Time–temperature–transformation diagram and microstructures of bulk glass forming Pd40Cu30Ni10P20

Abstract

Isothermal crystallization studies were performed on the bulk glass forming alloy Pd 40 Cu 30 Ni 10 P 20 in the undercooled liquid region between the glass transition and liquidus temperature, resulting in a complete time-temperature-transformation ͑TTT͒ diagram for crystallization. The TTT diagram shows a typical ''C'' shape with the nose at 50 s and 680 K. Assuming steady state nucleation and a diffusion-controlled growth rate, the TTT diagram was successfully fit over the entire range of the measurement. The microstructure after isothermal crystallization shows a modulation in Cu and P for all degrees of undercooling. The primary solidified phase is Cu 3 Pd, which forms distinct dendrites at low undercooling. From additional constant cooling experiments, the critical cooling rate to bypass crystallization was determined to be 0. 3 has an excellent glass forming ability that has initiated a series of crystallization studies over a wide temperature range below the melting temperature. A complete time-temperaturetransformation ͑TTT͒ diagram for crystallization was measured by containerless electrostatic levitation ͑ESL͒ over the entire temperature range of the undercooled liquid, i.e., from the melting point down to the glass transition temperature, T g . 4 This TTT diagram showed a typical ''C'' shape with the nose at 51 s and 850 K. The critical cooling rate to bypass crystallization was found to be 1.8 K/s. The TTT diagram could not be described by kinetic formulations as given, for example, by Uhlmann 5 and Davis. 6 This was attributed to the relatively complex crystallization behavior of Vit1, particularly at low temperatures where decomposition precedes nucleation. This method is more user friendly compared to ESL and has the advantage of a more reliable temperature reading.Recently, the new Pd based bulk amorphous glass Pd 40 Cu 30 Ni 10 P 20 ͑PCNP͒ was found, 10 which has a glass forming ability far exceeding that of Pd 40 Ni 40 P 20 and approaching or even exceeding that of Vit1. In contrast to Vit1, this Pd based alloy shows no decomposition on the nanometer scale at temperatures near T g . 11In this letter, we report on crystallization studies of PCNP. Processing this alloy in graphite crucibles, using boron oxide flux, enabled us to measure the complete TTT diagram for crystallization in the undercooled melt and to determine the critical cooling rate. We present results of microstructure analysis of the PCNP melt after crystallization at temperatures near the nose of the TTT diagram. We further give a kinetic formulation which fits the TTT diagram over the entire range of the measurement.Amorphous PCNP was produced by induction melting of Pd, Cu 73.4 P 26.6 , Ni 2 P, and P in a silica tube of 10 mm diameter, using B 2 O 3 oxide flux, and subsequent water quenching. For the crystallization studies, we used a differential thermal analysis ͑DTA͒ setup, 12 equipped with two graphite crucibles. The material was introduced to one of the crucibles, whereas the other was used as a reference. The crucibles w...

A study of cooling process in bulk metallic glasses fabrication

“…Besides, the experimental measurements of critical cooling rate were mainly performed in milligram-scaled samples (in the order of 10∼100 mg [44][45][46] ). In smaller samples, it's easier to achieve homogeneous composition and remove impurities to avoid crystallization.…”

Elastic properties of Pd40Cu30Ni10P20 bulk glass in supercooled liquid region

“…For example, a cooling rate of merely 0.1 K/s is required to suppress crystallization, and to form a metallic glass sample with diameter up to 72 mm for the Pd 40 Cu 30 Ni 10 P 20 alloy. 3 Measurements of viscosity, 4 crystallization, 5 diffusion, 6 density, 7 thermal expansion, 8 electron transport, 9 structure, 10 and specific heat capacity, 11 have been performed on bulk Pd 40 Cu 30 Ni 10 P 20 glass. Recently, Wang et al, 12 performed ultrasonic measurements at ambient temperature for as-cast bulk Pd 39 Cu 30 Ni 10 P 21 glass and samples annealed at various temperatures for 1.5 h, and found that two different crystallization processes are likely to exist in the supercooled liquid region.…”

Calculating glass-forming ability in absence of key kinetic and thermodynamic parameters

“…The experimental values of T l , T g , and H F were taken from Refs. [13][14][15][16]. Note that the total probability presented in Fig.…”

“…13,15 Here we quote the t onset at only four arbitrary T iso 's for each glass, as shown in Table II in Ref. 18.…”