Amorphous intergranular phases in mature natural tooth enamel are found to provide better adhesion and could dramatically affect their mechanical performance as a structure reinforcing phase. This ...study successfully synthesized an amorphous intergranular phase enhanced fluorapatite array controlled by Mg
(FAP-M) at room temperature. Furthermore, atom probe tomography (APT) observation presents that Mg
is enriched at grain boundaries during the assembly of enamel-like fluorapatite arrays, leading to the formation of intergranular phases of Mg-rich amorphous calcium phosphate (Mg-ACP). APT results also demonstrated that the segregation of Mg
caused the chemical gradient in nanocrystalline attachment and realignment under the drive of inherent surface stress. These results indicate that the amorphous intergranular phases served like glue to connect each nanorod to reinforce the enamel-like arrays. Therefore, the as-received FAP-M artificial enamel exhibits excellent mechanical properties, with hardness and Young's modulus of 2.90 ± 0.13 GPa and 67.9 ± 3.4 GPa, which were ∼8.3 and 2.2 times higher than those of FAP arrays without controlled by Mg
, respectively.
Cubic garnet Li
6.24
La
3
Zr
2
Al
0.24
O
11.98
(LLZO) is a candidate material for use as an electrolyte in Li–Air and Li–S batteries. The use of LLZO in practical devices will require LLZO to have ...good mechanical integrity in terms of scratch resistance (hardness) and an adequate stiffness (elastic modulus). In this paper, the powders were fabricated by powder processing of cast ingots. All specimens were then densified via hot pressing. The room temperature elastic moduli (Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio) and hardness were measured by resonant ultrasound spectroscopy, and Vickers indentation, respectively. For volume fraction porosity,
P
, the Young’s modulus was 149.8 ± 0.4 GPa (
P
= 0.03) and 132.6 ± 0.2 GPa (
P
= 0.06). The mean Vickers hardness was 6.3 ± 0.3 GPa for
P
= 0.03 and 5.2 ± 0.4 for
P
= 0.06.
The current work seeks to discover and choose the proper friction stir processing (FSP) settings for aluminum alloy 7075 surface composites enhanced by adding three unique nanoparticles of titanium ...dioxide (TiOsub.2), Bsub.4C, and graphene for superior performance. FSP is the only method that produces higher amounts of particle distribution and nanoscale reinforcing. For the sample fabrication, a special relatively high rotational speed of 2000 rpm and feed rate of 45 mm/min were tested with a suitable range of processing parameters (800–2000 rpm, 25–45 mm/min). To measure the micro-hardness and surface roughness of three different surface nano composites, they were studied under various FSP conditions. The findings showed that surface composites produced at high rotational speeds of 1400 rpm and 45 mm/min decreased surface roughness and granule distributions by 39% and 73%, respectively, and increased surface micro-hardness by 54%. According to the microstructure investigations, good bonding was produced between the AA7075 substrate generated at 1200 rpm and the base metal and friction stir processed specimens at 800 and 2000 rpm. The AA7075/Bsub.4C surface composite produced at 1200 rpm rotating speed had a higher micro-hardness than the other two surface composites.
The lattice parameters, formation energy and electronic structure as well as elastic property and Debye temperature of Ca-doped Ti.sub.2Ni alloy have been calculated. The results show that the ...structural stability of Ca replacing the Ti atomic site is more stable than that of Ca replacing the Ni atom. This is consistent with the calculated energy band structure and electronic density of the state. The elastic properties approximated by Voigt-Reuss-Hill formulae show that the ratio of bulk modulus to shear modulus and Poisson's ratio of Ca replacing Ni system are greater than that of Ca replacing Ti system, the interstitial doping system and the pure Ti.sub.2Ni alloy, implying that Ca replacing Ni is more malleable and the ductility of Ti.sub.2Ni alloy can be tailored by Ca doping. The hardness and Debye temperature also indicate that both ratios of Ca replacing Ti system are higher than that of Ca replacing Ni system.
The stabilities, mechanical and electronic properties and Debye temperature of three novel Cr.sub.2C structures (Pnnm, Amm2 and P-31m space groups) are investigated and discussed in this paper. All ...of them are thermodynamically, mechanically and dynamically stable. Notably, the hardness of Amm2 Cr.sub.2C is 26.30 GPa at ambient pressure, better than the known Cr.sub.2C structures. Based on the results of the density of state and Mulliken overlap population simulation, there is strong covalent-ionic Cr-C bonding interaction in Amm2 Cr.sub.2C, which is also revealed by the analysis of Debye temperature. Furthermore, the relative enthalpy as functional of pressure of all structures were calculated to understand their stabilities under high pressure. Overall, the predicted stable structures will provide more options to facility the synthesis and application of transition metal carbides.
In engineering projects (dams, tunnels, slope stability) the strength characteristics of the rocks affect the construction operations. It is sometimes difficult, time-consuming, and expensive to ...evaluate the engineering properties of solid rocks by performing direct tests. For this reason, various laboratory studies have been carried out by many researchers to predict important engineering properties such as uniaxial compressive strength (UCS) and elastic modulus (E) of rocks in a practical way. One of the engineering properties used to estimate UCS-E practically is the hardness of rocks. Hardness tests are easy to apply and non-destructive, and in many of these tests very small specimens are needed. The main objective of this study is to analyze the relations between the UCS-E of the rocks and the various hardness methods (Schmidt hammer hardness, SHH; Shore Scleroscope hardness, SSH; Vickers hardness, HV; Brinell hardness, HB; and Indentation hardness index, IHI). For this purpose, the most appropriate and meaningful relations between hardness tests and UCS-E were determined by simple regression (SR) techniques. Relationships between main engineering properties (UCS, E) and physicomechanical properties were analyzed by multiple regression (MR) techniques using SPSS software. The statistical analyses made revealed the existence of strong correlations between UCS-E and hardness properties of rocks.
Schmidt hammer hardness; Shore scleroscope hardness; Vickers hardness; Brinell hardness; Indentation hardness index; Multiple regression
The physical properties of molybdenum semi-carbide (Mo.sub.2C) that usually serves as reinforced phases of engineering alloys are crucial for mechanical properties of bulk materials. In this work, ...multi-element doping is employed to modify physical properties of Mo.sub.2C. The thermodynamic stability, mechanical and electronic properties of doped L'3- and ζ-(Mo, M).sub.2C (M = V, Cr, Fe and W) were examined by first-principles calculations and experiments. The results show that W stabilizes both L'3- and ζ-(Mo, M).sub.2C, whereas Cr and Fe destabilize them. Among the four dopants, W greatly enhances the elastic anisotropy and Cr increases the ductility while retaining high hardness. Compared with L'3-(Mo, M).sub.2C, ζ-(Mo, M).sub.2C exhibits higher thermodynamic stability and stronger elastic anisotropy. Multi-element doping alters the relative fractions of covalent, ionic and metallic bonds in the compounds, accounting for the correlation between various dopants and physical properties. Further experiments confirm the structural and compositional dependence of thermal stability, which agrees well with the theoretical predictions.
The near-infinite compositional space of high-entropy-alloys (HEAs) is a huge resource-intensive task for developing exceptional materials. In the present study, an algorithmic framework has been ...developed to optimize the composition of an alloy with chosen set of elements, aiming to maximize the hardness of the former. The influence of phase on hardness prediction of HEAs was thoroughly examined. This study aims to establish generalized prediction models that aren't confined by any specific set of elements. We trained the HEA identification model to classify HEAs from non-HEAs, the multi-labeled phase classification model to predict phases of HEAs also considering the processing route involved in the synthesis of the alloy, and the hardness prediction model for predicting hardness and optimizing the composition of the given alloy. The purposed algorithmic framework uses twenty-nine alloy descriptors to compute the composition that demonstrates maximum hardness for the given set of elements along with its phase(s) and a label stating whether it is classified as HEA or not.
Most data complexity studies have focused on characterizing the complexity of the entire data set and do not provide information about individual instances. Knowing which instances are misclassified ...and understanding why they are misclassified and how they contribute to data set complexity can improve the learning process and could guide the future development of learning algorithms and data analysis methods. The goal of this paper is to better understand the data used in machine learning problems by identifying and analyzing the instances that are frequently misclassified by learning algorithms that have shown utility to date and are commonly used in practice. We identify instances that are hard to classify correctly (
instance hardness
) by classifying over 190,000 instances from 64 data sets with 9 learning algorithms. We then use a set of hardness measures to understand why some instances are harder to classify correctly than others. We find that class overlap is a principal contributor to instance hardness. We seek to integrate this information into the training process to alleviate the effects of class overlap and present ways that instance hardness can be used to improve learning.
The paper suggests dependences of the energy flux and specific energy onto the substrate on the pulse duty cycle during the dual magnetron-sputter deposition of the TiAlN coating. It is shown that ...the energy flux at the substrate increases by 20-30% with decreasing duty cycle from 40 to 6% at the constant average discharge power. Together with a decrease in the deposition rate at the high pulsed power, the specific energy grows sixfold on the substrate during the coating growth. The duty cycle can be thus considered as a way to control the energy flux onto the deposited coating, which affects its structure and properties. It is found that the TiAlN coating obtained at low duty cycle and high energy flux onto the substrate, possesses the high hardness and wear resistance. Keywords: dual magnetron sputtering, TiAlN coating, energy flux, hardness, wear resistance.
