合金之间产生电偶腐蚀,采用中频-直流磁控溅射技术在钛合金表面制备铝涂层,利用SEM、EDS进行微观形貌和成分分析,采用拉伸和划痕法评价涂层结合性能,使用微米压痕法研究涂层硬度、压痕蠕变和循环力学行为,并对涂层进行低温循环性能测试。结果表明:涂层的拉伸结合强度为61.75 MPa,划痕结合力为(2.46±0.37)N,70 m N下硬度为(0.348±0.015)GPa。压痕蠕变加载时间由5 s增加到30 s,蠕变位移从87.0 nm减小至49.3 nm,保载时间由5 s增加到30 s,位移从27.8 nm增大到92.9 nm,硬度随加载及保载时间增加均下降,随循环保载时间和循环次数增加均降低。当保温时间从1 h增加到6 h,划痕形貌由耕犁状向切削状转变,边缘剥离程度加大,末端堆积增加;涂层结合力下降,硬度先升高后降低。     

一种Zr基块体金属玻璃的纳米压入蠕变行为研究

通过斜坡-保载的球形纳米压痕法研究了Zr55Cu28Ni5Al10Nb2块体金属玻璃的室温蠕变行为。蠕变实验同时考虑了加载速率和峰值载荷水平的影响,并采用基于弹性-粘弹性对应原理的现象学法来描述材料的压痕蠕变行为。结果显示,蠕变位移显示了明显的速率和载荷依赖性。五组元Kelvin模型能很好地拟合蠕变位移-时间数据,不同加载速率条件下的拟合-预测效果非常好。对于缓慢的加载过程,斜坡段对蠕变行为的影响不可忽略。     

固溶态和时效态7075铝合金的微纳米压痕力学行为

采用微纳米压痕实验研究了固溶态和时效态7075铝合金的力学性能和压痕蠕变行为，获得了其力学本构方程、应力-应变曲线和蠕变应力指数。结果表明：两种状态铝合金的硬度和弹性模量均随着载荷的增大而减小，并在压痕深度小于1μm时表现出明显的尺寸效应。固溶态和时效态铝合金的屈服强度分别为446 MPa和497 MPa,抗拉强度分别为594 MPa和691 MPa。两种状态合金的最大蠕变深度和蠕变应力指数变化趋势相似，均随载荷和加载速率的增大而增大。     

2205双相不锈钢摩擦焊接头显微组织及微区蠕变性能

对2205不锈钢进行连续驱动摩擦焊接,通过光学显微镜观察接头显微组织,利用纳米压痕仪对接头组织中铁素体(δ相)和奥氏体(γ相)进行硬度测试及压痕蠕变行为分析。结果表明,摩擦焊接头由塑性变形区及焊合区构成,变形区内γ相与δ相相比,因塑性流动而硬化的现象更为显著,且具有更高的纳米硬度和弹性模量;基于保载过程中应变率和硬度对数关系,经线性拟合得到蠕变应力指数n,能够较好地反映δ相和γ相的蠕变特性,而且纳米硬度值越高,蠕变应力指数越小。     

Ce基非晶合金制备及室温变形行为的研究

采用铜模吸铸法制备φ2 mm的Ce70Al10Cu20、Ce69Al10Cu20Co1和Ce69Al10Cu20Ag1合金棒材.利用X射线衍射(XRD)、示差扫描量热法(DSC)和纳米压痕法(Nanoindentation)研究添加元素Ag、Co对Ce基非晶合金形成能力、热稳定性及室温变形行为的影响.结果表明,添加Ag、Co能显著提高Ce基非晶合金的玻璃形成能力和热稳定性能.Ce70Al10Cu20和Ce69Al10Cu20Ag1合金在高加载速率下出现锯齿流变;而Ce69Al10Cu20Co1合金在实验加载速率下表现为连续塑性变形.此外,三种Ce基非晶合金在压痕保载段均出现明显的蠕变现象且蠕变量随加载速率增加而增大.     

纳米压入下镁基非晶合金的间歇性塑性流动

镁基非晶合金通常表现出显著的宏观脆性,因此用常规拉伸、压缩等方法对该合金的变形行为进行研究具有很大困难。本研究利用具有高时间分辨率和高空间分辨率的纳米压痕技术观察了不同加载速率下镁基非晶合金的锯齿流变行为。结果表明,低加载速率促进锯齿的形成,而高加载速率则抑制锯齿的形成。其原因是在低加载速率下,单一剪切带足以耗散外加应变;而在高加载速率条件下,由于单一剪切带不能将应变耗散掉,因此需要更多的剪切带参与变形。为了进一步解释这一锯齿流变行为,本研究采用遍历处理对每个锯齿的应变突变进行了统计分析。结果表明,在不同的加载速率下,小的应变突变服从幂律分布,且幂指数为1．45;而大的应变突变则呈现指数衰减规律。最后,借助硬度对应变速率的敏感性,估算了镁基非晶合金在纳米压人条件下剪切转变区的体积,为4．5nm^3。     

Rate-dependent inhomogeneous creep behavior in metallic glasses

Creep deformation can be classified as homogeneous flow and inhomogeneous flow in bulk metallic glass (BMG). In order to understand the conversion conditions of the two types of creep deformation, the effect of loading rate on the creep behavior of a Ti₄₀Zr₁₀Cu₄₇Sn₃ (at.%) BMG at ambient temperature was investigated using nanoindentation and molecular dynamic simulation. Results indicate that at low loading rates, many serrations appear in loading stage, leading to inhomogeneous serrated flow in the creep stage. When the loading rate is high enough, the creep deformation tends to be homogeneous. The related mechanism responsible for the rate-dependent creep behavior is attributed to the number of pre-existing major shear bands which is influenced significantly by the loading rate.     

多晶铜膜纳米压入蠕变性能

在JGP560V磁控溅射镀膜设备上镀制多晶铜膜,利用纳米压入技术测量了其室温下的蠕变性能.结果表明:由于不同加载方式下,材料加工硬化程度的不同造成了应力指数的差异,因而,不同加载方式对测得的铜膜蠕变应力指数有比较大的影响;由于材料在高载荷时在压头下端产生更多的位错,阻碍了压头的压入,使蠕变率降低,因而,随着保载载荷的升高,蠕变应力指数变大.     

Dependence of strain rate sensitivity upon deformed microstructures in nanocrystalline Cu

The creep behavior of nanocrystalline copper was experimentally characterized with nanoindentation using two sequential regimes, i.e., loading and holding. Significantly enhanced strain rate sensitivity was found within an unusually narrow range of creep rate in the holding regime, which is attributed to the deformed microstructure generated during the loading regime. By quantitatively analyzing the creep rate and rate sensitivity exponent of NC Cu in the holding regime, both the grain boundary sliding (GBS) and dislocation activities are found to be responsible for the observed abnormal behavior, with the contribution of GBS decreasing with increasing grain size and increasing with decreasing loading strain rate. These findings provide a potential way of adjusting the mechanical properties of nanocrystalline metals by pre-straining.     

时效对Al-Cu合金中锯齿形流动的影响

研究了不同热处理条件下,时效对Al-Cu合金中锯齿形流动的影响．实验发现,随着自然时效时间的延长,PLC（Portevin—Le Chatelier）效应出现的时间推迟．随着时效的进一步强化（自然时效24h,或在353K下保温20min的人工时效）,应力-时间曲线上锯齿幅值减小,出现的频率迅速降低,直至消失．同时,还研究了变形和时效相耦合对锯齿形应力流动的影响．针对所得的实验结果,肯定了基于可动位错和障碍之间的相互作用的动态应变时效微观机制假设,并探讨了出现锯齿形应力流动而无PLC变形带产生的现象．     

加载速率对Al膜纳米压入蠕变性能的影响

纳米压入仪对Si片上晶Al膜进行的压入蠕变实验表明,加载方式对Al膜的蠕变性能有明显影响.随加载速率和载荷的增大, Al膜的总蠕变量和应力指数均有较大升高 且蠕变初期可能存在异常高蠕变率.分析认为这与是加载过程中未及发生的塑性变形的持续释放有关.对于确定的薄膜材荆及组织结构,加载过程中积攒的塑性变形量及其释放速率将影响不同加载条件下的总蠕变量和应力指数.     

晶粒尺寸与保载载荷对Cu膜纳米压入蠕变性能的影响

利用纳米压入仪对Si片上的多晶Cu膜进行压入蠕变研究．实验结果显示晶粒尺寸大于200nm时，应力指数对晶粒尺寸不敏感．当晶粒尺寸小于200nm时，因压头底部更多的晶粒参与变形，应力指数随晶粒尺寸的降低而增大．认为薄膜材料存在一个对应力指数不敏感的最小If缶界晶粒尺寸ιc，Cu膜的应力指数随保载载荷增大而增大，其主要原因在于高载荷下位错强化机制使蠕变率降低。     

一种铁基块体金属玻璃纳米压痕蠕变行为的加载速率敏感性(英文)

通过纳米压痕蠕变实验研究了加载速率对{[(Fe0.6Co0.4)0.75B0.2Si0.05]0.96Nb0.04}96Cr4块体金属玻璃室温蠕变变形的影响。结果表明,该铁基块体金属玻璃的蠕变变形随着加载速率的增加而增大。此外,根据经验幂率函数计算得到了材料室温蠕变应力指数,当加载速率从1mN/s增加到50mN/s时,应力指数从28.1逐渐下降到4.9,显示出显著的压痕加载速率敏感性。最后,基于自由体积理论和剪切转变区理论对该铁基块体金属玻璃的纳米压痕蠕变行为进行了探讨,并对实验结果和分析结果提供了半定量的解释。     

A nanoindentation study of serrated flow in bulk metallic glasses

Plastic deformation of two Pd- and two Zr-based bulk metallic glasses (BMGs) is investigated through the use of nanoindentation, which probes mechanical properties at the length scale of shear bands, the carriers of plasticity in such alloys. These materials exhibit serrated flow during nanoindentation, manifested as a stepped load-displacement curve punctuated by discrete bursts of plasticity. These discrete “pop-in” events correspond to the activation of individual shear bands, and the character of serrations is strongly dependent on the indentation loading rate; slower indentation rates promote more conspicuous serrations, and rapid indentations suppress serrated flow. Analysis of the experimental data reveals a critical applied strain rate, above which serrated flow is completely suppressed. Furthermore, careful separation of the plastic and elastic contributions to deformation reveals that, at sufficiently low indentation rates, plastic deformation occurs entirely in discrete events of isolated shear banding, while at the highest rates, deformation is continuous, without any evidence of discrete events at any size scale. All of the present results are consistent with a kinetic limitation for shear bands, where at high rates, a single shear band cannot accommodate the imposed strain rapidly enough, and consequently multiple shear bands must operate simultaneously.     

Indentation creep of an Fe-based bulk metallic glass

In this study, the room temperature creep behavior of Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ bulk metallic glass was investigated using nanoindentation technique with the maximum applied load ranging from 1 mN to 100 mN under different loading rates (0.01–2.5 mN s^?1). The creep stress exponent was derived from the recorded displacement–holding time curve. It was found that the stress exponent increases rapidly from 2.87 to 6.37 with increasing indentation size, i.e. exhibiting a positive indentation size dependence. Furthermore, as the indentation loading rate increases from 0.01 mN s^?1 to 2.5 mN s^?1, the stress exponent decreases gradually from 4.93 to 0.94. The deformation mechanism causing the nanoindentation creep is discussed in the light of the “shear transformation zone” (STZ) which provides qualitative explanation for the observed plasticity in amorphous alloy.