Degassing Behavior of Nanostructured Al and Its Composites

Abstract

The synthesis of bulk ultrafine-grained (UFG) and nanostructured Al via cryomilling can frequently require a degassing step prior to consolidation, partly due to the large surface area of the as-milled powders. The objective of this study is to investigate the effects associated with cryomilling with stearic acid additions (as a process-control agent) on the degassing behavior of Al powders. This objective was accomplished by completing select experiments with Al-7.5Mg, Al-6.4 wt pct Al 85 Ni 10 La 5 , and Al-14.3 wt pct B 4 C. The interaction between Al and stearic acid was determined using thermal analysis combined with Fourier transform infrared spectroscopy (FTIR). The degassing experiments were carried out under high vacuum (10 À4 to~10 À6 torr) in a range from room temperature to 400°C, with the pressure of the released gases monitored using a digital vacuum gage. The results showed that the liberation of chemisorbed water was suppressed in cryomilled Al powders and both the chemisorbed water and stearic acid were primarily released in the form of hydrogen. It was also demonstrated that under certain conditions, a nanostructure (grain size~100 nm) can be retained following the hot vacuum degassing of cryomilled Al.

Influence of Nitrogen Content on Thermal Stability and Grain Growth Kinetics of Cryomilled Al Nanocomposites

“…For effective H release, higher degassing temperatures are favorable, but can lead to grain growth. Previous studies have demonstrated an average grain size increase from 25 nm to 78 nm in 12-hour cryomilled Al 14.3 wt pct B 4 C when degassed at temperatures as high as 673 K (400°C) for 14 hours, [10] and from 50 nm to 118 nm in 8-hour cryomilled Al 5083 after degassing for only 2 hours at 773 K (500°C). [12] In addition, the increase of the average grain size with an increasing degassing temperature from 673 K (400°C) to 773 K (500°C) was confirmed; yet, higher degassing temperatures helped eliminate porosity.…”

“…For instance, cryomilled Al powders are often degassed prior to powder consolidation in an effort to remove the majority of H, which is introduced into the powder through the stearic acid commonly used as a process control agent. [8][9][10] The H, which can lead to hydrogen embrittlement, [11] is adsorbed on the powder surface and can be released through exposure to high temperatures under vacuum. The degassing conditions must be properly selected so that the H is removed yet the nanostructure is retained.…”

TG/FT-IR characterization of additives typically employed in EPDM formulations

“…is assigned to the CH 3 group [17,18] . The TG/FT-IR spectra corresponding to TMQ degradation at 362 and 473 °C are shown in Figures 3c and 3d, respectively.…”

Gas Atomization of Amorphous Aluminum: Part I. Thermal Behavior Calculations

“…[1,11,12] Although the product of gas atomization is in powder form and is small in size, the amorphous powder can be further processed through various powder metallurgical techniques into engineering MG components. [12][13][14][15] The thermal history experienced by atomized powder is one of the key factors that affect the initial formation and eventual retention of the amorphous phase. To maximize cooling rate, and thereby maximize the extent of amorphous fraction in atomized powders, controllable processing parameters that affect the cooling rate and the solidification process of atomized droplets require careful selection and control, particularly, if optimized GA is the goal.…”