2.1.U(Mo)/Al-4wt%Si miniplates [11] and U3Si2/Pure Al plates.
Depleted U-7wt%Mo alloy (U-7Mo) as atomized particles provided by KAERI were used as fuel alloy. The powders used as matrices were prepared in two different ways: by mixing pure Al and pure Si particles (Al-4Si) or pure Al particles with eutectic Al-Si alloy particles (which Si concentration is 12 wt%) (Al-4SiE). In both cases the final nominal concentration is Al-4wt%Si.
U-7Mo and matrix particles were mixed and cold pressed to obtain 7 gU/cm3 compacts which
were positioned in an AA6061 frame and fully welded to AA6061 covers by TIG. Hot rolling at 500 ºC up to 82 % reduction was used to obtain final size followed by a heat treatment of 1 h at 500 ºC and cold rolled.
U3Si2 compound was fabricated in CNEA by melting low enriched uranium (20% 235U) and pure
Si in an induction furnace. After melting, the material was milled and sieved to obtain the powder. Silicide particles were mixed with pure Al ones and cold pressed to obtain 4.8 gU/cm3
compacts which were positioned in an AA6061 frame and welded, with open corners, to AA6061 covers by TIG. Hot rolling at 500 ºC up to 90 % reduction was used to obtain final size followed by a heat treatment of 1 h at 480 ºC and cold rolled.
Samples were cut from each miniplate or plate and one of the Al6061 cladding was removed by a rough polishing until reaching the meat followed by a final mechanical polishing up to 1 m diamond paste. The samples were characterized by optical microscopy (OM-Olympus BX60M), scanning electron microscopy (SEM –Philips SEM 515, and FEI QUANTA 200), energy dispersive spectroscopy (EDS-EDAX Phoenix 3.2) and X-Ray diffraction (XRD- PANalytical- Empyrean with Cu kα radiation). Crystal structures identification and the estimation of lattice parameters were obtained by direct comparison between theoretical spectrum of each phase with the experimental spectra using POWDERCELL software [12].
Table 1 summarizes identification and characteristics of the miniplates and plates studied in this work.
TABLE 1. Identification and fabrication details of the sample taken from the miniplates and plates.
2.2.Diffusion couples
Al(Si) binary alloys were made by arc melting in a small non-consumable tungsten electrode arc- furnace with a copper crucible under highly pure argon atmosphere using high purity Al and Si. Six different alloys were fabricated: Al-0.6wt%Si (Al-0.6Si); Al-2 wt%Si (Al-2Si); Al-4wt% Si (Al- 4Si); Al-5.2wt%Si (Al-5.2Si); Al-6 wt%Si (Al-6Si) y Al-7.1wt%Si (Al-7.1Si). Si concentrations corresponding to 0.6; 5.2 and 7.1 were chosen in accordance to nominal Si concentration in AA6061, AA4043 and AA356 commercial Al alloys. After melting process the Al(Si) alloys were hot rolled at 480 ºC and heat treated 1 h at 550 ºC. This last temperature is the same one at which diffusion couples will be studied.
Same melting procedure is used to fabricate the U–7wt%Mo alloy. Only part of the as-cast U- 7Mo alloy will be heat treated at 1000°C during 2h and quenched to room temperature to promote composition homogenization. The remaining alloy will be used in the as cast condition to represent more closely U(Mo) alloy in the miniplates. Stainless-steel mechanical clamps will be used to keep in contact the alloys. Table II shows the configuration of the seven diffusion couples.
Table II. Configuration of the seven diffusion couples.
As it is shown in Table II, in the first six diffusion couples U(Mo) will be positioned in between two Al(Si) alloys [i.e. Al-xSi/U-7Mo/Al-ySi]. This configuration allows comparison of relative IL
I
Iddeennttiiffiiccaattiioonn 22IInn0011RR44RR[[FF11MM11]] FFuueell MMaattrriixx RRoolllliinnggFFaabbrriiccaattiioonnpprroocceessss T
Teemmpp TTaaTTnnFFddTTtteeiimmmmeepp.. CCoooolliinngg
U(Mo)/Al-4Si 4Si-FF-FW U-7wt%Mo Al-4Si
500 ºC
500 ºC – 1 h Inside furnace U(Mo)/Al-4SiE 4SiE-FF-FW U-7wt%Mo Al-4SiE
U3Si2/Al-IF - U3Si2 Pure Al
480 ºC – 1 h
Inside Furnace U3Si2/Al-OF - U3Si2 Pure Al Furnace Outside
1 Al-0.6Si U-7Mo Non homog. Al-5.2Si 2 Al-0.6Si U-7Mo Non homog. Al-7.1Si 3 Al-2Si U-7Mo Non homog. Al-5.2Si
4 Al-2Si U-7Mo Non homog. Al-6Si
5 Al-4Si U-7Mo Non homog. Al-6Si
6 Al-4Si U-7Mo Non homog. Al-7.1Si 7 Non homog. U-7Mo Al-4Si Homogenized. U-7Mo
widths minimizing any effect introduced during diffusion couple fabrication. The last one will be used to study the influence of metastable U phase decomposition [13] on IL formation.