Based on YU’s solids and molecules emperical electron theory(EET), interface valence electron structure of TiC-Fe3Al composites was set up, and the valence electron density of different atomic states TiC and Fe3Al co...Based on YU’s solids and molecules emperical electron theory(EET), interface valence electron structure of TiC-Fe3Al composites was set up, and the valence electron density of different atomic states TiC and Fe3Al composites in various planes was determined. The results indicate that the electron density of (1 00)Fe3Al is consistent with that of (110)TiC in the first-class a pproximation, the absolute value of minimum electron density difference along the interface is 0.007 37 nm?2, and the relative value is 0.759%. (1 10)TiC //(100)Fe3Al preferred orientation is believed to benefit the formation of the cuboidal shape TiC. In the other hand, it shows that the particle growth is accompanied by the transport of electron, the deviation continuity of electron density intrinsically hinders the grain growth. The electron density of (100)TiC is not consistent with Fe3Al arbitrary crystallographic plane, thus it well explains that the increased titanium and carbon contents do not increase the size of large particles. The crystallographic orientation of (1 10)TiC //(100)Fe3Al will improve the mechanical properties. Therefore interface electron theory is an effective theoretical implement for designing excellent property of composites.展开更多
TiC/Ni_3Al composites have been prepared using upward infiltration method. The densification was performed by both Ni_3Al melt filling and TiC sintering during the infiltration. The dissolution of TiC in liquid Ni_3A...TiC/Ni_3Al composites have been prepared using upward infiltration method. The densification was performed by both Ni_3Al melt filling and TiC sintering during the infiltration. The dissolution of TiC in liquid Ni_3Al has been evidenced by finding Ni_3(Al,Ti)C after fast cooling in the TiC/Ni_3Al composites. The dissolution may be responsible for the infiltration and sintering. Compared with downward infiltration, the upward infiltration brought about higher strength and fracture toughness and shorter infiltration time. TiC/20 vol. pct Ni_3Al composite processed by upward infiltration had a flexural strength of 1476 MPa with a statistic Weibull modulus of 20.2 and a fracture toughness of 20.4 MPa . Better mechanical properties may be attributed to melt unidirectional movement in upward infiltration.展开更多
The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was disc...The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference （ΔT） and number of thermal cycles （Ⅳ） on fatigue crack growth （Δa）. The mechanical properties and thermal fatigue resistance of TiC/Al203 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a ＂true＂ cycling effect （thermal fatigue）. Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.展开更多
Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were...Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m(1/2) at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.展开更多
Pressureless melt infiltration is an economic route f or preparation of high-density ceramic/melt composites. In this study, the Fe40 Al iron aluminide intermetallic, a low cost material of excellent oxidation and cor...Pressureless melt infiltration is an economic route f or preparation of high-density ceramic/melt composites. In this study, the Fe40 Al iron aluminide intermetallic, a low cost material of excellent oxidation and corrosion resistance, was used as binder for fabricating Fe40Al/TiC composites b y pressureless melt infiltration. The wetting ability of liquid Fe40Al in porous TiC pre-form was studied by in-situ monitoring the melting and infiltration p rocess. The infiltration ability was investigated by observing the distance of l iquid Fe40Al intrusion in porous TiC pre-forms at different infiltration temper atures and times by using optical microscope. Porous TiC per-forms with density of 60%～88%TD (theoretical density), prepared under pre-defined sintering temp e rature cycles, were used for fabricating Fe40Al/TiC composites in the range of 1 2%～40% metal content by volume. Almost full dense Fe40Al/TiC composites were su c cessfully fabricated by this technique. Liquid Fe40Al exhibited excellent infilt ration ability, the distance of complete intrusion of liquid Fe40Al in the TiC s intered pre-form with density of 88%TD was over 7 mm after 5 min at the inf iltration temperature of 1 450 ℃. Microstructural observation by SEM and TEM also showed that liquid Fe40Al filled the very narrow gaps among TiC particles, the interfaces of TiC particles and F e40Al plastic ligaments being metallurgical bonded. TEM revealed that high densi ty of dislocations formed in Fe40Al ligaments during solidification, which favor the mechanical properties. Ti decomposed from TiC particles and dissolved into Fe40Al during infiltration. According to the compositional analysis of TEM-EDS, the concentration of Ti in Fe40Al ranges at 1at%～4at% depending on composite f a bricating conditions and the distance from the measuring point to the closest Ti C particles. XRD analysis indicated that the composites were composed of two pha ses, the original TiC and Fe 0.4Al 0.6 intermetallic. No new phase formed during infiltration, but the lattice parameter of Fe 0.4Al 0.6 was expended due to the Ti in the solid solution.展开更多
Ceramic tapes, containing Al2O3-25 wt pct TiB2(B) and Al2O3-25 wt pct nano-TiC (c), have been obtained by tape casting process. Numerous tapes (about 60～80 tapes) were prepared by stacking in turn the composition (B)...Ceramic tapes, containing Al2O3-25 wt pct TiB2(B) and Al2O3-25 wt pct nano-TiC (c), have been obtained by tape casting process. Numerous tapes (about 60～80 tapes) were prepared by stacking in turn the composition (B) and (C), laminating under 10 MPa pressure, eliminating the solvent and burning out the polymer additives. The final green bodies were hot pressed at 1750℃ and 30 MPa. The composite has a bending strength of 568 MPa and a fracture toughness of 5.8 M Pa·m1/2. SEM analysis exhibits that Al2O3 particle growth was inhibited by TiC particles in C. but TiB2 particles could not hinder Al2O3 growth in B. The curves of GTA indicates that all organic additives could be removed completely above 600℃展开更多
When Cr, Mo and Ti were added to Fe Al/Al 2O 3 composite, the bending strength and fracture toughness of the composite were increased sharply. The highest value of bending strength can exceed 600 MPa and the average v...When Cr, Mo and Ti were added to Fe Al/Al 2O 3 composite, the bending strength and fracture toughness of the composite were increased sharply. The highest value of bending strength can exceed 600 MPa and the average value of fracture toughness exceed 12 MPa·m 1/2 . With increasing content of Mo and Ti, the bending strength and fracture toughness both express the trend of increasing first and then decreasing. When the alloying elements were added to the composites the alloying extent is improved. The fracture mode of the composites are mainly transcrystalline.展开更多
The creep behaviour of β-Si3N4 whisker reinforced Al-8.5Fe-1.3V-1.7Si composite has been investigated at the temperature 773 and 823 K. The results are characterized by high stress exponent and high apparent creep ac...The creep behaviour of β-Si3N4 whisker reinforced Al-8.5Fe-1.3V-1.7Si composite has been investigated at the temperature 773 and 823 K. The results are characterized by high stress exponent and high apparent creep activation energy The creep data can be interpreted based on the incorporation of a threshold Stress and a load transfer coefficient into the power-law creep equation. A good correlation between the normalized creep rate and normalized effective stress is available which demonstrates that the creep behaviour of both the alloy and the composite is controlled by the matrix lattice self-diffusion in AI. EXamination on microstructure shows that edge dislocations exist at the interfaces between two adjacent whiskers and the intedeces emit edge dislocations in parallel paired-columns.展开更多
A new hardfacing process, reactive braze coating process (RBCC) was studied, and (TiC+Cr_3C_2)/Fe composite coatings were prepared by RBCC using carbon, Cr_3C_2, iron, ferrochromium and titanium powder as the raw mate...A new hardfacing process, reactive braze coating process (RBCC) was studied, and (TiC+Cr_3C_2)/Fe composite coatings were prepared by RBCC using carbon, Cr_3C_2, iron, ferrochromium and titanium powder as the raw materials in vacuum braze furnace. The results show that TiC is in-situ synthesized in the coatings. The methods of introducing Cr_3C_2 have great effects on the distribution of TiC. Adding Cr_3C_2 directly to the raw materials for coatings, fine TiC particles aggregate into discoids parallel to the coating surface, whereas, in-situ synthesizing Cr_3C_2 in coatings, the aggregations of TiC are lumpish. During braze coating, Cr_3C_2 particles directly added dissolve and precipitate to become needle-shaped. The coatings have an even and smooth surface and are combined with their mild steel substrates by a metallurgical bonding.展开更多
基金Project(Q99F01) supported by the Natural Science Foundation of Shandong Province, China
文摘Based on YU’s solids and molecules emperical electron theory(EET), interface valence electron structure of TiC-Fe3Al composites was set up, and the valence electron density of different atomic states TiC and Fe3Al composites in various planes was determined. The results indicate that the electron density of (1 00)Fe3Al is consistent with that of (110)TiC in the first-class a pproximation, the absolute value of minimum electron density difference along the interface is 0.007 37 nm?2, and the relative value is 0.759%. (1 10)TiC //(100)Fe3Al preferred orientation is believed to benefit the formation of the cuboidal shape TiC. In the other hand, it shows that the particle growth is accompanied by the transport of electron, the deviation continuity of electron density intrinsically hinders the grain growth. The electron density of (100)TiC is not consistent with Fe3Al arbitrary crystallographic plane, thus it well explains that the increased titanium and carbon contents do not increase the size of large particles. The crystallographic orientation of (1 10)TiC //(100)Fe3Al will improve the mechanical properties. Therefore interface electron theory is an effective theoretical implement for designing excellent property of composites.
文摘TiC/Ni_3Al composites have been prepared using upward infiltration method. The densification was performed by both Ni_3Al melt filling and TiC sintering during the infiltration. The dissolution of TiC in liquid Ni_3Al has been evidenced by finding Ni_3(Al,Ti)C after fast cooling in the TiC/Ni_3Al composites. The dissolution may be responsible for the infiltration and sintering. Compared with downward infiltration, the upward infiltration brought about higher strength and fracture toughness and shorter infiltration time. TiC/20 vol. pct Ni_3Al composite processed by upward infiltration had a flexural strength of 1476 MPa with a statistic Weibull modulus of 20.2 and a fracture toughness of 20.4 MPa . Better mechanical properties may be attributed to melt unidirectional movement in upward infiltration.
文摘The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference （ΔT） and number of thermal cycles （Ⅳ） on fatigue crack growth （Δa）. The mechanical properties and thermal fatigue resistance of TiC/Al203 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a ＂true＂ cycling effect （thermal fatigue）. Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.
文摘Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m(1/2) at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.
文摘Pressureless melt infiltration is an economic route f or preparation of high-density ceramic/melt composites. In this study, the Fe40 Al iron aluminide intermetallic, a low cost material of excellent oxidation and corrosion resistance, was used as binder for fabricating Fe40Al/TiC composites b y pressureless melt infiltration. The wetting ability of liquid Fe40Al in porous TiC pre-form was studied by in-situ monitoring the melting and infiltration p rocess. The infiltration ability was investigated by observing the distance of l iquid Fe40Al intrusion in porous TiC pre-forms at different infiltration temper atures and times by using optical microscope. Porous TiC per-forms with density of 60%～88%TD (theoretical density), prepared under pre-defined sintering temp e rature cycles, were used for fabricating Fe40Al/TiC composites in the range of 1 2%～40% metal content by volume. Almost full dense Fe40Al/TiC composites were su c cessfully fabricated by this technique. Liquid Fe40Al exhibited excellent infilt ration ability, the distance of complete intrusion of liquid Fe40Al in the TiC s intered pre-form with density of 88%TD was over 7 mm after 5 min at the inf iltration temperature of 1 450 ℃. Microstructural observation by SEM and TEM also showed that liquid Fe40Al filled the very narrow gaps among TiC particles, the interfaces of TiC particles and F e40Al plastic ligaments being metallurgical bonded. TEM revealed that high densi ty of dislocations formed in Fe40Al ligaments during solidification, which favor the mechanical properties. Ti decomposed from TiC particles and dissolved into Fe40Al during infiltration. According to the compositional analysis of TEM-EDS, the concentration of Ti in Fe40Al ranges at 1at%～4at% depending on composite f a bricating conditions and the distance from the measuring point to the closest Ti C particles. XRD analysis indicated that the composites were composed of two pha ses, the original TiC and Fe 0.4Al 0.6 intermetallic. No new phase formed during infiltration, but the lattice parameter of Fe 0.4Al 0.6 was expended due to the Ti in the solid solution.
文摘Ceramic tapes, containing Al2O3-25 wt pct TiB2(B) and Al2O3-25 wt pct nano-TiC (c), have been obtained by tape casting process. Numerous tapes (about 60～80 tapes) were prepared by stacking in turn the composition (B) and (C), laminating under 10 MPa pressure, eliminating the solvent and burning out the polymer additives. The final green bodies were hot pressed at 1750℃ and 30 MPa. The composite has a bending strength of 568 MPa and a fracture toughness of 5.8 M Pa·m1/2. SEM analysis exhibits that Al2O3 particle growth was inhibited by TiC particles in C. but TiB2 particles could not hinder Al2O3 growth in B. The curves of GTA indicates that all organic additives could be removed completely above 600℃
文摘When Cr, Mo and Ti were added to Fe Al/Al 2O 3 composite, the bending strength and fracture toughness of the composite were increased sharply. The highest value of bending strength can exceed 600 MPa and the average value of fracture toughness exceed 12 MPa·m 1/2 . With increasing content of Mo and Ti, the bending strength and fracture toughness both express the trend of increasing first and then decreasing. When the alloying elements were added to the composites the alloying extent is improved. The fracture mode of the composites are mainly transcrystalline.
文摘The creep behaviour of β-Si3N4 whisker reinforced Al-8.5Fe-1.3V-1.7Si composite has been investigated at the temperature 773 and 823 K. The results are characterized by high stress exponent and high apparent creep activation energy The creep data can be interpreted based on the incorporation of a threshold Stress and a load transfer coefficient into the power-law creep equation. A good correlation between the normalized creep rate and normalized effective stress is available which demonstrates that the creep behaviour of both the alloy and the composite is controlled by the matrix lattice self-diffusion in AI. EXamination on microstructure shows that edge dislocations exist at the interfaces between two adjacent whiskers and the intedeces emit edge dislocations in parallel paired-columns.
文摘A new hardfacing process, reactive braze coating process (RBCC) was studied, and (TiC+Cr_3C_2)/Fe composite coatings were prepared by RBCC using carbon, Cr_3C_2, iron, ferrochromium and titanium powder as the raw materials in vacuum braze furnace. The results show that TiC is in-situ synthesized in the coatings. The methods of introducing Cr_3C_2 have great effects on the distribution of TiC. Adding Cr_3C_2 directly to the raw materials for coatings, fine TiC particles aggregate into discoids parallel to the coating surface, whereas, in-situ synthesizing Cr_3C_2 in coatings, the aggregations of TiC are lumpish. During braze coating, Cr_3C_2 particles directly added dissolve and precipitate to become needle-shaped. The coatings have an even and smooth surface and are combined with their mild steel substrates by a metallurgical bonding.
