Stress distribution around Fe₅Si₃ and its effect on interface status and mechanical properties of Si₃N₄ ceramics

Abstract

Si3N4 ceramics with different amount of Fe5Si3 were prepared by adding FeSi2. Residual thermal stress distribution and elastic energy around Fe5Si3 particles in various depths were calculated. The interface status between second phase particles and matrix was analyzed in terms of stress and energy. High tangential compressive stresses and low radial tensile stresses were generated along the surface of the ceramics. Elastic strain energy caused by unit interface was high around big particles in deep area of the ceramics. Microcracks are observed around the big Fe5Si3 particles. Furthermore, accord to our calculation, microcracks are easily generated around particles in superficial layer of matrix when second phase particles have lower thermal expansion coefficient than the matrix, while microcracks tend to be generated in deep layer of matrix preferentially when the thermal expansion coefficient of second phase particles is higher than matrix. Residual stresses and microcracks around Fe5Si3 particles greatly influenced mechanical properties. Fracture toughness of Si3N4 ceramics with similar Si3N4 particle size distribution increased with the amount of Fe5Si3, and fine Fe5Si3 particles could enhance the strength of Si3N4 ceramics. Si3N4 ceramics exceeding 1.2 GPa strength were prepared.

In situ synthesis of cobalt silicide particle reinforcing and coloring Si3N4 ceramics

“…As a comparison, the apparent interfacial debonding (Figure 4E,F) is found in the sintered sample with 2.5 mol% CoO. The corresponding cracks may result from the high residual thermal stress, caused by the large CTE difference between CoSi x and Si 3 N 4 , and lead to the decrease of samples strength correspondingly 10,16 …”

“…The reinforcing mechanism of particles derives from the residual stress, induced by different coefficient of thermal expansion (CTE) with the matrix, which may generate flaws to consume some fracture energy and improve fracture toughness 29 . Coincidentally, cobalt silicide exhibits a much higher thermal expansion coefficient (11 × 10 −6 K −1 ) than Si 3 N 4 (3.2 × 10 −6 K −1 ) 16 . Thermal residual stress generated around the interface has a great effect on the mechanical properties of materials.…”

“…[6][7][8][9] However, the boring gray color cannot satisfy consumers' pursuit for colorful appearance of back plate. According to considerable research results, [10][11][12][13][14][15][16] Si 3 N 4 could react sensitively with many metals (Co, Cr, Mo, etc.) and some metallic oxides (MoO 3 , Fe 2 O 3 , etc.…”

“…29 Coincidentally, cobalt silicide exhibits a much higher thermal expansion coefficient (11 × 10 −6 K −1 ) than Si 3 N 4 (3.2 × 10 −6 K −1 ). 16 Thermal residual stress generated around the interface has a great effect on the mechanical properties of materials. Additionally, cobalt silicide has lower density (approximates to 4.95 g/cm 3 at room temperature) and higher thermal conductivity than most metals.…”

Microstructure and Mechanical Properties of Si3N4-Fe3Si Composites Prepared by Gas-Pressure Sintering

“…For instance, using Ni 3 Al intermetallic compound as a second phase, an Al 2 O 3 composite with high strength and high toughness can be prepared [25]. Toughening effects that result from intermetallic particles can be attributed to crack deflection, crack bridging, plastic deformation [26,27], and residue stress caused by a coefficient of thermal expansion (CTE) mismatch [28]. Among the component of Fe-Si 3 N 4 , not only Si 3 N 4 , but also Fe 3 Si—which is an intermetallic compound—have good thermal mechanical properties [29,30].…”