Dehydrogenation Treatment Research Articles

Tensile property and microstructure assessment of hydrogen treated Ti-6Al-4V alloy

Temporary hydrogen alloying (THA) treatment was used to refine the coarse-grained microstructure of a Ti-6Al-4V alloy with the intention of modifying tensile strength and ductility. Microstructure evolution was characterised using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results indicate that THA treatment does not refine the coarse network of prior beta grains, but it alters the coarse Widmanstätten microstructure by nucleating submicron beta grains within the individual lamellae. The modified microstructure increases ultimate tensile strength (UTS) in the order of 100 MPa. The dehydrogenation temperature affected tensile ductility. The lowest dehydrogenation temperature (675 °C) had the highest ductility loss, and increasing the dehydrogenation temperature recovered ductility until full ductility was recovered at 750 °C. The ductility loss was attributed to the embrittling effect of the hydrogen induced phase Ti3Al which remains in the microstructure even after hydrogen removal and only completely dissolves at 750 °C. The results demonstrate that THA treatment significantly alters the initial coarse-grained microstructure with concomitant improvement in strength, but that the promotion of Ti3Al precipitation can cause embrittlement unless the dehydrogenation treatment is controlled to optimise Ti3Al dissolution.

Mechanical Properties and Fracture Analysis of High Strength Bolts in Nuclear Power Plant

A high-strength bolt of a steel structure of a nuclear power plant failed and fell off. In order to determine the cause of the bolt’s fracture, a series of tests such as macro inspection, physical and chemical performance test, and microscopic analysis of the fracture were carried out on the failed bolt. The results show that the cause of bolt fracture is hydrogen embrittlement. Hydrogen infiltrated into the bolt during the phosphating process and the corrosion process during use, and then hydrogen continued to accumulate eventually causing hydrogen embrittlement fracture. Dehydrogenation treatment should be performed immediately after the phosphorylation treatment, and the anti-corrosion method of the bolt should be optimized, which is an effective measure to prevent the hydrogen embrittlement of high strength bolts.

The effect of hydrogen treatment on microstructures evolution and mechanical properties of titanium alloy fabricated by selective laser melting

The selective laser melting additive manufacturing can realize near-net forming and produce complex high-precision parts. However, β-columnar crystals will be formed in building direction, which leads to the decrease of material reliability, causing stress concentration and accelerating material fracture. Here, we perform hydrogenation treatment, solution treatment, aging treatment, and finally dehydrogenation treatment on Ti-6Al-4V titanium alloy fabricated by selective laser melting. The results show that the β grains of hydrogenated samples are refined after subsequent heat treatment. After the solution treatment, α' and α'' martensite coexist in the microstructure and decomposed during the subsequent aging and dehydrogenation treatment, resulting in the refinement of the structure within the grains, but still retaining the grain morphology of the previous alloy. When compressed at room temperature，the compressive strain and ultimate compressive strength of hydrogenated samples after heat treatment increase with the increase of hydrogen concentration, and the yield strength decreases. After dehydrogenation, the yield strength and ultimate compressive strength are increase.

Optimization Study of Post-Weld Heat Treatment for 12Cr1MoV Pipe Welded Joint

In order to clarify the role of different post-weld heat treatment processes in the manufacturing process, welding tests, post-weld heat treatment tests, and finite element analysis (FEA) are carried out for 12C1MoV steel pipes. The simulated temperature field and residual stress field agree well with the measured results, which indicates that the simulation method is available. The influence of post-weld heat treatment process parameters on residual stress reduction results is further analyzed. It is found that the post weld dehydrogenation treatment could not release residual stress obviously. However, the residual stress can be relieved by 65% with tempering treatment. The stress relief effect of “post weld dehydrogenation treatment + temper heat treatment” is same with that of “temper heat treatment”. The higher the temperature, the greater the residual stress reduction, when the peak temperature is at 650–750 °C, especially for the stress concentration area. The longer holding time has no obvious positive effect on the reduction of residual stress.

Grain refinement mechanism of Ti-55 titanium alloy by hydrogenation and dehydrogenation treatment

The average grain size of Ti-55 titanium alloy is refined by hydrogenation and dehydrogenation treatment from 5.96 μm to 0.5 μm. The refinement mechanism is discussed through microstructural observations. The main refining effects may derive from recrystallization and phase transformation. The micro-strain field in the matrix by the formed hydride during the hydrogenation process results in serious distortion and many dislocations. The recrystallization nucleation and growth during the dehydrogenation process are promoted. Additionally, the eutectoid transformation of βH → δ + α during hydrogenation process and the hydride decomposition of δ → α + H2↑ as well as the hydrogen release in the form of solid solution transformation of αH → α + H2↑ and βH → α + β + H2↑ during dehydrogenation stage break the matrix structure into smaller microstructure.

One-step preparation of hydrogenated ZrO2 microspheres by cathode plasma electrolysis

Hydrogenated ZrO2 microspheres were directly prepared by cathode plasma electrolysis (CPE) in an aqueous solution of Zr(NO3)4•5H2O. Owing to the energy of plasma and the cathodic hydrogen evolution reactions, the CPE method combined the preparation of ZrO2 ceramic and the hydrogen treatment into only one step. The results showed regular microspheres consisting of tetragonal-ZrO2 and monoclinic-ZrO2 with 1–10 µm in diameter were formed at relatively high concentration of Zr(NO3)3•5H2O. These ZrO2 microspheres contained about 52.54 µg g−1 hydrogen which caused a narrow band gap (3.10 eV). Thus, the microspheres showed good photocatalytic activity under simulated sunlight, and the degradation of RhB dye reached nearly 58% for 3 h of irradiation, much better than the ZrO2 microspheres after dehydrogenation treatment.

Preparation of submicron-sized Sm2Fe17N3 fine powder with high coercivity by reduction-diffusion process

Submicron-sized Sm2Fe17N3 powders having high coercivity were prepared by a newly-developed synthesis procedure for submicron-sized Sm2Fe17 powders and nitridation process with a proper post-process for the powders. It was revealed that the washing step, which is performed to remove excess Ca, supplied hydrogen into the Sm2Fe17N3 crystal structure, and elongation of the crystal structure along the c-axis by the supplied hydrogen reduced coercivity. This phenomenon was observed clearly in powder with a smaller size and good dispersity. When the powders were subjected to dehydrogenation treatment, they showed high coercivity, as expected from the particle size, and coercivity of 24.7 kOe was achieved with the 0.5 μm powder. The fact that the intrinsic good thermal stability of Sm2Fe17N3 is maintained at the submicron-scale was also confirmed. In addition, the obtained powder exhibited a high maximum energy product after disintegration treatment under appropriate conditions. This study demonstrated the high potential of Sm2Fe17N3 for surpassing the performance of NdFeB magnets under hot environments.

Stabilization of pitch-based carbon fibers accompanying electron beam irradiation and their mechanical properties

Carbon fibers are prepared by stabilizing pitch fibers accompanying electron beam (E-beam) irradiation. The carbon fibers pretreated by E-beam irradiation achieve a higher stabilization index than the carbon fibers that are only heat-stabilized. In addition, the carbon fibers subjected to E-beam irradiation in the stabilization step exhibit a comparable tensile strength to that of general purpose carbon fibers. The carbon fibers pretreated with an absorbed dose of 3000 kGy have a tensile strength of 0.54 GPa for a similar fiber diameter. Elemental, Fourier-transform infrared spectroscopy, and thermogravimetric analyses indicate that Ebeam irradiation is an efficient oxidation and dehydrogenation treatment for pitch fibers by showing that the intensity of the aliphatic C?H stretching and aromatic CH2 ben

Effects of dehydrogenation heat-treatment on electrical–mechanical properties for hydrogenated Cu–3 mass%Ti alloys

In our previous study, we reported that remarkable simultaneous improvements of mechanical strength and electrical conductivity are achieved in the hydrogenated Cu–3mass%Ti alloy. The hydrogen heat-treatment at 350°C under hydrogen pressure of 7.5MPa for 48h proceeds with the decomposition to Cu-rich phase and Ti-hydride. The present investigation focused on dehydrogenation heat-treatment for the hydrogenated Cu–Ti alloys. Two kinds of hydrogen desorption peaks of the hydrogenated Cu–3mass%Ti alloy at 250°C and 550°C were observed in the TDS measurement. The lower peak would be caused by desorption of hydrogen trapped by the defects such as dislocations. The higher temperature peak would be corresponded to the decomposition Ti hydride. In consequence, the tensile strength of the hydrogenated alloy decreased with increasing dehydrogenation temperature more than 400°C. The plastic deformations of the alloys with dehydrogenation at more than 350°C were observed in the S–S curves, and then the yield strains of the alloys drastically increased. High tensile stress and ductility were simultaneously obtained by optimum dehydrogenation treatment at 350–375°C.

Electrodeposition of Zn–Ni coatings as Cd replacement for corrosion protection of high strength steel

Electrodeposition of Zn–Ni coatings performed in acidic baths are not suitable for high strength steels due to their high susceptibility to hydrogen embrittlement. In this work, Zn–Ni coatings were deposited on a high strength steel (4340) upon stirring conditions from an alkaline bath. A complete characterisation of the coatings (corrosion, morphology and composition) has been accomplished, correlating the electrodeposition conditions with these features. The best protective properties of the grown coatings were achieved for the alloys with a single phase structure of γ-Ni 5Zn 21 and a denser morphology. Additionally, the hydrogen content incorporated is lower than even cadmium-coated 4340 steel which has undergone a postbaking dehydrogenation treatment.

サブナノ格子物質中における水素が誘起する新機能

This paper includes some results of “Hydrogen-Induced New Functions in Sub-Nano Lattice Matters” accomplished by MEXT's program “Elements strategy Project”. In the 21st century, the era concerning about environment, this research achievement utilizing hydrogen as the technology for strengthening alloys will be expected to make a breakthrough in the metal heat-treatment and processing technology as the new environmental conscious process. Hydrogen heat-treatments for grain-size refinements of alloys were performed. The grain size of Cu-3 mass%Ti alloy turned into about 20~50 nm after hydrogenation and dehydrogenation treatment. Moreover, grain-size refined Ti-based alloy showed large super-elastic elongation. On the other hand, hydrogen induced functions in the alloys were also investigated. Hydrogen transmitting films with Pd nanogranular particles dispersed in ceramic material were developed as attachment of metal-hydride switchable mirrors. Metamagnetism transition temperature (Tc) could be increased by hydrogen introduction in La(FexSi1-x)13. Pd/Pt core-shell type nano-particles were also investigated.

Formation of nanocrystalline structure of Ti–6Al–4V alloy by cyclic hydrogenation–dehydrogenation treatment

Ti–6Al–4V (Ti64) sheet specimens were cathodically hydrogenated in sulfuric acid solution at ambient conditions. The hydrogenated specimens were then sent to go through the designed thermohydrogen processing (THP) twice to obtain a nano-sized grain structure. The average grain size of resulted microstructure was found to be 10–20 nm obtained by TEM. Qualitative and quantitative analyses performed by employing X-ray diffractometry (XRD) and elemental analysis (EA) showed that the addition of As 2O 3 as hydrogenation promoter in electrolyte significantly increased the hydrogen uptake. The high concentration of hydrogen arising from promoter action is the key factor in grain refinement. The optimal processing parameter found for grain-refining Ti64 was: (1) electrolytic hydrogenation at 100 mA cm −2 for 3 h in 1 N H 2SO 4(aq) by adding 0.1 g L −1 As 2O 3; (2) β transformation carried out at 850 °C for 1 h in air furnace, followed by a furnace cooling to 590 °C and held for 6 h; (3) oxide film removed and then dehydrogenated at 650 °C and 1.0 × 10 −6 Torr for 10 h; (4) repeated the same processes once more.

Formation of Highly Uniform Micrometer-Order-Thick Polycrystalline Silicon Films by Flash Lamp Annealing of Amorphous Silicon on Glass Substrates

Polycrystalline silicon (poly-Si) films as thick as 4.5 µm are prepared by flash lamp annealing (FLA) of amorphous silicon (a-Si) films without thermal damage onto glass substrates. The a-Si films are deposited by catalytic chemical vapor deposition (Cat-CVD) at 320 °C. Since the hydrogen content in Cat-CVD a-Si films is as low as 3 at. %, they are easily converted to poly-Si without any dehydrogenation treatment. Chromium (Cr) films 60 nm thick are coated onto glass substrates to achieve high area uniformity of poly-Si formation. Secondary ion mass spectroscopy (SIMS) reveals that no diffused Cr atoms are detected inside poly-Si films and that crystallization is not the well-known metal-induced crystallization. Raman spectra from the poly-Si films show high crystallinity close to 1, and the photoluminescence (PL) spectrum demonstrates clear band-to-band transition, indicating the formation of device-quality poly-Si by FLA of Cat-CVD a-Si.

Effect of thermohydrogen treatment on mechanical and process properties of low-carbon steel

The effect of etching followed by dehydrogenation treatment on mechanical and process properties of thin hot-rolled normalized sheets from steel 10 and of cold-rolled sheets from steel 08kp is studied. Results of operating tests of the steels for bending strength and of mechanical tensile tests are described. Load-extension curves are plotted for the sheets in the state as delivered and after thermohydrogen treatment.

An X-ray investigation of hydrogenated Mg–30Al magnesium alloy

The X-ray diffraction analysis of hydrogenated Mg–30Al magnesium alloy was used to determine the effect hydrogen on phase changes and lattice parameters as well as hydride formation in the investigated alloy. The results of XRD analysis showed that the β-Mg 17Al 12 phase was significantly affected by hydrogenation up to 12 h causing considerable lattice expansion accompanied by an increase in the interplanar spacing, X-ray line broadening and decrease in crystallite size while the α-Mg phase was slightly affected by hydrogenation treatment. Further hydrogenation (i.e. beyond 12 h) resulted in disappearance of α-Mg and β-Mg 17Al 12 peaks and formation of MgH 2 hydride and aluminum phases in the alloy. The dehydrogenation treatment followed hydrogenation resulted in increasing the lattice parameters of Mg–30Al alloy, decomposition of MgH 2 and reappearance of α-Mg peaks as well as disappearance of Al peak throughout the material X-ray diffraction patterns. Dehydrogenation at higher temperature resulted in faster decomposition of MgH 2 hydride and more hydrogen diffuses out of the specimens.

Microstructural features of thermochemical processing in a Ti-6Al-4V alloy

Thermochemical processing (TCP) with hydrogen acting as a temporary alloying element to refine the microstructure of a Ti-6Al-4V alloy has been evaluated in order to examine the microstructural variations. The processing includes a hydrogenation treatment, an elevated-temperature β solution treatment, a moderate-temperature eutectoid decomposition and finally a vacuum dehydrogenation treatment. After the hydrogenation treatment, an atmosphere containing hydrogen is introduced to stop the hydrogen from escaping from the hydrogenated specimens in the subsequent solution treatment and eutectoid decomposition treatment, which is different from conventional TCP. The results have shown that γ titanium hydride precipitates in the α phase in the hydrogenated specimen. Also, during the eutectoid decomposition treatment a mixture consisting of α + γ hydride nucleates from the β H matrix while being continuously cooled to the decomposition temperature. The mixture continues to nucleate in the same way during the subsequent isothermal aging treatment. Finally, during the dehydrogenation treatment, the γ hydrides gradually lose their hydrogen content, resulting in the recrystallization of fine α/β phases. In this investigation, the microstructure resulting from each step of TCP is carefully examined, and particular attention is paid to the control of eutectoid decomposition conditions to shorten the time required to achieve a fully transformed microstructure. In addition, the optimal conditions pertaining to eutectoid decomposition treatment are proposed in this study.

Low-Temperature PECVD Polysilicon Crystallization by Rapid Thermal Processing

AbstractThis work investigates the solid phase crystallization of PECVD amorphous silicon films by rapid thermal processing (RTP) as an alternative to laser crystallization. It is shown that PECVD films can be crystallized by RTP at temperatures compatible with glass substrates. A statistical design approach was used to investigate the effect of the various deposition and annealing conditions on the crystallization temperature, material properties and TFT device performance. The investigated variables include deposition temperature, rf power, pressure, surface treatments, dehydrogenation treatment, source gas, dilutant gas, and RTP scan speed. Important deposition and crystallization parameters will be discussed regarding polysilicon film optimization.

Preparation of Ultra-Fine Titanium Powder by Arc-Plasma Process

Preparation of ultra-fine titanium powder was tried by subjecting molten titanium to an arc-plasma generated in the argon-hydrogen atmosphere. The arc voltage, current and hydrogen/argon ratio were varied to optimize the powder generation. The optimum conditions were obtained at 40 V and 150 A for stabilizing arc and the hydrogen/argon ratios of 0.5 to 0.7 for achieving the generation rates of 0.18 to 0.30 g/min over reasonable periods of time. The powder generated under optimum conditions have a surface area of approximately 22 m 2 /g, and the average particle size of 65 nm calculated from the surface area measurement coincides with TEM observations. XRD confirmed that particles are mostly titanium hydride (TiH 1.924 ) containing small amounts of titanium (Ti) and its oxides (TiO and Ti 2 O 3 ). All of the particulate sizes for these phases are less than 20 nm. Powder can be dehydrogenated by heating in vacuum above 673 K, the activation energy for dehydrogenation being determined to be 95±5 kJ/mol by DSC experiments. This activation energy value matches well with the sum of diffusion energy of hydrogen in α-Ti and the hydrogenation energy of α-Ti. Also the dehydrogenation treatment does not provoke grain growth. It is therefore concluded that ultra-fine titanium powder of nano-sized crystallite sizes can be produced at a reasonable yield rate by a plasma arc process in hydrogen/Argon atmosphere and dehydrogenating the product between 673 and 873 K.

High-Field Magnetization Study of Sm2Fe17Nx and Related Compounds

Magnetic and crystallographic properties of Sm2Fe17Nx with x>3.0, nitrogenated by using a mixed gas of NH3 and H2, have been investigated by comparing the results of two groups of samples: as-nitrogenated samples which contain hydrogen (0.2 to 0.4/f.u.) and annealed samples which are hydrogen-free. The lattice constant c of the Th2Zn17 structure of the hydrogen-free sample is found to be slightly smaller than that of hydrogen-contained sample, the former value, however , being still larger than that of Sm2Fe17N3.0. The saturation magnetization increased slightly by the dehydrogenation treatment, although it is still considerably smaller than that of Sm2Fe17N3.0.