Si-Al-Y co-deposition coatings were prepared on Ti-Al alloy by pack cementation processes at 1 050 ℃ for 4 h with different halide activators in the packs for enhancing the high temperature oxidation resistance of Ti...Si-Al-Y co-deposition coatings were prepared on Ti-Al alloy by pack cementation processes at 1 050 ℃ for 4 h with different halide activators in the packs for enhancing the high temperature oxidation resistance of Ti-Al alloy. The structure, constituent phases, formation process and oxidation behavior of the coatings were investigated. The experimental results showed that the coatings prepared respectively with NaF and NH_4Cl as activators were composed of a（Ti, X）_5Si_4,（Ti, X）_5Si_3（X represents Nb and Cr）, and TiSi_2 outer layer, a TiAl_2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi_2 in the outer layer and（Ti, X）_5Si_4 and（Ti, X）_5Si_3 phases were observed in the middle layer of the coating prepared with AlCl_3·6H_2O activator. Among the halide activators studied, the coating prepared with AlCl_3·6H_2O was thicker and denser, which is the only suitable activator for pack Si-Al-Y co-deposition coatings on a Ti-Al alloy. The oxidation results show that the coating can protect the Ti-Al alloy from oxidation at 1000 ℃ in air for at least 80 h. The excellent oxidation resistance of the coating is attributed to the formation of a dense scale mainly consisted of TiO_2, SiO_2 and Al_2O_3.展开更多
A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were st...A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.展开更多
To improve the wear resistance and corrosion resistance of magnesium alloys, a 5 kW continuous wave CO2 laser was used to investigate the laser surface cladding on AZ31 B magnesium alloys with Al-Si/Al2O3-TiO2 composi...To improve the wear resistance and corrosion resistance of magnesium alloys, a 5 kW continuous wave CO2 laser was used to investigate the laser surface cladding on AZ31 B magnesium alloys with Al-Si/Al2O3-TiO2 composite powders. A detailed microstructure, chemical composition, and phase analysis of the composite coatings were studied by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and X-ray diffraction （XRD）. The laser cladding shows good metallurgical bonding with the substrate. The composite coatings are composed of Mgl7Al12, Al3Mg2, Mg2Si, Al2O3, and TiO2 phases. Compared to the average microhardness （50HV0.05） of the AZ3 1 B substrate, that of the composite coatings （230HV0.05） is improved significantly. The wear resistances of the surface layers were evaluated in detail. The results demonstrate that the wear resistances of the laser surface-modified samples are considerably improved compared to the substrate. It also show that the composite coatings exhibit better corrosion resistance than that of the substrate in 3.5wt% NaCI solution.展开更多
The halide-activated pack cementation method is utilized to codeposit aluminum and silicon on Mo substrate. Emphasis is placed on the microstructure and elevated-temperature oxidation resistance of coatings. The resul...The halide-activated pack cementation method is utilized to codeposit aluminum and silicon on Mo substrate. Emphasis is placed on the microstructure and elevated-temperature oxidation resistance of coatings. The results show that hexagonal Mo(Si, Al)2 as a main phase and a little amount of the lower disilicide Mo5Si3 was formed on Mo substrate through the halide-activated pack cementation method. The resultant Si-Al coating on Mo substrate exhibits excellent cyclic oxidation resistance. The excellent cyclic oxidation resistance of the coatings is attributed to the formation of alumina on the coatings during the oxidation.展开更多
The microstructure and wear resistance of a cast Al-Si alloy coated with metal and rare earth elements and treated by the laser rapid melt-solidification(LRMS)are studied in the pres- ent work.Optical and SEM microgra...The microstructure and wear resistance of a cast Al-Si alloy coated with metal and rare earth elements and treated by the laser rapid melt-solidification(LRMS)are studied in the pres- ent work.Optical and SEM micrographic analyses showed that a superfine microstructure was ob- tained,and the hardness was remarkably enhanced by the LRMS treatment.Wear test showed that the rapid melt-solidified microstructure had higher wear resistance than that treated by ordinary solid solution treatment.展开更多
The microstructure and chemical composition of the hot impregnated Al-Si coating on 08Al steel sheet were analysed by SEM,EPMA and X-ray diffraction.The coating consists of three parts:the outer is an α-Al solid solu...The microstructure and chemical composition of the hot impregnated Al-Si coating on 08Al steel sheet were analysed by SEM,EPMA and X-ray diffraction.The coating consists of three parts:the outer is an α-Al solid solution enriched Si and γ-(Fe,Al,Si)phases;the in- termediate FeAl_3 and Fe_2Al_5 phases mainly and the inner neighbouring the substrate mainly Fe_2Al_5 phase.展开更多
The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated...The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated to propose the theoretical basis of search for an optimum of mechanical properties of the high temperature coating on Ni-base alloys.展开更多
Optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer (EDS) and X-ray Diffraction(XRD) were used to study the effects of rare earth on the microstructural characteristics of 55%Al-Zn-...Optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer (EDS) and X-ray Diffraction(XRD) were used to study the effects of rare earth on the microstructural characteristics of 55%Al-Zn-1.6%Si hot -dip coatings on steel.The results of OM,SEM and EDS showed that by adding RE into the 55%Al-Zn-1.6%Si bath,the saw-toothed shape of intermetallic reaction layer of coating became smooth,and the thickness of the overlay and intermetallic reaction layer decreased.The XRD results revealed that the intermetallic reaction layer was comprised of two different regions,a bright phase closest to the steel substrate with phases of Fe_2Al_3 and a dark phase closest to the metallic coating with phases of FeAl_3/α-Fe-Al-Si.展开更多
The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has bee...The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has been observed,and the coating shows significant influence on the fatigue behavior.The difference of elastic modulus between coating and substrate led to the main cracks perpendicular to the loading direction.The coating close to fracture exfoliated thinly,while the coating far away from the fracture kept integrated.Though the specimen was polished to obtain high surface quality,3 types of cracks occurred during the fatigue test.What’s more,inclusion particles were proved to play a crucial role in causing these cracks.展开更多
基金the Key Scientific Research Projects in 2017 at North Minzu University(2017KJ05)
文摘Si-Al-Y co-deposition coatings were prepared on Ti-Al alloy by pack cementation processes at 1 050 ℃ for 4 h with different halide activators in the packs for enhancing the high temperature oxidation resistance of Ti-Al alloy. The structure, constituent phases, formation process and oxidation behavior of the coatings were investigated. The experimental results showed that the coatings prepared respectively with NaF and NH_4Cl as activators were composed of a（Ti, X）_5Si_4,（Ti, X）_5Si_3（X represents Nb and Cr）, and TiSi_2 outer layer, a TiAl_2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi_2 in the outer layer and（Ti, X）_5Si_4 and（Ti, X）_5Si_3 phases were observed in the middle layer of the coating prepared with AlCl_3·6H_2O activator. Among the halide activators studied, the coating prepared with AlCl_3·6H_2O was thicker and denser, which is the only suitable activator for pack Si-Al-Y co-deposition coatings on a Ti-Al alloy. The oxidation results show that the coating can protect the Ti-Al alloy from oxidation at 1000 ℃ in air for at least 80 h. The excellent oxidation resistance of the coating is attributed to the formation of a dense scale mainly consisted of TiO_2, SiO_2 and Al_2O_3.
基金supported by the National "973"Project under grant No. 2006CB600908
文摘A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.
基金Funded by the national Natural Science Foundation of China (No. 51075293)the Foundation for Development of Science and Technology of Taiyuan University of Technology,China(No.K201014)
文摘To improve the wear resistance and corrosion resistance of magnesium alloys, a 5 kW continuous wave CO2 laser was used to investigate the laser surface cladding on AZ31 B magnesium alloys with Al-Si/Al2O3-TiO2 composite powders. A detailed microstructure, chemical composition, and phase analysis of the composite coatings were studied by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and X-ray diffraction （XRD）. The laser cladding shows good metallurgical bonding with the substrate. The composite coatings are composed of Mgl7Al12, Al3Mg2, Mg2Si, Al2O3, and TiO2 phases. Compared to the average microhardness （50HV0.05） of the AZ3 1 B substrate, that of the composite coatings （230HV0.05） is improved significantly. The wear resistances of the surface layers were evaluated in detail. The results demonstrate that the wear resistances of the laser surface-modified samples are considerably improved compared to the substrate. It also show that the composite coatings exhibit better corrosion resistance than that of the substrate in 3.5wt% NaCI solution.
文摘The halide-activated pack cementation method is utilized to codeposit aluminum and silicon on Mo substrate. Emphasis is placed on the microstructure and elevated-temperature oxidation resistance of coatings. The results show that hexagonal Mo(Si, Al)2 as a main phase and a little amount of the lower disilicide Mo5Si3 was formed on Mo substrate through the halide-activated pack cementation method. The resultant Si-Al coating on Mo substrate exhibits excellent cyclic oxidation resistance. The excellent cyclic oxidation resistance of the coatings is attributed to the formation of alumina on the coatings during the oxidation.
文摘The microstructure and wear resistance of a cast Al-Si alloy coated with metal and rare earth elements and treated by the laser rapid melt-solidification(LRMS)are studied in the pres- ent work.Optical and SEM micrographic analyses showed that a superfine microstructure was ob- tained,and the hardness was remarkably enhanced by the LRMS treatment.Wear test showed that the rapid melt-solidified microstructure had higher wear resistance than that treated by ordinary solid solution treatment.
文摘The microstructure and chemical composition of the hot impregnated Al-Si coating on 08Al steel sheet were analysed by SEM,EPMA and X-ray diffraction.The coating consists of three parts:the outer is an α-Al solid solution enriched Si and γ-(Fe,Al,Si)phases;the in- termediate FeAl_3 and Fe_2Al_5 phases mainly and the inner neighbouring the substrate mainly Fe_2Al_5 phase.
文摘The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated to propose the theoretical basis of search for an optimum of mechanical properties of the high temperature coating on Ni-base alloys.
文摘Optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer (EDS) and X-ray Diffraction(XRD) were used to study the effects of rare earth on the microstructural characteristics of 55%Al-Zn-1.6%Si hot -dip coatings on steel.The results of OM,SEM and EDS showed that by adding RE into the 55%Al-Zn-1.6%Si bath,the saw-toothed shape of intermetallic reaction layer of coating became smooth,and the thickness of the overlay and intermetallic reaction layer decreased.The XRD results revealed that the intermetallic reaction layer was comprised of two different regions,a bright phase closest to the steel substrate with phases of Fe_2Al_3 and a dark phase closest to the metallic coating with phases of FeAl_3/α-Fe-Al-Si.
基金National Natural Science Foundation of China （No. 51275185, No. 51405171） National Basic Research Program of China （No. 2010CB630802-3）+1 种基金 Graduate Innovation and Entrepreneurship Fund of Huazhong University of Science and Technology （No. 0109070112） Fundamental Research Funds for the Central Universities （No. 0118110621）
文摘The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has been observed,and the coating shows significant influence on the fatigue behavior.The difference of elastic modulus between coating and substrate led to the main cracks perpendicular to the loading direction.The coating close to fracture exfoliated thinly,while the coating far away from the fracture kept integrated.Though the specimen was polished to obtain high surface quality,3 types of cracks occurred during the fatigue test.What’s more,inclusion particles were proved to play a crucial role in causing these cracks.
