Mechanical and Wear Properties of Nanostructured Surface Layer in Iron Induced by Surface Mechanical Attrition Treatment

A porosity-free and contamination-free surface layer with grain sizes ranging from nanometer to micrometer in Fe samples was obtained by surface mechanical attrition treatment (SMAT) technique. Mechanical and wear properties of the surface layer in the SMATed and annealed Fe samples were measured by means of nanoindentation and nanoscratch tests, respectively. Experimental results showed that the hardness of the surface layer in the SMATed Fe sample increased evidently due to the grain refinement. The elastic moduli of the surface layers in the SMATed and annealed Fe samples were unchanged, independent of grain size in the present grain size regime. Compared with the original Fe sample, the wear resistance enhanced and the coefficient of friction decreased in the surface layer of the SMATed Fe sample.     

Microstructure and Mechanical Properties of Nanocrystalline Tungsten Thin Films

Tungsten (W) thin films were prepared by magnetron sputtering onto Si (100) substrates. Their microstructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The hardness and modulus were evaluated by nanoindentation. It is found that a 30 nm Cr sticking layer induces structure changes of deposited W film from β-W to α-W structure. In addition, remarkable hardness enhancement both for the deposited and annealed W...     

Mechanical properties of single crystal tungsten microwhiskers characterized by nanoindentation

The nanoindentation results in this work showed that the one-dimensional single crystal tungsten microwhiskers fabricated by vapor deposition possess unique yielding behavior. The average hardness of the microwhiskers measured on their (1 1 1) surfaces was 8.44 GPa, significantly higher than that of the bulk tungsten ranged from 3.4 to 5.8 GPa. The hardness increase was attributed to the lacking of dislocation avalanche in the 1D single crystal tungsten that was often observed in the nanoindentation of the bulk tungsten. However, the values of elastic modulus of the microwhiskers measured on the (1 1 1) surfaces were considerably scattered, whose average value is much lower than the reported value of 410 GPa for the bulk tungsten.     

Mechanical properties of hybrid sol-gel derived films as a function of composition and thermal treatment

Sol-gel coatings derived from glycidoxypropyltrimethoxysilane (GLYMO) and/or methyltrimethoxysilane (MTMS) and silica nanoparticle filler were prepared. The mechanical properties of the coatings were measured as a function of coating composition and thermal treatment temperature using nanoindentation. Thermogravimetric analysis was used to determine the material loss rate during heating and the thermal stability of the materials. The coating hardness (H) and reduced modulus (E_r) strongly increased with increasing thermal treatment temperatures. The changes in the mechanical properties were found to correlate with the conversion of silanol groups measured by infrared spectroscopy. The partial replacement of MTMS by GLYMO in the coatings initially increased the hardness and modulus but larger proportions of GLYMO reduced H and E_r. It was found that both thermal treatment temperature and variation in coating composition could result in large changes in the key material ratio of H³/E_r², that in turn could strongly influence the mechanical response of the coating.     

Mechanical characterization of LiPON films using nanoindentation

Nanoindentation has been used to characterize the elastic modulus and hardness of LiPON films ranging in thickness from 1 to 10 μm. Four fully dense, amorphous films were deposited on glass and sapphire substrates with one film annealed at 200 °C for 20 min. The modulus of LiPON is found to be approximately 77 GPa, and argued to be independent of the substrate type, film thickness, and annealing. Based on the numerical analysis of Monroe and Newman, this value may be sufficiently high to mechanically suppress dendrite formation at the lithium/LiPON interface in thin film batteries [1]. Using Sneddon's stiffness equation and assuming the modulus is 77 GPa, the hardness is found to be approximately 3.9 GPa for all but the annealed film. The hardness of the annealed film is approximately 5% higher, at 4.1 GPa. Atomic force microscopy images of the residual hardness impressions confirm the unexpected increase in hardness of the annealed film. Surprisingly, the indentation data also reveal time-dependent behavior in all four films. This indicates that creep may also play a significant role in determining how LiPON responds to complex loading conditions and could be important in relieving stresses as they develop during service.     

Nanoindention study of indium nitride thin films grown using RF plasma-assisted molecular beam epitaxy

In this study, we used an RF plasma-assisted molecular beam epitaxy (RF-MBE) system to grow single-crystalline indium nitride (InN) films onto aluminum nitride (AlN) buffer layers on Si (111) substrates. We then used nanoindentation techniques and reflection high-energy electron diffraction (RHEED) to study the influence of the c-axis-oriented InN films on the mechanical performance. From morphological observations, we compared the stiffness and resistance against contact-induced damage of the InN films in the presented shrinkage of the area. InN films prepared at growth temperatures of 440, 470, and 500 °C had nanohardnesses (H) of 3.6 ± 0.2, 4.5 ± 0.25, and 9.1 ± 0.8 GPa, respectively, and Young’s moduli (E) of 97.4 ± 1.2, 147.7 ± 1.8, and 176.0 ± 2.3 GPa, respectively.     

Mechanical characterization of grain boundaries using nanoindentation

Grain boundaries and other mesoscale interfaces play an important role in controlling macroscale mechanical properties of various hierarchical materials needed for advanced technologies. Recent enhancements in both instrumentation and data analyses protocols have demonstrated the tremendous potential of nanoindentation as a high-throughput technique for robust and quantitative assessment of the mechanical role of these mesoscale interfaces. These new protocols are geared to address some of the most critical gaps impeding the efforts aimed at the accelerated and cost-effective design and development of new and improved materials. This review summarizes recent advances and identifies specific research directions that are likely to produce the maximum benefit and impact in these pursuits.     

Small-scale mechanical property characterization of ferrite formed during deformation of super-cooled austenite by nanoindentation

The mechanical properties of dynamically and statically transformed ferrites were analyzed using a nanoindentater-EBSD (Electron BackScattered Diffraction) correlation technique, which can distinguish indenting positions according to the grains in the specimen. The dilatometry and the band slope and contrast maps by EBSD were used to evaluate the volume fractions of two kinds of ferrite and pearlite. Fine ferrites induced by a dynamic transformation had higher nano-hardness than the statically transformed coarse ferrites. Transmission electron microscopy (TEM) showed the dynamic ferrites to have a higher dislocation density than the statically transformed ferrites.     

Mechanical properties of porous silicon by depth-sensing nanoindentation techniques

Porous silicon (PS) was prepared using the electrochemical corrosion method. Thermal oxidation of the as-prepared PS samples was performed at different temperatures for tuning their mechanical properties. The mechanical properties of as-prepared and oxidized PS were thoroughly investigated by depth-sensing nanoindentation techniques with the continuous stiffness measurements option. The morphology of as-prepared and oxidized PS was characterized by field emission scanning electron microscope and the effect of observed microstructure changes on the mechanical properties was discussed. It is shown that the hardness and Young's elastic modulus of as-prepared PS exhibit a strong dependence on the preparing conditions and decrease with increasing current density. In particular, the mechanical properties of oxidized PS are improved greatly compared with that of as-prepared ones and increase with increasing thermal oxidation temperature. The mechanism responsible for the mechanical property enhancement is possibly the formation of SiO₂ cladding layers encapsulating on the inner surface of the incompact sponge PS to decrease the porosity and strengthen the interconnected microstructure.     

An investigation on the onset of plastic deformation of nanocrystalline solid solution Ti-Al-N films

The nanoscale deformation behavior of the solid solution Ti_0.5Al_0.5N thin film was systematically investigated by nanoindentation measurements. The effect of the tip radius of the indenter on the behavior of elastic-plastic deformation was also evaluated. The Hertzian stress analysis was used to determine the distribution of resolved shear stress at the initiate plastic deformation, and the obtained critical resolved shear stress was compared to the theoretical shear strength to establish correlations and differences. Comparison of the calculated critical shear stress and theoretical shear strength also indicated that new complete dislocation nucleation during nanoindentation was not the prerequisite of the onset of plastic deformation, even at very shallow indentation depth.     

Microstructure and mechanical properties of TiC–WC–(Ti,W)C–Ni cermets

(Ti_0.93W_0.07)C solid-solution powder is synthesized via high-energy milling and carbothermal reduction. When the solid-solution carbide is sintered after blending with Ni and commercial single-phase carbides such as TiC and WC, a complex microstructure is developed, typically featuring a core–rim structure along with the initial solid-solution phase. Furthermore, an increase in total volume of the solid-solution phase with (Ti_0.93W_0.07)C in the cermets results in significantly enhanced mechanical properties: fracture toughness (K_1C) is 7.5–12.7 MPa m^1/2 and hardness (H_v) is 11.9–14.1 GPa. These properties are in contrast with those of conventional cermets, which yield K_1C = 6 MPa m^1/2 and H_v = 12.6 GPa.     

Structural evolution of Ti-Al-Si-N nanocomposite coatings

Ti-Si-Al-N films were prepared by rf reactive magnetron sputtering, in static and rotation modes, using a wide range of different deposition conditions, which created conditions to obtain Ti-Al-Si-N coatings with different structural arrangements.Films prepared below a critical nitrogen flow, under conditions out of thermodynamic equilibrium, revealed a preferential growth of an fcc (Ti,Al,Si)N_x compound with a small N deficiency. With nitrogen flow above that critical value, the reduction of the lattice parameter was no longer detected. However, a thermal annealing showed that a complete thermodynamically driven segregation of the TiN and Si₃N₄ phases was not yet obtained. The segregation upon annealing induced a self-hardening and showed a multiphase system, where the crystalline TiN, (Ti,Al)N and (Ti,Al,Si)N_x phases were identified by X-ray diffraction. This behavior is due to the de-mixing of the solid solution associated to a small N deficiency.     

Mechanical properties determined by nanoindentation tests of [Pb(Zr,Ti)O3] and [Pb(Mg1/3Nb2/3)1−xTixO3] sputtered thin films

As the introduction of piezoelectric materials into micro electromechanical systems increases, there is a correlating requirement for understanding the mechanical properties of these films. We have investigated the mechanical properties of unpoled PZT [Pb(Zr,Ti)O₃] and PMNT [Pb(Mg_1/3Nb_2/3)_1−xTi_xO₃] thin films deposited by sputtering. In this study, nano-indentation, a technique which allows determination of the transverse mechanical properties, is used. It is the easiest method for assessing the biaxial elastic modulus and the hardness of thin films. It was confirmed that neither cracks, nor pile-ups, were observed for indentation depths below 20% of the film's thickness.The continuous stiffness method was used and allowed us to demonstrate that the indentation modulus decreases continuously with increasing grain diameter. This can be explained by the orientation changes of the crystallites with increasing grain diameter. The indentation modulus measured under load, or at almost null load (that is when the ferroelectric domains are or are not oriented by the stress) are coherent with those determined by the same method with a hard bulk ceramic. These results tend to show that the compliance C_ij of the hard bulk ceramic can possibly be used with sputtered thin films. The hardness is almost independent of the grain diameter (H_b ≅ 7.5 ± 0.9 GPa) and higher than that for the bulk PZT ceramics considered in this study. PMNT and PZT films have appreciably the same mechanical characteristics. No influence of the film thickness was found on the values of both of these parameters.     

Role of samarium additions on the shape memory behavior of iron based alloys

The effect of samarium contents on shape memory behavior of iron based shape memory alloys has been studied. It is found that the strength of the alloys increases with the increase in samarium contents. This effect can be attributed to the solid solution strengthening of austenite by samarium addition. It is also noticed that the shape memory effect increases with the increase in samarium contents. This improvement in shape memory effect presumably can be regarded as the effect of improvement in strength, increase in c/a ratio and obstruction of nucleation of ? in the microstructure.     

Bionic design methodology for wear reduction of bulk solids handling equipment

Large-scale handling of particulate solids can cause severe wear on bulk solids handling equipment surfaces. Wear reduces equipment life span and increases maintenance cost. Examples of traditional methods to reduce wear of bulk solids handling equipment include optimizing transport operations and utilizing resistant materials. To our knowledge, the so-called bionic design has not been utilized. Bionic design is the application of biological models, systems, or elements to modern engineering. Bionic design has promoted significant progress on the development of engineering products and systems. In order to use bionic design for wear reduction of bulk solids handling equipment surfaces, this paper introduces bionic design to bulk solids handling on the basis of analogies between biology and bulk solids handling. In addition, a bionic design methodology for the wear reduction of bulk solids handling equipment surfaces is formulated. Based on the bionic design methodology, two bionic models used for abrasive and erosive wear reduction of bulk solids handling equipment surfaces are proposed.     

Influence of remelting on microstructure,hardness and corrosion behaviour of AlCoCrFeNiTi high entropy alloy

Abstract

High entropy alloys are a newly developed class of alloys, which tend to form a single solid solution or a mixture of solid solutions with simple crystal structures. These alloys possess excellent mechanical properties, thermal stability and corrosion resistance. In the present paper, an AlCoCrFeNiTi high entropy alloy was obtained by induction melting, and the influence of the remelting process on the mechanical and corrosion resistance characteristics of the alloy was investigated. Thus, optical and scanning electron microscopy revealed less phase segregation and a fine dendritic structure for the remelted alloy, while corrosion tests indicated that present alloy, in remelted state, has better corrosion resistance than as cast alloy and stainless steel. The Vickers microhardness measurements demonstrated an improvement of the alloy microhardness by remelting process due to the decrease in phase segregation and the increase in dendrite refinement level.     

Laser hardening of aluminum bronzes

The susceptibility of two-phase aluminum bronzes to harden by quenching is well known. This work deals with the features of hardening from liquid or solid phases of several bronzes with 9-11% Al under the action of CO₂ continuous wave laser beam with a power of 1300 W coupled with a table in x-y-z coordinates digitally controlled. In order to determine the hardening conditions, the influence of the processing parameters on the geometry of the hardened layer and surface hardness was analyzed. By the microstructural analysis of the hardened layer, the hardening degree measured by the microhardness meter and structural changes were correlated. The microhardness profile on the depth of the heat-affected zone was traced. The range of the analyzed bronzes points out the influence of the initial condition and of the Ni, Fe, and Mn alloy elements contents on the microstructure, size, and hardness of the hardened layer. The effect of subsequent tempering was investigated.     

One parameter model for strength properties of hardenable aluminium alloys

Models for strength properties are proposed for commercially aluminium alloys. The alloy group investigated are the hardenable alloys from the 2000 (Al–Cu and Al–Cu–Mg), 6000 (Al–Mg–Si) and 7000 (Al–Zn–Mg) series. The same model for solid solution hardening that has successfully been applied to non-hardenable alloys has been used. For precipitation hardening, particle cutting and the Orowan mechanism have been considered. The same basic model is used for all strength properties. It is demonstrated that with one fitting parameter for each property, a representation with reasonable accuracy can be obtained that is applicable to a wide range of alloys. Such models are useful in materials optimisation and selection.