High Temperature Stability of an Al-Zr-Ti Alloy Prepared using Gas Atomization and Spark Plasma Sintering Technology

Abstract

The aim of this study was to prepare an aluminium alloy with high temperature stability using the powder metallurgical route. Gas atomized powder of the Al-Zr-Ti alloy was consolidated by the spark plasma sintering (SPS) technology. The fine grained structure (grain size between 2 and 3 µm) observed in the gas atomized powder was retained after sintering both at 425 • C and 550 • C. The microhardness of 49 HV observed in the gas atomized powder was increased up to about 100 HV in the SPS compacts. Precipitation of the Al3(Zr,Ti) phase during sintering can explain this strengthening. The materials stability was tested by annealing at temperatures above 450 • C. The grain size remained stable even after 10 h of annealing. A decrease in microhardness by about 20% can be attributed especially to the formation of the stable modification of the Al3(Zr,Ti) phase.

Bimodal Microstructure in an AlZrTi Alloy Prepared by Mechanical Milling and Spark Plasma Sintering

“…Regardless of the relatively low equilibrium solid solubility of Zr and Ti in the Al matrix, mechanical milling extended the solid solubility of alloying elements in the matrix. This was confirmed by XRD showing the absence of second phase particles, although, the atomized powders contained 3.2 wt % of them [ 21 ]. Contrary to the findings made by XRD, the SEM and even more detailed TEM inspections revealed areas containing elements with a higher atomic number than Al.…”

“…The gas atomized powder particles exhibited a mostly spherical shape ( Figure 1 a) with the mean size of 20 µm. The detailed investigation revealed [ 21 ] that the internal microstructure of gas atomized powder particles changes with their size from segregation free microstructure in the smallest particles to microcellular one in larger particles, the typical grain size was 2–3 µm. The repeated fracture and cold welding during milling of the atomized powder led to irregularly shaped powder particles with a very wide size range as presented in Figure 1 b by SEM-SE imaging.…”

“…During SPS, densification proceeds during exposition of powders to high pressure and temperature. Usually this is sufficient to make a fully dense sintered sample as it was reported for the sample prepared by gas atomization followed by SPS from the same AlZrTi alloy as presented here [ 21 ]. The compact sample sintered from gas atomized powder showed a more uniform microstructure, no bimodal grain size distribution or excessive differences in displacement of second phase particles were observed [ 21 ].…”

“…Usually this is sufficient to make a fully dense sintered sample as it was reported for the sample prepared by gas atomization followed by SPS from the same AlZrTi alloy as presented here [ 21 ]. The compact sample sintered from gas atomized powder showed a more uniform microstructure, no bimodal grain size distribution or excessive differences in displacement of second phase particles were observed [ 21 ]. In the case of the herein reported milled powder, the SPS led to a non-homogeneous microstructure from the viewpoint of second phase particle distribution and grain size.…”

“…The microhardness of the gas atomized powder was reported to be 49 HV0.01 [ 21 ]. The severe deformation during milling increased this value up to 163 ± 15 HV0.01 due to a common effect of deformation strengthening, remarkable grain refinement and dissolution of alloying elements.…”