MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagatin...MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis （SHS）. Pure MoSi2 was obtained and a compound of MoSi2 and WSi2was synthesized in the form of predominant solid solution （Mo,W）Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2and hexagonal C40 Mo（Si,Al）2. The （Mo,W）Si2-Mo（Si,Al）2-W（Si,Al）2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.展开更多
The in situ synthesized MoSi2-SiC composite is proved to be of higher fracture toughness than the monolithic MoSi2. The TEM and HREM study reveals that the interface between MoSi2/SiC is of direct atomic bonding witho...The in situ synthesized MoSi2-SiC composite is proved to be of higher fracture toughness than the monolithic MoSi2. The TEM and HREM study reveals that the interface between MoSi2/SiC is of direct atomic bonding without any amorphous glassy phase, such the SiO2 structure. Based on the fractography and the observation of crack propagation path from indentation, it is concluded that the toughening of such composite at room temperature can be attributed to the high interfacial binding energy, the refinement of the MoSi2 matrix and the deflection and bridging behavior in the crack propagation.展开更多
Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardnes...Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardness testing belong to the Palmquist crack system. The value of highest fracture toughness of MoSi 2+ZrO 2+SiC composite is 7.58?MPa·m 1/2 , which is nearly three times that of monolithic MoSi 2. This can be attributed to well distributed ZrO 2 and SiC particles along the boundaries of very fine MoSi 2 grains.展开更多
The compressive creep behavior at 1?200 ～ 1?400?℃ of an in situ synthesized MoSi 2 30%SiC (volume fraction) composite and a traditional PM MoSi 2 30%SiC (volume fraction) composite is investigated. The creep rate of...The compressive creep behavior at 1?200 ～ 1?400?℃ of an in situ synthesized MoSi 2 30%SiC (volume fraction) composite and a traditional PM MoSi 2 30%SiC (volume fraction) composite is investigated. The creep rate of the in situ synthesized MoSi 2 30%SiC (volume fraction) composite is about 10 -7 s -1 under stress of 60 ～ 120?MPa, and significantly lower than that made by PM method above 1?300?℃. The reason is that the interface between SiC particle and MoSi 2 matrix in in situ synthesized SiC p/MoSi 2 is of direct atomic bonding without any amorphous glassy phase, such as SiO 2 structure. Creep deformation occurs primarily by dislocation motion and the dislocations have Burgers vectors of the type of <110> and <100>.展开更多
A composites of (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> + 15vol% ZrO<sub>2</sub> was prepared with powder metallurgy and Pressure- Less Sintering (PLS) method, ...A composites of (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> + 15vol% ZrO<sub>2</sub> was prepared with powder metallurgy and Pressure- Less Sintering (PLS) method, aiming at applications of high temperature structural materials. Mechanical properties of the composites were assessed with hardness, indentation fracture toughness K<sub>c</sub> and K<sub>IC</sub> tested using SEVNB, flexure strength at room temperature and 1200?C, and isothermal oxidation at 1400?C. The results showed that the native silica oxide and molybdenum-oxides on the silicide feedstock surface were significantly reduced in terms of Cr-alloying. (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> and its composite also exhibited improved sinterability and grain growth, owing to the presence of (Cr, Mo)<sub>5</sub>Si<sub>3</sub> at grain boundaries. Fracture toughness of the composite was increased by a factor of 1.6 to that in the monolithic silicide. Mechanical property of the composite at high temperature was not affected by Cr addition. However, the high temperature oxidation resistance was greatly improved in the (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> + 15vol% ZrO<sub>2</sub> compared with the non Cr-alloyed counterpart. The Cr-alloying effects on the microstructure, fracture behaviour, and high temperature oxidation resistance were discussed.展开更多
基金This project was financially supported by the National Natural Science Foundation of China (No. 50025412)
文摘MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis （SHS）. Pure MoSi2 was obtained and a compound of MoSi2 and WSi2was synthesized in the form of predominant solid solution （Mo,W）Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2and hexagonal C40 Mo（Si,Al）2. The （Mo,W）Si2-Mo（Si,Al）2-W（Si,Al）2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.
基金the National Natural Science Foundation of China (No. 59895150-04-02).
文摘The in situ synthesized MoSi2-SiC composite is proved to be of higher fracture toughness than the monolithic MoSi2. The TEM and HREM study reveals that the interface between MoSi2/SiC is of direct atomic bonding without any amorphous glassy phase, such the SiO2 structure. Based on the fractography and the observation of crack propagation path from indentation, it is concluded that the toughening of such composite at room temperature can be attributed to the high interfacial binding energy, the refinement of the MoSi2 matrix and the deflection and bridging behavior in the crack propagation.
文摘Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardness testing belong to the Palmquist crack system. The value of highest fracture toughness of MoSi 2+ZrO 2+SiC composite is 7.58?MPa·m 1/2 , which is nearly three times that of monolithic MoSi 2. This can be attributed to well distributed ZrO 2 and SiC particles along the boundaries of very fine MoSi 2 grains.
文摘The compressive creep behavior at 1?200 ～ 1?400?℃ of an in situ synthesized MoSi 2 30%SiC (volume fraction) composite and a traditional PM MoSi 2 30%SiC (volume fraction) composite is investigated. The creep rate of the in situ synthesized MoSi 2 30%SiC (volume fraction) composite is about 10 -7 s -1 under stress of 60 ～ 120?MPa, and significantly lower than that made by PM method above 1?300?℃. The reason is that the interface between SiC particle and MoSi 2 matrix in in situ synthesized SiC p/MoSi 2 is of direct atomic bonding without any amorphous glassy phase, such as SiO 2 structure. Creep deformation occurs primarily by dislocation motion and the dislocations have Burgers vectors of the type of <110> and <100>.
文摘A composites of (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> + 15vol% ZrO<sub>2</sub> was prepared with powder metallurgy and Pressure- Less Sintering (PLS) method, aiming at applications of high temperature structural materials. Mechanical properties of the composites were assessed with hardness, indentation fracture toughness K<sub>c</sub> and K<sub>IC</sub> tested using SEVNB, flexure strength at room temperature and 1200?C, and isothermal oxidation at 1400?C. The results showed that the native silica oxide and molybdenum-oxides on the silicide feedstock surface were significantly reduced in terms of Cr-alloying. (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> and its composite also exhibited improved sinterability and grain growth, owing to the presence of (Cr, Mo)<sub>5</sub>Si<sub>3</sub> at grain boundaries. Fracture toughness of the composite was increased by a factor of 1.6 to that in the monolithic silicide. Mechanical property of the composite at high temperature was not affected by Cr addition. However, the high temperature oxidation resistance was greatly improved in the (Mo<sub>0.9</sub>Cr<sub>0.1</sub>)Si<sub>2</sub> + 15vol% ZrO<sub>2</sub> compared with the non Cr-alloyed counterpart. The Cr-alloying effects on the microstructure, fracture behaviour, and high temperature oxidation resistance were discussed.
