单晶氮化镓纳米压痕与划痕实验

为分析单晶氮化镓的微观变形机理,使用纳米压痕仪对单晶氮化镓进行压痕与划痕实验.结果表明单晶氮化镓压痕过程存在弹塑转变过程即"pop-in"现象,分析得出此现象是由材料的位错萌生和扩展导致,压痕周围产生凸起现象导致计算硬度和弹性模量偏大,通过模型修正得到更真实的硬度和弹性模量数据.单晶氮化镓的变载划痕过程发生弹塑转变和脆塑转变,弹塑变形阶段深度-位移曲线波动平稳,表面光滑;而脆性阶段曲线波动幅度较大,表面产生侧向裂纹且朝着划痕方向45°对称分布.得到弹塑转变的临界载荷为389 mN,脆塑转变临界载荷为1227 mN,因此单晶氮化镓塑性加工区域应在389～1227 mN之间,该区域内易加工出光滑表面.通过不同载荷划痕实验,发现划痕压头所受的切削力和摩擦系数随划痕载荷的增大而增大,因此氮化镓加工时应选择合理的加工载荷.     

脆性材料超精密磨削时脆转变临界条件的研究

以脆性材料的压痕实验为基础,从理论上分析了脆性材料磨削时脆塑转变的临界条件,并利用超精密磨床进行脆性材料的磨削实验。实验结果表明,只有当脆性材料的磨削深度小于其临界磨深时,才能实现脆性材料的塑性域磨削,以获得超光滑的加工表面。     

KDP晶体单点金刚石切削脆塑转变机理的研究

加工超光滑表面的KDP晶体是现代超精密加工技术领域的重点研究课题。实验采用维氏压痕法研究KDP晶体脆性材料(001)面不同晶向的硬度、断裂韧性的变化规律。通过建立KDP晶体脆塑转变临界切削厚度模型,研究了KDP晶体金刚石切削脆塑转变机理。结果表明,脆塑转变临界最小切削厚度出现在断裂韧性最小而硬度最大的[110]方向;脆塑转变临界切削最大厚度出现在断裂韧性最大而硬度最小的[001]方向。并利用超精密机床加工了KDP晶体,加工结果与理论推导结论相符合,在[001]方向加工出表面粗糙度为7.5nm(RMS)的超光滑表面。     

Ni-P化学镀层在动态加载条件下的塑脆转变

利用单摆划痕法的动态加载特性，研究了Ni—P化学镀层本身的塑脆转变。镀层的塑脆转变除可采用Lamy建议的塑脆转变深度D′判据外，还提出用新定义的临界法向力Fnc来表征。根据划痕深度d和法向力Fnc的大小，可把坡层在划痕过程中的力学行为分为塑性变形、塑脆转变和脆性断裂三个阶段。分析讨论了磷含量和热处理温度对塑脆转变的影响。     

单晶锗纳米尺度分层多次切削的分子动力学模拟

运用分子动力学方法研究了单晶锗材料在多次切削过程中晶体结构的演化和相变.比较了在相同的总加工深度下采用两次不同预设切削深度加工单晶锗后表面/亚表面损伤程度、温度和应力的变化.研究结果表明:切削过程中切削区原子发生高压相变,原子结构从Ge-Ⅰ结构转变为无定形结构,使工件发生塑性变形,切屑以塑性方式去除;切削结束后由于压力和温度释放,少量无定形结构原子重新转变为Ge-Ⅰ结构或六方金刚石结构,而无定形结构主要是β-tin结构和非晶体结构;预设切削深度增加,材料的去除量和亚表面损伤深度增加,其损伤深度不受前一次切削深度影响,仅与最终预设切削深度相关,并且在同样条件下,多次切削比单次切削更有利于降低亚表面损伤深度和提升加工效率.此外,原子相变与σxx和σHyd相关,亚表面损伤深度与σyy相关,两次预设切削深度接近或相等时,工件内部应力均衡有利于形成较好的加工表面.     

基于分子动力学单晶锗的纳米压痕特性分析

单晶锗属于硬脆性光学半导体材料,加工时易产生裂纹和凹坑等缺陷,严重影响其表面质量.为了达到纳米级的表面质量,本文采用分子动力学模拟从不同晶面和晶向对单晶锗进行纳米压痕分析,在纳米尺度下对其进行压痕加载和卸载,分析该过程中载荷的变化情况,得到弹性模量的变化差异.结果表明,加载前后弹性模量差异小的单晶锗(111)晶面可以作为实际生产中的加工面,从而获得高质量的加工表面.     

金刚石刀具单点切削单晶硅加工表面特性

本文利用超精密机床对单晶硅进行了斜切及车削实验,采用拉曼光谱仪测量单晶硅材料切削表面的损伤,利用高斯和洛伦兹分布拟合拉曼光谱得到单晶硅表面相变层厚度及残余应力信息．结果表明,单晶硅切削表面与磨削、纳米划擦表面不同,除了非晶相外,测不到其他高压相．随着切削厚度的增大,单晶硅表面非晶层的厚度和表层的残余应力也会相应增加．较大的切削厚度使得残余应力变得不均匀,最终导致单晶峰退简并分裂成2个或3个峰．一般单晶硅的塑性车削生成表面由于切削厚度相对较小,其表面非晶层相对较薄,表面存在轻微残余压应力．当车削生成表面的切削厚度较大时,表面有脆性凹坑,非晶层相对较厚,残余压应力较大．车削过程是对已加工表面的切削,由于已加工表面非晶硅的存在,采用较高的切削速度可以增加切削区域温度,提高单晶硅表面非晶层的塑性,可加工出更好的光学表面．     

熔石英光学元件纳米划痕亚表面损伤特性

为了实现熔石英光学元件激光损伤阈值的提升,本文分析了划痕对熔石英激光损伤的影响,利用纳米压痕实验区分塑脆划痕,通过时域有限差分(FDTD)算法仿真给出不同深度、不同宽深比的划痕对光场调制的影响结果,最后选取典型划痕进行R-on-1激光阈值测试实验.结果表明,深度在53 nm以下的塑性划痕对激光损伤无影响,处于塑脆转变阶段的划痕有一定几率诱导损伤,脆性划痕处损伤阈值远远低于基底阈值,仅为基底阈值的43.1%,是降低光学元件激光损伤阈值的重要因素.实验数据与理论仿真具有一致性.     

Li2O-A12O3-SiO2微晶玻璃超光滑表面纳米划痕产生机理及抑制实验研究

对Li2O-A12O3-SiO2微晶玻璃超光滑表面进行了纳米划痕实验,测得微晶玻璃超光滑表面弹性一塑性与塑性．脆性转变的临界载荷分别为3．906mN和29．78mN．通过对微晶玻璃超光滑表面划痕产生机理进行分析,得出在纳米尺度的抛光加工过程中,抛光颗粒的载荷越接近弹塑转变临界载荷,则样品表面产生的划痕越少,越易获得无划痕的超光滑表面．通过对比抛光工艺优化前后的实验结果,可以看出优化后的抛光工艺对超光滑表面划痕的抑制效果较明显,证实了上述研究结果的正确性．该研究结果对于Li2O-A12O3-SiO2微晶玻璃超光滑表面加工具有一定的指导意义．     

Li_2O-Al_2O_3-SiO_2微晶玻璃超光滑表面纳米划痕产生机理及抑制实验研究

对Li2O-Al2O3-SiO2微晶玻璃超光滑表面进行了纳米划痕实验,测得微晶玻璃超光滑表面弹性-塑性与塑性-脆性转变的临界载荷分别为3.906 mN和29.78 mN.通过对微晶玻璃超光滑表面划痕产生机理进行分析,得出在纳米尺度的抛光加工过程中,抛光颗粒的载荷越接近弹塑转变临界载荷,则样品表面产生的划痕越少,越易获得无划痕的超光滑表面.通过对比抛光工艺优化前后的实验结果,可以看出优化后的抛光工艺对超光滑表面划痕的抑制效果较明显,证实了上述研究结果的正确性.该研究结果对于Li2O-Al2O3-SiO2微晶玻璃超光滑表面加工具有一定的指导意义.     

法向载荷对紫铜的微米划痕测试的影响

使用Rockwell C金刚石圆锥压头对紫铜进行微米划痕实验,研究了法向载荷对样品的微米划痕测试的影响。结果表明:随着法向载荷的增大,压入深度和残余深度均线性增加,弹性恢复率线性减小;划痕宽度随压入深度的增加先非线性地增大,之后趋于线性增加。当法向载荷在0.08~0.11N的范围内时,摩擦力线性增大,摩擦系数趋于一个常数,摩擦机制为粘着摩擦;当法向载荷在0.11~17N的范围内时,摩擦力和摩擦系数非线性地增大,摩擦机制为犁沟摩擦;当法向载荷在17~28N的范围内时,摩擦系数趋于一个常数,摩擦力线性增大,摩擦机制为微切削。     

Investigation of nanoscratch processes in semiconductor materials for application to maskless patterning

Features of nanoscratching processes with a diamond 90 degrees cube corner tip in semiconductor materials have been studied with different tip orientations and scratch procedures: constant and linearly increasing normal load during scratching, multi-scratching and the direct analysis of the generated scratch by re-scanning the scratch with a strongly reduced normal load. These scratch functions allowed a detailed investigation of the materials response due to the mechanical deformation process. Elastic material recovery, plastic deformation and material removal contribute to the generation of scratch groove profiles. For low applied normal loads mainly elastic deformation occurs whereas for larger normal loads stick-slip processes with periodic hillocks at the groove bottom and irregular pile-up along the scratch rim dominate the process. From the analysis of the scratch groove profile in Si(100), GaAs(100) and thin InSb films, quantitative values for the elastic deformation, the friction coefficient, stick-slip pattern, material removal and scratch depth as a function of the applied normal load are obtained. With multi-scratching a definite removal pattern with a reproducible scratch depth is obtained. These results can be used to optimise the scratch technique for application to maskless patterning.     

多孔氧化铝模板的纳米力学性能测试与分析

为了掌握多孔氧化铝模板的纳米力学性能,采用二次氧化法制备孔径在30～40nm之间且高度有序的纳米阵列氧化铝模板,并使用扫描电子显微镜(SEM)对其形貌进行表征;在原位纳米力学测试系统上进行微压痕实验,对样品表面力学性能(纳米硬度、模量)进行测试;利用原子力成像功能对实验区域扫描成像,在纳米尺度下观察和分析样品形貌.结果表明,AAO模板在同一深度处对应的硬度、模量值明显高于相应的基体材料铝,膜基体系的抗载能力明显提高;在压入深度为70～240nm时,AAO膜板的硬度和模量值分别为5.8GPa和106GPa,但从深度250nm时开始出现减小趋势;单晶铝与压针的接触为理想刚塑性接触,AAO模板与压针的接触为弹塑性接触.     

Influence of weathering and substrate roughness on the interfacial adhesion of acrylic coating based on an increasing load scratch test

An increasing normal load scratch test was employed to study the scratch behavior of acrylic coatings. The effects of weathering and substrate surface roughness on the interfacial adhesion of acrylic-coated thermoplastic polyolefin (TPO) systems were investigated. The increasing load test gives valuable information regarding the onset location to failure and the critical normal load for interfacial delamination. Both flatbed scanner and scanning electron microscope are utilized to characterize the scratch-induced damage mechanism of the coated TPO system. An increase in weathering time and in surface roughness of the virgin TPO leads to the increase in scratch resistance of acrylic coating. In addition, with increasing weathering time there is an increase in discoloration, while a decrease in gloss occurs. The correlation between the change of scratch coefficient of friction and the onset location of interfacial delamination is discussed.     

圆锥压头递增载荷对材料的划痕行为

用Rockwell C金刚石压头对16种材料(2种玻璃、2种聚合物、4种陶瓷、4种金属和4种金属玻璃)进行微米划痕测试。结果表明,这些材料都存在与弹性恢复相关的最大划痕保持率(残余深度与压入深度之比),可作为表观摩擦系数变化曲线的分段过渡点。划痕的表观摩擦系数由黏着摩擦系数和犁沟摩擦系数组成,使用三维力学接触模型可较为准确地表征除金属玻璃外的摩擦系数。材料的初始摩擦系数与泊松比有一定的关系。聚合物(PC和PMMA)因堆积和下沉效应出现独有的双划痕沟槽现象。16种材料的划痕硬度与压痕硬度的比值为0.33~2.5,划痕硬度与体积模量呈线性关系。使用线弹性断裂力学(LEFM)模型和微观能量尺寸效应(MESEL)模型计算了材料的断裂韧性。结果表明,LEFM模型、Akono's MESEL和Hubler's MESEL模型都能较为准确地表征断裂韧性较低材料(玻璃、陶瓷和高分子)的断裂韧性,而对断裂韧性较大的金属材料其表征结果偏差较大。用Liu's MESEL模型可表征断裂韧性较大材料(金属材料和部分金属玻璃)的断裂韧性。材料的断裂韧性,与泊松比呈分段线性相关。     

类金刚石薄膜的表面纳米划擦性能评价

用射频等离子体增强化学气相沉积在钛合金表面制备了类金刚石薄膜,利用纳米压入仪及其附件研究了薄膜与纳米划擦有关的力学性能．结果表明：随薄膜厚度的增加,其硬度略有增加,但增幅较小,弹性模量没有明显的相应规律;薄膜在划擦过程中,随载荷增加,先后经历薄膜变形、薄膜与基体共同变形及薄膜剥离三个阶段;在薄膜变形阶段,划擦对薄膜的损害较小;当压头进入薄膜一定深度后,划擦后薄膜与基体的变形不同步,造成薄膜沿划痕向两边形成整齐排列的小裂纹,呈鱼骨状;达到临界载荷值时,薄膜在界面处发生脆性剥落;随膜厚增加,薄膜的临界载荷增大,因其残余应力的相应增大而发生大面积脆性剥落．     

Study on the morphology and tribological properties of acrylic based polyurethane/fumed silica composite coatings

Two fumed silica (one hydrophilic and one hydrophobic) were used in the high solid acrylic based polyurethane coatings by directly mixing. The dispersion of fumed silica particles in the bulk of polyurethane coats was characterized by transmission electron microscope (TEM) and surface morphology examined using a scanning probe microscope (SPM). Micro indentation and scratching tests were carried out with a nano-indenter. Both hydrophilic and hydrophobic fumed silica nearly have the same dispersion in acrylic based polyurethane coats. The surface roughness of polyurethane coats increases as fumed silica increases, however, the surfaces of polyurethane coatings containing hydrophobic fumed silica are rougher than that containing hydrophilic fumed silica at the same content. Addition of fumed silica can obviously enhance the micro indentation hardness (MIH) and elastic modulus of polyurethane coats and the higher the content of fumed silica is, the higher the MIH is for hydrophilic one but for hydrophobic one only under normal load less than 20 mN. In the micro scratch experiment, the elastic response and plastic deformation nearly keep constant with normal force increasing for pure acrylic based polyurethane coats. But the percentage of elastic response decreases and the percentage of plastic deformation increases as normal force increases for the polyurethane coats with fumed silica. Crack occurs when scratching under normal force higher than 50 mN for the polyurethane coats with fumed silica, and as the content of fumed silica increases, the critical force for crack increases. Additionally, both hydrophilic and hydrophobic fumed silica have no obvious influence on the response to marring stress and micro mar resistance (MMR) of acrylic based polyurethane.     

Atomic force microscopy tip torsion contribution to the measurement of nanomechanical properties

The nanomechanical properties of polymethyl methacrylate and indium phosphide were measured with an atomic force microscope and a nanoindentation system. The elastic moduli measured with the atomic force microscope are in good agreement with the values obtained with the nanoindentation system. The hardness is shown to be affected by the tip radius used in our experiments. The cantilever vertical and lateral movements were independently analyzed during nanoindentation, and the tip torsion can be attributed to a change from elastic to plastic deformation regimes of materials during force microscopy nanoindentation. An analysis of the lateral movement of the laser beam associated with the cantilever torsion was used to determine the material yield stress.     

磁控溅射法制备铁氧体薄膜的界面结合强度研究

利用磁控溅射法在单硅晶基底和玻璃基底上沉积铁氧体薄膜,采用AFM观察薄膜的微观形貌,采用划痕法测试薄膜的界面结合强度,测试结果表明:由于两种不同材质上沉积的薄膜粗糙度缘故,硅晶/铁氧体薄膜的临界载荷为19.7N,其划痕形貌为裂纹状扩展,玻璃/铁氧体薄膜的临界载荷为5.3N,其划痕形貌为剥落状。     

Analysis of spherical indentations of coating-substrate systems: Experiments and finite element modeling

The influence of surface layers and thin coatings on the load-bearing capacity of elements under contact load conditions has yet to be sufficiently described theoretically. In this study, the deformations of coated surfaces were analyzed using spherical indentation and finite element method (FEM) modeling. The paper presents a complex procedure of indentation result analysis, based on the transformation of load-penetration depth curves into stress–strain curves. Such a procedure was applied for 0.7–2.4 μm thick titanium nitride (TiN) coatings deposited by the Pulsed Laser Deposition (PLD) technique on steel substrates. Indentation experiments showed that the critical stress for fracture of TiN coatings deposited on steel substrates is 2–3 GPa. The result of the theoretical analysis, FEM modeling and experiments is the map of failure, which shows elastic, elastic–plastic and fracture regimes of the tested coating-substrate systems.