Metallurgical Preparation of Nb–Al and W–Al Intermetallic Compounds and Characterization of Their Microstructure and Phase Transformations by DTA Technique

Abstract

The possibilities of metallurgical preparation of 40Nb-60Al and 15W-85Al intermetallic compounds (in at.%) by plasma arc melting (PAM) and vacuum induction melting (VIM) were studied. Both methods allow easy preparation of Nb–Al alloys; however, significant evaporation of Al was observed during the melting, which affected the resulting chemical composition. The preparation of W–Al alloys was more problematic because there was no complete re-melting of W during PAM and VIM. However, the combination of PAM and VIM allowed the preparation of W–Al alloy without any non-melted parts. The microstructure of Nb–Al alloys consisted of Nb2Al and NbAl3 intermetallic phases, and W–Al alloys consisted mainly of needle-like WAl4 intermetallic phase and Al matrix. The effects of melting conditions on chemical composition, homogeneity, and microstructure were determined. Differential thermal analysis was used to determine melting and phase transformation temperatures of the prepared alloys.

Processing and Microstructure of As-Cast Ti-45Al-2W-xC Alloys

“…The increase in C content in the ingots leads to an increase in Vickers hardness HV10, as seen in Figure 11 a. This increase in HV10 can be attributed to solid solution strengthening of both α 2 and γ phases by carbon [ 19 , 53 , 64 ]. The solubility of carbon in the γ phase and α 2 phase was determined to be 0.025–0.25 at.% [ 18 , 64 ] and about 1 at.% [ 19 , 65 ], respectively.…”

“…Pure Ti (grade 2) and Al (99.99%) and pieces of 15W-85Al (at.%) master alloy (see Figure 1 ) were used as the charge. The master alloy, composed of WAl 4 and WAl 12 phases distributed in the Al matrix, had a relatively low melting point of 1350 °C compared to that of pure W, which was used to facilitate the fast dissolution of W during VIM [ 53 ]. Isostatically pressed graphite crucibles ϕ65/135 mm (diameter/length) were applied to melt a charge with a weight of 410 g. An alumina-based crucible connected with a graphite mould was used to protect the graphite melting crucible.…”

Phase Structure Evolution of the Fe-Al Arc-Sprayed Coating Stimulated by Annealing

“…The main Materials 2021, 14, 3210 2 of 16 disadvantage that limits the use of Fe-Al intermetallics is their brittleness at room temperature and the difficulty of shaping ready-made elements to desired dimensions by means of mechanical machining methods [38,39]. Due to the significant differences in properties like melting point and specific heat of Fe and Al, it is difficult to obtain materials with a reproducible composition and homogeneous structure [40].…”