The Effect Of Liquid State On The Behavior Of Electrical Resistivtity And Internal Friction Of Zr-based And Al-based Metallic Glasses

The amorphous alloys are generally obtained by rapidly cooling. The short-range order andlong-range disorder of amorphous alloy has similarity with the melt structure. So the amorphousalloy might be considered as the solids with the frozen-in liquid structure and some features of meltstructure could be inherited by the resultant amorphous alloy. In the present work, by the methods ofelectrical resistance （ER） and internal friction, the influences of melt temperature on the glassforming ability （GFA）, crystallization behavior and mechanical relaxation of the amorphous alloyswere systematically studied. The innovative points and main results of this paper are listed below.（1） The structure change of the Al₈₆Ni₉La₅liquid was examined by means of ER duringcontinuous heating. Abnormal behaviors with temperature of the melts were observed within therange from1320K to1490K, indicating the change of the liquid state and the possible temperatureinduced liquid-liquid structure transition （LLST）. The results also have been verified by DTA. Basedon the anomalous behavior of temperature-induced liquid-liquid structure transition observed in themelt, different melt temperatures were chosen to prepare the amorphous samples and then they wereannealed at the same conditions. It is found that the final crystallization phases are the same, but thecrystallization behavior during different crystallization stages are significantly different among thesamples. For the crystallization behavior of the sample prepared above the LLST temperature range,the precipitation temperature of primary phase α-Al is earlier, but the formation of intermetalliccompounds is later than that of the sample prepared below the LLST temperature. These conclusionscould improve the preparation and performance of Al-based amorphous/nanocrystalline compositematerial, and also indirectly confirm the speculation of liquid-liquid structural change. The resultthat the precipitation of second crystallization of amorphous sample prepared above the LLSTtemperature range, may be attributed to the dissolved short-range order corresponding to theseintermetallic compounds. Therefore, the nucleation and precipitation of the intermetallic compoundsis more difficult.（2） For the Zr₆₅Al_7.5Ni₁₀Cu_17.5amorphous alloys, it is difficult to measure ER of melt because oftheir proneness to be easily oxidized. So based on the crystallization behavior of amorphous ribbonsprepared at different melt temperatures, the structural change in the melt is indirectly explored. Itwas found that primary phase is different among the samples. The primary phase is Ni₂Zr₃for thesample prepared below1573K, while that is f.c.c NiZr₂for the sample prepared at above1573K,and the begging crystallization temperature moves to higher temperature. The final crystallizationphases are also different for the two kinds of the samples. So based on the signficant differentcrystallization behaviors of amorphous Zr₆₅Al_7.5Ni₁₀Cu_17.5ribbons prepared at different melt temperatures, the reason that crystallization phases reported in some literatures are inconsistentmight originate from the different structures of the amorphous ribbons resulting from different melttemperatures. Besides, it also suggested that the structure of melt changed above1573K.（3） For different alloy system, the melt structure has significant influence on GFA. Bycomparing the characteristic parameters of GFA Zr₆₅Al_7.5Ni₁₀Cu_17.5ribbons, the GFA is improvedwith the increasing melt temperature, especially higher than1573K. But for Al₈₆Ni₉La₅alloy, basedon the characteristic parameters of GFA and the critical thickness of the wedge-shaped samplesprepared at diifferent melt temperature, the GFA is decreased due to the change of the melt structure.（4） For the influence of the quenching temperature on the GFA of the metallic glasses, it is nodoubt to conduct a comprehensive analysis of the negative effects, i.e. the high-temperatureoxidation and the cooling rate slowing down and the positive effects, i.e. high temperature meltmakes the heterogeneous nucleation substrate to dissipate, according to the aspects such as the alloysystem, preparation condition and raw materials. Based on the research results, the authorsemphasize that the liquid-liquid structure transition causes some of the pre-existing clustersdisappearing as the melt structure state itself. If the local structure and composition of the cluster arecorresponding to the primary phase during the rapid cooling of the melt, the GFA will be certainlyimproved. As an example of Zr₆₅Al_7.5Ni₁₀Cu_17.5alloy, it is corresponding to the chemical short rangeorder of Ni₂Zr₃which is broken under the high melt temperature. On the contrary, if the disappearedcluster is not corresponding to the primary phase during crystallization and instead of facilitating thenucleation of the primary phase in the aspects of thermodynamic and/or kinetic, the GFA will becertainly decreased. As an example of Al₈₆Ni₉La₅alloy, the liquid-liquid structure transition causethe disappearing of the chemical short-range order and much more Al atoms will be free resulting inthe increasing of the Al-rich cluster. Meantime, the increasing free volume of the melt （lower density）is favor of the atomic diffusion. Both of the factors promote the nucleation of the primary phasefcc-Al of the alloy.（5） By the method of internal friction, the influence of melt temperature on the mechanicalrelaxation of Zr₅₅Al₁₀Ni₅Cu₃₀bulk metallic glass was studied. By comparing the internal friction-temperature curves of different samples, the positions of peak move to higher temperature and thethe internal friction value increases with the melt temperature increasing. By comparing the internalfriction-frequency curves of different samples, BMGs structure relaxation can be divided into threeregions before Tx, which are the stages of linear increase, complicated transition and monotonereducing. The beginning and end temperature at which the anelastic behaviour change intoviscoelastic relaxation move toward the lower temperature for the BMG prepared at higher melttemperature. In order to analyze the IF behavior of BMG in the vicinity of the glass transition temperature, based on the theory of Perez, the correlation parameter is compared, which isdeduced from tan-f curves. The sample prepared at1603K has the largest. And the criticaltemperature determined by the correlation parameter increases with the quenching temperatureincerasing. The results show that the higher the melt temperature, the larger the degree of disorder ofthe sample and thus the higher the thermal stability.（6） Finally, the Zr-based BMGs with different glass forming ability were selected to study therelationship between GFA and internal friction. By comparing the internal friction-temperaturecurves of different samples, it is found that the higher the value of internal friction peak, the betterthe GFA. So a new criterion evaluating the GFA is proposed, i.e. internal friction peak. Comparingthe activation energy obtained from the fitted background internal friction, the higher the glassforming ability, the larger the activation energy before the glass transition temperature and in thesupercooled liquid region.