Time-resolved x-ray microdiffraction studies of phase transformations during rapidly propagating reactions in Al/Ni and Zr/Ni multilayer foils

Abstract

We showed how intermetallic formation reactions can be studied under rapid heating ͑10 6 -10 7 K s −1 ͒ using x-ray microdiffraction with temporal resolution on microsecond time scales. Rapid heating was achieved by initiating an exothermic reaction in multilayer foils comprising alternating nanoscale layers of elemental metals. The reaction occurred in a front ϳ100 m wide which propagated across the foil at ϳ1-10 m s −1 . By using synchrotron x-rays focused to a small spot ͑60 m diameter͒ and a fast pixel-array detector, we were able to track the evolution of phases in the reaction front during the initial heating transient, which occurred in approximately 1 ms, through cooling over a period of hundreds of milliseconds. In Al/Ni multilayer foils, the first phases to form were an Al-rich liquid and the cubic intermetallic AlNi ͑which likely formed by nucleation from the liquid͒. In foils of overall composition AlNi, this is the stable intermetallic and the only phase to form. In foils of composition Al 3 Ni 2 , during cooling we observed a peritectic reaction between AlNi and the remaining liquid to form Al 3 Ni 2 , which is the stable phase at room temperature and the final product of the reaction. This is in contrast to the sequence of phases under slow heating, where we observed formation of nonequilibrium Al 9 N 2 first and do not observe formation of a liquid phase or the AlNi intermetallic. We also observed formation of an amorphous phase ͑along with crystalline ZrNi͒ during rapid heating of Zr/Ni multilayers, but in this system the temperature of the reaction front never reached the lowest liquidus temperature on the Zr-Ni phase diagram. This implies that the amorphous phase we observed was not a liquid arising from melting of a crystalline phase. We suggest instead that a Zr-rich amorphous solid formed due to solid-state interdiffusion, which then transformed to a supercooled liquid when the temperature exceeded the glass transition temperature. Formation of the supercooled liquid presumably facilitated continued rapid intermixing, which may be necessary to sustain a self-propagating reaction front in this system.

Coating of Tungsten Wire with Ni/Al Multilayers for Self-Healing Applications

“…The as-reacted microstructure is in good agreement with that published by Trenkle et al [19]. The formation of the Al3Ni2 phase is also in accordance with SEM/EDS measurements pointing to Al enrichment in the as-deposited multilayers.…”

In situ transmission electron microscopy investigation of the interfacial reaction between Ni and Al during rapid heating in a nanocalorimeter

“…[6][7][8][9] One of the best characterized thin film reactions is between Al and Ni. [10][11][12][13][14][15][16][17][18][19][20] Al and Ni have a large, negative heat of mixing, making the reaction highly exothermic. Multilayer foils consisting of nanoscale layers of Al and Ni can release this energy very quickly.…”

“…The shift in phase sequence with heating rate is attributed to a reduction in the amount of atomic intermixing that occurs prior to reaching temperatures where the intermediate intermetallic phases are no longer stable. 18 To-date this characterization has only been performed on sputtered Al/Ni multilayers, but evaporated multilayers are likely to exhibit the same sequence given that the vast majority of mixing occurs through Ni dissolving into molten Al.…”

“…These interfaces tend to be more intermixed in sputtered and ion-beam deposited samples, which in turn can impact the nucleation of the Al 9 Ni 2 and Al 3 Ni phases which have similar free energies of formation. 17 When sputter-deposited Al/Ni multilayers are reacted in the rapid, self-propagating mode (heating rates exceeding 10 6 K/s) and characterized using synchrotron x-ray diffraction 18,19 or timeresolved TEM, 20 the observed phase transformation sequence becomes…”

“…Since quenching is difficult for reactions progressing at these rates, in situ a mgrapes1@jhu.edu; david.lavan@nist.gov; and weihs@jhu.edu characterization methods are preferred in this regime. To-date such studies have been accomplished using two techniques: synchrotron x-ray microdiffraction 18,19 and time-resolved transmission electron microscopy (TEM). 20 For multilayers with a 1:1 Al:Ni atomic ratio, slow heating experiments typically have identified two phase transformation sequences depending on the deposition method.…”