Thermal Desorption Spectrometry Analysis Research Articles

Effect of reverted austenite fraction on hydrogen embrittlement of TRIP-aided medium Mn steel (0.1C-5Mn)

Abstract The present work was attempted to evaluate the influence of reverted austenite (RA) fraction on hydrogen embrittlement (HE) of a hot rolled transformation-induced plasticity (TRIP)-aided medium Mn steel (0.1C-5Mn) by using electrochemical charging, slow strain rate tensile (SSRT) test and thermal desorption spectrometry (TDS) analysis. Different volume fractions of RA (~10–30 vol%) in the tested steel sheet were obtained by changing intercritical annealing time. The result of TDS analysis demonstrated that the charged hydrogen is primarily diffusible hydrogen corresponding to low-temperature hydrogen desorption peak and its concentration increases almost linearly with an increase in the volume fraction of RA. It was found that the intercritically annealed specimen exhibits an increasing susceptibility to HE with an increase in the volume fraction of RA primarily due to the increased RA transformation to martensite during tensile deformation. It is thus regarded that the TRIP effect is harmful to the HE resistance of TRIP-aided steels, and therefore both the mechanical stability and amount of RA have a strong influence on the HE behavior of TRIP-aided medium Mn steel.

The Effect of Lubricant Additives on Hydrogen Permeation Under Rolling Contact

This study describes the effects of lubricant additives on the permeation of hydrogen into high-strength-bearing steel in rolling contact conditions. Oil-lubricated tests were conducted in a hydrogen atmosphere under high temperature/pressure. Trioctylphosphate and zinc dialkyldithiophosphate (ZDDP) were used as lubricant additives. Thermal desorption spectrometry (TDS) was performed to measure the amount of permeated hydrogen immediately after the rolling contact tests. TDS analysis suggested that ZDDP is very efficient at preventing hydrogen permeation into the substrate. Auger electron spectroscopy revealed the generation of a protective chemical tribofilm containing zinc, sulphur, oxygen and phosphorus at the interface. This tribofilm should be responsible for the lower rates of hydrogen permeation into the bearing steel.

Exposure of liquid lithium confined in a capillary structure to high plasma fluxes in PILOT-PSI—Influence of temperature on D retention

Experiments on deuterium retention on liquid lithium confined in a capillary structure followed by ex-situ thermal desorption spectrometry (TDS) at high plasma fluxes (∼1023m2s−1) and high temperatures (440°C and 580°C) have been performed. Deuterium plasmas were generated at the PILOT-PSI linear plasma device and the targets were a 30mm diameter stainless steel disc, 5mm thick, covered with a porous mesh and filled with lithium. The settings (current) of the plasma source were varied in order to get different sample surface temperatures during irradiation. The targets were kept at floating potential during the exposure. Hydrogen and Li emission signals were monitored during the plasma exposure and TDS analysis was made afterwards in a separated system.Decreased retention at high exposure temperatures was deduced from the analysis of the hydrogen emission signals. Nevertheless, the results from TDS signal analysis were not conclusive.

Study of Void Formation Mechanism in Electroplated SnAg Solder Bump

AbstractSnAg electroplating method is widely used in the formation of LF solder bump for flip chip connection. While electroplating is able to form void free solder bump in a suitable operating condition, void may occur suddenly when used in mass production. This study aims at understanding the gas source in the void of electroplated SnAg solder bumps and determining the manufacturing process factors which affect the void formation.There are various types of void formation mode. One mode is H2 gas generation on cathode surface during electroplating. Both the cross-sections of solder bumps, as well as an analysis data of the gas in the void taken by the TDS (Thermal Desorption Spectrometry) were evaluated. The cross-section of the solder bump which contains void due to the reflow process revealed the existence of several tens of nm to several μm size pits in the solder bump before reflow. TDS analysis indicates that the pits consisted of mainly H2O, H2 and the decomposition of organics. A possible void formation mechanism is the evaporation of H2 gas and the incorporated electrolyte solution in the bump by reflow. These pits in the solder were caused by various process parameters. One of the causes is due to the setting of the current density in the SnAg electroplating process being inappropriate. The current density should be adjusted corresponding to the electrolyte performance and bump design such as PR thickness, opening diameter and bump density. The computer simulation demonstrated that a thick PR limits the diffusion of the Sn2+ ions into via holes and having the current density too high causes a lack of Sn2+ ions on the cathode surface and causes H2 gas generation.The other mode of void formation is Ag displacement of the under bump metallization (UBM) surface in dwell time in the SnAg electrolyte solution before the start of plating. The adjustment of each process parameter can eliminate the source of the void and achieve a high reliability of SnAg bump formation.

Influence of cold deformation and annealing on hydrogen embrittlement of cold hardening bainitic steel for high strength bolts

The influence of cold drawing and annealing on hydrogen embrittlement (HE) of newly developed cold hardening bainitic steel was investigated by using slow strain rate testing (SSRT) and thermal desorption spectrometry (TDS), for ensuring safety performance of 10.9 class high strength bolts made of this kind of steel against HE under service environments. Hydrogen was introduced into the specimen by electrochemical charging. TDS analysis shows that the hydrogen-charged cold drawn specimen exhibits an additional low-temperature hydrogen desorption peak besides the original high-temperature desorption peak of the as-rolled specimen, causing remarkable increase of absorbed hydrogen content. It is found that cold drawing significantly enhances the susceptibility to HE, which is mainly attributed to remarkable increase of diffusible hydrogen absorption, the occurrence of strain-induced martensite as well as the increase of strength level. Annealing after cold deformation is an effective way to improve HE resistance and this improvement strongly depends on annealing temperature, i.e. HE susceptibility decreases slightly with increasing annealing temperature up to 200°C and then decreases significantly with further increasing annealing temperature. This phenomenon is explained by the release of hydrogen, the recovery of cold worked microstructure and the decrease of strength with increasing annealing temperature.

Evaluation of hydrogen trapping mechanisms during performance of different hydrogen fugacity in a lean duplex stainless steel

Hydrogen trapping behavior in a lean duplex stainless steel (LDS) is studied by means of thermal desorption spectrometry (TDS). The susceptibility of a metal to hydrogen embrittlement is directly related to the trap characteristics: source or sink (reversible or irreversible, respectively). Since trapping affects the metal's diffusivity, it has a major influence on the hydrogen assisted cracking (HAC) phenomenon. It is known from previously published works that the susceptibility will depend on the competition between reversible and irreversible traps; meaning a direct relation to the hydrogen's initial state in the steel. In this research the trapping mechanism of LDS, exposed to different hydrogen charging environments, is analyzed by means of TDS. The TDS analysis was supported and confirmed by means of X-ray diffraction (XRD), hydrogen quantitative measurements and microstructural observations. It was found that gaseous charging (which produces lower hydrogen fugacity) creates ∼22% higher activation energy for hydrogen trapping compared with cathodic charging (which produces higher hydrogen fugacity). These results are due to the different effects on the hydrogen behavior in LDS which causes a major difference in the hydrogen contents and different hydrogen assisted phase transitions. The highest activation energy value in the cathodic charged sample was ascribed to the dominant phase transformation of γ → γ∗, whereas in the gaseous charged sample it was ascribed to the dominant formation of intermetallic compound, sigma (σ). The relation between hydrogen distribution in LDS and hydrogen trapping mechanism is discussed in details.

Effect of microstructure on hydrogen diffusion and notch tensile strength of large steel forging

Microstructure, hydrogen diffusion coefficient and notch tensile strength (NTS) in two different parts (1/2 radius and 3/4 radius) of a large steel forging have been investigated by means of microscopy, thermal desorption spectrometry (TDS), and slow strain rate tensile tests (SSRT), respectively. The microstructure in the 1/2R part is granular pearlite while that in the 3/4R part is composed of granular pearlite and bainite with many fine M23C6 carbides. Results of TDS analysis indicate that hydrogen content in the 3/4R part is much higher than in the 1/2R part, corresponding to a hydrogen diffusion coefficient about one order lower. SSRT results showed that although NTS decreased with the increase of hydrogen content in both parts, the 3/4R part showed a higher NTS at the same H content. The higher H content, lower H diffusion coefficient and higher NTS in the 3/4R part can be attributed to the fine M23C6 carbides which can act as hydrogen trapping sites.

Hydrogen Embrittlement of a 1500-MPa Tensile Strength Level Steel with an Ultrafine Elongated Grain Structure

A deformation of a tempered martensitic structure (i.e., tempforming) at 773 K (500 °C) was applied to a 0.6 pct C-2 pct Si-1 pct Cr steel. The hydrogen embrittlement (HE) property of the tempformed (TF) steel was investigated by a slow strain rate test (SSRT) and an accelerated atmospheric corrosion test (AACT). Hydrogen content within the samples after SSRT and AACT was measured by thermal desorption spectrometry (TDS). The tempforming at 773 K (500 °C) using multipass caliber rolling with an accumulative are reduction of 76 pct resulted in the evolution of an ultrafine elongated grain (UFEG) structure with a strong 〈110〉//rolling direction (RD) fiber deformation texture and a dispersion of spheroidized cementite particles. The SSRT of the pre-hydrogen-charged notched specimens and the AACT demonstrated that the TF sample had superior potential for HE resistance to the conventional quenched and tempered (QT) sample at a tensile strength of 1500 MPa. The TDS analysis also indicated that the hydrogen might be mainly trapped by reversible trapping sites such as grain boundaries and dislocations in the TF sample, and the hydrogen trapping states of the TF sample were similar to those of the QT sample. The QT sample exhibited hydrogen-induced intergranular fracture along the boundaries of coarse prior-austenite grains. In contrast, the hydrogen-induced cracking occurred in association with the UFEG structure in the TF sample, leading to the higher HE resistance of the TF sample.

Hydrogen Embrittlement of Low Carbon HSLA Steel during Slow Strain Rate Test

The hydrogen embrittlement of a low carbon HSLA steel has been investigated by means of slow strain rate test (SSRT) on circumferentially notched specimens. Hydrogen was introduced into specimens by electrochemical charging and the diffusible hydrogen content was measured by thermal desorption spectrometry (TDS) analysis. The activation energy of hydrogen desorption in the present steel was calculated to be 12.75 kJ/mol after TDS analysis. The peak stress and displacement during notch tensile tests had been found to decrease simultaneously with diffusible hydrogen content, which could be expressed by two power law relationships, respectively. Fracture surface was a cleavage type indicating that the steel had high susceptibility of hydrogen embrittlement.

Microstructural influences on hydrogen delayed fracture of high strength steels

This study was aimed at investigating the effect of the microstructural constituents of high strength steels on their hydrogen delayed fracture properties. For this purpose, a series of constant loading tests, slow strain rate tests, cyclic corrosion tests, and thermal desorption spectrometry analysis was conducted on the hydrogen pre-charged specimens with tempered martensite or full pearlite showing a similar tensile strength level of 1600 MPa. Constant loading tests and slow strain rate tests revealed that the tempered martensitic steel was more susceptible to hydrogen delayed fracture than the fully pearlitic steel. In slow strain rate tests, the maximum tensile strength decreased with increasing diffusible hydrogen content in a power-law manner. The content of hydrogen inflowing from environment was also simulated by cyclic corrosion tests. It was found that the fully pearlitic steel has the higher equilibrium hydrogen content than the tempered martensitic steel. The primary trapping sites were prior austenite grain boundaries for the tempered martensitic steel, and ferrite/cementite interfaces and dislocations for the fully pearlitic steel. SEM fractographs revealed that the cracks induced by hydrogen propagated along the prior austenite grain boundaries resulting in brittle intergranular fracture for the tempered martensitic steel while the fully pearlitic steel was fractured in a ductile manner.

Effect of hydrogen and stress concentration on the notch tensile strength of AISI 4135 steel

The quantitative relationship between notch tensile strength and diffusible hydrogen content has been investigated for the AISI 4135 steel at 1320MPa. The notch tensile strength was obtained by means of a slow strain rate test on circumferentially notched round bar specimens with stress concentration factors of 2.1, 3.3 and 4.9 after hydrogen charging, and the diffusible hydrogen content was then measured by thermal desorption spectrometry analysis. The diffusible hydrogen has been found to decrease the notch tensile strength in a power law manner, and the decrease is more prominent at a higher stress concentration factor. The finite element analysis results of stress and hydrogen distributions in the vicinity of the notch root have shown that the local fracture stress decreases with increasing local hydrogen concentration as the diffusible hydrogen content or stress concentration factor increases, resulting in the decrease in the notch tensile strength.

Observation of hydrogen distribution in high-strength steel

“The diffusible hydrogen” in Cr-Mo steels are observed with autoradiography technique. Specimens with “the diffusible hydrogen” are prepared by an electrochemical cathodic charging method and those without “the diffusible hydrogen” by annealing at 373 K after charging hydrogen. TEM autoradiographs suggests, by the developed silver grains, that the hydrogen trapping sites are the grain boundary and internal interface of ferrite-cementite and ferrite-lath structure. After keeping the sample at 373 K, the silver grains disappeared. Most of hydrogen trapping sites release almost all the hydrogen at 373 K. It is clear that these sites of high-strength steels supplies “the diffusible hydrogen”. Hydrogen absorption characteristics of quench hardening tempering Cr-Mo steels have been evaluated by thermal desorption spectrometry (TDS). From tritium electron microscopic autoradiography and TDS analysis, the lower temperature (360 K–370 K) peaks show “the diffusing hydrogen” which is released a few days. “The diffusible hydrogen” from trapping sites such as the internal interface of ferrite-cementite or ferrite-lath structure are distinguished to “the diffusing hydrogen.”

冷間伸線加工した純鉄および共析鋼の昇温脱離法による水素吸蔵特性評価

Hydrogen absorption characteristics of pure iron and eutectoid steel fabricated by cold drawing have been evaluated by thermal desorption spectrometry (TDS). The pure iron specimens with ferrite (α) structure and the eutectoid steel specimens with α and Fe3C structures, were produced under various degrees of reduction and also under various heat treatment conditions. These amount of hydrogen absorbed in specimens dipped in 20 mass%NH4SCN solution were measured using TDS. TDS analysis showed that hydrogen evolution rate of pure iron has only one peak, while that of eutectoid steel has two peaks. From transmission electron microscopy and TDS analysis, the lower temperature peak was attributed to hydrogen released from the trapping sites such as point defects, clustered defects, and dislocations in α. The higher temperature peak was found to correspond to hydrogen released from the trapping sites such as defects in Fe3C, and/or such as the disordered interface between α and Fe3C.

昇温脱離した高強度鋼中水素の二次イオン質量分析法によるトラップサイトの同定

The trapping sites of hydrogen detected by Thermal Desorption Spectrometry (TDS) have been identified by Secondary Ion Mass Spectrometry (SIMS). High-strength steel specimens were given applied loads in D2O and 20% NH4SCN solution at 323 K. In SIMS analysis, deuterium ions can be detected with greater sensitivity than hydrogen ions and measurement can be started in a matter of minutes. TDS analysis shows that hydrogen thermal desorption rate has two peaks, corresponding to trap activation energies of 20.7∼22.5 kJ/mol and 82.2∼87.4 kJ/mol for the lower and higher temperature peaks, respectively. These values are close to 26.8 kJ/mol reported in the literature as the trap activation energy for desorption from dislocations and ≥72.3 kJ/mol from the interfaces of inclusions and precipitates. By applying SIMS image-analysis to specimens cooled after the respective peak temperatures, we could identify the trapping sites corresponding to the lower temperature peak as sites within the matrix such as defects including dislocations, and those corresponding to the higher temperature peaks as inclusion interfaces, precipitate interfaces, and segregation bands of phosphorus. These SIMS results confirm the location of the trapping sites to be the same as those estimated from trap activation energy by TDS.