The pore filling behavior in yttria-stabilized zirconia air plasma sprayed (APS) thermal barrier coatings (TBCs) during calcium-magnesium-alumino-silicate (CMAS) infiltration process was investigated. After fully infiltration, the total porosity of the coating decreased. However, the total porosity of the top region increased due to severe microstructural change. For the bottom region, whose microstructure did not change significantly, its total porosity dropped and almost all crack network disappeared, but 48 vol.% of globular pores still existed and larger globular pores were more likely to remain. This study indicates that introducing relatively large globular pores into APS TBCs may mitigate CMAS damage.

In this work, a comparative electrochemical impedance spectroscopy (EIS) study of the native oxide layer of selective laser melted and wrought 316 L stainless steel is conducted. A careful examination of the data is carried out in order to properly identify the appropriate model to fit the EIS response. From the parameters calculated by fitting the EIS data and a complementary XPS analysis, the electrical and dielectric characteristics of the passive oxide layers of the specimens were obtained. Clear differences were noticed between the two materials, which could definitely contribute to the overall understanding of the corrosion behavior of these materials.

Poor oxidation resistance represents one of the main shortcomings of refractory metal based alloys. This work shows an innovative way to intrinsically protect such materials. Our approach relies on the alloying with Cr and Ta allowing the formation of CrTaO4. The CrTaO4 scale formed on the novel refractory equiatomic high entropy alloy Ta-Mo-Cr-Ti-Al reveals a unique combination of the following properties: (i) easy formation in a wide temperature range from 500 °C to 1500 °C, (ii) excellent adherence after cooling, (iii) low growth rates, and (iv) wide stability range of the stoichiometric composition that suppresses the formation of non-protective oxides.

The effect of coupling of unalloyed Mg and Mg-alloys (AZ91 and WE43) with Ti6Al4V alloy on corrosion and degradation behaviours of produced composites has been investigated in simulated body fluid (SBF) by hydrogen evolution, and surface and electrochemical characterization techniques. Combining of unalloyed Mg with Ti6Al4V intensified galvanic corrosion and catastrophic failure occurred by initiation of microcracks formed by sudden hydrogen gas evolution. In contrast to other composites, Ti6Al4V-AZ91 composites, containing new TiAl3 interface layer formed during composite production, preserved their mechanical integrities due to lowest corrosion and degradation rate of AZ91 alloy.

Liquid metal dealloying is a newly available technology used to create bulk porous materials. In this study, a commercial nickel-based superalloy, Incoloy 800, was dealloyed to elaborate a fully porous ferritic stainless steel. The Mg selective dissolution in nitric acid solution acts as a passivation treatment that enhances the passive film resistance. Corrosion tests confirm the beneficial effect of the nitric acid treatment on the Cr enrichment of the passive film thus improved the material resistance. The electrochemical characterizations show a higher effect of the size porosities on the diffusion kinetics of the electrolyte rather than on the pitting sensitivity.

The effects of temperature on the corrosion of 316 stainless steel (316SS) in purified NaCl-MgCl2 eutectic salt under Ar were investigated through immersion test. The corrosion of samples accelerated and intergranular corrosion became obvious with increased temperature. The corrosion of 316SS was attributed to the selective dissolution of Cr, and corrosion had strong temperature dependence. The corrosion mechanism under the NaCl-MgCl2 eutectic salt was the combined effect of a dissolution mechanism with matrix metal element, which was attributed to the accelerating effect of surface chromium-dissolution and intergranular-diffusion rates with increased molten salt temperature.

The effect of surface preparation and crystal orientation was investigated for a TMS-138 single crystal superalloy under Type I and Type II hot corrosion conditions. The superalloy was cut along the {100} and {110} planes on which grit blasting, mechanical polishing and electro-polishing surface finishes were conducted. At 900 °C grit blasting or electropolishing distorted the surface and altered the γ-γ’ structure of the alloy provoking higher corrosion rates than on mechanically polished surfaces. The electropolished surface revealed that crystal planes with higher atomic number density have an increased corrosion resistance. The anisotropy effects were not observed with Type II exposures.

One of the biggest obstacles for superhydrophobic films in applications is their poor mechanical resistance. In this research, robust superhydrophobic SiO2 films were constructed on mild steel (MS) for corrosion protection by the combination of rough electrodeposited SiO2 (E-SiO2) films and durable polydimethylsiloxane (PDMS) polymer with low surface energy. Results show that the PDMS content has a great effect on the microtopography, wettability, roughness, and wear-resistance of the final films. EIS measurements indicate that as-prepared robust superhydrophobic E-SiO2/PDMS films exhibit good corrosion inhibition efficiency of up to 99.99% for MS substrates in 3.5 wt.% NaCl solution.

The influence of rare earth addition on the mechanism of localised corrosion induced by inclusions in Zr-Ti deoxidised steel was investigated in a simulated marine environment. Inclusion size and composition changed after rare earth addition, profoundly affecting the localised corrosion. Current sensing atomic force microscopy results showed that no galvanic couple formed between inclusions and matrix owing to the insulating property of different inclusions. Matrix dissolution resulting from the microcrevices and lattice distortion surrounding ZrO2-Ti2O3-Al2O3 inclusions initiated localised corrosion in Zr-Ti deoxidised steel. After adding RE, localised corrosion was induced by dissolution of the (RE)2O2S-(RE)xSy part of the inclusion.

Plasma nitriding was applied to ferritic stainless steel substrates to improve their performances as interconnects for solid oxide fuel cell devices. The samples underwent electrical conductivity test and SEM/EDS, TEM/EDS, environmental-SEM analyses. The first stages of corrosion were recorded in-situ with the e-SEM. Nitriding is effective in limiting the undesired chromium evaporation from the steel substrates and accelerates the corrosion kinetics, but its influence of the electrical conductivity is ambiguous. No intergranular corrosion is found in the steel substrate after long time operation. Nitriding helps commercially competitive porous coating to improve chromium retention properties of metal interconnects.

An Al-Mg-Si aluminium alloy was shaped by using a two-pass equal-channel angular pressing (ECAP) process. This led to fragmentation of the coarse Fe-rich intermetallics (IMCs), a decrease in grain size and an increase in the high angle grain boundary (HAGB) density, with overconcentration of HAGBs around the IMCs. Corrosion tests in NaCl solution showed that, before and after ECAP, only pitting corrosion occurred. However, for ECAP samples, pits were more numerous due to the fragmentation of the IMCs; they were also larger and less deep, their propagation being strongly influenced by the presence of very small grains around the IMCs.

The effect of Sn addition on the oxidation behavior of high-Nb containing TiAl alloys was investigated with isothermal oxidation tests conducted in static air at 1000 °C. Sn addition can improve the high-temperature oxidation resistance of TiAl alloys by forming a protective Ti3Sn layer to diminish the inward oxygen diffusion. Moreover, the generated Al2O3 oxide pegs provide a mechanical locking to enhance the spallation resistance. The alloy containing 3 at.% Sn exhibits superior oxidation resistance, with no spallation occurring. The lowest mass gain after being oxidized for 100 h was 3.29 mg/cm2, which is 42.1% lower than the Sn-free alloy.

Ti45Al8.5Nb was anodized in ethylene glycol and NH4F containing solution to improve the oxidation resistance. Isothermal oxidation test shows that the anodized specimens can provide excellent oxidation resistance and spallation resistance under 1000 °C. During the high temperature oxidation process, a compact and continuous alumina layer would generate on the anodized Ti45Al8.5Nb alloy. This protective alumina layer can efficiently decrease the inward diffusion of oxygen and outward diffusion of the substrate element. The improved oxidation resistance is assigned to the halogen effect caused by the fluorine component generated during the anodization process.

The effect of corrosion products on the inhibition effect of pyrimidine derivative inhibitor (DABTP) for the corrosion of N80 carbon steel in supercritical CO2 oilfield produced water was studied by electrochemical measurements, surface characterization, and theoretical calculations. It is found that DABTP exhibits high inhibition performance for bare carbon steel, while the formation of corrosion products (Fe3C, FeCO3) after pre-corrosion reduces the inhibition effect of DABTP. Theoretical calculations indicate that DABTP preferentially adsorb on FeCO3 film instead of Fe surface, which results in the reduction of inhibition effect of DABTP after FeCO3 film formed on the carbon steel surface.

TG-201 inhibitor could minimize corrosion of HP-13Cr SS in the process of live acid. Moreover, it accelerated the probability of serious corrosion of SS during the well completion. The failure mechanism of TG-201 inhibitor was investigated using surface analysis and electrochemical measurements. TG201 inhibitor contains amounts of Cu2+, which would acquire the electrons prior to H+ to form Cu film. The failure mechanism was due to the synergistic effect attributed to the Cu film. Cu film promoted the formation of the occluded cell and the changes of fluid state evoked by the increase in interfacial roughness during the well completion.

To explore the corrosion behavior of carbon steel at medium hydrofluoric acid concentration, the corrosion and stress corrosion cracking behavior of Q345R in 40 wt.% hydrofluoric acid are investigated. An almost constant corrosion rate is observed which is attributed to the loose structure of corrosion products that cannot prevent fluorion from penetrating. Pits are found as a consequence of hydrogen escaping and uneven distribution of corrosion products. These pits transform into cracks during stress corrosion cracking, and the higher the stress, the shorter the pit-to-crack transition time, while the change in crack propagation rate with stress is different.

Intergranular corrosion of welded joints using multi-strand winded welding wire was investigated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) tests, intergranular corrosion tests and scanning Kelvin probe force microscopy (SKPFM) tests. The results revealed welded joint in high heat input and low cooling rate shows the highest DOS value, and undergoes the most important weight loss during intergranular corrosion tests. While welded joint in low heat input and cooling rate has the highest corrosion resistance. SKPFM also indicated that welded joint in the low cooling rate and heat input presents low potential and is not easy for electrochemical reaction.

The oxidation kinetics of β-SiAlON with different particle sizes, synthesized using bauxite, Si and Al powders at 1773 K in flowing N2, were investigated. The kinetic feature of β-SiAlON particles varied little with particle size, and the oxidation curves were parabolic due to a glass film formed on the β-SiAlON particle surface. Small β-SiAlON particles had larger surface areas and lower activation energies than the large particles and were easily oxidized at the initial stage because of the increased probability of contact with O2.

Ferritic-Martensitic (F/M) steels with various amounts of alloying elements (Cr: 12 wt. %, Si: 0.6-2.2 wt. %, Mn: 0.6-1.8 wt. %) were exposed to Supercritical Water (SCW) environments at 500 °C and 25 MPa for up to 1000 hours. Gravimetric, Scanning Electron Microscope, Transmission Electron Microscopy (TEM), Energy-dispersive X-ray Spectroscopy (EDX) and X-ray Diffraction (XRD) analyses were conducted to characterize the corrosion behavior of F/M steels in supercritical water. The results showed that the contents of the alloying elements (Si, Mn) affected both the oxidation kinetics and the oxidation scales formed on F/M steels. The F/M steel (Si: 0.6 wt. %, Mn: 1.8 wt.%) showed the highest corrosion rate in SCW with an intermittent oxide scale formed on the surface. Increasing the Si content in F/M steel improved the oxidation resistance and promoted the formation of a uniform oxide scale. The mechanism associated with the corrosion of these F/M steels under SCW conditions is discussed.

A detailed thermodynamic assessment has for the first time shown that the rapid oxide film formation on stainless steels subjected to the natural air atmosphere at room temperature is actually facilitated by “oxygen dissolution induced surface directed spinodal decomposition” in the Fe-Cr-O solid solution. The proposed mechanism has led to a clear explanation of the following until now un-explained observations: i) complete compositional stratification involving a sub-surface segregation of Cr atoms within the oxide film on stainless steels; ii) necessity of a minimum of about 11 at.% Cr in stainless steels for rapid passivation characteristics.

This study investigated the effects of dislocation patterns introduced by cold rolling deformation on the hydrogen absorption properties, hydrogen trap behaviors and hydrogen embrittlement (HE) resistance for Armco iron under electrochemical charging. The surface hydrogen coverage first increases and then decreases with increasing deformation, and reaches a maximum at 50% deformation. Dislocation cell walls appear when the deformation is greater than 50%. Furthermore, the HE resistance is improved when the deformation reaches 80%. Because the dislocation cell walls can be used as effective hydrogen traps when the dislocation density reaches a sufficiently high value.

A novel Ti-0.5Nb-0.5Si (in wt.%) alloy is oxidized at 650∼850 °C for 100 h in air, which shows a significant higher oxidation resistance than pure Ti. The advantage of the alloy becomes more obvious with increasing temperature. At 850 °C for 100 h, mass gain of the alloy only accounts for 12.7% of that of the pure Ti. A key reason is the formation of a Ti2N layer coherent with Ti matrix. The oxide scale of the alloy with less porosity and alleviated stratification creates an environment at the scale/substrate interface favorable for the formation of Ti2N.

The microstructural optimization for selective laser melted 15-5PH stainless steel via heat treatment to enhance corrosion resistance was investigated. The results showed that after aging treatment, Cu-rich nanoparticles (about 10 nm) diffusely precipitated, and approximately 18∼25% austenite was distributed near the molten pool boundary. The surface potential of the austenite was approximately 15 mV higher than that of martensite by scanning Kelvin probe force microscopy. However, the austenite phase disappeared and the new NbC-(Mn, Si)O duplex particles precipitated after solution treatment and aging treatment, which decreased the pitting corrosion resistance and passive film stability of the SLM 15-5PH stainless steel.

The effect of Ce on the oxidation behaviour and microstructure evolution of nickel-saving austenitic heat-resistant cast steel in air at 900 °C was investigated by performing the isothermal oxidation tests. After 200 hrs of oxidation, the oxidation resistance of Ce-containing steel was about 20% higher than that of Ce-free steel. In addition to its role as a reactive element, alloyed Ce slowed the rate of manganese depletion from the substrate and subsurface ferrite formation, leading to the improvement of the oxidation resistance of Ce-containing steel.

The erosion-enhanced corrosion behavior of electroless Ni–P coating was investigated by single particle impingement coupled with in-situ electrochemical measurements. The transient anodic dissolution of Ni–P coating induced by the single particle impingement is enhanced with the rising impact velocity, followed by a rapid repassivation that obeys a bi-exponential decaying law. The coating demonstrates a good erosion-corrosion resistance due to its strong capability of repassivation that is scarcely affected by the changing hydrodynamics under the test conditions. The erosion-enhanced corrosion rate of Ni–P coating in flowing slurry is well predicted based on the repassivation kinetic parameters determined from single particle impingement.

Corrosion product film (CPF) formation and its beneficial effect on corrosion protection of a Ni advanced weathering steel (WS), 3Ni WS, was investigated under the harsh marine environment in Maldives. The influence of Ni on the structure and the corrosion resistance mechanism of CPF was in detail studied. The CPF of 3Ni WS exhibits superiority in physical structure, phase composition, elemental distribution, and electrochemical properties over that of the conventional WS studied. These advantages are attributed to the formation and aggregation of NiFe2O4 in the inner layer of the CPF, which refines the crystal phases, transforms γ-FeOOH to fine-grained α-FeOOH, and forms an electronegative inner layer to resist Cl.

Thermal cycling behavior of thermal barrier coatings deposited on Hf-doped (Ni,Pt)Al bond coats were investigated, comparing with conventional (Ni,Pt)Al at 1100 °C, to elucidate the effect of Hf addition into (Ni,Pt)Al bond coat on failure mode of TBCs. The results revealed that thermal cycling resistance of TBCs was significantly improved with addition of Hf, where relatively lower oxidation rate constant and decreased scale rumpling tendency were achieved. The effects of Hf incorporation on scale rumpling tendency and failure modes of the TBCs were discussed. Moreover, residual stress, Young’s modulus and hardness in top coat were determined with increasing thermal cycles.

The effect of Cr addition on the oxidation behaviour of multiphase Mo–28Ti–14Si–6C–6B (at. %) alloy composed of Mo solid solution, Mo5SiB2, Ti5Si3, and TiC phases was investigated. Replacement of 10 at. % Cr for Mo hardly changed the microstructure of the alloy and significantly enhanced its oxidation resistance at 800 °C. At 1100 °C, the Cr-added MoSiBTiC alloy showed less weight loss than the Cr-free base alloy. However, Cr addition had little effect on the substrate reduction, particularly for longer oxidation periods, due to the high volatility of Cr oxide at higher temperatures.

316 L stainless steel samples were passivated in NaClO containing solutions in order to simulate disinfection processes. Passive films were grown at the open circuit potential by immersion in NaClO aqueous solutions at different concentrations and temperature in order to understand, how exposure to aggressive environments could affect subsequent corrosion resistance of SSs. In the attempt to study the passive film growth mechanism, in-situ Open Circuit Potential measurements were performed in the same growth solutions. Photoelectrochemical and impedance investigation of passive films was carried out in order to link their solid state properties with their corrosion behaviour.

The intergranular corrosion behavior of the low-chromium ferritic stainless steel without Cr-carbide precipitation was investigated by the methods of qualitative and quantitative corrosion testing and microstructural analysis. The intergranular corrosion susceptibility of the aged stainless steels can be attributed to the Cr-depleted zone formation induced by Cr-C co-segregation to grain boundaries before Cr-carbide nucleation. The change of intergranular corrosion morphology after aging at 450 °C from discontinuous (aged for 2 h) to semi-continuous (aged for 20 h) and to continuous (aged for 200 h) is discussed in detail.

The stress corrosion cracking behaviour of laser MIG-hybrid welded 7B05-T5 aluminum alloy joint was studied by using pre-cracked wedge-open loading (WOL) specimens immersed in 3.5%NaCl solution. The critical stress intensity factor for stress corrosion cracking (KISCC), and the cracks propagation rate (da/dt) were determined. The stress corrosion cracking propagation mechanism of welded joints was analyzed by fracture scanning and microstructure analysis. The results illustrated that both the base metal (BM) and the heat-affected zone (HAZ) were susceptible to stress corrosion cracking (SCC), but the weld zone (WZ) was not sensitive to SCC. The fracture mode of the aluminum alloy in SCC appeared the intergranular and transgranular mixed fracture. It was considered that the coaction of anodic dissolution and hydrogen embritt-lement contributed to SCC.

The pitting corrosion resistance of 316 L stainless steel (316 L SS) additively manufactured by selective laser melting (SLM) has been reported to be substantially higher than its commercial counterpart due to the elimination of MnS inclusions. Here we report that the pitting corrosion resistance of the SLM-produced 316 L SS declines drastically after thermal post-processing above 1000 °C. This unanticipated drastic decline in pitting resistance is explained based on the formation of deleterious MnS inclusions in the SLM-produced 316 L SS after high-temperature thermal post-processing. This finding may have wide implications for determining suitable post-processing and industry application conditions for SLM-produced 316 L SS.

The inhibition performances of benzimidazole (BI), 2-mercaptobenzimidazole (MBI) and benzotriazole (BTA) on the galvanic corrosion of copper coupled with silver in 3.5 wt.% NaCl solution have been investigated by electrochemical measurements, surface analysis, quantum chemical calculations and molecular dynamics simulations. The results demonstrate that the introduction of nitrogen atom and sulfhydryl group into benzimidazole molecule enhances the physisorption and chemisorption of inhibitors on the copper surface and improves the inhibition efficiency of inhibitors, while the galvanic effect between copper and silver reduces the inhibition efficiency of inhibitors. The difference of the inhibition performances of the three inhibitors is also elucidated.

The failure of 316 stainless steel under tribo-corrosion in molten zinc alloy (Zn-0.2Al, wt%) at 460 °C was investigated and compared with corrosion or the sole wear. In the absence of wear, intact Fe2Al5Znx layer forms and protects the steel from dramatic corrosion. Without liquid-metal corrosion, the steel suffers from plastic deformation on friction and slight adhesive wear. While for tribo-corrosion, the synergy of corrosion and wear accounts for 90% of material loss. Firstly, corrosion generates a brittle scale and leads to embrittlement at subsurface, which accelerate wear. Secondly, wear promotes the formation of less-protective FeZn10 scale, accelerating corrosion.

Three types of NiAlSiY coatings with different aluminum concentration were prepared. The isothermal oxidation behavior and mechanism of coatings at 500 °C were studied. The results indicate a multilayer oxide layer composed of NiO outer layer and Al2O3 inner layer is formed on the surface. The diffusion of aluminum in the coating and the phase transition from β-NiAl to γ'-Ni3Al promote the formation of Al2O3. Silicon plays an important role in the diffusion of aluminum by refining grains. When the aluminum is 21 wt.%, a dense Al2O3 layer can be formed on the NiAlSiY coating after oxidation for 30 hours.

Ni-W alloys with 16-28 at% tungsten (W) content were electrodeposited from citrate bath utilizing various pulse parameters. The influence of pulse parameters on microstructure, composition and mechanical properties was systematically studied. The corrosion behavior was analyzed in 1 M H2SO4 using Potentiodynamic polarization and electrochemical impedance spectroscopy. Nanocrystalline Ni-W coatings were found to have superior corrosion resistance compared to their duplex nanocrystalline-amorphous counterpart. The corrosion behavior was rationalized based semiconducting properties of oxide film using Mott–Schottky analysis and depth wise composition analysis utilizing X-ray Photoelectron Spectroscopy. An attempt is made to correlate corrosion current with intercrystalline defects.

The corrosion of austenite and δ-ferrite phases and the respective phase boundary was investigated in unirradiated and proton-irradiated 308 L stainless steel weld metal in a simulated-PWR environment. The results revealed that the inner oxide thickness was increased by irradiation for austenite but was largely unaffected for δ-ferrite. This behavior was attributed to the fact that irradiation generated numerous structure defects in austenite, but not in δ-ferrite. Following the 3-dpa (displacements per atom) irradiation, enhanced corrosion of δ-ferrite/austenite phase boundary occurred due to the irradiation-induced Cr-depletion. M23C6 carbides along the phase boundary further enhanced corrosion regardless of the irradiation condition.

The influence of diffusive Nb redistribution on the microstructure and Volta potential of U-5.5Nb alloys thermally aged at 400 °C for durations between 1 h and 100 h was investigated and their surfaces were examined post-corrosion using various microscopy techniques. The results demonstrated that Nb-depleted lamellae resulting from Nb redistribution have the lowest Volta potential in the microstructure and are extremely sensitive to pitting, as demonstrated by immersion experiments and potentiometric polarization tests. However, the pitting potential of the aged alloys (205.2 ± 3.9 mV) did not change with the content of Nb-depleted lamellae.

To reveal the fundamental role of structural order of the parent alloy on the oxidation mechanism, thermal oxidation of amorphous and crystalline Al–Zr alloys with identical compositions were investigated in detail. An (Al0.68Zr0.32)O1.66 amorphous oxide emerged on crystalline Al2Zr, whereas an (Al0.33Zr0.67)O1.83 amorphous oxide formed on amorphous Al68at.%Zr32at.% under the same conditions. Oxidation kinetics was fast and linear for crystalline Al2Zr but slow and parabolic for amorphous Al68at.%Zr32at.%. The underlying mechanisms of such striking differences were disclosed by molecular dynamics simulations. The findings thus offer new prospects in the field of surface engineering.

Electrochemical analysis, XPS, and ToF-SIMS are combined to characterize the passive properties of 254SMO stainless steel in the simulated condensates after flue gas desulfurization at different temperatures. Increase in condensate temperature causes the enhanced transpassive dissolution and surface deterioration as well as the involvement of oxygen reduction. Solution deaeration counteracts with the reaction rate acceleration, yielding an invariable donor density from 40 to 60 ºC. Dissolution and precipitation of Fe and oxidation of Mo are facilitated, resulting in the mixed Cr(III)-Fe(III)-Mo(VI/IV) oxide/hydroxide surface layer and the strengthened enrichment of oxidized Cr and oxidized Mo at high temperatures.

The modifications of the passive film formed on 316 L stainless steel surface during stepwise heating in ultra-high vacuum up to 300 °C have been studied in situ by ToF-SIMS. The pre-formed passive film (in 0.05 M H2SO4) has a bilayer structure, comprising Fe-rich, Mo-rich (outer) and Cr-rich (inner) layers. Below 100 °C, the passive film is stable. At 100 °C - 250 °C, dehydroxylation and dehydration is observed. Above 250 °C, the main modification in the film is formation of chromium oxide at the expense of oxidized iron. At higher temperature, thicker Cr-rich inner layer with sharper inner/outer oxide interface is formed.

The study investigated the effect of high hydrostatic pressure on stress corrosion cracking (SCC) of Ti-6Al-4 V alloy in 3.5% NaCl solution at 2 °C, by slow strain rate testing at 0.1 MPa and20 MPa. The fractography exhibited a mixed fracture with small and shallow dimples, as well as cleavage and quasi-cleavage surfaces at the two pressures. High hydrostatic pressure enhances SCC of Ti-6Al-4 V alloy at 20 MPa, by facilitating the dissolution of titanium and decreasing the resistance of oxide film. The hydrostatic pressure also promotes the formation of δ hydrides at the α/β interface of Ti-6Al-4 V alloy.