基于纳米压痕测试的超细晶Si_2N_2O-Si_3N_4陶瓷常温弹塑性仿真

对分别在1 600℃、1 650℃、1 700℃条件下热压烧结制备的Si2N2O-Si3N4超细晶陶瓷进行纳米压痕试验测试,获得了材料的硬度值、弹性模量值和载荷-深度曲线。考虑试验中波士压针的磨损缺陷,通过理论和数值模拟相结合的方法,确定压针的尖端球面半径RBerk=500nm。以纳米压痕试验数据为依据,利用MSC.Marc有限元仿真软件模拟纳米压痕试验压针压入材料表面的过程,反推出所测试材料的应力应变关系曲线,其屈服应力随弹性模量的减小而降低,分别为47GPa、43GPa、35GPa。通过比较分析压痕区域的应变场和应力场,分析纳米压痕试验中材料的变形特征。     

纯钼高压扭转过程中微纳尺度的力学性能演化

对工业烧结纯钼在室温下进行了压力为6 GPa,扭转圈数为1、2和5圈的高压扭转实验,借助纳米压痕测试技术对变形前后试样进行了力学性能表征,通过有限元模拟获得了不同变形程度试样的应力-应变曲线。结果表明：高压扭转对纯钼力学性能具有显著的强化作用,变形前后试样的纳米硬度和屈服强度分别从3.02 GPa和970 MPa升高至7.80 GPa和3370 MPa,分析认为细晶强化和位错强化是强度提升的主要因素。然而,高压扭转变形导致的位错增殖和残余应力升高使材料的弹性模量随应变量的增大而逐步降低。此外,基于有限元模拟所得的应力-应变曲线,建立了高压扭转过程中应力和等效应变之间的关系,讨论了大塑性变形过程中的硬化行为。     

一种典型近α型钛合金绝热剪切带组织特征研究

本文采用帽形试样对一种典型近α型Ti-6Al-2Zr-1Mo-1V钛合金在不同应变率条件下的绝热剪切特征开展了研究,结果表明：合金的动态应力应变曲线呈现典型的三阶段特征,分别对应于应变硬化、热软化和剪切局部化阶段,最终形成绝热剪切带(ASB)。在近剪切带处,初生α相和次生α相在过渡区内发生扭曲变形,甚至断裂,出现孪晶变形特征,近剪切带区域微观取向差增大,利于位错滑移/孪晶取向的α相优先发生塑性变形,形成亚结构,晶粒碎化,发生动态再结晶;随着应变率的提高,剪切带宽度呈增大趋势,且出现旋涡结构以协调和适应变形;通过纳米压痕试验,分析了ASB及其附近与基体α相、β相的弹性模量和显微硬度,表明该合金的绝热剪切带为一条软化带,影响区的宽度在ASB附近30μm以内。     

纯钨高压扭转组织与性能的微观尺度分析

采用高压扭转技术在550 ℃、1.5 GPa压力下成功制得具有细晶组织的难熔金属钨,借助EBSD技术研究了高压扭转变形组织晶粒尺寸、晶界角度以及晶粒取向的演化规律,结合纳米压痕实验结果,分析了应变对工业烧结纯钨微观力学性能的影响机理。实验结果表明,高压扭转后材料内部微孔隙有效闭合,组织细化显著,大角度晶界含量快速升高。在应变较低时出现较为明显的沿<101>方向的择优取向;随着应变的增加,择优取向消失,组织趋于均匀。应变较高(扭转5圈)时在三叉晶界处出现了细小的动态再结晶晶粒。高压扭转变形引起的孔隙闭合、晶粒细化、晶格畸变、位错密度增加和大角度晶界形成,导致屈服强度和纳米硬度随变形量的增大而不断提升;而在致密度、残余内应力和高密度位错的共同作用下,变形试样的弹性模量显著高于工业烧结纯钨,但随着应变量的增大略有降低。     

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。     

热变形对TC11-Ti2AlNb电子束焊接件力学性能的影响

本文应用纳米压痕和维氏硬度的方法表征了TC11/Ti2AlNb电子束焊接焊缝区域在不同状态下的硬度和弹性模量分布,结合组织的演变分析了微纳米尺度的力学的变化。结果表明：在TC11合金的热影响区,马氏体α&quot;相的分解是显微硬度降低的主要原因;而在焊缝以及Ti2AlNb热影响区区域,相的析出导致了显微硬度的增加。通过热变形以及锻后热处理都能够提高焊接区域的弹性模量。相比较而言,焊接态的焊缝弹性模量只有92GPa;而在变形和热处理后,弹性模量的值达到了130GPa。通过拉伸实验结果分析,焊缝在变形及热处理后屈服强度得到了较大提高,这和焊缝区域硬度和弹性模量的变化趋势一致。     

纳米压痕法确定TSV-Cu的应力-应变关系

为得到硅通孔电镀填充铜(TSV-Cu)的力学性能,对TSV-Cu进行了Berkovich纳米压痕实验.基于Oliver-Pharr算法和连续刚度法确定TSV-Cu的弹性模量和硬度分别为155.47 GPa和2.47 GPa;采用有限元数值模拟对纳米压痕加载过程进行反演分析,通过对比最大模拟载荷与最大实验载荷,确定TSV-Cu的特征应力和特征应变;由量纲函数确定的应变强化指数为0.4892;将上述实验结果代入幂强化模型中,确定TSV-Cu的屈服强度为47.91 MPa.最终确定了TSV-Cu的幂函数型弹塑性应力-应变关系.     

激光表面熔化对Ti-30Nb-4Sn合金晶体织构、显微组织、弹性模量和硬度的影响（英文）

骨科植入物的生物相容性与其弹性模量和表面性能密切相关。本研究的目的是阐明冷轧、再结晶和表面激光熔化(LSM)对双相(α″+β)Ti-30Nb-4Sn合金显微组织和力学性能的影响。对冷轧态基体进行X射线衍射织构分析(XRD)显示有[302]_α″//ND织构成分,而对再结晶态基体的分析显示有[302]α″//ND和[110]_α″//ND织构成分。XRD不能直接检测出β相织构,但是通过考虑α′′相和β相之间的位向关系可成功预测出[111]_β||ND织构的存在。纳米压痕测试结果表明,冷轧态基体的弹性模量(63 GPa)低于再结晶态基体(74 GPa)。根据已有文献和本文研究结果,认为这种差异是由冷变形过程中晶体缺陷的引入造成的。纳米压痕/EBSD分析表明,纳米压痕结果不受晶体取向的影响。LSM对变形合金硬度、弹性模量和晶体织构产生的变化类似于再结晶热处理产生的变化,均在表面和基体之间产生刚度梯度。     

用原子显微镜纳米压痕法研究Gr／Al复合材料热循环后的微观力学性能

采用原子力显微镜纳米压痕法测量了Gr/Al复合材料热循环后界面附近的纳米硬度和塑性变形能力的分布。随热循环次数的增加,纤维和基体中的纳米硬度小,而基体的塑性变形能力增加。纳米硬度和塑性变形能力的大小是随距纤维／基体界面的距离的变化而变化的。纳米硬度的变化可提供有关残余应变方面的信息,这是因为材料内部局部区域的弹性或塑性残余应变会影响此处的硬度大小。     

纳米压痕法研究n-Al2O3/Ni复合镀层的微观力学性能

应用纳米压痕法测试钢基体上n-Al2O3/Ni复合电刷镀层的硬度、弹性模量以及抗蠕变等性能,研究了镀层力学性能随镀层厚度的分布规律.结果表明,在整个厚度范围内复合镀层的力学性能一致,无明显的梯度分布.镀层内部存在缺陷的区域硬度和弹性模量降低,特别是枝状晶内部的组织疏松引起较大区域的性能降低,而枝状晶交界处形成的空隙对周围镀层性能没有明显影响.复合镀层的平均硬度和弹性模量分别为6.34GPa和161GPa,硬度为钢基体的2.4倍,复合镀层的压痕蠕变与传统单轴压缩蠕变过程相似,稳态蠕变速率约0.1nm/s.     

An analysis of load–penetration curves from instrumented indentation

A new empirical method is proposed for analyzing nano-indentation load–displacement curves. This method is based on experimental results and finite element (FEM) calculations reported in the literature. This method proposes to link the indentation–unloading curve to elastic modulus and strain-hardening properties. Through the analysis, elastic modulus, yielding stress and strain hardening properties are derived from the complete indentation load–displacement curve. This new method has then applied to the nano-indentation experiments of 14 different materials in which the elastic modulus ranges from 3 to 650 GPa and the hardness ranges from 0.1 to over 30 GPa. The elastic modulus, hardness and yielding stress derived from the new method agreed well with the literature values. An analysis of the loading curve also shows that there is a transition region, in which of the exponent of the loading curve changes from 1.5 to 2 corresponding to the change of the loads from low to high. This implicates that to avoid this transition region in loading curve, one should keep the load of the nano-indentation larger than approx. 30 mN.     

Nanomechanical properties of novel intermetallic coatings developed on austenitic stainless steels by siliconisation in liquid phase

Advanced nanomechanical testing has been used to evaluate mechanical properties of Ni-free Al₁₂(Fe,Cr)₃Si₂ intermetallic coatings grown on the 316 LVM steel by hot dipping in a Al-12.6 at.% Si liquid alloy for various immersion times. Despite the ultrafine-grained structure of the coating (～200 nm), the indentation size effect is more pronounced for the intermetallic coating than for the steel, which is explained by the higher geometrical necessary dislocation (GND) density of the intermetallic coating. To determine the true hardness of the coatings, the model of Nix and Gao was used. It has been shown that the hardness of the coating decreases from 6.2 GPa for the shortest time of immersion (60 s), to 3.36 GPa for the highest immersion time (600 s), which is always much higher than that for the substrate (1.82 GPa). The decrease in both hardness and GND with increasing immersion time is related to the relaxation of residual stresses, which act as a hardening factor. The net effect is an increase of the plasticity index of the coating. Young’s modulus for the intermetallic phase (146 GPa) is lower than that for the austenitic steel 316 LVM (220 GPa), which will favour the load transfer at the bone/metal interface, weakening the so-called “stress shielding effect”. Hence, the nanomechanical properties of this novel Ni-free intermetallic coating, tightly adhered to the substrate, offer a window of opportunity for orthopaedic applications.     

Numerical simulation of the stress-strain curve and the stress and strain distributions of the titanium-duplex alloy

The stress-strain curve of an a-β Ti-8Mn alloy was measured and then it was calculated with finite element method (FEM) based on the stress-strain curves of the single α and β phase alloys.By comparing the calculated stress-strain curve with the measured one,it can be seen that they fit each other very well.Thus,the FE model built in this work is effective.According to the above mentioned model,the distributions of stress and strain in the α and β phases were simulated.The results show that the stress gradients exist in both α and β phases,and the distributions of stress are inhomogeneons.The stress inside the phase is generally higher than that near the interface.Meanwhile,the stress in the α phase is lower than that in the β phase,whereas the strain in the a phase is higher than that in the β phase.     

Fabrication of in-situ Ti-Si-C fine grained composite by the self propagating high temperature synthesis (SHS) process

An attempt has been made to synthesise a Ti-Si-C composite with fine TiC and Ti-Si phase dispersed composite, using titanium, silicon and carbon powders using SHS dynamic compaction. The Ti-Si-C bulk composite with a high hardness (22.50 GPa), with a homogeneous distribution of a softer Ti-Si phase having more than 99% density of theoretical value has been successfully synthesised by the SHS dynamic process. The composite was found to be consisting of titanium carbide and titanium silicide. SEM and EDX analysis showed uniform distribution of phases and an average grain size varying around 1-2 μm. Nanoindentation studies revealed modulus of composite about 400 GPa with an elastic recovery of 30%.     

Direct synchrotron x-ray measurements of local strain fields in elastically and plastically bent metallic glasses

In situ high-energy synchrotron X-ray diffraction was conducted on elastically and plastically bent bulk metallic glass (BMG) thin plates, from which distinct local elastic strain fields were mapped spatially. These directly measured residual strain fields can be nicely interpreted by our stress analysis, and also validate a previously proposed indirect residual-stress-measurement method by relating nanoindentation hardness to residual stresses. Local shear strain variations on the cross sections of these thin plates were found in the plastically bent BMG, which however cannot be determined from the indirect indentation method. This study has important implications in designing and manipulating internal strain fields in BMGs for the purpose of ductility enhancement.     

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。     

Influence of nickel silicides presence on hardness,elastic modulus and fracture toughness of gas-borided layer produced on Nisil-alloy

The two-stage gas boriding in N₂?H₂?BCl₃ atmosphere was applied to producing a two-zoned borided layer on Nisil-alloy. The process was carried out at 910 °C for 2 h. The microstructure consisted of two zones differing in their phase composition. The outer layer contained only a mixture of nickel borides (Ni₂B, Ni₃B) only. The inner zone contained additionally nickel silicides (Ni₂Si, Ni₃Si) occurring together with nickel borides. The aim of this study was to determine the presence of nickel silicides on the mechanical properties of the borided layer produced on Ni-based alloy. The hardness and elastic modulus were measured using the nanoindenter with a Berkovich diamond tip under a load of 50 mN. The average values of indentation hardness (H_I) and indentation elastic modulus (E_I) obtained in the outer zone were respectively (16.32±1.03) GPa and (232±16.15) GPa. The presence of nickel silicides in the inner zone reduced the indentation hardness (6.8?12.54 GPa) and elastic modulus (111.79?153.99 GPa). The fracture toughness of the boride layers was investigated using a Vickers microindentation under a load of 0.981 N. It was confirmed that the presence of nickel silicides caused an increase in brittleness (by about 40%) of the gas-borided layer.     

用纳米压痕仪测量Cu50Zr43Ti7非晶合金的硬度和弹性模量

用Berkovich和Cube-Corner压头分别测量了Cu50Zr43Ti7非晶合金的硬度(H)和弹性模量(E).结果发现,该合金的H和E与压头形状及测量所用载荷无关,H=(6.5±0.2)GPa,E=(114.4±2.1)GPa;相对于Berkovich压头,用Cube-Corner压头得到的压痕周围观察到较多的剪切带.该合金没有硬度的尺寸效应,变形也没有明显的加工硬化.用有限元(FE)计算得到该合金的屈服强度(σ)约为1.8 GPa,与压缩试验结果相符.     

Micro mechanical properties of n-Al2O3/Ni composite coating by nanoindentation

A new type of nano test system was introduced, the test principle and the indentation data analysis method were described. It was used to test the micro mechanical properties, such as hardness, elastic modulus and indentation creep property of n-Al2O3/Ni composite coating on steel prepared by brush plating, and the variety of mechanical properties with coating thickness was researched. The results show that the mechanical properties are basically identical within the whole coating, the hardness and modulus decrease in the defect fields, especially within the dendritic crystals, whereas the mechanical properties are not influenced greatly at the interspaces among dendritic crystals. The average hardness and elastic modulus of n-Al2O3/Ni coating are 6.34 GPa and 154 GPa respectively, and the hardness is 2.4 times higher than that of steel and the indentation creep curve of n-Al2O3/Ni coating is similar to that of the uniaxial compression creep, and the creep rate of steady-state is about 0. 104 nm/s. These results will supply useful data for process improvement, new type material development and application expansion.     

Influence of the residual stress on the nanoindentation-evaluated hardness for zirconiumnitride films

The influence of the residual stress on the evaluated hardness and modulus for zirconium nitride films has been investigated using nanoindentation experiments in this work, and a variety of indentation load–displacement curves have been examined by analyzing the contribution of the residual stress to the indentation load. Atomic force microscopy (AFM) is performed to reveal the behavior of deformation (e.g. pile-up) around the indent on the surface of the film. The pile-up occurs for the film under a compressive stress, and is enlarged with increasing the compressive stress, which leads to that the actual contact area by indenter significantly deviates to the one calculated by Oliver–Pharr method. After correcting the contact area contributed by pile-up via AFM experiments, the residual stress does not affect the nanoindentation-measured hardness and modulus.