Correlation of tensile test properties with those predicted by the shear punch test

In the development of experimental alloys having sufficient material to do a standard tensile test procedure is not always possible. Thus in this work, we have evaluated the ability of the shear punch test to predict the strength and ductility of materials in place of the tensile test.This correlation study was carried out experimentally using six different alloys, and validated using finite element modelling. Both the experimental and modelling data confirmed that the yield point and ultimate tensile stress can be accurately elucidated from the shear punch data.However, the punch displacement at failure was found to be a function of both the ductility of the material and its work hardening rate. Although corrections were developed using the FE simulations which satisfactorily predicted tensile ductility from to the simulated shear punch displacement, back extrapolation of the tensile ductility from experimentally measured shear punch tests were not possible.It was concluded that the shear punch test suitable for determining the strength of a material, but not able to be used to infer the equivalent tensile ductility due to both experimental error in determining the point of failure as well as the interdependence of the punch displacement on multiple material properties.     

Effect of annealing on tensile properties of electrodeposited nanocrystalline Ni with broad grain size distribution

Abstract

The microstructures and tensile properties of electrodeposited nanocrystalline Ni (nc-Ni) with a broad grain size distribution after annealing at 150, 200 and 300°C for 500 s were investigated. The as deposited broad grain size distribution nc-Ni sample exhibited a moderate strength σ_UTS of ～1107 MPa but a markedly enhanced ductility ?_TEF of ～10%, compared with electrodeposited nc-Ni with a narrow grain size distribution. Annealing below 200°C increased the strength but caused a considerably reduction in tensile elongation. This behaviour is attributed to the grain boundary relaxation and the increased order of grain boundaries after annealing, which can make the grain boundary activities, such as the grain boundary sliding and grain rotations, more difficult. Further annealing at 300°C decreased both the yield strength and tensile elongation significantly due to significant grain growth.     

Enhanced tensile ductility in bulk nanocrystalline nickel electrodeposited by sulfamate bath

Electrodeposition is one of the fabrication techniques to produce nanocrystalline materials. In this paper, bulk nanocrystalline Ni (nc-Ni) was electrodeposited by using a sulfamate bath which generated low residual stress. In order to enhance tensile property of bulk nc-Ni, we investigated influences of glossing agents and bath condition on tensile properties, as these are reported to have an influence on surface condition, grain size and microhardness. It was found that saccharin contents and current density have significant effects on tensile properties of bulk nc-Ni. Moreover, we successfully obtained bulk nc-Ni displaying tensile ductility of over 10%. In particular, bulk nc-Ni from sulfamate bath with 5.0 g/l saccharin exhibited superior plastic deformation and good tensile strength (UTS = 1.2 GPa, ε_f = 15%). We were able to develop the relationship between tensile strength and ductility to a higher level on nc-Ni.     

Mechanical properties of nanocrystalline materials

The mechanical properties of nanocrystalline materials are reviewed, with emphasis on their constitutive response and on the fundamental physical mechanisms. In a brief introduction, the most important synthesis methods are presented. A number of aspects of mechanical behavior are discussed, including the deviation from the Hall-Petch slope and possible negative slope, the effect of porosity, the difference between tensile and compressive strength, the limited ductility, the tendency for shear localization, the fatigue and creep responses. The strain-rate sensitivity of FCC metals is increased due to the decrease in activation volume in the nanocrystalline regime; for BCC metals this trend is not observed, since the activation volume is already low in the conventional polycrystalline regime. In fatigue, it seems that the S-N curves show improvement due to the increase in strength, whereas the da/dN curve shows increased growth velocity (possibly due to the smoother fracture requiring less energy to propagate). The creep results are conflicting: while some results indicate a decreased creep resistance consistent with the small grain size, other experimental results show that the creep resistance is not negatively affected. Several mechanisms that quantitatively predict the strength of nanocrystalline metals in terms of basic defects (dislocations, stacking faults, etc.) are discussed: break-up of dislocation pile-ups, core-and-mantle, grain-boundary sliding, grain-boundary dislocation emission and annihilation, grain coalescence, and gradient approach. Although this classification is broad, it incorporates the major mechanisms proposed to this date. The increased tendency for twinning, a direct consequence of the increased separation between partial dislocations, is discussed. The fracture of nanocrystalline metals consists of a mixture of ductile dimples and shear regions; the dimple size, while much smaller than that of conventional polycrystalline metals, is several times larger than the grain size. The shear regions are a direct consequence of the increased tendency of the nanocrystalline metals to undergo shear localization.The major computational approaches to the modeling of the mechanical processes in nanocrystalline metals are reviewed with emphasis on molecular dynamics simulations, which are revealing the emission of partial dislocations at grain boundaries and their annihilation after crossing them.     

Uniaxial tensile and shear deformation tests of gold-tin eutectic solder film

This paper describes a novel experimental technique for measuring mechanical properties of gold-tin (Au-Sn) eutectic solder film used for soldering package in microelectromechanical systems (MEMS). Dual-source DC magnetron sputtering was employed to deposit Au-20 weight % (wt%) Sn film. The tensile test with in situ X-ray diffraction (XRD) measurement evaluates the Young's modulus and Poisson's ratio at intermediate temperatures. The Young's modulus and Poisson's ratio at room temperature were found to be 51.3 GPa and 0.288, lower than bulk values. The Young's modulus decreased with increasing temperature, whereas the Poisson's ratio did not depend on temperature. The XRD tensile test also showed creep deformation behavior of Au-Sn film. We have developed a shear deformation test technique, which is performed by using Au-Sn film sandwiched by two single crystal silicon (Si) cantilever structures, to characterize the shear properties of the film. The shear moduli obtained from the shear deformation tests ranged from 11.5 to 13.3 GPa, about 38% lower than those from the XRD tensile tests. The measured shear strength from 12 to 17 MPa exhibited a temperature dependency. Information about the tensile and shear characteristics would likely to be of great use in designing Au-Sn soldering packages for MEMS.     

Mechanical properties of concrete to cyclic uniaxial tensile loading using variable waveforms

The mechanical properties of concrete under cyclic tensile loading using square waveform, sine waveform and ramp waveform are studied. The experiments are performed on a closed-loop electro-hydraulic servo-controlled material testing system (MTS). The axial strain, dissipated energy per loading cycle, the damage evolution law and deformation modulus are mainly studied. The results show that the three-stage evolution law of axial strain and damage variable of concrete under ramp waveform and sine waveform are more obvious than those under the square waveform. The dissipated energy changes at different stages of fatigue life. At the beginning and end of the fatigue life, the rate of dissipated energy is higher than that at the medium stage of the fatigue time, which is attributed to the formation of cracks. The evolution of deformation modulus of concrete subjected to cyclic tensile loading using three loading waveforms also shows three stages: fast increase in the damage—increase at a slow constant rate—and accelerated increase in damage until failure.     

Physico-chemical, photoelectrochemical and photocatalytic properties of electrodeposited nanocrystalline titanium dioxide thin films

Crystal structure and microstructural properties of titanium dioxide (TiO₂) thin films prepared by cathodic electrodeposition on indium-tin-oxide coated glass substrates from aqueous peroxo-titanium complex solutions have been investigated. The electrodeposited TiO₂ thin film electrode exhibited anodic photocurrent upon visible light irradiation, indicating the typical behavior of n-type semiconductor. The photodecomposition of CH₃CHO by such thin films on exposure to ultraviolet light illumination was also observed.     

电沉积制备纳米镍的拉伸变形行为

为了系统研究纳米材料的超塑性变形特点,用电沉积方法制备了平均晶粒尺寸为70 nm的纳米镍.采用单向拉伸实验研究了其在室温和高温时的力学性能,并用透射电子显微镜TEM、扫描电子显微镜SEM和X射线能谱仪EDS观察分析了纳米镍变形前后的显微组织.实验结果表明:制备的纳米镍在室温时表现出的延伸率很低,但强度可达1000 MPa以上.当温度升高至450℃,应变速率为1.67×10-3 s-1时单向拉伸实验得到380%的延伸率,说明制备的纳米镍具有低温超塑性性能.实验过程中,材料内部的晶粒发生明显的长大与拉长.拉伸过程中形成的氧化物夹杂成为裂纹源,断口表现为沿晶断裂.     

Determination of the fracture properties of metallic materials using pre‐cracked small punch tests

In this paper, the use of pre‐cracked small punch test (p‐SPT) miniature specimens to obtain the fracture parameters of a material is presented. The geometry of the specimens used was square of 10 × 10 mm with a thickness of 0.5 mm. An initial crack‐like notch was created in the SPT specimens by means of a laser micro‐cutting technique. In order to obtain the fracture parameters from p‐SPT specimens three different approaches have been considered here. The first approach is based on the crack tip opening displacement concept, the second is based on the measure of the fracture energy using the area under the load–displacement curve for different crack sizes, and the third approach is based on the direct numerical simulation of the p‐SPT specimen and the numerical calculation of the J‐integral. In order to study the crack initiation in these p‐SPT specimens, several interrupted tests and the subsequent scanning electron microscope analysis have been carried out. The results indicate that p‐SPT specimens can be used as an alternative method for determining the fracture properties of a material in those cases where there is not enough material to undertake conventional fracture tests. For these p‐SPT specimens, the multi‐specimen method for the determination of the fracture energy is the most promising approach. The results indicate that this small specimen size allows the value of the material toughness, under low constraint conditions to be obtained.     

Microstructure and growth of electrodeposited nanocrystalline nickel foils

In the present work, the structure of electrodeposited pure Ni foils has been investigated by X-ray diffractometry, transmission electron microscopy and by measuring their electrical transport properties. It was found that the as-deposited Ni foils have a nanocrystalline structure covered by a thin amorphous Ni layer on the substrate side: the growth of the electrodeposited foils starts in amorphous form followed by nanocrystalline layers. To explain the formation of the amorphous Ni layer, it is supposed that foreign atoms are incorporated into the nucleating Ni films.     

Mechanical and tribological properties of nanocrystalline and nanolaminated surface coatings

The mechanical and tribological (friction/wear)properties were determined for nanocrystalline aluminum, as-sputtered Ti, Zr and Cu films, and nanolaminated Al-Al₂O₃, TiTiN, TiCu and TiZr composite films. The aluminum grain size varied between 15 and 10⁶ nm. The Al and Ti layer thicknesses in Al-Al₂O₃ and TiTiN composites ranged from 70 to 500 nm and from 150 to 450 nm, respectively. Within the grain size range of 15–100 nm, the hardness of the aluminum follows a Hall-Petch type relationship. The hardness of the TiTiN and Al-Al₂O₃ fllms also follows a Hall-Petch relationship with the Ti orAl layer thickness. The TiCu composites show a softening effect with decreasing Ti layer thickness. The coefficient of friction and wear rate for nanolaminated TiTiN and Al-Al₂O₃ composites are consistently reduced as the metal layer thickness is reduced. The micromechanisms responsible for the differences in mechanical and tribological properties are examined and the results compared with published literature.     

Comparison of microstructures and tensile properties of pulse electrodeposited Ni on polycrystalline and amorphous substrates

Abstract

Ultrafine grained nickel (UFG Ni) and microcrystalline nickel (MC Ni) were fabricated on two types of substrates, i.e. the amorphous (Ni–P) and polycrystalline (stainless steel) substrates by pulse electrodeposition without additives. This study demonstrates that when inhibiting the epitaxial growth by first depositing a thin amorphous layer on the polycrystalline substrates, the grain size of the subsequent Ni deposit decreases dramatically from microscale to the UFG regime, which depends on the deposition conditions. Compared with MC Ni, which has an ultimate tensile strength σ_UTS of 397 MPa and an elongation to failure ε_TEF of 11·98%, UFG Ni with an average grain size of 120·72 nm exhibits an enhanced σ_UTS of 807 MPa and a comparable ε_TEF of 10·44%. The electrodeposited method used in this study provides an effective and low cost way to produce UFG materials with both high strength and ductility, which can meet the demands for practical application as structural materials.     

On the prediction of tensile properties from hardness tests

The possibility of correlating the hardness to the tensile properties of a material has been investigated using Assab 760 steel, mild steel and API Std 5LX grade X60 pipeline steel that have been heat-treated for different times at various tempering temperatures and 6063-T1 aluminium that has been solution heat-treated. It is found that the strain hardening coefficient and the strength coefficient of all materials tested were linearly related to the hardness, irrespective of the type of hardness measurement used. Using these relationships, equations were defined to estimate the yield and ultimate tensile stresses of the materials. Good agreement between experimental results and estimated values was obtained for all materials studied. The feasibility of using the present findings in non-destructive field testing is discussed.     

Mechanical properties of cement foams in shear

Existing models indicate that the mechanical properties of brittle foams in shear depend on relative density, cell size, cell geometry and the modulus of rupture of solid cell walls. A series of mechanical testing on alumina cement foams with various relative densities were conducted to measure their shear modulus, shear strength and fracture toughness. Experimental data are compared to the existing theoretical models. Results suggest that the existing models for closed-cell foams are applicable to describe the mechanical properties of alumina cement foams in shear. Also, the microstructure coefficients included in the theoretical expressions for mechanical properties of alumina cement foams have been determined.     

On the intrinsic ductility of electrodeposited nanocrystalline metals

While nanocrystalline materials hold promise for structural applications in which increased strength is beneficial, their adoption has been hindered by concerns over the achievable ductility, resulting largely from considerable data scatter in the literature. A statistically significant set of 147 electrodeposited nanocrystalline tensile specimens was used to investigate this topic, and it was found that while necking elongation obeys similar processing quality and geometrical dependencies as conventional engineering metals, the intrinsic ductility as measured by uniform plastic strain was unexpectedly independent of microstructure over the grain size range of 10–80 nm. This indicates that the underlying physical processes of grain boundary-mediated damage formation are strain-oriented phenomena that can be defined by a critical plastic strain regardless of the strength of the material as a whole.     

Studies of electrical resistivity and magnetic properties of nanocrystalline CoFeCu thin films electrodeposited from citrate-added baths

In this study, nanocrystalline CoFeCu thin films were electrodeposited at different current densities from baths with natural pH (around 5.2) and containing 20 g/L citrate sodium. The relationship of films structure with soft magnetic properties and electrical resistivity, which are required for new generation magnetic head core, were investigated. SEM, EDS, XRD, TEM, VSM and four probe-point methods were used for characterization of the deposited films. The deposited films exhibited very uniform and homogenous structure with co-axis grains (confirmed by (111) and (110) poles figures and TEM images) throughout the coating. Overall, it was noticed that increasing current density from 1 to 24 mA/cm² reduced both grain size (from 63 to 8 nm) and coercivity (from 20 to 1 Oe) of the films. In addition, plotting Log (Hc) versus Log (D ⁶) demonstrated that the coercivity of the films followed “D ⁶ law”. Moreover, increasing current density changed phase structures of the films from FCC (Cu)+FCC (Co) to FCC (Co) and then to FCC (Co)+BCC (Fe). The double phase films exhibited the lowest coercivity in comparison with single phase films due to their finer grain size. However, grain size had no effect on saturation magnetization of the films. An increase in current density up to 10 mA/cm² also caused the substitution of diamagnetic copper with cobalt and iron in the deposit which led to reduction in saturation magnetization. Increasing current density also led to increasing grain boundaries in the deposits and hence, according to “scattering hypotheses”, enhanced the electrical resistivities.     

Effects of simultaneous polishing on electrodeposited nanocrystalline nickel

Nanocrystalline nickel was electrodeposited by combining with the simultaneous polishing of free particles. The polishing could strengthen the nickel deposition by affecting the structure of the deposits and refining grains. Nickel deposition with grain size of 30-80 nm and tensile strength of about 1400 MPa was achieved.     

Severe embrittlement of copper pillar bumps electrodeposited using JGB as leveler

Journal of Materials Science: Materials in Electronics - In this work, the electroplating of copper pillar bumps in wafer used for chip-scale interconnect was investigated. It was found that the...     

Mechanical and elastic properties of transparent nanocrystalline TeO2-based glass-ceramics

Mechanical and elastic properties of transparent TeO₂-based glass-ceramics (15K₂O · 15Nb₂O₅ · 70TeO₂) consisting of nanocrystalline particles (each particle size: 40–50 nm) and showing optical second harmonic generation were evaluated by means of usual Vickers indentation and nanoindentation tests. The precursor glass has Vickers hardness H _v of 2.9 GPa, Young's modulus E of 54.7 GPa, the fracture toughness K _c of 0.25 MPam^1/2 and Poisson's ratio of 0.24. The transparent nanocrystalline glass-ceramic heat-treated at 420°C for 1 h has H _v = 3.8 GPa, E = 75.9 GPa and K _c = 0.34 MPam^1/2, and the opaque glass-ceramic heat-treated at 475°C for 1 h has H _v = 4.5 GPa, E = 82.9 GPa and K _c = 0.68 MPam^1/2, demonstrating that poor mechanical and elastic properties of the precursor TeO₂-based glass are improved through sufficient crystallization. The fracture surface energy, brittleness and elastic recoveries (about 44%) after unloading (the maximum load: 30 mN) of transparent nanocrystalline glass-ceramics are almost the same as those of the precursor glass, implying that the interaction among nanocrystalline particles is not so strong.