Microstructure,Hardness, and Elastic Modulus of a Multibeam-Sputtered Nanocrystalline Co-Cr-Fe-Ni Compositional Complex Alloy Film

A nanocrystalline Co-Cr-Ni-Fe compositional complex alloy (CCA) film with a thickness of about 1 micron was produced by a multiple-beam-sputtering physical vapor deposition (PVD) technique. The main advantage of this novel method is that it does not require alloy targets, but rather uses commercially pure metal sources. Another benefit of the application of this technique is that it produces compositional gradient samples on a disk surface with a wide range of elemental concentrations, enabling combinatorial analysis of CCA films. In this study, the variation of the phase composition, the microstructure (crystallite size and defect density), and the mechanical performance (hardness and elastic modulus) as a function of the chemical composition was studied in a combinatorial Co-Cr-Ni-Fe thin film sample that was produced on a surface of a disk with a diameter of about 10 cm. The spatial variation of the crystallite size and the density of lattice defects (e.g., dislocations and twin faults) were investigated by X-ray diffraction line profile analysis performed on the patterns taken by synchrotron radiation. The hardness and the elastic modulus were measured by the nanoindentation technique. It was found that a single-phase face-centered cubic (fcc) structure was formed for a wide range of chemical compositions. The microstructure was nanocrystalline with a crystallite size of 10–27 nm and contained a high lattice defect density. The hardness and the elastic modulus values measured for very different compositions were in the ranges of 8.4–11.8 and 182–239 GPa, respectively.     

Microstructure,Micro-Mechanical and Tribocorrosion Behavior of Oxygen Hardened Ti–13Nb–13Zr Alloy

In the present work, an oxygen hardening of near-β phase Ti–13Nb–13Zr alloy in plasma glow discharge at 700–1000 °C was studied. The influence of the surface treatment on the alloy microstructure, tribological and micromechanical properties, and corrosion resistance is presented. A strong influence of the treatment on the hardened zone thickness, refinement of the α’ laths and grain size of the bulk alloy were found. The outer hardened zone contained mainly an oxygen-rich Ti α’ (O) solid solution. The microhardness and elastic modulus of the hardened zone decreased with increasing hardening temperature. The hardened zone thickness, size of the α’ laths, and grain size of the bulk alloy increased with increasing treatment temperature. The wear resistance of the alloy oxygen-hardened at 1000 °C was about two hundred times, and at 700 °C, even five hundred times greater than that of the base alloy. Oxygen hardening also slightly improved the corrosion resistance. Tribocorrosion tests revealed that the alloy hardened at 700 °C was wear-resistant in a corrosive environment, and when the friction process was completed, the passive film was quickly restored. The results show that glow discharge plasma oxidation is a simple and effective method to enhance the micromechanical and tribological performance of the Ti–13Nb–13Zr alloy.     

Effect of Thermal Properties of Aggregates on the Mechanical Properties of High Strength Concrete under Loading and High Temperature Conditions

The effect of the thermal properties of aggregates on the mechanical properties of high-strength concrete was evaluated under loading and high-temperature conditions. For the concrete, granite was selected as a natural aggregate, and ash-clay and clay as lightweight aggregates. The mechanical properties of the concrete (stress–strain, compressive strength, elastic modulus, thermal strain, and transient creep) were evaluated experimentally under uniform heating from 20 to 700 °C while maintaining the load at 0, 20, and 40% of the compressive strength at room temperature. Experimental results showed that the concrete containing lightweight aggregates had better mechanical properties, such as compressive strength and elastic modulus, than that of the concrete with a granite aggregate at high temperature. In particular, the concrete containing lightweight aggregates exhibited high compressive strength (60–80% of that at room temperature) even at 700 °C. Moreover, the concrete containing granite exhibited a higher thermal strain than that containing lightweight aggregates. The influence of the binding force under loaded conditions, however, was found to be larger for the latter type. The transient creep caused by the loading was constant regardless of the aggregate type below 500 °C but increased more rapidly when the coefficient of the thermal expansion of the aggregate was above 500 °C.     

Creep Resistance of S304H Austenitic Steel Processed by High-Pressure Sliding

Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500–700 °C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500 °C. However, a further increase in creep temperature to 600 °C and 700 °C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600 °C and its formation was enhanced after recrystallization at 700 °C.     

FeZrN Films: Magnetic and Mechanical Properties Relative to the Phase-Structural State

The paper presents results of investigation of Fe_65.3–100Zr_34.7–0N_7.5–0 films prepared by dc magnetron deposition on glass substrates and subsequent 1-hour annealing at temperatures of 300–600 °C. The influence of the chemical and phase compositions and structure of the films, which were studied by TEM, SEM, XRD, and GDOES, on their mechanical properties determined by nanoindentation and static magnetic properties measured by VSM method is analyzed. The studied films exhibit the hardness within a range of 14–21 GPa, low elastic modulus (the value can reach 156 Gpa), and an elastic recovery of 55–83%. It was shown that the films are strong ferromagnets with the high saturation induction Bs (up to 2.1 T) and low coercive field Hc (as low as 40 A/m). The correlations between the magnetic and mechanical properties, on one hand, and the chemical composition of the films, their phase, and structural states as well, on the other hand, are discussed.     

Molecular Dynamics Study on Mechanical Properties of Nanopolycrystalline Cu–Sn Alloy

Molecular dynamics simulation is one kinds of important methods to research the nanocrystalline materials which is difficult to be studied through experimental characterization. In order to study the effects of Sn content and strain rate on the mechanical properties of nanopolycrystalline Cu–Sn alloy, the tensile simulation of nanopolycrystalline Cu–Sn alloy was carried out by molecular dynamics in the present study. The results demonstrate that the addition of Sn reduces the ductility of Cu–Sn alloy. However, the elastic modulus and tensile strength of Cu–Sn alloy are improved with increasing the Sn content initially, but they will be reduced when the Sn content exceeds 4% and 8%, respectively. Then, strain rate ranges from 1 × 10⁹ s⁻¹ to 5 × 10⁹ s⁻¹ were applied to the Cu–7Sn alloy, the results show that the strain rate influence elastic modulus of nanopolycrystalline Cu–7Sn alloy weakly, but the tensile strength and ductility enhance obviously with increasing the strain rate. Finally, the microstructure evolution of nanopolycrystalline Cu–Sn alloy during the whole tensile process was studied. It is found that the dislocation density in the Cu–Sn alloy reduces with increasing the Sn content. However, high strain rate leads to stacking faults more easily to generate and high dislocation density in the Cu–7Sn alloy.     

Effect of Al Layer Thickness on the Bonding and Mechanical Behavior of a Mg-(Al-)Ti Laminated Sheet Prepared by Hot-Rolling after Differential Preheating Treatment

Mg-(Al-)Ti laminated sheets with large bonding interfaces were prepared by a differential temperature hot-rolling process, in which the preheating treatment of Ti was 25–100 °C higher than that of Mg. The rolled sheets contained different Al layer thicknesses (≤0.05 mm), and the thickness of the diffused region at the interface of 3–7 μm was formed by rolling at 175 °C. The interfaces were the solid-solution regions of Mg(Al) and Ti(Al), and no intermetallic compounds were generated during both the rolling process and annealing treatment. The hardness of the interfaces was 16–30% greater than that of the Mg matrix and Ti matrix. The results of mechanical tests displayed that the Mg-(Al-)Ti sheets exhibited higher strength and elastic modulus compared to those of the rolled AZ31B sheet. Their UTS and YTS were about 223–460 MPa and 303–442 MPa, respectively, with an elongation of 0.04–0.17 and high elastic modulus of 52–68 GPa. The Mg-Ti (containing about 62 at.% Mg) rolled sheet exhibited the most excellent strength. The UTS and YTS were about 460 MPa and 442 MPa, with an elongation of 0.04 and elastic modulus of 61.5 GPa. Additionally, Mg-Ti sheets with thin Ti thickness possessed a higher work-hardening rate (n), as well as hardening rate, than the rolled Mg-Al-Ti sheets. This is because fractured Ti pieces around the interfaces have a significant strengthening effect. This study provides a simple method for fabricating Mg-(Al-)Ti sheets with high elastic modulus.     

Bulk TiB2-Based Ceramic Composites with Improved Mechanical Property Using Fe–Ni–Ti–Al as a Sintering Aid

The densification behavior, microstructure and mechanical properties of bulk TiB₂-based ceramic composites, fabricated using the spark plasma sintering (SPS) technique with elements of (Fe–Ni–Ti–Al) sinter-aid were investigated. Comparing the change of shrinkage displacement of pure TiB₂ and TiB₂–5 wt% (Fe–Ni–Ti–Al), the addition of elements Fe–Ni–Ti–Al into TiB₂ can facilitate sintering of the TiB₂ ceramics. As the sintering temperature exceeds 1300 °C, the relative density does not significantly change. Alumina particles and austenite (Fe–Ni–Ti) metallic binder distributed homogeneously in the grain boundary of TiB₂ can inhibit the growth of the TiB₂ grains when the sintering temperature is below 1300 °C. The density and particle size of TiB₂ greatly influence the mechanical behavior of TiB₂–5 wt% (Fe–Ni–Ti–Al) composites. The specimen sintered at 1300 has the highest microhardness of 21.1 ± 0.1 GPa with an elastic modulus of 461.4 GPa. The content of secondary borides (M₂B, being M = Fe, Ni), which are more brittle than TiB₂ particles, can also influence the fracture toughness. The specimen sintered at 1500 °C has the highest fracture toughness of 6.16 ± 0.30 MPa·m^1/2 with the smallest M₂B phase. The results obtained provide insight into fabrication of ceramic composites with improved mechanical property.     

Experimental Research on Mechanical Properties of Carbon Fiber-Reinforced Reactive Powder Concrete after Exposure to Cryogenic Temperatures

This study aims to evaluate the mechanical properties of carbon fiber-reinforced reactive powder concrete (CFRPC) after exposure to cryogenic temperature. The mechanical properties of plain RPC and CFRPC with carbon fiber volume contents of 0, 0.5%, 1.0%, and 1.5% were examined after exposure to 20 °C, −5 °C, −15 °C, and −25 °C for 72 h. The effect of fiber contents and exposure temperatures on the cubic and axial compressive strength, splitting tensile strength, elastic modulus, and peak strain were systematically reported and analyzed. The results showed adding carbon fiber to RPC could significantly enhance the strength and slightly improve ductility performance. Additionally, CFRPC with 1.0% fiber content showed the best mechanical properties. The maximum increases in cubic and axial compressive strength and tensile strength were 26.0%, 25.7%, and 21.8%, the elastic modulus was 13.2%, and the peak strain was 13.0% over the plain RPC. Additionally, all mechanical properties continued to degrade with decreasing temperature. After exposure to −25 °C, the cubic, axial compressive strength, and tensile strength of CFRPC degraded to 82.2–84.9%, 80.7–87.5%, and 72.7–73.7% of the normal temperature strength, respectively. In addition, the linear relationship equation between the discount factor of each mechanical property and the temperature was established. Finally, the equation for the stress–strain ascending curve of CFRPC described by a quadratic polynomial was proposed, which fitted well with the experimental results.     

An Overview of Nano Multilayers as Model Systems for Developing Nanoscale Microstructures

The microstructural transformations of binary nanometallic multilayers (NMMs) to equiaxed nanostructured materials were explored by characterizing a variety of nanoscale multilayer films. Four material systems of multilayer films, Hf-Ti, Ta-Hf, W-Cr, and Mo-Au, were synthesized by magnetron sputtering, heat treated at 1000 °C, and subsequently characterized by transmission electron microscopy. Binary systems were selected based on thermodynamic models predicting stable nanograin formation with similar global compositions around 20–30 at.%. All NMMs maintained nanocrystalline grain sizes after evolution into an equiaxed structure, where the systems with highly mobile incoherent interfaces or higher energy interfaces showed a more significant increase in grain size. Furthermore, varying segregation behaviors were observed, including grain boundary (GB) segregation, precipitation, and intermetallic formation depending on the material system selected. The pathway to tailored microstructures was found to be governed by key mechanisms and factors as determined by a film’s initial characteristics, including global and local composition, interface energy, layer structure, and material selection. This work presents a global evaluation of NMM systems and demonstrates their utility as foundation materials to promote tailored nanomaterials.     

Mechanical Properties of Cu2O Thin Films by Nanoindentation

In this study, the structural and nanomechanical properties of Cu₂O thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and nanoindentation techniques. The Cu₂O thin films are deposited on the glass substrates with the various growth temperatures of 150, 250 and 350 °C by using radio frequency magnetron sputtering. The XRD results show that Cu₂O thin films are predominant (111)-oriented, indicating a well ordered microstructure. In addition, the hardness and Young’s modulus of Cu₂O thin films are measured by using a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. Results indicated that the hardness and Young’s modulus of Cu₂O thin films decreased as the growth temperature increased from 150 to 350 °C. Furthermore, the relationship between the hardness and films grain size appears to closely follow the Hall-Petch equation.     

High-Temperature Tensile and Creep Behavior in a CrMoV Steel and Weld Metal

The 2.25Cr1Mo0.25V steel is a vanadium-modified 2.25Cr1Mo steel and is being widely used in the manufacture of heavy-wall hydrogenation reactors in petrochemical plants. However, the harsh service environment requires a thorough understanding of high-temperature tensile and creep behaviors of 2.25Cr1Mo0.25V steel and its weld for ensuring the safety and reliability of hydrogenation reactors. In this work, the high-temperature tensile and creep behaviors of base metal (BM) and weld metal (WM) in a 2.25Cr1Mo0.25V steel weldment used for a hydrogenation reactor were studied experimentally, paying special attention to its service temperature range of 350–500 °C. The uniaxial tensile tests under different temperatures show that the WM has higher strength and lower ductility than those of BM, due to the finer grain size in the WM. At the same time, the short-term creep tests at 550 °C reveal that the WM has a higher creep resistance than that of BM. Moreover, the creep damage mechanisms were clarified by observing the fracture surface and microstructures of crept specimens with the aid of scanning electron microscopy (SEM). The results showed that the creep damage mechanisms of both BM and WM are the initiation and growth of creep cavities at the second phase particles. Results from this work indicate that the mismatch in the high-temperature tensile strength, ductility, and creep deformation rate in 2.25Cr1Mo0.25V steel weldment needs to be considered for the design and integrity assessment of hydrogenation reactors.     

Nickel Oxide Films Deposited by Sol-Gel Method: Effect of Annealing Temperature on Structural,Optical, and Electrical Properties

In our study, transparent and conductive films of NiO_x were successfully deposited by sol-gel technology. NiO_x films were obtained by spin coating on glass and Si substrates. The vibrational, optical, and electrical properties were studied as a function of the annealing temperatures from 200 to 500 °C. X-ray Photoelectron (XPS) spectroscopy revealed that NiO was formed at the annealing temperature of 400 °C and showed the presence of Ni⁺ states. The optical transparency of the films reached 90% in the visible range for 200 °C treated samples, and it was reduced to 76–78% after high-temperature annealing at 500 °C. The optical band gap of NiOx films was decreased with thermal treatments and the values were in the range of 3.92–3.68 eV. NiO_x thin films have good p-type electrical conductivity with a specific resistivity of about 4.8 × 10⁻³ Ω·cm. This makes these layers suitable for use as wideband semiconductors and as a hole transport layer (HTL) in transparent solar cells.     

Influence of Heat Treatment and Reinforcements on Tensile Characteristics of Aluminium AA 5083/Silicon Carbide/Fly Ash Composites

The effect of reinforcements and thermal exposure on the tensile properties of aluminium AA 5083–silicon carbide (SiC)–fly ash composites were studied in the present work. The specimens were fabricated with varying wt.% of fly ash and silicon carbide and subjected to T6 thermal cycle conditions to enhance the properties through “precipitation hardening”. The analyses of the microstructure and the elemental distribution were carried out using scanning electron microscopic (SEM) images and energy dispersive spectroscopy (EDS). The composite specimens thus subjected to thermal treatment exhibit uniform distribution of the reinforcements, and the energy dispersive spectrum exhibit the presence of Al, Si, Mg, O elements, along with the traces of few other elements. The effects of reinforcements and heat treatment on the tensile properties were investigated through a set of scientifically designed experimental trials. From the investigations, it is observed that the tensile and yield strength increases up to 160 °C, beyond which there is a slight reduction in the tensile and yield strength with an increase in temperature (i.e., 200 °C). Additionally, the % elongation of the composites decreases substantially with the inclusion of the reinforcements and thermal exposure, leading to an increase in stiffness and elastic modulus of the specimens. The improvement in the strength and elastic modulus of the composites is attributed to a number of factors, i.e., the diffusion mechanism, composition of the reinforcements, heat treatment temperatures, and grain refinement. Further, the optimisation studies and ANN modelling validated the experimental outcomes and provided the training models for the test data with the correlation coefficients for interpolating the results for different sets of parameters, thereby facilitating the fabrication of hybrid composite components for various automotive and aerospace applications.     

Mechanical Properties of Titanium Nitride Nanocomposites Produced by Chemical Precursor Synthesis Followed by High-P,T Treatment

We investigated the high-P,T annealing and mechanical properties of nanocomposite materials with a highly nitrided bulk composition close to Ti₃N₄. Amorphous solids were precipitated from solution by ammonolysis of metal dialkylamide precursors followed by heating at 400–700 °C in flowing NH₃ to produce reddish-brown amorphous/nanocrystalline materials. The precursors were then densified at 2 GPa and 200–700 °C to form monolithic ceramics. There was no evidence for N₂ loss during the high-P,T treatment. Micro- and nanoindentation experiments indicate hardness values between 4–20 GPa for loads ranging between 0.005–3 N. Young''s modulus values were measured to lie in the range 200–650 GPa. Palmqvist cracks determined from microindentation experiments indicate fracture toughness values between 2–4 MPa·m^1/2 similar to Si₃N₄, SiC and Al₂O₃. Significant variations in the hardness may be associated with the distribution of amorphous/crystalline regions and the very fine grained nature (~3 nm grain sizes) of the crystalline component in these materials.     

Synthesis and Characterisation of Nanocomposite Mo-Fe-B Thin Films Deposited by Magnetron Sputtering

Several ternary phases are known in the Mo-Fe-B system. Previous ab initio calculations have predicted that they should exhibit a tempting mix of mechanical and magnetic properties. In this study, we have deposited Mo-Fe-B films with a Fe-content varying from 0–37 at.% using non-reactive DC (direct current) magnetron sputtering. The phase composition, microstructure, and mechanical properties were investigated using X-ray diffraction, scanning transmission electron microscopy, and nanoindentation measurements. Films deposited at 300 °C and with >7 at.% Fe are nanocomposites consisting of two amorphous phases: a metal-rich phase and a metal-deficient phase. Hardness and elastic modulus were reduced with increasing Fe-content from ~29 to ~19 GPa and ~526 to ~353 GPa, respectively. These values result in H³/E² ratios of 0.089–0.052 GPa, thereby indicating brittle behaviour of the films. Also, no indication of crystalline ternary phases was observed at temperatures up to 600 °C, suggesting that higher temperatures are required for such films to form.     

Wear-Resistance Improvement of 65Mn Low-Alloy Steel through Adjusting Grain Refinement by Cyclic Heat Treatment

Refined microstructures achieved by cyclic heat treatment significantly contribute to improving the wear resistance of steels. To acquire the refined microstructures of 65Mn low-alloy steel, first, the specimens were solid solution-treated; then, they were subjected to cyclic heat treatment at cyclic quenching temperatures of 790–870 °C and quenching times of 1–4 with a fixed holding time of 5 min. The mechanical properties of 65Mn low-alloy steel in terms of hardness, tensile strength, elongation and wear resistance were characterized. Afterwards, the effect of cyclic heat treatment on microstructure evolution and the relationships between grain refinement and mechanical properties’ improvement were discussed. The results show that the average grain size firstly decreased and then increased with the increase in the quenching temperature. Hardness increased with grain refinement when the temperature was lower than 830 °C. Once the temperature exceeded 830 °C, hardness increased with the temperature increase owing to the enrichment of carbon content in the martensite. With the increase in cyclic quenching times, hardness continuously increased with grain refinement strengthening. In addition, both tensile strength and elongation could be significantly improved through grain refinement. The relationships among wear loss, hardness and average grain size showed that wear resistance was affected by the synthesis reaction of grain refinement and hardness. Higher hardness and refined grain size contributed to improving the wear resistance of 65Mn low-alloy steel.     

A 2.9 GPa Strength Nano-Grained and Nano-Precipitated 304L-Type Austenitic Stainless Steel

Austenitic stainless steel has high potential as nuclear and engineering materials, but it is often coarse grained and has relatively low yield strength, typically 200–400 MPa. We prepared a bulk nanocrystalline lanthanum-doped 304L austenitic stainless steel alloy by a novel technique that combines mechanical alloying and high-pressure sintering. The achieved alloy has an average grain size of 30 ± 12 nm and contains a high density (~10²⁴ m⁻³) of lanthanum-enriched nanoprecipitates with an average particle size of approx. 4 nm, leading to strong grain boundary strengthening and dispersion strengthening effects, respectively. The yield strength of nano-grained and nano-precipitated stainless steel reaches 2.9 GPa, which well exceeds that of ultrafine-grained (100–1000 nm) and nano-grained (<100 nm) stainless steels prepared by other techniques developed in recent decades. The strategy to combine nano-grain strengthening and nanoprecipitation strengthening should be generally applicable to developing other ultra-strong metallic alloys.     

Effect of Processing Conditions on the Flash Onset Temperature in Hydroxyapatite

When heat and electric field are applied to the sample, sintering takes place within a short time of a few seconds by the flash phenomenon that occurs. In what condition flash does occur is a main issue for the flash sintering technique. In this study, the effect of processing conditions such as sintering atmosphere, sample size, density and grain size on the flash onset of hydroxyapatite was investigated. In a vacuum atmosphere, a flash occurred at a lower temperature by 50–100 °C than in air. The smaller the thickness of the sample, the higher the flash onset temperature due to the larger specific surface area. Flash was also observed in samples which were presintered, having a density of 86–100% and a grain size of 0.2–0.9 μm. When the density and grain size of the sample were higher and larger, the flash onset temperature was higher. It was because the diffusion and conduction path through the grain boundary and the inner surface of the pores with high defect concentration are blocked with an increase of density or grain size. When an electric field was applied during flash sintering, a color change of the sample was observed and the reason was discussed.     

Al2O3/ZrO2/Y3Al5O12 Composites: A High-Temperature Mechanical Characterization

An Al₂O₃/5 vol%·ZrO₂/5 vol%·Y₃Al₅O₁₂ (YAG) tri-phase composite was manufactured by surface modification of an alumina powder with inorganic precursors of the second phases. The bulk materials were produced by die-pressing and pressureless sintering at 1500 °C, obtaining fully dense, homogenous samples, with ultra-fine ZrO₂ and YAG grains dispersed in a sub-micronic alumina matrix. The high temperature mechanical properties were investigated by four-point bending tests up to 1500 °C, and the grain size stability was assessed by observing the microstructural evolution of the samples heat treated up to 1700 °C. Dynamic indentation measures were performed on as-sintered and heat-treated Al₂O₃/ZrO₂/YAG samples in order to evaluate the micro-hardness and elastic modulus as a function of re-heating temperature. The high temperature bending tests highlighted a transition from brittle to plastic behavior comprised between 1350 and 1400 °C and a considerable flexural strength reduction at temperatures higher than 1400 °C; moreover, the microstructural investigations carried out on the re-heated samples showed a very limited grain growth up to 1650 °C.