The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre- sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction...The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre- sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction (XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were prepared by mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas- eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most of their hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. The crystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphous Mg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep- tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on the crystallization of amorphous alloys was discussed.展开更多
Crystallization temperature of the metallic glass Zr_(70)Cu_(30),observed by X-ray diffraction analysis,may be increased about 20℃,the superior limit of increase range of the temperature is about 30℃,under high pres...Crystallization temperature of the metallic glass Zr_(70)Cu_(30),observed by X-ray diffraction analysis,may be increased about 20℃,the superior limit of increase range of the temperature is about 30℃,under high pressure up to 2GPa.Besides α-Zr and CuZr_2, the Cu_(10)Zr_7 phase was newly obtained as another crystallization product.展开更多
A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment...A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment a non catalytic nucleation composite glass lined coating (B F) was prepared on the inner surface of mould and the Cu 70 Ni 30 alloy was selected to perform undercooling experiment in the B F non catalytic coating mould. Its ratio of undercooling heredity was 0.76. The results prove that the B F coating is an ideal non catalytic media for purified Cu 70 Ni 30 alloy melts due to its small contact angle between the melt and coating layer. Considering that various microstructures form under different undercoolings, two critical undercoolings, Δ T 1 and Δ T 2, and their corresponding microstructures of Cu 70 Ni 30 alloy are well defined. Moreover, it is found that the manned trigging solidification in the non catalytic coating mould could be used to get directional undercooling dendrite structure while the melt undercooling is larger than the critical undercooling Δ T 2.展开更多
X-ray diffraction (XRD) and differential scanning calorimetry (DSC) wereemployed to investigate the influence of Ni content on the crystallization of amorphousZr_(70)Cu_(30-x)Ni_x (atom fraction in percent) alloys. Ex...X-ray diffraction (XRD) and differential scanning calorimetry (DSC) wereemployed to investigate the influence of Ni content on the crystallization of amorphousZr_(70)Cu_(30-x)Ni_x (atom fraction in percent) alloys. Experimental results show that with the Nicontent increasing the activation energies for crystallization of amorphous Zr_(70)Cu_(30-x)Ni_xalloys increase correspondingly, indicating that the thermal stability is greatly improved. All theDSC traces of amorphous Zr_(70)Cu_(30-x)Ni_x alloys exhibit two exothermic peaks, suggesting thatthe crystallization process proceeds via a double-stage mode. The first exothermic peak at lowertemperature mainly corresponds to the precipitation and growth of Zr_2Cu particles, while the secondone corresponds to the precipitation of nano-scale Zr_2Ni phase and crystallization of residualamorphous phase. The mechanism on the crystallization of amorphous Zr_(70)Cu_(30-x)Ni_x alloys wasdiscussed.展开更多
文摘The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre- sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction (XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were prepared by mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas- eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most of their hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. The crystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphous Mg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep- tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on the crystallization of amorphous alloys was discussed.
文摘Crystallization temperature of the metallic glass Zr_(70)Cu_(30),observed by X-ray diffraction analysis,may be increased about 20℃,the superior limit of increase range of the temperature is about 30℃,under high pressure up to 2GPa.Besides α-Zr and CuZr_2, the Cu_(10)Zr_7 phase was newly obtained as another crystallization product.
文摘A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment a non catalytic nucleation composite glass lined coating (B F) was prepared on the inner surface of mould and the Cu 70 Ni 30 alloy was selected to perform undercooling experiment in the B F non catalytic coating mould. Its ratio of undercooling heredity was 0.76. The results prove that the B F coating is an ideal non catalytic media for purified Cu 70 Ni 30 alloy melts due to its small contact angle between the melt and coating layer. Considering that various microstructures form under different undercoolings, two critical undercoolings, Δ T 1 and Δ T 2, and their corresponding microstructures of Cu 70 Ni 30 alloy are well defined. Moreover, it is found that the manned trigging solidification in the non catalytic coating mould could be used to get directional undercooling dendrite structure while the melt undercooling is larger than the critical undercooling Δ T 2.
基金This work is financially supported by the National Natural Science Foundation of China (No. 59871025).
文摘X-ray diffraction (XRD) and differential scanning calorimetry (DSC) wereemployed to investigate the influence of Ni content on the crystallization of amorphousZr_(70)Cu_(30-x)Ni_x (atom fraction in percent) alloys. Experimental results show that with the Nicontent increasing the activation energies for crystallization of amorphous Zr_(70)Cu_(30-x)Ni_xalloys increase correspondingly, indicating that the thermal stability is greatly improved. All theDSC traces of amorphous Zr_(70)Cu_(30-x)Ni_x alloys exhibit two exothermic peaks, suggesting thatthe crystallization process proceeds via a double-stage mode. The first exothermic peak at lowertemperature mainly corresponds to the precipitation and growth of Zr_2Cu particles, while the secondone corresponds to the precipitation of nano-scale Zr_2Ni phase and crystallization of residualamorphous phase. The mechanism on the crystallization of amorphous Zr_(70)Cu_(30-x)Ni_x alloys wasdiscussed.
