Carbide Ti Research Articles

Elucidation and verification of cracking behavior in additive manufacturing of alloy 718 based on fractography

This study identified a cracking that occurred continuously in the built direction of an additive manufactured part of alloy 718 by the laser metal deposition method and clarified the cracking behavior. The solidification microstructure of alloy 718 was evaluated by EDS, EPMA, and extraction residue, and it was found that Laves phase, Ti carbides, and Al oxides were formed between the dendrite microstructures. A fracture surface analysis of the cracks revealed that the cracking in the additive manufacturing was hot cracking associated with the liquid film and that the cracking occurred along the grain boundaries. The fracture surface at the beginning of the cracking showed a solidification cracking fracture surface. The experimental investigation for crack propagation during additive manufacturing and the analytical evaluation of the mechanical state around the cracking using thermal elastic-plastic analysis elucidated the cracking behavior during additive manufacturing. If the cracking exists at the fusion boundary, it is suggested that the cracking initiates from the solid-liquid interface towards the solidification direction. Moreover, tensile strain occurred around the cracks during additive manufacturing, particularly the strain was biggest at the crack edge on the fusion boundary. Therefore, the continuous cracking that occurred beyond each layer in the additive manufacturing of alloy 718 in this study can be considered solidification cracking, and its behavior can be further explained as a notch extension cracking that starts from the solidification cracking and continuously occurs in the solid-liquid coexistence temperature region.

Microstructure and constitutive modeling of an ultrafine-grained refractory high-entropy alloy fabricated by powder metallurgy

In the present study, a novel AlCr0.3FeMoNbTiV2 alloy was prepared by means of mechanical alloying and subsequent spark plasma sintering, resulting in an ultrafine-grained (UFG) microstructure consisting of a bcc matrix phase with an average grain size of 0.32 μm accompanied by Ti carbide, Laves phases, and minor contents of Al2O3. Excellent thermal stability was exhibited by the alloy, since no considerable phase transformations were observed after a heat treatment at 1350 °C for 16 h, beyond microstructural coarsening, as can be appreciated from the increase of the average bcc grain size up to 1.50 μm. Compression tests were performed at elevated temperatures (950–1100 °C) at strain rates ranging 0.0005–0.01 s−1. According to the constitutive analysis of the peak stress using the hyperbolic sine law, an experimental creep exponent of 2.17 was obtained, which indicates that deformation is mainly controlled by grain boundary sliding, as typically observed in UFG materials, with a large apparent activation energy of 527.7 kJ mol−1, superior to that of other RHEAs reported in literature.

Синтез карбидов (Ti,Cr)xCy в сплаве ВТ6 методом прямого лазерного нанесения материалов

The possibility of forming carbides of the (Ti,Cr)xCy type in the Ti6Al4V alloy by the method of direct laser deposition of materials (DLD) is shown. A new method for the synthesis of carbides of the (Ti,Cr)xCy type consists in preliminary laser cladding of carbon fibers with chromium, adding them to the VT6 powder mixture, and fusing the resulting DLD composition. Thus, a new Ti6Al4V/CFs/Cr alloy was obtained. The formation of carbides of the CrxCy type was revealed in the coating on carbon fibers (CF/Cr). The appearance of CrxCy carbides in CF/Cr samples is due to the interaction of carbon with chromium as a result of laser processing. The average microhardness of the Ti6Al4V/CFs/Cr alloy was 700 ± 100 HV0.01. At the same time, the hardness of the detected carbides (Ti,Cr)xCy in the Ti6Al4V/CFs/Cr alloy was 1000 ± 40 HV0.01. During the DLD process, the carbon fiber can be completely or partially dissolved. In the composite material Ti6Al4V/CFs/Cr, carbides (Ti,Cr)xCy are formed. It is shown that the hardness of the detected carbides is 2 times higher than the hardness of the composite material. It has been established that the friction coefficient of the VT6 alloy under increased load decreases by 1.5 times after 20 min of testing, while the friction coefficient of the Ti6Al4V/CFs/Cr alloy remains stable and equals 0.27 over the entire test interval.

Impact of Low Catalyst Loading and Incorporation of Additives on Structure and Performance of PEM Electrolyzer Catalyst Layers

Polymer electrolyte membrane water electrolyzers (PEMWEs) are an important technology that can produce renewable hydrogen on demand, although with challenges posed by the slow kinetics of the anodic oxygen evolution reaction (OER) and degradation issues. The degradation of membrane electrode assemblies (MEAs) prepared with Ir-based catalysts is not well understood, especially with lower-loading catalyst layers and intermittent load inputs. This work investigates low-loading IrO2 catalyst layers made with different carbon-based additives, including high-surface-area carbon (HSC), graphitized HSC (gHSC), Vulcan, graphitic carbon nanofibers (gCNFs), graphitic nanoplatelets (gNPs), nitrogen-doped carbon spheres (NCs), Ti carbide (TiC) and Ti carbonitride (TiCN). While carbon-based supports have issues with corrosion at high oxidizing potentials, these materials provide a range of variations in morphology, shape, size, surface area, graphitization, and composition, allowing exploration of the impact of these parameters on catalyst layer structure to identify promising routes to improve catalyst layer structures. Catalyst layers were characterized with electron microscopy and x-ray spectroscopy to assess the distribution of catalyst, carbon additive, and ionomer. This information was correlated with electrochemical performance measurements to elucidate the impact on kinetic site access and mass transport. Selected samples were also subjected to more extended operation to investigate how the initial structures and their performance evolved.

Localized Corrosion Behavior of UNS N07718 in a Solution Simulating a Diluted-sour Environment

The localized corrosion behavior of precipitation-hardened UNS N07718 was investigated by immersion tests in 6 wt% FeCl3 + 1.0 wt% HCl and the use of electrochemical techniques in a simulating solution of a diluted-sour environment of 25 wt% NaCl + 0.5 wt% CH3COOH. The Ti carbides and Nb-Mo carbides with 1-10 µm size were distributed in the alloy. After immersion at a solution temperature higher than 45oC, localized corrosion with a depth of over 25 µm was identified, and the critical pitting temperature was determined to be 45oC. Potentiodynamic polarization showed that the surface of the UNS N07718 was immediately passivated in the experimental solution. The passivity-maintaining current density was gradually increased with increasing solution temperature, and finally, localized corrosion was initiated or propagated at 0.5 VSSE in 80oC. The localized corrosion was initiated or propagated at the interface between the Ti and Nb-Mo carbides and the alloy substrate. Scanning Kelvin probe microscopic images revealed that the contact-potential difference values were in the order of Ti carbide > Nb-Mo carbide > alloy substrate, indicating that the carbides and alloy substrate act as a cathode and an anode, respectively, forming a micro-galvanic couple. Therefore, it is concluded that localized corrosion is initiated at the interface between the carbides and substrates in UNS N07718.

Wet Ball Milling Applied to Production of Composites and Coatings Based on Ti, W, and Nb Carbides

The paper demonstrates the potential of wet ball milling of metals for the synthesis of various carbides and carbohydrides. The work reports on multicomponent carbides formed in Ti-(Cu/Fe/Si)-C, W-Fe-C, and Nb-(Cu/Fe/Si/Al)-C systems, as well as metastable or high-temperature intermetallics formed in Ti-Si, Nb-Si, Nb-Al, and Nb-Cu-Fe systems, which are stabilized with interstitial carbon. The formation of phase composition of powders fabricated under mechanochemical synthesis and subsequent thermal treatment has been studied. The as-fabricated powders have been used to produce bulk compacts and to apply wear-resistant coatings on steel (iron).

Corrosion behavior of TiC/amorphous carbon coated stainless steel as bipolar plate for proton exchange membrane fuel cell

PurposeThe purpose of this paper is to improve the corrosion resistance of stainless-steel bipolar plate by magnetron sputtering.Design/methodology/approachTiC/amorphous carbon composite film was deposited by magnetron sputter at four different temperature of 25°C, 200°C, 300°C and 400°C. The morphology, composition and structure of the film were characterized by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. And its corrosion behavior was analyzed through electrochemical impedance spectroscopy, potentiodynamic and potentiostatic polarization tests.FindingsA compact TiC/amorphous carbon film was prepared by magnetron sputtering on 316L stainless steel, and the particles of the film were refined with the increase in sputtering temperature. High temperature promoted the formation of TiC and C–C sp2 hybrid carbon, but excessively high temperature caused the oxidation of Ti and a significant decrease in sp2 hybrid carbon. The corrosion resistance of the film increased with the temperature, and the corrosion current density polarization at 0.86 V and 1.8 V for TiC/a–C film prepared at 400 °C is only 1.2% and 43.2% of stainless steel, respectively.Originality/valueThe corrosion resistance of amorphous carbon films was improved by the doping of Ti carbide, and the appropriate sputtering temperature was obtained.

Microstructure and Wear Resistance of Ni–WC–TiC Alloy Coating Fabricated by Laser

In this study, a Ni–WC–TiC alloy coating was fabricated by laser to improve the wear resistance and service life of Cr12MoV die steel. The microstructures and phases of the coating were analyzed by a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The properties of the coating were tested by a hardness and friction wear tester. The results show that the coating has a good metallurgical bond with the substrate. The microstructures from top to bottom are mainly equiaxed crystal, columnar dendrite, and cellular dendrite. Combined with the physical phase analysis and elemental distribution of the coating, there are some phases, such as γ~(Fe, Ni), Cr23C6, WC, TiC, Fe3W3C, and Cr2Ti. Compared with the Cr12MoV steel substrate, the Ni–WC–TiC alloy coating has good properties of hardness and wear resistance. In the coating, the background region of the grains is γ~(Fe, Ni). From the EDS results, it can be seen that there are some rod-like particles, Cr23C6, which are uniformly distributed on the top of the coating. Some W and Ti carbides form in grains. The addition of TiC particles improves the WC particles refinement. The highest hardness of the coating is 770.7 HV0.5, which is approximately 3.3 times higher than that of the substrate. The wear volume is 0.26 mm3, or approximately 8.6% of the substrate, which is contributed to the reinforced phases and finer microstructure of the coating. The wear volumes of the Cr12MoV substrate are 1.8 and 4.5 mm3 at 20 and 60 min, respectively. While the wear volumes of the Ni–WC–TiC coating are 0.2 and 0.7 mm3 at 20 and 60 min, respectively. The increased amplitude of the coating’s wear volume is smaller than that of the substrate. The results show that this Ni–WC–TiC alloy coating is helpful for improving the properties and service life of Cr12MoV die steel.

Molybdenum alloy Mo-Ti-Zr-C adapted for laser powder bed fusion with refined isotropic microstructure and excellent high temperature strength

The molybdenum‑titanium‑zirconium‑carbon alloy TZM is one of the few molybdenum alloys that can be processed crack-free in laser powder bed fusion (LPBF). However, the parts have a coarse-grained, columnar microstructure comprising epitaxially grown grains, and their strength is limited by residual porosity. Consequently, the mechanical properties do not reach the values of their conventionally powder-metallurgically produced pendants. In this work, the conventional alloy composition of TZM was adapted to the unique processing conditions in laser powder bed fusion by increasing the carbon content, and the effects on the microstructure and mechanical properties were investigated.Increasing the carbon content to 2.3 at.% yielded a significantly refined and isotropic microstructure. In addition, C led to the formation of a cellular subgrain structure consisting of (Mo, Ti) cells 0.4 ± 0.1 μm in size surrounded by a closed network of ternary (Mo, Ti) carbide. Residual oxygen impurities in C-modified TZM were partly dissolved in the ternary (Mo, Ti) carbide network and partly bound by Zr as nanometer-sized ZrO2 particles. These two mechanisms for binding oxygen minimized oxygen segregation—a major issue limiting the grain boundary strength in Mo and Mo alloys—and thus purified and strengthened the grain boundaries. The mechanical strength increase due to the increase in carbon content was 50% (0.5 at.% C vs 2.3 at.% C). At elevated test temperatures of 800 °C and 1200 °C, TZM-2.3 at.% C exceeded the ultimate tensile strength (UTS) of conventionally produced TZM by 24% and 16%, respectively.

Topography of high-speed steel substrates sputter cleaned by an Ar/Ti cathodic arc plasma

Hard coated high-speed steels are often used for tooling applications and consist of three different microstructural constituents: a martensitic matrix, M6C and MC carbides. The behavior of these three during the various tool manufacturing steps has a detrimental effect on the final tool performance. The focus of the current work is the surface topography change due to variation of the substrate bias voltage applied during the Ar/Ti arc plasma sputter cleaning process which changed the sputtering behavior of the high-speed steel's microstructural constituents and the appearance of droplets on the sputtered surface. The surface topography was characterized by laser confocal and scanning electron microscopy. Furthermore, microstructural analysis was carried out on cross-section lamellae prepared by a focus ion beam technique and analyzed by transmission electron microscopy. At each of the three investigated substrate bias voltages (Ub) of −600, −800 and −1000 V during the Ar/Ti arc plasma sputter cleaning process, the mentioned microstructural constituents behaved differently. At an Ub threshold of −600 V, sputter erosion starts at M6C carbides in an inhomogeneous material erosion pattern. At −800 V, a homogeneous sputter behavior was established for the entire sample. M6C carbides showed the highest sputter erosion rate, on MC carbides Ti deposition occurred instead of sputter erosion, and the martensitic matrix was smoothened, as peaks and exposed features were sputtered preferentially. As of Ub = −1000 V, the sputter erosion behavior of the martensitic matrix changed and exposed features were preserved. The reason for this change was identified to be Ti+ ion implantation indicated by Monte Carlo simulations and the associated increase of the matrix' cohesive strength, calculated using Density Functional Theory. The published results in this study will help to further utilize Ar/Ti arc plasma sputter cleaning processes for intentional surface topography design.

Identifying the surface properties of Ti3C2Tx MXene through transmission electron microscopy

The titanium carbide Ti 3 C 2 T x (T x = surface functional groups) MXene exhibits promising physical properties and chemical activity as one of the most commonly and extensively investigated materials, but the participating surface structures and properties have yet to be clarified. Here, we reveal the superficial nature of etching-processed Ti 3 C 2 T x using transmission electron microscopy/spectroscopy, first-principles calculation, and molecular dynamics simulation. An O-rich, but C-deficient, diffusion layer (approximately 3 nm) with an inverse gradient distribution is identified. Associated with the superficial substitution of O for C, an amorphous overlayer (approximately 2 nm) containing oxyfluoride of Ti, Al, and C is also revealed. The stable diffusion layer has a high density of states at the Fermi level and a low shear modulus to bulk modulus ratio, implying that the formation of the diffusion layer is not detrimental to Ti 3 C 2 T x ’s conductivity and ductility. These findings are significant for improving oxidation strategies and understanding the structural properties of this material. • O-rich, but C-deficient, diffusion layer and oxyfluoride overlayer are identified • Diffusion layer preserves layered structure, and oxyfluoride overlayer is amorphous • Electron transfer is found between Ti and C and between Ti and O in diffusion layer • Stable diffusion layer is no harm to conductivity and ductility of Ti 3 C 2 T x Wang et al. reveal the atomic configurations and electrical and mechanical properties of superficial Ti 3 C 2 T x MXene using transmission electron microscopy, first-principles calculation, and molecular dynamics simulation. The discovery of the diffusion layer and oxyfluoride overlayer is critical for improving oxidation strategies and understanding the structural properties of this material.

Effect of Ti addition and cast part size on solidification structure and mechanical properties of medium carbon, low alloy cast steel

In this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated. The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was found that the addition of Ti in the higher concentrations refines the solidification macrostructure (dendritic pattern) for both cast part sizes evaluated. Regarding mechanical properties, the addition of Ti does not significantly vary the ultimate tensile strength but reduces the total elongation for cast part sizes

Unveiling the phase evolution and mechanical properties of Ni1.5Co1.5CrTix alloys with ultrafine/nano structure

Oxide dispersion strengthening (ODS) is an effective way to optimize mechanical performance, radiation tolerance and wear resistance in alloys. Therefore, in this research, lightweight and oxyphilic element Ti was utilized to induce oxides particles for in-situ fabricating ODS alloys. We investigated systematically the influence of Ti content on the phase evolution and mechanical behaviors of Ni1.5Co1.5CrTix (x = 0, 0.2, 0.4, molar ratio) multi-principal element alloys (MPEAs) fabricated by mechanically alloying and high-pressure sintering (HPS). The Ni1.5Co1.5CrTix powders presented BCC phase, FCC phase and few additional oxides. Following HPS, the BCC phase transformed to FCC phase in these MPEAs. Ni1.5Co1.5Cr MPEA was composed of FCC, Cr7C3 and Cr2O3 phases. As Ti content increased, Cr oxides or carbides gradually transformed into Ti oxides or carbides. The Ni1.5Co1.5CrTix (x = 0.2, 0.4) MPEAs after HPS displayed ultrafine grained FCC matrix and uniformly dispersed ultrafine/nano Cr-C or TiOC complex compounds. With Ti content increasing, the grain sizes of FCC matrix and precipitates had a tendency to decrease. Quantitative increment of precipitation-strengthening and fine-grain-strengthening clarifies the influence of Ti content on MPEAs. The investigations may provide key insights into tuning Ti content into the MPEAs for being available structural materials.

Beneficiation of Nb and Ti carbides from pyrochlore ore via carbothermic reduction followed by magnetic separation

Beneficiation of niobium and titanium carbides from pyrochlore ore via carbothermic reduction followed by magnetic separation was investigated in this work. During carbothermic reduction, Nb, Ti and Fe oxides within the pyrochlore ore could be reduced into NbC, TiC and metallic iron, respectively. The carbides gather around and dissolve into the metallic iron grains, enabling the enrichment of niobium and titanium carbides by magnetic separation with the carrier of metallic iron. Under the optimal conditions: coke dosage of 6%, reducing temperature of 1400 °C and time of 120 min, a magnetic concentrate with 4.18% Nb, 4.60% Ti and 70.57% Fe can be obtained followed by wet magnetic separation. The corresponding recoveries of Nb, Ti and Fe were 70.5%, 59.8% and 92.6%, respectively.

Corrosion characteristics of Mo and TZM alloy for plasma facing components in molten lithium at 623 K

In this study, the corrosion behaviours of molybdenum (Mo) and a Mo-based alloy (TZM) were investigated using a static immersion corrosion technique. Weight loss, surface microstructure, and corrosion depth of Mo and the TZM alloy were correlated with elements. The compatibility of Mo and the TZM alloy in static liquid Li was suitable. Mo demonstrated uniform corrosion with a homogenous dissolution of free C and Mo, and TZM alloy exhibited a nonuniform corrosion behaviour with a preferential grain boundary attack caused by the selective dissolution of free C, Ti, and Zr. When the surface oxidation layer of the samples was consumed, free C from Mo and TZM diffused into molten Li to form Li2C2 and then was captured by Zr, Ti, and Mo to form thermodynamically stable carbides, which resulted in the enrichment of the C layer near the sample surfaces. In addition, Ti and Zr acted as N-trappers in liquid Li; the formation of Zr and Ti nitrides resulted in the enrichment of N, Ti, and Zr elements on the surface and led to TZM corrosion increase. Thus, Zr and Ti depletion, pitting, and grain boundary corrosion were problematic for TZM under long-term exposure to liquid Li. Reducing the content of free C and nonmetallic N and increasing the amount of Ti and Zr carbides on the surface of and inside the raw TZM alloy helped improve the corrosion resistance of TZM in liquid Li.

Changes in Abrasive Wear Resistance During Miller Test of Cr-Ni Cast Steel with Ti Carbides Formed in the Alloy Matrix

Changes in Abrasive Wear Resistance During Miller Test of Cr-Ni Cast Steel with Ti Carbides Formed in the Alloy Matrix

Metal (Mo, W, Ti) Carbide Catalysts: Synthesis and Application as Alternative Catalysts for Dry Reforming of Hydrocarbons-A Review.

Dry reforming of hydrocarbons (DRH) is a pro-environmental method for syngas production. It owes its pro-environmental character to the use of carbon dioxide, which is one of the main greenhouse gases. Currently used nickel catalysts on oxide supports suffer from rapid deactivation due to sintering of active metal particles or the deposition of carbon deposits blocking the flow of gases through the reaction tube. In this view, new alternative catalysts are highly sought after. Transition metal carbides (TMCs) can potentially replace traditional nickel catalysts due to their stability and activity in DR processes. The catalytic activity of carbides results from the synthesis-dependent structural properties of carbides. In this respect, this review presents the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide.

Comparative Study of Plasma Cladded Fe-Based Composite Hardfacings with <i>In Situ</i> Synthesized Cr and Ti Carbide Reinforcement

This study aimed to compare the X3CrNiMo17-13-3 stainless steel based plasma transferred arc (PTA) cladded hardfacings, reinforced with the in-situ synthesized Cr and Ti carbides. Carbon black and either pure Cr, pure Ti, or TiO2 were utilized as reinforcement precursors (the respective hardfacings are further referred to as Cr+C, Ti+C and TiO2+C). The pre-placed mixtures of matrix and reinforcement precursor powders were remelted by the plasma transferred arc, applying the preliminarily optimized process parameters (95 A, 22 – 24 V, 0.2 mm/s). As a reference, the unreinforced stainless steel hardfacing was used. The carbide reinforcement was successfully in-situ synthesized in all the hardfacings. The Cr + C hardfacing exhibited the largest average hardness (556 ± 29 HV1), while the TiO2 + C hardfacing had the largest average Young’s modulus (156.3 ± 19.7 GPa). The Cr + C and Ti + C hardfacings demonstrated the 2.3 and 2.1 times higher resistance to abrasive wear than the reference hardfacing. The TiO2 + C hardfacing showed 1.5 times lower wear resistance than the reference hardfacing presumably due to a lack of the reinforcement and a lower strain hardening ability.

Reduction in Work Functions of Transition-Metal Carbides and Oxycarbides upon Oxidation.

Herein, the work functions of group 4 and group 5 transition-metal (Ti, Zr, Hf, V, Nb, and Ta) carbides and transition-metal oxycarbides (TMCOs) were investigated by first-principles calculations for their potential application as electron emitters. The work functions of both groups decreased as the substitution of carbon atoms with oxygen proceeded, and the reduction in group 4 was more than that of group 5. In particular, ZrC1–xOx and HfC1–xOx (x ≥ 0.25) exhibited work functions of less than 3 eV, which were comparable with those of LaB6- and ZrO-coated tungsten. The reduction in the work functions could be explained by the rigid-band model of the electronic density of states. The increase in valence electrons increased the Fermi energy, while it demonstrated a less significant influence on the vacuum potential, resulting in a reduction in the work functions. The phonon dispersion curves indicated that the NaCl-type group 5 TMCOs were less stable than the group 4 TMCOs. This agrees with the experimental findings that TaC1–xOx was not synthesized and NbC1–xOx was synthesized only for smaller values of x (i.e., x < 0.28). From the viewpoints of the work functions and structural stabilities, group 4 (Ti, Zr, and Hf) TMCOs exhibit better potential for application as electron emitters than group 5 (V, Nb, and Ta) TMCOs.

Precipitated phase in the β phase of IN783 alloy

Abstract In Inconel 783 alloy, there are mainly two kinds of strengthening phases of β and γ’. In addition, it is found that there are other precipitated phases in the alloy’s β phase. By means of multiple testing methods, the types and functions of the precipitated phase in the β phase were determined. The results showed that the precipitated phases from β phase were nanoscale Nb and Ti carbides and a large number of white needle-like Laves phases. The former, due to its small size, which can improve the grain boundary slip resistance of the alloy, thus improves the shaping of the material. While the latter, due to its sharp shape and due to its large amount, destroys the original structure of the β phase and greatly reduces the room temperature plasticity of the alloy.