Trace rare earth elements were used in order to strengthen the Sn60 Pb40 solder alloy. The experimental results show that the high temperature tensile strength of near eutectic Sn60 Pb40 solder alloy is increased b...Trace rare earth elements were used in order to strengthen the Sn60 Pb40 solder alloy. The experimental results show that the high temperature tensile strength of near eutectic Sn60 Pb40 solder alloy is increased by about 70% after adding trace rare earth elements. Analysis shows that the high affinity between rare earth element and Sn leads to the variation of contact angle at the three phase junction of S/L interface during eutectic growth and further changes the Pb concentration at the S/L interface needed for coupled eutectic growth. Thus the eutectic microstructure can directly grow upon the primary Pb rich phase and the formation of coarse Sn rich halo is suppressed. Therefore homogeneous metallurgical microstructure can be obtained.展开更多
Diesel engines, characterized by higher breakout pressure and compression ratio in comparison with gasoline engines, require particularly elevated tensile properties for their engine parts. In order to maintain both h...Diesel engines, characterized by higher breakout pressure and compression ratio in comparison with gasoline engines, require particularly elevated tensile properties for their engine parts. In order to maintain both high strength and high ductility in the cylinder head, i.e., to obtain higher percent elongation without further reducing the tensile strength, Al Si9Cu1 alloy was used to prepare the cylinder head in an aluminum diesel engine. At the same time, the effect of different modification elements, Na or Sr, and Fe content on the reduction of secondary dendrite arm spacing(SDAS) was discussed, and the design of T7 heat treatment parameters were analyzed in order to improve the tensile ductility. The result shows:(1) The SDAS is as small as 18±3 μm for the Sr modified alloy.(2) The percent elongation of the alloy with Sr modification increases by 66.7% and 42.9%, respectively, compared with the unmodified alloy and the alloy with Na modification.(3) Lower Fe content alloy(0.10%) gives good results in percent elongation compared to the alloy with higher Fe content(0.27%); in particular, after Sr modification and T7 heat treatment, the elongation of over 5% is obtained.展开更多
Silicon carbide (SiC) fiber has recently received considerable attention as promising next-generation fiber because of its high strength at temperatures greater than 1300 ℃ in air.High-quality SiC fiber is primarily ...Silicon carbide (SiC) fiber has recently received considerable attention as promising next-generation fiber because of its high strength at temperatures greater than 1300 ℃ in air.High-quality SiC fiber is primarily made through a curing and heat treatment process.In this study,the chemical vapor curing method,instead of the thermal oxidation curing method,was used to prepare cured polycarbosilane (PCS) fiber.During the high temperature heat treatment of the cured PCS fiber,varied heating rates of 10,20,30,and 40 ℃/min were applied.Throughout the process,the fiber remained in the amorphous silicon carbide phase,and the measured tensile strength was the greatest when the oxygen content in the heat-treated fiber was low,due to the rapid heating rate.The fiber produced through this method was also found to have excellent internal oxidation properties.This fast,continuous process shows a great promise for the production of SiC fiber and the development of high-quality products.展开更多
文摘Trace rare earth elements were used in order to strengthen the Sn60 Pb40 solder alloy. The experimental results show that the high temperature tensile strength of near eutectic Sn60 Pb40 solder alloy is increased by about 70% after adding trace rare earth elements. Analysis shows that the high affinity between rare earth element and Sn leads to the variation of contact angle at the three phase junction of S/L interface during eutectic growth and further changes the Pb concentration at the S/L interface needed for coupled eutectic growth. Thus the eutectic microstructure can directly grow upon the primary Pb rich phase and the formation of coarse Sn rich halo is suppressed. Therefore homogeneous metallurgical microstructure can be obtained.
基金supported by the major project of Shandong Science and Technology(No.2015ZDZX03004)the project of Shandong Science and Technology Development Plan(No.2014GGX103035)the National“Thousand Talents Plan”of China
文摘Diesel engines, characterized by higher breakout pressure and compression ratio in comparison with gasoline engines, require particularly elevated tensile properties for their engine parts. In order to maintain both high strength and high ductility in the cylinder head, i.e., to obtain higher percent elongation without further reducing the tensile strength, Al Si9Cu1 alloy was used to prepare the cylinder head in an aluminum diesel engine. At the same time, the effect of different modification elements, Na or Sr, and Fe content on the reduction of secondary dendrite arm spacing(SDAS) was discussed, and the design of T7 heat treatment parameters were analyzed in order to improve the tensile ductility. The result shows:(1) The SDAS is as small as 18±3 μm for the Sr modified alloy.(2) The percent elongation of the alloy with Sr modification increases by 66.7% and 42.9%, respectively, compared with the unmodified alloy and the alloy with Na modification.(3) Lower Fe content alloy(0.10%) gives good results in percent elongation compared to the alloy with higher Fe content(0.27%); in particular, after Sr modification and T7 heat treatment, the elongation of over 5% is obtained.
文摘Silicon carbide (SiC) fiber has recently received considerable attention as promising next-generation fiber because of its high strength at temperatures greater than 1300 ℃ in air.High-quality SiC fiber is primarily made through a curing and heat treatment process.In this study,the chemical vapor curing method,instead of the thermal oxidation curing method,was used to prepare cured polycarbosilane (PCS) fiber.During the high temperature heat treatment of the cured PCS fiber,varied heating rates of 10,20,30,and 40 ℃/min were applied.Throughout the process,the fiber remained in the amorphous silicon carbide phase,and the measured tensile strength was the greatest when the oxygen content in the heat-treated fiber was low,due to the rapid heating rate.The fiber produced through this method was also found to have excellent internal oxidation properties.This fast,continuous process shows a great promise for the production of SiC fiber and the development of high-quality products.
