Cleavage Plane Research Articles

Subsurface damage evolution of β-Ga2O3 (010) substrates during lapping and chemical mechanical polishing

For semiconductor single crystal substrates, subsurface damage (SSD) is an important factor for device failure. For β-Ga2O3 with two cleavage planes, the SSD is the key issue that needs to be addressed. In this work, β-Ga2O3 (010) substrates were lapped and polished precisely. The formation and evolution mechanisms of SSD were analyzed by cross-section transmission electron microscopy and wet chemical etching techniques. The linear distribution of scratches was found on the substrates after lapping. After chemical mechanical polishing (CMP), the surface scratches were eliminated. However, the SSD layer may still exist under the surface. Chemical etching was developed to identify the "invisible damage" to the CMP-finished (010) substrate. The SSD including nanocrystalline, tilt boundary, twist boundary, and high-density dislocations in β-Ga2O3 was first reported. Distinctively, there was no slip occurrence in the SSD of the (010) plane different from the (100) and (001) planes. The Schmid factor of multiple slip systems was calculated to analyze the cause of no slip on the subsurface. The formation mechanism of SSD was believed that when the slip system could not be activated, the stress was released through rotation and distortion of the crystal plane. The accumulation of grain boundary dislocations at twist grain boundary junctions provided a driving force for the formation of nanovoids. The relationship of substrate damage evolution and crystal strain with different machining parameters was established by high-resolution X-ray diffraction and Raman spectra. A non-damaging β-Ga2O3 (010) substrate with a surface roughness of less than 0.2 nm was obtained by the optimized CMP process. The research results had guiding significance for damage control of β-Ga2O3 and other brittle crystals in ultra-precision machining.

Effect of Microwave Irradiation on Mechanical Properties and Microstructures of Minerals

Microwave-assisted rock breaking is a new and promising technology for the tunneling and drilling industry. Minerals in rocks have an important influence on the effect of microwave-assisted rock breaking. In this paper, common minerals in rocks such as potash feldspar (hereafter referred to as K-feldspar), calcite and pyroxene were selected as samples, and a lot of microwave irradiation tests were carried out by using a hamilab-v1500 microwave oven. The mass, strength and microstructure of the rock samples were tested before and after microwave irradiation. The change law of the mineral mass, strength and microstructure with regard to temperature was analyzed, and the influence mechanism was discussed. The results show that the strength of K-feldspar increases from 20 °C to 400 °C but decreases significantly when it is higher than 400 °C; the strength of pyroxene increases from 20 °C to 600 °C but decreases when it is higher than 600 °C; the strength of calcite decreases with the increase in temperature. As for the weakening pattern, pyroxene shows drawstring, step and flow with the increase in temperature, but K-feldspar and calcite show that failure occurs along the cleavage plane of the crystal structure. The higher the temperature of microwave irradiation, the finer the pattern at the fractured zone is, and the more fragmented it becomes; the loss of mineral mass increases with the increase in the temperature of microwave irradiation.

Gypsum ridges as conduits for deep methane emission in an evaporite basin– Insights into the origin of atmospheric methane on Mars

The origin of atmospheric methane on Mars is attracting much attention because of its possible biological origin. We report the first detection of methane-dominated hydrocarbons trapped between the {010} cleavage planes of gypsum megacrysts from the evaporative Qaidam Basin, in the northern Tibetan Plateau. The gypsum makes ridges of kilometers long, tens of meters wide, and high that are deposited from deep circulated brine and later exhumed to the surface by wind erosion. The δ13C of methane (-33.3 ± 4.1 ‰), high CO2/CH4 ratio but low C1/(C2+C3) ratio indicate their thermogenic sources. These gypsum ridges are formed on intrabasin salt domes and form conduits for the volatile hydrocarbons to diffuse upward and escape into the atmosphere. We suggest the atmospheric methane on Mars is also derived from the deep basins and is emitted by the same pathway since the gypsum ridges/seams/veins in the Qaidam Basin show striking similarities to the irregular polygonal ridge networks and veins on Mars.

Intrinsic mechanism of grain size effect and grain boundary misorientation angle effect on crack propagation in martensitic steels

Grain size and grain boundary misorientation angle as two important parameters in the polycrystalline system have a significant influence on the mechanical properties of advanced martensitic steels. A phase field model is used to investigate the intrinsic mechanism of the effects of grain size and grain boundary misorientation angle on the crack propagation process which considers the coupling damage behavior between grains and grain boundaries in martensitic steels by means of the finite element finite method. The transgranular (through grain boundaries) and intergranular (along grain boundaries) failure can be simulated by this model through constructing a grain boundary energy function and using a specific order parameter to track crack propagation in the grain boundary area. This model can directly display the crack propagation path inside the grain (martensite and austenite phases) and grain boundary area with the stress distribution. The preferential cleavage planes in austenite and martensite phases are 111γ and 100α in grains with different orientations, respectively. Moreover, the simulation results show that the crack mainly bifurcates near the trifurcated grain boundary. The crack tip tends to induce transgranular fracture in low-angle grain boundaries and intergranular fracture in high-angle grain boundaries when it reaches the grain boundary area. Consequently, this model will be a powerful tool to investigate the influence of grain size and grain boundary misorientation angle on the mechanical properties of polycrystalline martensitic steels.

Exploring fracture anisotropy in tantalum carbide compounds: A density functional theory approach

AbstractIn this paper, we examine the cleavage fracture anisotropy in tantalum carbides, namely, TaC, α‐Ta2C, and ζ‐Ta4C3 − x, using density functional theory (DFT) calculations. Our investigation identifies the presence of multiple low‐energy cleavage planes indicating multiple potential pathways for crack propagation in these ceramics, even the low symmetry compounds. The anisotropy characteristics of cleavage fractures exhibited by α‐Ta2C and ζ‐Ta4C3 − x closely align with the intrinsic fracture anisotropy observed in TaC. Notably, there exist at least three pyramidal planes in ζ‐Ta4C3 − x whose cleavage energies are less than those of the carbon‐depleted basal planes, previously reported to have the lowest cleavage energy. The observed preference in experiments for cleavage along carbon‐depleted basal planes, exclusive of other identified low‐energy planes, points to factors beyond cleavage energy influencing cleavage plane preference.

Interfacial Optimization for AlN/Diamond Heterostructures via Machine Learning Potential Molecular Dynamics Investigation of the Mechanical Properties.

AlN/diamond heterostructures hold tremendous promise for the development of next-generation high-power electronic devices due to their ultrawide band gaps and other exceptional properties. However, the poor adhesion at the AlN/diamond interface is a significant challenge that will lead to film delamination and device performance degradation. In this study, the uniaxial tensile failure of the AlN/diamond heterogeneous interfaces was investigated by molecular dynamics simulations based on a neuroevolutionary machine learning potential (NEP) model. The interatomic interactions can be successfully described by trained NEP, the reliability of which has been demonstrated by the prediction of the cleavage planes of AlN and diamond. It can be revealed that the annealing treatment can reduce the total potential energy by enhancing the binding of the C and N atoms at interfaces. The strain engineering of AlN also has an important impact on the mechanical properties of the interface. Furthermore, the influence of the surface roughness and interfacial nanostructures on the AlN/diamond heterostructures has been considered. It can be indicated that the combination of surface roughness reduction, AlN strain engineering, and annealing treatment can effectively result in superior and more stable interfacial mechanical properties, which can provide a promising solution to the optimization of mechanical properties, of ultrawide band gap semiconductor heterostructures.

THE APEX TALKS…CARDIAC METASTASIS MIMICKING ST SEGMENT ELEVATION MYOCARDIAL INFARCTION

Abstract A 78–year–old man with a recent diagnosis of lung squamous cell carcinoma was referred to our cardiology department for marked ECG abnormalities (ST segment elevation in V2–V4 and T waves inversion in the antero–lateral leads, Fig.1) in the absence of ischemic symptoms and for the detection of an intramyocardial mass at the apical segments on the CT scan. He had no significant previous cardiovascular history. A transthoracic echocardiogram (TTE) was performed and showed an isoechoic mass at the LV apical segments measuring 3 x 4 cm apparently incorporating the myocardial wall without a clear cleavage plane (Fig.2a). The EF was normal. No pericardial effusion present. The contrast echocardiography with Sonovue revealed a late uptake of the contrast (Fig.2b). Cardiac magnetic resonance (CMR) showed an ovular image in the para–apical area of 40 x 23 cm consistent with a secondary lesion (Fig.3). Unfortunately, the exam was interrupted early due to a patient’s claustrophobic crisis, without having acquired the post–contrast images. Due to infiltrative appearance of the mass and the oncology history, this formation was highly suspicious for metastasis. No complicated ventricular arrhythmias were detected on ECG monitoring. No symptoms of heart failure were reported. Due to the marked EKG repolarization abnormalities the patient underwent coronary angiography which excluded significant stenosis. FDG PET/CT showed areas of increased metabolism also at liver and adrenal left gland. Finally, the patient was transferred to the oncology department for specific management. Cardiac metastases are more common than primary cardiac malignancy and are more frequently related to primary lung cancer, followed by breast cancer and hematologic malignancies. Typical presentation includes arrhythmias or conduction disturbances. The imaging findings of cardiac metastases are non–specific but mostly infiltrative, heterogeneous, and multiple masses may be present. Echocardiography is the initial imaging test for the detection of cardiac metastasis, although CMR, CT and PET/CT may be helpful. Herein we described a case of cardiac metastasis with EKG mimicking acute coronary syndrome. This finding is not uncommon among these patients. EKG findings of myocardial ischemia or injury, particularly localized and prolonged ST elevation, in the absence of ischemic symptoms have been reported in previous studies as high specificity for cardiac metastasis in patients with malignancy.

Structural geology of El Peñón karst system along an anticlinorium of the northern Andes, Colombia

Structural control is one of the most important factors in developing the karstic system since the fractures facilitate the infiltration and circulation of groundwater. This accelerates the mineral dissolution processes responsible for the formation of endo and exokarstic geomorphological features, such as sinkholes and underground cavities, among other landforms that characterize this environment. This study provides information on the structural geology of the El Peñón karstic system, considered one of the most significant and extensive karstic regions in Colombia. The karst is tectonically controlled by joints with a preferential NW-SE orientation and cleavage planes with an NE-SW trend, guiding the development of drainage systems, closed depressions, and underground cavities. The stress tensor obtained with a NW-SE direction (127°) explains the deformation in the area and its influence on the development of the karstic system. It was also established that the potential groundwater flow occurs through open fractures with a direction of 120°–130° (parallel to the stress tensor) and along the cleavage planes (40°–50°). The fracture patterns are characterized by intermediate intensity values, predominantly low fracture density, minimal lengths, and good connectivity between fracture planes.

How are microstructural defect interactions linked to simultaneous intergranular and transgranular fracture modes in polycrystalline systems?

The major objective of this investigation is to fundamentally understand and predict how intergranular (IG) and transgranular (TG) fracture modes nucleate and propagate in f.c.c. polycrystalline systems due to defects, such as total and partial dislocation densities and grain boundary (GB) structures and misorientations. A dislocation density crystalline plasticity (DCP) formulation based on the evolution and interaction of total and partial dislocation densities was integrated with a recently developed fracture approach to investigate the fracture nucleation and propagation of simultaneous multiple fracture events, including both IG and TG fracture events. The aggregate grains and GB orientations and morphologies are based on EBSD measurements that are representative of polycrystalline copper aggregates with a broad range of random high angle and low angle GBs. The predictions indicate that dislocation density pileups induce IG fracture due to interrelated stress, slip, and total and partial dislocation density accumulations and interactions for both high angle GBs (HAGBs) and low angle GBs (LAGBs). TG fracture nucleation and propagation occurred due to normal stress accumulations, which exceeds the fracture stress, along cleavage planes. Furthermore, it is shown how IG cracks transition from the GB plane to the cleavage planes as cracks nucleate and propagate. Accumulated plastic zones due to different slip system activities can impede and blunt crack propagation and fronts. These plastic zones form due to high Lomer and Shockley partial dislocation densities. These predictions, which are consistent with experimental observations, provide a fundamental understanding of how simultaneous failure modes initiate and propagate for physically representative microstructures.

A Systematic Study of the Temperature Dependence of the Dielectric Function of GaSe Uniaxial Crystals from 27 to 300 K.

We report the temperature dependences of the dielectric function ε = ε1 + iε2 and critical point (CP) energies of the uniaxial crystal GaSe in the spectral energy region from 0.74 to 6.42 eV and at temperatures from 27 to 300 K using spectroscopic ellipsometry. The fundamental bandgap and strong exciton effect near 2.1 eV are detected only in the c-direction, which is perpendicular to the cleavage plane of the crystal. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that incorporates the Bose-Einstein statistical factor and the temperature coefficient to describe the electron-phonon interaction. To determine the origin of this anisotropy, we perform first-principles calculations using the mBJ method for bandgap correction. The results clearly demonstrate that the anisotropic dielectric characteristics can be directly attributed to the inherent anisotropy of p orbitals. More specifically, this prominent excitonic feature and fundamental bandgap are derived from the band-to-band transition between s and pz orbitals at the Γ-point.

The role of hydrogen embrittlement in the near-neutral pH corrosion fatigue of pipeline steels

This study confirms that "Near-neutral pH Stress Corrosion Cracking" in steel pipelines propagates by hydrogen-enhanced corrosion fatigue. A critical cyclic loading frequency where maximum growth rate per cycle exists. The critical frequency at different temperatures is verified to correspond to hydrogen diffusion predictions. Growth is limited by crack-tip blunting below this frequency and hydrogen diffusion above this frequency. The critical frequency occurs when crack-tip deformation mechanisms that blunt the crack during the stress cycle overwhelm additional enhancement from diffusion. Growth occurs along cleavage planes and ductile slip planes, indicating hydrogen embrittlement, hydrogen-induced plasticity, and fatigue contribute to crack growth.

Anisotropic Tensile Properties of a 14YWT Nanostructured Ferritic Alloy: On the Role of Cleavage Fracture

Two plates of nanostructured ferritic alloy NFA-1 were processed by ball milling atomized Fe-14Cr-3W-0.4Ti-0.2Y (wt.%) with FeO powders, canning, and hot-extrusion at 850 °C, followed by annealing and multipass cross-rolling at 1000 °C. This produces a severe (001) brittle cleavage texture on planes running parallel to the plate faces. In the first plate (P1), pre-existing microcracks (MCs) formed on the cleavage planes during cross-rolling. The second plate (P2) contained far fewer, if any, MCs. Here, we compare the tensile data for out-of-plane (S) and in-plane (L) tensile axis orientations, at temperatures from −196 °C to 800 °C. We also assess the tensile property differences between P1 and P2, and the effect of specimen size. The L-orientation strength and ductility were excellent; for example, the room temperature (RT) yield stress, σy ≈ 1042 ± 102 MPa, and the total elongation, εt ≈ 12.9 ± 1.5%. In contrast, the S-orientation RT σy ≈ 708 ± 57 MPa, and εt ≤ 0.2%. These differences were due to cleavage on the brittle (001) planes. Cleavage leads to beneficial delamination toughening, but is deleterious to deformation processing and through-wall heat transfer. Therefore, it is important to quantitatively characterize the pronounced NFA-1 strength anisotropy due to severe crystallographic texturing and cleavage fracture.

Retrograde Assemblages in the Muscovite-Biotite Gneiss of Oluyole Southwestern Nigeria, an Indication of Shear-Zone Environment

Petrographic and whole-rock geochemical study of biotite-muscovite gneiss was determined in order to interpret the metamorphic evolution of the Basement Complex of Southwestern, Nigeria. The gneiss shows a millimetric banding, and in some cases the quartzo-feldspathic bands running up to 10 cm. The gneiss has mineral assemblage biotite + plagioclase + quartz + garnet + K-feldspar + muscovite + chlorite + ilmenite ±titanite. Chlorite occurs along cleavage planes of biotite, and in some cases forms reaction rims around porphyroblasts of garnet. K-feldspar crystals are surrounded by muscovite. Titanite crystals are sub-idioblastic to xenoblastic in form, and have inclusions of ilmenite. Titanite, where present, occurs in close association with biotite and opaque minerals (ilmenite). Also, titanite forms a reaction rim around apatite. Mylonitic texture, fine-grained matrix of mica and quartz ribbons were observed. In addition, there is stretching of the quartz crystals. The SiO2 content is greater than 60 wt %, while CaO ranges from 3.05-6.91 wt %. The M1 foliation comprise of mineral biotite some of which are included in the opaque mineral, M2 represents the metamorphism which gave rise to porphyroblasts of ilmenite, while the M3 gave rise to foliations that forms a wraparound structure on the porphyroblasts of ilmenite. The last metamorphism gave rise to retrograde minerals; chlorite, titanite, and muscovite. The study suggests that this area of the Basement Complex has been subjected to multiple deformations, as well as multiple episodes of metamorphism. The structures observed are similar to those associated with shear zone environment.

Molecular insights into the interaction mechanism of triethylenetetramine target-deposited quartz from smithsonite in carbonate ionic liquids and its adsorption on minerals

In order to induce alterations in the mineral surface’s hydrophobicity and subsequently separate smithsonite from quartz, the current study introduces an innovative amine depressant termed triethylenetetramine (TETA). Micro-flotation experiments clearly demonstrated that adding a relatively modest dosage (20 mg/L) of TETA at pH 10 reduced the recovery of quartz from 92.2 % to 22.5 % without reducing the recovery of smithsonite. ICP-OES and zeta potentials revealed that TETA selectively adsorbed on the quartz surface effectively reduced Zn2+ dissolution and altered the setting of the quartz surface to preferentially adsorb NaOL on the smithsonite surface. X-ray photoelectron spectroscopy (XPS) and Quartz crystal microbalance with dissipation (QCM-D) analyses support that TETA is more susceptible to Zn atoms in Zn5(OH)6(CO3)2(s) through a bonding process and preferentially chemisorbs on the quartz surface to the exclusion of Zn-CO3 on the smithsonite surface. Density functional theory (DFT) calculations revealed that electron acceptance by Zn and electron loss by N resulted in hybridization reactions between Zn 2 s, 3d, 4p and N 2p orbitals to form stable Zn-N covalent bonds. Chemical bonds characterized by ionic bonding were formed between TETA and Zn atoms on the cleavage plane of smithsonite, which led to the susceptibility of TETA adsorption on the surface of smithsonite to be broken.

Effect of annealing temperature on the evolution of microstructure, texture, and mechanical properties of hot-rolled 12Cr-ODS steel

To achieve high thermal efficiency, today's nuclear reactor structures are exposed to higher temperatures and pressures, which requires the use of high-strength steels with specific properties, such as ODS steels. There is a need to clarify the evolution of the microstructure and properties of steels at elevated temperatures. This study systematically investigates the evolution of microstructure, texture, and mechanical property variations of 12Cr-ODS steels after hot-rolling and subsequent annealing at 1000 °C and 1200 °C. The investigation utilizes optical microscopy, electron backscatter diffraction technique, and mechanical property measurements. The microstructure of hot-rolled samples shows a layered alternating distribution, which is distinguished by a notable presence of the α-fiber texture. Following annealing at 1000 °C, the martensite grains are smaller with a reduced hardness, while maintaining a strong α-fiber texture. After annealing at 1200 °C, there is a rapid increase in the growth of martensite grains, a significant rise in hardness, a reduction in the α-fiber texture characteristics, and an improvement in the γ-fiber texture characteristics. Moreover, the maximum intensity of the α-fiber texture diminishes as the annealing temperature increases. The mechanical properties of the samples deteriorated after annealing at 1200 °C, which can be attributed to the coarse martensite grains and the texture components containing the {001} cleavage plane dominating the occurrence of brittle cleavage fracture. The 0.1Y sample after annealing at 1000 °C exhibits an excellent combination of strength (1458 MPa) and ductility (20.3%), which is owing to the unique heterogeneous grain structure and the evolution of favorable texture.

Mechanical properties and toughening mechanism of B4C–Al2O3 composite ceramics prepared by hot-press sintering

Boron carbide-alumina (B4C–Al2O3) composite ceramics were fabricated using boron carbide (B4C) as the matrix and alumina (Al2O3) as the second phase by hot-press sintering at 1950 °C. The phase composition, microstructure, relative density, mechanical properties, and toughening mechanism of the composite ceramics were evaluated. When the content of Al2O3 is 30 wt%, the composite ceramics show the best comprehensive mechanical properties. The relative density, Vickers hardness, flexural strength, and fracture toughness of the obtained B4C-30 wt%Al2O3 composite ceramics reach up to 98.8 %, 24.7 GPa, 477 MPa, and 4.64 MPa m1/2, respectively. The introduction of Al2O3 as the second phase can significantly improve the fracture toughness of the B4C ceramics. Firstly, when cracks extend to the Al2O3 grains, the cleavage fracture of the Al2O3 grains resulting from its crystal structure causes the crack deflection along the cleavage plane. Secondly, due to the mismatch of the coefficient of thermal expansion between B4C and Al2O3, residual stress is generated at the grain boundary of the two phases and within the grains. The tensile stress at the grain boundary can cause some cracks to extend along the grain boundary, making cracks deflected, and the compressive stress within the B4C grains can inhibit crack extension. Thirdly, submicron-sized Al2O3 grains wrapped within the B4C grains form a subboundary structure, which can lead to crack extension along the subboundary. All of these factors consume the crack extension energy, which can contribute to increasing the fracture toughness of B4C–Al2O3 composite ceramics.

Hydrogen blistering and cracking of high-strength pipeline steel welds produced by electrochemical hydrogen charging

Pipeline steel system always faces a challenge of hydrogen embrittlement (HE) not only due to corrosion environments but also because of cathodic protection strategy. Especially in welded joint, heterogeneous microstructures lead to the difference in intrinsic HE resistance for different subzones. However, this aspect was often neglected when external loading was applied during evaluation of the HE. To eliminate the effect of external loading, the hydrogen damage behaviors of X100 pipeline steel weld were investigated only based on electrochemical hydrogen charging and the intrinsic HE resistance of each subzone was explored. The results showed that the HE resistance of the main regions in weld was decreased in order of weld metal, heat affected zone (HAZ) and base metal (BM), with different surface damage modes: the BM had predominantly hydrogen blistering; while others displayed mainly hydrogen cracking. The corresponding features for cross-sectional cracking were intergranular propagation along the pancaked grain boundaries in the BM and trangranular propagation in HAZ. For transgranular cracking propagation, the path first trended to initiate on the {100} cleavage plane, then grew on the {110} slip planes. The intergranular cracking was mainly attributed to the lamellar-structural prior grain boundaries that inherited numerous deformation dislocations during hot rolling of the base metal.

Effect of processing temperature on interface microstructure of diffusion welded joint of super-duplex stainless steel and zirconium alloy with nickel alloy interlayer

In the present study, super-duplex stainless steel (SDSS) and zirconium alloy (ZrA) was vacuum welded using nickel alloy (NiA) interlayer by the diffusion welding process. The welded joints were processed from 800 to 950 °C in steps of 50 °C using 4-MPa compressive load for 75 min. The joints were characterised using optical microscopy, scanning electron microscopy, electron probe micro-analyser, and x-ray diffractometer. The SDSS│NiA interface is planar in nature for all welding temperatures; however, layer-wise Ni5Zr, Ni10Zr7, NiZr, and NiZr2 reaction products were observed at the NiA│ZrA interfaces. The reaction products and width of these products increase with welding temperature. At both the interfaces, hardness values gradually increase with an increase in welding temperature. NiA│ZrA interface exhibited higher hardness as compared to the SDSS│NiA interface due to the presence of layer wise intermetallics. Joints reached a maximum tensile strength of ∼370 MPa (with an elongation of ∼7.9 %) when the joints were processed at 900 °C due to optimal reaction zone width and the least embrittling effect of the respective intermetallics. At lower temperatures, fracture surfaces of welded assemblies showed featureless morphology and voids present due to the poor coalescence of mating surfaces. At higher welding temperatures, the fracture surface of the transition joint preferred brittle fracture mode due to the cleavage planes with different alignments with insignificant volume fraction of voids on the fractography.

Fittability and mechanical properties of laser shock liquid warm microforming of AZ31B magnesium alloy foils with complex features

Difficult-to-form materials and complex mold characteristics have an important effect on the fittability and mechanical properties of microforming components. This study focuses on the fittability and mechanical properties of laser shock liquid warm microforming based on AZ31B magnesium alloy foils and a complex microcamera shell die. The characteristics of formed parts under varying temperatures and laser energies were discussed. Single-pulse and double-pulse forming experiments were conducted and compared. At 140 °C and 1260 mJ, double-pulse forming achieved a maximum depth of 184.5 μm, demonstrating near-perfect workpiece conformity to the die. In contrast, single-pulse forming did not achieve such results. This implies that double-pulse forming notably improves the fittability of workpieces and effectively mitigates springback. Finite element simulations corroborate the experimental findings. Moreover, simulation elucidates phenomena observed during experiments, including springback and crack formation. Additionally, the study delves into the microhardness, thickness distribution, and surface roughness of the formed parts. The results indicate that double-pulse forming yields workpieces with superior microhardness, reduced roughness, and a more uniform thickness distribution. Microstructural analysis reveals that grain refinement and substantial occurrence of twinning in the double-pulse forming process are the primary factors contributing to enhanced plasticity. The study also conducts a failure analysis of formed parts at room temperature, revealing the presence of numerous river patterns and cleavage planes, indicative of brittle fracture. Conversely, warm forming avoids fracture failure.

Origin of shear induced ‘catching bonds’ on half Heusler thermoelectric compounds XFeSb (X = Nb, Ta) and SnNiY (Y = Ti, Zr, Hf)

Half Heusler materials exhibit excellent thermoelectric and mechanical properties, rendering them potential candidates for advanced thermoelectric devices. Currently, the developments on interrelated devices are impeded by their inherent brittleness and limited ductility. Nevertheless, it exists the potential ductility on half Heusler materials with face-centered cubic sub-lattices through the expectation of the occurrence of shear-induced ‘catching bonds’ which can result in excellent ductility on other face-centered cubic materials. This work focuses on half Heusler thermoelectric materials XFeSb (X = Nb, Ta) and SnNiY (Y = Ti, Zr, Hf), the shear deformation failure processes are deeply investigated through the first principle calculations. Shear-induced ‘catching bonds’ are found on XFeSb (X = Nb, Ta) along the (111)/<-1-12> slip system, which releases the internal stress and exactly resulting in the potential ductility. According to the thermodynamic criterion based on generalized stacking fault energy, the essence of shear-induced ‘catching bonds’ are interpreted as the (111)/<-110> slips formed by several 1/3(111)/<-1-12> partial dislocations motions. During the (111)/<-1-12> shear on SnNiY (Y = Ti, Zr, Hf), the structural integrity is maintained without inducing ‘catching bonds’. Different deformation processes occurring in the identical crystal structure are elucidated through the energy explanation, revealing that shear-induced ‘catching bonds’ originate from the crystal plane cleavage on the (111) plane. The present works offer significant advantages for the assessment and comprehension of shear-induced ‘catching bonds’ in other materials and facilitate the development of XFeSb (X = Nb, Ta)-based thermoelectric devices with excellent ductility.