Whisker Pull-out Research Articles

Design and evaluation of alkali-activated slag-calcined coal gangue cement and the shrinkage control by calcium carbonate whisker

The rapid solidification and significant shrinkage of alkali-activated slag cement are key issues that restrict its practical engineering application. This paper explores the composition design of alkali-activated cements (AAC) with slow coagulation and shrinkage reduction. This paper adjusts the proportion of slag (SG) and calcined coal gangue powder (CCGP), regulates the content of Na2O·2.4SiO2-NaOH-Na2CO3 ternary activator components, and uses calcium carbonate whiskers (CW) instead of SG to prepare AAC with slow coagulation and shrinkage reduction. When the activator is composed of (66 %) Na2O·2.4 SiO2-(2 %) NaOH-(32 %) Na2CO3 mixed composition, the CO32- and Ca2+ in the system react preferentially to produce CaCO3. The decrease of Ca2+ concentration delays the formation of C-(A)-S-H, resulting in the initial and final setting time of AAC reaching 334 min and 346 min, respectively. When the CW substitution rate is 3 %, the 28d compressive strength of AAC reaches 102.2 MPa. The 49d drying shrinkage of the AAC is 7020μm/m and the 49d autogenous shrinkage is 2387μm/m. This is attributed to the combined effect of enhancement mechanisms such as whisker bridging, crack deflection, whisker pullout, whisker–matrix coalition pullout and whisker breakage. This study establishes the relationship between the composition and performance of high performance AAC, which is significance for the resource utilization of coal gangue and the practical engineering application of AAC.

Morphology Control and Mechanism of Different Bath Systems in Cu/SiCw Composite Electroplating.

With the rapid development of electronic technology and large-scale integrated circuit devices, it is very important to develop thermal management materials with high thermal conductivity. Silicon carbide whisker-reinforced copper matrix (Cu/SiCw) composites are considered to be one of the best candidates for future electronic device radiators. However, at present, most of these materials are produced by high-temperature and high-pressure processes, which are expensive and prone to interfacial reactions. To explore the plating solution system suitable for SiCw and Cu composite electroplating, we tried two different Cu-based plating solutions, namely a Systek UVF 100 plating solution of the copper sulfate (CuSO4) system and a Through Silicon Via (TSV) plating solution of the copper methanesulfonate (Cu(CH3SO3)2) system. In this paper, Cu/SiCw composites were prepared by composite electrodeposition. The morphology of the coating under two different plating liquid systems was compared, and the mechanism of formation of the different morphologies was analyzed. The results show that when the concentration of SiCw in the bath is 1.2 g/L, the surface of the Cu/SiCw composite coating prepared by the CuSO4 bath has more whiskers with irregular distribution and the coating is very smooth, but there are pores at the junction of the whiskers and Cu. There are a large number of irregularly distributed whiskers on the surface of the Cu/SiCw composite coating prepared with the copper methanesulfonate (Cu(CH3SO3)2) system. The surface of the composite is flat, and Cu grows along the whisker structure. The whisker and Cu form a good combination, and there is no pore in the cross-section of the coating. The observation at the cross-section also reveals some characteristics of the toughening mechanism of SiCw, including crack deflection, bridging and whisker pull-out. The existence of these mechanisms indicates that SiCw plays a toughening role in the composites. A suitable plating solution system was selected for the preparation of high-performance Cu/SiCw thermal management materials with the composite electrodeposition process.

Fabrication and mechanical properties of TiN whisker toughening TiB2 based ceramic cutting tool composite

A TiB2 based ceramic cutting tool composite toughened by TiN whisker was developed. The results show that when the content of TiN whisker powder is 30 vol%, the flexural strength, Vickers hardness and fracture toughness of the composite are 862 MPa, 22.5 GPa, and 8.1 MPa m1/2, respectively. Compared with the composite reinforced by 30 vol% TiN particle, the fracture toughness of the composite toughened by 30 vol% TiN whisker only increases by 11.0 %. Improvement in the fracture toughness of the TiN particle reinforcing composite can be mainly due to the contribution of the mechanisms such as crack deflection and ductile metal phase toughening. These toughening mechanisms almost disappear in the TiN whisker toughening composite because of the high proportion of transgranular fracture. At the same time, the TiN whisker toughening composite also faces the problem of difficulty in whisker pullout. These problems mean that there is still a possibility of further improvement in the fracture toughness of the TiN whisker toughening TiB2 based ceramic cutting tool composite.

Combination of direct ink writing and reaction bonded for rapid fabrication of SiCw/SiC composites

Silicon carbide ceramic matrix composites are widely used in aerospace field due to their advantages of high temperature resistance, high strength and corrosion resistance. However, its application is greatly limited because of the difficulty in preparing complex shape structures by traditional machining methods. Here, a new strategy for preparing SiC w /SiC complex structure by combining direct ink writing with reaction bonding is proposed. A water-based slurry consisting of silicon carbide, carbon powder and silicon carbide whisker was developed. The influence laws of C content and SiC w content in slurry on sintering properties of direct-written samples were studied. The reaction bonding mechanism and whisker reinforcing and toughening mechanism were analyzed by means of microstructure and phase composition. The results show that the slurry exhibits shear thinning behavior with stress yield point, and its flow behavior and plasticity meet the requirements of direct writing. When the carbon content is 6.4 wt%, the maximum flexural strength is 239.3 MPa. When 15 wt% SiC w was added, the flexural strength of the composite reached 301.6 MPa, and when 20 wt% SiC w was added, the fracture toughness of the composite reached 4.02 MPa m 1/2 , which was increased by 26% and 18% compared with single-phase SiC, respectively. The reinforcing and toughening mechanisms of the whiskers mainly include whisker pullout, crack deflection and whisker bridging. After direct ink writing and reaction bonded, the whole process shows good near net forming ability. 3D printed SiC w /SiC composites have great application prospects in aerospace field.

Tensile and Fracture Properties of Silicon Carbide Whisker-Modified Cement-Based Materials

Silicon carbide whiskers (SiCw) have many excellent properties such as high strength, high elastic modulus, and high temperature resistance. In this paper, by using water reducer as dispersant, a stable SiCw dispersion was obtained, and SiCw-modified cement-based composites were prepared. Tensile strength tests for 8-shaped specimens were carried out on the materials. The fracture properties of the materials were measured using a three-point bending test with pre-cracks based on the digital image correlation method. The microstructure of the SiCw-modified mortar was observed by SEM. The results showed that the SiCw improved the tensile strength of the cement-based materials, and the addition of SiCw effectively improved the fracture toughness of mortar. The SiCw caused crack deflection during crack propagation, accompanied by whisker pull-out and bridging phenomena. The SiCw bridging effect and pull-out mechanism effectively controlled the crack propagation and played a toughening role, thus enhancing the crack resistance of mortar.

Mechanical properties and microstructure of spark plasma sintered Al2O3-SiCw-Si3N4 composite ceramic tool materials

In this study, Al2O3-SiCw-Si3N4-based ceramic tool materials were fabricated by spark plasma sintering technique. The impact of sintering temperature on mechanical properties and local microstructure was thoroughly investigated. Moreover, detailed comparison was performed between spark plasma sintering and early hot-pressing sintering methods. Evolution law and mechanism of high-temperature mechanical properties were also investigated. Composites with higher density and enhanced mechanical properties were obtained by spark plasma sintering at temperature of 1500 °C, which was 100 °C lower than hot-pressing temperature. The cross-interlocking structure of generated β-Sialon particles and silicon carbide (SiC) whiskers could effectively improve mechanical properties of material configuration. Moreover, Vickers hardness and fracture toughness of ceramic composites decreased by elevating temperature (20–1000 °C); however, following percentages at 1000 °C were still maintained with respect to values at room temperature, i.e., 67 and 51%. This effect is attributed to existence of Sialon phase, healing of partial cracks, as well as manifestation of whisker pullout process. As a result, decreased attenuation rate under high-temperature conditions of respective mechanical properties was observed. Our approach provides useful insights into potential fabrication of novel material configurations with relatively low thermal budget and enhanced mechanical performance.

Mechanical Properties and Microstructure of Calcium Sulfate Whisker-Reinforced Cement-Based Composites.

This study aims to investigate the effect of calcium sulfate whisker (CSW) on the properties and microstructure of cement-based composites. Further, nanosilica (NS) was used as a comparison. The results show that the compressive strength and fracture toughness of cement-based composites increased by 10.3% and 10.2%, respectively, with 2% CSW. The flexural strength, splitting tensile strength, and fracture energy increased by 79.7, 34.8 and 28.7%, respectively, with 1% CSW. With the addition of CSW, shrinkage deformation was aggravated, and the capillary water absorption coefficients were clearly reduced. Compared with NS, CSW-reinforced cement-based composites show better tensile, flexural, and fracture properties and smaller shrinkage deformations and capillary water absorption coefficients. The residual mechanical properties of all groups improve when the treating temperature is lower than 400 °C and decline rapidly when the temperature goes over 600 °C. When treated at 900 °C, the residual mechanical properties are 40% less than those at ambient temperature, with the NS group showing the best performance, followed by the control group and the CSW group. X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests show that the addition of CSW improves the microstructure of the matrix. CSW can reinforce and toughen composites by generating ettringite and whisker pullout, whisker breakage, crack bridging, and crack deflection at the microstructure level.

Property evolution of geopolymer composites with SiC whiskers loaded with BN coating at elevated temperatures

This article investigates the key interface properties of geopolymers reinforced by SiC whiskers loaded with BN coating (BN/SiCw) and the insight of mechanical performance and microstructures of the resulting composites. The interesting diverse strength evolutions of geopolymer composites calcinated at various temperatures suggest a result of rivalries of multiple factors including BN coating, geopolymer matrix transformations, SiC whiskers. A positive effect on whisker pull-out phenomenon has been achieved via the chemical bonding between SiC whisker (SiCw) and BN coating and the rough physical interface between BN coating and geopolymers; the addition of SiCw and BN/SiCw promotes the polycondensation reaction of geopolymers and the addition of the latter is superior. Through changing the pore structure characteristics of the composites, the SiCw in composites can release their excessive vapor pressure in the closed pores which is the main reason attributing to the strength loss of geopolymers at 900 °C. In addition, BN coating can make up for the mismatch of thermal expansion coefficient between SiCw and geopolymers, increasing the strength of the composites by 30.9% at 900 °C, whereas whisker pull-out and crack deflection are the main toughening effect for BN/SiCw.

Textured and toughened high-entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiCw ceramics

High-entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C ceramics, with different contents (0, 5, 10, and 20 vol.%) of SiC whiskers (SiCw), were fabricated by spark plasma sintering using raw powders synthesized via carbothermal reduction. The application of a uniaxial compaction force led to texture development of the SiCw within the (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C matrix. Fracture toughness increased with the increase in SiCw content, while Vickers hardness remains almost unchanged. The toughness of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-20 vol.% SiCw ceramics reached 4.3 ± 0.3 MPa m1/2, which was approximately 43% higher than that of the monolithic (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C ceramic (3.0 ± 0.2 MPa m1/2). The main toughening mechanisms were attributed to crack deflection, whisker debonding, and whisker pullout.

Microstructure and strengthening mechanism of boride in-situ reinforced titanium matrix composites prepared by plasma activated sintering

In this study, titanium matrix composites (TMCs) were prepared by plasma activated sintering. The microstructure and mechanical properties of the composites were studied, and the strengthening mechanism was determined. The results showed that the main phases of Ti-rich samples are TiB, α-Ti and β-Ti, while the primary phases of TiB2-rich samples are TiB2 and TiB. The composites containing 70 wt%TC4-30 wt%TiB2 demonstrated the best performance which achieved a balance of high strength and ductility, with a yield strength of 1800 ± 28 MPa and compressive strength of 2215 ± 39 MPa. The key reinforcing and toughening mechanisms were due to the dislocation defects and stacking faults in the samples, which consume more fracture energy during crack propagation and comprehensively improve the strength and toughness of the composites. Furthermore, crack deflection and whisker pull-out caused by TiB can toughen the composites.

Efficient multiscale strategy for toughening HfB2 ceramics: A heterogeneous ceramic–metal layered architecture

AbstractA multiscale structural design was innovatively adopted herein to increase the toughness of monolithic HfB2 ceramics. SiC whiskers (SiCw) and graphene oxide (GO) were used as fillers for the HfB2 matrix, whereas a ductile W foil was introduced as an interlayer to synthesize laminated HfB2‐SiCw‐rGO/W ceramics. Monolithic HfB2‐SiCp (particulate) and laminated HfB2‐SiCp/W ceramics were prepared using the same routes and used as controls. Following tape casting and spark plasma sintering at 1800°C, the toughness of the prepared laminated HfB2‐SiCw‐rGO/W samples was increased to 14.2 ± 0.6 MPa·m1/2, with minimal sacrifice in flexural strength (421 ± 16 MPa). Morphological analysis of the fracture surface revealed the synergistic effects of micro‐toughening (including bridging and pullout of whiskers and rGO) and macro‐toughening (including crack deflection, bifurcation, and delamination) mechanisms responsible for improving the fracture toughness of the laminated HfB2‐SiCw‐rGO/W composites.

SiCw-Al2O3-epoxy composites with enhanced 3D interlocking skeleton

Nacre’s 3D interlocking skeleton was replicated in the novel SiCw-Al2O3-epoxy composites. The 3D skeleton architecture consists of trans-lamellar ceramic columns and bridges between parallel ceramic lamellae. The ceramic columns or bridges are composed of SiC whiskers with Al2O3 coating, showing a core-shell structure. During the fracture of the composites, Al2O3 shells of the SiCw-Al2O3 columns or bridges break and fall off, while their SiC-whisker cores play important roles in strengthening and toughening for the composites by whisker pull-out and bridging respectively. The strength and toughness of the 6 wt.%SiCw-Al2O3-epoxy composites with the 3D interlocking skeleton are 181 MPa and 0.56 MJ/m3 respectively, which are 51% and 93% higher than those of the conventional lamellar Al2O3-epoxy composite respectively.

A novel magnesium hydroxide sulfate hydrate whisker-reinforced magnesium silicate hydrate composites

Magnesium hydroxide sulfate hydrate (MHSH) whiskers are used to reinforce magnesium silicate hydrate (M-S-H) cement mortars as novel microfibrous materials because of their similar pH. The microstructure, mechanical performance, and reinforcement mechanism were investigated, and the results showed that the addition of between 1 and 5 wt% MHSH whiskers improved the compressive and flexural strengths of M-S-H cement mortars. The optimal compressive and flexural strengths were obtained at MHSH whisker contents between 3 and 4 wt%. The MHSH whiskers had a limited effect on the toughness of M-S-H cement, and mortars reinforced with MHSH whiskers exhibited brittle failure due to the small size of MHSH whiskers and low fiber bridging traction. Scanning electron microscopy (SEM) revealed that the microscale reinforcement mechanism of MHSH whiskers involved whisker pullout, crack deflection, whisker-cement coalition pullout, and whisker fracture. These mechanisms helped dissipate energy and optimize the stress distribution and transfer, which were crucial to improving the flexural strength. The SEM images revealed the rough and grooved surfaces of MHSH whiskers, and X-ray photoelectron spectroscopy (XPS) showed the presence of polar functional groups on the surface which resulted in the adhesion of M-S-H gel on MHSH whiskers due to good interfacial bonding. The mercury intrusion porosimetry (MIP) results indicated that the addition of MHSH whiskers reduced the porosity of M-S-H cement mortars, which also contributed to the increased compressive strength.

Microstructure and thermal shock resistance of AlBOw- and BNw-whisker-modified thermal barrier coatings

To improve the crack propagation resistance of YSZ thermal barrier coatings during the thermal cycle, three kinds of thermal barrier coatings were prepared by atmospheric plasma spraying: YSZ, AlBOw-modified YSZ and BNW-modified YSZ. SEM, EDS and XRD were used to analyse the morphology, composition and phase composition of the sprayed powder and coating section. The phase structures of the YSZ, YSZ+AlBOw and YSZ+BNw coatings were t' phase. The cross-section of the coating presents a layered structure with pores inside. The porosity values of the YSZ, YSZ+AlBOw and YSZ+BNw coatings are 10.33%, 14.17% and 12.52%, respectively. The thermal shock resistance of three groups of coatings after 5 min at 1000 °C was analysed. The failure behaviour of the coatings after several thermal cycles was studied. The results show that the thermal shock resistance of the coatings with AlBOw is slightly lower than that of the YSZ coatings. The thermal shock resistance of the BNw coatings is 62.2% higher than that of the YSZ coatings. The whisker inhibits the crack propagation and prolongs the life of the coatings via crack deflection, whisker pull-out and whisker bridging.

Erosion resistance and toughening mechanism of AlBO and BNw whiskers modified thermal barrier coatings

In order to improve the erosion resistance and toughness of thermal barrier coatings, YSZ coatings, 20 vol%-AlBOw whisker modified YSZ coatings and 20 vol%-BNw whisker modified YSZ coatings were prepared by plasma spraying. The cross-section structure, morphology, composition and phase composition of coatings and powders were analyzed by SEM, EDS and XRD. The erosion resistance of three coatings was tested by self-made erosion tester. The crack growth resistance of coatings was tested and calculated by Vickers hardness tester. The results show that the density of the coating is improved by adding AlBOw and BNw. The whisker inhibits the crack propagation through the mechanisms of crack deflection, whisker pull-out and whisker bridging. The addition of whisker improves the erosion resistance of YSZ coating by 8.17% and 13.94%, which can effectively improve the service life of thermal barrier coating.

Mechanical Properties and Microstructure of CaSO4 Whisker Reinforced Cement Mortar

Calcium sulfate whisker (CaSO4 whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO4 whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO4 whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO4 whiskers were identified by X-ray diffraction (XRD) and scanning electron microscope (SEM). Conclusion can be drawn that CaSO4 whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO4 whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry (MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.

Influence of MgO whisker addition on microstructures and mechanical properties of WC-MgO composite

WC-MgO whisker composite (abbreviated as WC-MgOw composites) has been sintered by hot pressing. The purpose of present study is to investigate the influence of various content of MgO whisker addition on mechanical performance of WC-MgOw composites. Vickers hardness and fracture toughness of WC-MgOw composites first increase and then decrease with the addition of MgO whisker. The optimal values of Vickers hardness and fracture toughness are achieved, respectively 20.92 GPa and 9.85 MPa m1/2, when the MgO whiskers content reaches 1 wt%. The fracture toughness of WC-MgOw composite is about higher 10.2% than the sample's without MgO whiskers. However, the relative density of the WC-MgOw composites decreases continuously with the addition of MgO whiskers. When the content of MgO whisker is relatively high, the fracture mode is changed and large pores appear. Thus, the mechanical properties of WC-MgOw composite is decreased. The main toughening mechanisms can attribute to crack deflection, crack bridging and whisker pull-out. The mixture of intergranular and transgranular fracture mode also increase the fracture toughness.

(SiC-Si3N4)w/SiBCN composite ceramics with tunable electromagnetic properties

In this study, composite ceramics with tunable electromagnetic properties were developed based on SiC-Si3N4 hybrids. First, SiC-Si3N4 whisker preforms with various SiC whisker (SiCw) concentrations were prepared by the nitridation of Si in SiCw-Si powder compacts. The in-situ-grown Si3N4 whiskers (Si3N4w) were dispersed uniformly in the voids inside the interconnected network formed by SiCw. The whisker reinforcements effectively toughened the SiBCN matrix through interface debonding, crack deflection and whisker pullout mechanisms. The electromagnetic properties of the composite ceramics can be tuned by adjusting the composition of (SiC-Si3N4)w preforms. The composite ceramic with 31.9 vol% SiCw exhibited the broadest effective absorption bandwidth (EAB) of 2.9 GHz in X band. Furthermore, a multilayer radar absorbing structure (RAS) composed of ceramic composites with gradient electromagnetic parameters was constructed to further improve the absorption properties. By adjusting the structure of the RAS, the resulting EAB of the RAS covered the entire X band.

Mechanical and Magnetic Properties of Hot-Deformed Nd-Fe-B Magnets Doped with SiC Whiskers

To improve the mechanical properties of hot-deformed Nd-Fe-B magnets, anisotropic Nd-Fe-B magnets doped with SiC whiskers were fabricated by hot-pressing and hot-deformation processes. The influence of the SiC whiskers on the microstructure and magnetic and mechanical properties of the Nd-Fe-B magnets was investigated. The bending strength of the hot-deformed Nd-Fe-B magnets reinforced with SiC whiskers first increased and then decreased with increasing SiC whisker content from 0 wt.% to 1.0 wt.%. The composite magnet with 0.5 wt.% SiC whiskers exhibited the highest average bending strength and still retained the maximum energy product of approximately 45.8 MGOe. The morphology of the fracture surface of the magnets revealed that the majority of the SiC whiskers were distributed at intergranular boundaries. The phenomenon of SiC whisker pullout from the matrix was observed, which results in increased bending strength. The improvement of the mechanical properties can be attributed to the high strength of the SiC whiskers, the whisker pullout phenomenon, and crack deflection.

Microstructure and properties of SiCw/SiC composites prepared by gel-casting combined with precursor infiltration and pyrolysis

Near net-shaped SiCw/SiC composites with higher fracture toughness and isotropic mechanical properties were successfully fabricated by gel-casting combined with precursor infiltration and pyrolysis (PIP). In the gel-casting process, the effects of dispersant dosage, pH value, and solid loading on the rheology of slurries were investigated in detail. A well-dispersed slurry was obtained when the pH was 11 and dispersant dosage was 1.2wt%. As the solid loading increased from 28 to 40vol%, the flexural strength of green bodies and SiCw/SiC composites increased from 62.34 and 260.38 to 80.21MPa and 308.29MPa, respectively, and the fracture toughness of SiCw/SiC composites increased from 4.56 to 5.32MPam1/2. However, when the solid loading reached 44vol%, uneven pores were observed in the green bodies. The highest density and mechanical properties of composites were obtained when the solid loading was 40vol%. The toughening mechanisms involved were whisker bridging, whisker pull-out and crack deflection.