Search Results (61)

This study investigated the thermophysical properties of TWIP steel with respect to grain size. The coefficient of thermal expansion (β) of TWIP steel was approximately 22.4 × 10⁻⁶ °C⁻¹, and this value was hardly affected by the grain size. Therefore the density of TWIP steel was also unaffected by grain size within the tested range. The β in TWIP steel was higher than that of plain carbon steels (13–15 × 10⁻⁶ °C⁻¹) such as interstitial free (IF) steel and low-carbon steel, and stainless steels (18–21 × 10⁻⁶ °C⁻¹) such as X10NiCrMoTiB1515 steel and 18Cr-9Ni-2.95Cu-0.58Nb-0.1C steel. The specific heat capacity (c_p) increased with temperature because the major factor affecting c_p is the lattice vibrations. As the temperature increases, atomic vibrations become more active, allowing the material to store more thermal energy. Meanwhile, c_p slightly increased with increasing grain size since grain boundaries can suppress lattice vibrations and reduce the material’s ability to store thermal energy. The thermal conductivity (k) in TWIP steel gradually increased with temperature, consistent with the behavior observed in other high-alloy metals. k slightly increased with grain size, especially at lower temperatures, due to the increased grain boundary scattering of free electrons and phonons. This trend aligns with the Kapitza resistance model. While TWIP steel with refined grains exhibited higher yield and tensile strengths, this came with a decrease in total elongation and k. Thus, optimizing grain size to enhance both mechanical and thermal properties presents a challenge. The k in TWIP steel was substantially lower compared with that of plain carbon steels such as AISI 4340 steel, especially at low temperatures, due to its higher alloy content. At room temperature, the k of TWIP steels and plain carbon steels were approximately 13 W/m°C and 45 W/m°C, respectively. However, in higher temperature ranges where face centered cubic structures are predominant, the difference in k of the two steels became less pronounced. At 800 °C, for example, TWIP and plain carbon steels exhibited k values of approximately 24 W/m°C and 29 W/m°C, respectively. Full article

The relevance of the study is related to the need to join dissimilar copper and nickel alloys by laser direct energy and material deposition (LDED). The purpose of research is studying the distribution of elements, structure, and properties of contact zone of nickel-based super alloy and CuCr1 bronze obtained by direct energy and material deposition with preliminary formation of relief of contact surface. For the purposes of research, samples were made from UNS C18200 copper alloy CuCr1 without relief, with a relief of 0.5 mm depth, and with a relief of 1 mm depth. The Ni₅₀Cr₃₃W_4.5Mo_2.8TiAlNb (EP648) alloy powder was deposited onto the bronze samples with a micro-relief. The deposition was produced by direct injection of energy and material. The influence of interphase interaction of CuCr-chromium carbide system on the possibility of initiation of a crack in the area of carbide secretions is not significant and does not exceed 3.1% according to CIC criterion from the background level for CuCr1 (CIC = 1.54% for CuCr1-Al₄C₃ interface and CIC = 3.1% for CuCr1-Cr₂₃C₆ interface). An X-ray analysis revealed the presence of tensile residual macro-stresses, arising from differences in thermal expansion coefficients in the CuCr1-EP648 interface area, which may be the main cause of crack formation. Cracks are generated and run along the grain boundaries, on which traces of excretion are visible. The contact surface in the CuCr1-EP648 interface area has no visible defects, which indicates the good adhesion of materials when applying an initial layer of EP648 by LDED. The presence of a 0.5-mm micro-relief on CuCr1 has a positive effect on the strength of the connection, as it increases the surface area of the contact CuCr1-EP648 and therefore reduces the contact stress of the breakout. Full article

High-strength bolts are prone to crack initiation from the threaded hole during fastening due to large loads, which can compromise their performance and reliability. To enhance the durability of these bolts, coatings are often employed to strengthen their surfaces. NbMoTaW refractory high-entropy alloy coatings are widely used in hard coating applications due to their exceptional mechanical properties. However, the brittleness of this alloy at room temperature limits its performance in high-stress environments. To enhance the ductility of NbMoTaW alloys, this study systematically investigates the effect of varying titanium (Ti) content on the alloy’s properties. First-principles calculations were employed to analyze the elastic properties of TixNbMoTaW alloys, including elastic constants, the elastic modulus, the bulk modulus (B)-to-shear modulus (G) ratio (Pugh’s ratio), Poisson’s ratio (ν), and Cauchy pressure (C12–C44). The results indicate that the addition of Ti significantly improves the alloy’s plasticity. Specifically, when the Ti content is x = 2, the B/G ratio increases to 3.23, and Poisson’s ratio increases to 0.39, indicating enhanced deformability. At x = 0.75, the elastic modulus (E) increases to 273.78 GPa, compared to 244.99 GPa for the original alloy. The experimental results further validate the computational findings. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicate that all alloys exhibit a single body-centered cubic (BCC) phase. Room-temperature compression tests show that as the Ti content increases, the yield strength, fracture strength, and plasticity of the alloys significantly improve. Specifically, for a Ti content of x = 0.75, the yield strength reaches 1551 MPa, the fracture strength is 1856 MPa, and the plastic strain increases to 14.6%. For Ti1.5NbMoTaW, the yield strength is 1506 MPa, the fracture strength is 1893 MPa, and the plastic strain is 17.3%. Overall, TixNbMoTaW refractory high-entropy alloys demonstrate significant improvements in both plasticity and strength, showing great potential for coating applications in high-stress environments. Full article

In response to the poor wear resistance and high-temperature oxidation resistance of titanium alloys during service, a series of lightweight refractory high-entropy alloys (RHEAs) can be designed for the laser cladding coating of titanium alloy surfaces, with due consideration of the compositional and structural characteristics of titanium alloys. Firstly, the structural stability, mechanical and thermal properties of four lightweight RHEAs (MoNbTiV, AlMoNbTiW, CrMoNbTiV, and AlCrMoNbTiV) with equal atomic ratios were designed and calculated using first principles combined with quasi-harmonic approximation (QHA). The results indicate that all four RHEAs are stable BCC, exhibiting elastic anisotropy and ductility. The lightest density is 6.409 g/cm³. Adding Al/Cr can cause structural distortion and affect its mechanical properties. Their Young’s moduli are in the following order: AlCrMoNbTiV > MoNbTiV > CrMoNbTiV > AlMoNbTiV. The thermal expansion coefficients of the four RHEAs and titanium alloys are very close, with a difference in linear expansion coefficient of less than 1.16 × 10⁻⁵/K. Meanwhile, the metallurgical bonding of four types of RHEA coatings was successfully achieved on a Ti-6Al-4V(TC4) substrate through laser cladding technology, and all coatings exhibited a unique BCC solid solution phase. Full article

Abstract: The refractory complex concentrated alloy (RCCA) 5Al–5Cr–5Ge–1Hf–6Mo–33Nb–19Si–20Ti–5Sn–1W (at.%) was studied in the as-cast and heat-treated conditions. The partitioning of solutes in the as-cast and heat-treated microstructures and relationships between solutes, between solutes and the parameters VEC and Δχ, and between these parameters, most of which are reported for the first time for metallic UHTMs, were shown to be important for the properties of the stable phases A15–Nb₃X and the D8_m βNb₅Si₃. The nano-hardness and Young’s modulus of the A15–Nb₃X and the D8_m βNb₅Si₃ of the heat-treated alloy were measured using nanoindentation and changes in these properties per solute addition were discussed. The aforementioned relationships, the VEC versus Δχ maps and the VEC, Δχ, time, or VEC, Δχ, Young’s modulus or VEC, Δχ, nano-hardness diagrams of the phases in the as-cast and heat-treated alloy, and the properties of the two phases demonstrated the importance of synergy and entanglement of solutes, parameters and phases in the microstructure and properties of the RCCA. The significance of the new data and the synergy and entanglement of solutes and phases for the design of metallic ultra-high temperature materials were discussed. Full article

The presented work considers the influence of the hafnium and molybdenum to zirconium ratio of Ti₂₀Ta₂₀Nb₂₀(HfMo)_20−xZr_x (where x = 0, 5, 10, 15, 20 at.%) high-entropy alloys in an as-cast state for potential biomedical applications. The current research continues with our previous results of hafnium’s and molybdenum’s influence on a similar chemical composition. In the presented study, the microstructure, selected mechanical properties, and corrosion resistance were investigated. The phase formation thermodynamical calculations were also applied to predict solid solution formation after solidification. The calculations predicted the presence of multi-phase, body-centred cubic phases, confirmed using X-ray diffraction and scanning electron microscopy. The chemical composition analysis showed the segregation of alloying elements. Microhardness measurements revealed a decrease in microhardness with increased zirconium content in the studied alloys. The corrosion resistance was determined in Ringer’s solution to be higher than that of commercially applied biomaterials. The comparison of the obtained results with previously reported data is also presented and discussed in the presented study. Full article

Micro-arc oxidation (MAO) is a versatile surface-modification method that promotes higher wear and corrosion resistance, osseointegration, and biological activity to titanium alloys’ surfaces. This study aimed to modify the surface of a recently developed metastable β Ti alloy, which exhibits more favorable mechanical properties for implant applications compared to some commercial Ti alloys, by incorporating Ag into the coatings to introduce a bactericidal function to the surface. The Ti-30Nb-5Mo alloy, with lower elastic modulus, was treated by the MAO method using electrolyte solutions containing calcium acetate, magnesium acetate, β-glycerol phosphate, and varied concentrations of silver nitrate (1.5 mM, 2.5 mM, and 3.5 mM). With an increase in the concentration of silver ions in the electrolyte, the galvanostatic period during the MAO process decreased from 1.7 s to 0.5 s. The Ca/P ratio increased from 0.72 up to 1.36. X-ray diffraction showed that the MAO coatings were formed by rutile and anatase TiO₂ main phases and calcium phosphates. X-ray photoelectron spectroscopy analysis detected the presence of amorphous Nb₂O₅, CaCO₃, and MgCO₃, and metallic and oxide forms of Ag. The increase in Ag in the electrolyte decreased the coating thickness (from 14.2 μm down to 10.0 μm), increased the contact angle (from 37.6° up to 57.4°), and slightly increased roughness (from 0.64 μm up to 0.79 μm). The maximum inhibition of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans strains growth was of 43%, 43%, and 61%, respectively. The Ag did not negatively affect the differentiation of adipose-tissue-derived mesenchymal stem cells. Therefore, the treatment of the surface of the innovative Ti-30Nb-5Mo alloy by the MAO method was effective in producing a noncytotoxic porous coating with bactericidal properties and improved osseointegration capabilities. Full article

β-type titanium alloys with a body-centered cubic structure are highly useful in orthopedics due to their low elastic modulus, lower than other commonly used alloys such as stainless steel and Co-Cr alloys. The formation of the β phase in titanium alloys is achieved through β-stabilizing elements such as Nb, Mo, and Ta. To produce new β alloys with a low modulus of elasticity, this work aimed to produce our alloy system for biomedical applications (Ti-50Nb-Mo). The alloys were produced by arc-melting and have the following compositions Ti-50Nb-xMo (x = 0, 3, 5, 7, and 12 wt% Mo). The alloys were characterized by density, X-ray diffraction, scanning electron microscopy, microhardness, and elastic modulus. It is worth highlighting that this new set of alloys of the Ti-50Nb-Mo system produced in this study is unprecedented; due to this, there needs to be a report in the literature on the production and structural characterization, hardness, and elastic modulus analyses. The microstructure of the alloys has an exclusively β phase (with bcc crystalline structure). The results show that adding molybdenum considerably increased the microhardness and decreased the elastic modulus, with values around 80 GPa, below the metallic materials used commercially for this type of application. From the produced alloys, Ti-50Nb-12Mo is highlighted due to its lower elastic modulus. Full article

This article presents the results of studies of the features of the development of thermoelastic martensitic transformations during cooling/heating in the free state and under load of Ti₅₀Ni_49.7−XNb_XMo_0.3 alloys (X = 0.5, 1.0 and 1.5 at% Nb) with shape memory effects. Using X-ray diffraction analysis, it was found that all the alloys studied at room temperature contained a multiphase mixture consisting of intermetallic compounds with the TiNi (B2, B19′), Ni₅₆Ti₂₉Nb₁₅, and Ti₂Ni compositions. Scanning electron microscopy was used to study the microstructure of TiNi (Nb,Mo) alloys and it was found that the distribution of fine Ni₅₆Ti₂₉Nb₁₅ particles in the matrix depends significantly on the concentration of the alloying element. A correlation was established between changes in the structural-phase state in TiNi (Nb,Mo) alloys and the occurrence of the B2↔B19′ martensitic transition in the free state and under load. Based on physical and mechanical studies, the temperature ranges of the martensitic transformations (MT) in the free state and under load were established. Based on the thermodynamic description of the MT and the analysis of the characteristic temperatures of the MT, it was found that the MT mechanism is strongly dependent on the concentration of the alloying element. Full article

Among the different surface modification techniques, micro-arc oxidation (MAO) is explored for its ability to enhance the surface properties of Ti alloys by creating a controlled and durable oxide layer. The incorporation of Cu ions during the MAO process introduces additional functionalities to the surface, offering improved corrosion resistance and antimicrobial activity. In this study, the β-metastable Ti-30Nb-5Mo alloy was oxidated through the MAO method to create a Cu-doped TiO₂ coating. The quantity of Cu ions in the electrolyte was changed (1.5, 2.5, and 3.5 mMol) to develop coatings with different Cu concentrations. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron and atomic force microscopies, contact angle, and Vickers microhardness techniques were applied to characterize the deposited coatings. Cu incorporation increased the antimicrobial activity of the coatings, inhibiting the growth of Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa bacteria strains, and Candida albicans fungus by approximately 44%, 37%, 19%, and 41%, respectively. Meanwhile, the presence of Cu did not inhibit the growth of Escherichia coli. The hardness of all the deposited coatings was between 4 and 5 GPa. All the coatings were non-cytotoxic for adipose tissue-derived mesenchymal stem cells (AMSC), promoting approximately 90% of cell growth and not affecting the AMSC differentiation into the osteogenic lineage. Full article

This article explores the utilization of cathodic-arc deposition Cr-Al overlay coatings as oxidation protection for Ti-Al-Nb intermetallic alloys. The primary objective is to investigate PVD Al-Cr coatings deposited via cathodic-arc deposition without subsequent vacuum annealing. The microstructure, phase, and chemical composition of the coatings were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis. Isothermal exposure of samples in a laboratory air furnace was conducted, revealing the efficacy of Cr-Al coatings in protecting the Ti49-11Al-40Nb-1.5Zr-0.75V-0.75Mo-0.2Si (mass%) intermetallic alloy VTI-4 against oxidation. The findings highlight that the as-deposited coatings possess a layered structure and contain Al-Cr intermetallics. Post-exposure to the furnace without prior vacuum annealing results in coatings exhibiting a porous microstructure, raising concerns regarding oxidation protection. This investigation of Cr-Al coatings on a VTI-4 alloy substrate yields valuable insights into their nanolaminate structure and challenges associated with aluminum droplet fractions. The proposed additional vacuum heat treatment at 650 °C for 500 h effectively homogenizes the coating, leading to predominant Cr₂Al and Ti-Al phases. Additionally, the formation of diffusion layers at the “coating–substrate” interface and the presence of oxide barriers contribute to the coatings’ heat resistance. Our research introduces possibilities for tailoring coating properties for specific high-temperature applications in aerospace, energy, or industrial contexts. Further refinement of the heat treatment process offers the potential for developing advanced coatings with enhanced performance characteristics. Full article

Inconel 718 (IN718) nickel-based superalloy is widely used in aerospace and nuclear applications owing to its excellent comprehensive mechanical properties, oxidation resistance, and hot corrosion resistance. However, the elemental segregation caused by heterogeneous solidification during casting has great influence on the mechanical properties. Therefore, accurately characterizing the segregation behavior is necessary. Traditional quantitative characterization of elemental segregation uses various sampling methods, in which only macroscopic segregation results are obtained. In this study, micro-beam X-ray fluorescence (μ-XRF) is used for the quantitative characterization of element micro-segregation in IN718 superalloy. The concentration distributions of Cr, Fe, Mo, Nb, and Ti in IN718 alloy are determined with optimized testing parameters, and the degree of elemental segregation in different regions of the analytical area is calculated. It is found that the segregation degree of Nb and Ti in the testing area is larger than other alloying elements. The correlation between the microstructure distribution and the segregation degree of Nb and Ti has been studied using scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). There is severe segregation of Nb and Ti in areas where Nb-containing precipitates are accumulated. The distribution of abnormal signals of Nb with a high fluorescence intensity has a close relationship with the area of precipitates-enriched Nb. Full article

A new generation of titanium alloys with non-toxic, non-allergenic elements and lower Young’s modulus (YM) have been developed, presenting modulus values close to that of bone. In titanium alloys, the value of the Young’s modulus is strongly dependent on the chemical composition. Young’s modulus also depends on the present phases and on the crystallographic texture related to the thermomechanical processing. A lower YM is normally attributed to the formation of the α″ phase into the β matrix, but there is no consensus for this assumption. In the present work, four alloys were designed and melted, based on the Ti-Nb-Mo-Zr system and heat-treated to favor the formation of the β phase. The alloys were produced by arc melting under argon atmosphere and heat-treated at 1000 °C for 24 h under high vacuum, being subsequently quenched in water to room temperature. Alloys were then characterized by optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Young’s modulus was determined by the impulse excitation technique and Vickers microhardness. The purpose of the study was to define an optimal chemical composition for the further production on a semi-industrial scale of a new Ti-Nb-Mo-Zr alloy for orthopedic implant manufacturing. The results showed that all of the four studied alloys are potential candidates for biomedical applications. Among them, the Ti-24Nb-4Mo-6Zr alloy has the lowest Young’s modulus and the highest microhardness. So, this alloy presents the highest HV/YM ratio, which is a key indicator in order to evaluate the mechanical performance of metallic biomaterials for orthopedic implants. Full article

A comparison of the results of studies on the influence of structural defects on the critical parameters of superconductivity has been made for the high-entropy alloy (NbTa)${}_{0.67}$(MoHfW)${}_{0.33}$ and for the conventional superconducting magnet material Nb-47wt%Ti. Positron annihilation lifetime spectroscopy (PALS), electrical resistivity, magnetization and magnetic susceptibility measurements were used. In addition, X-ray powder diffraction studies were performed on the high-entropy alloy (NbTa)${}_{0.67}$(MoHfW)${}_{0.33}$. Due to the rapid cooling of the materials after melting in the arc furnace, they contain a higher concentration of structural defects compared to the heat-treated materials. Magnetic property measurements showed that both the critical temperatures $T_{\mathrm{c}}$ and the upper critical fields ${\mu }_0{H}_{\mathrm{c}2}$ of bulk superconductivity-related materials are improved in the presence of structural defects. Full article

High-chromium cast iron (HCCI) coatings with multicomponent carbides were prepared on low-alloy steel substrates using a laser cladding technique in this work. The microstructure and wear resistance of the coatings were characterized via optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and block-on-ring wear testing. Multicomponent carbides (Ti, Nb, Mo, W, V)C with an FCC structure and multicomponent compounds (Nb, Mo, W, V) (B,C) with an FCC structure were found in the microstructures of coatings after multielement doping. In addition, (Cr, Mo, W, V)₂₃C₆ compounds could be obtained by heat treatment. These multicomponent compounds were beneficial for obtaining coatings with an excellent hardness (60 HRC) and high wear resistance. This multielement doping method provides an effective modified method for preparing high-wear-resistance laser cladding coatings. Full article