Increasing SiC Content Research Articles

Study on Strengthening of Mullite by Dispersion of Carbide Ceramics Particles.

Both mullite/SiC (0.27 μm and 1.20 μm) and mullite/TiC composite ceramics were prepared by hot-pressing at 1650°C under 35 MPa for 4h. Room-temperature bending strength, Young's modulus, Vicker's hardness and fracture toughness were investigated as functions of SiC and TiC volume fractions (0-20%). Grain growth of mullite was prevented by the existence of dispersed particles (SiC, TiC) in the matrix. As a result, bending strength of both mullite/SiC and mullite/TiC composite ceramics was improved. In the case of the mullite/SiC system, bending strength increased with increasing SiC content and showed a maximum value of 604 MPa at 20 vol%, which was about 80% higher than that of monolithic mullite. On the other hand, fracture toughness of mullite/TiC ceramic composite was observed to increase from 2.65 to 3.9 MPa√(m) with the addition of 20 vol% TiC. Correspondingly, the bending strength increased from 330-410 MPa. The strengthening mechanism by thermal treatment in air was also investigated for mullite/SiC composite ceramics and it was concluded to be useful to increase bending strength. Detailed research on the microstructure showed that a Hall-Patch relationship was recognized for grain size and bending strength.

Microstructure and mechanical properties of yttria-stabilised tetragonal zirconia polycrystals (Y-TZP) containing dispersed silicon carbide particles

Abstract The microstructure and mechanical properties of pressureless sintered and subsequently hot isostatic pressed Y-TZP ceramics containing up to 20 vol% of SiC particles were studied. The grain growth of the ZrO 2 matrix was not significantly affected by SiC additions. It was found that the hardness, Young's modulus and fracture toughness K IC increased, and the bending strength, σ b , decreased with increasing SiC content. The maximum K IC and σ b were 7·8 MPa√m and 849 MPa, respectively. Silicon carbide additions caused increased flaw sizes, and reduced thermal stability of tetragonal zirconia during low-temperature ageing. The dominant toughening mechanism was microcracking. Stress-induced phase transformation played only a secondary role.

ＳｉＣ粒子強化アルミニウム合金基複合材料の被削性

Aluminum alloy matrix composite materials are expected to be used for various applications because of the low density and superior properties at high temperatures. However, the composite materials give problems in the tool wear because of their difficulty in cutting. In this work the turning test for SiC particle reinforced aluminum alloy composite materials was performed and the effects of SiC particle size and content on the tool wear and surface roughness were discussed. The tool wear increased with increasing SiC particle size and content. Only the diamond tool was useful to cut the SiC particle reinforced aluminum alloy composite material. In the case of using a carbide tool, the cutting condition should be low cutting speed as well as high feed rate. To suck the chips during cutting was effective to decrease the tool wear. In the wet cutting, however, to suck the chips resulted in the increased tool wear. While the increased SiC particle size resulted in the worsened surface roughness, the increased SiC content improved the surface roughness.

Effects of sic content on fatigue crack growth in Aluminum Alloys Reinforced with SiC Particles

An experimental study has been conducted with the purpose of examining the fatigue crack growth characteristics of cast aluminum alloy matrix composites reinforced with different vol- ume fractions of silicon carbide particles. Particular attention has been paid to developing com- posite microstructures with similar matrix aging condition, precipitation, matrix strength, reinforcement particle size distribution, and interfacial characteristics but with different con- trolled amounts of reinforcement particles. Fatigue crack growth experiments have been con- ducted using constant stress amplitude methods with a fixed load ratio as well as constant Kmax control involving a varying load ratio. The development of crack closure and the microscopic path of the crack through the composite microstructure are monitored optically and using the electron microscope in an attempt to examine the mechanisms of fatigue fracture. The results indicate that an increase in SiC content results in the suppression of striation formation in the ductile matrix. Although ductile matrix failure involving the formation of striations in the low SiC content composite or of void growth in the high SiC content composite is evident, the results also show that fracture of the reinforcement particles plays a significant role in dictating the rates of fatigue crack growth. Detailed quantitative analyses of the extent of particle fracture as a function of the reinforcement content have been performed to elucidate the mechanistic origins of fatigue resistance. The propensity of particle fracture increases with particle size and with the imposed value of stress intensity factor range. While discontinuously reinforced metal- matrix composites with predominantly matrix cracking are known to exhibit superior fatigue crack growth resistance as compared to the unreinforced matrix alloy, the tendency for particle fracture in the present set of experiments appears to engender fatigue fracture characteristics in the composite which are inferior to those seen in the unreinforced matrix material. Particle fracture also results in noticeable differences in the microscopic fracture path and causes a reduction in crack closure in the composites as compared to that in the matrix alloy. The results of this work are discussed in light of other related studies available in the literature in an attempt to develop a mechanistic perspective on fatigue crack growth resistance in metal-matrix composites.

Mechanical Properties and Microstructure of Si<sub>3</sub>N<sub>4</sub> Matrix Composite with Nano-Meter Scale SiC Particles

Si3N4 matrix composites with dispersed SiC particles were prepared by hot-pressing compacts of powder mixtures of sub-micron size SiC and Si3N4 particles. SiC particles in nano-meter scale were dispersed uniformly inside Si3N4 grains. After adding SiC particles, the configuration of β-Si3N4 grains changed from equiaxed/platelet-like to rod-like structure. At 20vol% SiC, grains were fine and equiaxed. With increasing SiC content, the α- to β-phase transformation was suppressed, and relative density was decreased. On the other hand, the bending strength reached a maximum value at 10vol% SiC and fracture toughness was maximum at 5vol% SiC. These changes are related closely to the shape of Si3N4 grains and relative density. Young's modulus was minimum at 5vol% SiC. This seems to be caused by the disorder of the interface structure between SiC and Si3N4. Vickers hardness was constant up to 10vol% SiC and increased beyond it.

Effect of dispersion parameters and cold deformation on recrystallisation of Al–SiC composites

The effect of SiC whisker concentration (1–4 vol.-%), Al2O3 fine particle size and concentration (f/r=0·25–0·5 μm−1f volume concentrationr radius of particles), and degree of deformation by cold rolling (50–90%) on the recrystallisation behaviour and grain size in Al–SiC composites was studied. The result is of general interest as the Al–Al2O3–SiC composite is an alloy system with stable coarse and fine particles, the parameters of which can be varied independently over a wide range. The microstructure in the cold rolled state and initial stages of recrystallisation was examined using transmission electron microscopy. The recrystallisation temperature in different composites was determined by microhardness measurement after an isochronal heat treatment. The average grain size and grain size distribution in fully recrystallised composites were measured. It was found that the SiC whiskers act as strong nucleation sites and also enhance dynamic recovery, whereas the Al2O3 fine particles have the opposite effect. The number density of nuclei and the recrystallisation temperature were greatly affected by Al2O3 concentration and degree of cold deformation. The average grain size and the width of the grain size distribution decreased with increasing SiC content and decreasing f/r ratio of Al2O3 particles. These results were discussed and related to the effect of the parameters studied on critical nuclei size, nucleation rate, nuclei-whisker interaction, and grain growth.MST/1270

無電解Ｎｉ‐Ｐ‐ＳｉＣ複合めっき皮膜の性質

Composite coatings consisting of SiC particles of 1, 5 and 10μm, codeposited into an electroless nickel matrix were produced, and their physical properties were sutdied. The hardness of the coatings increased with increasing SiC content, and remained about equal for coatings of the same SiC content irrespective of particle size. The coatings were found to have excellent wear resistance, but this decreased with increased in particle size, and with heat treatment at 673K. The coatings were also found to have excellent wear resistance when applied to parts of a wire twisting machine.

電析法によるＳｉＣ複合Ｎｉ‐Ｐ非晶質合金めっきの作製について

SiC composite Ni-P alloys were electrodeposited from normal Watt's type baths in which 20-160g/L SiC powder was suspended. The SiC particles were easily codeposited using baths containing H3PO3. Uniformity of the particle dispersion in the deposit, and the soundness of the interface between SiC and the amorphous Ni-P matrix were examined by scanning and transmission electron microscopes. The thermal stability of the amorphous Ni-P matrix in the composite alloys was studied by differential scanning calorimetry. Vickers hardness tests were also done to study the effects of SiC content and heat treatment. It was found that 1) Composite Ni-P-SiC alloys containing 3.5-7.2wt%SiC were obtained by suspending 20-160g/L SiC in the electrolytic bath; 2) The crystallization temperature of the amorphous matrix decreased with an increase in SiC content; 3) The hardness of the amorphous Ni-P deposites tended to increase slightly with an increase in SiC content. These deposits hardened greatly after being heat treated up to 450°C.

Solid Particle Erosion of Brittle Materials (Part 6)

Al2O3-SiC composites containing up to 30wt% SiC particle or whisker were hot-pressed at 1500°-1850°C for 1h under 25MN·m-2, and their erosive wear was studied using SiC and Al2O3 abrasives. The erosion rate of Al2O3-SiC composites decreased with an increase in SiC content regardless of the abrasive. The erosion rate of Al2O3 containing 30wt% SiC whisker was four times smaller than that for pure Al2O3. The decrease in erosion rate was related to the increase of hardness and fracture toughness of composites due to SiC addition. The composites were considered to be homogeneous from erosive wear characteristics.

Sintering and HIPping of silicon nitride-silicon carbide composite materials

Si 3N 4 composite materials containing up to 60 vol.% of dispersed β-SiC particles were sintered with Y 2O 3 and Al 2O 3 at 1850°C and 0·1 MPa N 2. Fractional density decreased from 0·97 to 0·91 when the SiC content increased from 0 to 60 vol.%. Simultaneously a retardation of grain growth and reduced pore size was found. Subsequent HIPping at 2000°C with N 2-pressure of 100 MPa resulted in almost complete elimination of presintered closed pores and a final density of 0·99 up to 20 vol.% of SiC. During HIPping Si 3N 4 is formed by reaction of SiC or C with the SiO 2 intergranular glass in the presence of high N 2-pressure. While fracture toughness shows no significant influence of SiC content, a reduction of critical defect size with increasing SiC content results in a distinct increase of fracture strength particularly after HIPping.

Structure and Mechanical Properties of Codeposited Pyrolytic C‐SiC Alloys

Alloys of pyrolytic carbon and silicon codeposited in beds of fluidized particles were investigated. X‐ray diffraction measurements revealed only two phases, turbostratic C and β‐SiC. Since the C crystallites are oriented randomly, the C was macroscopically isotropic, with apparent crystallite sizes in the range found for pure C deposited under similar conditions. Transmission and scanning electron microscopy showed that the SiC was generally distributed as small particles which tended toward larger particles and continuous laminations at high SiC concentrations. The fracture stress and Young's modulus were measured in 3‐point bending; they increased continuously with increasing SiC content from values for pure isotropic carbons to values for chemically‐vapor‐deposited SiC.