Liquid Metal Embrittlement Research Articles

Morphology and Distribution of the Liquid Metal Embrittlement Crack in the Resistance Spot Welded Joint of the Galvanized Q&P980 Steel

Morphology and Distribution of the Liquid Metal Embrittlement Crack in the Resistance Spot Welded Joint of the Galvanized Q&P980 Steel

Deformation behavior of aluminum pillars produced by Xe and Ga focused ion beams: Insights from strain rate jump tests

Micro-compression testing of focused ion beam fabricated pillars is a popular technique for mechanical characterization at small scales. However, there are concerns associated with these ion-prepared samples, including irradiation damage from Ga ions and Ga segregation at grain boundaries resulting in liquid metal embrittlement. In this work, this is investigated using strain rate jump nanoindentation and micro-compression of single crystalline and ultrafine-grained aluminum with different grain boundary conditions. The extracted strain rate sensitivity and activation volume are used to study the effects of Ga and Xe ion species from fabrication and testing methods on deformation behavior of aluminum samples. Results show that the measured strain-rate sensitivity of non-equilibrium, ultrafine-grained aluminum is significantly affected by the dosage of Ga. Activation volumes suggest that the dominant deformation mechanism remains consistent despite Ga at the boundaries. Atom probe tomography reveals that Ga was observed to segregate to aluminum grain boundaries up to 2.2 at.% in the FIB prepared sample.

Liquid Metal Embrittlement of Copper Brazed Plate Heat Exchangers

Plate heat exchangers are widely used for heating and cooling activities in domestic and industrial applications. The plates of all these components were made of stainless steel (e.g. type X2 CrNiMo 17-12-2) and they were brazed with pure copper. After cutting and metallographic preparation, the samples were investigated by light optical microscopy (LOM) to measure the depth of copper penetration into the plates (liquid metal embrittlement (LME)). For seven heat exchangers the penetration depth was between 25 and 60 μm, but for one the depth was about 150 μm. At the steel-copper interfaces an additional phase was identified as chromium-rich ferrite by electron beam micro analysis (EBMA). To get information about the sensitivity against corrosion electrochemical tests were performed in two electrolytes (HCO3- + SO42- and HCO3- + SO42- + Cl-). It can be summarized that in the Cl- free electrolyte the copper was attacked mainly. In case of the Cl- containing electrolyte beside the copper braze, the LME zones in the steel were corroded additionally.

Forging of Copper and Iron Plates by the Damascus Technique

Forging of different steel grades is called Damascus technique and results in a layered composite material termed “Damascus steel”, but forging of different copper alloys is termed “mokume gane”. In this paper the joining of copper and iron plates by forging is described. Metallographic investigations showed well bonded interfaces of copper and iron. A very small diffusion zone was observed. To study the diffusion between copper and iron two heat treatments were performed in Ar atmosphere. After 30 minutes at 1000 °C a marginal Cu-Fe interaction took place. Above the melting point of Cu at 1100 °C an intense Cu-Fe interaction was observed, which significantly changes the interface of both metals. Cu penetrated Fe along the grain boundaries and Fe droplets were formed sporadically. This correlates with the typical morphologies of liquid metal embrittlement (LME). Moreover, Fe is dissolved in Cu at 1100 °C and after cooling fine Fe precipitates in the Cu phase were detected.

Non-destructive Characterization of Polycrystalline Materials in 3D by Laboratory Diffraction Contrast Tomography

Laboratory diffraction contrast tomography (LabDCT) enables the user to reconstruct three-dimensional (3D) grain maps of polycrystalline materials. For each grain, the size, orientation, and 3D morphology including the number of faces can be derived. Since the technique is non-destructive, LabDCT opens up new possibilities for studies of microstructural evolution at the level of individual grains. The LabDCT setup is integrated on a commercial X-ray microscope, enabling correlation of the resulting grain map with complimentary information on, e.g., cracks, porosities, and inclusions. Here, the LabDCT principle is introduced, and recent materials science applications are presented. The first example on liquid metal embrittlement highlights the correlation of grain boundary properties and complimentary absorption information on grain boundary wetting. It is shown that the grain boundary energy determines whether wetting occurs or not. The second example is on grain growth. The grain statistics in this study, more than 1200 grains at two different time steps, were large enough to capture rare events such as abnormal grain growth and the annihilation of a grain with only three faces.

High Temperature Oxidation Resistance of Cr Coatings on 22MnB5 Steel Electroplated in Trivalent Cr Baths

22MnB5 steel is one kind of advanced high-strength steels commonly used for vehicles to enhance passengers’ safety and reduce carbon dioxide emission[1]. However, 22MnB5 steel is vulnerable to high-temperature oxidation and a protective coating is essential to inhibit oxidation during hot stamping process. For example, hot-dip Al-10 wt % Si coating has been extensively applied on press hardening steel although it does not provide sacrificial protection on the steel parts[2]. In contrast, hot-dip Zn coating, which confers sacrificial protection, tends to suffer oxidation and liquid metal embrittlement during hot stamping[3, 4]. This study investigated the structure and properties of Cr coatings on 22MnB5 steel electroplated in a trivalent Cr (Cr(III)) bath. The DC electroplating was conducted in a chloride-based Cr(III) electrolyte with and without the addition of sulfur-containing organic compounds. The morphology, microstructure, and composition of the Cr coating were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), and electron dispersive spectroscopy (EDS). The thickness of the deposit before and after high-temperature heat treatment (900℃ for 5 min in air) was measured using cross-sectional SEM. Experimental results show that the sulfur-containing organic compound in the electrolyte reduces the carbon content and increases the sulfur content of the Cr coating, which, in turn, reduces the residual stress of the coating. As a result, a crack-free Cr coating can be obtained in the electrolyte with the organic additive. In contrast, many cracks develop on the Cr coating plated in the electrolyte without the organic additive. After the heat treatment at 900℃ for 5 min, extensive oxidation was observed on the crack-free Cr coating, but not on the Cr coating with cracks. It is likely that the presence of sulfur in Cr coating deteriorates the oxidation resistance. Crack openings of the Cr coating free of sulfur are filled with compact oxides after 900℃heat treatment for 5 min. The steel substrate with a Cr overlay remains intact, indicating the Cr coating prevents the steel substrate from oxidation at 900℃.Finally, a 2-mm-thick Cr coating can be electroplated in the Cr(III) bath without the organic additive at a current density of 10 A/dm2and a plating time of 1 min and effectively protects the 22MnB5 steel from high-temperature oxidation. Reference [1] H. Karbasian, A.E. Tekkaya, Journal of Materials Processing Technology, 210 (2010) 2103-2118. [2] D.W. Fan, H.S. Kim, J.-K. Oh, K.-G. Chin, ISIJ international, 50 (2010) 561-568. [3] C.W. Lee, D.W. Fan, I.R. Sohn, S.-J. Lee, B.C. De Cooman, Metallurgical and Materials Transactions A, 43 (2012) 5122-5127. [4] M. Razmpoosh, A. Macwan, E. Biro, D. Chen, Y. Peng, F. Goodwin, Y. Zhou, Materials & Design, (2018).

Zn-Assisted Liquid Metal Embrittlement of 980MPa Grade Advanced High Strength Steels

Recently, the weight reduction of automotive body and crash safety become much more important factors. In addition, the corrosion resistance must be ensured for any material used in a structural part of automotive components. In an effort to satisfy these requirements, zinc-coated high strength steels have been developed. However, challenges to resistance spot weldability of zinc-coated high strength steel such as liquid metal embrittlement (LME) have emerged. In this study, the high temperature tensile test was conducted for 980MPa DP steel. And resistance spot welding was conducted for 980MPa DP steel and CP steel. The results show that the fracture behavior during tensile test are influenced by the temperature and strain rate. Cracks were formed on the weld surface of the DP steel after welding.

Studying the Machinability of Tin-Bearing Free-Cutting Steel

The machinability of 0.2% Sn free-cutting steel produced by vacuum melting and hot shaping under pressure using the method of hammer forging has been studied. The distribution of elements (Sn, S, Mn) in the steel has been investigated by secondary ion mass spectrometry (SIMS). It has been established that the doping with tin appreciably increases the machinability index of the free-cutting steel to kv = 1.72. The effect of S and Mn segregation with the formation of manganese sulfide MnS precipitates has been revealed. Tin in the form of fine particles is uniformly distributed in crystalline grains and along their boundaries and segregates on MnS particles. In the process of cutting, low-melting tin particles are melted to initiate the Rehbinder effect (liquid-metal embrittlement), thus embrittling the steel. Moreover, tin has a lubricating effect at the point of contact between the cutter and the machined surface. All these effects improve the machinability of tin-bearing free-cutting steel.

Study of Crack Initiation of 15-15Ti Austenitic Steel in Liquid PbBi

The austenitic steel 15-15Ti is being considered as one of the candidate materials for internal structural components of future heavy liquid metal (HLM) nuclear systems. This work studies the steel compatibility with liquid PbBi. Constant extension rate tensile (CERT) tests of tapered specimens were used to study sensitivity to liquid metal embrittlement (LME) and crack initiation. The taper creates a variation of stress along the gauge length which allows the identification of the stress and strain for the crack appearance. Testing was performed in air and in PbBi with 10−6 to 10−12 wt % oxygen content at 300 °C. Post-test observation by scanning electron microscopy (SEM) highlighted the crack morphology. An evaluation of the environmental effect on the crack initiation is presented.

Impact of liquid metal embrittlement cracks on resistance spot weld static strength

ABSTRACTAdvanced high strength steels used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement (LME) during welding. Although LME cracks are known to form, limited research has found any detrimental impact of LME cracks on weld strength. In this work, a comparison of zinc coated and uncoated advanced high strength steel joints showed LME decreased strength in welds from transformation induced plasticity type microstructures and an 1100 MPa ultimate tensile strength by 43.6%. LME cracks were observed to propagate until final fracture. However, only cracks located in the periphery of the weld area were found contribute to a loss in strength.

Experimental and Numerical Analysis of Liquid Metal Embrittlement Crack Location

Advanced high-strength steels used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement during welding. Although liquid metal embrittlement cracks are known to form, the current literature does not include crack location when assessing crack severity. In this work, TRIP1100 joints showed that LME cracks decreased strength from 7.8 to 42.2%, depending on location, between the coated (cracked) and uncoated (non-cracked) condition. Liquid metal embrittlement cracks in critical locations were observed to propagate until fracture from lap shear testing. However, cracks in non-critically loaded areas were not part of the fracture path and did not result in a significant loss in strength. This shows LME crack location can be controlled to improve joint performance and vehicle safety. In addition, a model of lap shear testing in a cracked sample showed how the presence of a crack can affect the internal stress field depending on its location.

Effect of Al and Zn-coated Layer of Scaffolding on Weldability of Cryogenic Material in LNG Carriers

Membrane type Cargo Containment System(CCS) of Liquefied Natural Gas Carrier(LNGC) are built with Stainless steel 304L(STS 304L) or Fe-36%Ni steel(Invar alloy) using manual and automatic tungsten inert gas welding, automatic Plasma arc welding and resistance seam welding. Lately, it is suggested that debris from coating layer on scaffolding of CCS induces Liquid Metal Embrittlement(LME) at lap joints of CCS. In this study, effect of Al and Zn-coated layer of scaffold on weldability and LME of cryogenic materials is investigated. Key words: Liquid metal embrittlement, Scaffolding, Zinc coated steel, Aluminum coated steel, Cryogenic material, LNGC, STS 304L, Invar alloy, TIG welding

Investigation of liquid metal embrittlement of dual phase steel joints by electro-thermomechanical spot-welding simulation

A 3D electro-thermomechanical model is established in order to investigate liquid metal embrittlement. After calibration to a dual phase steel of the 1000 MPa tensile strength class, it is used to ...

Quantifying the link between crack distribution and resistance spot weld strength reduction in liquid metal embrittlement susceptible steels

Zinc-coated advanced high-strength steels (AHSS) used in the automotive industry are vulnerable to liquid metal embrittlement (LME) during welding. In this work, a “crack index” is used to link LME crack distributions in resistance spot welds to the weld performance. Other commonly used LME metrics, such as maximum crack length, are unable to predict an effect on weld performance. Because both crack size and location have been established as critical characteristics for loss in weld strength, both of these factors must be taken into account when characterizing LME severity. The crack lengths measured in LME-affected welds were observed to fit a lognormal distribution; therefore, the lognormal median is used as the parameter to account for crack size. Long cracks are more likely to adversely impact mechanical performance. Number of cracks can be used to account for the probability that a crack will be found in a critical location. These parameters are multiplied together and divided by the sheet thickness to produce the crack index. A large crack indicates that LME cracks in the weld are likely to impact the mechanical performance of the weld. A simpler version of the crack index may be calculated using the normal median.

Influencing surface plastic flow in metals using common chemical media

ABSTRACTWe demonstrate a unique mechanochemical effect – change in surface plastic flow by action of chemical media such as inks and glues – in large-strain deformation of metals. Unlike other well-known phenomena such as stress corrosion cracking and liquid metal embrittlement, the effect is not catastrophic and is largely material independent. High-speed in situ imaging shows that the media influence the flow by effecting a local ductile-to-brittle transition – from unsteady, large-amplitude, plastic folding, to repeated fracture and segmentation – with large decrease in deformation forces. The benign nature of the media offers opportunities for enhancing performance of metal cutting and deformation processes.

Evaluation of the grain boundary precipitate microstructure in some Al-Mg-Si alloys by applying liquid metal embrittlement

Evaluation of the grain boundary precipitate microstructure in some Al-Mg-Si alloys by applying liquid metal embrittlement

A Review of Recent Advances in the Understanding of Liquid Metal Embrittlement

Significant advances in the study of liquid metal embrittlement have occurred since 2000 but there have been few reviews of the liquid metal embrittlement literature since that time. This review discusses recent advances in modeling and testing. Specific solid–liquid systems (including steel exposed to molten lead–bismuth and aluminum–gallium) are reviewed. Relationships between various studies are considered and the need for careful test protocols is emphasized. The individual effects of wetting, crack initiation, and propagation are discussed. Mechanisms of liquid metal embrittlement including interatomic and mass transport-based phenomena are analyzed.

Microstructural Investigation of LME Crack Initiated in Ferritic/Martensitic Steel T91 Loaded in Liquid Lead-Bismuth Eutectic at 300 °C.

Liquid lead-bismuth eutectic (LBE) is one of the candidate materials for advanced nuclear systems. The structural materials used in contact with LBE are selected according to the resistance to liquid metal corrosion, irradiation embrittlement, and compatibility with the coolant. However, simultaneous presence of mechanical strain and LBE environment can induce liquid metal embrittlement (LME) in these materials. In this study, a specimen from candidate ferritic-martensitic steel T91 was tested by Constant Extension Rate Tensile (CERT) test exposed to PbBi environment with oxygen concentration 6 × 10−6 wt % at 300 °C up to rupture. Post-test examination using scanning electron microscopy (SEM) showed a deep crack indicating features of LME in the plastic strained region of the tested specimen. Further investigations focused on characterization of the fracture path and microstructure determination using focused ion beam (FIB) and energy dispersive X-ray spectrometry/electron backscatter diffraction (EDX/EBSD). This observation revealed that the dominant LME failure mode of the observed crack is translath or transgranular and the crack stopped at the high-angle grain boundary. The role of oxides in the crack initiation is discussed.

Effect of Applied Stress on T91 Steel Performance in Liquid Lead at 400 °C.

The environmental performance of structural materials (e.g., corrosion and environmental assisted cracking) is one of the critical issues being addressed in the development of Generation IV fast reactors. This work aims to support the study of the performance of the ferritic-martensitic steel T91 in liquid lead, under close to operation conditions, in order to assess its suitability for an application in lead fast reactors. T91 steel was tested in air and liquid lead at 400 °C using static and slow loading regimes. Applied stresses were chosen to be slightly above the yield strength in order to evaluate the threshold stress and strain for crack initiation. Three-point bending static exposure and constant extension tests of tapered specimens were performed. Post-test surfaces and cross sections of specimens were observed using scanning electron microscopy techniques in order to detect cracks and to analyze oxide layers. The effect of strain rate of the oxide layer cracking was observed. In conclusion, T91 was not susceptible to liquid metal embrittlement, a special case of environmentally assisted cracking under the testing conditions. The cracking conditions are discussed based on previous experience.

Microstructural evolution of liquid metal embrittlement in resistance-spot-welded galvanized TWinning-Induced Plasticity (TWIP) steel sheets

The weldability is one of the key factors governing applications of TWinning-Induced Plasticity (TWIP) steels to automotive industries demanding high economy, environmental friendliness, and high performance. During spot welding of Zn-coated Al-containing TWIP steel sheets, liquid metal embrittlement (LME) frequently occurs by Zn infiltration into grain boundaries to form cracks, but the direct observation and detailed analysis of LME cracking are quite difficult because it occurs instantaneously within a second. Here in the present study, the LME was investigated by detailed microstructural evolutions of small Zn infiltrations or cracks as well as formation behavior of various intermetallic phases. In the heat-affected zone, the applied tensile stress and spot-welding heat tore down a diffusion-inhibiting Fe2Al5 layer formed between the Zn-coated layer and the TWIP steel substrate, and formed Zn-containing ferrite (α-Fe(Zn)) particles on the steel surface which provided paths for liquid Zn infiltration. α-Fe(Zn) particles played critical roles in accelerating the LME by reducing the ductility because they were brittle due to high contents of Zn and Al. In the present Al-containing TWIP steels, the increase in welding current generally aggravates the LME.