High Transverse Rupture Strength Research Articles

Enhanced properties of a novel medium-entropy alloy base diamond composite by introducing coherent L12 phase at interface

In this study, a medium-entropy alloy (MEA) was used as a new binder to fabricate diamond composite. The MEA base diamond composite (MEA-Comp) shows a much higher transverse rupture strength (TRS, 1453.5 MPa) and a stronger bonding interface than the referenced Co base diamond composite (TRS, 744.9 MPa). It is for the first time found that a (Ni, Co)3Al L12-type phase was in-situ formed between diamond and the MEA matrix. The L12 phase is fully coherent with the diamond in orientation relationship of [001]L12//[001]Diamond and (010)L12//(010)Diamond. Thus, the metallurgical bonding between diamond and metal matrix can be greatly improved, resulting in an enhanced wearing performance. Additionally, chromium carbides (majority Cr7C3 and minor Cr3C2) were also in-situ formed in the interlayer between diamond and matrix. The interlayer composed of L12 phase and chromium carbides can also block the direct contact between diamond and metal matrix, which might slow down the graphitization of diamond under service condition.

Investigation of thermal phase evolution in Cr2(C,N) inhibitor for optimizing high-performance cemented carbide sintering process

The introduction of inhibitors containing nitrogen has demonstrated its efficacy in the fabrication of high-performance cemented carbides. Nevertheless, the thermal instability of nitrogen-doped compounds also presents a heightened risk of nitrogen removal, which can adversely affect the density of the carbides. Hence, this study aimed to explore the thermal stability of a widely employed nitrogen-containing Cr2(C,N) inhibitor. The findings reveal that a well-established denitrification process commences at 950 °C and intensifies above 1200 °C, accompanied by a Cr2(C,N) → Cr7C3 → Cr23C6 phase evolution. Utilizing the aforementioned insights, the sintering process was optimized by adding an isothermal treatment to obtain dense and refined cemented carbide exhibiting high performance. As a result, the sintered ultrafine WC-10Co alloy maintains a series of excellent comprehensive performances combined with high transverse rupture strength (4850 MPa), high fracture toughness (10.6 MPa·m1/2), and high hardness (1870 kg/mm2). This work provides basic guidance on sintering strategy design for preparing high quality cemented carbides with nitrogen-contained inhibitors.

The Effect of Carbon Content on the Microstructure and Mechanical Properties of Cemented Carbides with a CoNiFeCr High Entropy Alloy Binder.

CoNiFeCr high entropy alloy (HEA) was used as a binder in cemented carbides for developing a new high-performance binder. The microstructure of WC-HEA cemented carbides with different binder components and carbon contents was subsequently studied. It was observed that the (Cr,W)C phase precipitated at the WC/HEA interface, and a coherent interface with a low degree of misfit was formed between WC and (Cr,W)C, thereby resulting in a significant reduction in the interfacial energy and stress concentration. The (Cr,W)C phase exerted a pinning force (Zener-drag) on the moving grain boundaries, which effectively inhibited the growth of WC grains. As a result, compared with WC-Co, WC-CoNiFeCr had smaller WC grain size, smoother grain shape and larger mean free path (MFP) of the binder, which resulted in slightly lower hardness and higher transverse rupture strength (TRS) and fracture toughness. The lower limit of carbon content in WC-CoNiFeCr was higher than that of WC-Co. With the addition of Ni, the width of the two-phase region became wider, whereas the width of the two-phase region became narrower with the addition of Fe and Cr.

Functionally Graded Material Production and Characterization using the Vertical Separator Molding Technique and the Powder Metallurgy Method

Functionally Graded Materials (FGMs) are advanced customized engineering materials that gradually and continuously change their composition. The current study investigated the production feasibility and some post-production mechanical/physical properties of B4C particle-reinforced (avg. 40µm) AA7075 matrix (avg. 60µm) FGM composites with the vertical separator molding technique using the high-temperature isostatic pressing powder metallurgy method. FGMs produced consist of three (0 – 30 – 60 wt. % B4C) and four (0 – 20 – 40 – 60 wt. % B4C) layers. The powders were mixed in a power blender mixer for 2h and were placed in the mold sections with a vertical separator. The lid was closed, and a pre-pressure of 10Mpa was applied. The FGM green sheet was transferred from the vertical separator mold to the hot work tool steel with a press. In this mold, FGMs were sintered at 560°C for 30 min under a pressure of 325MPa. Microstructural examinations did not reveal any separation or crack formation in the layer transition regions of the FGMs. In addition, a relatively homogeneous B4C reinforcing distribution was observed in the layers with a low reinforcement ratio (wt. 20% and 30%) compared to the other layers. The highest hardness was 170 HBN in one layer of the four-layer FGM containing 40% by weight B4C reinforcement. The highest transverse rupture strength was measured in the test performed from the region with the most reinforcement of the four-layer FGM at 482MPa.

The enhancement of the microstructure and mechanical performances of ultrafine WC-Co cemented carbides by optimizing Cr2(C,N) addition and WC particle sizes

Ultrafine WC-10Co cemented carbides with different Cr2(C,N) inhibitor contents and different-scaled WC powders were prepared by low-pressure sintering. Their influence on the microstructure and mechanical performances were investigated and expounded in this work. The result shows that the Cr2(C,N) addition homogenized the microstructure of the cemented carbides and refined WC grains. With the Cr2(C,N) addition increasing, hardness increased to 1870 kg/mm2, transverse rupture strength (TRS) first increased to 4435 MPa and then sharply decreased to 3230 MPa due to the existence of more pores with excessive Cr2(C,N). With the reduction of WC particle size, the mean WC grain size and mean free path of Co phase decreased, while the contiguity of the WC grains increased. The hardness and TRS of the specimens reduced, while fracture toughness increased. The comprehensive mechanical properties namely the TRS, hardness, and fracture toughness in the cemented carbides with 0.5 wt% Cr2(C,N) and 0.4 μm WC powder, were 4748 MPa, 1786 kg/mm2, 10.1 MPa· m1/2, respectively. A good combination of high TRS and hardness could be obtained in the cemented carbides by adopting appropriate amount of Cr2(C,N) and reducing the WC particle size.

Surface quality of cemented tungsten carbide finished by direct cutting using diamond-coated carbide end mill

• Superiority of direct cutting of cemented carbide with diamond-coated tool was shown. • Surface quality in direct cutting, electrical machining, and polishing was compared. • Specularity of finished surface similar to polishing was obtained via direct cutting. • Large compressive residual stress can also be obtained via direct cutting. • Higher transverse rupture strength can be achieved compared with polishing. This study addresses the finished surface quality of cemented tungsten carbide obtained via direct cutting with a diamond-coated carbide end mill under ultrasmall feed rates. The surface appearance, composition distribution, profile, roughness, residual stress, and transverse rupture strength were experimentally investigated. The finished surfaces obtained via electric discharge machining with two types of machining conditions and mechanical polishing processes were also evaluated to compare the surface quality. Two types of cemented tungsten carbide materials, TAS VC-70 and VM-40, were applied as the workpiece materials. A mirror surface can be obtained via direct cutting and mechanical polishing with both materials. The microstructure morphologies of the finished surface obtained via direct cutting were different from those obtained via mechanical polishing. In the case of VC-70 which has larger tungsten carbide grain size and higher cobalt content, the flat cross-section of the tungsten carbide grain under ductile mode cutting was conspicuous in direct cutting under small feed rate and depth of cut. In contrast, an extremely thin layer composed of fine grains of tungsten carbide and cobalt was observed on the finished surface in direct cutting under comparatively large feed rate and depth of cut. The surface roughness and profile of the finished surface resulting from direct cutting were comparatively rougher than those resulting from mechanical polishing, although the finished surface was significantly smoother than that resulting from electric discharge machining. The residual stress of the subsurface obtained via direct cutting showed larger compressive stress than that obtained via electric discharge machining and mechanical polishing under all cutting conditions and materials. Moreover, satisfactory transverse rupture strength can be obtained via direct cutting in both materials compared with other processes, and two times more transverse rupture strength can be achieved via direct cutting compared with the case of electric discharge machining in VM-40 cutting.

Synthesis and crystal structure of Mo2Ni1-xCrxB2 hard materials

Boride-based cermets possess attractive mechanical properties and are promising candidates for hard materials. Mo2NiB2–Ni-based cermet, which is a boride-based cermet, exhibits high hardness and attractive transverse rupture strength (TRS) properties through the crystal structure deformation that is caused by Cr or V substitution of Ni in the Mo2NiB2 phase. In this study, the effects of Cr substitution on the crystal structure, mechanical properties, and consistency were investigated. Cr-substituted Mo2Ni1-xCrxB2 samples were synthesized via the powder metallurgy method. A first-principle calculation was also conducted to obtain the bulk modulus of the Cr-substituted Mo2Ni1-xCrxB2. With the increase of the Cr content x, the tetragonal-Mo2NiB2 phase appeared, while the orthorhombic Mo2NiB2 phase disappeared. In the x = 0.6 samples, the Mo2Ni0.4Cr0.6B2, tet-Mo2NiB2 phase was observed. According to the Rietveld analysis, substituted Cr atoms occupied the Ni and Mo sites in the tet-Mo2NiB2 structure. The Rockwell A-scale hardness (HRA) measurement was performed to investigate the effects of the Cr content on the mechanical properties. The HRA values increased with the Cr content, and the maximum HRA value was approximately 87.1 for the x = 0.6 sample. The bulk modulus was also affected by the Cr content x in Mo2Ni1-xCrxB2, and the maximum value was attained at x = 0.75.

Effect of W/B atomic ratio on the microstructure and mechanical properties of WCoB-TiC ceramic composites: first-principles calculations and experiment

The thermodynamic stability, mechanical properties and electronic properties of the WCoB and W2CoB2 hard phases in WCoB-TiC ceramic composites are analyzed by the first-principles calculations. The microstructure, hardness, transverse rupture strength (TRS) and fracture toughness (KIC) of WCoB-TiC ceramic composites with various W/B atomic ratios are measured by experiments. First-principles calculations indicate that W2CoB2 has better thermodynamic stability and comprehensive mechanical properties than WCoB. The poor mechanical properties of WCoB are due to the heterogeneous nature of Co-W anti-bonds. The better mechanical properties of W2CoB2 are mainly derived from the stronger BB covalent bonds. Experimental results show that the density of WCoB-TiC ceramic composites increases rapidly with increasing of W/B atomic ratio initially and then gradually stabilized. Hardness, TRS and KIC of WCoB-TiC ceramic composites increases firstly and then decreases with the increase of W/B atomic ratio. When W/B atomic ratio is 0.6, hardness is the highest at 92.3 ± 0.3 HRA. When the W/B atomic ratio is 0.5, the WCoB-TiC ceramic composite has the highest TRS and KIC, which are 853.6 ± 30.3 MPa and 11.48 ± 0.33 MPa m1/2, respectively.

Effect of WO3 content on microstructure and mechanical properties of dual-grain structured hardmetals fabricated by in-situ carbothermal reduction of WO3

In this study, the effects of WO3 content on the microstructure of dual-grain structured hardmetals prepared through in-situ carbothermal reduction of WO3 were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, mechanical properties of hardmetals with different WO3 content were measured by mechanical property testing devices. Results showed that fine WC grains were formed through in-situ reaction between WO3 and carbon black, and the hardmetals mixed with WO3 exhibited obvious bimodal distribution. As the WO3 content increased, the average WC grain size first decreased and then increased, however, the trend of density change was opposite. Overall, microstructures of hardmetals with a WO3 content of 30 wt% were most homogeneous and dense. Moreover, in hardmetal with a WO3 content of 30 wt%, a low-angle grain boundary at the WC/WC interface was observed. In addition, a perfectly coherent state was observed at the interface between binder phase and fine WC grain formed via in-situ reaction of WO3 and carbon. Both hardness and transverse rupture strength (TRS) first increased and subsequently decreased, while fracture toughness (KIC) initially decreased slightly and then decreased considerably. The dual-grain structured hardmetal with 30 wt% WO3 could achieve a combination of high hardness, TRS and KIC.

Effect of WC grain size on mechanical properties and microstructures of cemented carbide with medium entropy alloy Co-Ni-Fe binder

For developing new binder phase with high performance, Co-Ni-Fe alloy was used as binder in cemented carbides. The mechanical properties of WC-CoNiFe and WC-Co cemented carbides with different grain sizes were studied. The results show that the reprecipitation of WC-CoNiFe is inhibited compared with that of WC-Co during sintering process, and the grains in WC-CoNiFe cemented carbides are more of smooth shape, resulting in a slightly lower hardness and higher transverse rupture strength. With the increase of the grain size, the hardness of the two cemented carbides decreases, and the transverse rupture strength increases. However, the slope values of K in Hall-Petch relationship are higher in WC-CoNiFe than those in WC-Co, indicating the high toughness of medium entropy alloy Co-Ni-Fe.

Combinatorial surface coating and greatly-improved soft magnetic performance of Fe/Fe3O4/resin composites

Structure-reinforced Fe/Fe3O4/resin soft magnetic composites (SMCs) have been fabricated through coating micron-sized Fe powders with high-purity Fe3O4 nanolayers and silicon resin films by combinatorial controlled oxidation and physical coating method. High magnetization Ms of 201 A m2 kg−1 can be reserved in the Fe/Fe3O4/resin SMCs due to high-purity ferrimagnetic Fe3O4 shells and low-content resin layers. The smooth Fe/Fe3O4 interfaces and uniform silicone resin coating layers in the Fe/Fe3O4/resin SMCs also lead to their low coercivity of 11.4 Oe and high compressed density of 7.50 g/cm3. For traditional metal-based SMCs fabricated by various common coating methods, their reduced core loss is usually achieved but accompanying with low magnetic induction and poor mechanical properties. In this work, high transverse rupture strength value of 92 MPa and greatly enhanced soft magnetic performance with both decreased core loss in accompany with high magnetic inductions are achieved for the fully densified Fe/Fe3O4/resin SMCs due to their well-structured composite interfaces, which promise their great latent applications for high-power and low-loss magnetic components.

Fabricating Ultrathin Plate-Like WC Grains in WC–8Co Hardmetals by Increasing Discharge Intensity During Plasma-Assisted Ball Milling

The effects of plasma discharge intensity on the microstructure evolution of ball-milled tungsten (W)–carbon (C)–cobalt (Co) mixtures and the formation mechanism of ultrathin plate-like tungsten carbide (WC) grains prepared by ball milling with and without plasma discharge were investigated. It was found that increasing the plasma discharge intensity during ball milling obviously promoted the formation of a thin flake-like W phase because of the electroplasticity effect and simultaneously lowered the carburization temperature between W and C. A combination of high hardness and transverse rupture strength of 92.9 HRA and 3659 MPa, respectively, was obtained for the WC–8Co alloy fabricated by plasma milling at a gas pressure of 5 × 103 Pa with a dielectric barrier discharge layer thickness of 3 mm. These properties were mainly attributed to the markedly lowered activation energy of the WC phase and generation of highly oriented ultrathin plate-like WC grains by plasma milling. The combination of the flake-like structure of the plasma-milled W aggregate and high specific interfacial area and short diffusion distance of W/C were readily inherited by the ultrathin plate-like WC grains in the sintered WC–Co hardmetals.

The influence of Mo/B atomic ratio on microstructural evolution and mechanical properties of Mo2FeB2-based cermets

AbstractMo2FeB2-based cermets were prepared with various Mo/B atomic ratios in the range of 0.8 to 1.1. The microstructure and crystalline phases were studied through scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray analysis and X-ray diffractometry. The results indicated that as the Mo/B atomic ratio increased, the morphology of the hard phase gradually transformed from long-strip to near-equiaxed. The tendency of transformation in the range of 1.0 to 1.1 was more significant. Two typical cermet samples (Mo/B = 1.0, Mo/B = 1.08) of different morphologies were studied with transmission electron microscopy. As the Mo/B atomic ratio increased, the average particle size decreased, inhibiting the nucleation of the particles, the anisotropy of different crystallographic planes reduced, the particles transformed from long-strip to the near-equiaxed shape. Moreover, it could be found from X-ray diffractometry results that the disparity between the crystal lattice constants c and a gradually diminished and the surface tension differences of the amorphous surfaces decreased, resulting in the anisotropy of different crystal-lographic planes gradually decreasing. The cermets with Mo/B = 1.02 demonstrated the highest transverse rupture strength, as well as the hardness and improved fracture toughness values of 2367.5 ± 50 MPa, 88.2 ± 0.1 HRA, and 27.6 ± 0.5 MPa · m1/2, respectively.

Investigation of mechanical properties of B4C/SiC/Al2O3 particle reinforced Al2024 hybrid composites

In the present study, Al2024 alloy powder (Al–Cu–Mg), frequently used in modern technology, reinforced with B4C, SiC and Al2O3 particles were used to produce hybrid composite. Pre-alloyed Al2024 powder and B4C, SiC, Al2O3 reinforcement components were mixed in a three dimensional mixer for 45 min. Mixed powders were compacted at 400 MPa under unidirectional press for the production of powder metal block. These block samples were sintered at 600 °C and then extruded at 500 °C. After then samples were cut with wire erosion method to ensure the appropriate standard dimension for transverse rupture strength tests. Transverse rupture strength and hardness values were determined depending on the type of the reinforcing components. In the study, maximum transverse rupture strength (920 MPa) and hardness value (104 HB) were obtained at Al2024 + 10 % wt B4C samples. On the other hand, the highest transverse rupture strength (901 MPa) and hardness (98 HB) in hybrid composite materials were obtained at Al2024 + B4C/SiC samples.

Improvement of thermal conductivity of WC-FeAl hard materials by elimination of oxide materials

The dependence of thermal conductivity in tungsten carbide- iron aluminide (WC-FeAl) hard materials on oxygen contained in the pre-sintered powders was investigated. The control of oxygen concentration in the hard materials was done by changing fabrication processes including heat treatment of raw WC powder. Although thermal conductivity of the hard materials strongly depended on the average WC grain size, it was apparently improved by reduction of oxygen Concentration. The maximum thermal conductivity was 169 W (mK)−1 with low volume fraction of FeAl binder (10 vol%Fe0.6Al0.4) to total WC-FeAl. The hardness and transverse rupture strength had negative relationship with the average WC grain size, indicating that they also had negative relationship with thermal conductivity. The improving technique such as uniform powder mixing with suppressing powder oxidation is required to fabricate WC-FeAl hard materials of high transverse rupture strength and thermal conductivity.

Effect of NbC addition on the microstructure, mechanical properties and thermal shock resistance of Ti(C,N)-based cermets

In this paper, Ti(C,N)-WC-TaC-xNbC--Mo-Ni cermets were prepared by vacuum sintering. The microstructure, mechanical properties and thermal shock resistance of Ti(C,N)-based cermets with different NbC contents was explored. The results showed that with the increase of NbC content from 0 to 3 wt%, the rim phases around black core became complete, which refined the grain size of the cermets. However, white core appeared with the further increase of NbC content to 9 wt%, and the volume proportion of rim phases increased. Subsequently, the thickness of rim phases around white core increased and the black cores without rim phases appeared. The mechanical properties and thermal shock resistance of the cermets increased first and then decreased with the increase of NbC content from 0 to 9 wt%. When the NbC content was 3 wt%, cermets showed the best mechanical properties with transverse rapture strength of 2387 MPa, hardness of 92.1 HRA and fracture toughness of 8.88 MPa·m1/2. Meanwhile, when the NbC content was 3 wt%, cermets showed the best thermal shock resistance with critical temperature difference of 360 °C, due to its higher transverse rupture strength and lower thermal expansion coefficient.

Evolution of Phase Microstructure and Properties of Mulit-core Cermets Based on (Ti,W,Ta)CN and TiCN Powders in Sintering Process

The phase, microstructure and properties of multi-core cermets based on (Ti,W,Ta)CN and TiCN powders were investigated in sintering process. The analyses of X-ray diffraction (XRD) and scanning electron microscope (SEM) indicate that the sintering behavior of the multi-core cermet in sintering process could be divided into three stages: (I) pre-densification stage (the sintering temperature < 1200 °C); (II) rapid densification stage (the sintering temperature between 1200 °C and 1350 °C); (III) final densification stage (the sintering temperature > 1350 °C). Meanwhile, the evolution of η-phase in multi-core cermets was discussed as well. Furthermore, the microstructural and chemical composition of η-phase were studied by transmission electron microscopy (TEM) using X-ray energy dispersive spectrometry (XEDS) and selected area electron diffraction (SAED). The thickness of the rim structure would increase with the rise of sintering temperature, while the mechanical properties of the material would firstly increase and then decrease with the rise of sintering temperature. The highest transverse rupture strength is achieved at 1450 °C, while the highest hardness at 1390 °C.

A novel route for the synthesis of ultrafine WC-15 wt %Co cemented carbides

In this study, a solution chemical route for the synthesis of ultrafine WC-15 wt %Co cemented carbides was proposed with WC-6Co aggregates as raw materials. The chemical Co was uniformly distributed around the WC-6Co aggregates and the Co layers in the raw materials had been well preserved. During sintering, the chemical Co could diffuse along the Co layers and thus avoid the aggregation and growth of WC grains. Additionally, the homogeneous distribution of Co phase and the existent of Co layers promoted the WC reprecipitations on the same crystal during the solution/re-precipitation process. The fine WC grains and the homogeneous of WC and Co phases resulted in the high hardness and transverse rupture strength.

Microstructural properties of sintered Al–Cu–Mg–Sn alloys

A non-commercial Al4Cu0.5Mg alloy has been used for investigating the effects of the elemental Sn additions. Uniaxial die compaction response of the alloys in terms of green density was examined, and the results showed that Sn addition has no effect when compacting conducted under high pressures. In total, 93–95% green density was achieved with an applied pressure of 400 MPa. Thermal events occurring during the sintering of the emerging alloys were studied by using differential scanning calorimetry (DSC). First thermal event on the DSC analysis of the Al4Cu0.5Mg1Sn alloy is the melting of elemental Sn, whereas for Al4Cu0.5Mg alloy, it is the formation of Al–Mg liquid nearly at 450 °C. Also it is clearly seen on the DSC analysis that Sn addition led to an increase in the formation enthalpy of Al–Mg liquid phase. High Sn content and high sintering temperature (620 °C), therefore high liquid-phase content, caused decrease on the mechanical properties due to thick intergranular phases and grain coarsening. Highest transverse rupture strength and hardness values were obtained from Al4Cu0.5Mg0.1Sn alloy sintered at 600 °C and measured as 390 MPa and 73 HB, respectively.

Investigation on microstructure and mechanical properties of Mo2FeB2 based cermets with and without PVA

Mo2FeB2 based cermets with and without PVA have been investigated by x-ray diffractometry (XRD), x-ray photoelectron spectroscope (XPS) and scanning electron microscopy (SEM). The density and transverse rupture strength (TRS) of green compact, relative density, hardness (HRA), fracture toughness (KIC) and TRS of Mo2FeB2 based cermets were also measured. The results indicate that, compared with the Mo2FeB2 based cermets without PVA, the density of green compact with PVA can be improved slightly at the same pressure. However, the much higher TRS is obtained for the green compact without PVA. Meanwhile, Mo2FeB2 particles exhibit the finer and less congruity feature for Mo2FeB2 based cermets without PVA. In addition, the higher relative density, hardness, fracture toughness and TRS can be acquired for the cermets without PVA. Obviously, considering the mechanical properties and preparation period of Mo2FeB2 based cermets, no adding PVA is the optimized process of powder molding in the manufacture of Mo2FeB2 based cermets.