Melt Hydrogenation Research Articles

Exploration and development of (TiB + TiC)/Ti6Al4V through the economically viable melt hydrogenation technique

Titanium matrix composites (TMCs) are widely used for their excellent properties. This paper explores fabricating (2.5vol.%TiB + 2.5vol.%TiC)/Ti6Al4V composites under varying hydrogen concentrations in a hydrogen-argon mixed atmosphere, analyzing the microstructure through optical microscopy and scanning electron microscopy with electron backscattered diffraction patterns. The results show that hydrogen leads to microstructure refinement in the matrix, increases β phase content, and modifies reinforcing phase distribution. Three-point bend tests reveal improved room temperature fracture toughness when hydrogen gets incorporated.

Towards enhancing the hot deformability of Ti2AlN/Ti46Al4Nb1Mo composites via melt hydrogenation

A new strategy called melt hydrogenation was introduced in this study to improve the hot deformability of Ti2AlN/Ti46Al4Nb1Mo composites, which was directly melting materials in mixed gas of H2 and Ar with different ratios (H2 percentage: 0, 20% and 40%). XRD results showed that melt hydrogenation decreased the proportion of α2 phase, which was due to the narrowed α phase region and enlarged β phase region since hydrogen acting as β stable element. The length of Ti2AlN particles in as-cast composites increased, because hydrogen induced overheat on melt surface and then promoted the growth rate of Ti2AlN particles along their long axis. Hot compression results indicated melt hydrogenation effectively reduced the peak stress from 695 MPa to 605/603 MPa at 1100 °C/0.1 s−1 when H2 percentage was 20% and 40%, respectively. Deformed microstructure indicated that hydrogen accelerated dynamic recrystallization (from 55.6% to 74.7%) and increased the fraction of area with low density of dislocations (from 82.3% to 87.8%). In addition, hydrogen facilitated the formation of deformed nano-twins, which was probably due to hydrogen reducing the stacking fault energy. Therefore, the increased DRX, decreased dislocations density and more deformed nano-twins all contributed to the enhanced hot deformability of Ti2AlN/Ti46Al4Nb1Mo composites.

Insights into hydrogen-induced strengthening mechanism of TiC/Ti6Al4V via experiments and first-principles calculations

This study is dedicated to summarize the strengthening mechanism of hydrogen microalloying for titanium matrix composites, i.e., 5 vol% TiC/Ti–6Al–4V, which is manufactured employing a unique technique called “melt hydrogenation” that involves melting alloys under a gas mixture of hydrogen and argon. This process enables the direct integration of trace hydrogen atoms into composites. The experimental results demonstrate that melt hydrogenation not only refines the microstructure of matrix but also promotes the network-like distribution of reinforcements. The three-dimensional atom probe tomography analysis of TMCs shows that the TiC/matrix interfaces can effectively trap hydrogen. Combining the high-resolution transmission microscopy observation and ab-initio calculation on the interface between matrix and reinforcement, it suggests that the addition of hydrogen improves the interfacial adhesion work, which has important implications for the improvement of load-bearing capacity of interface. Therefore, thanks to the above-mentioned structural changes, the room-temperature strength and plasticity can be simultaneously improved with the minor addition of hydrogen. These findings are of great significance for the further development of high-performance titanium matrix composites.

Hydrogen-induced microstructure optimization and mechanical properties enhancement of forged (TiB + TiC)/Ti6Al4V

This study investigates the impact of hydrogen on the mechanical properties and microstructure of forged titanium matrix composites (TMCs) reinforced with 2.5 vol% TiB and 2.5 vol% TiC. Melt hydrogenation technology was used to fabricate the TMCs with different hydrogen contents, which were then forged at 880 °C. Microstructural analysis revealed that hydrogen accelerated atomic diffusion, resulting in an approximate network microstructure. Hydrogen also promoted dynamic recrystallization during forging, leading to grain refinement and reduced dislocation density. Room temperature tensile tests showed that hydrogen significantly improved the strength and ductility of the forged TMCs within a certain range of hydrogen content. The greatest improvement was observed in the forged TMCs with a hydrogen content of 7.87 × 10−2 wt%, which exhibited a 10.48% increase in yield strength and a 31.36% increase in ductility relative to those without hydrogen. The effects of hydrogenation on crack propagation mechanisms are also discussed in detail. Overall, these findings provide valuable insights into the strengthening and toughening of forged titanium matrix composites through hydrogenation.

Effects of Melt Hydrogenation on the Microstructure Evolution and Hot Deformation Behavior of TiBw/Ti-6Al-4V Composites

In this study, Ti-6Al-4V matrix composites reinforced with TiB ceramic whiskers were in situ synthesized and hydrogenated using the melt hydrogenation technique (MHT). The effects of MHT on the microstructure evolution and hot compression behavior of the composites were investigated by optical microscopy (OM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Hot compression tests were performed at strain rates of 0.1/s, 0.01/s, and 0.001/s and temperatures of 800 °C, 850 °C, and 900 °C; the hot workability of composites significantly improved after hydrogenation, for example, the 900 °C peak flow stress of hydrogenated composites (43 MPa) decreased by 53.76% compared with that of unhydrogenated ones (93 MPa) at a strain rate of 0.01/s. Microstructural observations show that MHT can effectively facilitate the dispersion of TiB whiskers and induce the α/β lath refinement of the matrix in our as-cast hydrogenated composite. During hot compression, MHT effectively promoted the as-cast composite microstructure refinement, accelerated the dynamic recrystallization (DRX) generation, and reduced the stress concentration at the interface between the reinforcement and matrix; in turn, the hydrogenated composites presented low peak stress during hot compression.

Superior hot workability of (TiB+TiC)/Ti-6Al-4V composites fabricated by melt hydrogenation

In order to improve the poor hot workability of titanium matrix composites (TMCs), an advanced melt hydrogenation method was introduced in this study. The (TiB+TiC)/Ti-6Al-4 V composites were fabricated by melt hydrogenation which was directly melting alloys in gas mixture of H2 and Ar. Microstructure of as-cast TMCs indicated that melt hydrogenation increased the length of TiB whiskers and aggravated the clustering of reinforcements at primary β grain boundaries, which was due to the increased overheat on melt surface. Hot compression results indicated melt hydrogenation improved the hot workability of TMCs in (α + β) phase region, and the peak stress was reduced from 371 to 271 MPa at 800 °C/1 s−1 and from 119 to 60 MPa at 900 °C/0.01 s−1, respectively, which expanded the optimal hot processing window. Microstructure after hot deformation showed that the proportion of DRX grains was increased from ∼56% to ∼81%, which was mainly attributed to the accelerated migration of DRX grain boundary and the decreased density of dislocations, which was due to the dislocation consumption by DRX formation and the improved mobility of dislocations. Therefore, the improvement of hot workability resulted from the formation of more DRX grains and enhanced mobility of dislocations.

Microstructural characterization and mechanical properties of (TiB + TiC) reinforced Ti–6Al–4V prepared by melt hydrogenation

TiB and TiC reinforced Ti–6Al–4V matrix composites were prepared by melt hydrogenation, in which the total fraction of the reinforcements was 5 vol % and the ratio of TiB to TiC was 1:1. The effects of melt hydrogenation on the solidification process, phase composition, and microstructure of the titanium matrix were studied. The morphology and distribution of the reinforcement without and with hydrogen were observed. Moreover, the nano-hardness of the composites was measured. The results show that the solidification process of the matrix can be changed by melt hydrogenation, which resulting the increase of β phase and refining of α lamellar in titanium alloy. Hydrogen increased the size of the reinforcements, which aggregated at the grain boundary of the primary β phase and formed a network structure. Hydrogen reduced the nano-hardness both of the titanium alloy and the reinforcements slightly. In summary, melt hydrogenation can maintain or slightly reduce the strength of the composites at room temperature and decrease the nano-hardness.

Microstructure Evolution and Enhanced Hot Workability of TiC/Ti-6Al-4V Composites Fabricated by Melt Hydrogenation.

Improving the hot workability and reducing the processing cost are critical steps to expanding the application of TiC/Ti-6Al-4V composites. This study employed melt hydrogenation to fabricate TiC/Ti-6Al-4V composites under a mixed atmosphere of hydrogen and argon. Experimental results indicated that hydrogen had an obvious influence on the growth and morphology of eutectic TiC particles, and the size of eutectic TiC and primary β grains was significantly increased. As a result, large-sized eutectic TiC was distributed along the grain boundaries of primary β grains. Hot compression results showed that the peak flowing stress of composites was reduced by hydrogen, which resulted in an improvement of hot workability, especially in the (α + β) phase region, and the best results were obtained at 900 °C/0.01 s-1, at which the peak stress decreased from 241 ± 9 to 190 ± 8 MPa (a decrease of 21.2%). Inspection of the microstructure after hot compression showed that hydrogen improved the proportion of DRX grains from ~62.7% to ~83.2%, and hydrogen also decreased the density of dislocations, which were attributed to hydrogen accelerating atomic diffusion. Enhanced hot workability resulted from hydrogen atoms decreasing the atomic bonding force of the titanium matrix, hydrogen reducing the β/(α + β) transition temperature, the higher proportion of DRX, and the higher mobility of dislocations. It is expected that the findings of this study may support the development of a simple and efficient method to reduce the processing cost of TiC/Ti-6Al-4V composites.

Hydrogen-induced modification of the interface between matrix and ceramic phase of (TiB + TiC)/Ti–6Al–4V

This work intends to investigate the effect of melt hydrogenation on the interface between reinforcements and matrix. A novel method for direct incorporation of trace hydrogen atoms into composites by melting alloys under a mixed gas of hydrogen and argon (termed “melt hydrogenation”) is used to fabricate (TiB+TiC)/Ti–6Al–4V. Experimental observations illustrate that the hydrogen optimizes interface bonding strength, which is manifested in that the load can be more efficiently transferred from the matrix to the reinforcement. It is found that the thickness of the “transition layer” at the interface becomes thinner as the hydrogen content increases, characterized by the line scan mode of the transmission electron microscope. When the hydrogen content reaches 7.87 × 10−2 wt%, the atomic arrangement at the interface gets so orderly that the interface is strictly coherent according to the orientation relationship. These findings are of great significance for revealing the optimization mechanism of hydrogen on composite interfaces.

Effect of melt hydrogenation on microstructure evolution and tensile properties of (TiB + TiC)/Ti-6Al-4V composites

In order to fabricate in-situ synthetic (TiB + TiC)/Ti-6Al-4V composites, we conducted arc-smelting in the atmosphere of hydrogen and argon gaseous mixture using a melting casting method of melt hydrogenation technology. Some experimental parameters such as arc current, voltage, gas partial pressure and smelting time were precisely controlled. The molar ratio of the ceramic phase is 1:1 at a total integral of 5%. The microstructure evolution, tensile properties and fracture mechanism of the composite at room temperature are revealed and discussed.The results of the tensile test demonstrate that melt hydrogenation technology remarkably improves the ultimate strength of (TiB + TiC)/Ti-6Al-4V composites accompanied by slight increase of elongation, in which the 5 vol% (TiB + TiC)/Ti-6Al-4V increased by 15.19% from 901.42 MPa to 1038.42 MPa with elongation increasing from 0.47% to 0.78%, compared with that of the unhydrogenated composites. The improvement in the strength of the composite can be attributed to the refinement in matrix α layer and the increasement of the aspect ratio of TiB whiskers. The use of melt hydrogenation technology is found to change the trend of segregation of ceramic phase to primary β phase at grain boundaries into random dispersion distribution.

Hot-deformation behaviour and hot-processing map of melt-hydrogenated Ti[sbnd]6Al[sbnd]4V/(TiB+TiC)

The hydrogen was straight-forward added to the Ti6Al4V/(TiC + TiB) composites (TiCTiB=5 vol.%) by melt hydrogenation. The results of hot compression show that the peak resistance of titanium matrix composites (TMCs) decreased by 17.2% when hydrogen content was 0.035 wt% compared with the TMCs without hydrogen. Therefore, the TMCs with a hydrogen content of 0.035 wt% was performed to a thermal compression experiment. Thermal-deformation characteristics and hot processing map of TMCs with a hydrogen content of 0.035 wt% were analyzed in the light of the flow stress curve, constitutive relations, and the dynamic-material model. The computed apparent activation energy was 284.54 kJ/mol, and the corresponding strain-rate sensitivity, power dissipation, and instability parameter were calculated. The hot-processing map exhibited maximum efficiencies of power dissipation at 780–840 °C/0.005–0.06 s−1 and there was only one instable region. The microstructures corresponding to the stable and instable region were verified, confirming the optimum processing parameters of hot-working that can be used as a reference for hot deformation of hydrogenated composites.

Hydrogen induced microstructure evolution of titanium matrix composites

The effect of melt hydrogenation on microstructure evolution of Ti-6Al-4V matrix composites was investigated in this study. Molten alloy was hydrogenated with a mixture of hydrogen and argon, and reinforced at 5% total volume fraction with a 1:1 mol ratio mixture of TiB and TiC particles. Microstructure of as cast composites showed hydrogen induced more TiB whiskers with higher length-diameter ratio (LDR), because hydrogen accelerated atomic diffusion and then increased growth rate of TiB whiskers. Hot compression results indicated hydrogen reduced peak flowing stress. Microstructure of as compressed composites indicated hydrogen encouraged decomposition of residual lamellas. Hydrogen eliminated most cracks and holes along the interface between ceramic particles and matrix. Compared with unhydrogenated composites, the original ceramic particles in hydrogenated composites were fragmented into smaller pieces after compression. Electron back-scattered diffraction and transmission electron microscopy results indicated hydrogen increased volume fraction of dynamic recrystallization (DRX). And hydrogen decreased the density of dislocations nearby the interface.

Positive effect of hydrogen on interface of in situ synthesized Ti-6Al-4V matrix composites

This paper presented another methodology, melt hydrogenation (melting alloys in gas mixture of argon and hydrogen), to produce in situ synthesized Ti-6Al-4V matrix composites (TMCs) with quality interface after hot deformation. Microstructure results of as cast TMCs indicated hydrogen didn’t obviously change morphology of interface, but induced more TiBw whiskers with higher length-diameter ratio, which was attributed to hydrogen improving growth rate of TiBw whiskers by accelerating atomic diffusion. After hot compression, experimental results indicated proper content of hydrogen addition decreased the flowing stress of both matrix and TMCs, and eliminated most cracks and holes along the interface, quality interface without defects was attributed to improvement on flowing ability of matrix alloy. The positive effect of hydrogen on interface was explained by hydrogen induced softening on matrix alloy. Electron back-scatter diffraction (EBSD) images indicated hydrogen increased softer β phase content which was favor to fill up the defects caused by crush of ceramic particles. And hydrogen promoted discontinuous dynamic recrystallization (DRX) by accelerating migration of grain boundaries which ended up at the interface, and then eliminated defects caused by disharmonious motion between ceramic particles and matrix.

New insights into melt hydrogenation effects on glass-forming ability in a Zr-based bulk metallic glass

Notable improvements in the glass-forming ability (GFA) of Zr-based metallic glasses with melt hydrogenation have been reported in our previous studies. The effects of hydrogen on GFA are usually explained via short-range structural order, local symmetry, structural free-volume, and bonding character. To fundamentally understand why hydrogen enhances GFA, thermal analyses were carried out on a Zr55Cu30Ni5Al10 amorphous alloy to assess how hydrogen affected viscosity, fragility, critical cooling rate, and Gibbs free energy difference, ∆G. Amorphous alloys subjected to melt hydrogenation were found to possess higher viscosity and lower fragility, indicating increased GFA. The critical cooling rate of hydrogenated alloy melts gradually decreased and the lowest critical cooling rate was 10K/s when the alloy was fabricated in Ar+10%H2. The liquid/solid ∆G of melt‑hydrogenated alloy was significantly smaller than that of the equivalent non‑hydrogen alloy. From thermodynamic and dynamic perspectives, viscosity, fragility, critical cooling rate, and ∆G demonstrated that melt hydrogenation improved these alloys' GFA and explained the present experimentally observed improvements in GFA.

Microstructures and mechanical properties of melt hydrogenated Nb-Si based alloy

Nb-20Si-6Mo (at.%) alloy was prepared by arc melting under Ar-H2 gas mixture atmosphere (Melt Hydrogenation Technology). It indicated that the microstructures of Nb-20Si-6Mo alloy change significantly after the melt hydrogenated treatment. The morphologies of primary Nb5Si3 phase change from polygon to dendrite shapes with the increase of H content. The room temperature compression at same strain rate indicates that the σmax decreases with the increase of hydrogen content. High temperature (1400 °C) compression at same strain rate indicates that H addition can cause the peak strain to take place in advance at high deforming temperature. The high temperature compression stress tends to firstly increase and then decrease due to the effect of H addition. The reason for the effects of hydrogenation on the high temperature compression stress of Nb-20Si-6Mo alloy has been discussed.

Hot deformation behavior and dynamic recrystallization of melt hydrogenated Ti-6Al-4V alloy

The effect of hydrogen on hot deformation behavior of Ti-6Al-4V alloy was investigated. Ti-6Al-4V alloy was hydrogenated by melting alloy in gas mixture of hydrogen and argon (melt hydrogenation). Experimental results of hot compression at same strain rate showed hydrogen decreased flow stress at higher deforming temperature, which was attributed to hydrogen induced dislocation movement and dynamic recrystallization (DRX). At lower temperature, peak stress firstly decreased and then increased with increasing hydrogen content. Hydrogen decreased the peak stress and improved the hot workability of alloy deformed at same temperature and different strain rates. Microstructure observation of as deformed alloy indicated hydrogen promoted DRX on both α and β phase, and encouraged the decomposition of residual lamella. Electron back-scattered diffraction results indicated that hydrogen mainly encouraged discontinues DRX and decreased the dislocation density in α phase. Compared to unhydrogenated alloy, when hydrogen content was 5.31 × 10−2 wt.%, volume fraction of DRX increased from 42% to 53% and 41.8%–72.1% at strain rate of 0.01 and 0.001 s−1, respectively.

High temperature deformation behavior of melt hydrogenated (TiB + TiC)/Ti-6Al-4V composites

Ti-6Al-4V matrix composites with 5vol% TiB and TiC particles were in situ synthesized in this study. Hydrogen was added into the composites directly by melting the composites in gas mixture of hydrogen and argon (Melt Hydrogenation Technology). Microstructure observation results showed that hydrogen addition changed the distribution of ceramic particles to near network structure. The effect of microstructure, deforming temperature, strain rate and hydrogen content on high temperature compressive behavior were investigated. Thermal simulation results of high temperature compression at same strain rate indicated that hydrogen addition caused softening effect at higher deforming temperature and hardening effect at lower temperature, competition of the dominant effect was decided by distribution of ceramic particles and microstructure of matrix. Experimental results of hot compression at same deforming temperature and increasing strain rate indicated that moderate hydrogen content decreased the peak stress and improved the hot workability of composites. Microstructure observation of as compressed composites indicated that hydrogen eliminated defects and encouraged the dynamic recrystallization (DRX) after hot compression, the mechanism of hydrogen induced improvement of DRX, and relationship among hydrogen content, dislocations density and percentage of DRX were discussed.

Hydrogen induced softening and hardening for hot workability of (TiB + TiC)/Ti-6Al-4V composites

(TiB + TiC)/Ti-6Al-4V composites were in situ synthesized and hydrogenated by melt hydrogenation technology (melting alloys in gas mixture of hydrogen and argon). Microstructure observation indicated that reinforcements were homogenously distributed in unhydrogenated composites, with the increase of hydrogen content, the reinforcements tend to locate at prior β grain boundaries to form near network structure. Results of high temperature deformation showed that the hot workability of titanium matrix composites was determined by the microstructure of titanium matrix and distribution of reinforcements. There was a competition between hydrogen induced hardening and softening effect. When deformed at 850 °C, hydrogen induced promotion of β phase content and dynamic recrystallization reduced the peak stress and lead to softening effect, below 850 °C, hydrogen induced near network structure caused hardening effect because the load bearing capacity of network structure was better than the homogenously distributed reinforcements.

Effect of hydrogen addition on the mechanical properties of a bulk metallic glass

The bending and nanomechanical behaviors of a Zr55Cu30Ni5Al10 bulk metallic glass were investigated in the present work via melt hydrogenation. The room temperature bending plasticity of samples after hydrogen addition is observed improving gradually with the increase of addition amount. A softening phenomenon is appeared in the results of nanoindentation, concomitantly with a decrease in the elastic modulus of the samples. A simple “spacer” model of hydrogen atoms can be used to describe for the softening behaviors of the Zr55Cu30Ni5Al10 samples prepared by melt hydrogenation in this work. The “spacer” can enhance the distance of the metal atoms and decrease the corresponding atomic cohesion which is represented as the elastic modulus. The local changes of the atomic configuration give rise to the emergence of large void structures which will facilitate the local atomic displacement. Consequently, the “spacer” effect promotes the shear band proliferation and weakens the local shear deformation, and this in turns, leads to the large plastic deformation in the amorphous alloy. The results may have some implications for improving the plasticity of bulk metallic glass and understanding its hydrogen-induced softening.

The influence of melt hydrogenation on Ti600 alloy

In this paper, melt hydrogenation, which is a new hydrogen treatment method, was used to hydrogenate Ti600 alloy, the relationship between the hydrogen partial pressure and the hydrogen content was built by analyzing experimental data, and microstructure was observed and mechanical properties was tested. It was found that hydrogen addition made the thickness of the solidified shell thinner and a big temperature gradient existed from the top to bottom surface of the alloy melt. With increasing hydrogen partial pressure, the directional solidification structure can be formed in the Ti600 alloy ingots. Microstructure of Ti600 alloy was modified significantly and the amount of α′ and β phases after melt hydrogenation. When increasing the content of hydrogen to 7.2 at.%, γ hydride was obtained in Ti600 alloy. The flow stress and yield stress decrease with increasing the hydrogen content.