Brittle Metals Research Articles

Femtosecond laser welding of sapphire-copper using a thin film titanium interlayer

The ability to weld metals and sapphire is widely required in aerospace, micro-electro-mechanical systems and microwave energy delivery devices. The experiments of femtosecond laser welding between sapphire and copper (Cu) were conducted under non-optical contact conditions. And the effect of pre-fabricating a Ti film on the sapphire surface using femtosecond laser on the bonding strength of ssapphire/Cu joint was investigated. The interface of the sapphire/Cu directly welded by femtosecond laser contains a mixture of sapphire and copper, and the shear strength of the sapphire/Cu interface was approximately 46.4 MPa. The results indicated that the laser-induced molten state of sapphire and the laser-ablated copper mixed together at the interface, filling the gaps and forming an effective metallurgical bond. And then, in the case that the Ti film was prepared on the sapphire surface through femtosecond laser-induced backward transfer (LIBT), a Ti transition layer between sapphire and cooper was observed on the bonding interface of the joint, and the shear strength of the joint increased to approximately 115.5 MPa. A mixture of sapphire, copper, titanium, and titanium oxide was observed at the interface of the joint. The Ti layer between sapphire and copper may effectively alleviated residual stresses at the interface and promoted bonding between copper and sapphire, thereby improving the strength of the joint. The methods and results of this study have reference value for the ultrafast laser bonding between other transparent brittle materials and metals.

Biodegradation Assay of Heavy Metals and Dyes Decolorization in Textile Industrial Effluent using Laccase Isolated from Pleurotus ostreatus

This study focused on the isolation of laccase enzyme from the fungus Pleurotus ostreatus and its application in the biodegradation of various pollutants present in textile industrial effluent, including chemicals, ions, salts, heavy metals, brittle metals, total suspended solids, total dissolved solids, chemical oxygen demand, biological oxygen demand, minerals, total hardness, total alkalinity, turbidity, electrical conductivity, and dyes. Textile industrial effluent poses a significant threat to the environment, contaminating water bodies and posing risks to human, animal, and plant life. This study employed an economical and ecofriendly biological approach for wastewater treatment, distinguishing it from traditional physical and chemical methods. The optimum temperature of laccase is found to be 30 degree Celsius and pH is 3. Enzyme activity of laccase is 7.25 U/ml. This fugal laccase decolorizes textile Industrial dye effluent containing various dyes, such as Turquoise VG, Black B, Yellow R, Methyl red, Trypan blue, and Acid Orange 7. Laccase depicts maximum decolorization efficacy on Black B dye. Similarly, Laccase from P.ostreatus shows higher decolorization efficacy when compared to other fungal laccase. Additionally, the study assessed the biodegradation of various wastewater quality parameters, including physical and chemical parameters like toxic heavy metals and ions. This research of isolation, characterization, and utilizing laccase from P. ostreatus for the bioremediation of textile industrial effluent wastewater containing dyes, toxic chemicals, ions and metals is effective, economical and ecofriendly.

Investigation of machining quality indicators and effect of tool geometry parameters during the machining of difficult-to-machine metal

Producing high-quality surfaces from hard and brittle metals presents a formidable challenge that calls for a meticulous machining strategy and an effective cutting tool. The mechanism of tool failure, chip formation behavior, and micro-morphology of the machined surface are crucial factors in determining a correlation between the used parameters and the machined surface quality. Among the metrics employed to assess the effectiveness of the tool. However, the determination of optimum machining parameters requires the repetition of precise experimental investigations with every change in the cutting conditions. The current research work proposes a set of suggestions for choosing the optimal tool parameters based on the micro-morphological characteristics of the tool and the machining performance indicators. A WC-Co ball end mill tool was used for the machining of an H13 tool steel workpiece to establish the relationship between changes in tool geometrical parameters and the machining performance indicators. Tool geometry with a rake angle of 3°, a clearance angle of 10°, and a helix angle of 32° was found to have the least wear band length at 56 μm. Moreover, the impact of tool geometry on the quality of the surface produced through machining was also investigated.

Microstructure evolution and mechanical properties of H13 steel produced by Selective Electron Beam Melting

As one of the additive manufacturing technologies, the Selective Electron Beam Melting (SEBM) process several advantages over Selective Laser Melting (SLM), including faster scanning velocity, higher energy utilization and higher preheating ability of up to 1100 °C. Thus, it is particularly advantageous for the production of high melting point and brittle metals, like the medium carbon high-alloy H13 steel. This study presents a systematic investigation of the microstructural evolution and mechanical properties of H13 steel fabricated using Selective Electron Beam Melting (SEBM) with varying deposition heights. The manufactured samples were examined using high-tech measuring instruments to evaluate different properties such as phase composition, microstructure, microhardness and grain morphology. The results reveal that the microstructure of the as-built SEBM-H13 sample consists of martensite, bainite, and residual austenite with a typical cellular/dendritic structure. As the deposition height decreases, the grain morphology degrades, and the grain boundary undergoes carbide precipitation ((Cr, Fe)7C3) and growth. Consequently, the sample exhibits a gradient hardness structure in the building direction with the highest hardness of 565.6 (±5.8) HV0.5 at the top surface, followed by a distinct decrease in hardness to approximately 506.7 (±3.3) HV0.5 at increased distances from the surface. This study provides a fundamental understanding of fabricating high-performance H13 steel using SEBM.

Fatigue Crack Growth Rate Description of RF-Plasma-Sprayed Refractory Metals and Alloys

A fitting method capable of describing the fatigue crack growth rate (FCGR) data in all stages of crack propagation by a simple Forman-style analytical formula was developed. To demonstrate its robustness, this method was used to quantify the fracture behavior of RF-plasma-sprayed W, Mo, W-Mo composite, and four selected Ni-based tungsten heavy alloys (WHA). The fitted FCGR parameters categorized the studied materials into two distinct sets. W, Mo, and W-Mo composite deposits made from inherently brittle refractory metals that contained a range of defects inherent to plasma spray process represented the first class. This class was characterized by low fracture toughness and a relatively wide range of fatigue crack growth thresholds. The second class of materials was represented by WHA. Here, the deposit defects were suppressed by liquid state diffusion that formed a typical WHA structure consisting of a Ni-rich matrix and large spherical W reinforcement particles. The WHA generally showed higher fatigue crack growth thresholds, but differed in fracture toughness values based on the W particle concentrations. The obtained fracture mechanical data represent a reference dataset of plasma-sprayed refractory materials, and their classification into groups clearly demonstrates the capabilities of the developed method to capture a wide range of different types of FCGR behavior.

Respite. Quiet. A House of Dreams.

Respite. Quiet. A House of Dreams.

Effect of Surface Dissolution on Dislocation Activation in Stressed FeSi6.5 Steel.

The effects of surface dissolution on dislocation activation in FeSi6.5 steel are quantitatively studied by analyzing the stress relaxation data using the thermal activation theory of dislocation. The stressed FeSi6.5 steel sample in acid solutions (H2SO4 or HCl) exhibits a much higher rate of stress reduction with time compared with that in air or deionized water. As the stress relaxation time is prolonged to 20 min, the relaxation rates are 0.055 MPa·min-1 in water and 0.074, 0.1, 0.11 MPa·min-1 in H2SO4 solutions with pH 4, 3, and 2, respectively. In a NaCl solution, a slight increase in the relaxation rate compared with air was found. Higher acidity (lower pH) of the solution inducing higher stress relaxation rate implies the softening is associated with the anodic dissolution of the surface layer and the accelerated (additional) flow of dislocations. The analyses using the thermal activation theory of dislocation during relaxation reveal the mechanism for the accelerated plastic flow induced by the corrosive medium. The variations of these parameters are related to the relaxation of the stress field of dislocations and the weakening of interaction between slip dislocations and short-range obstacles. The chemomechanical effect, including a reduction in apparent activation energy and a decrease in waiting time for dislocation to obtain sufficient thermal activation energy to cross obstacles, causes an increase in the stress relaxation rate (plastic strain rate). The study confirms that surface dissolution accelerates the plastic flow of metals and supports the view that surface dissolution facilitates dislocation slip. It is helpful to improve the formability of brittle metals.

Distribution of shear fragments classified by morphology

In studies on metal shell under internal explosive loading, unlike brittle metals, ductile metals usually exhibit shear fracture. Existing literature mostly focuses on slip fracture caused by unidirectional shear fracture, in fact, the shell fractures in the two directions of maximum shear stress, making morphology of the fragments diversified, considering fragment morphology in the distribution may achieve a better description. In previous studies, Poisson mixtures and Weibull mixtures model are only used for fragment distribution statistics as a functional form, and parameters (weight coefficient and distribution modulus) in the function lack physical process description. In this paper, an experimental study on the fragmentation of 50SiMnVB steel shell under TNT internal explosive loading was carried out. Through the observation and analysis of recovered fragments, the shear fragments with cross-sections of parallelogram, right-angled trapezoid, and isosceles right-angled triangle are divided into three types: A, B, and C. According to “A-type fragments created by the parallel through-the-thickness fractures, B-type and C-type fragments created by interaction of intersecting fractures,” the morphological parameters of fragments in the distribution model were derived, including fragment size (width, length, thickness, mass, etc.), shape parameters, and weight coefficient. Weibull mixture distribution model is used to describe the distribution of the total fragments, whereas Weibull distribution is used to describe the distribution of each type of fragment. Through the comparison of theoretical calculations and experimental data, the applicability of the theoretical model in the field of “shear fracture of ductile steel shell under internal explosive loading” is verified.

Моделирование дислокационного электропластического эффекта в монокристалле методом молекулярной динамики

The electro-plastic effect is a decrease in the resistance of metal crystals to deformation under the influence of a high-density pulsed electric current. Applying this effect allows deformation processing of relatively brittle metals without a sharp increase in temperature while reducing the probability of temperature negatively affecting the material. The paper discusses the influence of the electro-plastic effect on the change in the deforming force and the dislocations dynamics for a two-dimensional single crystal model based on the molecular dynamics method using the Morse potential. The authors propose a model implementing the electro-plastic effect by increasing the total kinetic energy of the system not uniformly over the entire crystal volume but depending on the potential energy of atoms. It is accepted that as a result of the electric current pulse traveling, the atom’s kinetic energy increases proportionally to the third degree of their potential energy. Atoms near defects have higher potential energy; therefore, the temperature will grow to a greater extent in the areas of defects, increasing their mobility. The authors simulated the motion of dislocations under the influence of shear stresses and temperature, considering the electric current pulse effect on the system. The paper describes the dependence of yield strength on temperature without taking into account the electro-plastic effect and then with it. The authors plotted the graphs of the dependence of the system’s kinetic energy on the frequency and the power of current pulses. The study shows that the electro-plastic effect sharply reduces the yield strength of a crystal, increasing the temperature in the system. It is caused by the fact that, besides general heating, the system is subjected to local heating of atoms near defects, which facilitates their motion.

Experimental and numerical investigation of model I dynamic fracture toughness of 95W-3.5Ni-1.5Fe alloy using the semi-circular bend specimens

Semi-circular bend specimens are used to measure the brittle materials' fracture toughness, such as brittle metals, rocks, and ceramic materials. The quasi-static and dynamic model I fracture toughness of tungsten heavy alloy, a typical brittle metal material, are measured using the semi-circular bend specimens under quasi-static compression and dynamic impact loadings. For quasi-static cases, the specimens are loaded on a universal testing machine with a constant loading speed. While for dynamic cases, the specimens are executed on a modified split Hopkinson pressure bar system with the impact pressures from 0.2 to 0.4 MPa. The results show that the dynamic fracture toughness of tungsten alloy increases with the increase of the loading rate. Further, a rate-dependent bilinear traction-separation law is introduced to explain the dynamic fracture behaviors of tungsten alloy. The parameters of the rate-dependent law are obtained from the experiments and the finite element simulations. Finally, the dynamic simi-circular bend simulations using the cohesive element with rate-dependent cohesive law are established to simulate the crack propagation, and the simulation results are in good agreement with the test data.

Brittle to quasi-brittle transition and crack initiation precursors in crystals with structural Inhomogeneities

Crack initiation emerges due to a combination of elasticity, plasticity, and disorder, and it displays strong dependence on the material’s microstructural details. The characterization of the structural uncertainty in the original microstructure is typically empirical and systematic characterization protocols are lacking. In this paper, we propose an investigational tool in the form of the curvature of an ellipsoidal notch: As the radius of curvature at the notch increases, there is a dynamic phase transition from notch-induced crack initiation to disorder-induced crack nucleation. We argue that the this transition may unveil the characteristic length scale of structural disorder in the material. We investigate brittle but elastoplastic metals with continuum, microstructural disorder that could originate in a manufacturing process, such as alloying. We perform extensive and realistic simulations, using a phase-field approach coupled to crystal plasticity, where microstructural disorder and notch width are systematically varied. We identify the brittle-to-quasi-brittle transition for various disorder strengths in terms of the damage and stress evolution. Moreover, we investigate precursors to crack initiation that we quantify in terms of the expected stress drops during displacement control loading.

Hole drilling and milling of magnetic alloys parts by shaped tube electrolytic machining

In this research shaped tube electrolytic machining of drilling and milling of magnetic alloys parts and difficult-to-cut metals, steels and alloys is presented. New research made in the field of space, aviation, automobile, medical, computer and electronics, and others has created the need for small and fine holes with high aspect ratio in these materials. The primary investigations of ECM with the tubular tool electrode are presented. Compared with mechanical machining, shaped tube electrolytic machining (STEM) exhibits an advantage in producing micro-holes with a high aspect ratio and in producing the curved holes. In order to realize the process of electrochemical machining, experimental assembly with the shaped tube tool electrode has been designed and manufactured. Completed researches indicate that this tool electrode has a high potential to machine difficult-to-cut and brittle metals economically and efficiently.

Strong ductile bulk tungsten

Tungsten has long faced the problem of limited to no ductility in bulk polycrystalline form, due in part to the low energy needed for intergranular fracture. This limited ductility can be overcome through processing by dramatically reducing the cross sectional area following a conventional temperature step-down method that improves ductility through elongation of grain boundaries and development of a {110} fiber texture along the length of the material. While this technology is over 100 years old, little progress has been made to improve the ductility of bulk material. In the current investigation plastically deformed bulk tungsten was observed to have a room temperature tensile ductility between 17% and 23% total elongation at failure in bend specimens, and a flexural yield strength near ~ 3GPa. This improvement in ductility following multipass equal channel angular extrusion processing appears to be caused by a similarity in microstructure and texture to that of ductile tungsten wire. The onset temperature for transition to noticeable ductility is seen to decrease dramatically with the level of plastic strain. The results indicate that severe plastic deformation processing at low homologous temperatures may be an effective way to improve the ductility and toughness of bulk tungsten and other brittle crystalline metals.

Comparison between frictional behavior of the soft and brittle materials at different contact pressures.

Coefficient of friction changed significantly by the change in contact pressure. Experimental measurement of the coefficient of friction in different contact pressures can be useful in numerical and analytical analysis of many engineering problems, such as metal forming process. This study dedicated to investigate the sensitivity of the friction coefficient to changes in contact pressures. To aim this goal the special tribometer device has been fabricated and the coefficient of friction of the soft and brittle metals when sliding with a low speed on a rigid body are measured for different contact pressures. The friction sensitivity of the soft (copper and aluminum) and brittle (steel) samples to changes in contact pressure are compared and discussed. The results showed that both brittle and soft metals are highly sensitive for change in contact pressure but their behaviour is slightly different. While the coefficient of friction of the steel sample when sliding on a steel substrate is reduced sharply by a little increase in contact pressure; the coefficient of friction of the soft material when sliding on a steel substrate is reduced slowly depending on the magnetude of the applied normal load.

A critical plane‐energy model for multiaxial fatigue life prediction

AbstractA new critical plane‐energy model is proposed in this paper for multiaxial fatigue life prediction of metals. A brief review of existing methods, especially on the critical plane‐based and energy‐based methods, is given first. Special focus is on the Liu–Mahadevan critical plane approach, which has been shown to work for both brittle and ductile metals. One potential drawback of the Liu–Mahadevan model is that it needs an empirical calibration parameter for non‐proportional multiaxial loadings because only the strain terms are used and the out‐of‐phase hardening cannot be explicitly considered. An energy‐based model using the Liu–Mahadevan concept is proposed with the help of the Mróz–Garud plasticity model. Thus, the empirical calibration for non‐proportional loading is not needed because the out‐of‐phase hardening is naturally included in the stress calculation. The model predictions are compared with experimental data from open literature, and the proposed model is shown to work for both proportional and non‐proportional multiaxial loadings without the empirical calibration.

Fatigue criterion improvement of Gough and Nishihara & Kawamoto to predict the fatigue damage of a wide range of metallic materials

An improved multiaxial high-cycle model based on the Gough and Nishihara & Kawamoto approaches is presented. The proposal is a compromise between the measure of the equivalent shear stress amplitude, obtained from a prismatic convex hull method, and the amplitude of the first stress invariant. This makes the criterion an effective approach to predict quickly the failure initiation for wide range of materials (from ductile metals to extremely brittle metals). The results obtained from our proposal are compared to experimental data reported in the literature.

Parametric Optimization of EDM on EN19 using Grey-Taguchi Analysis

Objectives: Electro discharge machining (EDM) has been widely and effectively utilized as one of the niche cost-effective technology for machining of extremely tough, brittle and unique metals and alloys. However, obtaining a larger material removal rate (MRR) as well as diminished tool wear rate (TWR) with improved surface finish and minimum amount of overcut is the major challenging issue in the research field of EDM. This paper puts light on the aforesaid aspects of EDM through optimization techniques using Taguchi and Grey Relational Analysis. Methods/Statistical Analysis: The work piece material selected is circular shaped EN19 alloy steel and the tool is rectangular shaped Copper. Taguchi parametric design with L27 orthogonal array is utilized to conduct 27 experiments. With an objective to optimize the machining performance variables such as material removal rate (MRR), tool wear rate (TWR), machined surface roughness (SR) as well as the overcut (OC), a number of operational parameters of the machining process such as Pulse on time (Ton), open circuit current (Ip) and pulse duty factor (Tau) are consciously chosen. A statistical technique, Analysis of variance (ANOVA), is pursued to determine the pertinent parameters swaying the responses. Finally, the contours of machining characteristics are drawn to get a clear visualization of the effect of the crucial input variables on the process performances. Findings: As an outcome of the research, pulse on time was observed to be a relatively more influential parameter swaying MRR and TWR followed by open circuit current and then pulse duty factor. Further, the work is extended by performing Grey Relational Analysis (GRA) to get a suitable combination of critical parameters in order to optimize the overall machining performance of EDM. The suitable combination of input parameters are I P = 30 A, T on = 3000 μs, Tau = 12 resulting maximum MRR, minimum TWR, minimum SR, and minimum OC. Application/Improvements: Very less paper are reported on optimization of all the crucial machining responses such as MRR, SR, TWR and OC simultaneously using a rectangular shaped tool. However, this paper results an appropriate combination of machining parameters in order to optimize all the aforesaid responses together taking the complexity of tool as well.

On the segmentation-driven vibration in milling titanium alloy

Numerous hard, brittle metals have been shown to form segmented chips during machining operations, which has been shown to be linked to high vibration levels in turning and milling processes. This article concerns quantitative comprehension of segmentation-driven vibration in end-milling process. First, dynamic model of milling process with impact of segmented chip is presented, and a periodic cutting force model related with segmented chip is proposed. Second, for experimental observation, a series of tests are carried out concerning modal test of cutting system; chip morphology, tool vibration during cutting, surface location error, and high-frequency sampling measurements of cutting force signal are realized. The method used for calculating the frequency of segmentation chip by oblique cutting is deduced. It is found that at low feed rate, the periodic cutting force is affected by the natural frequency of cutting system, segmentation chip, and tool vibration. Finally, amplitude–frequency response for quasi-single degree of freedom is employed to elaborate the relationship between segmentation frequency and natural modes of system. The results show that when the ratio (frequency of segmented chip to natural frequency of system) is a noninteger value or above 3, no significant vibrations of cutting system are observed in milling titanium alloy Ti6Al4V.

Applying the grain orientation dependence of deformation twinning to improve the deformation properties of an Fe-6.5 wt%Si alloy

The deformation behaviours of the equiaxed-grained and columnar-grained Fe-6.5 wt%Si alloy were comparatively studied and the mechanism of the enhanced deformation properties of columnar-grained alloys was discussed. A grain orientation dependence of the deformation twinning was identified in the Fe-6.5 wt%Si alloy. Twins tend to occur in grains with a tensile orientation near the <001> corner and a compressive orientation near the <101>–<111> line, which is closely related to the Schmid factor value of each orientation. The significant enhancement of the deformation properties of the columnar-grained Fe-6.5 wt%Si alloy was mainly ascribed to the promotion of twinning deformation by the grain orientation control. These results provide a theoretical guide for the microstructure design of brittle metals, such as Fe-6.5 wt%Si alloy.

Calculating crack initiation directions for in-phase biaxial fatigue loading

Crack initiation direction in smooth specimens subjected to fatigue loading is known to depend on material ductility. Thus, in ductile (mild) metals, cracks initiate mainly in the plane of maximum shear stress (mode II) while in brittle (hard) metals they do in the plane of maximum normal stress (mode I). In this work the ratio between the pure torsion and tension fatigue strengths, τ0/σ0, is used as an indicator of ductility and a microstructural model that describes the interaction between the crack and the microstructural barriers is used to calculate the direction of crack initiation under proportional biaxial tension–torsion loads for any degree of ductility. Results obtained for both perfectly ductile (τ0/σ0≃0.5) and perfectly brittle (τ0/σ0≃1) materials agree with the classical description. Furthermore, statistical calculations show that, for the type of relatively ductile metals usually employed in fatigue problems in practice, the likelihood of crack initiation taking place in a plane located within a few degrees of the plane of maximum shear stress is much higher than the chance of initiation occurring in a plane near the maximum normal stress plane, which accounts for the fact that in many occasions initiation is simply reported to happen at 45° from the principal stress direction.