A high temperature embrittlement occures in Fe-15Cr-4AI and Fe-20Cr-4Al alloys treated over 1000 C.It is caused mainly by 475℃ brittleness during cooling.When a secondary treatment at 500℃ was conducted,the 475℃ br...A high temperature embrittlement occures in Fe-15Cr-4AI and Fe-20Cr-4Al alloys treated over 1000 C.It is caused mainly by 475℃ brittleness during cooling.When a secondary treatment at 500℃ was conducted,the 475℃ brittleness developed very rapidly.After only 15 rain of the treating,little plasticity was remained for all samples pretreuted at the temper- atures over 1000℃ and cooled in water.However,no 475℃ brittleness was generated when pretreating temperature was below 1000℃,Addition of Yttrium can inhibit not only grain growth,but also 475℃ brittleness.For the alloys with 0.2—0.4 wt-%Y,after treating at 800—1300℃,the plasticity did not decrease and the properties of furnace cooled samples were not lower than those of water cooled samples.展开更多
The microstructure of a composite coating system, which was composed of an inner layer of Fe-Cr-Al and an outer layer of aluminum, was studied after it was respectively oxidized and sulfurdized at elevated temperature...The microstructure of a composite coating system, which was composed of an inner layer of Fe-Cr-Al and an outer layer of aluminum, was studied after it was respectively oxidized and sulfurdized at elevated temperatures. Apart from the Al2O3 scale formed on the surface, the microstructure of the composite coatings exposed at 900℃ in air for 4h was a three-layer structure. The first layer consisted of a solid solution of Cr and Fe in α aluminum and an intermetallic compound FeAl3 while the second layer was a single phase of the aluminide and the third layer still remained the same appearance as the original Fe-Cr-Al coating. The microstructural observation of the specimen tested at 850-900℃ at low oxygen pressure and high sulfur pressure for 576h revealed that the surface coatings of the specimen had transformed into a duplex structure containing an outer layer and a thicker aluminide layer beneath. X-ray diffraction results showed that the out layer was composed of Al2S3 and Al2O3 and that AlCrFee was the main phase composition of the aluminide layer, with a few of Al2S3 and Al2O3 accompanied.展开更多
The 1100 degreesC isothermal oxidation behavior of Fe-23Cr-5Al alloy modified by yttrium addition was studied by means of thermogravimetric analysis, scanning electron microscopy and energy dispersive X-ray analysis. ...The 1100 degreesC isothermal oxidation behavior of Fe-23Cr-5Al alloy modified by yttrium addition was studied by means of thermogravimetric analysis, scanning electron microscopy and energy dispersive X-ray analysis. Yttrium was added to this alloy in the forms of metallic addition, yttrium oxide and ion implant. Cracking and spalling occurred on the convoluted scale formed on Y-free alloy and exposed the substrate. A flat dense scale without spallation was formed on the yttrium alloying addition or yttrium oxide dispersion alloy. The scale adhesion was also improved by 1x10(17)Y(+)/cm(2)-implantation. The results indicate the convoluted morphology of the scale on Fe-23Cr-5Al-0.21Ti alloy is related to the growth mechanism of the alumina scale, and the spallation of the scale is related to sulfur segregation at the scale/alloy interface. The main reason that the adhesion of alumina scale is improved by yttrium addition lies in the following. Yttrium is liable to form a stable yttrium sulfide with sulfur in the alloy and prevent sulfur interface from segregation. Another reason is that the growth mechanism of alumina scale is changed by yttrium addition.展开更多
文摘A high temperature embrittlement occures in Fe-15Cr-4AI and Fe-20Cr-4Al alloys treated over 1000 C.It is caused mainly by 475℃ brittleness during cooling.When a secondary treatment at 500℃ was conducted,the 475℃ brittleness developed very rapidly.After only 15 rain of the treating,little plasticity was remained for all samples pretreuted at the temper- atures over 1000℃ and cooled in water.However,no 475℃ brittleness was generated when pretreating temperature was below 1000℃,Addition of Yttrium can inhibit not only grain growth,but also 475℃ brittleness.For the alloys with 0.2—0.4 wt-%Y,after treating at 800—1300℃,the plasticity did not decrease and the properties of furnace cooled samples were not lower than those of water cooled samples.
文摘The microstructure of a composite coating system, which was composed of an inner layer of Fe-Cr-Al and an outer layer of aluminum, was studied after it was respectively oxidized and sulfurdized at elevated temperatures. Apart from the Al2O3 scale formed on the surface, the microstructure of the composite coatings exposed at 900℃ in air for 4h was a three-layer structure. The first layer consisted of a solid solution of Cr and Fe in α aluminum and an intermetallic compound FeAl3 while the second layer was a single phase of the aluminide and the third layer still remained the same appearance as the original Fe-Cr-Al coating. The microstructural observation of the specimen tested at 850-900℃ at low oxygen pressure and high sulfur pressure for 576h revealed that the surface coatings of the specimen had transformed into a duplex structure containing an outer layer and a thicker aluminide layer beneath. X-ray diffraction results showed that the out layer was composed of Al2S3 and Al2O3 and that AlCrFee was the main phase composition of the aluminide layer, with a few of Al2S3 and Al2O3 accompanied.
文摘The 1100 degreesC isothermal oxidation behavior of Fe-23Cr-5Al alloy modified by yttrium addition was studied by means of thermogravimetric analysis, scanning electron microscopy and energy dispersive X-ray analysis. Yttrium was added to this alloy in the forms of metallic addition, yttrium oxide and ion implant. Cracking and spalling occurred on the convoluted scale formed on Y-free alloy and exposed the substrate. A flat dense scale without spallation was formed on the yttrium alloying addition or yttrium oxide dispersion alloy. The scale adhesion was also improved by 1x10(17)Y(+)/cm(2)-implantation. The results indicate the convoluted morphology of the scale on Fe-23Cr-5Al-0.21Ti alloy is related to the growth mechanism of the alumina scale, and the spallation of the scale is related to sulfur segregation at the scale/alloy interface. The main reason that the adhesion of alumina scale is improved by yttrium addition lies in the following. Yttrium is liable to form a stable yttrium sulfide with sulfur in the alloy and prevent sulfur interface from segregation. Another reason is that the growth mechanism of alumina scale is changed by yttrium addition.
