The microstructures and mechanical properties of Al matrix composites reinforced by different volume fractions of Al-Ni-Co intermetallic particles were investigated.Three different volume fractions of Al-Ni-Co particl...The microstructures and mechanical properties of Al matrix composites reinforced by different volume fractions of Al-Ni-Co intermetallic particles were investigated.Three different volume fractions of Al-Ni-Co particles were added to pure Al matrix using a stir-casting method.Microstructural analysis shows that with the increasing of the reinforcement volume fraction,the matrix grain size decreases and the porosity increases.The mechanical properties of the composites are improved over the matrix materials,except for the decreasing of the ductility.Fracture surface examination indicates that there is a good interfacial bonding between the Al matrix and the Al-Ni-Co particles and the fracture initiation does not occur at the particle-matrix interface.展开更多
The main Iimitation to the toughening of the α-Al2O3/Ni composite is the poor bonding atthe interface. which causes the nickel particles to be pulled-out during crack propagation with-out obvious plastic deformation....The main Iimitation to the toughening of the α-Al2O3/Ni composite is the poor bonding atthe interface. which causes the nickel particles to be pulled-out during crack propagation with-out obvious plastic deformation. A proper control of oxygen content at the Al2O3-Ni interfacecan promote wetting at the intedece, and produce a mechanically interlocked and chemically strengthened intedece, causing most of the nickel particles to be stretched to failure and to expe-rience severe plastic deformation during crack propagation in the composite. Fracture toughnesstesting using a modified double cantilever beam method with in situ observation of crack prop-agation in a scanning electron microscope shows that the composite with the strengthenedinterface has a more desirable R-curve behaviour and a higher fracture toughness value than thenormal composite.展开更多
Composites are materials that are made up of two or more chemically dissimilar phases. In this project aluminum was chosen as matrix material because it was inexpensive, light-weight, strong, tough and corrosion resis...Composites are materials that are made up of two or more chemically dissimilar phases. In this project aluminum was chosen as matrix material because it was inexpensive, light-weight, strong, tough and corrosion resistant. For the main load bearing phase it was hard, corrosion resistant at room temperature and thermally stable. The stir casting method was used because it was cost-effective and easy, and the particulate reinforcement (nickel) was uniformly distributed throughout the matrix phase. Sand moulding was used to cast the specimens. Specimens with 10, 20, 30 and 40 percentage Nickel were tested and the optimal specimen contained 20% Nickel. The Brinell hardness of Al + 20% Ni increased by 14.80%, Rockwell hardness increased by 2.43%, ultimate tensile strength increased by 1.003% and thermal conductivity of Al + 20% Ni decreased by 24.98% with respect to Aluminum.展开更多
The initiation and propagation of the short fatigue crack in a 10vol% titanium carbide particulate reichreed cast Fe-26Cr-14Ni mathe coopsite at 1023K were investigated.It is shown that the titanium carbide particulat...The initiation and propagation of the short fatigue crack in a 10vol% titanium carbide particulate reichreed cast Fe-26Cr-14Ni mathe coopsite at 1023K were investigated.It is shown that the titanium carbide particulate may hinder the crack propagation and fatigue fracture of the composite. The relationships between fatigue crack propagation rate and stress intensity factor are da/dN=4.2×10-c(△K)4 for the matrix alloy and da/dN=1.4×10-19(△K)c for the composite. The fatigue thresholds of the composite and mathe alloy are 78 and 3.2MPa.m1/2, respectively. Microcracks initiate at the intedece between titanium carbide particulate and austenite and then propagate in carkide particles. The fracture sudece of the composite shows a distinct transition from wavy and serated cleavage near the threshold regime to striation-type splitting in the stable fatigue crack propagation stage and to a veined morphology characteristic in unstable rapid region.展开更多
Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating und...Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.展开更多
Electroformed diamond tools have been used for many years in grinding and cutting fields while electrodeposited diamond composite coatings have been widely studied due to their desirable hardness,wear and corrosion re...Electroformed diamond tools have been used for many years in grinding and cutting fields while electrodeposited diamond composite coatings have been widely studied due to their desirable hardness,wear and corrosion resistance.This article reports the detrimental impact of diamond magnetism on the composites microstructure and gives explanations.Microstructure differences between composites that,respectively,contained no-further-treated diamond,magnetism-strengthening treated diamond and magnetism weakening treated diamond were carefully observed.It is shown that diamond magnetization treatment drastically harms the composite microstructure(e.g.,roughening the coating surface,coarsening the matrix grain,and more seriously,reducing the mechanical retention of diamond grains in the matrix) while demagnetization treatment does the opposite.All the observed facts could be explained by the electromagnetic interaction between magnetic fields produced by magnetic diamond grains and electric current(moving cations) during the electrodeposition process.展开更多
基金Project(50571081)supported by the National Natural Science Foundation of ChinaProject(04G53024)supported by the Aviation Foundation of China
文摘The microstructures and mechanical properties of Al matrix composites reinforced by different volume fractions of Al-Ni-Co intermetallic particles were investigated.Three different volume fractions of Al-Ni-Co particles were added to pure Al matrix using a stir-casting method.Microstructural analysis shows that with the increasing of the reinforcement volume fraction,the matrix grain size decreases and the porosity increases.The mechanical properties of the composites are improved over the matrix materials,except for the decreasing of the ductility.Fracture surface examination indicates that there is a good interfacial bonding between the Al matrix and the Al-Ni-Co particles and the fracture initiation does not occur at the particle-matrix interface.
文摘The main Iimitation to the toughening of the α-Al2O3/Ni composite is the poor bonding atthe interface. which causes the nickel particles to be pulled-out during crack propagation with-out obvious plastic deformation. A proper control of oxygen content at the Al2O3-Ni interfacecan promote wetting at the intedece, and produce a mechanically interlocked and chemically strengthened intedece, causing most of the nickel particles to be stretched to failure and to expe-rience severe plastic deformation during crack propagation in the composite. Fracture toughnesstesting using a modified double cantilever beam method with in situ observation of crack prop-agation in a scanning electron microscope shows that the composite with the strengthenedinterface has a more desirable R-curve behaviour and a higher fracture toughness value than thenormal composite.
文摘Composites are materials that are made up of two or more chemically dissimilar phases. In this project aluminum was chosen as matrix material because it was inexpensive, light-weight, strong, tough and corrosion resistant. For the main load bearing phase it was hard, corrosion resistant at room temperature and thermally stable. The stir casting method was used because it was cost-effective and easy, and the particulate reinforcement (nickel) was uniformly distributed throughout the matrix phase. Sand moulding was used to cast the specimens. Specimens with 10, 20, 30 and 40 percentage Nickel were tested and the optimal specimen contained 20% Nickel. The Brinell hardness of Al + 20% Ni increased by 14.80%, Rockwell hardness increased by 2.43%, ultimate tensile strength increased by 1.003% and thermal conductivity of Al + 20% Ni decreased by 24.98% with respect to Aluminum.
文摘The initiation and propagation of the short fatigue crack in a 10vol% titanium carbide particulate reichreed cast Fe-26Cr-14Ni mathe coopsite at 1023K were investigated.It is shown that the titanium carbide particulate may hinder the crack propagation and fatigue fracture of the composite. The relationships between fatigue crack propagation rate and stress intensity factor are da/dN=4.2×10-c(△K)4 for the matrix alloy and da/dN=1.4×10-19(△K)c for the composite. The fatigue thresholds of the composite and mathe alloy are 78 and 3.2MPa.m1/2, respectively. Microcracks initiate at the intedece between titanium carbide particulate and austenite and then propagate in carkide particles. The fracture sudece of the composite shows a distinct transition from wavy and serated cleavage near the threshold regime to striation-type splitting in the stable fatigue crack propagation stage and to a veined morphology characteristic in unstable rapid region.
基金This research was financially supported by the Major Project of National Natural Science Foundation of China(No.50235030)the National 973 Planning Project(No.G1999065009)+1 种基金the Science and Technology Cooperation Project between China and Poland Governments in 2002(No.2002M3)their supports are gratefully acknowledged.
文摘Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.
基金This work was supported by Henan Agricultural University,the Natural Science Foundation of Henan Province(0411051300)the Project for Excel-lent University Teachers under the supervision of Henan Provincial Bureau of Education.
文摘Electroformed diamond tools have been used for many years in grinding and cutting fields while electrodeposited diamond composite coatings have been widely studied due to their desirable hardness,wear and corrosion resistance.This article reports the detrimental impact of diamond magnetism on the composites microstructure and gives explanations.Microstructure differences between composites that,respectively,contained no-further-treated diamond,magnetism-strengthening treated diamond and magnetism weakening treated diamond were carefully observed.It is shown that diamond magnetization treatment drastically harms the composite microstructure(e.g.,roughening the coating surface,coarsening the matrix grain,and more seriously,reducing the mechanical retention of diamond grains in the matrix) while demagnetization treatment does the opposite.All the observed facts could be explained by the electromagnetic interaction between magnetic fields produced by magnetic diamond grains and electric current(moving cations) during the electrodeposition process.
