钨单晶纳米压痕尺寸效应研究（英文）

利用纳米压痕仪和扫描探针显微镜对高纯钨单晶的载荷-位移曲线、弹性模量、压痕形貌、纳米硬度-加载深度以及弹性回复率的变化情况进行了研究。结果表明,W(111)晶面在加载和卸载过程中分别经历了弹性变形和塑性变形阶段,荷载-位移曲线未出现不连续现象,表明在加载过程中压痕内部未产生裂纹或脆性断裂;钨单晶的残余压痕表现出堆积形貌,表明钨单晶有较低的加工应变硬化趋势;采用连续刚度法测量了钨单晶的纳米压痕硬度以及弹性模量,结果表明,钨单晶纳米压痕硬度和弹性模量存在尺寸效应,即随着加载深度的增加,单晶的纳米压痕硬度和弹性模量减小;采用Nix-Gao模型对钨单晶的纳米压痕力学特征进行了分析,计算了钨单晶的微观特征长度(h*)为1490 nm,无压痕尺寸效应时的纳米硬度值(H0)为6.79 GPa,尺寸效应因子(m)为0.18,即压入深度小于1490 nm时,钨单晶具有明显的尺寸效应,当压入深度超过1490 nm时,尺寸效应将减弱。当压入深度超过2450 nm时,钨单晶的纳米尺寸效应将消失。     

不同晶体取向Mo-Nb单晶的纳米压痕尺寸效应

采用纳米压痕仪和扫描探针显微镜对Mo-Nb合金单晶(110)、(111)、(112)晶面的载荷-位移曲线、弹性模量,压痕形貌、纳米硬度-加载深度以及弹性回复率的变化进行了研究。结果表明,Mo-Nb单晶具有较好的塑性变形能力,Mo-Nb单晶的各晶面在加载和卸载过程中分别经历了弹性变形和塑性变形阶段,荷载-位移曲线未出现突进或突退现象,表明在加载和卸载过程中压痕内部未产生裂纹或脆性断裂;材料的残余压痕呈现凸起形貌,表明Mo-Nb单晶有相对较低的加工应变硬化趋势;采用连续刚度法测量了Mo-Nb单晶的纳米硬度和弹性模量,3个晶面的纳米硬度均呈现出随着加载深度的增加而减小的趋势,表现出明显的压痕尺寸效应;3个晶面纳米硬度和弹性模量的大小关系为:(110)晶面(112)晶面(111)晶面;基于Nix-Gao模型计算了(110)、(111)、(112)晶面的无压痕尺寸效应时的纳米硬度(H_0)分别为3.96、2.61和3.47 GPa,尺寸效应因子(i)分别为0.18、0.16和0.18,微观特征长度(h*)分别为1196、2753和1559 nm。压入深度小于微观特征长度时,Mo-Nb单晶具有明显的尺寸效应,压入深度超过该长度时,尺寸效应将减弱,当压入深度分别超过4106、5645和4693 nm时,纳米压痕尺寸效应将消失。     

铱单晶的纳米压痕尺寸效应研究

采用纳米压痕技术和原子力显微镜对铱(Ir)单晶(100)和(110)取向的载荷-位移曲线、弹性模量、压痕形貌、压痕硬度-加载深度等进行了研究。结果表明,Ir(100)与Ir(110)单晶的弹性模量分别为477和493 GPa;加载深度为10~2500 nm时,Ir单晶的纳米压痕硬度存在压痕尺寸效应,在10~500nm时表现更为强烈,表明随着加载深度的增加,单晶材料的硬度减小;基于Nix-Gao模型,计算出Ir(100)和Ir(110)单晶的纳米硬度H0分别为2.32和2.46 GPa,当加载深度分别大于4910和5220 nm时,Ir单晶的纳米硬度不存在尺寸效应,可作为金属铱硬度测试的重要依据;采用硬度和深度的幂律关系计算出Ir(100)和Ir(110)单晶的尺寸效应因子(m)分别为0.44和0.48,该值远远大于其他金属和半导体材料,这种反常现象可能与铱原子间的异常强的交互作用有关。     

利用纳米压痕法研究单晶锗的力学行为

利用纳米压痕仪和原子力显微镜对单晶锗(100)晶面进行纳米压痕试验。通过载荷-压深曲线和弹性回复率的变化情况对材料的变形机理以及硬度和弹性模量进行研究。结果表明:单晶锗(100)晶面在不同的压入深度下分别经历了弹性变形、塑性变形和脆性断裂;载荷-压深曲线中出现明显的突进和突退现象,该现象与材料的内部结构发生相变密切相关;单晶锗(100)晶面存在明显的压痕尺寸效应。该材料弹性模量的变化趋势与硬度相一致。     

利用纳米压痕加载曲线计算硬度-压入深度关系及弹性模量

通过对纳米压痕法基本原理的分析与实验研究,证明了一般材料的接触刚度-位移（压入深度）为线性关系．该关系可从两个不同压入深度的压痕实验得到,利用该关系可从任意一条加载曲线计算出材料的硬度-位移关系及弹性模量值．实验结果表明这个计算结果是可靠的．     

基于准连续介质法预测薄膜材料纳米硬度和弹性模量

采用准连续介质法模拟了单晶Al和单晶Cu纳米压痕实验中的初始塑性变形过程,获得了压头在不同压深下的加载和卸载曲线.在计算得到的载荷-压深曲线基础上,根据Oliver-Pharr法计算了薄膜材料的接触刚度、纳米硬度和弹性模量,并与相关文献的实验结果进行了比较.研究表明,接触刚度-位移曲线呈线性关系;纳米硬度测量中存在尺寸效应,而在弹性模量测量中却不存在尺寸效应.单晶Al和单晶Cu纳米硬度和弹性模量计算值分别为(0.584±0.013)和(84.088±0.332)GPa,(0.755±0.027)和(131.833±4.449)GPa.预测值与实验结果吻合,表明使用该方法预测薄膜材料的纳米硬度和弹性模量是可行的.     

TC17钛合金的微观力学性能研究

采用微米压痕测试仪对TC17钛合金进行压痕实验,对比研究了不同处理制度下的微观力学性能。基于获得的压痕载荷-位移曲线,采用Oliver-Pharr(OP)方法计算了显微硬度及杨氏模量,分析了加载过程中材料的性能随压痕深度的变化。结果显示:当压入深度小于一定值时,硬度和弹性模量变化较大,均随压入深度的增加而减小,表现出明显的尺寸效应;当压入深度超过一定值后,硬度和弹性模量趋于稳定。对比发现:处理制度对材料性能有明显影响。     

用纳米压痕法表征钨纳米晶须的力学性能

通过化学气相沉积方法合成截面为六边形的单晶钨纳米晶须,利用纳米压痕仪和原子力显微镜对硅基底上的钨纳米晶须的力学性能进行表征。纳米压痕测试结果表明,钨纳米晶须的硬度为(6.2±1.7) GPa,弹性模量为(225±20) GPa。对比研究结果表明,钨纳米晶须的硬度与钨微米晶须的硬度相当,但比块体钨单晶高35%。这种硬度的增高是由于具有完好晶体结构的钨晶须在压痕测试中不会出现块体钨单晶中的位错崩。钨纳米晶须的弹性模量相当于钨微米晶须的80%,主要是由于纳米晶须的尺寸效应和测量过程中的基底效应所致。     

纳米压痕法测量Cu的室温蠕变速率敏感指数

介绍一种测量室温蠕变速率敏感指数m的新方法。即通过纳米压痕仪精确测量压头的压入位移h和材料的硬度值来计算m值。用该法分别测得单晶Cu(123)压痕蠕变的m的平均值约为0.0045;多晶Cu和纳米晶Cu(晶粒尺寸为30nm)的m的平均值分别为0.007和0.0094。压痕蠕变曲线与传统的单轴蠕变曲线十分相似;室温m的平均值与加载条件无关,而由材料的微观结构决定。     

Ti-24Nb-4Zr-8Sn合金单晶纳米压痕研究

利用纳米压痕仪研究Ti-24Nb-4Zr-8Sn (Ti2448)合金不同取向单晶体的硬度和弹性模量.结果表明:Ti2448合金单晶表现出各向异性,不同晶面的压入模量和纳米压痕硬度值不同,(001)、(011)和(111)晶面的压入模量分别为68.1、69.1和78.9 GPa,纳米压痕硬度分别为3.5、3.5和3.0 GPa;不同晶面压入模量和纳米压痕硬度的相对大小规律与常规方法测量结果一致,但无法相互换算.     

Effect of Strain Rate on Deformation Behavior of AlCoCrFeNi High-Entropy Alloy by Nanoindentation

In this study, nanoindentation tests with continuous stiffness measurement technique were measured to investigate the deformation behavior of a high-entropy alloy AlCoCrFeNi under different indentation strain rates at room temperature. Results suggest that the creep behavior exhibits remarkable strain rate dependence. In-situ scanning images showed a conspicuous pileup around the indents, indicating that an extremely localized plastic deformation occurred during the nanoindentation. Under different strain rates, elastic modulus basically remains unchanged, while the hardness decreases with increasing indentation depth due to the indentation size effect. Furthermore, the modulus and hardness of AlCoCrFeNi HEAs are greater than that of the Al _x CoCrFeNi (x = 0.3,0.5) at the strain rate of 0.2 s^?1 due to its higher negative enthalpy of mixing related to the atomic binding force, and the solid solution strengthening induced by the lattice distortion, respectively.     

热浸铝钢等离子体电解氧化陶瓷层的微观力学特性

采用纳米压入方法表征了热浸镀铝钢表面由Al2O3层、Al层和FeAl层组成的复合涂层的纳米硬度、弹性模量及断裂韧性等微观力学性能,采用扫描电镜(SEM)观察了纳米压痕形貌,并分析了孔洞对陶瓷层的纳米压入行为和压痕裂纹扩展的影响.结果表明:等离子体电解氧化(PEO)陶瓷层中包含许多微米和亚微米尺度的细小孔洞,陶瓷层弹性模量约为226.4 Gpa,纳米硬度约为19.6 Gpa.当纳米压入深度为250 nm时,所测得陶瓷层的力学参数分散性较大.与FeAl层比较,PEO陶瓷层具有较高的裂纹扩展阻力. FeAl层纳米压痕顶端产生了沿直线扩展的径向裂纹;而陶瓷层纳米压痕中除径向裂纹外出现了侧边裂纹.     

纳米压痕过程的多尺度模拟与Rice-Thomson位错模型分析

采用多尺度准连续介质法（简称QC方法）对单晶Ag薄膜纳米压痕过程进行模拟,研究压头宽度对纳米压痕过程中接触应力分布、位错形核临界载荷以及纳米硬度的影响,并用Rice-Thomson位错模型（简称R-T位错模型）进行分析。结果表明,纳米压痕获得的载荷-位移曲线呈现出的不连续性与位错之间的协同作用密切相关;压头尺寸对纳米压痕过程中接触应力分布、位错形核临界载荷以及纳米硬度具有明显的影响：随着压头宽度的增加,法向和切向接触应力以及纳米硬度值递减,呈现出明显的压头尺寸效应;而压头下方薄膜内位错形核临界载荷却递增,且与压头半宽度的平方根成正比。模拟结果与相应实验结果以及R-T位错模型计算结果吻合     

纳米压痕法测量经深冷处理后铝青铜的硬度和弹性模量

借助纳米力学测试系统测试经深冷处理后铝青铜的硬度和弹性模量。结果表明:深冷处理后铝青铜的硬度和弹性模量分别为3.82GPa和117.67GPa,且铝青铜的硬度随压入深度的增加而逐渐降低,反映出硬度存在的尺寸效应,但弹性模量不存在尺寸效应现象。     

Mechanical characterization of nano-structured materials using nanoindentation

The principal strengths of the nanoindentation technique, which is used extensively to measure the mechanical properties of nano/micro materials, are easy sample preparation and simple experimental method. Hardness and Young's modulus are essential properties measured by nanoindentation; hardness corresponds to resistance to plastic deformation whereas Young's modulus is related to elastic deformation. Two key difficulties arise in association with nanoindentation on small volumes: measurement accuracy and material response. Here we discuss the indentation size effect (ISE) considering tip bluntness and variation in hardness of nano-multilayers with a bilayer period, representative research on measurement improvement, and material response at nanoscales.     

The Instrumented Indentation Study of HVOF-Sprayed Hardmetal Coatings

Elastic-plastic properties, namely, hardness and Young’s modulus, of four HVOF-sprayed hardmetal coatings were measured by instrumented indentation using Oliver-Pharr method Nanoindenter XP MTS with a continuous stiffness measurement (CSM) module. The results show that with sufficient number of CSM measurements, one can distinguish between indents made in the hard particles and indents made in the binder material. This can be accomplished by analyzing the plots of hardness and Young’s modulus versus load (or versus indentation depth). Further development of the dependence curves enables the load (or indentation depth) to be set to correspond to the point of transition from a single structure component to the composite material and to determine the properties of both. Comparison of results of CSM measurement with the results of single indentation measurement at a defined load reveals a new perspective on the origin of the indentation size effect in hardmetal coatings. The measurements show that the increase in both the hardness and Young’s modulus with decreasing load is caused mainly by the predominant influence of hard particles in the coatings.     

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.     

Dependence of nanohardness upon indentation size and grain size – A local examination of the interaction between dislocations and grain boundaries

Pulse-electrodeposited nanocrystalline nickel was heat-treated to produce grain sizes from the nanoscale to microscale. By always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically, the dependence of nanohardness upon indentation size and grain size was studied. The plastic zone size related to the indentation size was measured quantitatively. The different dependences of hardness upon indentation depth in this work reveals clearly the local interaction between dislocations and grain boundaries in single grains. The experiments also show that the dislocations, which nucleate below the indenter tip, only interact directly with the surrounding interfaces for grains below 900 nm, where the nanohardness and pop-in width are grain size dependent.     

聚苯乙烯薄膜表面粘弹性行为的纳米压痕研究

目的通过研究聚苯乙烯薄膜不同深度下的加载力曲线,分析得到其随着深度的不同而导致测量硬度和模量的差异,研究聚苯乙烯薄膜表面粘弹性行为,从而为高分子薄膜受限效应的理论和应用探索提供参考和借鉴。方法采用纳米压痕方法对聚苯乙烯薄膜样品(厚度约500 nm)进行了系列纳米压痕测量与分析。结果加载速率较低时,其加载曲线与P-h~2关系会发生不同程度的偏离。加载速率为0.01、0.02、0.03、0.06、0.1 mN/s时,P-h~2关系中的指数从1.609逐渐增大到1.628。通过在最大载荷时保载60 s,得到了压入深度随时间变化的关系,进而计算得到蠕变柔量,并根据Zener模型拟合得到压入深度为300~400 nm时,薄膜样品存在具有不同粘弹性的两种结构。而根据不同压入深度的卸载曲线,得到样品的硬度和折合弹性模量都在压入深度约为200~400 nm的区域存在粘弹性的非均匀现象。结论在不同压入深度处存在两种不同的粘弹性结构,根据当前人们普遍接受的高分子薄膜层模型,这两种结构分别对应聚苯乙烯薄膜样品的自由表面层和本体层。