Si3N4 Ceramic Ball Research Articles

Tailored carburization gradient microstructure and enhanced wear properties of M50NiL steel via introduced prior cold rolling

M50NiL (Chinese grade G13Cr4Mo4Ni4V) steel is widely used in aircraft bearing raceways that require excellent wear resistance under harsh service conditions. However, the impact of cold rolling, as an advanced forming process for bearings, on the carburization process and wear properties is still unknown. Therefore, the gradient microstructure and dry sliding wear performance of the cold-rolled M50NiL disc against Si3N4 ceramic ball have been investigated. The results show that with the increase of cold rolling reduction to 40 %, the carbon concentration of surface is increased by 17.1 % due to the growing percentage of grain boundaries (GB) and dislocation density. The carbide content is increased by 29 % with average size declined by 21.2 %, which contributes to a 7.4 % increase in the surface hardness. Additionally, the wear test indicates that the average friction coefficient and wear rate are respectively reduced by 17.3 % and 47.1 % when the rolling reduction increases to 40 %. After prior rolling, the wear mechanism changes from severe abrasion to adhesion and tribochemical reactions accompanied with the enhancement of wear properties, which is mainly attributed to the uniform distribution of finer carbides with higher fraction on the surface and subsurface.

Study on the preparation of CeO2-doped AlCoCrFeNiTi high entropy alloy bioinert coatings by laser cladding: The effect of CeO2 particle size on the tribological properties of the coatings

The AlCoCrFeNiTi high entropy alloy (HEA) bioinert wear-resistant coatings reinforced by doping CeO2 particles were prepared on the surface of Ti6Al4V via laser cladding technique. In order to find out the effect of CeO2 particle size on the tribological properties of AlCoCrFeNiTi HEA coatings, the coatings doped with 1 wt% nano, submicron, and micron CeO2 particles were prepared respectively. The phase composition and microstructure of the coatings were analyzed, and the fracture toughness values of the coatings were tested. Friction and wear properties of the coatings sliding against Si3N4 ceramic grinding balls were tested under dry friction and wet friction (simulated body fluid, SBF) conditions, respectively. The results showed that the CeO2 particle size had a significant impact on the wear mechanisms of the coating and thereby improved its tribological properties. Doping with submicron CeO2 particles had the most significant improvement on the tribological properties of the coatings, followed by micron CeO2 particles, and doping with nano CeO2 particles had the weakest improvement on the tribological properties of the coatings. The distribution of submicron CeO2 particles in the coating was more dispersed and uniform, which significantly reduced the crack sensitivity of the coatings, inhibited the peeling off of the oxide film on the coating surfaces, and played a lubricating role. Under dry friction and SBF conditions, the friction coefficient of the coatings doped with submicron CeO2 particles decreased by 41.81% and 27.27%, respectively, and the wear resistance increased by 55.14% and 50.69%, respectively. This study has important reference value for the development of new bioinert wear-resistant coatings.

Study on wear behavior and mechanism of 6007 Si3N4 full-ceramic ball bearing under different load conditions

This study investigated the effects of various load conditions on the wear characteristics of Si3N4 full-ceramic ball bearings in response to 6007 Si3N4 full-ceramic ball bearing operation-related wear problems. Using an ABLT-1A tester, the wear behavior of 6007 Si3N4 ceramic ball bearings was investigated under loads of 100, 500, and 800 N, with a rotation speed of 6000 r/min and a duration of 12,000 min. The test load, and the 100 and 500 N radial loads had an equilibrium temperature difference of about 1.91°C, while the 500 and 800 N radial loads exhibited an equilibrium temperature difference of about 2.35°C. Each group’s temperature rate difference is evident. Bearing internal clearance increased by 35.7%, 50.34%, and 56.1%, respectively, and the fault frequencies of the bearing elements appeared within the vibration signal. The surface roughness of each component of the bearing increased with the increase in the test load, while a large number of plow grooves and spalling appeared on the surface, and severe cage wear was observed. Results show that when load, temperature, clearance, runout, and frequency domain amplitude increased, the following were observed: development of rolling body surface spalling and a large area of wear spot; raceway surface crater along the direction of movement of the fur-row; obvious scratches were observed on the cage surface in the pocket hole edge melting phenomenon; the cage became the bearing system’s "weak link.” The test results are a reference value for the wear behavior of Si3N4 full-ceramic ball bearings under this test load.

Surface tribological and electrochemical properties of TiAlSiN coating in seawater

To investigate the effects of friction surface and electrochemical properties on the tribological behavior of TiAlSiN coatings in seawater, the tribological properties of TiAlSiN coatings in air and seawater are comparatively studied using a ball-on-disk tribometer with Si3N4 ceramic balls as the counter material. The results show that under both friction conditions, the wear rate of TiAlSiN coating is decreased compared with 316 l steel substrate, and the coating presents a good protective effect. When friction occurs in air, the abrasive debris in the wear area cannot be discharged in time, resulting in the accumulation of abrasive debris and accelerating the wear of the coating. When friction occurs in seawater, although seawater is corrosive, the lubricating barrier surface formed by the friction oxide during the friction process significantly reduces the wear rate of the coating. In addition, the excellent electrochemical properties and the dense coating microstructure improve the tribocorrosion resistance of the TiAlSiN coating in seawater. It proves that friction surface has a great impact on the tribological performance of TiAlSiN coatings, and how to form a more favorable friction layer in the tribochemical environment is worthy of further research in the field of marine equipment.

Effect of CH4 Flow Rate on the Tribological Behaviors of TiCN Films against Si3N4 Ceramic and Steel Ball

Control of the structural, mechanical and tribological properties of TiCN films play an important role in its numerous applications, including the cutting tools, mechanical components, aeronautical and biomedical engineering industries. Direct-current magnetron sputtering (DCMS) system was applied to deposit TiCN films onto n-type silicon (100) at room temperature. The Ti-TiN interlayer was used to enhance the adhesive strength between the coating and the substrate. The composition and microstructure of the TiCN films were studied using X-ray photoelectron spectroscopy (XPS) and field-emitted scanning electron microscopy (FESEM). The mechanical properties of the films as a function of methane (CH4) flow ratio were then characterized using nano-indentation measurements. The tribological behavior of TiCN films was investigated by UMT-2MT tribometer against a Si3N4 ceramic and AISI52100 steel ball. After the tribological tests, the wear rate of the films was obtained by the 3D surface profiler and the component content of wear debris was evaluated by energy dispersive X-ray spectroscopy (EDS). The results show that the tribological properties of TiCN films are a function of CH4 flow rates. The film obtained at a 10 sccm CH4 flow rate possesses a minimum average COF value of 0.1964 and reaches 72,000 cycles against a Si3N4 ball over the test duration. Furthermore, the wear rate was only 2.076 × 10−6 mm3/N·m. Furthermore, the TiCN films exhibited longer lifespan against the Si3N4 ball than against the steel ball under the normal load of 1 N, indicating that the TiCN films present better lubricative properties when against low-hardness counterparts than high-hardness counterparts.

The Effect of High-Velocity Air-Fuel WC-12Co Coatings on the Wear and Corrosion Resistance of TC18 Titanium Alloy

TC18 titanium alloy is an essential material for aircraft landing gear. To reveal the wear and corrosion mechanisms of landing gear in service, a WC-12Co coating on a TC18 substrate was prepared by High-Velocity Air-Fuel (HVAF) spraying based on optimized process parameters, and an analysis of the microscopic characterization results for the materials involved was performed. Based on the computational fluid dynamics (CFD) method, the combustion reaction and discrete phase models of HVAF spraying were established. The flame characteristics under compressible turbulence and the flight temperature and velocity of particles were calculated. The effect of the spraying parameters on the flight temperature and velocity of particles was evaluated based on the response surface method (RSM) through multiple groups of orthogonal experiments, and the optimized process parameters were determined. The mass flow rate of reactants was 0.051 kg/s, the oxygen/fuel ratio was 2.83, the mass flow rate of the nitrogen was 0.000325 kg/s, the pressure of oxygen and fuel inlet was 1 MPa, the pressure at the particles inlet was 0.6 MPa and the maximum temperature and velocity of spraying particles were 1572 K and 417 m/s, respectively. The coatings prepared with the optimized process were subjected to the Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), wear, hardness, artificial seawater soaking and neutral salt spray experiments. The results showed that the mean hardness of the TC18 substrate was 401.2 HV0.3, the mean hardness of the WC-12Co coating was 1121 HV0.3, the friction coefficient between the TC18 substrate and the Si3N4 ceramic ball was 0.55 and the friction coefficient between the WC-12Co coating and the Si3N4 ceramic ball was 0.4. Compared to the TC18 substrate, the hardness of the WC-12Co coating was increased by 720 HV0.3, the friction coefficient with the Si3N4 ceramic ball decreased by 0.11, the corrosion resistance significantly improved and the maximum depth of the corrosion pits was 5 μm. The properties of the TC18 titanium alloy were effectively improved by the WC-12Co coating. The results of this study provide guidance for surface protection technologies of aircraft landing gear.

Research on the Roundness Approximation Search Algorithm of Si3N4 Ceramic Balls Based on Least Square and EMD Methods

This paper aims to obtain the best shape accuracy evaluation algorithm for silicon nitride ceramic balls after lapping, and to extract the initial signal of the ball surface to improve the accuracy and reliability of the algorithm. The research methods of this paper are as follows: Firstly, an analysis of the uniform envelope of the lapping trajectory of ceramic balls is carried out to verify whether the lapping trajectory after processing can achieve a consistent envelope on the balls' surface. On this basis, it is found through experiments that the standard deviation SD between the roundness deviations of different contour sections is small. The value is maintained at approximately 0.03 μm, and the roundness deviation can approximately replace the spherical deviation. Then the different contour sections of the sphere are sampled by the Taylor roundness instrument. Considering the uncertainty, the sampling points of different contour sections are averaged and used as the original signal of the sphere surface. Then the EMD method is used to process the signal to be detected on the sphere surface. The initial signal of the sphere surface is extracted by judging whether the number of ripples Kc obtained by decomposition is greater than the critical value. Then the initial signal is used as the input value of the approximation algorithm. Through the roundness deviation approximation algorithm based on the least square method, the given minimum approximation domain range is finely processed. The divided fine points are used as the center of the circle to intersect with the initial signal. The maximum, minimum, and range of each circle are calculated to obtain the roundness error based on the minimum circumscribed circle, the maximum inscribed circle, and the minimum region method. Finally, the calculated values are compared with those obtained by the traditional algorithm. The experimental results of this paper show that the algorithm is consistent with the roundness error measured by the instrument, compared with the mainstream evaluation criteria. In summary, the conclusions can be drawn as follows: Through a large number of experimental cases and comparative experiments, the algorithm has high accuracy and reliability. The research results of this paper have essential reference significance for accurately evaluating the shape accuracy of ceramic balls in actual production.

Investigation of cryogenic friction and wear properties of Invar 36 alloy against Si3N4 ceramic balls

The existing materials for liquefied natural gas (LNG) cryogenic submersible pump bearings are very susceptible to wear and failure in LNG environments where oil lubricants and greases are ineffective, posing a major hazard to the safety of LNG storage and transportation. Therefore, searching for a type of material with excellent cryogenic tribological properties for improving the life of LNG bearings has become a huge challenge for researchers. Invar 36 alloy, as a low expansion nickel-titanium alloy, is used in control instruments, moulds, laser control equipment, and materials of LNG transport hull at temperatures below −162 °C. However, there is a lack of research data in the field of bearings. Currently, the Si3N4 ceramic balls are widely used in ceramic hybrid ball bearings and exhibit excellent tribological properties. In this work, the tribological performance of Invar 36 alloy is mainly investigated against Si3N4 ceramic ball under extremely cryogenic and dry conditions using the modified ball-on-disk tribometer with a cryogenic module, with temperatures as low as −196 °C. All experiments are performed at loads of 0.5 N, 1 N, 1.5 N, and 2 N, and at temperatures of 20 °C, 0 °C, −78 °C, and −196 °C, respectively. The experimental results show that the coefficient of friction (COF) and wear rate decrease with temperature and load, with a minimum value of −196 °C. The Invar 36 alloy exhibits excellent tribological properties, whose COF decreases gradually from 20 °C to −78 °C. However, as the temperature drops to −196 °C, the COF decreases abruptly, reaching a minimum value at −196 °C. On the contrary, the COF gradually increases with load. In addition, a commercial bearing grade material (G95Cr18 steel) is tested and compared under the same conditions, proving that Invar 36 alloy exhibits better tribological properties than G95Cr18 steel, with a wear rate 55.43% lower than G95Cr18 steel at −196 °C. Further simulation comparisons demonstrate that, due to its extremely low coefficient of thermal expansion, Invar 36 alloy exhibits higher toughness and strength than G95Cr18 steel under cryogenic conditions. This study complements the tribological data of Invar 36 alloy and G95Cr18 steel against Si3N4 ceramic balls under different temperatures and loads and provides important theoretical guidance and technical support for the bearings’ future development of LNG cryogenic submersible pump.

Tribological properties and wear mechanisms of TixVNbTaWy RHEAs sliding against Si3N4 ceramic balls: The effects of Ti and W contents

Three new TixVNbTaWy RHEAs with different contents of Ti and W were prepared by mechanical mixing and spark plasma sintering. The effects of Ti and W contents on the mechanical and tribological properties were explored, with a focus on the wear mechanisms of the alloys sliding against Si3N4 ceramics from room temperature to 900 °C. The results showed that all three alloys exhibited high compressive strength and plastic strain of > 12% at room temperature. More crucially, the wear rate of the optimized alloy can be as low as 6.8 × 10−6 mm3/(N·m) at 600 °C. Friction-induced subsurface strengthening and the formation of continuous oxide films and plastic deformation layers played an important role in reducing the wear rate.

Abrasion Power of Ti and Ni Diamond-Coated Coatings Deposited by Cold Spray

In this work, the cold spray technique was used to deposit nickel and titanium coated diamond powder on cast iron and aluminum substrates. To analyze the deposition mechanism, the diamond powders were observed before and after the process using a microscope and scanning electron microscope (SEM). The adhesion response of the Ni and Ti coatings was investigated during the study. Pin-on-disk tests were then performed to identify the abrasion mechanism of the coated samples and the wear resistance of the Si3N4 ceramic balls. Experimental tests were adopted to determine the significant operating variables, i.e., the local linear speed and the applied load. The modification of the diamond particles in shape, distribution, and the residual debris of Si3N4 on disk were compared before and after the tribological test to analyze the abrasion and wear resistance of the ceramic balls.

Adaptive finite element simulation and experimental verification for fretting wear of PVDF piezoelectric thin films

An adaptive finite element method linked with user-defined subroutine UMESHMOTION is developed for simulating the tangential fretting wear of PVDF piezoelectric thin films. The three-dimensional (3D) sphere-on-flat contact model is established for the fretting wear simulation by using commercial software ABAQUS, where the Si3N4 ceramic ball is used as the punch in contact with PVDF piezoelectric thin films. The variable friction coefficient obtained from experiments is taking into consideration. The calculation of wear is based on the Archard's wear model. The tangential fretting motion with different loads and variable friction coefficients are applied in the finite element simulation. The fretting wear test are carried out to verify the numerical results under the same conditions. The results indicate that the present adaptive finite element model has a certain accuracy comparable to the experiment results for the fretting wear of PVDF piezoelectric thin films.

Wear behaviour of gradient-multilayer diamond coatings deposited on cemented-carbide substrates

ABSTRACT HFCVD method was used to prepare and characterize single and gradient multi-layered diamond coatings on tungsten carbide. The wear behaviour was evaluated in ambient air, against Si3N4 ceramic balls. The results demonstrated that with the increase of carbon-source concentration from 1% to 5%, the diamond surface grains gradually refined and formed crystal clusters, and the roughness (Ra) of diamond surface decreased from 62.3 to 32.54 nm. Concerning the 100, 300, and 600 nm gradient of multilayer diamond coatings, the roughness Ra was 31.3, 35.6, and 40.5 nm, respectively. The diamond film obtained with 1% CH4 concentration exhibited poor wear resistance. For higher CH4 concentration, the abrasion resistance increased gradually. The average friction coefficient of multilayer diamond coatings decreased from 0.052 to 0.023 as the modulated layer thickness increased from 100 to 600 nm. The gradient multilayer structure significantly improved the tribological behaviour.

Preparation and high-temperature tribological performance of laser clad MoNi coatings with chromium addition

In order to enhance the wear resistance of MoNi matrix coatings at elevated temperature, high-temperature wear resistant MoNi matrix coatings with different Cr contents (3.0 wt%, 7.0 wt% and 11.0 wt%) were prepared on the 718 alloy substrate by laser cladding. The high-temperature tribological performance was investigated sliding against Si3N4 ceramic ball by using ball-on-disk tribo-tester from room temperature to 1000 °C. The effects of chromium addition on the microstructure and the tribological performance of coatings were systematically studied. The coatings with dendritic structure consisted of Mo, Cr9Mo21Ni20 and Cr1.12Ni2.88 phases. The coatings showed a good metallurgical bonding interface with the substrate. There was a critical value of Cr content which could best reinforce the high-temperature wear resistance of MoNi matrix coating. The coating containing 7 wt% Cr had the best wear resistance over a wide temperature range, which was due to the in-situ formed salt compounds, high hardness and oxide lubricating film. The wear mechanism of three coatings transferred from the fatigue wear and abrasive wear to the oxidative wear with the increase in testing temperature.

Improving abrasive wear resistance of Si3N4 ceramics with self-matching through tungsten induced tribochemical wear

Si3N4 ceramics with 0 vol% and 5 vol% tungsten particles were fabricated by gas pressure sintering. Commercial Si3N4 ceramic balls were used as the tribo-pair to test the influence of the tungsten particles on the wear resistance of Si3N4 ceramics. The tungsten particles in the samples were exfoliated and oxidized during the rubbing process. The tungsten oxide was uniformly doped into the wear debris, which turned the harmful exfoliated abrasives into a useful tribo-film. Compared with the monolithic Si3N4 ceramic, the abrasive wear of Si3N4 ceramics with introducing tungsten particles was almost eliminated, and the oxidative wear and surface fatigue were also reduced. The specific wear rate was reduced by more than an order of magnitude, from 4.70 × 10−6 mm3 N−1·m−1 to 3.78 × 10−7 mm3 N−1·m−1.

Microstructure and tribological performance of adaptive MoN–Ag nanocomposite coatings with various Ag contents

MoN–Ag coatings with different silver contents were synthesized using DC and RF magnetron sputtering. The microstructure and mechanical performance of the as-prepared coatings were investigated in detail. The friction and wear behaviors of the MoN–Ag coatings sliding against Si3N4 ceramic ball at RT and elevated temperature were also evaluated by a ball-on-disc tester with rotation method. The results showed that the MoN–Ag coatings were polycrystalline structures composed of γ-Mo2N and c-Ag. And the MoN–Ag coating with a 2.2% Ag content had the highest hardness and elastic modulus. The friction interface between the MoN–Ag coating and Si3N4 ball presented distinct oxidation after sliding at RT. In addition, the temperature greatly impacted the friction and wear behaviors of the MoN and MoN–Ag coatings. The friction coefficients of the investigated coatings decreased gradually when the temperature rose from 100 °C to 700 °C. However, the wear rates displayed opposite trends. The decrease in the friction coefficient for the coatings could be ascribed to the formation of lubricating phases (MoO3, Ag2MoO4, Ag2Mo4O13), while the increases in the wear rate were proven to be due to decreases in the residual compressive stresses of the coatings with increasing temperature. The MoN–Ag coating with 2.2% Ag had excellent tribological properties and an extremely low friction coefficient of 0.27 at 700 °C, which was superior to that of the pure MoN coating.

Si3N4 Ceramic Ball Surface Defects’ Detection Based on SWT and Nonlinear Enhancement

In order to improve the detection accuracy and efficiency of silicon nitride ceramic ball surface defects, a defect detection algorithm based on SWT and nonlinear enhancement is proposed. In view of the small surface defect area and low contrast of the silicon nitride ceramic ball, a machine vision-based nondestructive inspection system for surface images is constructed. Sobel operation is used to eliminate the nonuniform background, and the silicon nitride ceramic ball surface image is decomposed by SWT. And frequency-domain index low-pass filtering is used to modify the decomposition coefficients, and an adaptive nonlinear model is proposed to enhance defects; finally, the image is reconstructed and segmented by the stationary wavelet inverse transform and the dynamic threshold method, respectively. The enhanced algorithm can effectively identify surface defects and is superior to traditional defect detection algorithms.

Comparative study on NiAl and FeAl intermetallic-bonded diamond tools and grinding performance for Si3N4 ceramic

Metal-bonded diamond tools are widely used for machining hard and brittle materials such as ceramic and stone. The metal bonds are normally based on alloys composed of Fe, Co, Ni, Cu, Sn, Zn, or Cr. However, high heavy metal concentrations are hazardous to the environment and tool operators. Furthermore, the high density of these metal bonds results in excessively heavy tools, requiring high energy and intensive labor during operation. Therefore, we propose two environmentally friendly and lightweight metal bonds based on NiAl and FeAl intermetallics for diamond tools by reactive hot-press sintering. The effect of sintering temperature on the microstructure and mechanical properties of NiAl and FeAl was examined and the tribological behavior of NiAl and FeAl on Si3N4 ceramic balls was investigated. Grinding performance of the sintered diamond tools on Si3N4 ceramic was also compared. Our results reveal that B2-ordered NiAl and FeAl are obtained at sintering temperatures in the range of 700–1100 °C. The relative density of sintered NiAl is higher than that of FeAl, while the Vickers hardness and flexural strength of NiAl are lower than that of FeAl. Compared with FeAl, NiAl demonstrates higher wear resistance in a friction test against Si3N4 ceramic, while FeAl-bonded diamond tools demonstrate a higher grinding ratio than NiAl-bonded diamond tools due to enhanced self-sharpening ability. Nevertheless, diamond tools based on both NiAl and FeAl can be used to grind Si3N4 ceramics.

Cyclic fatigue life characteristics of ceramic balls under variable thermal shock loadings

Ceramic balls made of silicon nitride (Si3N4) exhibited excellent mechanical properties are used in high-end components operating at ultra-high speeds, and high and low temperatures. Previously, studies have involved the cyclic mechanical and thermal fatigue tests of ceramic balls under a constant temperature. However, the thermal fatigue characteristics of brittle materials have not been theoretically or experimentally investigated under variable thermal shock loadings to date. Herein, cyclic thermal shock fatigue (CTSF) life characteristics of Si3N4 ceramic balls subjected to single- and two-stage cyclic thermal shock loadings were theoretically and experimentally investigated using a probabilistic model based on slow crack growth concept in conjunction with Weibull distribution. Consequently, the fracture criterion derived from the probabilistic model was related to the linear cumulative damage law (Miner’s rule). Thereafter, the predicted CTSF life of the ceramic balls was compared with the experimental results to validate the proposed probabilistic model. Therefore, the proposed model accurately reproduced the experimental results to a certain extent.

Processing, microstructure and high temperature dry sliding wear of a Cr-Fe-Hf-Mn-Ti-Ta-V high-entropy alloy based composite

High-entropy materials are promising for high-temperature applications. In order to achieve high-temperature wear resistance, a novel high-entropy alloy based composite, (CrMnFeHf)7.14(TiTaV)23.81, was designed and consolidated by spark plasma sintering at 1320 °C following thermodynamic simulations using the CALPHAD method. The microstructure of the sintered composite revealed a Ti30V36Ta19Cr5Mn5Fe4Hf1 body-centered cubic (bcc) high-entropy alloy matrix with C14 Laves phase and carbide particles. The Laves phase and carbide particles of higher hardness were formed in situ during the sintering in a bcc matrix. The dry sliding wear behavior of the composite against Si3N4 ceramic counter ball (10 N, 30 min) from room temperature to 600 °C was investigated. The high-entropy alloy composite showed a superior resistance to wear against Si3N4 ceramic due to the presence of reinforcing C14 laves phase and carbide particles in the high-entropy alloy matrix. Furthermore, the wear rate reduced with increasing temperature. The dominating wear mechanisms of the high-entropy alloy composite were adhesive wear and abrasive wear at room temperature and 200 °C, oxidation wear and abrasive wear at 400 °C and oxidation wear and delamination wear at 600 °C. The formation of multiple oxides, presence of Laves and carbide phase contributed to the low volume loss of high-entropy alloy composite during wear tests at high temperatures.

Effect of particle size of Y2O3-Al2O3 additives on microstructure and mechanical properties of Si3N4 ceramic balls for bearing applications

Si3N4 ceramic balls were prepared by gas pressure sintering with Y2O3 and Al2O3 as sintering additives. The effects of particle size of Y2O3-Al2O3 additives on densification, microstructure and mechanical properties of Si3N4 ceramic balls were investigated. The reliability of Si3N4 ceramic balls was evaluated through the Weibull modulus. The results showed that Si3N4 ceramic balls containing nanosized Y2O3-Al2O3 additives have a higher relative density and better comprehensivemechanical properties compared with the samples containing microsized additives, with relative density of 98.9 ? 0.2%TD, Vickers hardness of 14.7 ? 0.1GPa, indentation fracture toughness of 6.5 ? 0.1MPa?m1/2 and crushing strength of 254 ? 8.5MPa. The more homogeneous and extensive dispersion of the nanosized sintering additives in the Si3N4 matrix is the main reason for the enhancement in density and mechanical properties of the Si3N4 ceramic balls.