No abstract

Since the oxygen-rich nanofeatures (NFs) in oxide-dispersion-strengthened (ODS) ferritic steels is a key factor for improving their whole mechanical properties [1][2][3], atom-probe tomography (APT) and transmission electron microscopy (TEM) have been widely employed to identify the oxygen-rich NFs in the materials [2][3][4][5]. The current work presents three challenges to deeply understand the chemical origin of the nano-sized precipitates containing Y, O, and Ti. First, the segregation of alloying elements at grain boundaries is observed. Secondly, we compare the concentrations of nano-sized precipitates with a size of ~3 nm to those of 10-nm precipitates. Finally, the existence of NF structure with the Y-rich cores and Ti-and Cr-enriched shells is confirmed as previously reported by APT. The nominal composition of the materials studied here is 14Cr, 3.0W, 0.4Ti in wt.%. Analyses were performed using a LEAP-4000HR microscope in voltage-pulsing mode at 200 kHz pulse repetition rate, 0.005 atom/pulse detection rate, 20% pulse fraction and 70 K. Fig. 1 shows reconstructed APT maps (a) of alloying solutes in ODS Ti-containing ferritic steels. We found that two grain boundaries are observed as indicated by the arrows. In particular, the Cr, W, and Ti atoms have high tendency to segregate to grain boundaries. Nevertheless, the other elements, especially carbon and oxygen atoms, are not detected to segregate at grain boundary. From the cylinder method and iso-surface analyzes, the 1D concentration profiles of Cr, W, and Ti are displayed in Fig.1(b). Note that the profiles were obtained by excluding the NF regions found in the grain boundary. The resulting concentrations of Cr, W, and Ti are estimated to be 27.9, 3.8, and 0.9 at.%, respectively. The Cr segregation is observed that extends slightly and shifts underneath the grain boundary further in the analysis direction than the segregation of W and Ti. This could be explained as being an evaporation artifact due to chromatic aberrations whereby atomic ion trajectory as described in previous report [5]. Fig. 2(a) shows the reconstructed maps of tip#2 for the steels. The grain boundary segregation of Cr, W, and Ti is also detected and the corresponding concentrations are 26.5 for Cr, 4.0 for W, and 1.2 at.% for Ti, respectively. As the above-mentioned, carbon and oxygen atoms are not segregate at grain boundary. The carbon and oxygen atoms are only partitioned to large NFs with a size of ~10 nm as well as metal ions (Al, Cr) and metal-oxides (CrO, YO, and TiO). In smaller NFs with a size of below 5 nm, only Y, Ti, O, and TiO ions are detected. This implies that the ratio of Y to Ti in NFs profoundly depends on the size of NFs. In addition, we found that the oxygen atoms exhibit wider lateral extent than Ti ions in NFs. This is explained by evaporation artifact of APT as described by Emmanuelle et al [6]. Besides the oxygen, the Y ions in all reconstructed particles appear more compressed in the depth direction of NFs than Ti and O ions, as shown in Fig. 2(b). Despite...

In the present study, the characteristics of the Ti powders fabricated by Hydride–Dehydride (HDH) were analyzed in terms of particle shape, size and size distribution. Ti powders were subjected to roll compaction and their microstructure and green densities were evaluated in terms of particle size, powder morphology, roll gap and rolling speed. Effects of blending elements having different powder sizes on densification properties were analyzed. The strip thickness was proportional to the roll gap up to 0.9 mm and the density of titanium strip was decreased with the increase in roll gap. As the roll speed increased, the strip density and thickness were decreased by using -200 mesh Ti powder. However, the effect of rolling speed for -400 mesh Ti powder was not greater than that of -200 mesh powder. The highest density by 93% was achieved by using -400 mesh Ti powder at 0.1 mm roll gap, however edge cracks and alligator cracks were occurred.

No abstract

The feasibility of using a high-entropy rare-earth oxide (REO) as a top coating material for thermal barrier coatings was explored using the atmospheric plasma spray technique. The microstructure and Vickers hardness of the coating layer were compared to those of an 8 mol % yttria-stabilized zirconia (8YSZ) top coating material. Macroscopic observations revealed the formation of a well-coated surface with no surface defects or delamination. Scanning electron microscopy images showed the presence of several parallel and vertical microcracks in the REO and 8YSZ coating layers. The origin of these cracks is attributed to differences in the coefficient of thermal expansion, very fast cooling, and process parameters. X-ray diffraction demonstrated the high phase stability and excellent thermal properties of REO due to the absence of phase transformation after plasma spray processing. The measured Vickers hardness of REO was 425 HV, which is lower than that of sintered REO powder and the 8YSZ coating.