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.     

A novel hybrid multiple criteria decision making model for material selection with target-based criteria

In engineering design, the decision to select an optimal material for a particular product is a problem requiring multi-criteria decision analysis that involves both qualitative and quantitative factors. The evaluation of alternative materials may be based on imprecise information or uncertain data. Furthermore, there can be significant dependence and feedbacks between the different criteria for material selection. However, most existing decision approaches cannot capture these complex interrelationships. In response, this paper proposes a general framework for evaluating and selecting the best material for a given application. A novel hybrid multiple criteria decision making (MCDM) model combining DEMATEL-based ANP (DANP) and modified VIKOR is used to solve the material selection problems of multiple dimensions and criteria that are interdependent. Moreover, target-based criteria as well as cost and benefit criteria can be addressed simultaneously in the proposed model. Finally, an empirical case concerning the bush material selection for a split journal bearing is presented to illustrate the potential of the new model. The results show that the proposed method for material selection is effective and provides meaningful implications for designers and engineers to refer.     

Influence of ductile interlayers on mechanical behaviour of hard coatings under depth-sensing indentation: a numerical study on TiAlN

In order to determine the influence of interlayers of ductile metals on the overall mechanical properties of the multilayer coatings, three-dimensional numerical simulations of depth-sensing indentation tests of titanium aluminium nitride (TiAlN) hard coatings with copper, silver, aluminium and titanium ductile interlayers were performed. The contribution of ductile interlayers to altering the hardness, the Young’s modulus and H/E and H ²/E ratios of the multilayer coating with respect to a monolithic TiAlN hard coating was established for the cases of composites with different number and thicknesses of interlayers.     

Correlation between hardness and elastic moduli of the covalent crystals

From a statistical manner, we collected and correlated experimental bulk (B), shear (G), Young’s modulus (E), and ductility (G/B) with Vickers hardness (H_v) for a number of covalent materials and fitted quantitative and simple H_v–G and H_v–E relationships. Using these experimental formulas and our first-principles calculations, we further predicted the microhardness of some novel potential hard/superhard covalent compounds (BC₂N, AlMgB₁₄, TiO₂, ReC, and PtN₂). It was found that none of them are superhard materials (H_v ? 40 GPa) except BC₂N. The present empirical formula builds up a bridge between Vickers hardness and first-principles calculations that is useful to evaluate and design promising hard/superhard materials.     

Material screening and choosing methods – A review

The selection of a material for a specific engineering purpose is a lengthy and expensive process. Approximately always more than one material is suitable for an engineering application, and the final selection is a compromise that brings some advantages as well as disadvantages. One of the issues that emerges from this review is that regardless of the relation of design stages and process selection with material selection, screening and ranking are two vital steps in the material selection. A variety of quantitative selection procedures have been developed to solve this issue, so that a systematic evaluation can be made. This paper seeks to address the following questions: (1) what is the contribution of the literature in the field of screening and choosing the materials? (2) What are the methodologies/systems/tools for material selection of engineering components? (3) Which approaches were prevalently applied? (4) Is there any inadequacy of the approaches? This research not only provides evidence that the multi-criteria decision making approaches has the potential to greatly improve the material selection methodology, but also aids the researchers and decision makers in applying the approaches effectively.     

The influence of low-energy ion bombardment on the microstructure development and mechanical properties of TiBx coatings

The influence of the deposition parameters on the growth, structure and mechanical properties of the TiB_x coatings is studied. The TiB_x coatings represent a nanocomposite system, in which random or oriented TiB₂ nanocrystallites are embedded in an amorphous matrix as is revealed by cross-sectional transmission electron microscopy. We show that low-energy ion bombardment (E_i ) of growing TiB_x coating, influences the preferred orientation of TiB₂ crystallites. The increase of ion current density (i_s) by means of negative substrate bias voltage (U_s) leads to change from random to the (0001) preferred crystal orientation whereby the electrical biasing promotes crystal growth in the coating and the (0001) texture appears gradually during the film growth. Together with the (0001) preferred orientation selection the composition B/Ti ratio was changed from 2.9 (floating potential, E_i = 8 eV) to 2.4 (E_i = 94 eV). The highest amount of oriented (0001) crystallites and highest hardness H = 53 GPa exhibit TiB_x coatings deposited at E_i = 94 eV and i_s = 2.69 mA.cm⁻².     

Effect of erodent properties on the solid particle erosion mechanisms of brittle materials

In order to study the effects of particle properties on the solid particle erosion mechanisms of brittle bulk materials, six target materials were tested using two different powders (alumina and glass) at velocities ranging from 25 to 75 m/s. Following in depth characterizations of the targets and of the particles before and after testing, it was found that lateral fracture was the dominant material removal mechanism as predicted by the elasto-plastic theory of erosion. In the case of glass powder, for which the hardness of the particle is lower than the hardness of the target, particle deformation and fragmentation were found to be important factors explaining lower erosion rates. The higher than predicted velocity exponents point toward a velocity-dependent damage accumulation mechanism which was found to be correlated to target yield pressure (H ³ /E ²). Although damage accumulation seems to be necessary for material removal when using both powders, the effect is more pronounced for the softer glass powder because of kinetic energy dissipation through different means.     

Influence of the connectivity pattern,the nature of the piezoelectric material,and rod thickness on the properties of 50 vol % PZT/50 vol % NiCo0.02Cu0.02Mn0.1Fe1.8O4 − δ magnetoelectric composites

We have studied the influence of the connectivity pattern, the nature of the piezoelectric material, and rod thickness on the properties of magnetoelectric composites with the composition 50 vol % PZT/50 vol % NiCo_0.02Cu_0.02Mn_0.1Fe_1.8O_{4 ? δ} (where PZT stands for various commercially available lead zirconate titanate based piezoelectric materials). The results indicate that the magnetoelectric conversion efficiency of the rod composites with any connectivity pattern (1-1, 1-3, or 3-1) is 10–20% higher than that of laminate composites. The largest magnetoelectric conversion coefficient ΔE/ΔH is offered by the 1-1 connectivity composites. The ΔE/ΔH of the composites correlates with both their piezoelectric sensitivity g ₃₃ and the piezoelectric sensitivity of the corresponding piezoelectric materials. ΔE/ΔH is shown to be inversely proportional to the thickness of the piezoelectric and ferrite rods. The highest ΔE/ΔH at a frequency of 1 kHz, 450 mV/(cm Oe), has been reached in the PZT-36 based composites with 1-1 connectivity and 0.3-mm-thick rods.     

A novel quantum-inspired evolutionary view selection algorithm

A data warehouse (DW) is designed primarily to meet the informational needs of an organization’s decision support system. Most queries posed on such systems are analytical in nature. These queries are long and complex, and are posed in an exploratory and ad-hoc manner. The response time of these queries is high when processed directly against a continuously growing DW. In order to reduce this time, materialized views are used as an alternative. It is infeasible to materialize all views due to storage space constraints. Further, optimal view selection is an NP-Complete problem. Alternately, a subset of views, from amongst all possible views, needs to be selected that improves the response time for analytical queries. In this paper, a quantum-inspired evolutionary view selection algorithm (QIEVSA) that selects Top-K views from a multidimensional lattice has been proposed. Experimental comparison of QIEVSA with other evolutionary view selection algorithms shows that QIEVSA is able to select Top-K views that are comparatively better in reducing the response times for analytical queries. This in turn aids in efficient decision making.     

Effects of High Pressure on the Physical Properties of MgB2

The synthesis of MgB₂-based materials under high pressure gave the possibility to suppress the evaporation of magnesium and to obtain near theoretically dense nanograined structures with high superconducting, thermal conducting, and mechanical characteristics: critical current densities of 1.8?C1.0×10⁶ A/cm² in the self-field and 10³ A/cm² in a magnetic field of 8 T at 20 K, 5?C3×10⁵ A/cm² in self-field at 30 K, the corresponding critical fields being H _c2=15 T at 22 K and irreversible fields H _irr=13 T at 20 K, and H _irr=3.5 T at 30 K, thermal conduction of 53±2 W/(m?K), the Vickers hardness H _V =10.12±0.2 GPa under a load of 148.8 N and the fracture toughness K _1C =7.6±2.0 MPa?m^0.5 under the same load, the Young modulus E=213 GPa. Estimation of quenching current and AC losses allowed the conclusion that high-pressure-prepared materials are promising for application in transformer-type fault current limiters working at 20?C30 K.     

Influence of the microstructure on the mechanical and tribological behavior of TiC/a-C nanocomposite coatings

The performance of protective thin films is clearly influenced by their microstructure. The objective of this work is to study the influence of the structure of TiC/a-C nanocomposite coatings with a-C contents ranging from ~ 0% to 100% on their mechanical and tribological properties measured by ultramicroindentation and pin-on-disks tests at ambient air, respectively. The microstructure evolves from a polycrystalline columnar structure consisting of TiC crystals to an amorphous and dense TiC/a-C nanocomposite structure when the amount of a-C is increased. The former samples show high hardness, moderate friction and high wear rates, while the latter ones show a decrease in hardness but an improvement in tribological performance. No apparent direct correlation is found between hardness and wear rate, which is controlled by the friction coefficient. These results are compared to the literature and explained according to the different film microstructures and chemical bonding nature. The film stress has also been measured at the macro and micro levels by the curvature and Williamson-Hall methods respectively. Other mechanical properties of the coating such as resilience and toughness were evaluated by estimating the H³/E?² and H/E? ratios and the percentage of elastic work (W_e). None of these parameters showed a tendency that could explain the observed tribological results, indicating that for self-lubricant nanocomposite systems this correlation is not so simple and that the assembly of different factors must be taken into account.     

Mechanical,tribological and anti-corrosive properties of polyaniline/graphene coated Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys

The mechanical, tribological and corrosion protection offered to Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys by the epoxy coating containing polyaniline/graphene (PANI/Gr) pigments is undertaken in the current work. PANI/Gr containing coatings were observed to be strongly adherent with a higher scratch hardness (H_s) and plowing hardness (H_p), i.e. H_s of 0.43 GPa, and H_p of 0.61 GPa, respectively when compared to that of neat epoxy coating (H_s of 0.17 GPa, and H_p of 0.40 GPa, respectively). Due to their higher H_s and H_p values, PANI/Gr based coatings displayed an enhanced wear resistance (Wear volume, W_v = 4.53 × 10^-3 m³) than that of neat epoxy coating (W_v = 5.15 × 10⁻³ m³). The corrosion protection efficiency in corrosive environment of 3.5 wt% NaCl solution was obtained to be >99% for PANI/Gr containing coatings when compared to that of neat epoxy coating. The charge-transfer resistance (R_ct) of the PANI/Gr containing coatings were estimated to be >10⁶ Ω cm², which indicates their highly protective nature when compared to that of neat epoxy coating (R_ct ˜10⁵ Ω cm²). Hence, PANI/Gr containing coatings can be potentially used for wear resistance and corrosion protection applications in marine environments.     

Nanoindentation of multilayered epitaxial YBa2Cu3O7-δ thin films and coated conductors

Nanoindenter tests were carried out on YBa₂Cu₃O_7-δ (YBCO) coatings with different buffer layers, in order to obtain the Hardness (H) tendency, Young's modulus (E), and the fracture mechanism activated during the indentation process. Different pop-ins were observed in the load-displacement curves, and correlated with their residual nanoindentation imprints visualized by Atomic Force Microscopy. A trench was made by Focused Ion Beam in order to better understand the plastic behaviour activated under the residual imprint at 650 mN of applied load. During the first steps of nanoindentation experiments an elastic regimen takes place and the Hertzian equations can be applied to obtain the E for each YBCO coating. All YBCO coatings present similar E values and H tendencies. However, the YBCO/CeO₂/Yttrium Stabilized Zirconia system exhibits a better mechanical stability probably due to the absence of microcracks under the indentation. In addition, an experimental process using nanoindentation technique is obtained in order to isolate the kind of buffer layer employed (single crystal substrate or metallic substrate).     

Mechanical characterization of zeolite low dielectric constant thin films by nanoindentation

With semiconductor technologies continuously pushing the miniaturization limits, there is a growing interest in developing novel low dielectric constant materials to replace the traditional dense SiO₂ insulators. In order to survive the multi-level integration process and provide reliable material and structure for the desired integrated circuits (IC) functions, the new low-k materials have to be mechanically strong and stable. Therefore the material selection and mechanical characterization are vital for the successful development of next generation low-k dielectrics. A new class of low-k materials, nanoporous pure-silica zeolite, is prepared in thin films using IC compatible spin coating process and characterized using depth sensing nanoindentation technique. The elastic modulus of the zeolite thin films is found to be significantly higher than that of other low-k materials with similar porosity and dielectric constants. Correlations between the mechanical, microstructural and electrical properties of the thin films are discussed in detail.     

Nanoindentation as a means for distinguishing clinical type of osteogenesis imperfecta

Due to abnormalities in basic bone building components (collagen and mineral), the intrinsic material properties of Osteogenesis Imperfecta (OI) bone were hypothesized to be degraded and correlated to clinical types. Nanoindentation techniques were used to compare intrinsic mechanical properties of OI types III and IV bone. Young’s modulus (E) and hardness (H) were measured using the Oliver–Pharr method. Analysis showed that no significant difference existed in Young’s modulus and hardness measurements. However, the ratio of E/H exhibited a significant decrease for OI type III bone tissue. Since the ratio is proportional to fracture toughness, the decreased E/H indicates less fracture resistance for OI type III, which is consistent to the clinical observation. The results of this study suggest that nanoindentation may serve as a means to distinguish clinical types of OI.     

基于相对关联度的工程选材决策模型及应用

 根据灰色关联度反映候选材料的理想解之间曲线形状的相似性,在综合考虑正、负理想解影响的基础上,通过构造相对关联度,建立工程选材决策模型.以低温存储罐材料选择为例,根据专家评分得到所选8种评价指标的权重,确定理想解和负理想解,继而分别计算10种候选低温材料的相对关联度,进行选材决策.结果表明：全硬态301型不锈钢的相对关联度最高,是最佳的低温存储罐材料,这与实际应用和加权性质分析法得出的选择结果一致,而且所得其他候选材料的测评效果排序也更加合理.该模型同时反映候选材料的理想解和负理想解之间曲线的相似性,物理含义更加明确,分析问题更加全面、客观,是工程选材决策的有力工具.     

Suitability of various excipients as carrier and coating materials for liquisolid compacts

Context: The liquisolid technology is a promising technique for the release enhancement of poorly soluble drugs. With this approach, liquids such as solutions or suspensions of poorly soluble drugs in a non-volatile liquid vehicle are transformed into acceptably flowing and compressible powders. As fast-release liquisolid compacts require a high amount of liquid vehicle, more effective tableting excipients for liquid adsorption are needed to reduce tablet weight.

Objective: The aim of this study was to investigate the suitability of various novel tableting excipients as carrier and coating materials for liquisolid compacts.

Materials and methods: Liquisolid compacts containing the liquid drug tocopherol acetate (TA) as model drug and various excipients were prepared. The effect of liquid drug content on the flowability and tabletability of the liquisolid powder blends as well as the disintegration of the liquisolid compacts was studied. From this data, the maximum liquid adsorption capacity of the respective mixtures of carrier and coating materials could be determined.

Results and discussion: The liquid adsorption capacity depends on the specific surface area of the investigated excipients. Fujicalin^® and especially Neusilin^® are more effective carrier materials for liquid adsorption than Avicel^®, which is often used for liquisolid systems. Moreover, Florite^® and Neusilin^® turned out to be more suitable as coating materials than the commonly used Aerosil^® due to their better tableting properties.

Conclusion: If Neusilin^® is used as carrier and coating material instead of Avicel^® (carrier material) and Aerosil^® (coating material), the TA adsorption capacity is increased by a factor of 7.     

A novel multiple attribute material selection approach with uncertain membership linguistic information

In engineering design, the decision to select an optimal material has become a challenging task for the designers, and the evaluation of alternative materials may be based on some multiple attribute decision making (MADM) methods. However, the current methods for material selection may induce the information losing and cannot represent the real preference of decision maker precisely. Therefore, in this paper, inspired by the idea of the intuitionistic linguistic variables, we define a new fuzzy variable called uncertain membership linguistic variable (UMLV) which composes two linguistic variables and membership degrees of elements to the linguistic variables. Meanwhile, the operational laws, score function, accuracy function and comparison rules of the UMLV are defined. Then, some aggregation operators are developed for aggregating the uncertain membership linguistic information such as the uncertain membership linguistic weighted average (UMLWA) operator, the uncertain membership linguistic weighted geometric (UMLWG) operator, the uncertain membership linguistic ordered weighted average (UMLOWA) operator and the uncertain membership linguistic ordered weighted geometric (UMLOWG) operator, and some desirable properties of these operators are discussed. Based on the proposed operators, an approach is proposed for material selection problems under uncertain membership linguistic environment. Finally, two numerical examples for material selection are given to illustrate the application of the proposed approach.     

MCM-41 deposition on alumina ceramic foams

Alumina-based macro-porous ceramic foams were successfully coated with MCM-41 meso-porous materials using an in-situ one step hydrothermal synthesis. Low H₂O/NaOH ratio in the starting mixture leads to a not uniform deposition of the meso-porous materials. Using higher H₂O/NaOH ratio and two cycles of deposition, a CF with a continuous and thick layer of well-ordered MCM-41 material coating was produced.     

Fatigue behavior of rigid polymeric materials and composites at room and elevated temperature

In order to characterize the fatigue behavior of rigid polymeric materials, various thermoplastics and glassfiber reinforced plastics (thermoplastics and thermosets) were tested under alternating plane bending stresses at room (20°C) and elevated (50°C) temperatures. Increase in surface temperature and decrease in flexural rigidity of specimens were also measured during the fatigue testing. The results revealed that

1. Rigid polymeric materials can be classified into 3 groups according to their temperature rise characteristics (ΔT) and rigidity decrease (ΔE) during fatigue testing as follows: Group I. lower ΔT and ΔE: for unreinforced thermoplastics and bulk molding compound. Group II. higher ΔT and ΔE: for glassfiber reinforced thermoplastics and thermosets. Group III. higher ΔT and ΔE: for unreinforced thermoplastics.
2. Fatigue strengths of 10⁷ cycles of these materials of groups I～III are well correlated with their elastic moduli, respectively.