陶瓷喷砂嘴的冲蚀磨损机理研究

以B4C和Al203／(W，Ti)C陶瓷材料制备喷砂嘴，以SiC和Al2O3作为冲蚀磨料进行了喷砂冲蚀试验。研究了陶瓷喷嘴材料的冲蚀磨损机理以及不同冲蚀磨科对陶瓷喷嘴冲蚀磨损的影响。结果表明：喷嘴材料的硬度对陶瓷喷嘴的冲蚀磨损起重要作用。在相同条件下，具有高硬度的B4C陶瓷喷砂嘴的磨损率较小，相对硬度较低的Al2O3/（W,Ti）C陶瓷喷嘴磨损率较大。B4C陶瓷喷嘴的主要磨损机理为脆性断裂，而Al2O3/（W,Ti）C陶瓷喷嘴的主要磨损机理为微观切削。冲蚀用磨科的硬度和粒度对陶瓷喷嘴的磨损也有一定的影响，磨料的硬度和粒度越大，陶瓷喷嘴的磨损速度加快。     

Layered structures in ceramic nozzles for improved erosion wear resistance in industrial coal-water-slurry boilers

The nozzle is the most critical part in the coal-water-slurry (CWS) boilers. Ceramics being highly wear resistant have great potential as CWS nozzle materials. In this paper, Al₂O₃/(W,Ti)C + Al₂O₃/TiC layered ceramics (LN1, LN2, and LN3) with different thickness ratios among constituent layers were developed to be used as nozzles in CWS boilers. CWS burning tests in a boiler with these nozzles were carried out. The erosion wear behavior of the layered nozzles was investigated and compared with an unstressed reference nozzle (N5). Results showed that the layered ceramic nozzles exhibited an apparent increase in erosion wear resistance over the unstressed reference one. The mechanisms responsible were found to be that layered structure in the CWS nozzles can improve the hardness and fracture toughness of the external layer, and reduce the temperature gradients and the thermal stresses at the exit of the nozzle during CWS burning processes. It is suggested that layered structures in ceramic nozzles is an effective way to improve the erosion wear resistance over the stress-free ceramic nozzles in industrial CWS boilers.     

Erosion behavior of B4C based ceramic nozzles by abrasive air-jet

TiC and Mo were introduced into B₄C-based ceramic nozzles, which were obtained by hot-press sintering. The effect of TiC content on mechanical properties and erosion behavior of B₄C-based ceramic nozzles were analyzed. XRD analysis showed that chemical reactions took place during the sintering process, which resulted in B₄C/Mo/TiB₂ ceramic nozzle with high density and improved mechanical properties compared with B₄C/Mo ceramic nozzle. The sintering temperature was decreased from 2150 °C for B₄C/Mo ceramic nozzle to 1950 °C for B₄C/Mo/TiB₂ ceramic nozzle. Results of erosion wear tests indicated that the hardness and toughness were the key factors influencing the erosion rate of B₄C/Mo/TiB₂ ceramic nozzle. Analysis of the eroded bore surfaces of B₄C/Mo/TiB₂ ceramic nozzle showed that the entry bore section exhibited a brittle fracture induced material removal process, and the center bore section showed plowing and polishing of material removal. Fracture and plowing of material removal occurred at the exit bore section.     

Wear properties and microstructures of alumina matrix composite ceramics used for drawing dies

The alumina matrix ceramics used for drawing dies were prepared by hot-press sintering method. The ceramics materials were made of Al₂O₃/TiC, Al₂O₃/(W,Ti)C and Al₂O₃/Ti(C,N). Mechanical and friction properties of these materials were tested and measured. The experiments for testing friction properties were carried on wear and tear machine. Mechanisms of frictions were analyzed with scanning electron microscope. Results showed that the alumina matrix composite ceramics have good physical and mechanical properties for used as drawing dies. Measured friction coefficients of alumina matrix composite ceramics showed a trend of decline and kept the value of 0.4–0.5 with the rotating speed of 550 rpm. Alumina matrix composite ceramics have smaller wear rate, while the wear rates of Al₂O₃/TiC and Al₂O₃/(W,Ti)C decrease gradually with a rising rotation speed. The wear of alumina matrix ceramics was severe at deformation zone. The primary wear behaviors of alumina matrix ceramics are scraping and furrowing. Even though the mechanisms for wear different, abrasive and adhesive wear were found to be the predominant wear mechanisms for the ceramic drawing die.     

B4C/SiCw陶瓷喷砂嘴的制备及其冲蚀磨损机理研究

采用热压烧结工艺制备了B4C/SiCw陶瓷喷砂嘴,研究了SiC晶须的含量对B4C/SiCw陶瓷材料性能的影响.以SiC和Al2O3磨料对B4C/SiCw陶瓷喷砂嘴进行冲蚀磨损试验,研究不同磨料对B4C/SiCw陶瓷喷砂嘴冲蚀磨损的影响,分析了其冲蚀磨损机理.结果表明:B4C/SiCw陶瓷喷砂嘴的冲蚀磨损机理主要表现为脆性断裂和磨料粒子对喷嘴的切入所造成的微观切削作用.磨料的硬度和粒度对陶瓷喷嘴的磨损有重要的影响,磨料的硬度和粒度越大,陶瓷喷嘴的磨损速度加快.     

Reliability prediction of a microwave sintered Si3N4-based composite ceramic tool

The wear life reliability prediction model of microwave sintered Si₃N₄/(W,Ti)C/Y₂O₃/MgO/Al₂O₃ composite ceramic tools based on the random distribution characteristics of hardness and fracture toughness of ceramic tool material was established. It showed that the Vickers hardness of ceramic tool materials followed a normal distribution and the fracture toughness followed a lognormal distribution. Distribution law of wear life can be determined by the joint distribution of hardness and fracture toughness. Experimental research on tool reliability of continuous dry cutting quenched high quality carbon steel T10A was carried out and the applicability of the tool reliability prediction model was verified. The results showed that the error between the theoretical reliable life and the actual life of the ceramic tool was less than 5% under the same reliability when the reliability was above 0.5.     

Effect of Ti amount on wear and corrosion properties of Ti-doped Al2O3 nanocomposite ceramic coated CP titanium implant material

Al₂O₃ and Ti-doped Al₂O₃ nanocomposite ceramic coatings were prepared by using a sol-gel dip-coating process. Corrosion and wear resistance of Al₂O₃ ceramic coatings in relation to Ti amount were carried out using pin-on-disk tribotester, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Surface characterizations before and after the corrosion and wear tests were investigated by the scanning electron microscope (SEM) and X-ray diffraction (XRD) and hardness analysis. The results of corrosion and wear tests exhibited that the corrosion and wear resistance of nanocomposite ceramic coatings became better than uncoated samples. Also, corrosion and wear resistance of nanocomposite ceramic coatings improved with Ti doping content increased.     

Microstructure and mechanical properties of hot-pressed SiC/(W,Ti)C ceramic composites

SiC/(W, Ti)C ceramic composites with different content of (W, Ti)C solid-solution were produced by hot pressing. The effect of (W, Ti)C content on the microstructure and mechanical properties of SiC/(W, Ti)C ceramic composites has been studied. Densification rates of the SiC/(W, Ti)C ceramic composites were found to be affected by addition of (W, Ti)C. Increasing (W, Ti)C content led to increase the densification rates of the composites. The sintering temperature was lowered from 2100 °C for monolithic SiC to 1900 °C for the SiC/(W, Ti)C composites. Results show that additions of (W, Ti)C to SiC matrix resulted in improved mechanical properties compared to pure SiC ceramic. The fracture toughness and flexural strength continuously increased with increasing (W, Ti)C content up to 60 vol.%, while the hardness decreased with increasing (W, Ti)C content.     

Microstructure and toughening mechanisms of Al2O3/(W,Ti)C/graphene composite ceramic tool material

To toughen the Al₂O₃ matrix ceramic materials, Al₂O₃/(W, Ti)C/graphene multi-phase composite ceramic materials were fabricated via hot pressing. The effects of the graphene nanoplates (GNPs) content on microstructure and mechanical properties were investigated. Results showed that the fracture toughness and flexural strength of the composite added with just 0.2?wt% GNPs were markedly improved by about 35.3% (~ 7.78?MPa?m^1/2) and 49% (~ 608.54?MPa) respectively compared with the specimens without GNPs while the hardness was kept about 24.22?GPa. However, the mechanical properties degrade with the further increase of GNPs’ content owing to the increased defects caused by agglomeration of GNPs. Synergistic toughening effects of (W, Ti)C and GNPs played an essential role in improving the fracture toughness of composites. By analyzing the microstructures of fractured surface and indentation cracks, besides GNPs pull-out, crack deflection, crack bridging, crack branching and crack arrest, new toughening mechanisms such as break of GNPs and crack guiding were also identified. Furthermore, interface stress can be controlled by means of stagger distributed strong and weak bonding interfaces correlated with the distribution of GNPs.     

Mechanical Properties and Solid Particle Erosion Behavior of LaMgAl11O19–Al2O3 Ceramic at Room and Elevated Temperatures

In this work, the mechanical properties and solid particle erosion wear behavior of LaMgAl₁₁O₁₉–Al₂O₃ ceramics toughened and reinforced with LaMgAl₁₁O₁₉ platelets were investigated. The effects of LaMgAl₁₁O₁₉ additions, impingement angles (30°, 45°, 60°, 75°, and 90°), and erosion temperatures varying from room temperature to 1400°C on the erosion rates and material removal mechanisms of LaMgAl₁₁O₁₉–Al₂O₃ composites were systematically studied. The results indicated that LaMgAl₁₁O₁₉–Al₂O₃ ceramics exhibited superior erosive wear resistance compared to monolithic Al₂O₃ ceramics at room and elevated temperatures due to their enhanced mechanical properties and improved microstructure resulting from the introduction of an appropriate amount of LaMgAl₁₁O₁₉ platelets. Examination of the eroded surfaces of LaMgAl₁₁O₁₉–Al₂O₃ composites revealed that erosion temperatures and impingement angles play important roles in determining the erosion behavior and mechanisms of the tested materials. For the case of elevated temperature and oblique erosion, plowing and subsurface intergranular fracture are the predominant mechanisms resulting in material removal, whereas at room temperature and normal impact, the erosion process of the targets is primarily dominated by grain ejection and lateral crack intersection.     

Improving the dry sliding-wear resistance of B4C ceramics by transient liquid-phase sintering

A critical comparison is made between the dry sliding-wear resistance of a B₄C composite fabricated by transient liquid-phase sintering with Ti-Al intermetallic additive and two reference monolithic B₄C ceramics fabricated by solid-state sintering. It is shown that, as a consequence of its full densification and super-hardness, the B₄C composite is, despite containing secondary phases, markedly more wear resistant (significantly lower coefficient of friction, specific wear rate, worn volume, and wear damage) than the reference monolithic B₄C ceramic fabricated under identical spark-plasma-sintering (SPS) conditions, and at least as wear resistant as the reference monolithic B₄C ceramic fabricated at much higher SPS temperature. In all materials, wear is nonetheless mild and occurred by two-body abrasion dominated by plastic deformation at the micro-contact level plus, in the porous reference monolithic B₄C ceramic, three-body abrasion dominated by fracture. Implications for the lower-cost manufacture of superhard B₄C tribocomponents are discussed.     

Progress in pressureless sintering of boron carbide ceramics – a review

ABSTRACT

Boron carbide (B₄C) ceramics has many outstanding performance, such as extremely high hardness, low density, high melting point, high elastic modulus, high thermoelectromotive force, high chemical resistance, high neutron absorption cross section, high impact and excellent wear resistance. Therefore, B₄C ceramics can be used in various industrial applications, such as lightweight ceramic armour, high temperature thermocouples, neutron absorber, reactor control rods in nuclear power engineering, polishing media for hard materials, abrasive media for lapping and grinding, and wear resistant components (blasting nozzles, die tips and grinding wheels). Pressureless sintering is the method with industrialised application value for B₄C ceramics, however, it is impossible to sinter pure B₄C ceramics to high densities without additives by pressureless sintering. So sintering additives must be used to promote the densification of B₄C ceramics. The different sintering additives used to promote the densification of boron carbide will be described in this review, including carbon additives, metallic additives, oxide additives, non-oxide additives, combined additives and rare earth oxide additives. Finally, the recent research trends for sintering methods and sintering additives of B₄C ceramics will also be proposed.     

Mechanical properties and sliding wear behaviour of Al2O3-SiC nanocomposites with 3–20 vol% SiC

Al₂O₃/SiC composites containing different volume fractions (3, 5, 10, 15, and 20 vol%) of SiC particles were produced by conventional mixing of alumina and silicon carbide powders, followed by hot pressing at 1740 °C for 1 h under the pressure of 30 MPa in the atmosphere of Ar. The influence of the volume fraction and size of SiC particles (two different powders with the mean size of SiC particles 40 and 200 nm were used), and final microstructure on mechanical properties and dry sliding wear behaviour in ball-on-disc arrangement were evaluated. The properties of the composites were related to a monolithic Al₂O₃ reference. Microstructure of the composites was significantly affected by the volume fraction of added SiC, with the mean size of alumina matrix grains decreasing with increasing content of SiC particles. The addition of SiC moderately improved the Vickers hardness. Fracture toughness was lower with respect to monolithic Al₂O₃, irrespective of the volume fraction and size of SiC particles. Al₂O₃/SiC nanocomposites conferred significant benefits in terms of wear behaviour under the conditions of mild dry sliding wear. Wear resistance of the alumina reference was poor, especially at the applied load of 50 N. The wear rates of composites markedly decreased with increasing volume fraction of SiC. Wear of the composites was also influenced by the material of counterparts, especially their hardness, with softer counterparts resulting in lower wear rates. All composites wore by a combination of grain pull-out with plastic deformation associated with grooving and small contribution of mechanical wear (micro-fracture). No influence of SiC particle size on wear rate or mechanism of wear was observed in the materials with identical volume fractions of SiC.     

Preparation and characterization of Si3N4-based composite ceramic tool materials by microwave sintering

Si₃N₄-based composite ceramic tool materials with (W,Ti)C as particle reinforced phase were fabricated by microwave sintering. The effects of the fraction of (W,Ti)C and sintering temperature on the mechanical properties, phase transformation and microstructure of Si₃N₄-based ceramics were investigated. The frictional characteristics of the microwave sintered Si₃N₄-based ceramics were also studied. The results showed that the (W,Ti)C would hinder the densification and phase transformation of Si₃N₄ ceramics, while it enhanced the aspect-ratio of β-Si₃N₄ which promoted the mechanical properties. The Si₃N₄-based composite ceramics reinforced by 15 wt% (W,Ti)C sintered at 1600 °C for 10 min by microwave sintering exhibited the optimum mechanical properties. Its relative density, Vickers hardness and fracture toughness were 95.73 ± 0.21%, 15.92 ± 0.09 GPa and 7.01 ± 0.14 MPa m^1/2, respectively. Compared to the monolithic Si₃N₄ ceramics by microwave sintering, the sintering temperature decreased 100 °C,the Vickers hardness and fracture toughness were enhanced by 6.7% and 8.9%, respectively. The friction coefficient and wear rate of the Si₃N₄/(W,Ti)C sliding against the bearing steel increased initially and then decreased with the increase of the mass fraction of (W,Ti)C., and the friction coefficient and wear rate reached the minimum value while the fraction of (W,Ti)C was 15 wt%.     

Effect of grain size on tribological behavior of hot-pressed boron carbide sliding against alumina balls

Boron carbide ceramics (B₄C) have extraordinary hardness and well-abrasive resistance, while the tribological behavior of ceramic materials is complicated, which are affected by microstructures, mechanical properties, and surface characteristics, and so on. In this paper, the effect of grain size on the mechanical properties especially the wear resistance of hot-pressed B₄C was investigated. The average coefficient of friction of the B₄C/Al₂O₃ friction pair ranges from .41 to .66. The sample with the minimum grain size possesses the lowest wear rate of about 2.15 × 10⁻⁶–7.66 × 10⁻⁶ mm³∙N⁻¹∙m⁻¹. The analysis of the wear rate (W_R) and grain size (G) indicates that the wear resistance (W_R⁻¹) and the reciprocal of the square root of grain size (G^−1/2) are in line with the Hall–Petch relation. Fracture and the resulting abrasive wear are the main wear mechanisms of B₄C in the dry sliding process. This success provides a theoretical basis and a design approach of microstructure to improve the tribological behavior of ceramic materials.     

Preparation and performance of an advanced multiphase composite ceramic material

According to the optimum composition achieved from the material design, an advanced 15 vol.% SiC and 15 vol.% Ti(C,N) containing alumina-based multiphase ceramic material with good comprehensive mechanical properties has been fabricated with hot pressing technique. Only under suitable hot pressing conditions and material compositions can better microstructures and mechanical properties be achieved. The optimum hot pressing parameters for the SiC/Ti(C,N)/Al₂O₃ material are as follows: the hot pressing temperature is 1780 °C, the time duration equals to 60 min and the pressure remains 35 MPa. The content of each dispersed SiC and Ti(C,N) phase has significant effects not only on the mechanical properties but on the engineering performances of the ceramic materials. Good wear resistance is found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel. Failure mechanisms are mainly the abrasive wear and the adhesive wear. The developed SiC/Ti(C,N)/Al₂O₃ multiphase ceramic material will be well used as the structural parts with the requirement of high wear resistance such as cutting tools.     

Microstructure,wear and corrosion characteristics of multiple-reinforced (SiC–B4C–Al2O3) Al matrix composites produced by liquid metal infiltration

In this study, AA7075 aluminum matrix composites reinforced with the combination of SiC, Al₂O₃, and B₄C particles were fabricated by the liquid metal infiltration method. The effects of the relative ratio of B₄C and Al₂O₃ particles on the microstructural, wear, and corrosion features of the composite samples were analyzed using XRD, light metal microscopy, SEM, EDS, Brinell hardness, ball-on-disc type tribometer, and potentiodynamic polarization devices. It was determined that infiltration occurred more successfully, and homogenously distributed particles with reduced porosity were obtained as the amount of Al₂O₃ increased. Worn surface studies revealed that the specimens were predominantly worn by abrasion and adhesion. The increase in B₄C/Al₂O₃ ratio caused a decrease in the hardness and wear strength, whereas it increased the corrosion resistance.     

Dry sliding wear behaviour of ZrB2-based ceramics: Self-mated and cross coupling with alumina

Systematic dry sliding wear tests with monolithic ZrB₂ and Al₂O₃ pins coupled to ZrB₂, ZrB₂-20 vol% SiC and Al₂O₃ discs were carried out in a disc-on-pin configuration. The steady state friction of ZrB₂ self-mated or cross coupled with Al₂O₃ was about 1.1. Self-mated monolithic ZrB₂ discs worn about three orders of magnitude more than self-mated Al₂O₃ discs. ZrB₂ pin wear rate was almost double when coupled to ZrB₂ or ZrB₂-20 vol% SiC discs than when coupled to Al₂O₃ discs. The wear track of ZrB₂-based materials showed an oxygen increment due to humidity-driven tribo-reaction. In all the systems, the main wear mechanisms observed were microfracture and abrasion. Numerical calculations and fracture models were employed to describe the wear mechanisms. By nanoindentation tests on worn and unworn areas, a significant lower hardness of the debris layer formed when ZrB₂ materials were involved.     

Fibrous monolithic ceramic with a single alumina phase: Fracture and high-temperature tribological behaviors

Fabrication of fibrous monolithic ceramic with bamboo-like structures is a promising method to improve the mechanical properties of ceramics through extrinsic reinforcement. Nevertheless, heterogeneous boundaries are easily oxidized at high temperatures, which seriously limits the long-term use of these materials when employed in high-temperature and high/low-temperature alternating environments. In this study, a “plain” ceramic—a single-component and complex-structure Al₂O₃ ceramic—was successfully designed and prepared using nano-sized Al₂O₃ as polycrystalline fibers and micro-sized Al₂O₃ as boundaries to obtain a structure with a fibrous monolithic architecture. Self-toughening of Al₂O₃ ceramics can be achieved by introducing hierarchical architectures derived from the difference between grain sizes of fibers and boundaries, which gives the ceramics high fracture toughness and reliability. Moreover, the material demonstrated a low friction coefficient and high wear-resistance properties when coupled with C/C composites at room temperature, 800°C, and in the alternating temperature enviroment between room temperature and 800°C.     

Influence of LaMgAl11O19 On Solid Particle Impact Erosion Wear Behavior of 3YSZ Ceramic at Elevated Temperatures

To study the improvement in solid particle impact erosion wear resistances of 3 mol% yttria‐stabilized zirconia (3YSZ) ceramic at elevated temperatures up to 1400°C, 2 wt% LaMgA1₁₁O₁₉ was added into 3YSZ to prepare LaMgA1₁₁O₁₉‐3YSZ ceramic for erosion resistance tests with angular corundum abrasive particles. The testing results show that the volume erosion rates of 3YSZ and LaMgA1₁₁O₁₉‐3YSZ ceramic were similar in the temperature range from room temperature to 600°C, then exhibited a sharp increase from 600°C to 1200°C, and dropped again at 1400°C. It was mainly caused by the change in material removal mechanisms from plastic deformation below 600°C to the interaction of transverse cracks in the temperature range from 600°C to 1400°C. The solid particle impact erosion wear properties of 3YSZ ceramic in the temperature range from 600°C to 1400°C were successfully improved by the addition 2 wt% LaMgA1₁₁O₁₉ platelets. Comparing with the volume erosion rate of pure 3YSZ ceramic (0.687 mm³/g) at 1200°C, the value of LaMgA1₁₁O₁₉‐3YSZ ceramic (0.551 mm³/g) has been decreased by 20%.