Fracture Of Carbides Research Articles

Unlocking the strength: the predictions of silicon carbide fracture toughness revealed through data-driven approach

Silicon carbide ceramics are widely used within various applications, including mechanical, chemical, aerospace and military; where the fracture toughness plays a crucial role. From the processing perspectives, the fracture toughness is controlled by the combination of starting phases and sintering conditions (including additives, atmosphere, temperature and pressure). However, the interplay of these factors makes the forward predictions of fracture toughness untreatable neither through experimentation nor physical modeling; not mention to the reverse estimations of optimal processing parameters. In this work, a data-driven strategy was proposed that firstly to predict the fracture toughness from processing parameters; and then to explore certain parameters that have large impacts on the fracture toughness. From running four different machine learning (ML) algorithms on a well-established dataset of SiC sintering recipe, it was found that the eXtreme Gradient Boosting (XGBoost) model possess the best performance with accuracy up to 88%. Further, the feature importance scores revealed that the sintering temperature and the types of sintering additives show their significant influence on fracture toughness. It was found that the sintering temperature is the most critical factor affecting the obtained fracture toughness of SiC, where the optimum temperature range is of 1800 °C–2000 °C; and also, the sintering additives of Al and Al2O3 have great influences on the obtained fracture toughness, where the optimum range of their mass fraction within the whole additives is 3–8 wt%. Finally, the developed model shows its capability to propose sintering strategy for the preparation of SiC ceramics with target fracture toughness.

Microstructural effects on impact-sliding wear mechanisms in D2 steels: The roles of matrix hardness and carbide characteristics

This study investigates the wear micromechanisms of D2 steels under impact-sliding conditions, offering insights into their performance when used in applications such as trimming dies for high-strength steel sheets where they undergo plastic deformation and chipping. Two D2 steel samples, both with a bulk hardness of 59.7 HRC but different matrix hardnesses and carbide distributions, are tested by using an impact-sliding wear test rig at Hertzian contact pressures exceeding 2 GPa. The sample with a softer matrix exhibits wear primarily through delamination caused by plastic deformation. This initiates cracks at the matrix/primary carbide interface, leading to material loss in the form of large chips. In contrast, the steel with a harder matrix shows reduced wear due to its resistance to plastic deformation. Initially, wear occurs through the fracture of primary carbides. However, with prolonged loading, the matrix begins to soften, adopting a wear mechanism similar to the D2 steel with softer matrix. Notably, smaller primary carbides are associated with improved wear resistance by limiting the initiation sites for cracks, especially at the matrix/primary carbide interface. This understanding enables the selection and design of heat treatments to optimize D2 steel microstructure, thus improving resistance to impact-sliding wear damages observed in processes like trimming.

Unveiling microstructural evolution and enhanced wear resistance of Co37Cr28Ni31Al2Ti2 multicomponent alloy via high-carbon addition

As a representative multicomponent alloy (MA) system, CoCrNi MAs and their derivatives have shown good strength-ductility combinations but the friction behaviors have been less studied. In this work, the influence of high-carbon addition on the microstructure, (nano)hardness, and wear behavior of the Co37Cr28Ni31Al2Ti2 MA are investigated in detail. Different from the face-centered-cubic (FCC) solid solution and ordered L12 precipitates in the base alloy, massive orthorhombic (Cr,Co,Ni)7C3 and FCC (Cr0.2Ti0.8)C particles together with some long-strip-shaped graphite-3R crystals appear in the L12-strengthened FCC matrix for the high-carbon-bearing sample, resulting in an enhancement of hardness from 292 ± 11 HV to 581 ± 29 HV. Moreover, the wear rates (WRs) and the friction coefficients (COFs) under dry sliding conditions for the base alloy are measured to be ∼9.55 × 10−5 mm3/N∙m and ∼0.6, and ∼6.02 × 10−4 mm3/N∙m and ∼0.8, respectively, at loads of 2 N and 10 N. After adding carbon, the wear resistance is significantly improved (average WR: ∼2.81 × 10−6 mm3/N∙m and ∼1.89 × 10−5 mm3/N∙m; average COF: ∼0.5 and ∼0.7 at loads of 2 N and 10 N). This improvement surpasses similar compositions prepared by casting and is comparable to surface-treated MAs. During friction and wear experiments, the fracture and detachment of hard carbides introduce additional abrasive particles into the tribosystem, resulting in a transformation from adhesive wear-dominated to abrasive wear-dominated. The wear resistance enhancement and friction mechanism transformation are further evidenced by the surface morphologies of the alumina counterbody materials after friction. The present findings indicate that the in-situ formation of carbides should be a promising strategy to enhance the wear resistance of MAs.

Evolution Behavior and Fracture Criterion of Carbides in D2 Cold‐Work Die Steel During Hot Working Process

Investigating the fracture mechanisms of carbides is of paramount importance for optimizing hot working processes in die steels. This work establishes a comprehensive criterion equation to predict the behavior of carbide fracture in D2 cold‐work die steel during hot working process. High‐temperature laser confocal microscope is employed to prepare samples with varying solidification rates. Subsequently, these samples are subjected to a range of heating temperatures spanning from 1000 °C and 1100 °C. The samples are analyzed utilizing scanning electron microscopy energy spectrum analysis and X‐ray diffraction. The activation energy of M7C3 carbides is calculated through the utilization of kinetic equations and the Arrhenius law. Additionally, a criterion model for the fracture behavior of M7C3 carbides in D2 cold‐work die steel is established. The results reveal that thin hollow rod‐shaped carbide is easy to fracture. Moreover, the activation energy for phase transition of M7C3 carbides in D2 cold‐work die steels is determined to be 226.974 KJ mol−1. Furthermore, the fracture behavior of carbides in D2 cold‐work steel is found to be influenced by various factors such as heating temperature, deformation rate, and peak stress. Finally, the criterion model demonstrates substantial agreement with the experimental observations gathered, affirming its reliability and accuracy.

Insights into stress corrosion cracking in scratched area of alloy 690TT steam generator tubes

To investigate the stress corrosion cracking behaviors and microscopic mechanism in a scratched area of alloy 690TT, the microstructures of typical cracks are systematically characterized. There is a severe structural mismatch at the interface between fine grain zone and severe deformation zone, and hence cracks tend to propagate continually along this interface. In addition, the scratching leads to fracture and displacement of carbides, which changes their morphologies and distribution. Carbides with small sizes are engulfed by the crack oxidation zone, while large carbides can change the propagation path, and thus the crack grows into the deformation layer.

Slurry erosion wear of high chromium cast iron samples from a slurry pump impeller. Effect of impact angle variation

In this work, the impact angle effect on the erosive wear resistance of high chromium cast iron (HCCI) samples from a slurry pump impeller was evaluated. For this purpose, equipment was designed and built to carry out wet erosion tests. Erosion tests were carried out at angles of 30°, 45°, 60° and 90° using an erosive slurry with a concentration of 20%, by weight, of silica sand. The results indicated that the erosive wear rate followed the classic behavior of variation with the impact angle for ductile materials. There was an increase in the erosion rate with increasing angle until reaching the peak wear at 45°, followed by a decrease in wear down to the minimum wear rate at 90°. Significant differences were observed in the mass loss of the HCCI samples: the samples eroded at 45° showed a mass loss 2.7 times greater than the eroded condition at 90°, indicating that, due to the condition of slurry contact with the surface of the samples, erosive and abrasive mechanisms acted synergistically favoring wear at 45°. On the other hand, samples eroded at 30° and 60° showed similar and intermediate mass losses. In general, for the samples eroded at a normal angle (90°) the mechanisms of wear due to plastic deformation of the matrix and carbide fracture were observed, while for smaller angles, the mechanisms of micro cutting and micro grooving were more evident.

Microstructure and bond strength of niobium carbide coating on GCr15 prepared by in-situ hot press sintering

The hardness and adhesion of protective hard coatings to the substrate are the most important parameters that influence the performance of the tool. Herein, we propose an effective strategy, by in-situ hot press sintering, to fabricate a novel niobium carbide coating with high hardness and excellent interfacial bond strength on GCr15. The coating is composed of Nb2C, NbC, and α-Fe phases. The volume fraction of niobium carbide (Nb2C and NbC) phases reaches 93%. Along the direction of coating thickness, the grain morphology of niobium carbide changes from equiaxed (Nb2C) to columnar (NbC), and then to equiaxed (NbC), presenting a gradient microstructure. The coating/substrate interface displays an excellent macro/micro interface. The formation of the gradient microstructure is attributed to the nucleation-growth process controlled by the carbon concentration gradient diffusion. The novel gradient coating can simultaneously achieve superhardness (20.2 ± 0.3 GPa) and excellent bond strength (>210 ± 20 MPa). The excellent bond strength is mainly attributed to the in-situ formation of the coating and the gradient microstructures. The tensile test results show that the fracture mechanism of the niobium carbide coating on GCr15 is mainly a brittle fracture of niobium carbide coating and a small amount of coating debonding.

Characterisation of the wear and friction behaviour of laser deposited cobalt and iron-based hardfacing alloys for nuclear applications

Valves and pumps in nuclear plants operate in a particularly aggressive environment of a high neutron flux, high contact loads and in superheated water up to 300 °C. Traditionally there has only been one material that can survive these conditions: cobalt based hardfacing alloys called Stellites. There is an urgent need to replace cobalt-based alloys because of the formation of cobalt-60 radioisotope, which causes radioactive exposure. In this study an iron-based hardfacing alloy, Tristelle 5183 was compared with Stellite 6. The hardfacings were manufactured via laser cladding. Wear testing was performed using a pin-on-flat configuration, with like-on-like couples, from room temperature up to 300 °C with loads of 50–500 N. The friction coefficient for the Tristelle was higher (typically 0.45) than the Stellite (typically 0.35) across all temperatures and loads. The wear rate of the Tristelle was higher than the Stellite, but the exact difference varied with both load and temperature. The specific wear rate increased with temperature, but only gradually. The operative wear mechanism was a combination of adhesive and oxidational wear, but there were significant differences found between the two alloys. For the Tristelle, the oxide became mechanically mixed with the heavily deformed surface metal. In contrast, the oxide on the Stellite was detached from the surface without any mechanical mixing. The extent of surface deformation was much greater for the Tristelle than the Stellite. The large (5–20 mm) NbC in the Tristelle fractured a considerable distance (up to 40 mm) below the worn surface and became increasingly fine as the worn surface was approached as a result of high strain deformation in the matrix. In the Stellite no carbide fracture was observed. The reasons for the marked difference in behaviour between the two alloys, each with the same mechanical properties, are discussed in detail.

Dislocation climbing dominated decomposition and fracture of carbides in a Ni-based superalloy

Metal carbides (MC) are typical strengthening phases in steels and superalloys. However, the decomposition of carbides can occur during high-temperature creep, which is generally considered to be detrimental to the high-temperature performance of superalloys. Here, through transmission electron microscopy and atomistic simulation, we report the atomistic to micro-scale mechanisms of MC decomposition. We identify that MC can deform plastically during high-temperature creep, which is supported by the observation of high-density dislocations within MC and steps at matrix/MC interfaces. This could release the stress concentration at the matrix/MC interfaces, thus improving the creep resistance. With Cr segregation along the dislocation line and continuous dislocation climb, decomposition of MC into M23C6 occurs in grain interiors, which could lead to crack inside the MC carbides, i.e., fracture at the partially coherent M23C6/MC interfaces. This is new to the existing knowledge that MC decomposition and fracture occur at matrix/MC interfaces.

Fabrication and Characterization of Aluminum-Graphene Nano-Platelets—Nano-Sized Al4C3 Composite

Reinforcement of aluminum and aluminum alloys with graphene has been intensively practiced by researchers in the past dozen years. The role of Al4C3, which could be produced unintentionally or purposefully during the composite production, was controversial until it was found that nano-sized carbides were beneficial for strengthening the composites. aluminum-graphene-nano-sized Al4C3 composites were produced by us using the powder metallurgical method and subsequent annealing. The microstructure was investigated using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy HRTEM. Nano-sized carbides were found at the interface aluminum-graphene. The formation of a chemical bond between aluminum and graphene during annealing was proved. Lower values of the microhardness and strength characteristics of the composites after extrusion and subsequent annealing during which nano-sized carbides are formed were found in comparison with those obtained after extrusion. It could be supposed that the annealing processes contribute more to the reduction in microhardness and strength characteristics than nano-sized carbides contribute to its increase. The presence of a strong chemical bond between the graphene and the aluminum is manifested in the failure pattern, which is characterized by graphene nano-platelets and nano-sized carbides fracture and semi-pulled out or semi-slipped Al4C3 from the matrix.

Study on sliding friction and wear behavior of M50 bearing steel with rare earth addition

This study aims to investigate the influence of rare earth (RE) addition on the friction and wear behavior of M50 bearing steel. The results show that RE addition has little effect on friction coefficient, but can reduce wear volume especially under harsh wear conditions. This mainly results from modification of RE elements to primary carbides. M50 steel without RE addition has bigger proportion slenderer rod-like M2C carbides, which are more likely to cause carbides fracture broken or peeling off, forming bigger wear debris with irregular shape to aggravate the wear. However, M50 steel with RE addition has more spherical MC carbides, which are more easily worn into spherical crowns, forming smaller wear debris which could not increase the subsequent wear.

In situ investigation of the fracture of primary carbides and its mechanism in M50 steel

The tensile crack initiation and propagation of M50 bearing steel were investigated. It is found that the primary carbides were fractured during the tensile test by in situ SEM, while decohesion of the carbide/matrix interface was hardly observed. In order to capture the initial tensile crack, quasi-in situ X-ray microtomography was performed, indicating that the earliest crack was formed from the broken interior carbides. This indicates that multiple cracks already existed in the matrix when they were observed on the sample surface. Electron backscattered diffraction (EBSD) and the finite element method (FEM) were applied to analyze the fracture behavior of carbide particles. The fracture of carbide particle is produced by the incompatible deformation between the matrix and carbides. The frequency of carbide fracture was found to be related with its fracture strength, size and shape. M 2 C carbide fracture was more easily broken than the MC carbide during tensile test. In addition, the long axis of most M 2 C carbides is approximately parallel to its (0001) plane and normal to tensile stress, leading to cracking more easily. Finally, a suggestion of adding pre-deformation is proposed to make M 2 C carbides broken sufficiently and further refine the primary carbides. • X-ray microtomography is applied to analyze the evolution of primary carbides. • Incompatible deformation between the matrix and particles leads to carbide fracture. • M 2 C carbide is more easily broken than MC carbide. • Pre-deformation before diffusion annealing should be applied to refine carbides.

Effects of Abrasive Rock Type on CVF-Dependent Performance Trends of White Cast Irons in the Inner Circumference Abrasion Test

Although the trends of abrasion performance versus carbide volume fraction (CVF) of white cast irons (WCIs) have been studied to some extent, there remain gaps in understanding of the factors controlling performance. This study addresses three knowledge gaps. Firstly, the influence of testing conditions, more closely reproducing ore chute service, has been determined using the inner circumference abrasion test (ICAT), which included different natural rock types. The benefit of WCI compared to steels was much greater in basalt than in granite or greywacke. Secondly, the current work shows monotonic behavior for granite and greywacke but performance reversal in basalt, demonstrating that the reversal is not due to “more severe” or “high stress” conditions. The literature variously shows monotonic, plateauing, or reversing CVF dependence but has not convincingly explained these behaviors. Thirdly, the Cr/C ratio (previously neglected) shows no effect in granite, but lower Cr/C gives poorer performance in basalt. The trends are explained by relative responses of the microconstituents to different minerals. Basalt abrades both steel and the WCI matrix but not M7C3, thus maximizing the benefit of WCI but creating roughened surfaces with protruding carbides. This promotes carbide fracture in hypereutectic alloys and, hence, the reversal. Harder minerals create less differential and hence less protrusion and no plateau.

In Situ Investigation of the Fracture of Primary Carbides and its Mechanism in M50 Steel

In Situ Investigation of the Fracture of Primary Carbides and its Mechanism in M50 Steel

In Situ Investigation of the Fracture of Primary Carbides and its Mechanism in M50 Steel

In Situ Investigation of the Fracture of Primary Carbides and its Mechanism in M50 Steel

Addressing amorphization and transgranular fracture of B4C through Si doping and TiB2 microparticle reinforcing

AbstractOver the last two decades, many studies have contributed to improving our understanding of the brittle failure mechanisms of boron carbide and provided a road map for inhibiting the underlying mechanisms and improving the mechanical response of boron carbide. This paper provides a review of the design and processing approaches utilized to address the amorphization and transgranular fracture of boron carbide, which are mainly based on what we have found through 9 years of work in the field of boron carbides as armor ceramics.

High-temperature mechanical properties and deformation behavior of carbides reinforced TiNbTaZrHf composite

Refractory high entropy alloys (RHEAs) have broad prospects in the field of high-temperature structural materials because of their outstanding mechanical properties at high temperatures. In this work, a novel TiNbTaZrHf based composite was fabricated by powder metallurgy in-situ method. By introducing carbides, the TiNbTaZrHf based composite exhibits an ultra-high yield strength of 2620 MPa at room temperature. Meanwhile, the composite still maintains a high strength of 508 MPa at 1000 °C. The significant strength improvement can be attributed to the load-bearing effect caused by the dispersed carbides with high volume fraction, while the intergranular fracture of carbides is responsible for the plastic instability. When the temperature rises to 1200 °C, the yield strength decreases significantly. The weakening of load-bearing effect and the activation of grain boundary sliding are the main reason for the strength reduction, while interfacial debonding between the matrix and carbides becomes the main failure behavior.

Erosive wear characteristics of high-chromium based multi-component white cast irons

Erosive wear characteristics of (18 and 27) wt.% Cr based multicomponent (3 wt% V, Mo, W, and Co) white cast iron have been systematically investigated with three conditions: as-cast (AC), as-quenched (Q), and as-quenched tempered (QT).The result shows that Q specimens has the better erosive wear resistance compared to AC due to the transforming of the austenite matrix to be martensite and precipitation of secondary carbide. However, the erosive wear resistance of Q specimens was slightly reduced by the tempering process due to a significant increment of M7C3 carbide fracture toughness. Therefore, it can be concluded that the excessive Cr addition can be a negative factor on erosive wear-resistance in heat-treated condition and the tempering process should be ignored.

Near-interface cracking in a TiN coated high speed steel due to combined shear and compression under cyclic impact loading

Hard coated tool steels are commonly used for metal working applications, where they are exposed to high levels of contact loads comprising normal and lateral force components. For such complex loading conditions, information on early stages of damage of hard coated steels is lacking. As these early stages provide information about damage mechanisms and possible weaknesses of the coated material, the current work investigates the damage behavior of the interface between a titanium nitride hard coating and a high speed steel. Specimens were subjected to cyclic impacts that combine shear and compression loading under unlubricated or lubricated conditions using an inclined impact tester. Investigation of crack formation below the substrate-coating interface by scanning electron microscopy on cross sections prepared by focused ion beam milling suggests that the predominating damage mechanism for unlubricated specimens is gradual coating wear. For lubricated specimens, the damage mechanisms are dominated by carbide fracture and fatigue crack growth between carbide and matrix occurring just below the substrate-coating interface.

Erosion–Wear Behaviors of High-Chromium Cast Iron with High Nitrogen Content in Water–Sand Slurry and Acid–Sand Slurry

High-chromium cast iron with high nitrogen content (HNHCCI) was prepared using a vacuum induction barotropic furnace, and the erosion–wear behaviors of HNHCCI were investigated with a rotary erosion–wear tester. Results show that most of the nitrogen in HNHCCI dissolves into the matrix and some nitrogen forms carbonitride in the solidification process. The relative wear resistance of HNHCCI can reach 1.34 times that of high-chromium cast iron. The erosion–wear morphologies are ploughing, indentation, and large chips in water–sand slurry, whereas it is galvanic corrosion and carbide fracture in acid–sand slurry. HNHCCI has better mechanical properties and corrosion resistance than HCCI, decreasing the synergism of corrosion and wear. Therefore, HNHCCI has a lower erosion–wear rate.