Liquid Metal Embrittlement Research Articles

Statistical in situ scanning electron microscopy investigation on the failure of oxide scales

AbstractOxide scales play a pivotal role in obstructing surface chemical and electrochemical reactions, hence hindering chemo‐mechanical effects such as liquid metal embrittlement of steels. Therefore, the critical conditions and failure mechanism of the oxide film are of major interest in the safe service of steels. Though in situ microscopic methods may directly visualize the failure mechanism, they are often challenged by the lack of statistically reliable evaluation of the critical conditions. Here, by combining in situ scanning electron microscopy with a tapered specimen tensile test in a single experiment, we uniquely achieve a mechanistic study with statistically reliable quantification of the critical strains for each step of the dynamic process of film rupture. This is demonstrated with the oxide films formed on a ferrite–martensite steel in liquid lead–bismuth eutectic alloy at elevated temperatures, with in situ results falling right into the predictions of the statistical analysis. Explicitly, the integrated experimental methodology may facilitate the materials genome engineering of steels with superior service performance.

Hydrogen production via hydrolysis of Al-eutectic GaInSn composites

A novel way of constant hydrogen generation via Al and liquid metal eutectic GaInSn (eGIS) was proposed. The cylindrical Al with a blind hole served as a container of liquid metal to generate hydrogen via hydrolysis, while eGIS was considered a window for triggering the reaction. The microstructure, hydrolysis evolution and hydrogen production performance of the semi-solid Al-eGIS composites were investigated. The results indicated that the liquid metal embrittlement occurs when the eGIS diffuses along the grain boundaries of polycrystalline Al, which increases the reaction activity of the composites; while the formation of In3Sn and InSn4 secondary phases was observed, which accelerated the hydrolysis of Al. Moreover, the Al-10wt.%eGIS and Al-20wt.%eGIS composites achieved nearly 100% conversion yield of hydrolysis. Consequently, the samples were practically applied to proton exchange membrane fuel for performance measurement, with a stable power supply of 0.54 W for 110 min.

Understanding fusion zone hardness in resistance spot welds for advanced high strength steels: Strengthening mechanisms and data-driven modeling

The fusion zone (FZ) hardness of resistance spot welds is a crucial factor affecting the performance and durability of the welds. Failure mode transition, tendency to fail in interfacial mode, interfacial failure load, and the impact of liquid metal embrittlement cracks on the weld strength are influenced by the FZ hardness. Therefore, accurately predicting the FZ hardness in resistance spot welds made on automotive steels is essential. A simple thermal model is used to calculate the time required for the temperature to drop from 800 °C to 500 °C (Δt85). With the aid of continuous cooling transformation (CCT) diagrams and experimental confirmation, it is shown that in most automotive steels, the FZ exhibits an almost full martensitic microstructure. Generally, the FZ hardness tends to increase in the order of interstitial-free (IF), drawing quality specially killed (DQSK), high strength low alloy (HSLA), ferrite-martensite dual-phase steels, transformation induced plasticity (TRIP), and quench & partitioning (Q&P) steels. To predict the FZ hardness, data-driven regression-based models have been developed based on carbon content, carbon equivalent concept, and the strengthening mechanisms of the martensite. Among these models, the model based on martensite strengthening mechanisms showed the best performance and robustness in estimating the FZ hardness. The assessment of the strengthening mechanism of the FZ showed that most important factors determining the FZ hardness are dislocation hardening due to carbon atoms, interface hardening due to block boundaries, and solid solution hardening due to substitutional alloying elements, respectively. A simple relation is proposed to estimate the load-bearing capacity of automotive steel spot welds during interfacial failure based on the FZ hardness.

Liquid Metal Embrittlement Susceptibility of Hot Formed Zn-Al-Mg Coated Steel with Eutectic Coating Microstructure

Liquid metal embrittlement (LME) in Zn-based coating plates during hot stamping is an abnormal phenomenon where intimate contact between liquid Zn and a steel matrix results in the penetration of liquid Zn into the matrix, causing ruptures. In order to alleviate LME phenomenon, this paper designed a series of eutectic Zn-Al-Mg coating alloys to improve the uniformity of the Zn element distribution in the coating during heat treatment and inhibit the reaction between Fe and Zn. The high temperature mechanical properties of the coated steels are determined using thermal simulation to calculate the relative reduction in fracture energy, which is used to evaluate the LME level of the different composition coatings. It is suggested that the Zn-4.5Al-3.0Mg coating shows the highest LME resistance at 920 °C. The microstructure of these Zn-Al-Mg coated steels is observed after austenitization at 850 °C~920 °C for 3 min, which shows that the uniformity of the microstructure after austenitizing is affected by the composition of the coating and the austenitizing temperature. The higher temperature benefits the homogenization of the coating and steel and inhibits LME. The findings of this study provide valuable insights for the development of ternary Zn based LME resistant coatings.

Strong resistance to Zn-assisted liquid metal embrittlement of austenitic-TWIP/martensitic-HSLA multi-layered steel sheets additively manufactured by laser cladding

As a novel design idea to overcome a shortcoming of liquid metal embrittlement (LME) occurred frequently in twinning-induced plasticity (TWIP) steel, multi-layered steel (MLS) sheets consisting of austenitic TWIP and high-strength low-alloy (HSLA) steel grades have been suggested. Two- and four-time clad MLS sheets (C2 and C4) were fabricated by a powder-fed laser additive manufacturing (AM) process using HSLA powders on the TWIP surface, and the LME was investigated in various resistance-spot-welding-time stages. The C2 and C4 sheets consisted of the austenitic TWIP substrate and tempered-martensitic HSLA-clad layer, and the HSLA layer had two or four sublayers having different C and Mn contents reduced step-wise from the TWIP/HSLA interface. LME cracks formed in the C2 spot-welded for 240 or 380 ms, whereas they did not form at all in the C4 spot-welded for 380 ms. This different LME susceptibility depended mainly on the HSLA-sublayer microstructures beneath the Zn coating after their high-temperature exposure during the spot welding. Since LME cracks propagated mainly along prior austenite grain boundaries, the whole austenite existed in the austenite range played a key role in determining whether the LME cracking occurred or not. The total volume fraction of reverted austenite (appeared as fresh martensite at room temperature) and retained austenite was very high at about 68% in the C2 welded for 240 ms, thereby leading to the LME cracking. It was lower than 20% in the C4 even under the severe welding condition of 380 ms, which provided the reason for no LME cracking.

Segregation-induced grain-boundary precipitation during early stages of liquid-metal embrittlement of an advanced high-strength steel

Segregation-induced grain-boundary precipitation during early stages of liquid-metal embrittlement of an advanced high-strength steel

The inhibition mechanism of liquid metal embrittlement cracks in the Fe–Cu system by Al: atomistic simulations and calculations

The inhibition mechanism of liquid metal embrittlement cracks in the Fe–Cu system by Al: atomistic simulations and calculations

Mitigating the influence of industrially relevant disturbances on LME severity of dissimilar resistance spot welded advanced high-strength steels

The third generation of advanced high-strength steels (3G-AHSS) has been developed to provide high strength and high ductility, which attract automakers. To protect these materials from corrosion during service, these materials are typically coated with zinc. During resistance spot welding (RSW), the zinc coating can melt, allowing it to penetrate into the grain boundaries (GBs), and lead to liquid metal embrittlement (LME) phenomena. Concerns regarding LME susceptibility have impacted the industrial application of 3G-AHSS; therefore, its mitigation has become a top focus for automakers. Several possible strategies for lowering LME severity by altering welding parameters have been proposed to mitigate LME in similar spot weld joints. However, these strategies were not tested on a dissimilar spot weld joint. Therefore, in this work, 1.4 mm gauge thickness galvanized (GI-coated) 3G-980 AHSS was joined with 0.6 mm thick Interstitial Free (IF) steel. In this work, current pulsation and ultra-short hold time were proposed to minimize LME severity. The robustness of the developed welding schedule was then tested on welds made with industrial disturbance factors such as pre-strained sheets (between 0 to 80% of 3G-980 material yield strength) and electrode misalignment (between 0° to 10° misalignment) compared to baseline parameters. In severe circumstances of disturbance factors, the resulting optimized welding schedule decreased LME cracking and showed improved resistance to LME, lowering LME severity by 41% for the extreme pre-strain condition and 27% for the extreme misalignment angle.

Comparative Investigation into the Liquid Metal Embrittlement Susceptibility during Resistance Spot Welding of Zn–Al–Mg and GI Coated Advanced High Strength Steels

Comparative Investigation into the Liquid Metal Embrittlement Susceptibility during Resistance Spot Welding of Zn–Al–Mg and GI Coated Advanced High Strength Steels

Kinetics calculation of Al/Ga interfacial diffusion in sandwich geometry model

Gallium alloys have been attracting significant renewed attention for actively triggerable metals of advanced manufacturing via liquid metal embrittlement. This study is devoted to understanding mechanism of liquid metal embrittlement by a new perspective on the diffusion kinetics of gallium in aluminum matrix. The interfacial diffusion between liquid gallium and pure aluminum has been systematically investigated through sandwich geometry diffusion model analysis at different temperatures. Diffusion activation energy and diffusion coefficient of Al/Ga diffusion couple were calculated, and the diffusion kinetics model was established as well. The diffusion activation energy of gallium in aluminum matrix can be estimated to be 41.5 kJ/mol. The relationship between the mean-squared diffusion distance, time and temperature is the following: d=0.178exp(−4990T)t.

The sandwich-structured advanced high strength steel to resist the liquid metal embrittlement

There exists a direct correlation between the alloy elements and the formation of the liquid metal embrittlement (LME) in the advanced high strength steel (AHSS). In the present study, a sandwich-structure AHSS-#2 + IF (Interstitial-free) sheet with the equivalent tensile strength compared with the AHSS-#1 sheet is designed and fabricated to resist the LME cracks. The welded joints with normal structure (RSW joint of galvanized steel AHSS-#1) reveal the higher LME susceptibility than the sandwich-structured one. The maximum length of the detected LME cracks is 1062.9 μm for type I crack (located at the center of the weld) and 152.2 μm for type II crack (located at the shoulder of the weld). Based on the results of the element distribution in the regions near the LME cracks, the internal oxide layer and element segregation are detected for the welded joint with normal structure. The formation of the internal oxide and the element segregation could largely deteriorate the cohesion of the boundaries especially for the region directly contacted with the Zn coating, triggering the formation of the LME cracks. With the protection of the IF steel as the covering layer on AHSS-#2, however, the regions with element segregation are successfully separated from the Zn coating, dramatically decreasing the corresponding LME susceptibility.

Interstitial Segregation has the Potential to Mitigate Liquid Metal Embrittlement in Iron.

The embrittlement of metallic alloys by liquid metals leads to catastrophic material failure and severely impacts their structural integrity. The weakening of grain boundaries (GBs) by the ingress of liquid metal and preceding segregation in the solid are thought to promote early fracture. However, the potential of balancing between the segregation of cohesion-enhancing interstitial solutes and embrittling elements inducing GB de-cohesion is not understood. Here, the mechanisms of how boron segregation mitigates the detrimental effects of the prime embrittler, zinc, in a Σ5 [001] tilt GB in α-Fe (4 at.% Al) is unveiled. Zinc forms nanoscale segregation patterns inducing structurally and compositionally complex GB states. Ab initio simulations reveal that boron hinders zinc segregation and compensates for the zinc-induced loss in GB cohesion. The work sheds new light on how interstitial solutes intimately modify GBs, thereby opening pathways to use them as dopants for preventing disastrous material failure.

Effects of lead, bismuth and alloying elements on elastic anisotropy and fracture toughness of α-Fe

First-principles calculations reveal the effects of lead, bismuth and alloying elements (M=Al, Si, V, Cr, Mn, Ni, Nb and Mo) on thermodynamic stability, elastic properties, elastic anisotropy and fracture toughness of alpha-Fe. Overall, Pb and Bi increase the elastic anisotropy of iron, and reduce the thermodynamic stability, elastic properties and fracture toughness of iron, but alloying elements have little effect on these properties of iron without liquid lead-bismuth eutectic (LBE). Moreover, V, Mn and Nb can hinder the influence from Pb and Bi on iron, while Al, Si, Cr, Ni and Mo would exacerbate these effects. Combined with the plastic dissipation coefficient, the calculations also show that Fe first breaks along the (100) plane, followed by the (110) plane in all cases, while the (111) and (112) planes are hard to crack. And it is also found that the elastic properties of Fe play an important role at its fracture toughness. In addition, a clear functional relationship between fracture toughness and elastic anisotropy is proposed, which provides a deep understanding of liquid metal embrittlement (LME) of iron in lead-bismuth eutectic. The obtained results are in good agreement with experimental measurements in the literature.

Westinghouse Test Facilities for Lead Fast Reactor Development

Westinghouse is developing a lead-cooled fast reactor (LFR) as its next-generation utility-scale nuclear power plant. To support its development, Westinghouse and its partners are building 10 test facilities to demonstrate key LFR phenomena, materials, and components in liquid lead. These test infrastructures are distributed across several institutions, and this paper focuses on those located within Westinghouse. It describes three state-of-the-art test rigs being installed in the Westinghouse facility in Springfields, United Kingdom, to test materials in liquid lead and to investigate key LFR phenomena, which will also be used to validate modeling and simulation tools. These facilities address material corrosion/erosion testing (MELECOR), lead freezing and under-lead viewing testing (LEFREEZ), and primary heat exchanger failure testing (LEWIN). This paper also describes the first liquid-lead test system to become operational at Westinghouse at the company’s site in Churchill, Pennsylvania, i.e., a test rig named HELMET to conduct tensile tests in a molten-lead environment to investigate the potential susceptibility of LFR candidate materials to liquid-metal embrittlement.

Mercury in natural gas: delivering accurate reservoir sampling and analysis

Natural gas is a critical part of the world’s energy supply and plays an important role in the transition to lower-carbon energy sources. The industry’s ability to process natural gas safely and efficiently will continue to rely on an accurate understanding of feed gas composition and contaminants, particularly in enabling future developments via existing infrastructure. Mercury is toxic to organisms, highly volatile and produced from hydrocarbon basins globally. Trace mercury concentrations in the hydrocarbon stream can potentially introduce liquid metal embrittlement hazards to industrial equipment, including cryogenic heat exchangers used to refrigerate liquefied natural gas. Inaccurate measurement of mercury levels can lead to adverse impacts measurable across the areas of health, process safety, environment, operations, waste disposal and decommissioning. Worldwide, significant project cost overruns and processing incidents have resulted from the uncertainty of mercury concentrations in hydrocarbon streams. Successful mercury management ideally begins early in a project’s lifecycle with development decisions informed by accurate measurement of mercury concentrations from reservoirs. Historically, this has been problematic, as mercury contamination and scavenging often result in a large range of uncertainty. The results from a multi-company collaborative study to reduce mercury uncertainty with new downhole sampling techniques will be shared in a case study, including production insights from the Julimar Field, west coast of Australia. The recommendations, procedures and operational best practices discussed will be applicable across the industry and beneficial to any party considering the impact of mercury in the development and processing of natural gas resources.

Investigation of the LME Susceptibility of Dual Phase Steel with Different Zinc Coatings

The application of anti-corrosion coated, high-strength steels in the automotive industry has increased in recent years. In combination with various zinc-based surface coatings, liquid metal embrittlement cracking can be observed in some of these materials. A high-quality, crack-free spot-welded joint is essential to realize the lightweight potential of the materials. In this work, the LME susceptibility of different coatings, which will be determined by the crack length and the occurrence rate, will be investigated using a welding under external load setup. The uncoated specimens did not show any LME. EG, GI and GA showed significantly less LME than ZM coatings. The latter coatings showed much larger crack lengths than the EG, GI and GA coatings. Furthermore, two mechanisms regarding the LME occurrence rate were observed: the occurrence of LME in zinc–magnesium coatings was theorized to be driven by the material properties of the coatings, whereas the occurrence of LME at EG, GI and GA samples was forced mainly by the application of the external tensile load. In the experimental setup of this work, the materials were exposed to unusually high mechanical loads (up to 80% of their yield strength) to evoke LME cracks.

Evaluation of liquid metal embrittlement-free weld by micro-plasma arc welding of Zn-coated interstitial free steel

The liquid metal embrittlement (LME) severity is a significant concern in the fusion welding of Zn-coated steel. The LME severity in galvannealed (GA) interstitial free (IF) steel processed through microplasma arc welding (MPAW) is investigated. The weld geometry, microstructure and mechanical properties of the 0.8 mm thin butt-welded structure are evaluated to check the welding quality. Optical microscopy and field emission scanning electron microscopy (FESEM) of the weld surface are considered to observe any LME cracks. The high-temperature tensile test is executed on GA-IF steel to simulate external stress-free MPAW conditions. The ultimate tensile strength of the welded joint is more than that of the base material, and it is LME-free, which signifies that the current MPAW system can be successfully used for joining GA-IF steel. The microstructure of the weld zone is having large grain structure and much more hardness than the base material. Even the high-temperature tension test does not show any LME cracks. Approximately, one-third of yield strength is reduced as the temperature rises from 600 °C to 700 °C. Overall, the parametric domain for MPAW of GA IF steel is successfully evaluated, which can produce any LME-free weld.

Multiplicity and Separability of the Mechanisms of Liquid Metal Embrittlement in the Ga–In–Al System

Multiplicity and Separability of the Mechanisms of Liquid Metal Embrittlement in the Ga–In–Al System

Optimization of Hot Forming Temperature to Minimize Liquid Metal Embrittlement Induced Cracking in Resistance Spot Welded Zinc‐Coated Medium Manganese Steel

Herein, an investigation on the influence of the hot press forming (HPF) temperature cycles of a medium manganese, high ductility, zinc‐coated steel with ≈1000 MPa final tensile strength (HPF1000‐GI), with a specific emphasis on the risks of liquid metal embrittlement (LME) induced cracking during resistance spot welding (RSW) is presented. The HPF1000‐GI steel is hot press formed using several temperature cycles, and subsequently the LME sensitivity of the variously hot press formed materials are investigated using both dedicated RSW experiments as well as high‐temperature tensile testing. It is shown that the LME sensitivity of the HPF1000‐GI steel is significantly reduced after hot forming at higher intercritical temperatures, and that this favorable behavior is caused by microstructural changes at the coating‐substrate interface.

Role of silicon on formation and growth of intermetallic phases during rapid Fe–Zn alloying reaction

The study of liquid metal embrittlement in Fe–Zn systems is challenging because of the high temperature and vapor pressure of Zn, which hinders in-situ investigations with sufficiently high spatial resolution. This is typically associated with subsecond processing steps and the coexistence of a solid substrate and a liquid Zn phase, which renders direct observations at the microstructural scale difficult. In this study, we comprehensively investigate the reactions occurring during the rapid heating and cooling stages of Fe–Zn systems using synchrotron X-ray diffraction. The phase transformation is analyzed for specimens with different interfacial structures, with focus on changes in the coating microstructure above and below the peritectic temperature (782 °C) of the Fe–Zn system. Advanced high-strength steel (AHSS) variants with 1.5 wt% Si content show a prominent destabilizing effect at the onset of Fe–Zn intermetallic compound formation and a simultaneous deceleration of the liquid Zn depletion rate compared with other AHSS alloys containing 0 wt% Si. Furthermore, the addition of Si suppresses the formation of the Γ phase, which is due to turbulence in the outburst Zn at temperatures above 773 K. Consequently, the fraction of Γ phase compounds with accumulated Zn deceases as the exposure time of the liquid Zn to the ferritic matrix increases owing to the solute redistribution of Si in the liquid Zn during rapid heating. Meanwhile, the absence of silicon in the substrate causes the formation of a ζ phase with a low melting point, which delays the formation of liquid Zn via an increase in the melting point of the Zn layer in the early stage of heating. Additionally, the amount of residual liquid Zn decreases due to the rapid depletion of Zn during the liquid initiation stage via an equilibrium Fe/Zn binary phase transformation. The results of this study provide a deeper understanding of the Fe–Zn intermetallic phase transformation and the sensitivity to liquid metal embrittlement of third-generation AHSSs based on silicon content.