Temperature and Orientation Dependence of the Mechanical Properties of Al0.3CoCrFeNi High-Entropy Alloy Single Crystals Hardened by Non-Coherent β- Phase Particles

Russian Physics Journal - Aging of the Al0.3CoCrFeNi high-entropy alloy single crystals for 50 h at a temperature of 973 K leads to the precipitation of non-coherent non-equiaxed β-phase...     

Studying the Effect of Cold Rolling and Heat Treatment on the Microstructure and Mechanical Properties of the Fe36Mn20Ni20Cr16Al5Si3 High Entropy Alloy

In this study, a multi-component FeMnNiCrAlSi high-entropy alloy, chosen through Thermo-Calc^® software (2021a, Stockholm, Sweden) calculation and produced by electric arc melting, was studied for phase continents and mechanical properties. The results elucidated that the cold rolled condition (area reduction ratio about 86%) was in the form of elongated grains with a dendritic structure. Also, small amounts of the BCC phase were precipitated at the grain boundaries. The annealed sample shows features of BCC phase and different sizes of intermetallics. These results coincided with the predictions of Thermo-Calc^® software calculations. A cold rolled sample showed high compressive yield strength of about 950 MPa, and the annealed sample had only half the strength of the cold rolled condition. The cold rolled sample shows the highest micro-hardness. The wear resistance of the annealed condition was significantly improved at room temperature and at 200 °C. The brittle phases in the annealed condition have a positive impact on the wear resistance.     

Nanoparticle-Reinforced Silica Gels with Enhanced Mechanical Properties and Excellent pH-Sensing Performance

Silica gels offer excellent wear resistance, high chemical stability, good insulation, and light transmittance, are therefore promising to engineer 2D sensing films. However, their practical applications are greatly hampered by their poor structural stability, low sensitivity, reliability, and repeatability. Incorporation of nanoelements into glasses and ceramics is a promising new pathway to tackle these challenges. Unfortunately, it is difficult to disperse nanoparticles uniformly in any glass and ceramics. Herein, a facile sol–gel approach is applied to synthesize novel silica gel nanocomposites with dispersed nanoparticles (NPs) as additives and thymol blue as an indicator. Titanium dioxide (TiO₂) NPs with a diameter of 5 nm can be dispersed uniformly in the silica gel, with enhanced modulus and hardness (up to 230% and 138%, respectively) and good alkaline resistance. The addition of nanoparticles improves the film's stability, sensitivity, and repeatability of spectral responses (in pH 1–12), and reduces the indicator leakage. The interaction of indicator with silica gel substrate, nanoparticles, and H⁺ is analyzed to elucidate the principle of reversible color change. This novel simplified method to produce glass-like functional materials under much lower temperatures is groundbreaking in materials science and engineering.     

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔS_mix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, Ti_xZr_2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of Ti_xZr_2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔS_mix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, Ti_xZr_2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti_2.0Zr_0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.     

Investigation on the microstructure of a τ-Mg32(Al,Zn)49 strengthened Mg–Zn–Al alloy with relatively low Zn content

In the present work different orthogonal tight-binding molecular dynamics methods have been employed for describing small silicon clusters. The cohesive energies calculated using these methods have been compared with those found from the first principles Car-Parrinello method. The comparison shows that the orthogonal tight binding matrix elements and repulsive potentials need to include the radial cutoff up to fourth neighbor distance in diamond structure in order to reproduce ab initio results. The environmental correction is not needed in this orthogonal tight-binding method.     

Synthesis and Properties of Polyacrylamide-Based Conducting Gels with Enhanced Mechanical Strength

A nanocomposite conducting hydrogel, polyacrylamide/MWNT/clay (abbreviated as PAM/MWNT/clay), prepared through in situ free radical aqueous polymerization and crosslinked by both clay, as a functional physical crosslinker, and N,N′-methylenebisacrylamide (MBA) as a chemical crosslinker, is reported. The morphology of the gels was characterized by scanning electron microscopy (SEM). The mechanical properties and electrical conductivity were also studied. The results show that the prepared hydrogels had the expected chemical components, with a highly porous structure, and the gels also showed high mechanical strength. The mechanical strength and electrical conductivity value increased with increasing content of multi-walled nanotube (MWNT), and decreased with increasing content of water.     

Microstructure and Mechanical Properties of Isotactic Polypropylene Films Fabricated via Melt-Extrusion and Uniaxial-Stretching

In this work, isotactic polypropylene (iPP) melt was slowly extruded through a slit die of a single-screw extruder. Once the iPP melt left the die, it was uniaxially stretched at different stretching rates (SRs). Via this process its microstructure can be manipulated, it was subsequently investigated by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and Fourier transform infrared spectroscopy (FTIR). Furthermore, the mechanical properties (including tensile strength, modulus, toughness, and strain-hardening) were investigated. The results showed that the tensile strength and modulus of the melt-stretched iPP films gradually increased with increasing SRs. In addition, the toughness and elongation at break showed maximum values for iPP films melt-stretched at 30 cm/min. Moreover, compared with other melt-stretched films, the iPP films melt-stretched at 90 cm/min exhibited an obvious strain-hardening behavior at lower strain.     

Effect of Silica and Silicone Oil on the Mechanical and Thermal Properties of Silicone Rubber

The effect of three types of silicas with varied loading and the loading of hydroxyl terminated silicone oil on the mechanical and thermal properties of silicone rubbers (SRs) were investigated. Mechanical properties were affected by the silica loading because of the interaction between fillers and polymer and the filler dispersion. Fumed silica filled SRs showed higher tanδ, tensile strength, and elongation at break compared to those containing two types of precipitated silicas. With increasing silicone oil loading, the tensile strength, tear strength, hardness, and tanδ of SRs first increased and then decreased.     

Influence of Mo on the Microstructure and Corrosion Behavior of Laser Cladding FeCoCrNi High-Entropy Alloy Coatings

FeCoCrNi and FeCoNiCrMo_0.2 high-entropy alloy powders were prepared by gas atomization. Two kinds of coatings were prepared on the surface of 304 stainless steel by laser cladding technology. The effect of Mo element on the microstructure of laser cladding FeCoCrNi coating and its corrosion behavior in 3.5 wt.% NaCl solution was investigated. Both FeCoCrNi and FeCoCrNiMo_0.2 powders exhibit a single-phase FCC structure. Due to the remelting and multiple heat treatments during the preparation of the laser cladding coating, a small amount of σ and μ phases appeared in the FeCoCrNiMo_0.2 coating. The microstructures of the two coatings from the bonding area to the top layer are planar, columnar and equiaxed grains, respectively. The addition of the Mo element causes the dendrite size in the middle region of the FeCoCrNiMo_0.2 coating increases significantly and exhibits obvious orientation characteristics. FeCoCrNiMo_0.2 coating has high corrosion potential (−0.01 V_SHE) and low current density (0.94 × 10⁻⁷ A/cm²) in 3.5 wt.% NaCl solution, showing excellent corrosion resistance. The passivation film formed on corroded the FeCoCrNiMo_0.2 coating contains high content of oxides of Cr and Mo. The addition of the Mo element enhances the compactness and pitting resistance of the passivation film.     

Microstructure and Properties of Polypropylene/Clay Nanocomposites

Nanocomposites of polypropylene (PP) containing various contents of Cloisite 15A nanoclay particles were prepared by one-step melt compounding in a twin screw extruder. Tensile and impact properties of the nanocomposite systems were investigated and correlated with their microstructures. The tensile modulus increased with an increase in Cloisite 15A content but the tensile strength, elongation at break, and impact strength were decreased. WAXS and TEM studies showed almost exfoliated structures. There was a decrease in permeability values with an increase in nanoclay content up to 5 wt. %. Exceeding this content of nanoclay had no significant effect on permeation due to the aggregation phenomenon at high concentrations of the nanoparticles. Most of the examined micromechanical models for prediction of the tensile modulus of the nanocomposite were successful despite being based on fiber-shaped fillers. An exfoliated structure of clay within the nanocomposite was assumed for the modeling using a molecular dynamics simulations approach, employing Dreiding, Forcite, and COMPASS force fields, in order to investigate the best one for a successful estimation of elastic modulus. Relative to the experimental modulus values of the nanocomposites, which were around 1100–1200 MPa, the COMPASS force field had the best correlation with the values with a slight departure of about 10%.     

Effect of Silanes on Mechanical and Thermal Properties of Silicone Rubber/EPDM Blends

The effect of four types of silane coupling agents on the mechanical and thermal properties of silicone rubber and ethylene–propylene–diene monomer (M-class) rubber (EPDM) blends is studied, namely, isobutyltriethoxysilane (BUS), acryloxypropyltriethoxysilane (ACS), aminopropyltriethoxysilane (AMS), and vinyltriethoxysilane (VIS). ACS and VIS increase the crosslink density of the blends, which results in higher tensile strength, modulus, and thermal stability, but lower elongation at break compared with the other silanes. However, the blend containing BUS shows highest tanδ in the temperature range of 45°C to 200°C. Thermogravimetric analysis shows two steps of degradation for all the samples, but little difference with the varied silanes.     

Mechanical Properties and Flow Behavior of Polymers for Enhanced Oil Recovery

The mechanical properties and flow behavior in porous media of three different polymer systems including a hydrophobically modified acrylamide-based copolymer (HMSPAM), a partially hydrolyzed polyacrylamide (HPAM), and a polysaccharide (xanthan gum) were evaluated to establish their functional differentiation as mobility control agents in enhanced oil recovery (EOR). The rheological properties of the polymers were described by the power-law model to investigate their non-Newtonian behavior. The first normal stress difference (N₁) and Weissenberg number (W_e) were also used to compare their elastic properties. The experimental results showed that, at comparable shear viscosity, HMSPAM exhibited significant elasticity compared to HPAM and xanthan gum. Shear resistance tests indicated that all of the polymers experienced an extra stress when converging into a capillary tube due to the “entrance effect.” Xanthan gum was the most mechanically stable polymer. Moreover, HMSPAM showed the superior reformability which was quantified by the regained viscosity with relaxation time. This could be explained by the rapid re-association of the hydrophobic interactions. Sandpack flood tests indicated that HMSPAM rendered extremely high mobility control ability during polymer flooding suggesting its potential in EOR. However, this polymer also experienced significant retention within the porous media (potential injectivity and plugging problems), which may be attributed to the formation of bulky associative polymer networks. In this work, UV spectrometry was employed to monitor the concentration of the produced polymer solutions and quantify the polymer retention within porous media. This analytical approach offers great reliability and simplicity. It was concluded that the use of a particular polymer system depends on the oil reservoir conditions and the target EOR application.     

Effect of Heat Treatment on the Mechanical and Tribological Properties of Polyphenylene Sulfide Fiber Materials

Polyphenylene sulfide (PPS) fiber materials, whose raw fibers had been heat treated previously for 1 to 5 days, were prepared by a hot-pressing method. The tribological properties of PPS resin and fiber materials against an AISI 1045 steel ring were evaluated using a block-on-ring wear tester. The results showed that the sample whose raw fibers had been heated at 240°C for 1 day (S1) exhibited the highest impact strength as well as the lowest friction coefficient and wear rate. The friction coefficient of S1 was 39% lower than that of the PPS resin material, and its wear rate was 1 to 2 orders of magnitude lower than those of the other samples. DSC analysis results indicated that the condensed structure of the samples gradually changed from the crystalline to the amorphous state with the increase of heat-treatment time of the raw fibers. DMA and DSC analysis results proved that severe, oxidative cross-linking reactions occurred when the raw fibers were heated over 3 days. It is concluded that proper heat treatment of the raw fibers is advantageous to improve the degree of crystallinity and appropriate oxidative cross-linking; therefore, the prepared PPS fiber material can exhibit better mechanical and tribological performances.     

Effect of Heat Treatememt on Microstructure and Mechanical Properties of the Precipitation Hardening Elinvar Alloy

Russian Physics Journal - This study presents the experimental results of structural analysis of the phase composition, grain size, plasticity, and hardness of the elinvar Ni-span-C alloy 902 after...     

Microstructure and Physical and Mechanical Properties of the Al90Gd10 Binary Alloy after Barothermal Treatment

Physics of the Solid State - Using the microindentation, X-ray diffraction, optical microscopy, and electron microscopy methods, the microstructure and bulk physical and mechanical properties...     

V-5Cr-5Ti合金弹性和力学性质的第一性原理研究

V-5Cr-5Ti合金作为核聚变堆第一包层的主要候选结构材料之一,但对其力学性质的理论研究相对较少.采用随机固溶体模型,利用第一性原理方法计算出V-5Cr-5Ti合金的弹性常数、体模量、剪切模量、杨氏模量、泊松比和柯西压力等,并与计算出的纯钒的相关数值进行对比,结果表明V-5Cr-5Ti合金具有良好的塑性和强度,但其塑性要略低于纯钒的.并对加入氧原子后的V-5Cr-5Ti合金进行了相关计算,通过对比计算结果发现,由于氧原子的加入,使V-5Cr-5Ti合金的塑性和强度都出现了不同程度的降低.最后对V-5Cr-5Ti合金和纯钒的理论强度进行了计算,并绘制出两者的应力-应变关系图,通过对比再次验证了上面的结论.     

Effects of Nb Additions and Heat Treatments on the Microstructure,Hardness and Wear Resistance of CuNiCrSiCoTiNbx High-Entropy Alloys

In this research, a set of CuNiCrSiCoTi (H-0Nb), CuNiCrSiCoTiNb_0.5 (H-0.5Nb) and CuNiCrSiCoTiNb₁ (H-1Nb) high-entropy alloys (HEAs) were melted in a vacuum induction furnace. The effects of Nb additions on the microstructure, hardness, and wear behavior of these HEAs (compared with a CuBe commercial alloy) in the as-cast (AC) condition, and after solution (SHT) and aging (AT) heat treatments, were investigated using X-ray diffraction, optical microscopy, and electron microscopy. A ball-on-disc configuration tribometer was used to study wear behavior. XRD and SEM results showed that an increase in Nb additions and modification by heat treatment (HT) favored the formation of BCC and FCC crystal structures (CS), dendritic regions, and the precipitation of phases that promoted microstructure refinement during solidification. Increases in hardness of HEA systems were recorded after heat treatment and Nb additions. Maximum hardness values were recorded for the H-1Nb alloy with measured increases from 107.53 HRB (AC) to 112.98 HRB, and from 1104 HV to 1230 HV (aged for 60 min). However, the increase in hardness caused by Nb additions did not contribute to wear resistance response. This can be attributed to a high distribution of precipitated phases rich in high-hardness NiSiTi and CrSi. Finally, the H-0Nb alloy exhibited the best wear resistance behavior in the aged condition of 30 min, with a material loss of 0.92 mm³.     

碲镉汞红外焦平面探测器封装用4J36合金深低温力学性能研究

为了提高碲镉汞红外焦平面探测器封装结构的可靠性,获得组件材料的深低温力学性能十分重要.4J36合金具有极低的膨胀系数且材料焊接性能较好,广泛应用于封装结构中的冷平台部分.本文在300 K～4.2 K温度区间内对4J36合金进行了热力学性能试验,获得了材料随温度变化的动态热力学参数;在300 K、77 K、4.2 K温度下对4J36试件进行了拉伸试验,获得了相应的工程应力应变曲线和力学性能参数;通过扫描电镜对断口形貌进行了微观结构分析,获得了4J36合金拉伸断口微观组织和性能的变化规律.试验结果表明4J36材料在300 K～4.2 K温度范围内平均线膨胀系数为2.08×10^-6/K,从300 K到77 K,4J36合金的比热容随温度降低而减小;在300K～4.2 K温度区间内,随温度降低,合金的抗拉强度和屈服强度显著提高,而弹性模量断后伸长率降低;由拉伸断口宏观和微观形貌看出在300 K、77 K和4.2 K下4J36合金拉伸试件的断裂模式均为韧性断裂.试验研究结果将对4J36合金在红外焦平面探测器组件的低温应用方面提供试验依据.     

Recent Advances in Friction Stir Welding/Processing of Aluminum Alloys: Microstructural Evolution and Mechanical Properties

Friction stir welding (FSW), a highly efficient solid-state joining technique, has been termed as “green” technology due to its energy efficiency and environment friendliness. It is an enabling technology for joining metallic materials, in particular lightweight high-strength aluminum and magnesium alloys which were classified as unweldable by traditional fusion welding. It is thus considered to be the most significant development in the area of material joining over the past two decades. Friction stir processing (FSP) was later developed based on the basic principles of FSW. FSP has been proven to be an effective and versatile metal-working technique for modifying and fabricating metallic materials. FSW/FSP of aluminum alloys has prompted considerable scientific and technological interest since it has a potential for revolutionizing the manufacturing process in the aerospace, defense, marine, automotive, and railway industries. To promote widespread applications of FSW/FSP technology and ensure the structural integrity, safety and durability of the FSW/FSP components, it is essential to optimize the process parameters, and to evaluate thoroughly the microstructural changes and mechanical properties of the welded/processed samples. This review article is thus aimed at summarizing recent advances in the microstructural evolution and mechanical properties of FSW/FSP aluminum alloys. Particular attention is paid to recrystallization mechanism, grain boundary characteristics, phase transformation, texture evolution, characteristic microstructures, and the effect of these factors on the hardness, tensile and fatigue properties as well as superplastic behavior of FSW/FSP aluminum alloys.     

应力下MnGa合金体电子性质及磁性质的研究

采用密度泛函理论方法系统研究分析了四方结构MnGa合金体在a轴1GPa应力下的结构、形成、电子性质和磁性质.结果表明,应力下MnGa合金a, b轴晶格参数增大,c轴晶格参数减小,三轴夹角有偏离90°的趋势,晶胞体积增大. Mn-Ga不成键,Mn-Mn之间的强键作用进一步增强,Ga-Ga之间的强键作用消失. Mn-Mn结合键长和Ga-Ga结合键长均减小,而Mn-Ga间距增大,排斥作用减弱.应力下MnGa合金形成焓由-4.85 eV减小到-5.4 eV,其更容易生成.应力下其能带整体向下移动,导带和浅能级价带分布较宽,有效质量较小;深能级价带分布较窄,有效质量较大.自旋向下的电子能带没有带隙,自旋向上的电子能带有0.26 eV的间接带隙. s电子和p电子主要形成导带和浅能级价带,自旋极化较弱,d电子主要形成深能级价带,定域性和自旋极化最强.两种占位的Ga具有近乎相同的电子形态,Ga的s电子和Ga的p电子产生较明显的自旋极化,形成弱的磁性,Ga的d电子主要贡献深能级处的态密度,基本不贡献磁性质.两种占位的Mn主要贡献费米能处的态密度,Mn的d电子自旋极化最强,在费米能级下方Mn1自旋向下的电...