Al_2O_3/TiO_2纳米复合粉体爆炸喷涂层微结构及纳米压痕力学特性

研究了纳米复合涂层(NCC)和传统涂层(MCC)的微观结构及纳米压痕力学性能. NCC孔洞小,具有良好的均质分布特征.MCC中存在多级尺度分布的孔洞及微裂纹等缺陷, 呈现明显的非均质分布特征.NCC中大量晶界、亚晶界和微裂纹使得涂层中Al2O3基质相细化为纳米晶粒,但MCC中存在大量未熔片层颗粒.NCC和MCC具有各向异性的弹性、塑性、硬度和弹性模量.NCC比MCC相应的断面和表面具有更优良的抵抗外加负载性能、弹性恢复能力,更高的纳米压痕硬度和弹性模量.

磁控溅射不同元素掺杂WS_(2)薄膜的组织和纳米压痕力学性能

采用磁控溅射法在不同沉积压力(0.8,1.2Pa)下分别制备WS_(2)薄膜、Ti/WS_(2)复合薄膜和La-Ti/WS_(2)复合薄膜,研究了薄膜的组织结构和纳米压痕力学性能。结果表明:WS_(2)薄膜呈疏松多孔结构,晶粒粗大,孔洞较多,组织致密性差;与WS_(2)薄膜相比,Ti/WS_(2)复合薄膜的晶粒尺寸减小,组织变得致密,掺杂镧后薄膜的晶粒尺寸进一步减小,组织更致密;镧的掺杂还降低了薄膜中硫与钨的原子比,增加了硬质钨相的相对含量,提高了薄膜的硬度和变形抗力。

磁控溅射制备Al-Cu合金薄膜的纳米压痕力学性能与强化机制

采用磁控溅射方法在不锈钢表面制备了铜原子分数在0~11.8%的Al-Cu合金薄膜,研究了铜含量对薄膜微观结构、纳米压痕力学性能和强化机制的影响。结果表明:纯铝薄膜呈现面心立方结构,铜原子分数在2.2%~6.5%时Al-Cu合金薄膜均形成过饱和固溶体相,当铜原子分数超过6.5%后,薄膜中生成了AlCu化合物。随铜含量的增加,薄膜的晶粒尺寸减小,硬度和弹性模量增加,当铜原子分数增至11.8%时,晶粒尺寸为34.7 nm,硬度和弹性模量分别比纯铝薄膜提高了212.5%,2.2%;当铜原子分数在0~6.5%时薄膜的强化主要来自于细晶强化和固溶强化,当铜原子分数超过6.5%后,薄膜的强化是细晶强化、固溶强化和第二相强化共同作用的结果。

Mechanical properties of tungsten nanowhiskers characterized by nanoindentation

The Mechanical properties of the hexagonal tungsten nanowhiskers, which were synthesized by chemical vapor deposition, were characterized by instrumented nanoindentation and atomic force microscope （AFM）. The nanoindentation results show that tungsten nanowhiskers exhibit a hardness of （6.2±1.7） GPa and an elastic modulus of （225±20） GPa. According to the comparative test results, the tungsten nanowhiskers possess a comparable hardness to tungsten microwhiskers, and an hardness increase of 35% to the bulk single-crystal tungsten. The increase in the hardness of whiskers is attributed to the lacking of dislocation avalanche observed in the bulk single-crystal tungsten. The measured modulus is about 80% that of the tungsten microwhiskers, which can be contributed to the size effects of the nanowhiskers and the substrate effects in the nanoindentation test.

Microscopic mechanical characteristics analysis of ultranano-crystalline diamond films

The microscopic mechanical characteristics of ultranano-crystalline diamond films which were prepared in four different atmospheres were investigated for the applications in microelectron-mechanical system（MEMS）.The loading-unloading curves and the change of modulus and hardness of samples along with depth were achieved through nanoindenter.The results show that the films which are made in atmosphere without Ar have the highest recovery of elasticity,hardness（72.9 GPa） and elastic modulus（693.7 GPa） among the samples.Meanwhile,samples fabricated at a low Ar content have higher hardness and modulus.All the results above demonstrate that atmosphere without Ar or low Ar content leads to better mechanical properties of nanodiamond films that are the candidates for applications in MEMS.

Mechanical properties of 3D carbon/carbon composites by nanoindentation technique

Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.

High-throughput determination of mechanical and diffusion properties of Ti–Ta–Fe alloys

The mechanical and diffusion properties of Ti-Ta-Fe alloys in the Ti-rich region were investigated by utilizing a high-throughput method, with the combination of nanoindentation and diffusion couple techniques.Five groups of ternary Ti-Ta-Fe diffusion couples were prepared after annealing at 1273 K for 25 h. The composition-dependent mechanical properties of bcc Ti-Ta-Fe system were experimentally determined by means of nanoindentation and electron probe microanalysis(EPMA) techniques. Moreover, the interdiffusion coefficients of Ti-Ta-Fe alloys at 1273 K were confirmed from the composition gradients of the ternary diffusion couples with the support of a pragmatic numerical inverse method. A composition-dependent database on the mechanical and diffusion properties of Ti-Ta-Fe alloys was carefully established and utilized for the discussion of the processability during the hot working. The results indicated that the content of Fe should be controlled for the Ti alloys with high hardness and low Young’s modulus.

Evaluation of microstructure and mechanical properties of Mg-xCe-0.5Zn alloys by nano-indentation

The microstructure and mechanical properties of Mg-xCe-0.5Zn （x=0.5, 1.5, 2.5, molar fraction, %） alloys were examined using a nano-indentation technique. The alloys were fabricated using a vacuum induction melting method under an argon atmosphere The microstruetures of Mg-xCe-0.5Zn alloys mainly consist ofa-Mg and eutectic Mg12Ce phase. The volume fraction and size of the eutectic Mgl2Ce phase increase with increasing Ce contents. Nano-indentation test results show that the indentation hardness and elastic modulus of the eutectic Mg12Ce phase are higher than those of the a-Mg matrix. In addition, the mean indentation hardness and elastic modulus of the Mg-xCe-0.5Zn alloys increase with the Ce addition amount increasing.

Mechanical properties of Cu matrix composite fabricated by extrusion process

Carbon nanotube （CNT）was applied in various fields for itssuperior electrical, mechanical and thermal characteristics. After composites were fabricated by extrusion processusing ball-milledCu-CNT powders, mechanicalpropertiesofCu-CNT composites according to CNT fraction were reviewed. CNT （1%, 5% and 10%）,Cu （d=100 nm）, zirconia balls （90 g） and ethanol （20mL） were mixed and dispersed for5h at a speed of 500 r/minusing a planetary ball mill. A billet （d=50 mm, length=100 mm） was made with Cu, and the composite powderswerefilled up into billet using the uni-axial press. In the extrusion process, after the billet was heated at 880℃for1h, specimens were produced in the shape of a round bar using the billet by applying a load of 200 t. The composite powdersweremeasured for particle size byparticlesize distributionequipment. Then the specimen surface fabricated by extrusion was observed by SEM. Mechanicalpropertiesmeasured by the indentation equipment increased with increasing CNT content. The yield strength, tensile strength and hardness of theCu–CNTs composites canbeobviously improved.

Application of nanoindentation to investigate chemomechanical properties change of cement paste in the carbonation reaction

Nanoindentation technique was adopted to investigate the chemomechanical properties change of hardened cement paste before and after carbonation.It was found that the mean elastic modulus and mean hardness obviously increase after the carbonation reaction.Specifically,the probability of the elastic modulus showed a sharp reduction for the elastic modulus at the range of 7-34 and 83-160 GPa,in comparison of a large increase for the elastic modulus between 34-83 GPa.For the same reason,the probability of the hardness showed a large decrease when the hardness fell within 0.15-1.75 and 4.15-8.20 GPa and a dramatic increase for the hardness at the range of 1.75-4.15 GPa.In addition,low density C-S-H was affected by the carbonation degradation more seriously than high density C-S-H.The carbonation reaction led to distinct decrease of the number and size of unhydrated cement paste particles.