Search Results (83)

A SiO₂-Al₂O₃-B₂O₃-CaO-MgO-Na₂O glass-based protective lubricant coating was developed for Ti-6Al-4V alloy forging, featuring a fully non-toxic formulation. The coating consisted of a composite glass matrix formed by blending two phases with distinct softening temperatures, extending its operational window to 700–950 °C. The composite glass showed initial softening at 700 °C and complete melting at 800 °C, with contact angle measurements confirming superior wettability (θ < 90°) across the forging range (800~950 °C). With an increase in temperature, the surface tension of the composite glass melt decreased, and subsequently, the wettability of the composite glass melt was significantly improved. XRD revealed that the uncoated Ti-6Al-4V formed a 22 μm thick rutile TiO₂ scale with a porous structure and interfacial cracks, while the coated sample retained an amorphous glass layer with no TiO₂. Cross-sectional SEM showed a crack-free, poreless interface with strong metallurgical bonding, in contrast to the uncoated sample’s spalled oxide layer. EDS showed minimal oxygen diffusion of the glass coating into the substrate. Ring upsetting tests showed that the coating reduced friction from 0.5–0.7 to 0.3 (50–57% decrease). Collectively, the glass protective lubricant coating showed good performance in terms of protection and lubrication. Full article

It is essential to develop the optimal hot-working process of the (CoCrNi)₉₄Al₃Ti₃ alloy, a recently developed precipitation-hardened medium-entropy alloy with promising mechanical properties, for its industrial application. In this study, the hot workability of the as-forged (CoCrNi)₉₄Al₃Ti₃ alloy was investigated over a temperature range of 1000 °C to 1150 °C and a strain rate ranging from 0.001 to 1 s⁻¹ using a Gleeble-1500D thermal simulation machine of Dynamic Systems Inc., USA. As a result, the constitutive relationship was established, and the hot deformation activation energy was calculated as 433.2 kJ/mol, suggesting its well-defined plastic flow behavior under low-energy-input conditions. Hot-processing maps were constructed to identify the stable hot-working regions. Microstructure analysis revealed that the hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy exhibited continuous dynamic recrystallization (CDRX) behavior under optimal hot-working conditions. Considering the hot-processing maps and DRX characteristics, the optimal hot-working window of hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy was identified as 1100 °C with a strain rate of 0.1 s⁻¹. This work offers valuable guidance for developing high-efficiency forming processes for (CoCrNi)₉₄Al₃Ti₃ medium-entropy alloy. Full article

Ti6Al4V titanium alloy is one of the most studied for its properties after additive manufacturing. Due to its widely use in medical applications, its properties are investigated in various aspects of surface layer property improvement and later compared to conventionally manufactured Ti-6Al-4V. In this study, the corrosion behavior in a 0.9% NaCl solution of shot peened Ti-6Al-4V prepared using direct metal laser sintering (DMLS) was examined using corrosion electrochemical testing and compared with conventionally forged titanium alloy. Shot peening was performed on previously polished samples and subsequently treated with the CrNi steel shots. Two sets of peening pressure were selected: 0.3 and 0.4 MPa. X-ray diffraction analysis (XRD), X-ray micro-computed tomography (Micro-CT), scanning electron microscope (SEM) tests with roughness and hardness measurements were used to characterize the samples. The conventional samples were characterized by an α + β structure, while the additive samples had an α’ + β martensitic structure. The obtained results indicate that the corrosion resistance of the conventionally forged Ti-6Al-4V alloy was higher than DMLSed Ti-6Al-4V alloy. The lowest corrosion rates were noted for untreated surfaces of CM/ref and DMLS/ref samples and reached 0.041 and 0.070 µA/cm², respectively. Moreover, the development of the surface has an influence on corrosion behavior. Therefore, increasing pressure results in inferior corrosion resistance. However, better performance for shot peened samples was reported in the low frequency range. This is due to the refinement of the grain acquired after the peening process. All the results obtained, related to the corrosion behavior, were satisfactory enough that the all samples can be characterized as materials suitable for implant applications. Full article

As an advanced high-temperature structural material, TiAl alloy, is often used in the manufacturing of hot-end components of aviation and aerospace engines. However, it is difficult to increase the strength at high temperature, which limits its wider application. Adopting composite material technology is one of the effective ways to improve the comprehensive mechanical properties of TiAl alloy. In this work, by adding 3 wt.% SiC micro-particles to Ti-47.5Al-7Nb-0.4W-0.1B (at.%) pre-alloyed powder, a core-shell structure dual-MAX-phase high-temperature strengthened TiAl matrix composite (also known as TiAl-SiC composite) was prepared by combining powder metallurgy and hot forging. The microstructure and high-temperature compressive properties of the prepared TiAl-SiC composites were studied and compared with TiAl alloy prepared by the same process, and the microstructural characteristics of the TiAl-SiC composite and its microstructure evolution during processing were revealed. The results show that the matrix of as-sintered TiAl-SiC composites was mainly composed of γ phase and a small amount of Ti₂AlC particles, while the reinforcement phase was a dual-MAX-phase core-shell structure, which was mainly composed of core Ti₂AlC phase, shell Ti₃SiC₂ phase, and small Ti₂AlC particles distributed in the outer layer. After hot forging, the microstructure of TiAl-SiC composite became more compact, finer, and more uniform; the phase composition was almost not changed, but the content of Ti₂AlC, Ti₃SiC₂, and TiB₂ phases increased significantly; the content of C in each constituent phase decreased obviously, and a granular Si-rich phase was generated in the core of the reinforcement phase. The yield strength of the as-forged TiAl-SiC composite was significantly higher than that of the as-forged TiAl alloy at temperature higher than 859 °C. This is because the core-shell structure dual MAX phases can effectively reduce the softening rate of TiAl alloy in the range of 800–900 °C, thus playing a strengthening role and increasing the service temperature of TiAl alloy. Full article

Microstructure control, especially the elimination of microtexture in Ti alloys such as Ti-6Al-4V and TIMETAL 834, is important to improve the fatigue life. In most research, small samples measuring 8–10 mm in diameter and 12–15 mm in height are utilized. However, the cooling rates of these small samples are always quite rapid, whereas the cooling rates of larger engine components, are relatively slow. Therefore, in this study, microstructural change involving different thermomechanical processing (TMP) was investigated using large TIMETAL 834 samples of 80 mm in diameter and 100 mm in height. The samples were forged at 940 and 1000 °C using a 1500 t forging simulator and heat treated at 900 and 1000 °C. Our goal is to attain a macroscopic understanding that connects the processing, microstructure, and fatigue life. The significant microstructure difference is that the deformed microstructure remains in the small sample due to rapid cooling, while the formation of a bimodal structure or an α phase globularization progressed in the large samples by diffusion during slow cooling. Improvement in the fatigue life was obtained by the 85% forging at 1000 $°$C. This is due to the refinement of the α grains and active slip in microtexture by alignment of the c-axis of α grains far from the tensile axis. Full article

The Ti-62222 (Ti-6Al-2Sn-2Zr-2Mo-2Cr) alloy has considerable potential for structural applications in the aerospace industry owing to its exceptional fracture resistance and specific strength. This study investigates the influence of local strain parameters and solution treatment and aging (STA) on the microstructure, texture evolution, and microhardness of a hot-forged Ti-62222 alloy. The strain distribution was simulated using the finite element method (FEM). The results showed that in the specimens before heat treatment, the morphology of the primary Ti α phase grains elongated perpendicular to the compression direction as the strain increased. In contrast, the post-heat-treated specimens (PHTSs) exhibited similar aspect ratios, regardless of the strain level, owing to grain spheroidization induced by the STA heat treatment process. Spheroidal primary Ti α phase and acicular Ti α’ phase were observed in the specimens before and after heat treatment. Texture analysis revealed that the specimens subjected to heat treatment had a weaker texture than the before-heat-treatment specimens. The near ($11\overline{2}0$)//FD texture tended to develop along the direction perpendicular to the forging direction. The microhardness analysis results indicated that strain had no significant effect on the microhardness of either the as-forged specimen or the PHTS. After heat treatment, the specimens showed consistent microhardness values regardless of the strain level. The PHTS exhibited increased microhardness, attributed to the aging process during STA. Full article

Vacuum isothermal forging is an ideal method for preparing high-performance TiAl alloy forgings, as it is carried out under the conditions of a uniform temperature field and oxygen isolation. The mechanical properties of TiAl alloys strongly depend on their microstructure, so it is important to study their microstructure evolution during the forging process to improve their properties. In this study, TiAl alloy forgings with different deformations were produced from the extruded billets by vacuum isothermal superplastic forging under lower temperatures and extremely low strain rate conditions. The results indicate that the streamlined structure in the extruded alloy was destroyed during the forging process. As the deformation increased, the dynamic recrystallization was more fully carried out, leading to a substantial decrease in remnant lamellar colonies and a significant increase in the γ phase, and the microstructure was transformed from nearly lamellar (NL) to near gamma (NG) structure. The proportion of high-angle grain boundaries (HAGB) increased with increasing deformation, while the grain size reduced from 20 μm to 4.6 μm. In addition, the streamlined features and textures exhibited a weakening trend with increasing deformation, leading to a decrease in the ultimate strength from 891 MPa to 722 MPa. To maintain the streamlined characteristics and retain strengthening effects, the forging deformation should not exceed 56.7%. Full article

The TNM alloy, a β_o-phase-containing TiAl alloy, has been withdrawn from use as a last-stage turbine blade in commercial jet engines as it suffered frequent impact fractures in service, raising doubts regarding the necessity of the β_o-phase in practical TiAl alloys. Here, we evaluate the practical properties required for jet engine blades for various TiAl alloys and investigate the effects of the β_o-phase thereupon. First, we explore the influence of the β_o-phase content on the impact resistance and machinability for forged Ti–43.5Al–xCr and cast Ti–46.0Al–xCr alloys; the properties deteriorate significantly at increasing β_o-phase contents. Subsequently, two practical TiAl alloys—TNM alloy and TiAl4822—were prepared with and without the β_o-phase by varying the heat treatment temperature for the former and the Cr concentration for the latter. In addition to impact resistance and machinability, the creep strength is significantly reduced by the presence of the β_o-phase. Overall, these findings suggest that the β_o-phase is an undesirable phase in practical TiAl alloys, especially those used for jet engine blades, because, although the disordered β-phase is soft at high temperatures, it changes to significantly more brittle and harder β_o-phase after cooling. Full article

Metal manufacturing processes based on deformation (forging, rolling) result in a fine grain structure with a complex dislocation substructure, which positively influence mechanical properties. Casting and additive manufacturing (powder- or wire-based) usually produce a coarse grain structure with a poorly developed dislocation substructure, which negatively affect mechanical properties. Heat treatment may alter phase balance and stimulate precipitation strengthening; however, precipitation kinetics depends on the dislocation substructure. In this paper, a comparative study of the microstructure and strength is presented for Monel K500 alloy containing 63 Ni, 30 Cu, 2.0 Mn, and 2.0 Fe (wt.%), and microalloyed with Al, Ti, and C hot-rolled to a round bar and deposited on a round surface using wire additive manufacturing (WAAM) technology. An increased dislocation density and number density of fine precipitates resulted in 8–25% higher hardness and 1.8–2.6 times higher compression yield stress in the hot-rolled alloy compared to these in the WAAM-produced alloy. However, due to a high work hardening rate, only 3–10% cold deformation was necessary to increase the strength of the WAAM alloy to this of the hot-rolled one. Age hardening heat treatment, through the intensification of the precipitation strengthening mechanism, reduced the value of cold deformation strain required to equalise the properties. Based on the obtained results, a new technology consisting of additive manufacturing, heat treatment, and cold deformation can be proposed. It can produce WAAM components with strength and hardness improved to the level of hot-rolled components, which is a significant development of additive manufacturing. 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

The evolution of microstructure, phase composition and physico-mechanical properties of the biocompatible Ti-39Nb-7Zr alloy (wt.%) after severe plastic deformation by rotary forging (RF) was studied using various methods including light optical microscopy, scanning and transmission electron microscopies, X-ray diffraction, microindentation, tensile testing and investigation of thermophysical properties during continuous heating. The hot-rolled Ti-39Nb-7Zr with initial single β-phase structure is subjected to multi-pass RF at 450 °C with an accumulated degree of true deformation of 1.2, resulting in the formation of a fibrous β-grain structure with imperfect 500 nm subgrains characterized by an increased dislocation density. Additionally, nano-sized α-precipitates formed in the body and along the β-grain boundaries. These structural changes resulted in an increase in microhardness from 215 HV to 280 HV and contact modulus of elasticity from 70 GPa to 76 GPa. The combination of strength and ductility of Ti-39Nb-7Zr after RF approaches that of the widely used Ti-6Al-4V ELI alloy in medicine, however, Ti-39Nb-7Zr does not contain elements with limited biocompatibility and has a modulus of elasticity 1.5 times lower than Ti-6Al-4V ELI. The temperature dependences of physical properties (elastic modulus, heat capacity, thermal diffusivity) of the Ti-39Nb-7Zr alloy after RF are considered and sufficient thermal stability of the alloy up to 450 °C is demonstrated. Full article

The mechanical properties of various Ti-6Al-4V alloys are influenced by their respective microstructures. This study generated an ultrafine-grain (UFG) Ti-6Al-4V alloy featuring bimodal grain distribution characteristics achieved through initial heat treatment, multi-axial forging (MF), and annealing. The study also extensively examined the evolution process of the alloy’s microstructure. By subjecting the materials to heat treatments at 900 °C with air cooling and 950 °C with air cooling, both materials were found to be consisted of primary α (α_p) and transformed β (α_s+β) regions with different proportions. Following MF, the sample treated at 900 °C displays a microstructure featuring UFGs of α+β surrounding larger micron-sized α_p grains. On the other hand, the sample treated at 950 °C displays a microstructure distinguished by twisted α_s lamellar and fragmented β grains surrounding larger micron-sized α_p grains. Following annealing, no significant grain growth was observed in the sample. The geometrically necessary dislocations (GNDs) within the UFGs were eliminated, though some GNDs persisted within the α_p grains. The samples undergoing the 900 °C heat treatment, MF, and subsequent annealing exhibited elevated strength (1280 MPa) and total elongation (10.7%). This investigation introduces a novel method for designing the microstructure of the Ti-6Al-4V alloy to achieve superior performance. Full article

In this work, the technique of equal-channel angular pressing (ECAP) that enables producing bulk billets was used to form a UFG structure in Ti-6Al-4V alloy. A subsequent warm upsetting simulates die forging and the production of a part. We studied the evolution of the UFG alloy’s crystallographic texture in the process of deformation during the production of a semi-product and/or a part, as well as its effect on the ductile–brittle transition region in the temperature range from −196 °C to 500 °C and the material’s fracture mechanisms. To test Charpy impact strength, standard samples of square cross-section with a V-shape notch were used (KCV). It was found that the impact toughness anisotropy is caused by textural effects and has a pronounced character at temperatures in the ductile–brittle transition range. Up to 100 °C the KCV values are close in the specimens processed by ECAP and ECAP+upsetting (along and perpendicularly to the upsetting axis—along the Z-axis and along the Y-axis, respectively), while a large difference is observed at test temperatures of 200 °C and higher. At a temperature of 500 °C, the impact toughness of the UFG Ti-6Al-4V alloy after ECAP reaches a level of that after ECAP+upsetting in the fracture direction along the Z-axis (1.60 and 1.77 MJ/m², respectively). Additionally, an additional ECAP upsetting after ECAP decreases the ductile–brittle transition temperature of the UFG Ti-6Al-4V alloy, which increases the temperature margin of the toughness of the structural material and reduces the risk of the catastrophic failure of a product. The fractographic analysis of the fracture surface of the specimens after Charpy tests in a wide temperature range revealed the features of crack propagation depending on the type of the alloy’s microstructure and texture in the fracture direction. Full article

We compiled, assessed, and ranked refractory high-entropy alloys (RHEAs) from the existing literature to identify promising coating materials for hot-forging dies. The selection methodology was rigorously guided by decision science principles, seamlessly integrating multiple attribute decision making (MADM), principal component analysis (PCA), and hierarchical clustering (HC). By employing a combination of twelve diverse MADM methods, we successfully ranked a total of 22 RHEAs. This analytical technique unveiled the top five RHEAs: Ti₂₀-Zr₂₀-Hf₂₀-Nb₂₀-Cr_20, Al_20.4-Mo_10.5-Nb_22.4-Ta_10.1-Ti_17.8-Zr_18.8, Ti₂₀-Zr₂₀-Hf₂₀-Nb₂₀-V₂₀, Al_11.3-Nb_22.3-Ta_13.1-Ti_27.9-V_4.5-Zr_20.9, and Al_7.9-Hf_12.8-Nb₂₃-Ta_16.8-Ti_18.9-Zr_20.6 pertinent for generating data on other significant properties, including wear resistance, fatigue (both thermal and mechanical), bonding compatibility with the substrate die material, oxidation resistance, potential reactions with the workpiece, cost-effectiveness, fabricability, and more. The three highest-ranked RHEAs share key characteristics, including a body-centered cubic (BCC) crystal structure, thermal conductivity below ~70 W/mK, and impressive yield strength at ambient and elevated temperatures, surpassing 1100 MPa. Moreover, they exhibit a remarkable ~73% similarity among themselves. The decision science-driven analyses yield sound metallurgical insights and provide valuable guidelines for developing RHEA coatings tailored for hot-forging dies. The strategy for designing RHEA-based coating materials for hot-forging dies should focus on compositions featuring a substantial presence of refractory metals while maintaining a BCC crystal structure. This combination is likely to deliver the desired blend of thermal and mechanical properties, rendering these coatings exceptionally well-suited for the demanding requirements of hot-forging operations. Full article

The purpose of this study is to determine if forged TiAl alloys are worth using for small parts such as jet engine turbine blades. As part of this goal, this study investigated ways to improve the impact resistance of forged TiAl alloys and compared them to cast TiAl alloys. The effects of additive elements and microstructure on the impact resistance of forged ternary TiAl alloys of 43.5 at. % Al were evaluated using the Charpy impact test on specimens heated to 500 °C prior to testing. The impact resistance of the forged alloys improved with the addition of Cr, V, and Mn and deteriorated with the addition of Nb. The impact resistance of the microstructure containing a β-phase, a common microstructure in forged TiAl alloys, was significantly lower. The fully lamellar structure obtained at the expense of forgeability showed much higher impact resistance than this. However, even the best impact resistance of the forged alloys was significantly inferior to that of cast ternary alloys of 46.5 at. % Al prepared with the same additive content. Combined with the high cost and low high-temperature strength of the forged TiAl alloys, it is concluded that it is pointless to use forged TiAl alloys for small parts that can be made via casting. Full article