Search Results (34)

This study systematically investigated the behavior of impurity removal during the electron beam melting (EBM) process of V-Al alloy. Characterization techniques such as ICP, GDMS, SEM, EPMA, and TEM were used to analyze the composition content and microscopic element distribution of V-Al alloy and purified metal samples. Additionally, based on thermodynamic principles, the saturation vapor pressure and evaporation coefficients of impurity elements were calculated. The results indicate that the evaporation coefficients of Al, Fe, Co, Ni, Cr, and Ti exceed 1, enabling their effective removal during the melting process, thereby reducing their concentrations. In contrast, Si, Mo, Nb, and W exhibit evaporation coefficients significantly lower than 1, making their removal difficult. Instead, their concentrations increase due to the enrichment effect. Microstructural analysis reveals that Al migrates toward high-temperature regions, forming enrichment zones at the surface layer in contact with the electron beam. In contrast, Si, C, and O exhibit bidirectional migration characteristics, accumulating at both the upper and lower surfaces of the plate-shaped ingot. TEM observations indicate that some C reacts with V to form V₂C, which has a higher melting point than vanadium, making further removal difficult. Full article

This study explores the enhancement of antimicrobial and biomedical properties in Fe-based bulk metallic glasses (BMGs) through the addition of Ag. Fe_55-xCr₂₀Mo₅P₁₃C₇Ag_x (x = 0, 1, 2, 3 at.%) master alloy ingots were synthesized by the induction melting technique and industrial-grade raw materials, the master alloy ingots were prepared as bulk metallic glasses (referred to as Ag0, Ag1, Ag2, and Ag3) by the water-cooled copper-mold suction casting technique, and their glass-forming ability, corrosion resistance, biocompatibility, and antimicrobial properties were systematically investigated. The results indicate that the glass forming ability (GFA) decreased with increasing Ag content, reducing the critical diameter for fully amorphous formation from 2.0 mm for Ag0 to 1.0 mm for Ag3. Electrochemical tests in Hank’s solution revealed the superior corrosion resistance of the Fe-based BMGs as compared with conventional 316 L stainless steel (316L SS) and Ti6Al4V alloy (TC4), with Ag3 demonstrating the lowest corrosion current density and the most stable passivation. Biocompatibility assessments, including fibroblast cell viability and adhesion tests, showed enhanced cellular activity and morphology on Fe-based BMG surfaces as compared with 316L SS and TC4, with minimal harmful ion release. Antimicrobial tests against E. coli and S. aureus revealed significantly improved performance with the Ag addition, achieving bacterial inhibition rates of up to 87.5% and 86.7%, respectively, attributed to Ag⁺-induced reactive oxygen species (ROS) production. With their excellent corrosion resistance, biocompatibility, and antimicrobial activity, the present Ag-containing Fe-based BMGs, particularly Ag3, are promising candidates for next-generation biomedical implants. Full article

The resistance to near-threshold fatigue crack growth and its correlation with the microstructure of the Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe alloy were investigated. K-decreasing fatigue crack propagation rate tests were conducted on compact tension samples (ASTM standard) with a stress ratio R of 0.1 and a frequency of 15 HZ in a laboratory atmosphere. At a similar strength level of 1200 MPa, the sample with a fine basket-weave microstructure (F-BW) displayed the slowest near-threshold fatigue crack propagation rate compared with the samples with equiaxed (EM) and basket-weave (BW) microstructures. The fatigue threshold value (ΔK_th) was 4.4 MPa·m^1/2 for F-BW, 3.6 for BW, and 3.2 for EM. The fracture surfaces and crack profiles were observed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to elucidate the mechanism of fatigue crack propagation in the near-threshold regime. The results revealed that the near-threshold crack growth in the three samples was primarily transgranular. The crack always propagated parallel to the crystal plane, with a high Schmid factor. In addition, the near-threshold fatigue crack growth behavior was synergistically affected by the crack tip plastic zone and crack bifurcation. The increased fatigue crack propagation resistance in F-BW was attributed to the better stress/strain compatibility and greater number of interface obstacles in the crack tip plastic zone. Full article

In this paper, enhancing the tribological characteristics of novel cast metallic materials—hybrid multi-component cast irons—by applying a strengthening heat treatment is described. The experimental materials were the cast alloys of a nominal composition (5 wt.% W, 5 wt.% Mo, 5 wt.% V, 10 wt.% Cr, 2.5 wt.% Ti, Fe is a balance) supplemented with 0.3–1.1 wt.% C and 1.5–2.5 wt.% B (total of nine alloys). The heat treatment was oil-quenching followed by 200 °C tempering. The quench temperature (QT) varied in the range of 900–1200 °C, with a step of 50 °C (with a 2-h holding at QT). The correlation of the QT with microstructure and properties was estimated using microstructure/worn surface characterization, differential scanning calorimetry, hardness measurement, and three-body-abrasive wear testing (using Al₂O₃ particles). The as-cast alloys had a multi-phase structure consisting of primary and/or eutectic borocarbide M₂(B,C)₅, carboborides M(C,B), M₇(C,B)₃, M₃(C,B), and the matrix (ferrite, martensite, pearlite/bainite) in different combinations and volume fractions. Generally, the increase in the quenching temperature resulted in a gradual increase in hardness (maximally to 66–67 HRC) and a decrease in the wear rate in most alloys. This was due to the change in the phase-structure state of the alloys under quenching, namely, the secondary carboboride precipitation, and replacing ferrite and pearlite/bainite with martensite. The wear rate was found to be inversely proportional to bulk hardness. The maximum wear resistance was attributed to QT = 1150–1200 °C, when the wear rate of the alloys was lowered by three to six times as compared to the as-cast state. With the QT increase, the difference in the wear rate of the alloys decreased by three times. The highest abrasive resistance was attributed to the alloys with 1.1 wt.% C, which had a 2.36–3.20 times lower wear rate as compared with that of the reference alloy (13 wt.% Cr cast iron, hardness of 66 HRC). The effects of carbon and boron on hardness and wear behavior are analyzed using the regression models developed according to the factorial design procedure. The wear mechanisms are discussed based on worn surface characterization. Full article

The CoCrFeNi₂Mo_x (x = 0, 0.4, 0.5, 1.0, x values in atomic ratio) high-entropy alloy coatings were designed and prepared on the Ti-6Al-4V substrate by laser cladding technology, their microstructures, and dry sliding wear resistance were studied in detail. When x < 0.4, the coatings were mainly composed of BCC solid solution phase, (Ni, Co)Ti₂ phase, and α-Ti phase. When x ≥ 0.4, the new σ phase appeared in the coatings. As the Mo content increases from 0 to 1.0, the hardness showed a trend of first increasing and then decreasing, especially when x = 0.5, the coating hardness reached its maximum (882 HV), which was 2.65 times the hardness of the Ti-6Al-4V substrate. The CoCrFeNi₂Mo_x high-entropy alloy coatings significantly improved the wear resistance of Ti-6Al-4V substrate, and with the increase in Mo content, the friction coefficient, widths/depths of worn tracks and wear rates of the coatings showed a trend of first decreasing and then increasing. In particular, when x = 0.5, the CoCrFeNi₂Mo_0.5 high-entropy alloy coating has the lowest friction coefficient (0.63), widths/depths of worn tracks (width: 803.690 μm; depth: 20.630 μm) and wear rate (5.136 × 10⁻⁵ mm³/(N·m)), which is one order of magnitude smaller than that of the substrate (3.694 × 10⁻⁴ mm³/(N·m)), demonstrating the best wear resistance. This is mainly because the appropriate proportion of hard α-Ti and σ phases effectively played a supporting role in resisting wear, while the relatively soft and dispersed BCC and (Ni, Co)Ti₂ phases could effectively prevent the occurrence of brittle fracture during wear test process. Full article

In industrial production, the deformation inhomogeneity after metal forging affects the mechanical properties of various parts of the forgings. The question of whether the organization and mechanical properties of β-titanium alloy can be improved by controlling the amount of forging deformation needs to be answered. Therefore, in this paper, a new sub-stable β-Ti alloy TB 18 (Ti-5.3Cr-4.9Mo4.9V-4.3Al-0.9Nb-0.3Fe) was subjected to three different levels of deformation, as well as solid solution-aging treatments, and the variation rules of microstructure and mechanical properties were investigated. During the solid solution process, the texture evolution pattern of the TB18 alloy at low deformation (20–40%) is mainly rotational cubic texture deviated into α-fiber texture; at high deformation (60%), the main components of the deformed texture are α-fiber texture with a specific orientation of (114)<1$\stackrel{\mathrm{-}}{13}$3>. After subsequent static recrystallization, the α-fiber texture is deviated to an α*-fiber texture, while the specific orientation (114)<1$\stackrel{\mathrm{-}}{13}$3> can still be inherited as a major component of the recrystallized texture. The plasticity of the alloy in the normal direction (ND) after the solid solution is influenced by the existence of the <110>//ND texture, and the plasticity of the alloy in the ND direction after aging is determined by a combination of the volume fraction of the <110>//ND texture in the matrix phase and the volume fraction of [11$\stackrel{\mathrm{-}}{2}$0]_α//ND in the α phase. The results show that it is feasible to change the characteristics of the recrystallization texture of TB18 by controlling the deformation level of hot forging, thus realizing the modulation of the mechanical properties. Full article

This research investigated the relationship between volume energy density and the microstructure, density, and mechanical properties of the Ti-5Al-5Mo-3V-1Cr-1Fe alloy fabricated via the SLM process. The results indicate that an increase in volume energy density can promote a transition from a columnar to an equiaxed grain structure and suppress the anisotropy of mechanical properties. Specifically, at a volume energy density of 83.33 J/mm³, the average aspect ratio of β grains reached 0.77, accompanied by the formation of numerous nano-precipitated phases. Furthermore, the relative density of the alloy initially increased and then decreased as the volume energy density increased. At a volume energy density of 83.33 J/mm³, the relative density reached 99.6%. It is noteworthy that an increase in volume energy density increases the β grain size. Consequently, with a volume energy density of 83.33 J/mm³, the alloy exhibited an average grain size of 63.92 μm, demonstrating optimal performance with a yield strength of 1003.06 MPa and an elongation of 18.16%. This is mainly attributable to the fact that an increase in volume energy density enhances thermal convection within the molten pool, leading to alterations in molten pool morphology and a reduction in temperature gradients within the alloy. The reduction in temperature gradients promotes equiaxed grain transformation and grain refinement by increasing constitutive supercooling at the leading edge of the solid–liquid interface. The evolution of molten pool morphology mainly inhibits columnar grain growth and refines grain by changing the grain growth direction. This study provided a straightforward method for inhibiting anisotropy and enhancing mechanical properties. Full article

Despite the significant potential advantages of processing Ti-5Al-5Mo-5V-1Cr-1Fe alloy (Ti-55511) using Electron Beam Melting (PBF-EB/M), when compared to conventional manufacturing technologies, the resulting internal defects are an important characteristic of such additive technologies and can highly decrease mechanical properties. One of the most dangerous defects formed during metal additive manufacturing processes are material discontinuities such as a lack of fusion. Defects of this type, due to their “flat” nature, are difficult to characterize. For cycle-loaded specimens, where the loading force acts perpendicular to the lack-of-fusion plane, defects of this type can significantly reduce fatigue properties. This paper presents the results of research aimed at improving the fatigue properties of Ti55511 alloy by reducing the influence of the lack-of-fusion defect on fatigue damage. The static and fatigue properties of specimens in the as-built state, as well as after hot isostatic pressing (HIP) treatment, were analyzed. The effect of HIP on both the reduction of pores and the degree of sphericity when using the X-ray computed tomography (XCT) system was presented. The change in the microstructure after HIP was analyzed in terms of the change in the size of individual phases, as well as the change in the phase ratio. This paper also contains a fractographic analysis of the samples after tensile and fatigue tests. Full article

High-cycle fatigue (HCF) is a critical property of metastable β Ti alloys in aerospace applications. In this work, the HCF behavior and corresponding microscale deformation mechanisms of a metastable Ti-5Al-5Mo-5V-1Cr-1Fe (Ti55511) alloy with a basket-weave structure were investigated. HCF and its deformation mechanisms of a Ti55511 alloy were systematically studied in the deformed condition by using a scanning electron microscope (SEM), a transmission electron microscope (TEM), and electron backscatter diffraction (EBSD). It was found that the Ti55511 alloy exhibited an excellent HCF strength (10⁷ cycles, K_t = 1, R = 0.06) of 738 MPa. The fractographic investigation demonstrated that fatigue striations and secondary cracks were the main features in the crack initiation zone. Dislocation analyses indicated that the HCF deformation of the basket-weave microstructure was mainly affected by the dislocation slipping of the primary α (α_p) phase. In addition, the dislocation pile-up at the α_p/β_trans interface led to crack initiation. EBSD analyses indicated that the prismatic <a> type slip system of the α_p phase was preferentially activated during the HCF deformation process of the Ti55511 alloy, followed by the basal <a> type and pyramid <a> type systems. Full article

In this work, the anisotropic microstructure and mechanical properties of selective laser melted (SLMed) Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy before and after aging treatment are investigated. Owing to the unique thermal gradient, the prior columnar β grains with {001} texture component grow in the building direction, and the mechanical properties of the as-fabricated Ti-55511 alloy exhibit slight anisotropy. Aging treatment creates uniform precipitation of the α phase at the boundaries as well as the interior of β grains. Due to the microstructure of the aged samples with a weak texture, the mechanical properties exhibit almost isotropic characteristics with an ultimate tensile strength of 1133 to 1166 MPa, yield strength of 1093 to 1123 MPa, and elongation from 13 to 16%, which meet the aerospace allowable specification very well. By XRD and EBSD analyses, the total dislocation density of the aged samples (~134.8 × 10¹³ m⁻²) is significantly lower than that of the as-fabricated samples (~259.4 × 10¹³ m⁻²); however, the aged samples exhibit a higher geometrically necessary dislocation (GND) density (~28.5 × 10¹³ m⁻²) compared with the as-fabricated samples GND density (~2.9 × 10¹³ m⁻²). Thus, a new approach to strengthening theory for estimating the anisotropic mechanical properties of AM alloys is proposed. Full article

The hot tensile deformation and fracture mechanisms of a Ti-5Al-5Mo-5V-1Cr-1Fe alloy with bimodal and lamellar microstructures were investigated by in situ tensile tests under scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that the main slip deformation modes are prismatic slip ({1$\overline{1}$00}<11$\overline{2}$0>) and pyramidal slip ({1$\overline{1}$01}<11$\overline{2}$0>) under tension at 350 °C. In the bimodal microstructure, several parallel slip bands (SBs) first form within the primary α (α_P) phase. As the strain increases, the number of SBs in the α_P phase increases significantly and multislip systems are activated to help further coordinate the increasing deformation. Consequently, the microcracks nucleate and generally propagate along the SBs in the α_P phase. The direction of propagation of the cracks deflects significantly when it crosses the α_P/β interface, resulting in a tortuous crack path. In the lamellar microstructure, many dislocations pile up at the coarse-lath α (α_L) phase near the grain boundaries (GBs) due to the strong fencing effect thereof. As a result, SBs develop first; then, microcracks nucleate at the α_L phase boundary. During propagation, the cracks tend to propagate along the GB and thus lead to the intergranular fracture of the lamellar microstructure. Full article

In this study, the cold rolling microstructure and static recrystallization mechanism of the high strength titanium alloy Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe were systematically investigated. Results show that the cold rolling microstructure is mainly composed of the elongated deformed β grains containing micro-shear bands. After annealing at 815 °C for 2 min, the fine SRXed grains are observed, mainly concentrated in the micro-shear band, the grain boundary and the interior of the deformed grain. The sub-grain structure obtained by static recovery inside the deformed grain produces continuous SRX during the annealing treatment. Meanwhile, geometric and discontinued SRXed grains are also observed in the large deformed β grain and at the trigeminal grain boundaries, respectively. Many ultra-fine grains appear inside the micro-shear band, exhibiting a phenomenon of the micro-shear band assisting SRX. With the increase in the annealing holding time, the elongated β grains are significantly refined and the degree of recrystallization is continuously improved. In addition, the recrystallization behavior also results in a significant change in the fiber texture. With the extension of the annealing holding time, the rolling texture type evolves gradually, with the {111} <112> γ-fiber texture to weak α-fiber, γ-fiber, and Goss-fiber. Full article

Despite the widespread use of TiAl alloys in many fields, their poor impact resistance has recently emerged again as a major issue. Therefore, in this study, the practical effects of additive elements were examined by considering impact resistance as the most important property of practical TiAl cast alloys. The impact resistance was evaluated via the Charpy impact test, which has been rarely applied to TiAl alloys, revealing that only V, Cr, Mn, and B slightly improved the impact resistance, compared to that of the Ti–Al binary alloy, both in the as-cast and heat-treated states. In contrast, Nb, Mo, W, Fe, Ni, Si, C, and N decreased the impact resistance. If a slight decrease in impact resistance is permitted, then only Si and C can improve the creep strength, and Nb and W can improve the anti-oxidation resistance. These results confirm the excellence of practical TiAl cast alloys developed a considerable time ago, containing these elements in addition to Cr, Mn, and B. Full article

The adiabatic shear sensitivity of ultra-high-strength steels is closely related to their thermal conductivity. Therefore, it is essential to investigate the effects of alloying elements on the thermal conductivity of ultra-high-strength steel. In this study, the variation in the scattering behavior of electrons with respect to temperature and the mechanism of three-phonon scattering were considered for obtaining the contributions of electrons and phonons, respectively, to the thermal conductivity of alloys while solving the Boltzmann transport equation. By predicting the effect of ten alloying elements on the electronic thermal conductivity (κ_e), it was found that, at 1200 K, the doping of iron with Ni and Cr endowed iron with κ_e values of 24.9 and 25.7 W/m K, respectively. In addition, the prediction for the lattice thermal conductivity (κ_L), which was performed without considering point defect scattering, indicated that elements such as Al, Co, Mn, Mo, V, and Cr demonstrate a positive effect on the lattice thermal conductivity, with values of 3.6, 3.7, 3.0, 3.1, 3.9, and 3.8 W/m K, respectively. The contribution of κ_L is only 5–15% of the total thermal conductivity (κ_total). The alloying elements exhibited a similar effect on κ_total and κ_e. Δκ_i; the change in thermal conductivity with respect to κ₀ owing to the alloying element i was evaluated according to the total thermal conductivity. These values were used to understand the effect of the concentration of alloying elements on the thermal conductivity of iron. The Δκ_i values of Ni, Co, and W were 6.44, 6.80, and 6.06, respectively, indicating a reduction in the thermal conductivity of iron. This paper provides theoretical guidance for the design of ultra-high-strength steels with a high thermal conductivity. Full article

The plastic deformation processes and fracture behavior of a Ti–5Al–5Mo–5V–1Cr–1Fe alloy with bimodal and lamellar microstructures were studied by room-temperature tensile tests with in situ scanning electron microscopy (SEM) observations. The results indicate that a bimodal microstructure has a lower strength but higher ductility than a lamellar microstructure. For the bimodal microstructure, parallel, deep slip bands (SBs) are first noticed in the primary α (α_p) phase lying at an angle of about 45° to the direction of the applied tension, while they are first observed in the coarse lath α (α_L) phase or its interface at grain boundaries (GBs) for the lamellar microstructure. The β matrix undergoes larger plastic deformation than the α_L phase in the bimodal microstructure before fracture. Microcracks are prone to nucleate at the α_p/β interface and interconnect, finally causing the fracture of the bimodal microstructure. The plastic deformation is mainly restricted to within the coarse α_L phase at GBs, which promotes the formation of microcracks and the intergranular fracture of the lamellar microstructure. Full article